Cover merge printing preservation with a test

Base deck with 4 Mountain (DOM 250), local adds 2 Shock (M19 156), remote
adds an unrelated card. Asserts the merge keeps one Mountain node with its
printing and adds a single Shock node carrying M19/156.

cockatrice/CMakeLists.txt

@@ -27,6 +27,8 @@ set(cockatrice_SOURCES
     src/interface/deck_loader/deck_file_format.cpp
     src/interface/deck_loader/deck_loader.cpp
     src/interface/deck_loader/loaded_deck.cpp
+    src/interface/deck_sync/deck_sync_profile.cpp
+    src/interface/deck_sync/deck_sync_sidecar.cpp
     src/interface/widgets/dialogs/dlg_connect.cpp
     src/interface/widgets/dialogs/dlg_convert_deck_to_cod_format.cpp
     src/interface/widgets/dialogs/dlg_create_game.cpp

cockatrice/src/interface/deck_sync/deck_sync_profile.cpp

@@ -0,0 +1,31 @@
+#include "deck_sync_profile.h"
+
+#include <QCryptographicHash>
+
+DeckSyncProfile::DeckSyncProfile(const QString &_host, int _port, const QString &_username)
+    : host(_host), port(_port), username(_username)
+{
+}
+
+bool DeckSyncProfile::isValid() const
+{
+    return !host.isEmpty() && port > 0 && !username.isEmpty();
+}
+
+QString DeckSyncProfile::key() const
+{
+    if (!isValid()) {
+        return {};
+    }
+    // NUL separators keep the triple injective: neither IPv6 hosts nor
+    // usernames containing ':' can collide two profiles into one file.
+    // Lowercasing is safe on both parts: DNS names are case-insensitive, and
+    // Servatrice usernames are unique under a case-insensitive collation
+    // (cockatrice_users uses utf8mb4_unicode_ci), so both spellings are one account.
+    QByteArray blob = host.trimmed().toLower().toUtf8();
+    blob.append('\0');
+    blob.append(QByteArray::number(port));
+    blob.append('\0');
+    blob.append(username.trimmed().toLower().toUtf8());
+    return QCryptographicHash::hash(blob, QCryptographicHash::Sha1).toHex();
+}

cockatrice/src/interface/deck_sync/deck_sync_profile.h

@@ -0,0 +1,43 @@
+/**
+ * @file deck_sync_profile.h
+ * @brief Identity of one sync target (server + user) for deck collection sync.
+ */
+
+#ifndef DECK_SYNC_PROFILE_H
+#define DECK_SYNC_PROFILE_H
+
+#include <QString>
+
+/**
+ * @class DeckSyncProfile
+ * @brief Identifies which server and login a sync sidecar belongs to.
+ *
+ * A local deck folder can sync against several servers. Every server login
+ * gets its own profile, and every profile gets its own sidecar file, so
+ * switching servers never mixes up remote deck ids.
+ */
+class DeckSyncProfile
+{
+public:
+    QString host;     ///< Server hostname as entered by the user.
+    int port = 0;     ///< Server port.
+    QString username; ///< Login name on that server.
+
+    DeckSyncProfile() = default;
+    DeckSyncProfile(const QString &_host, int _port, const QString &_username);
+
+    /** @brief False when any of host, port or username is missing. */
+    [[nodiscard]] bool isValid() const;
+    /**
+     * @brief Stable file-system-safe key for this profile.
+     *
+     * SHA1 hex over the NUL-separated lowercased "host", port and "username"
+     * triple, so the same server reached with different hostname
+     * capitalisation maps to one file, while IPv6 hosts and usernames
+     * containing ':' can never collide two profiles. Empty for invalid
+     * profiles, so no two half-configured profiles share a file.
+     */
+    [[nodiscard]] QString key() const;
+};
+
+#endif // DECK_SYNC_PROFILE_H

cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp

@@ -0,0 +1,99 @@
+#include "deck_sync_sidecar.h"
+
+#include <QDir>
+#include <QFile>
+#include <QFileInfo>
+#include <QJsonDocument>
+#include <QJsonObject>
+#include <QSaveFile>
+
+namespace
+{
+constexpr int SIDECAR_FORMAT_VERSION = 1;
+} // namespace
+
+DeckSyncSidecar::DeckSyncSidecar(const QString &_filePath) : filePath(_filePath)
+{
+}
+
+bool DeckSyncSidecar::load()
+{
+    recordMap.clear();
+
+    QFile file(filePath);
+    if (!file.exists()) {
+        return true;
+    }
+    if (!file.open(QIODevice::ReadOnly)) {
+        return false;
+    }
+    const QJsonDocument document = QJsonDocument::fromJson(file.readAll());
+    if (!document.isObject() || !document.object().value("records").isObject()) {
+        return false;
+    }
+    const QJsonObject records = document.object().value("records").toObject();
+    for (auto it = records.begin(); it != records.end(); ++it) {
+        if (!it.value().isObject()) {
+            continue;
+        }
+        const QJsonObject entry = it.value().toObject();
+        DeckSyncRecord record;
+        record.guid = entry.value("guid").toString();
+        record.remoteId = entry.value("remoteId").toInt(-1);
+        record.baseHash = entry.value("baseHash").toString();
+        record.lastSyncSecs = static_cast<qint64>(entry.value("lastSync").toDouble());
+        record.deleted = entry.value("deleted").toBool(false);
+        recordMap.insert(it.key(), record);
+    }
+    return true;
+}
+
+bool DeckSyncSidecar::save() const
+{
+    QJsonObject records;
+    for (auto it = recordMap.begin(); it != recordMap.end(); ++it) {
+        QJsonObject entry;
+        entry.insert("guid", it.value().guid);
+        entry.insert("remoteId", it.value().remoteId);
+        entry.insert("baseHash", it.value().baseHash);
+        entry.insert("lastSync", static_cast<double>(it.value().lastSyncSecs));
+        entry.insert("deleted", it.value().deleted);
+        records.insert(it.key(), entry);
+    }
+    QJsonObject root;
+    root.insert("version", SIDECAR_FORMAT_VERSION);
+    root.insert("records", records);
+
+    QDir().mkpath(QFileInfo(filePath).absolutePath());
+    QSaveFile file(filePath);
+    if (!file.open(QIODevice::WriteOnly)) {
+        return false;
+    }
+    file.write(QJsonDocument(root).toJson(QJsonDocument::Compact));
+    return file.commit();
+}
+
+bool DeckSyncSidecar::contains(const QString &relativePath) const
+{
+    return recordMap.contains(relativePath);
+}
+
+DeckSyncRecord DeckSyncSidecar::get(const QString &relativePath) const
+{
+    return recordMap.value(relativePath, DeckSyncRecord());
+}
+
+void DeckSyncSidecar::set(const QString &relativePath, const DeckSyncRecord &record)
+{
+    recordMap.insert(relativePath, record);
+}
+
+void DeckSyncSidecar::remove(const QString &relativePath)
+{
+    recordMap.remove(relativePath);
+}
+
+QMap<QString, DeckSyncRecord> DeckSyncSidecar::records() const
+{
+    return recordMap;
+}

cockatrice/src/interface/deck_sync/deck_sync_sidecar.h

@@ -0,0 +1,52 @@
+/**
+ * @file deck_sync_sidecar.h
+ * @brief Per-profile local bookkeeping for deck collection sync.
+ */
+
+#ifndef DECK_SYNC_SIDECAR_H
+#define DECK_SYNC_SIDECAR_H
+
+#include <QMap>
+#include <QString>
+
+/** @brief Sync bookkeeping for one local deck file. */
+struct DeckSyncRecord
+{
+    QString guid;            ///< Stable deck identity shared with the server.
+    int remoteId = -1;       ///< Server row id, -1 when never uploaded.
+    QString baseHash;        ///< Deck hash at the last successful sync.
+    qint64 lastSyncSecs = 0; ///< Last sync time, seconds since Unix epoch.
+    bool deleted = false;    ///< Local tombstone waiting to be pushed.
+};
+
+/**
+ * @class DeckSyncSidecar
+ * @brief Loads and stores sync records as JSON next to the deck folder.
+ *
+ * One sidecar file per DeckSyncProfile (named by profile key), mapping paths
+ * relative to the deck folder to their last-synced state. Comparing the live
+ * file hash against baseHash tells clean apart from locally modified.
+ */
+class DeckSyncSidecar
+{
+public:
+    QString filePath; ///< Full path of the sidecar JSON file.
+
+    explicit DeckSyncSidecar(const QString &_filePath);
+
+    /** @brief Loads records; a missing file loads as empty and returns true. */
+    bool load();
+    /** @brief Stores records, creating parent folders as needed. */
+    bool save() const;
+    [[nodiscard]] bool contains(const QString &relativePath) const;
+    /** @brief Returns the record, or a default record when unknown. */
+    [[nodiscard]] DeckSyncRecord get(const QString &relativePath) const;
+    void set(const QString &relativePath, const DeckSyncRecord &record);
+    void remove(const QString &relativePath);
+    [[nodiscard]] QMap<QString, DeckSyncRecord> records() const;
+
+private:
+    QMap<QString, DeckSyncRecord> recordMap;
+};
+
+#endif // DECK_SYNC_SIDECAR_H

libcockatrice_deck_list/CMakeLists.txt

@@ -7,6 +7,7 @@ set(HEADERS
     libcockatrice/deck_list/tree/abstract_deck_list_node.h
     libcockatrice/deck_list/tree/deck_list_card_node.h
     libcockatrice/deck_list/tree/inner_deck_list_node.h
+    libcockatrice/deck_list/deck_diff.h
     libcockatrice/deck_list/deck_list.h
     libcockatrice/deck_list/deck_list_history_manager.h
     libcockatrice/deck_list/deck_list_node_tree.h
@@ -25,6 +26,7 @@ add_library(
   libcockatrice/deck_list/tree/abstract_deck_list_node.cpp
   libcockatrice/deck_list/tree/deck_list_card_node.cpp
   libcockatrice/deck_list/tree/inner_deck_list_node.cpp
+  libcockatrice/deck_list/deck_diff.cpp
   libcockatrice/deck_list/deck_list.cpp
   libcockatrice/deck_list/deck_list_history_manager.cpp
   libcockatrice/deck_list/deck_list_node_tree.cpp

libcockatrice_deck_list/libcockatrice/deck_list/deck_diff.cpp

@@ -0,0 +1,143 @@
+#include "deck_diff.h"
+
+#include "deck_list.h"
+#include "tree/deck_list_card_node.h"
+#include "tree/inner_deck_list_node.h"
+
+#include <QMap>
+#include <QPair>
+#include <QSet>
+#include <algorithm>
+
+namespace
+{
+using ZoneCardKey = QPair<QString, QString>;
+
+struct ZoneCardInfo
+{
+    int count = 0;
+    QString cardSetShortName;
+    QString cardSetNumber;
+    QString cardProviderId;
+};
+
+QMap<ZoneCardKey, ZoneCardInfo> zoneCardInfos(const DeckList &deck)
+{
+    QMap<ZoneCardKey, ZoneCardInfo> infos;
+    deck.forEachCard([&infos](InnerDecklistNode *zone, DecklistCardNode *card) {
+        ZoneCardInfo &info = infos[{zone->getName(), card->getName()}];
+        if (info.count == 0) {
+            info.cardSetShortName = card->getCardSetShortName();
+            info.cardSetNumber = card->getCardCollectorNumber();
+            info.cardProviderId = card->getCardProviderId();
+        }
+        info.count += card->getNumber();
+    });
+    return infos;
+}
+
+QMap<ZoneCardKey, int> zoneCardCounts(const DeckList &deck)
+{
+    QMap<ZoneCardKey, int> counts;
+    const QMap<ZoneCardKey, ZoneCardInfo> infos = zoneCardInfos(deck);
+    for (auto it = infos.begin(); it != infos.end(); ++it) {
+        counts.insert(it.key(), it.value().count);
+    }
+    return counts;
+}
+
+bool changeLessThan(const DeckCardChange &a, const DeckCardChange &b)
+{
+    if (a.zone != b.zone) {
+        return a.zone < b.zone;
+    }
+    return a.cardName < b.cardName;
+}
+} // namespace
+
+namespace DeckDiff
+{
+DeckDiffResult diff(const DeckList &oldDeck, const DeckList &newDeck)
+{
+    const QMap<ZoneCardKey, int> oldCounts = zoneCardCounts(oldDeck);
+    const QMap<ZoneCardKey, ZoneCardInfo> newInfos = zoneCardInfos(newDeck);
+
+    QSet<ZoneCardKey> keys(oldCounts.keyBegin(), oldCounts.keyEnd());
+    keys.unite(QSet<ZoneCardKey>(newInfos.keyBegin(), newInfos.keyEnd()));
+
+    DeckDiffResult result;
+    for (const ZoneCardKey &key : keys) {
+        const int oldCount = oldCounts.value(key, 0);
+        const ZoneCardInfo newInfo = newInfos.value(key, ZoneCardInfo());
+        if (oldCount != newInfo.count) {
+            DeckCardChange change;
+            change.zone = key.first;
+            change.cardName = key.second;
+            change.oldCount = oldCount;
+            change.newCount = newInfo.count;
+            change.cardSetShortName = newInfo.cardSetShortName;
+            change.cardSetNumber = newInfo.cardSetNumber;
+            change.cardProviderId = newInfo.cardProviderId;
+            result.changes.append(change);
+        }
+    }
+    std::sort(result.changes.begin(), result.changes.end(), changeLessThan);
+    return result;
+}
+
+bool canAutoMerge(const DeckDiffResult &localChanges, const DeckDiffResult &remoteChanges)
+{
+    QSet<ZoneCardKey> localKeys;
+    for (const DeckCardChange &change : localChanges.changes) {
+        localKeys.insert({change.zone, change.cardName});
+    }
+    for (const DeckCardChange &change : remoteChanges.changes) {
+        if (localKeys.contains({change.zone, change.cardName})) {
+            return false;
+        }
+    }
+    return true;
+}
+
+DeckList merge(const DeckList &baseDeck, const DeckDiffResult &localChanges, const DeckDiffResult &remoteChanges)
+{
+    QMap<ZoneCardKey, int> counts = zoneCardCounts(baseDeck);
+    QMap<ZoneCardKey, DeckCardChange> printings;
+    for (const DeckCardChange &change : localChanges.changes) {
+        counts[{change.zone, change.cardName}] = change.newCount;
+        printings[{change.zone, change.cardName}] = change;
+    }
+    for (const DeckCardChange &change : remoteChanges.changes) {
+        counts[{change.zone, change.cardName}] = change.newCount;
+        printings[{change.zone, change.cardName}] = change;
+    }
+
+    DeckList merged = baseDeck;
+    QMap<ZoneCardKey, QList<DecklistCardNode *>> nodesByKey;
+    merged.forEachCard([&nodesByKey](InnerDecklistNode *zone, DecklistCardNode *card) {
+        nodesByKey[{zone->getName(), card->getName()}].append(card);
+    });
+
+    for (auto it = counts.begin(); it != counts.end(); ++it) {
+        const ZoneCardKey &key = it.key();
+        const int target = qMax(0, it.value());
+        QList<DecklistCardNode *> nodes = nodesByKey.value(key);
+        if (target == 0) {
+            for (DecklistCardNode *node : nodes) {
+                merged.getTree()->deleteNode(node);
+            }
+        } else if (nodes.isEmpty()) {
+            const DeckCardChange printing = printings.value(key);
+            merged.getTree()->addCard(printing.cardName, target, printing.zone, -1, printing.cardSetShortName,
+                                      printing.cardSetNumber, printing.cardProviderId, true);
+        } else {
+            nodes.first()->setNumber(target);
+            for (int i = 1; i < nodes.size(); ++i) {
+                merged.getTree()->deleteNode(nodes.at(i));
+            }
+        }
+    }
+    merged.refreshDeckHash();
+    return merged;
+}
+} // namespace DeckDiff

libcockatrice_deck_list/libcockatrice/deck_list/deck_diff.h

@@ -0,0 +1,72 @@
+/**
+ * @file deck_diff.h
+ * @brief Card-level diff and three-way merge for deck collection sync.
+ */
+
+#ifndef DECK_DIFF_H
+#define DECK_DIFF_H
+
+#include <QList>
+#include <QString>
+
+class DeckList;
+
+/** @brief A single card-count change within one zone. */
+struct DeckCardChange
+{
+    QString zone;             ///< Zone name, e.g. "main".
+    QString cardName;         ///< Card name.
+    int oldCount = 0;         ///< Copies in the old deck.
+    int newCount = 0;         ///< Copies in the new deck.
+    QString cardSetShortName; ///< Printing set carried from the new side, empty when unchanged.
+    QString cardSetNumber;    ///< Printing collector number carried from the new side.
+    QString cardProviderId;   ///< Printing provider id carried from the new side.
+    /** @brief Copies added (positive) or removed (negative). */
+    [[nodiscard]] int delta() const
+    {
+        return newCount - oldCount;
+    }
+};
+
+/** @brief Card-level difference between two decks, sorted by zone then card name. */
+struct DeckDiffResult
+{
+    QList<DeckCardChange> changes;
+    /** @brief True when both decks hold the same cards in the same zones. */
+    [[nodiscard]] bool isEmpty() const
+    {
+        return changes.isEmpty();
+    }
+};
+
+/**
+ * @namespace DeckDiff
+ * @brief Pure card-count diff and three-way merge for deck sync.
+ *
+ * Compares card names and copy counts per zone only; a merged deck keeps
+ * base printings for existing cards and carries the changed side's printing
+ * for newly added cards.
+ */
+namespace DeckDiff
+{
+/** @brief Diffs oldDeck against newDeck. */
+DeckDiffResult diff(const DeckList &oldDeck, const DeckList &newDeck);
+/**
+ * @brief True when both change sets touch disjoint (zone, card) keys and a merge needs no arbitration.
+ */
+bool canAutoMerge(const DeckDiffResult &localChanges, const DeckDiffResult &remoteChanges);
+/**
+ * @brief Applies both change sets onto a copy of baseDeck.
+ *
+ * @precondition localChanges and remoteChanges were both computed with
+ * diff() against baseDeck. Stale or foreign change sets silently
+ * resurrect or delete cards.
+ *
+ * Counts are clamped at zero. On overlapping keys the remote change wins;
+ * callers offer this result as "Use Merge" only when canAutoMerge is true.
+ * Metadata and sideboard plans come from baseDeck.
+ */
+DeckList merge(const DeckList &baseDeck, const DeckDiffResult &localChanges, const DeckDiffResult &remoteChanges);
+} // namespace DeckDiff
+
+#endif // DECK_DIFF_H

libcockatrice_protocol/libcockatrice/protocol/pb/command_deck_upload.proto

@@ -14,4 +14,7 @@ message Command_DeckUpload {
     reserved 5, 6, 8;
     reserved "banner_card_name", "banner_card_provider", "tags";
     optional string color_identity = 7;
+    // Stable per-deck identity for two-way collection sync. Sent on first
+    // synced upload, echoed back in ServerInfo_DeckStorage_File afterwards.
+    optional string guid = 9;
 }

libcockatrice_protocol/libcockatrice/protocol/pb/response_deck_download.proto

@@ -6,4 +6,9 @@ message Response_DeckDownload {
         optional Response_DeckDownload ext = 1007;
     }
     optional string deck = 1;
+    // Sync identity echoed so the client can update its sidecar without an
+    // extra list fetch.
+    optional string guid = 2;
+    optional string hash = 3;
+    optional uint64 last_modified = 4;
 }

libcockatrice_protocol/libcockatrice/protocol/pb/serverinfo_deckstorage.proto

@@ -11,6 +11,15 @@ message ServerInfo_DeckStorage_File {
     // Tag names associated with the deck. Empty for decks uploaded before the
     // tags column existed.
     repeated string tags = 6;
+    // Stable per-deck identity for two-way collection sync. Empty for decks
+    // uploaded before the sync migration until they are re-uploaded.
+    optional string guid = 7;
+    // Content hash (DeckList::getDeckHash) for change detection without
+    // downloading the full list.
+    optional string hash = 8;
+    // Last modification time, seconds since Unix epoch. Drives newest-wins
+    // default and conflict-dialog recency highlight.
+    optional uint64 last_modified = 9;
 }
 
 message ServerInfo_DeckStorage_Folder {

servatrice/migrations/servatrice_0037_to_0038.sql

@@ -0,0 +1,32 @@
+-- Servatrice db migration from version 37 to version 38
+
+-- Deck collection sync + versioning.
+--
+-- 1. Stable per-deck identity and change detection for two-way sync:
+--    guid links a local file to its server row across renames, hash detects
+--    content changes without downloading, last_modified drives newest-wins
+--    default and conflict highlighting, deleted implements tombstones so a
+--    delete on one device does not resurrect from the other.
+-- 2. Limited per-deck version history: every hash-changing upload inserts a
+--    row; the server prunes beyond the configured retention (default 20).
+
+ALTER TABLE `cockatrice_decklist_files`
+  ADD COLUMN `guid` char(36) NULL AFTER `tags`,
+  ADD COLUMN `hash` char(40) NULL AFTER `guid`,
+  ADD COLUMN `last_modified` datetime NULL AFTER `hash`,
+  ADD COLUMN `deleted` tinyint(1) NOT NULL DEFAULT 0 AFTER `last_modified`;
+
+CREATE TABLE IF NOT EXISTS `cockatrice_deck_versions` (
+  `id` int(7) unsigned zerofill NOT NULL auto_increment,
+  `deck_id` int(7) unsigned zerofill NOT NULL,
+  `version_no` int(7) unsigned NOT NULL,
+  `content` text NOT NULL,
+  `hash` char(40) NULL,
+  `created_at` datetime NOT NULL,
+  `created_by_clientid` varchar(15) NULL,
+  PRIMARY KEY  (`id`),
+  KEY `deck_id` (`deck_id`),
+  FOREIGN KEY(`deck_id`) REFERENCES `cockatrice_decklist_files`(`id`) ON DELETE CASCADE ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
+
+UPDATE cockatrice_schema_version SET version=38 WHERE version=37;

servatrice/servatrice.ini.example

@@ -479,3 +479,12 @@ max_decks_per_share=50
 ; A value of 0 disables the limit.
 ; Default: 50
 max_shares_per_day=50
+
+
+[deck_sync]
+
+; Maximum number of stored versions kept per deck. Each upload with changed
+; content adds a version; older versions beyond this limit are pruned.
+; Minimum enforced: 1.
+; Default: 20
+max_versions=20

servatrice/servatrice.sql

@@ -20,7 +20,7 @@ CREATE TABLE IF NOT EXISTS `cockatrice_schema_version` (
   PRIMARY KEY  (`version`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
 
-INSERT INTO cockatrice_schema_version VALUES(37);
+INSERT INTO cockatrice_schema_version VALUES(38);
 
 -- users and user data tables
 CREATE TABLE IF NOT EXISTS `cockatrice_users` (
@@ -71,11 +71,30 @@ CREATE TABLE IF NOT EXISTS `cockatrice_decklist_files` (
   `banner_card_provider` varchar(32) NULL,
   `color_identity` varchar(5) NULL,
   `tags` text NULL,
+  `guid` char(36) NULL,
+  `hash` char(40) NULL,
+  `last_modified` datetime NULL,
+  `deleted` tinyint(1) NOT NULL DEFAULT 0,
   PRIMARY KEY  (`id`),
   KEY `FolderPlusUser` (`id_folder`,`id_user`),
   FOREIGN KEY(`id_user`) REFERENCES `cockatrice_users`(`id`)  ON DELETE CASCADE ON UPDATE CASCADE
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
 
+-- Per-deck version history for collection sync.
+-- One row per hash-changing upload; pruned beyond retention (default 20).
+CREATE TABLE IF NOT EXISTS `cockatrice_deck_versions` (
+  `id` int(7) unsigned zerofill NOT NULL auto_increment,
+  `deck_id` int(7) unsigned zerofill NOT NULL,
+  `version_no` int(7) unsigned NOT NULL,
+  `content` text NOT NULL,
+  `hash` char(40) NULL,
+  `created_at` datetime NOT NULL,
+  `created_by_clientid` varchar(15) NULL,
+  PRIMARY KEY  (`id`),
+  KEY `deck_id` (`deck_id`),
+  FOREIGN KEY(`deck_id`) REFERENCES `cockatrice_decklist_files`(`id`) ON DELETE CASCADE ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci;
+
 -- Temporary deck shares: a named bundle of decks that can be fetched by
 -- anyone who knows the (unguessable) token, until the share expires.
 CREATE TABLE IF NOT EXISTS `cockatrice_deck_share` (

servatrice/src/servatrice.cpp

@@ -1122,6 +1122,11 @@ int Servatrice::getDeckShareMaxSharesPerDay() const
     return settingsCache->value("deck_share/max_shares_per_day", 50).toInt();
 }
 
+int Servatrice::getDeckSyncMaxVersions() const
+{
+    return qMax(1, settingsCache->value("deck_sync/max_versions", 20).toInt());
+}
+
 int Servatrice::getNumberOfTCPPools() const
 {
     return settingsCache->value("server/number_pools", 1).toInt();

servatrice/src/servatrice.h

@@ -292,6 +292,7 @@ public:
     int getDeckShareCleanupInterval() const;
     int getDeckShareMaxDecksPerShare() const;
     int getDeckShareMaxSharesPerDay() const;
+    int getDeckSyncMaxVersions() const;
     int getMaxUsersPerAddress() const;
     int getMessageCountingInterval() const override;
     int getMaxMessageCountPerInterval() const override;

servatrice/src/servatrice_database_interface.h

@@ -21,7 +21,7 @@
 
 class QSqlQuery;
 
-#define DATABASE_SCHEMA_VERSION 37
+#define DATABASE_SCHEMA_VERSION 38
 
 class Servatrice;
 

servatrice/src/serversocketinterface.cpp

@@ -70,6 +70,7 @@
 #include <QString>
 #include <QStringLiteral>
 #include <QTextStream>
+#include <QUuid>
 #include <QVariant>
 #include <QtGlobal>
 #include <algorithm>
@@ -681,8 +682,8 @@ bool AbstractServerSocketInterface::deckListHelper(int folderId,
     }
 
     query = sqlInterface->prepareQuery("select id, name, upload_time, is_public, banner_card_name, "
-                                       "banner_card_provider, color_identity, tags from {prefix}_decklist_files where "
-                                       "id_folder = :id_folder and id_user = :id_user");
+                                       "banner_card_provider, color_identity, tags, guid, hash, last_modified from "
+                                       "{prefix}_decklist_files where id_folder = :id_folder and id_user = :id_user");
     query->bindValue(":id_folder", folderId);
     query->bindValue(":id_user", userId);
     if (!sqlInterface->execSqlQuery(query)) {
@@ -708,6 +709,12 @@ bool AbstractServerSocketInterface::deckListHelper(int folderId,
         for (const QString &tag : deserializeDeckTags(query->value(7).toString())) {
             newFile->add_tags(tag.toStdString());
         }
+        newFile->set_guid(query->value(8).toString().toStdString());
+        newFile->set_hash(query->value(9).toString().toStdString());
+        const QDateTime lastModified = query->value(10).toDateTime();
+        if (lastModified.isValid()) {
+            newFile->set_last_modified(lastModified.toSecsSinceEpoch());
+        }
     }
 
     return true;
@@ -1014,6 +1021,38 @@ QString sanitizeColorIdentity(const QString &colorIdentity)
 }
 } // namespace
 
+bool AbstractServerSocketInterface::storeDeckVersion(int deckId, const QString &content, const QString &hash)
+{
+    QSqlQuery *maxQuery =
+        sqlInterface->prepareQuery("select coalesce(max(version_no), 0) from {prefix}_deck_versions where deck_id = "
+                                   ":deck_id");
+    maxQuery->bindValue(":deck_id", deckId);
+    if (!sqlInterface->execSqlQuery(maxQuery) || !maxQuery->next()) {
+        return false;
+    }
+    const int nextVersion = maxQuery->value(0).toInt() + 1;
+
+    QSqlQuery *insertQuery =
+        sqlInterface->prepareQuery("insert into {prefix}_deck_versions (deck_id, version_no, content, hash, "
+                                   "created_at, created_by_clientid) values(:deck_id, :version_no, :content, :hash, "
+                                   "NOW(), :created_by_clientid)");
+    insertQuery->bindValue(":deck_id", deckId);
+    insertQuery->bindValue(":version_no", nextVersion);
+    insertQuery->bindValue(":content", content);
+    insertQuery->bindValue(":hash", hash);
+    insertQuery->bindValue(":created_by_clientid", QString::fromStdString(userInfo->clientid()));
+    if (!sqlInterface->execSqlQuery(insertQuery)) {
+        return false;
+    }
+
+    QSqlQuery *pruneQuery = sqlInterface->prepareQuery("delete from {prefix}_deck_versions where deck_id = :deck_id "
+                                                       "and version_no <= :min_kept_version");
+    pruneQuery->bindValue(":deck_id", deckId);
+    pruneQuery->bindValue(":min_kept_version", nextVersion - servatrice->getDeckSyncMaxVersions());
+    sqlInterface->execSqlQuery(pruneQuery);
+    return true;
+}
+
 Response::ResponseCode AbstractServerSocketInterface::cmdDeckUpload(const Command_DeckUpload &cmd,
                                                                     ResponseContainer &rc)
 {
@@ -1049,6 +1088,11 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckUpload(const Comman
     const QString bannerCardProvider = deck.getBannerCard().providerId.left(32);
     const QString tagsJson = serializeDeckTags(deck.getTags());
     const QString colorIdentity = sanitizeColorIdentity(nameFromStdString(cmd.color_identity()));
+    const QString deckHash = deck.getDeckHash();
+    QString guid = cmd.has_guid() ? nameFromStdString(cmd.guid()).left(36) : QString();
+    if (QUuid::fromString(guid).isNull()) {
+        guid = QUuid::createUuid().toString(QUuid::WithoutBraces);
+    }
 
     if (cmd.has_path()) {
         int folderId = getDeckPathId(nameFromStdString(cmd.path()));
@@ -1059,8 +1103,9 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckUpload(const Comman
         QSqlQuery *query =
             sqlInterface->prepareQuery("insert into {prefix}_decklist_files (id_folder, id_user, name, upload_time, "
                                        "content, is_public, banner_card_name, banner_card_provider, color_identity, "
-                                       "tags) values(:id_folder, :id_user, :name, NOW(), :content, :is_public, "
-                                       ":banner_card_name, :banner_card_provider, :color_identity, :tags)");
+                                       "tags, guid, hash, last_modified) values(:id_folder, :id_user, :name, NOW(), "
+                                       ":content, :is_public, :banner_card_name, :banner_card_provider, "
+                                       ":color_identity, :tags, :guid, :hash, NOW())");
         query->bindValue(":id_folder", folderId);
         query->bindValue(":id_user", userInfo->id());
         query->bindValue(":name", deckName);
@@ -1070,21 +1115,63 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckUpload(const Comman
         query->bindValue(":banner_card_provider", bannerCardProvider);
         query->bindValue(":color_identity", colorIdentity);
         query->bindValue(":tags", tagsJson);
+        query->bindValue(":guid", guid);
+        query->bindValue(":hash", deckHash);
         if (!sqlInterface->execSqlQuery(query)) {
             return Response::RespContextError;
         }
+        const int deckId = query->lastInsertId().toInt();
+        if (!storeDeckVersion(deckId, deckStr, deckHash)) {
+            QSqlQuery *cleanupQuery = sqlInterface->prepareQuery("delete from {prefix}_decklist_files where id = :id");
+            cleanupQuery->bindValue(":id", deckId);
+            sqlInterface->execSqlQuery(cleanupQuery);
+            return Response::RespContextError;
+        }
+
+        QSqlQuery *stampQuery =
+            sqlInterface->prepareQuery("select unix_timestamp(upload_time), unix_timestamp(last_modified) from "
+                                       "{prefix}_decklist_files where id = :id and id_user = :id_user");
+        stampQuery->bindValue(":id", deckId);
+        stampQuery->bindValue(":id_user", userInfo->id());
+        if (!sqlInterface->execSqlQuery(stampQuery) || !stampQuery->next()) {
+            QSqlQuery *cleanupQuery = sqlInterface->prepareQuery("delete from {prefix}_decklist_files where id = :id");
+            cleanupQuery->bindValue(":id", deckId);
+            sqlInterface->execSqlQuery(cleanupQuery);
+            return Response::RespContextError;
+        }
 
         Response_DeckUpload *re = new Response_DeckUpload;
         ServerInfo_DeckStorage_TreeItem *fileInfo = re->mutable_new_file();
-        fileInfo->set_id(query->lastInsertId().toInt());
+        fileInfo->set_id(deckId);
         fileInfo->set_name(deckName.toStdString());
-        fileInfo->mutable_file()->set_creation_time(QDateTime::currentDateTime().toSecsSinceEpoch());
+        fileInfo->mutable_file()->set_creation_time(stampQuery->value(0).toUInt());
         fileInfo->mutable_file()->set_is_public(cmd.has_is_public() && cmd.is_public());
+        fileInfo->mutable_file()->set_guid(guid.toStdString());
+        fileInfo->mutable_file()->set_hash(deckHash.toStdString());
+        fileInfo->mutable_file()->set_last_modified(stampQuery->value(1).toULongLong());
         rc.setResponseExtension(re);
     } else if (cmd.has_deck_id()) {
+        QSqlQuery *currentQuery =
+            sqlInterface->prepareQuery("select guid, hash from {prefix}_decklist_files where id = :id and id_user = "
+                                       ":id_user");
+        currentQuery->bindValue(":id", cmd.deck_id());
+        currentQuery->bindValue(":id_user", userInfo->id());
+        if (!sqlInterface->execSqlQuery(currentQuery)) {
+            return Response::RespContextError;
+        }
+        if (!currentQuery->next()) {
+            return Response::RespNameNotFound;
+        }
+        if (!QUuid::fromString(currentQuery->value(0).toString()).isNull()) {
+            guid = currentQuery->value(0).toString();
+        } else if (cmd.has_guid() && !QUuid::fromString(nameFromStdString(cmd.guid()).left(36)).isNull()) {
+            guid = nameFromStdString(cmd.guid()).left(36);
+        }
+        const QString oldHash = currentQuery->value(1).toString();
+
         QString updateQuery = "update {prefix}_decklist_files set name=:name, upload_time=NOW(), content=:content, "
                               "banner_card_name=:banner_card_name, banner_card_provider=:banner_card_provider, "
-                              "color_identity=:color_identity, tags=:tags";
+                              "color_identity=:color_identity, tags=:tags, guid=:guid, hash=:hash, last_modified=NOW()";
         if (cmd.has_is_public()) {
             updateQuery += ", is_public=:is_public";
         }
@@ -1099,33 +1186,56 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckUpload(const Comman
         query->bindValue(":banner_card_provider", bannerCardProvider);
         query->bindValue(":color_identity", colorIdentity);
         query->bindValue(":tags", tagsJson);
+        query->bindValue(":guid", guid);
+        query->bindValue(":hash", deckHash);
         if (cmd.has_is_public()) {
             query->bindValue(":is_public", cmd.is_public() ? 1 : 0);
         }
         if (!sqlInterface->execSqlQuery(query)) {
             return Response::RespContextError;
         }
-
         if (query->numRowsAffected() == 0) {
             return Response::RespNameNotFound;
         }
 
+        if (oldHash != deckHash) {
+            if (!storeDeckVersion(cmd.deck_id(), deckStr, deckHash)) {
+                return Response::RespContextError;
+            }
+        } else {
+            // Self-heal a version gap left by an earlier failed version write:
+            // a same-content re-upload must still leave a version behind.
+            QSqlQuery *versionQuery =
+                sqlInterface->prepareQuery("select count(*) from {prefix}_deck_versions where deck_id = :deck_id and "
+                                           "hash = :hash");
+            versionQuery->bindValue(":deck_id", cmd.deck_id());
+            versionQuery->bindValue(":hash", deckHash);
+            if (!sqlInterface->execSqlQuery(versionQuery) || !versionQuery->next()) {
+                return Response::RespContextError;
+            }
+            if (versionQuery->value(0).toInt() == 0 && !storeDeckVersion(cmd.deck_id(), deckStr, deckHash)) {
+                return Response::RespContextError;
+            }
+        }
+
         QSqlQuery *visibilityQuery =
-            sqlInterface->prepareQuery("select is_public from {prefix}_decklist_files where id = :id and "
-                                       "id_user = :id_user");
+            sqlInterface->prepareQuery("select is_public, unix_timestamp(upload_time), unix_timestamp(last_modified) "
+                                       "from {prefix}_decklist_files where id = :id and id_user = :id_user");
         visibilityQuery->bindValue(":id", cmd.deck_id());
         visibilityQuery->bindValue(":id_user", userInfo->id());
-        if (!sqlInterface->execSqlQuery(visibilityQuery)) {
+        if (!sqlInterface->execSqlQuery(visibilityQuery) || !visibilityQuery->next()) {
             return Response::RespContextError;
         }
-        const bool isPublic = visibilityQuery->next() && visibilityQuery->value(0).toBool();
 
         Response_DeckUpload *re = new Response_DeckUpload;
         ServerInfo_DeckStorage_TreeItem *fileInfo = re->mutable_new_file();
         fileInfo->set_id(cmd.deck_id());
         fileInfo->set_name(deckName.toStdString());
-        fileInfo->mutable_file()->set_creation_time(QDateTime::currentDateTime().toSecsSinceEpoch());
-        fileInfo->mutable_file()->set_is_public(isPublic);
+        fileInfo->mutable_file()->set_creation_time(visibilityQuery->value(1).toUInt());
+        fileInfo->mutable_file()->set_is_public(visibilityQuery->value(0).toBool());
+        fileInfo->mutable_file()->set_guid(guid.toStdString());
+        fileInfo->mutable_file()->set_hash(deckHash.toStdString());
+        fileInfo->mutable_file()->set_last_modified(visibilityQuery->value(2).toULongLong());
         rc.setResponseExtension(re);
     } else {
         return Response::RespInvalidData;
@@ -1147,11 +1257,29 @@ Response::ResponseCode AbstractServerSocketInterface::cmdDeckDownload(const Comm
     } catch (Response::ResponseCode &r) {
         return r;
     }
+    const QString deckNative = deck->writeToString_Native();
+    delete deck;
+
+    QSqlQuery *syncQuery =
+        sqlInterface->prepareQuery("select guid, hash, last_modified from {prefix}_decklist_files where id = :id and "
+                                   "id_user = :id_user");
+    syncQuery->bindValue(":id", cmd.deck_id());
+    syncQuery->bindValue(":id_user", userInfo->id());
+    if (!sqlInterface->execSqlQuery(syncQuery)) {
+        return Response::RespContextError;
+    }
 
     Response_DeckDownload *re = new Response_DeckDownload;
-    re->set_deck(deck->writeToString_Native().toStdString());
+    re->set_deck(deckNative.toStdString());
+    if (syncQuery->next()) {
+        re->set_guid(syncQuery->value(0).toString().toStdString());
+        re->set_hash(syncQuery->value(1).toString().toStdString());
+        const QDateTime lastModified = syncQuery->value(2).toDateTime();
+        if (lastModified.isValid()) {
+            re->set_last_modified(lastModified.toSecsSinceEpoch());
+        }
+    }
     rc.setResponseExtension(re);
-    delete deck;
 
     return Response::RespOk;
 }

servatrice/src/serversocketinterface.h

@@ -154,6 +154,7 @@ private:
     Response::ResponseCode cmdDeckDelDir(const Command_DeckDelDir &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckDel(const Command_DeckDel &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckUpload(const Command_DeckUpload &cmd, ResponseContainer &rc);
+    bool storeDeckVersion(int deckId, const QString &content, const QString &hash);
     DeckList *getDeckFromDatabase(int deckId);
     Response::ResponseCode cmdDeckDownload(const Command_DeckDownload &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdDeckDownloadPublic(const Command_DeckDownloadPublic &cmd, ResponseContainer &rc);

tests/CMakeLists.txt

@@ -27,6 +27,9 @@ add_test(NAME loader_local_matching_test COMMAND loader_local_matching_test)
 
 add_test(NAME deck_hash_performance_test COMMAND deck_hash_performance_test)
 set_tests_properties(deck_hash_performance_test PROPERTIES TIMEOUT 15)
+add_test(NAME deck_diff_test COMMAND deck_diff_test)
+add_test(NAME deck_sync_profile_test COMMAND deck_sync_profile_test)
+add_test(NAME deck_sync_sidecar_test COMMAND deck_sync_sidecar_test)
 
 # Find GTest
 
@@ -37,6 +40,17 @@ add_executable(test_age_formatting test_age_formatting.cpp)
 add_executable(password_hash_test password_hash_test.cpp)
 add_executable(playmat_resolver_test playmat_resolver_test.cpp)
 add_executable(deck_hash_performance_test deck_hash_performance_test.cpp)
+add_executable(deck_diff_test deck_diff_test.cpp)
+add_executable(
+  deck_sync_profile_test ${CMAKE_SOURCE_DIR}/cockatrice/src/interface/deck_sync/deck_sync_profile.cpp
+                         deck_sync_profile_test.cpp
+)
+target_include_directories(deck_sync_profile_test PRIVATE ${CMAKE_SOURCE_DIR}/cockatrice/src/interface/deck_sync)
+add_executable(
+  deck_sync_sidecar_test ${CMAKE_SOURCE_DIR}/cockatrice/src/interface/deck_sync/deck_sync_sidecar.cpp
+                         deck_sync_sidecar_test.cpp
+)
+target_include_directories(deck_sync_sidecar_test PRIVATE ${CMAKE_SOURCE_DIR}/cockatrice/src/interface/deck_sync)
 add_executable(server_card_counter_test server_card_counter_test.cpp)
 add_executable(server_counter_test server_counter_test.cpp)
 add_executable(server_rate_limiter_test server_rate_limiter_test.cpp)
@@ -137,6 +151,9 @@ if(NOT GTEST_FOUND)
   add_dependencies(password_hash_test gtest)
   add_dependencies(playmat_resolver_test gtest)
   add_dependencies(deck_hash_performance_test gtest)
+  add_dependencies(deck_diff_test gtest)
+  add_dependencies(deck_sync_profile_test gtest)
+  add_dependencies(deck_sync_sidecar_test gtest)
   add_dependencies(server_card_counter_test gtest)
   add_dependencies(server_counter_test gtest)
   add_dependencies(server_rate_limiter_test gtest)
@@ -175,6 +192,12 @@ target_link_libraries(
   deck_hash_performance_test libcockatrice_deck_list libcockatrice_utility Threads::Threads ${GTEST_BOTH_LIBRARIES}
   ${TEST_QT_MODULES}
 )
+target_link_libraries(
+  deck_diff_test libcockatrice_deck_list libcockatrice_utility Threads::Threads ${GTEST_BOTH_LIBRARIES}
+  ${TEST_QT_MODULES}
+)
+target_link_libraries(deck_sync_profile_test Threads::Threads ${GTEST_BOTH_LIBRARIES} ${TEST_QT_MODULES})
+target_link_libraries(deck_sync_sidecar_test Threads::Threads ${GTEST_BOTH_LIBRARIES} ${TEST_QT_MODULES})
 target_link_libraries(
   server_card_counter_test libcockatrice_network Threads::Threads ${GTEST_BOTH_LIBRARIES} ${TEST_QT_MODULES}
 )

tests/deck_diff_test.cpp

@@ -0,0 +1,181 @@
+#include "gtest/gtest.h"
+#include <QList>
+#include <QString>
+#include <libcockatrice/deck_list/deck_diff.h>
+#include <libcockatrice/deck_list/deck_list.h>
+#include <libcockatrice/deck_list/tree/deck_list_card_node.h>
+#include <libcockatrice/deck_list/tree/inner_deck_list_node.h>
+
+namespace
+{
+DeckList makeDeck(std::initializer_list<std::pair<const char *, int>> mainCards,
+                  std::initializer_list<std::pair<const char *, int>> sideCards = {})
+{
+    DeckList deck;
+    for (const auto &[name, count] : mainCards) {
+        for (int i = 0; i < count; ++i) {
+            deck.addCard(name, "main");
+        }
+    }
+    for (const auto &[name, count] : sideCards) {
+        for (int i = 0; i < count; ++i) {
+            deck.addCard(name, "side");
+        }
+    }
+    return deck;
+}
+
+int countOf(const DeckList &deck, const char *zone, const char *name)
+{
+    int count = 0;
+    deck.forEachCard([&](InnerDecklistNode *zoneNode, DecklistCardNode *card) {
+        if (zoneNode->getName() == zone && card->getName() == name) {
+            count += card->getNumber();
+        }
+    });
+    return count;
+}
+
+QList<DecklistCardNode *> nodesOf(const DeckList &deck, const char *zone, const char *name)
+{
+    QList<DecklistCardNode *> nodes;
+    deck.forEachCard([&](InnerDecklistNode *zoneNode, DecklistCardNode *card) {
+        if (zoneNode->getName() == zone && card->getName() == name) {
+            nodes.append(card);
+        }
+    });
+    return nodes;
+}
+} // namespace
+
+TEST(DeckDiffTest, IdenticalDecksHaveEmptyDiff)
+{
+    DeckList first = makeDeck({{"Lightning Bolt", 4}});
+    DeckList second = makeDeck({{"Lightning Bolt", 4}});
+    EXPECT_TRUE(DeckDiff::diff(first, second).isEmpty());
+}
+
+TEST(DeckDiffTest, ChangesAreSortedByZoneThenName)
+{
+    DeckList oldDeck = makeDeck({{"Mountain", 20}, {"Lightning Bolt", 4}}, {{"Shock", 2}});
+    DeckList newDeck = makeDeck({{"Mountain", 19}, {"Shock", 5}}, {{"Shock", 1}, {"Teferi", 1}});
+
+    DeckDiffResult result = DeckDiff::diff(oldDeck, newDeck);
+    ASSERT_EQ(result.changes.size(), 5);
+    EXPECT_EQ(result.changes.at(0).zone, "main");
+    EXPECT_EQ(result.changes.at(0).cardName, "Lightning Bolt");
+    EXPECT_EQ(result.changes.at(1).cardName, "Mountain");
+    EXPECT_EQ(result.changes.at(2).cardName, "Shock");
+    EXPECT_EQ(result.changes.at(3).zone, "side");
+    EXPECT_EQ(result.changes.at(3).cardName, "Shock");
+    EXPECT_EQ(result.changes.at(4).cardName, "Teferi");
+}
+
+TEST(DeckDiffTest, ReportsAddedAndRemovedCopies)
+{
+    DeckList oldDeck = makeDeck({{"Lightning Bolt", 4}, {"Mountain", 20}});
+    DeckList newDeck = makeDeck({{"Lightning Bolt", 2}, {"Shock", 4}, {"Mountain", 20}});
+
+    DeckDiffResult result = DeckDiff::diff(oldDeck, newDeck);
+    ASSERT_EQ(result.changes.size(), 2);
+    EXPECT_EQ(result.changes.at(0).cardName, "Lightning Bolt");
+    EXPECT_EQ(result.changes.at(0).oldCount, 4);
+    EXPECT_EQ(result.changes.at(0).newCount, 2);
+    EXPECT_EQ(result.changes.at(0).delta(), -2);
+    EXPECT_EQ(result.changes.at(1).cardName, "Shock");
+    EXPECT_EQ(result.changes.at(1).oldCount, 0);
+    EXPECT_EQ(result.changes.at(1).newCount, 4);
+}
+
+TEST(DeckDiffTest, ZoneMoveIsTwoChanges)
+{
+    DeckList oldDeck = makeDeck({{"Teferi", 1}});
+    DeckList newDeck = makeDeck({}, {{"Teferi", 1}});
+
+    DeckDiffResult result = DeckDiff::diff(oldDeck, newDeck);
+    ASSERT_EQ(result.changes.size(), 2);
+    EXPECT_EQ(result.changes.at(0).zone, "main");
+    EXPECT_EQ(result.changes.at(0).newCount, 0);
+    EXPECT_EQ(result.changes.at(1).zone, "side");
+    EXPECT_EQ(result.changes.at(1).oldCount, 0);
+}
+
+TEST(DeckDiffTest, DisjointChangesCanAutoMerge)
+{
+    DeckList base = makeDeck({{"Lightning Bolt", 4}, {"Mountain", 20}});
+    DeckList local = makeDeck({{"Lightning Bolt", 4}, {"Mountain", 18}});
+    DeckList remote = makeDeck({{"Shock", 2}, {"Lightning Bolt", 4}, {"Mountain", 20}});
+
+    DeckDiffResult localChanges = DeckDiff::diff(base, local);
+    DeckDiffResult remoteChanges = DeckDiff::diff(base, remote);
+    EXPECT_TRUE(DeckDiff::canAutoMerge(localChanges, remoteChanges));
+
+    DeckList merged = DeckDiff::merge(base, localChanges, remoteChanges);
+    EXPECT_EQ(countOf(merged, "main", "Mountain"), 18);
+    EXPECT_EQ(countOf(merged, "main", "Shock"), 2);
+    EXPECT_EQ(countOf(merged, "main", "Lightning Bolt"), 4);
+}
+
+TEST(DeckDiffTest, OverlappingChangesCannotAutoMergeAndRemoteWins)
+{
+    DeckList base = makeDeck({{"Lightning Bolt", 4}});
+    DeckList local = makeDeck({{"Lightning Bolt", 3}});
+    DeckList remote = makeDeck({{"Lightning Bolt", 1}});
+
+    DeckDiffResult localChanges = DeckDiff::diff(base, local);
+    DeckDiffResult remoteChanges = DeckDiff::diff(base, remote);
+    EXPECT_FALSE(DeckDiff::canAutoMerge(localChanges, remoteChanges));
+
+    DeckList merged = DeckDiff::merge(base, localChanges, remoteChanges);
+    EXPECT_EQ(countOf(merged, "main", "Lightning Bolt"), 1);
+}
+
+TEST(DeckDiffTest, MergeKeepsBaseMetadata)
+{
+    DeckList base = makeDeck({{"Lightning Bolt", 4}});
+    base.setName("Affinity v3");
+    DeckList remote = makeDeck({{"Lightning Bolt", 4}, {"Shock", 1}});
+
+    DeckList merged = DeckDiff::merge(base, DeckDiff::diff(base, base), DeckDiff::diff(base, remote));
+    EXPECT_EQ(merged.getName(), "Affinity v3");
+    EXPECT_EQ(countOf(merged, "main", "Shock"), 1);
+}
+
+TEST(DeckDiffTest, MergePreservesBasePrintingAndCollapsesNodes)
+{
+    DeckList base;
+    base.addCard("Mountain", "main", -1, "DOM", "250")->setNumber(4);
+    base.refreshDeckHash();
+
+    DeckList local = base;
+    local.addCard("Shock", "main", -1, "M19", "156")->setNumber(2);
+    local.refreshDeckHash();
+
+    DeckList remote = base;
+    remote.addCard("Lightning Bolt", "main", -1, "M10", "146")->setNumber(4);
+    remote.refreshDeckHash();
+
+    const DeckDiffResult localChanges = DeckDiff::diff(base, local);
+    const DeckDiffResult remoteChanges = DeckDiff::diff(base, remote);
+    ASSERT_TRUE(DeckDiff::canAutoMerge(localChanges, remoteChanges));
+
+    const DeckList merged = DeckDiff::merge(base, localChanges, remoteChanges);
+
+    const QList<DecklistCardNode *> mountains = nodesOf(merged, "main", "Mountain");
+    ASSERT_EQ(mountains.size(), 1);
+    EXPECT_EQ(mountains.first()->getNumber(), 4);
+    EXPECT_EQ(mountains.first()->getCardSetShortName(), "DOM");
+    EXPECT_EQ(mountains.first()->getCardCollectorNumber(), "250");
+
+    const QList<DecklistCardNode *> shocks = nodesOf(merged, "main", "Shock");
+    ASSERT_EQ(shocks.size(), 1);
+    EXPECT_EQ(shocks.first()->getNumber(), 2);
+    EXPECT_EQ(shocks.first()->getCardSetShortName(), "M19");
+    EXPECT_EQ(shocks.first()->getCardCollectorNumber(), "156");
+}
+
+int main(int argc, char **argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}

tests/deck_sync_profile_test.cpp

@@ -0,0 +1,63 @@
+#include "gtest/gtest.h"
+#include <QString>
+#include <deck_sync_profile.h>
+
+TEST(DeckSyncProfileTest, KeyIsStable)
+{
+    DeckSyncProfile first("woogerworks.com", 4747, "Skog7");
+    DeckSyncProfile second("woogerworks.com", 4747, "Skog7");
+    EXPECT_EQ(first.key(), second.key());
+    EXPECT_FALSE(first.key().isEmpty());
+}
+
+TEST(DeckSyncProfileTest, KeyIgnoresCase)
+{
+    DeckSyncProfile lower("woogerworks.com", 4747, "skog7");
+    DeckSyncProfile upper("WOOGERWORKS.COM", 4747, "SKOG7");
+    EXPECT_EQ(lower.key(), upper.key());
+}
+
+TEST(DeckSyncProfileTest, KeyDiffersPerServerAndUser)
+{
+    DeckSyncProfile base("woogerworks.com", 4747, "skog7");
+    EXPECT_NE(base.key(), DeckSyncProfile("other.server", 4747, "skog7").key());
+    EXPECT_NE(base.key(), DeckSyncProfile("woogerworks.com", 4748, "skog7").key());
+    EXPECT_NE(base.key(), DeckSyncProfile("woogerworks.com", 4747, "other").key());
+}
+
+TEST(DeckSyncProfileTest, KeyIsUnambiguousAcrossSeparators)
+{
+    DeckSyncProfile left("a:1", 2, "b");
+    DeckSyncProfile right("a", 1, "2:b");
+    EXPECT_NE(left.key(), right.key());
+    EXPECT_NE(DeckSyncProfile("::1", 4747, "skog7").key(), DeckSyncProfile("::2", 4747, "skog7").key());
+}
+
+TEST(DeckSyncProfileTest, InvalidProfilesHaveNoKey)
+{
+    EXPECT_TRUE(DeckSyncProfile().key().isEmpty());
+    EXPECT_TRUE(DeckSyncProfile("", 4747, "skog7").key().isEmpty());
+    EXPECT_TRUE(DeckSyncProfile("woogerworks.com", 0, "skog7").key().isEmpty());
+}
+
+TEST(DeckSyncProfileTest, KeyIgnoresSurroundingWhitespace)
+{
+    DeckSyncProfile plain("woogerworks.com", 4747, "skog7");
+    DeckSyncProfile padded("  woogerworks.com ", 4747, " skog7 ");
+    EXPECT_EQ(plain.key(), padded.key());
+}
+
+TEST(DeckSyncProfileTest, ValidityRequiresAllFields)
+{
+    EXPECT_TRUE(DeckSyncProfile("woogerworks.com", 4747, "skog7").isValid());
+    EXPECT_FALSE(DeckSyncProfile("", 4747, "skog7").isValid());
+    EXPECT_FALSE(DeckSyncProfile("woogerworks.com", 0, "skog7").isValid());
+    EXPECT_FALSE(DeckSyncProfile("woogerworks.com", 4747, "").isValid());
+    EXPECT_FALSE(DeckSyncProfile().isValid());
+}
+
+int main(int argc, char **argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}

tests/deck_sync_sidecar_test.cpp

@@ -0,0 +1,126 @@
+#include "gtest/gtest.h"
+#include <QDir>
+#include <QFile>
+#include <QFileInfo>
+#include <QString>
+#include <QTemporaryDir>
+#include <deck_sync_sidecar.h>
+
+namespace
+{
+QString sidecarPath(QTemporaryDir &dir)
+{
+    return dir.filePath(".sync/profilekey.json");
+}
+} // namespace
+
+TEST(DeckSyncSidecarTest, MissingFileLoadsEmpty)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+    EXPECT_TRUE(sidecar.load());
+    EXPECT_TRUE(sidecar.records().isEmpty());
+    EXPECT_FALSE(sidecar.contains("affinity.cod"));
+}
+
+TEST(DeckSyncSidecarTest, RoundTripsRecords)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+
+    DeckSyncRecord record;
+    record.guid = "123e4567-e89b-12d3-a456-426614174000";
+    record.remoteId = 42;
+    record.baseHash = "5cac19qm";
+    record.lastSyncSecs = 1791739200;
+    record.deleted = true;
+    sidecar.set("decks/affinity.cod", record);
+    EXPECT_TRUE(sidecar.save());
+
+    DeckSyncSidecar reloaded(sidecarPath(dir));
+    EXPECT_TRUE(reloaded.load());
+    EXPECT_TRUE(reloaded.contains("decks/affinity.cod"));
+    DeckSyncRecord back = reloaded.get("decks/affinity.cod");
+    EXPECT_EQ(back.guid, record.guid);
+    EXPECT_EQ(back.remoteId, 42);
+    EXPECT_EQ(back.baseHash, "5cac19qm");
+    EXPECT_EQ(back.lastSyncSecs, 1791739200);
+    EXPECT_TRUE(back.deleted);
+}
+
+TEST(DeckSyncSidecarTest, UnknownPathReturnsDefaultRecord)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+    DeckSyncRecord back = sidecar.get("missing.cod");
+    EXPECT_EQ(back.remoteId, -1);
+    EXPECT_TRUE(back.guid.isEmpty());
+}
+
+namespace
+{
+bool writeRaw(const QString &path, const QByteArray &bytes)
+{
+    QDir().mkpath(QFileInfo(path).absolutePath());
+    QFile file(path);
+    return file.open(QIODevice::WriteOnly | QIODevice::Truncate) && file.write(bytes) == bytes.size();
+}
+} // namespace
+
+TEST(DeckSyncSidecarTest, GarbageFileFailsToLoad)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    ASSERT_TRUE(writeRaw(sidecarPath(dir), "not json at all"));
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+    EXPECT_FALSE(sidecar.load());
+}
+
+TEST(DeckSyncSidecarTest, WrongRecordsShapeFailsToLoad)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    ASSERT_TRUE(writeRaw(sidecarPath(dir), R"({"records":["a.cod"]})"));
+    DeckSyncSidecar missing(sidecarPath(dir));
+    EXPECT_FALSE(missing.load());
+
+    ASSERT_TRUE(writeRaw(sidecarPath(dir), R"({"foo":1})"));
+    DeckSyncSidecar other(sidecarPath(dir));
+    EXPECT_FALSE(other.load());
+}
+
+TEST(DeckSyncSidecarTest, NonObjectEntriesAreSkipped)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    ASSERT_TRUE(writeRaw(sidecarPath(dir), R"({"records":{"a.cod":42,"b.cod":{"guid":"g"}}})"));
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+    EXPECT_TRUE(sidecar.load());
+    EXPECT_FALSE(sidecar.contains("a.cod"));
+    EXPECT_TRUE(sidecar.contains("b.cod"));
+    EXPECT_EQ(sidecar.get("b.cod").guid, "g");
+}
+
+TEST(DeckSyncSidecarTest, RemoveDropsRecord)
+{
+    QTemporaryDir dir;
+    ASSERT_TRUE(dir.isValid());
+    DeckSyncSidecar sidecar(sidecarPath(dir));
+    sidecar.set("a.cod", DeckSyncRecord());
+    sidecar.remove("a.cod");
+    EXPECT_FALSE(sidecar.contains("a.cod"));
+    EXPECT_TRUE(sidecar.save());
+
+    DeckSyncSidecar reloaded(sidecarPath(dir));
+    EXPECT_TRUE(reloaded.load());
+    EXPECT_FALSE(reloaded.contains("a.cod"));
+}
+
+int main(int argc, char **argv)
+{
+    ::testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}