[Client] DeckSyncProfile + sidecar + DeckDiff with tests

cockatrice/src/interface/deck_sync/deck_sync_profile.h

@@ -0,0 +1,42 @@
+/**
+ * @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>
+
+/**
+ * @struct 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.
+ */
+struct DeckSyncProfile
+{
+    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