[Filters] Extract the color filter mode derivation into libcockatrice_filters

The mode table and the 'which mode produced this filter set' derivation are
filter semantics, not widget code, so they belong next to CardFilter rather
than in an anonymous namespace in the client. Moving them also makes them
testable: filter_mode_test pins every mode, the Custom fallback and the
'keep the live mode when it still fits' rule.

tests/carddatabase/CMakeLists.txt

@@ -52,6 +52,20 @@ if(WITH_ORACLE OR WITH_CLIENT)
     libcockatrice_filters
   )
 
+  # ------------------------
+  # Filter Mode Test
+  # ------------------------
+  cockatrice_add_test(
+    NAME
+    filter_mode_test
+    SOURCES
+    ${VERSION_STRING_CPP}
+    filter_mode_test.cpp
+    mocks.cpp
+    LIBS
+    libcockatrice_filters
+  )
+
   # ------------------------
   # Visual Display Model Test
   # ------------------------

tests/carddatabase/filter_mode_test.cpp

@@ -0,0 +1,147 @@
+#include "libcockatrice/filters/filter_mode.h"
+
+#include <gtest/gtest.h>
+
+class FilterModeTest : public ::testing::Test
+{
+protected:
+    ~FilterModeTest() override
+    {
+        for (CardFilter *filter : owned) {
+            delete filter;
+        }
+    }
+
+    /** @brief Create a filter owned by the fixture and append it to the set under test. */
+    const CardFilter *
+    add(const QString &term, CardFilter::Type type, CardFilter::Attr attr = CardFilter::Attr::AttrColor)
+    {
+        owned.append(new CardFilter(term, type, attr));
+        filters.append(owned.last());
+        return owned.last();
+    }
+
+    QList<CardFilter *> owned;
+    QList<const CardFilter *> filters;
+};
+
+TEST(FilterModeInfoTest, EachModeDescribesItsOwnFilters)
+{
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Includes).includeType, CardFilter::Type::TypeOr);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Includes).excludeType, CardFilter::Type::TypeEnd);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Includes).attr, CardFilter::Attr::AttrColor);
+
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Excludes).includeType, CardFilter::Type::TypeAndNot);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Excludes).excludeType, CardFilter::Type::TypeEnd);
+
+    EXPECT_EQ(getFilterModeInfo(FilterMode::IncludeExclude).includeType, CardFilter::Type::TypeOr);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::IncludeExclude).excludeType, CardFilter::Type::TypeAndNot);
+
+    EXPECT_EQ(getFilterModeInfo(FilterMode::ExactMatch).includeType, CardFilter::Type::TypeAnd);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::ExactMatch).excludeType, CardFilter::Type::TypeAndNot);
+
+    // Color identity only excludes: the selected colors must be the identity, so nothing is included positively.
+    EXPECT_EQ(getFilterModeInfo(FilterMode::ColorIdentity).includeType, CardFilter::Type::TypeEnd);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::ColorIdentity).excludeType, CardFilter::Type::TypeAndNot);
+    EXPECT_EQ(getFilterModeInfo(FilterMode::ColorIdentity).attr, CardFilter::Attr::AttrColorIdentity);
+
+    EXPECT_EQ(getFilterModeInfo(FilterMode::Custom).attr, CardFilter::Attr::AttrEnd);
+}
+
+TEST_F(FilterModeTest, EmptyFilterSetKeepsACompatibleMode)
+{
+    // Includes and Color identity both allow an empty set, so the live mode is not swapped for another.
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Includes), FilterMode::Includes);
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::ColorIdentity), FilterMode::ColorIdentity);
+}
+
+// Include / Exclude and Exact match always hold one filter per color, so an empty set cannot have come from
+// them and falls back to the first mode that can describe it.
+TEST_F(FilterModeTest, EmptyFilterSetFallsBackWhenTheModeNeedsOneFilterPerColor)
+{
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::IncludeExclude), FilterMode::Includes);
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::ExactMatch), FilterMode::Includes);
+}
+
+TEST_F(FilterModeTest, IncludesFromOrFilters)
+{
+    add("W", CardFilter::Type::TypeOr);
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Includes), FilterMode::Includes);
+    // A single OR filter cannot come from Excludes, so the first mode that can produce it is selected.
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Excludes), FilterMode::Includes);
+}
+
+TEST_F(FilterModeTest, ExcludesFromAndNotFilters)
+{
+    add("W", CardFilter::Type::TypeAndNot);
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Excludes), FilterMode::Excludes);
+    // Includes needs an OR or an end filter, so an AND NOT filter selects Excludes.
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Includes), FilterMode::Excludes);
+}
+
+TEST_F(FilterModeTest, IncludeExcludeNeedsOneFilterPerColor)
+{
+    add("W", CardFilter::Type::TypeOr);
+    for (const QChar color : QString("UBRG")) {
+        add(QString(color), CardFilter::Type::TypeAndNot);
+    }
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::IncludeExclude), FilterMode::IncludeExclude);
+}
+
+TEST_F(FilterModeTest, IncludeExcludeRejectsAnIncompleteColorSet)
+{
+    add("W", CardFilter::Type::TypeOr);
+    add("U", CardFilter::Type::TypeAndNot);
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::IncludeExclude), FilterMode::Custom);
+}
+
+TEST_F(FilterModeTest, ExactMatchFromAndAndAndNotFilters)
+{
+    add("W", CardFilter::Type::TypeAnd);
+    for (const QChar color : QString("UBRG")) {
+        add(QString(color), CardFilter::Type::TypeAndNot);
+    }
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::ExactMatch), FilterMode::ExactMatch);
+}
+
+TEST_F(FilterModeTest, ColorIdentityFromIdentityAndNotFilters)
+{
+    for (const QChar color : QString("BRG")) {
+        add(QString(color), CardFilter::Type::TypeAndNot, CardFilter::Attr::AttrColorIdentity);
+    }
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::ColorIdentity), FilterMode::ColorIdentity);
+}
+
+TEST_F(FilterModeTest, MixedAttributesAreCustom)
+{
+    add("W", CardFilter::Type::TypeOr, CardFilter::Attr::AttrColor);
+    add("U", CardFilter::Type::TypeAndNot, CardFilter::Attr::AttrColorIdentity);
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Includes), FilterMode::Custom);
+}
+
+TEST_F(FilterModeTest, CustomLeavesAsSoonAsAModeCanExplainTheFilters)
+{
+    add("W", CardFilter::Type::TypeOr);
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Custom), FilterMode::Includes);
+}
+
+// Exact match with no color selected stores one AND NOT filter per color. That is a legitimate Exact match
+// state, so the live mode is kept; a mode that cannot produce the set re-derives to Excludes, which produces
+// the identical filters.
+TEST_F(FilterModeTest, FullyExcludedColorSetIsExactMatchOrExcludes)
+{
+    for (const QChar color : QString("WUBRG")) {
+        add(QString(color), CardFilter::Type::TypeAndNot);
+    }
+
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::ExactMatch), FilterMode::ExactMatch);
+    EXPECT_EQ(deriveFilterMode(filters, FilterMode::Includes), FilterMode::Excludes);
+}