using System.Collections.Frozen;
using System.Diagnostics.CodeAnalysis;

namespace AcDream.Core.CharGen;

/// <summary>
/// Top-level, presentation-free, immutable projection of retail's CharGen
/// DAT table (portal.dat 0x0E000002, <c>ACCharGenData::Serialize @
/// 0x005C36D0</c>) PLUS the global SkillTable (portal.dat 0x0E000004) that
/// retail falls back to when a heritage's own skill-cost list has no entry
/// for a given skill id. Retail's <c>ACCharGenData::GetSkillTrainedCost @
/// 0x005C26D0</c> / <c>GetSkillSpecializedCost @ 0x005C27D0</c> both scan
/// the heritage's own list first and, on a miss (or an empty list), fall
/// through to <c>DBCache::GetFromEnumStatic(4, 2, 0x10000004)</c> — the
/// SAME global SkillTable every other skill-cost lookup in the client
/// reads — rather than treating the skill as free or invalid. See
/// <see cref="GlobalSkillCostsBySkillId"/>. Production builds create this
/// from the installed DAT through Content's
/// <c>AcDream.Content.CharGen.ChargenTableReader.Load</c>; this type itself
/// has no DAT/Chorizite dependency so it is safe to hand to plugin-facing
/// or test code. Every collection is frozen/immutable at construction (a
/// caller cannot downcast an <see cref="IReadOnlyDictionary{TKey,TValue}"/>
/// back to a mutable <see cref="Dictionary{TKey,TValue}"/> and mutate this
/// process-shared model out from under other readers). Everything a "typed
/// chargen options model" needs — starter areas, heritages, templates,
/// per-gender appearance option lists, skill costs — hangs off this one
/// root.
/// </summary>
/// <param name="GlobalSkillDetailsBySkillId">
/// Campaign CC gate round 1 closeout (Group 2): the global SkillTable's
/// MinLevel/Description/Formula per skill (see <see cref="ChargenSkillDetail"/>'s
/// own doc for why these are GLOBAL-only, unlike <paramref name="GlobalSkillCostsBySkillId"/>
/// which also has a per-heritage counterpart). Defaults to null (not an
/// empty dictionary) so every pre-existing caller that builds a
/// <see cref="ChargenOptions"/> without this parameter — five test fixtures
/// plus <c>ChargenOptions.Empty</c> below — compiles and behaves exactly as
/// before; <see cref="TryGetSkillDetail"/> treats null the same as "empty."
/// </param>
public sealed record ChargenOptions(
    IReadOnlyList<ChargenStarterArea> StarterAreas,
    IReadOnlyDictionary<uint, ChargenHeritageOptions> HeritagesById,
    IReadOnlyDictionary<uint, ChargenSkillCost> GlobalSkillCostsBySkillId,
    IReadOnlyDictionary<uint, ChargenSkillDetail>? GlobalSkillDetailsBySkillId = null)
{
    public static ChargenOptions Empty { get; } = new(
        Array.Empty<ChargenStarterArea>(),
        FrozenDictionary<uint, ChargenHeritageOptions>.Empty,
        FrozenDictionary<uint, ChargenSkillCost>.Empty);

    public bool TryGetHeritage(uint heritageId, [MaybeNullWhen(false)] out ChargenHeritageOptions heritage) =>
        HeritagesById.TryGetValue(heritageId, out heritage);

    public bool TryGetStarterArea(int index, [MaybeNullWhen(false)] out ChargenStarterArea area)
    {
        if (index >= 0 && index < StarterAreas.Count)
        {
            area = StarterAreas[index];
            return true;
        }
        area = default;
        return false;
    }

    /// <summary>See <see cref="GlobalSkillDetailsBySkillId"/>'s own doc.</summary>
    public bool TryGetSkillDetail(uint skillId, [MaybeNullWhen(false)] out ChargenSkillDetail detail)
    {
        if (GlobalSkillDetailsBySkillId is { } details && details.TryGetValue(skillId, out detail))
            return true;
        detail = default;
        return false;
    }
}