using AcDream.Plugin.Abstractions;

namespace AcDream.Plugins.MossTank;

/// <summary>
/// Decides which self-buffs are missing and in what order to cast them.
/// </summary>
/// <remarks>
/// <para>
/// Pure function of (known self-buffs, active enchantments). No host calls, no
/// state, no clock — so the buff policy can be reasoned about and tested
/// without a live session, which is the whole reason it lives here rather than
/// in the host.
/// </para>
/// <para>
/// <b>Why the spellbook is the source of truth.</b> The obvious reading of
/// "buff every trained and specialised skill" is to enumerate skills and map
/// each to its buff line. The client cannot do that honestly: the link between
/// a spell and the stat it modifies arrives from the <em>server</em>, in the
/// enchantment message, and is absent from the client's own spell table. What
/// the client does know is which spells the character has learned — and a
/// character only learns the buffs for the skills they actually use. Driving
/// from the spellbook reaches the same set without inventing a mapping the
/// client has no grounds for.
/// </para>
/// </remarks>
internal static class BuffPlan
{
    /// <summary>
    /// The strongest known buff per family that is not already in force at an
    /// equal or higher tier, ordered so the plan is stable between passes.
    /// </summary>
    public static List<PluginSpellInfo> Build(
        IReadOnlyList<PluginSpellInfo> knownSelfBuffs,
        IReadOnlyList<PluginActiveEnchantment> active,
        double refreshWhenUnderSeconds)
    {
        // Best known candidate per family. Family 0 is retail's "does not
        // stack" bucket: those spells share no family identity, so collapsing
        // them would drop all but one unrelated buff.
        var bestByFamily = new Dictionary<uint, PluginSpellInfo>();
        var unstackable = new List<PluginSpellInfo>();

        foreach (PluginSpellInfo spell in knownSelfBuffs)
        {
            if (spell.Family == 0)
            {
                unstackable.Add(spell);
                continue;
            }
            if (!bestByFamily.TryGetValue(spell.Family, out PluginSpellInfo held)
                || spell.Tier > held.Tier)
            {
                bestByFamily[spell.Family] = spell;
            }
        }

        // Strongest in-force tier per family, and how long it has left.
        var activeByFamily = new Dictionary<uint, (int Tier, double Seconds)>();
        var activeSpellSeconds = new Dictionary<uint, double>();
        foreach (PluginActiveEnchantment enchantment in active)
        {
            activeSpellSeconds[enchantment.SpellId] = enchantment.SecondsRemaining;
            if (enchantment.Family == 0)
                continue;
            if (!activeByFamily.TryGetValue(enchantment.Family, out var held)
                || enchantment.Tier > held.Tier)
            {
                activeByFamily[enchantment.Family] =
                    (enchantment.Tier, enchantment.SecondsRemaining);
            }
        }

        var plan = new List<PluginSpellInfo>();

        foreach (PluginSpellInfo candidate in bestByFamily.Values)
        {
            if (!activeByFamily.TryGetValue(candidate.Family, out var inForce))
            {
                plan.Add(candidate);
                continue;
            }
            // A weaker enchantment in force is still worth replacing: recasting
            // at a higher tier supersedes it.
            if (candidate.Tier > inForce.Tier
                || inForce.Seconds < refreshWhenUnderSeconds)
            {
                plan.Add(candidate);
            }
        }

        foreach (PluginSpellInfo candidate in unstackable)
        {
            if (!activeSpellSeconds.TryGetValue(candidate.SpellId, out double seconds)
                || seconds < refreshWhenUnderSeconds)
            {
                plan.Add(candidate);
            }
        }

        // Cheapest first: if mana runs out mid-pass, more buffs landed than if
        // the expensive ones had gone first.
        plan.Sort(static (a, b) =>
            a.ManaCost != b.ManaCost
                ? a.ManaCost.CompareTo(b.ManaCost)
                : a.SpellId.CompareTo(b.SpellId));
        return plan;
    }
}