using System;
using System.Collections.Generic;
using DatReaderWriter.DBObjs;
using DRWSound = DatReaderWriter.Enums.Sound;

namespace AcDream.Core.Audio;

/// <summary>
/// Probabilistic entry picker over a retail <see cref="SoundTable"/>.
///
/// <para>
/// Each <see cref="DatReaderWriter.Enums.Sound"/> key in
/// <c>SoundTable.Sounds</c> maps to a list of
/// <see cref="DatReaderWriter.Types.SoundEntry"/> items each carrying a
/// probability weight. Retail picks one entry per trigger by rolling the
/// cumulative distribution — that's how footsteps sound slightly
/// different each step, how weapon swings have 3 swoosh variants, etc.
/// </para>
///
/// <para>
/// r05 §4: the picker samples a uniform random in [0,1) and walks the
/// entries accumulating probabilities; the first entry whose running total
/// exceeds the sample wins. If all probabilities sum to &lt; 1, the
/// remaining mass means "silence" — the call returns null. If probabilities
/// sum to &gt; 1 the picker still works correctly (it clamps on the last
/// entry).
/// </para>
/// </summary>
public static class SoundCookbook
{
    /// <summary>
    /// Pick one entry from a sound's variant list, weighted by probability.
    /// Returns <c>null</c> when the rolled sample falls into the "silence"
    /// remainder of the distribution (probability sum &lt; 1).
    /// </summary>
    public static DatReaderWriter.Types.SoundEntry? Roll(
        IReadOnlyList<DatReaderWriter.Types.SoundEntry> entries,
        Random rng)
    {
        ArgumentNullException.ThrowIfNull(entries);
        ArgumentNullException.ThrowIfNull(rng);

        if (entries.Count == 0) return null;
        if (entries.Count == 1) return entries[0];

        float sample = (float)rng.NextDouble();
        float cum = 0f;
        for (int i = 0; i < entries.Count; i++)
        {
            cum += Math.Max(0f, entries[i].Probability);
            if (sample < cum) return entries[i];
        }
        // Fell past the last entry — either probabilities sum to >1 (return
        // last) or < 1 and we rolled into the "silence" tail (return null).
        float total = 0f;
        for (int i = 0; i < entries.Count; i++)
            total += Math.Max(0f, entries[i].Probability);

        return total > 0.999f ? entries[entries.Count - 1] : null;
    }

    /// <summary>
    /// Convenience lookup: given a SoundTable + a retail
    /// <see cref="DRWSound"/> key (e.g. Swoosh1, Footstep1), roll the
    /// entry list and return the winning entry. Returns null if:
    /// <list type="bullet">
    ///   <item><description><paramref name="table"/> has no mapping for
    ///   <paramref name="sound"/>.</description></item>
    ///   <item><description>The mapping's entry list is empty.</description></item>
    ///   <item><description>The probability roll hits the silence
    ///   tail.</description></item>
    /// </list>
    /// </summary>
    public static DatReaderWriter.Types.SoundEntry? Roll(
        SoundTable table,
        DRWSound sound,
        Random rng)
    {
        ArgumentNullException.ThrowIfNull(table);
        if (!table.Sounds.TryGetValue(sound, out var soundData)) return null;
        return Roll(soundData.Entries, rng);
    }
}