using System;
using System.Collections.Generic;
using UnityEngine;

namespace ADOFAIRenderer.Util.Audio.Clip;

/// <summary>
/// Copies a Unity <see cref="AudioClip"/> into memory for clips without a file on disk
/// (built-in hit sounds from Resources, official/DLC level audio).
/// <see cref="AudioClip.GetData(float[], int)"/> runs on the main Unity thread only, so the whole clip is copied once on the main Unity thread
/// and the decoder thread reads the copy through a <see cref="MemoryPCMReader"/>.
/// Streaming clips (<see cref="AudioClipLoadType.Streaming"/>) are rejected because GetData does not read them.
/// Reference: https://docs.unity3d.com/ScriptReference/AudioClip.GetData.html
/// </summary>
internal static class UnityClipLoader
{
    /// <summary>
    /// Copies <paramref name="clip"/> in blocks of <see cref="AudioClipSource.ChunkFloats"/> floats or less
    /// (FramesPerBlock = ChunkFloats / channels frames per GetData call). Main thread only.
    /// Block memory is counted in <paramref name="store"/> and released block by block as the decoder thread reads it.
    /// </summary>
    public static MemoryPCMReader Load(AudioClip clip, AudioClipStore store)
    {
        if (!clip) throw new ArgumentNullException(nameof(clip));
        if (clip.loadType == AudioClipLoadType.Streaming)
            throw new NotSupportedException($"AudioClip '{clip.name}' is a streaming clip; GetData cannot read it.");

        // Clips with preloadAudioData off start unloaded; LoadAudioData loads the data synchronously, or asynchronously for
        // clips with loadInBackground (GetData below then fails while the data is still loading).
        // Reference: https://docs.unity3d.com/ScriptReference/AudioClip.LoadAudioData.html
        if (clip.loadState == AudioDataLoadState.Unloaded)
            clip.LoadAudioData();

        var channels = clip.channels;
        var totalFrames = (long)clip.samples;
        var framesPerBlock = AudioClipSource.ChunkFloats / channels;
        var blocks = new List<float[]>();
        try
        {
            for (long start = 0; start < totalFrames; start += framesPerBlock)
            {
                var frames = (int)Math.Min(framesPerBlock, totalFrames - start);
                var block = store.AllocateExactArray(frames * channels);
                blocks.Add(block);
                // GetData fills the whole array; the offset is in frames (samples per channel).
                if (!clip.GetData(block, (int)start))
                    throw new InvalidOperationException($"AudioClip.GetData failed for '{clip.name}' at frame {start} (load state {clip.loadState}).");
            }
        }
        catch
        {
            foreach (var block in blocks) store.FreeExactArray(block);
            throw;
        }

        return new MemoryPCMReader(blocks, framesPerBlock, channels, clip.frequency, totalFrames, store.FreeExactArray);
    }
}