using System;
using System.Collections.Generic;

namespace Skafinity;

/// <summary>
/// The WAV container — 16-bit PCM, the one format both targets can hand straight to a player.
/// Stateless: it wraps samples somebody else rendered.
/// </summary>
static class Wav
{
	/// <summary>Clamp a −1..1 mix sample to signed 16-bit.</summary>
	public static short ToS16( float v ) => (short)(Math.Clamp( v, -1f, 1f ) * 32767f);

	/// <summary>Wrap already-rendered 16-bit samples in a WAV. Mono or interleaved stereo per
	/// <paramref name="channels"/>.</summary>
	public static byte[] FromSamples( short[] samples, int channels, int sampleRate )
	{
		int dataSize = samples.Length * 2;
		int blockAlign = channels * 2;
		var bytes = new List<byte>( 44 + dataSize );
		void Str( string s ) { foreach ( var ch in s ) bytes.Add( (byte)ch ); }
		void U32( uint v ) { bytes.Add( (byte)v ); bytes.Add( (byte)(v >> 8) ); bytes.Add( (byte)(v >> 16) ); bytes.Add( (byte)(v >> 24) ); }
		void U16( ushort v ) { bytes.Add( (byte)v ); bytes.Add( (byte)(v >> 8) ); }
		Str( "RIFF" ); U32( (uint)(36 + dataSize) ); Str( "WAVE" );
		Str( "fmt " ); U32( 16 ); U16( 1 ); U16( (ushort)channels );
		U32( (uint)sampleRate ); U32( (uint)(sampleRate * blockAlign) ); U16( (ushort)blockAlign ); U16( 16 );
		Str( "data" ); U32( (uint)dataSize );
		foreach ( var s in samples ) { ushort u = (ushort)s; bytes.Add( (byte)u ); bytes.Add( (byte)(u >> 8) ); }
		return bytes.ToArray();
	}
}

public sealed partial class MusicGen
{
	// ── Output ──
	short[] ToShorts( float gain )
	{
		int n = _bufL.Length;
		var s = new short[n * Channels];
		for ( int i = 0; i < n; i++ )
		{
			s[i * 2] = Wav.ToS16( _bufL[i] * gain );
			s[i * 2 + 1] = Wav.ToS16( _bufR[i] * gain );
		}
		return s;
	}

	/// <summary>Wrap already-rendered 16-bit samples in a WAV (for export). Mono or
	/// interleaved stereo per <paramref name="channels"/>.</summary>
	public static byte[] WavFromSamples( short[] samples, int channels, int sampleRate )
		=> Wav.FromSamples( samples, channels, sampleRate );

	byte[] EncodeWav( float gain ) => Wav.FromSamples( ToShorts( gain ), Channels, _sr );
}