using System;
using System.Diagnostics;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace axXez.TS3.Audio
{
    public static class FFmpeg
    {
        public const int SampleRate = 48000;
        public const int Channels = 2;

        /// <summary>Returns true if ffmpeg is installed and accessible on PATH.</summary>
        public static bool IsAvailable()
        {
            try
            {
                using var p = Process.Start(new ProcessStartInfo("ffmpeg")
                {
                    ArgumentList = { "-version" },
                    UseShellExecute = false,
                    RedirectStandardOutput = true,
                    RedirectStandardError = true,
                    CreateNoWindow = true,
                });
                p?.WaitForExit();
                return p?.ExitCode == 0;
            }
            catch { return false; }
        }

        /// <summary>Converts any audio file to raw PCM (48kHz stereo s16le).</summary>
        public static async Task<byte[]> ToPcmAsync(string filePath, CancellationToken ct = default)
        {
            using var p = Start("-i", filePath);
            using var ms = new MemoryStream();
            _ = p.StandardError.BaseStream.CopyToAsync(Stream.Null, ct); // drain to prevent deadlock
            await p.StandardOutput.BaseStream.CopyToAsync(ms, ct);
            await p.WaitForExitAsync(ct);
            if (p.ExitCode != 0) throw new Exception($"ffmpeg exited with code {p.ExitCode}.");
            return ms.ToArray();
        }

        /// <summary>
        /// Starts ffmpeg streaming PCM from a URL with reconnect support.
        /// The caller must dispose the returned <see cref="Process"/> when done.
        /// </summary>
        public static (Process process, Stream stdout) StartPcmStream(string url)
        {
            var p = Start("-reconnect", "1", "-reconnect_streamed", "1", "-reconnect_delay_max", "5", "-i", url);
            return (p, p.StandardOutput.BaseStream);
        }

        private static Process Start(params string[] inputArgs)
        {
            var psi = new ProcessStartInfo("ffmpeg")
            {
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                UseShellExecute = false,
                CreateNoWindow = true,
            };
            foreach (var a in inputArgs) psi.ArgumentList.Add(a);
            foreach (var a in new[] { "-vn", "-f", "s16le", "-acodec", "pcm_s16le",
                                      "-ar", SampleRate.ToString(), "-ac", Channels.ToString(),
                                      "-loglevel", "error", "pipe:1" })
                psi.ArgumentList.Add(a);
            return Process.Start(psi) ?? throw new InvalidOperationException("ffmpeg not found.");
        }
    }
}