using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

namespace axXez.TS3.Audio
{
    public static class YtDlp
    {
        /// <summary>Returns true if yt-dlp is installed and accessible on PATH.</summary>
        public static bool IsAvailable()
        {
            try
            {
                using var p = Start("--version");
                p.WaitForExit();
                return p.ExitCode == 0;
            }
            catch { return false; }
        }

        /// <summary>Resolves a yt-dlp-supported URL to a direct audio stream URL.</summary>
        public static async Task<string> ResolveAsync(string url, IReadOnlyList<string> extraArgs = null, CancellationToken ct = default)
        {
            using var p = Start([.. (extraArgs ?? []), "-f", "bestaudio", "--no-playlist", "-g", url]);

            // Read concurrently — sequential reads risk deadlock if either buffer fills up
            var stdoutTask = p.StandardOutput.ReadToEndAsync(ct);
            var stderrTask = p.StandardError.ReadToEndAsync(ct);
            await p.WaitForExitAsync(ct);
            string stdout = await stdoutTask;
            string stderr = await stderrTask;

            if (p.ExitCode != 0)
            {
                string err = stderr.Trim();
                throw new Exception($"yt-dlp failed: {err[..Math.Min(200, err.Length)]}");
            }

            string resolved = stdout.Trim().Split('\n')[0];
            if (string.IsNullOrEmpty(resolved)) throw new Exception("yt-dlp returned no URL.");
            return resolved;
        }

        /// <summary>Resolves all entries of a playlist URL to individual watch URLs without downloading audio.</summary>
        public static async Task<string[]> GetPlaylistUrlsAsync(string url, IReadOnlyList<string> extraArgs = null, CancellationToken ct = default)
        {
            using var p = Start([.. (extraArgs ?? []), "--flat-playlist", "-g", url]);

            var stdoutTask = p.StandardOutput.ReadToEndAsync(ct);
            var stderrTask = p.StandardError.ReadToEndAsync(ct);
            await p.WaitForExitAsync(ct);
            string stdout = await stdoutTask;
            string stderr = await stderrTask;

            if (p.ExitCode != 0)
            {
                string err = stderr.Trim();
                throw new Exception($"yt-dlp failed: {err[..Math.Min(200, err.Length)]}");
            }

            string[] urls = stdout.Trim().Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
            if (urls.Length == 0) throw new Exception("Playlist is empty or could not be resolved.");
            return urls;
        }

        /// <summary>Runs yt-dlp --update to self-update the binary in place.</summary>
        public static async Task UpdateAsync(CancellationToken ct = default)
        {
            using var p = Start("--update");
            await p.WaitForExitAsync(ct);
        }

        private static Process Start(params string[] args)
        {
            var psi = new ProcessStartInfo("yt-dlp")
            {
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                UseShellExecute = false,
                CreateNoWindow = true,
            };
            foreach (var a in args) psi.ArgumentList.Add(a);
            return Process.Start(psi) ?? throw new InvalidOperationException("yt-dlp not found.");
        }
    }
}