using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace ytLive.Services;

/// <summary>
/// TASK 65: where clips live and how many survive.
///
/// <para><b>Not clip management.</b> There is no gallery, no naming, no per-clip decision. A clip is
/// written to <c>clips\</c>, the oldest is deleted when the next one lands, and the only knobs are the
/// length (10 or 15 s) and how many to keep (3, 4 or 5). Anything richer belongs to a video editor.</para>
/// </summary>
public sealed class ClipLibrary
{
    public const string Extension = ".mp4";
    public const string FilePrefix = "clip-";

    private readonly Func<string> _folder;

    public ClipLibrary(Func<string> folder) => _folder = folder;

    /// <summary>Bytes the ring should hold for a length and bitrate, with 25% headroom for bitrate
    /// movement. This is a memory cap, not a duration — the ring trims whole fragments.</summary>
    public static long RingBytesFor(int seconds, int bitrateKbps)
        => Math.Max(1, seconds) * (long)bitrateKbps * 1000 / 8 * 5 / 4;

    /// <summary>Writes a clip and prunes to <paramref name="keep"/>; returns the file path, or null when
    /// there was nothing to write (an empty snapshot must never become a zero-byte file).</summary>
    public string? Save(byte[] mp4Bytes, DateTime nowLocal, int keep)
    {
        if (mp4Bytes.Length == 0) return null;
        try
        {
            var folder = EnsureFolder();
            var path = Path.Combine(folder, $"{FilePrefix}{nowLocal:yyyyMMdd-HHmmss}{Extension}");
            var unique = path;
            for (var n = 2; File.Exists(unique); n++)
                unique = Path.Combine(folder, $"{FilePrefix}{nowLocal:yyyyMMdd-HHmmss}-{n}{Extension}");

            File.WriteAllBytes(unique, mp4Bytes);
            Prune(keep);
            return unique;
        }
        catch (Exception ex)
        {
            Helpers.AppLog.Write(ex, "Clip save failed");
            return null;
        }
    }

    /// <summary>Newest first. The replay layer's playlist is this list, so its order matters.</summary>
    public IReadOnlyList<string> Recent()
    {
        try
        {
            var folder = EnsureFolder();
            return Directory.EnumerateFiles(folder, FilePrefix + "*" + Extension)
                .OrderByDescending(p => p, StringComparer.OrdinalIgnoreCase)
                .ToList();
        }
        catch (Exception ex)
        {
            Helpers.AppLog.Write(ex, "Clip list failed");
            return Array.Empty<string>();
        }
    }

    /// <summary>Deletes everything past the retention count. Missing folders are not an error.</summary>
    public int Prune(int keep)
    {
        if (keep < 1) keep = 1;
        var removed = 0;
        foreach (var stale in Recent().Skip(keep))
        {
            try
            {
                File.Delete(stale);
                removed++;
            }
            catch (Exception ex)
            {
                Helpers.AppLog.Write(ex, $"Clip prune failed: {stale}");
            }
        }
        return removed;
    }

    /// <summary>The folder beside the recordings, created on demand.</summary>
    public string EnsureFolder()
    {
        var folder = Path.Combine(_folder(), "clips");
        Directory.CreateDirectory(folder);
        return folder;
    }
}