using System;
using System.IO;

namespace MediaBrowser.Controller.MediaEncoding;

/// <summary>
/// Represents a durable record of an HLS transcoding session for HA pod recovery.
/// </summary>
public sealed class TranscodeSession
{
    /// <summary>
    /// Gets or sets the unique play session identifier.
    /// </summary>
    public string PlaySessionId { get; set; } = string.Empty;

    /// <summary>
    /// Gets or sets the name of the pod that currently owns this session's lease.
    /// </summary>
    public string OwnerPod { get; set; } = string.Empty;

    /// <summary>
    /// Gets or sets the UTC time at which the owning pod's lease expires.
    /// </summary>
    public DateTime LeaseExpiresUtc { get; set; }

    /// <summary>
    /// Gets or sets the absolute path to the HLS manifest (.m3u8) file on shared storage.
    /// </summary>
    public string ManifestPath { get; set; } = string.Empty;

    /// <summary>
    /// Gets or sets the path prefix for transcoded segment files on shared storage.
    /// </summary>
    public string SegmentPathPrefix { get; set; } = string.Empty;

    /// <summary>
    /// Gets or sets the media source identifier associated with this session.
    /// </summary>
    public string MediaSourceId { get; set; } = string.Empty;

    /// <summary>
    /// Gets or sets the zero-based index of the last segment that was fully written to durable storage.
    /// </summary>
    public int LastCompletedSegmentIndex { get; set; }

    /// <summary>
    /// Gets or sets the last durable playback offset in ticks, used to resume playback after failover.
    /// </summary>
    public long LastDurablePlaybackOffset { get; set; }

    /// <summary>
    /// Creates a session record for an HLS output, deriving <see cref="ManifestPath"/> and
    /// <see cref="SegmentPathPrefix"/> from the playlist path so that cleanup can recognise
    /// every file the session owns.
    /// </summary>
    /// <param name="playSessionId">The play session identifier.</param>
    /// <param name="mediaSourceId">The media source identifier.</param>
    /// <param name="ownerPod">The name of the pod that owns the session.</param>
    /// <param name="playlistPath">The absolute path of the HLS playlist (.m3u8) file.</param>
    /// <param name="leaseDuration">The initial lease duration.</param>
    /// <returns>The new <see cref="TranscodeSession"/>.</returns>
    public static TranscodeSession CreateForPlaylist(
        string playSessionId,
        string mediaSourceId,
        string ownerPod,
        string playlistPath,
        TimeSpan leaseDuration)
        => new TranscodeSession
        {
            PlaySessionId = playSessionId,
            OwnerPod = ownerPod,
            LeaseExpiresUtc = DateTime.UtcNow.Add(leaseDuration),
            ManifestPath = playlistPath,
            SegmentPathPrefix = GetSegmentPathPrefix(playlistPath),
            MediaSourceId = mediaSourceId,
        };

    /// <summary>
    /// Gets the prefix every segment file of the HLS output at <paramref name="playlistPath"/> starts with.
    /// Segments are written as <c>&lt;playlist path without extension&gt;&lt;index&gt;&lt;segment extension&gt;</c>.
    /// </summary>
    /// <param name="playlistPath">The absolute path of the HLS playlist (.m3u8) file.</param>
    /// <returns>The segment path prefix.</returns>
    public static string GetSegmentPathPrefix(string playlistPath)
        => Path.ChangeExtension(playlistPath, null) ?? playlistPath;
}