using System;
using UnityEngine;
using UnityEngine.Video;

/// <summary>
/// Plays a list of clips sequentially on the sibling <see cref="VideoPlayer"/>. Each entry
/// defines the portion of its clip to play as a normalized start/end range (drawn as a
/// percent min-max slider). With an empty list the component leaves the player untouched,
/// so a plain single-clip setup keeps working.
/// For material-override screens (e.g. the TV) a second player pre-buffers the next entry
/// while the current one plays; both players run API-only and this component drives the
/// screen texture via a property block, flipping it only once the incoming player delivers
/// frames — transitions are gapless. Other render modes fall back to single-player playback.
/// </summary>
[RequireComponent(typeof(VideoPlayer))]
[DisallowMultipleComponent]
public class VideoClipPlaylist : MonoBehaviour
{
    [Serializable]
    public class Item
    {
        [Tooltip("Clip to play for this entry. Entries without a clip are skipped.")]
        public VideoClip clip;

        [Tooltip("Portion of the clip to play, normalized 0..1 (shown as percent).")]
        public Vector2 range = new Vector2(0f, 1f);
    }

    [Tooltip("Played top to bottom; entries without a clip are skipped.")]
    public Item[] items = Array.Empty<Item>();

    [Tooltip("Restart from the first entry after the last one finished.")]
    public bool loop = true;

    [Tooltip("Second player used to pre-buffer the next entry for gapless transitions. " +
             "Auto-created on a child when left empty (material-override screens only).")]
    public VideoPlayer secondaryPlayer;

    // Segment end is checked slightly early so ranges ending at 100% advance via the time
    // check even when VideoPlayer's loop-point event races it (both paths advance safely).
    private const double EndEpsilon = 0.05;
    private const double MinSegmentSeconds = 0.05;

    private VideoPlayer _active;
    private VideoPlayer _standby; // null => single-player fallback (non material-override)
    private Renderer _screen;
    private int _screenProperty;
    private MaterialPropertyBlock _block;
    private Texture _presented;
    private bool _setupDone;

    private int _index = -1;
    private double _segmentEnd = double.MaxValue;
    private bool _activePreparing;
    private bool _endReached;

    private int _standbyIndex = -1;
    private double _standbySegmentEnd;
    private bool _standbyReady;
    private bool _switching;

    private void Awake()
    {
        _active = GetComponent<VideoPlayer>();
        Hook(_active);
    }

    private void OnDestroy()
    {
        Unhook(_active);
        Unhook(_standby);
    }

    private void OnEnable()
    {
        int first = NextPlayableIndex(0);
        if (first < 0) return; // empty list: leave the player's own setup alone

        SetupOnce();
        Configure(_active);
        if (_standby) Configure(_standby);
        PlayItem(first);
    }

    private void OnDisable()
    {
        _activePreparing = false;
        _standbyReady = false;
        _switching = false;
        _endReached = false;
        _index = -1;
        _standbyIndex = -1;
        if (_active) _active.Stop();
        if (_standby) _standby.Stop();
    }

    private void Update()
    {
        if (_index < 0) return;

        if (_switching)
        {
            // Hold the old frame until the incoming player actually delivers.
            if (_standby.frame >= 0 && _standby.texture) CompleteSwitch();
        }
        else if (!_activePreparing)
        {
            if (_endReached || (_active.isPlaying && _active.time >= _segmentEnd))
                Advance();
        }

        Present();
    }

    /// <summary>Advances to the next playable entry (wraps when <see cref="loop"/> is on).</summary>
    public void Next()
    {
        if (_index < 0)
        {
            int first = NextPlayableIndex(0);
            if (first >= 0 && isActiveAndEnabled) PlayItem(first);
            return;
        }
        _endReached = true;
    }

    private void SetupOnce()
    {
        if (_setupDone) return;
        _setupDone = true;

        // Gapless playback needs to own the output; that is only possible when the player
        // drives a renderer material — then both players run API-only and this component
        // applies the current texture itself.
        if (_active.renderMode != VideoRenderMode.MaterialOverride) return;
        _screen = _active.targetMaterialRenderer ? _active.targetMaterialRenderer : GetComponent<Renderer>();
        if (!_screen) return;

        string property = _active.targetMaterialProperty;
        _screenProperty = Shader.PropertyToID(string.IsNullOrEmpty(property) ? "_MainTex" : property);
        _block = new MaterialPropertyBlock();

        if (!secondaryPlayer) secondaryPlayer = CreateSecondaryPlayer();
        _standby = secondaryPlayer;
        Hook(_standby);
    }

    private VideoPlayer CreateSecondaryPlayer()
    {
        var go = new GameObject("Video Player (Playlist Buffer)");
        go.transform.SetParent(transform, false);
        var player = go.AddComponent<VideoPlayer>();
        player.playbackSpeed = _active.playbackSpeed;
        player.audioOutputMode = _active.audioOutputMode;

        if (_active.audioOutputMode == VideoAudioOutputMode.AudioSource)
        {
            AudioSource template = _active.GetTargetAudioSource(0);
            if (!template) template = GetComponent<AudioSource>();
            if (template)
            {
                var audio = go.AddComponent<AudioSource>();
                CopyAudioSettings(template, audio);
                player.SetTargetAudioSource(0, audio);
            }
            else
            {
                player.audioOutputMode = VideoAudioOutputMode.Direct;
            }
        }
        return player;
    }

    private static void CopyAudioSettings(AudioSource from, AudioSource to)
    {
        to.playOnAwake = false;
        to.loop = false;
        to.outputAudioMixerGroup = from.outputAudioMixerGroup;
        to.mute = from.mute;
        to.volume = from.volume;
        to.pitch = from.pitch;
        to.priority = from.priority;
        to.panStereo = from.panStereo;
        to.spatialBlend = from.spatialBlend;
        to.spatialize = from.spatialize;
        to.spatializePostEffects = from.spatializePostEffects;
        to.reverbZoneMix = from.reverbZoneMix;
        to.bypassEffects = from.bypassEffects;
        to.bypassListenerEffects = from.bypassListenerEffects;
        to.bypassReverbZones = from.bypassReverbZones;
        to.dopplerLevel = from.dopplerLevel;
        to.spread = from.spread;
        to.rolloffMode = from.rolloffMode;
        to.minDistance = from.minDistance;
        to.maxDistance = from.maxDistance;
    }

    private void Configure(VideoPlayer player)
    {
        player.playOnAwake = false;
        player.isLooping = false;
        player.source = VideoSource.VideoClip;
        if (_screen) player.renderMode = VideoRenderMode.APIOnly;
    }

    private void Hook(VideoPlayer player)
    {
        player.prepareCompleted += OnPrepareCompleted;
        player.loopPointReached += OnLoopPointReached;
    }

    private void Unhook(VideoPlayer player)
    {
        if (!player) return;
        player.prepareCompleted -= OnPrepareCompleted;
        player.loopPointReached -= OnLoopPointReached;
    }

    private int NextPlayableIndex(int start)
    {
        for (int i = start; i < items.Length; i++)
            if (items[i] != null && items[i].clip)
                return i;
        return -1;
    }

    private int NextPlayableAfter(int index)
    {
        int next = NextPlayableIndex(index + 1);
        if (next < 0 && loop) next = NextPlayableIndex(0);
        return next;
    }

    private void PlayItem(int index)
    {
        _index = index;
        _activePreparing = true;
        _segmentEnd = double.MaxValue;
        _active.Stop();
        _active.clip = items[index].clip;
        _active.Prepare();
    }

    private void PrepareStandby(int index)
    {
        _standbyIndex = index;
        _standbyReady = false;
        if (index < 0) return; // last entry without loop: nothing to buffer
        _standby.Stop();
        _standby.clip = items[index].clip;
        _standby.Prepare();
    }

    private void Advance()
    {
        if (_standby)
        {
            if (_standbyIndex < 0)
            {
                _endReached = false;
                StopPlayback();
                return;
            }
            if (!_standbyReady) return; // buffer not ready yet: hold the frame, retry next Update
            _endReached = false;
            _standby.Play();
            _switching = true;
        }
        else
        {
            _endReached = false;
            int next = NextPlayableAfter(_index);
            if (next < 0) StopPlayback();
            else PlayItem(next);
        }
    }

    private void CompleteSwitch()
    {
        _switching = false;
        _active.Stop();
        (_active, _standby) = (_standby, _active);
        _index = _standbyIndex;
        _segmentEnd = _standbySegmentEnd;
        PrepareStandby(NextPlayableAfter(_index));
    }

    private void StopPlayback()
    {
        _index = -1;
        _active.Stop();
    }

    private void Present()
    {
        if (!_screen) return;
        Texture texture = _active.texture;
        if (!texture || texture == _presented) return;
        _presented = texture;
        _screen.GetPropertyBlock(_block);
        _block.SetTexture(_screenProperty, texture);
        _screen.SetPropertyBlock(_block);
    }

    private double ComputeSegment(int index, double length, out double segmentEnd)
    {
        Vector2 range = items[index].range;
        double start = length * Mathf.Clamp01(Mathf.Min(range.x, range.y));
        double end = length * Mathf.Clamp01(Mathf.Max(range.x, range.y));
        // Degenerate ranges still play a minimal moment instead of skip-looping forever.
        end = Math.Min(Math.Max(end, start + MinSegmentSeconds), length);
        segmentEnd = end - EndEpsilon;
        return start;
    }

    private void OnPrepareCompleted(VideoPlayer source)
    {
        if (source == _active && _activePreparing && _index >= 0)
        {
            _activePreparing = false;
            source.time = ComputeSegment(_index, source.length, out _segmentEnd);
            source.Play();
            if (_standby && !_switching) PrepareStandby(NextPlayableAfter(_index));
        }
        else if (source == _standby && _standbyIndex >= 0 && !_standbyReady)
        {
            // Pre-seek now so the switch starts on the right frame without a visible jump.
            source.time = ComputeSegment(_standbyIndex, source.length, out _standbySegmentEnd);
            _standbyReady = true;
        }
    }

    private void OnLoopPointReached(VideoPlayer source)
    {
        // Natural clip end (range up to 100%) — advance if this is the presenting player.
        if (source == _active && !_activePreparing && !_switching && _index >= 0 && isActiveAndEnabled)
            _endReached = true;
    }

    private void OnValidate()
    {
        if (items == null) return;
        foreach (Item item in items)
        {
            if (item == null) continue;
            // Fresh array elements zero-initialize the range; default to "full clip".
            if (item.range == Vector2.zero) item.range = new Vector2(0f, 1f);
        }
    }
}