/**
 * @file
 * @brief Source file for VideoCacheThread class
 * @author Jonathan Thomas <jonathan@openshot.org>
 *
 * @ref License
 */

// Copyright (c) 2008-2025 OpenShot Studios, LLC
//
// SPDX-License-Identifier: LGPL-3.0-or-later

#include "VideoCacheThread.h"
#include "CacheBase.h"
#include "Exceptions.h"
#include "Frame.h"
#include "Settings.h"
#include "Timeline.h"
#include <thread>
#include <chrono>
#include <algorithm>

namespace openshot
{
    // Constructor
    VideoCacheThread::VideoCacheThread()
        : Thread("video-cache")
        , speed(0)
        , last_speed(1)
        , last_dir(1)                  // Assume forward (+1) on first launch
        , is_playing(false)
        , userSeeked(false)
        , requested_display_frame(1)
        , current_display_frame(1)
        , cached_frame_count(0)
        , min_frames_ahead(4)
        , max_frames_ahead(8)
        , timeline_max_frame(0)
        , should_pause_cache(false)
        , should_break(false)
        , reader(nullptr)
        , force_directional_cache(false)
    {
    }

    // Destructor
    VideoCacheThread::~VideoCacheThread()
    {
    }

    // Seek the reader to a particular frame number
    void VideoCacheThread::setSpeed(int new_speed)
    {
        // Only update last_speed and last_dir when new_speed is non-zero.
        if (new_speed != 0) {
            last_speed = new_speed;
            last_dir   = (new_speed > 0 ? 1 : -1);
        }
        speed = new_speed;
    }

    // Get the size in bytes of a frame (rough estimate)
    int64_t VideoCacheThread::getBytes(int width, int height, int sample_rate, int channels, float fps)
    {
        // Estimate memory for RGBA video frame
        int64_t bytes = static_cast<int64_t>(width) * height * sizeof(char) * 4;

        // Approximate audio memory: (sample_rate * channels) samples per second,
        // divided across fps frames, each sample is sizeof(float).
        bytes += ((sample_rate * channels) / fps) * sizeof(float);

        return bytes;
    }

    // Play the video
    void VideoCacheThread::Play()
    {
        is_playing = true;
    }

    // Stop the audio
    void VideoCacheThread::Stop()
    {
        is_playing = false;
    }

    // Is cache ready for playback (pre-roll)
    bool VideoCacheThread::isReady()
    {
        // Return true when pre-roll has cached at least min_frames_ahead frames.
        return (cached_frame_count > min_frames_ahead);
    }

    // Start the thread
    void VideoCacheThread::run()
    {
        using micro_sec        = std::chrono::microseconds;
        using double_micro_sec = std::chrono::duration<double, micro_sec::period>;

        // Index of the most recently cached frame; starts “behind” the playhead.
        int64_t last_cached_index = 0;

        while (!threadShouldExit()) {
            Settings* settings = Settings::Instance();
            CacheBase* cache   = reader ? reader->GetCache() : nullptr;

            // If caching is disabled or no reader is assigned, wait briefly and retry
            if (!settings->ENABLE_PLAYBACK_CACHING || !cache) {
                std::this_thread::sleep_for(double_micro_sec(50000));
                continue;
            }

            Timeline* timeline    = static_cast<Timeline*>(reader);
            int64_t  timeline_end = timeline->GetMaxFrame();
            int64_t  playhead     = requested_display_frame;
            bool     paused       = (speed == 0);

            // Determine effective direction: use speed if non-zero, otherwise keep last_dir.
            int dir = (speed != 0 ? (speed > 0 ? 1 : -1) : last_dir);

            // On any non-seek iteration, update last_dir if speed changed from zero
            if (speed != 0) {
                last_dir = dir;
            }

            // Handle user-initiated seek: reset last_cached_index to just behind playhead.
            if (userSeeked) {
                last_cached_index = playhead - dir;
                userSeeked        = false;
            }

            // Determine how many frames ahead/behind to cache based on settings & memory
            int64_t bytes_per_frame = getBytes(
                (timeline->preview_width ? timeline->preview_width : reader->info.width),
                (timeline->preview_height ? timeline->preview_height : reader->info.height),
                reader->info.sample_rate,
                reader->info.channels,
                reader->info.fps.ToFloat()
            );

            int64_t max_bytes = cache->GetMaxBytes();
            if (max_bytes <= 0 || bytes_per_frame <= 0) {
                std::this_thread::sleep_for(double_micro_sec(50000));
                continue;
            }

            int64_t capacity = max_bytes / bytes_per_frame;
            if (capacity < 1) {
                std::this_thread::sleep_for(double_micro_sec(50000));
                continue;
            }

            // Number of frames to keep ahead (or behind) based on settings
            int64_t ahead_count = static_cast<int64_t>(capacity * settings->VIDEO_CACHE_PERCENT_AHEAD);

            // Compute window bounds around playhead each iteration:
            //  - If moving forward (dir > 0): [playhead ... playhead + ahead_count]
            //  - If moving backward (dir < 0): [playhead - ahead_count ... playhead]
            int64_t window_begin = (dir > 0)
                ? playhead
                : (playhead - ahead_count);
            int64_t window_end = (dir > 0)
                ? (playhead + ahead_count)
                : playhead;

            // Clamp to valid timeline range
            window_begin = std::max<int64_t>(window_begin, 1);
            window_end   = std::min<int64_t>(window_end, timeline_end);

            // If we're paused and the playhead moves outside cache, clear & rebuild
            if (paused && !cache->Contains(playhead)) {
                timeline->ClearAllCache();
                last_cached_index = playhead - dir;
            }

            // If playing, ensure last_cached_index is within one step of window
            // If it's already beyond the window, reset so caching continues from playhead
            bool outside_window = (dir > 0 && last_cached_index > window_end) ||
                                  (dir < 0 && last_cached_index < window_begin);
            if (!paused && outside_window) {
                last_cached_index = playhead - dir;
            }

            // Prefetch frames from last_cached_index + dir up to window_end (or down to window_begin)
            int64_t next_frame  = last_cached_index + dir;
            bool    window_full = true;

            while ((dir > 0 && next_frame <= window_end) ||
                   (dir < 0 && next_frame >= window_begin))
            {
                if (threadShouldExit()) {
                    break;
                }
                // If a new seek arrives mid-cache, break and start over next loop
                if (userSeeked) {
                    break;
                }

                if (!cache->Contains(next_frame)) {
                    // Missing frame: fetch and add to cache
                    try {
                        auto framePtr = reader->GetFrame(next_frame);
                        cache->Add(framePtr);
                        ++cached_frame_count;
                    }
                    catch (const OutOfBoundsFrame&) {
                        break;
                    }
                    window_full = false;
                }
                else {
                    cache->Touch(next_frame);
                }

                last_cached_index = next_frame;
                next_frame       += dir;
            }

            // If paused and the window was already filled, just touch playhead to keep it fresh
            if (paused && window_full) {
                cache->Touch(playhead);
            }

            // Short sleep to throttle CPU (quarter-frame interval)
            int64_t sleep_us = static_cast<int64_t>(
                1000000.0 / reader->info.fps.ToFloat() / 4.0
            );
            std::this_thread::sleep_for(double_micro_sec(sleep_us));
        }
    }

    void VideoCacheThread::Seek(int64_t new_position, bool start_preroll)
    {
        if (start_preroll) {
            userSeeked = true;
        }
        requested_display_frame = new_position;
    }

    void VideoCacheThread::Seek(int64_t new_position)
    {
        Seek(new_position, false);
    }

} // namespace openshot