/*
    FFmpeg Factory - Convert
    Runs an ffmpeg conversion and writes progress to a JSON file.
    The same endpoint also cancels a running conversion (action=cancel), so the
    frontend only needs the task ID it already knows to stop a job.

    Expected POST parameters:
      action     - optional; "cancel" stops the running conversion of taskId.
                   Any other value (or omitted) starts a new conversion.
      src        - virtual path of the input file
      outputExt  - desired output file extension (e.g. "mp3", "mp4")
      convType   - "audio" | "video" | "image" | "generic"
      taskId     - unique task ID generated by the frontend
      options    - JSON string with format-specific options:
                     audio:   { sample_rate: 44100 }
                     video:   { resolution: "720p", compression: 23 }
                     image:   { scale: 0.5, compression: 80 }
                     generic: {}
*/
requirelib("filelib");
requirelib("ffmpeg");

// Ensure task folder exists
var taskDir = "tmp:/ffmpeg_factory";
if (!filelib.fileExists(taskDir)) {
    filelib.mkdir(taskDir);
}

function taskFileOf(id)     { return taskDir + "/" + id + ".task.json"; }
function progressFileOf(id) { return taskDir + "/" + id + ".progress.json"; }

// Read a task file back into an object, or null when it is missing / unreadable
function readTaskObject(id) {
    var taskFile = taskFileOf(id);
    if (!filelib.fileExists(taskFile)) {
        return null;
    }
    var content = filelib.readFile(taskFile);
    if (content === false || content === "") {
        return null;
    }
    try {
        return JSON.parse(content);
    } catch (e) {
        return null;
    }
}

var isCancelRequest = (typeof action !== "undefined" && action === "cancel");
var haveTaskId      = (typeof taskId !== "undefined" && taskId !== "" && taskId !== "undefined");

if (isCancelRequest) {
    // ── Cancel an already running conversion ──
    if (!haveTaskId) {
        sendJSONResp(JSON.stringify({ error: "Missing taskId" }));
    } else {
        // Stop the ffmpeg process; false means it already finished on its own
        var stopped = ffmpeg.cancel(progressFileOf(taskId));

        // Mark the task as cancelled. The still-running convert request re-reads
        // this file before writing its own result, so the cancelled state wins.
        var pendingTask = readTaskObject(taskId);
        if (pendingTask !== null) {
            pendingTask.status = "cancelled";
            pendingTask.error  = "Cancelled by user";
            filelib.writeFile(taskFileOf(taskId), JSON.stringify(pendingTask));
        }

        sendJSONResp(JSON.stringify({
            success: true,
            taskId:  taskId,
            stopped: stopped
        }));
    }

} else if (typeof src === "undefined" || typeof outputExt === "undefined" ||
           typeof convType === "undefined" || !haveTaskId) {
    // ── Validate required parameters ──
    sendJSONResp(JSON.stringify({ error: "Missing required parameters" }));

} else {
    // ── Start a new conversion ──

    // Parse options
    var opts = {};
    if (typeof options !== "undefined" && options !== "" && options !== "undefined") {
        try { opts = JSON.parse(options); } catch (e) {}
    }

    // Determine output virtual path (same directory as the source, new extension)
    var lastSlash = src.lastIndexOf("/");
    var inputDir   = src.substring(0, lastSlash);
    var inputFile  = src.substring(lastSlash + 1);
    var lastDot    = inputFile.lastIndexOf(".");
    var baseName   = (lastDot > 0) ? inputFile.substring(0, lastDot) : inputFile;
    var outputVpath = inputDir + "/" + baseName + "." + outputExt;

    // Progress file virtual path (written by the Go ffmpeg functions every ~500 ms).
    // It doubles as the cancellation key of this conversion.
    var progressVpath = progressFileOf(taskId);

    // Write initial task file so the frontend can resume the session if the tab is closed
    var taskObj = {
        id:           taskId,
        input_vpath:  src,
        output_vpath: outputVpath,
        conv_type:    convType,
        options:      opts,
        status:       "running",
        error:        "",
        created_at:   Date.now()
    };
    filelib.writeFile(taskFileOf(taskId), JSON.stringify(taskObj));

    // --- Run the conversion ---
    var success = false;
    var errMsg  = "";

    try {
        if (convType === "audio") {
            var sr = (opts.sample_rate && parseInt(opts.sample_rate) > 0) ? parseInt(opts.sample_rate) : 0;
            success = ffmpeg.audioConvert(src, outputVpath, sr, progressVpath);

        } else if (convType === "video") {
            var res  = (opts.resolution && opts.resolution !== "undefined") ? opts.resolution : "";
            var crf  = (opts.compression) ? parseInt(opts.compression) : 0;
            success = ffmpeg.videoConvert(src, outputVpath, res, crf, progressVpath);

        } else if (convType === "image") {
            var scale = (opts.scale) ? parseFloat(opts.scale) : 1.0;
            var qual  = (opts.compression) ? parseInt(opts.compression) : 0;
            success = ffmpeg.imageConvert(src, outputVpath, scale, qual, progressVpath);

        } else {
            // generic / cross-media (e.g. mp4 → gif)
            success = ffmpeg.convertWithProgress(src, outputVpath, progressVpath);
        }
    } catch (e) {
        errMsg  = e.toString();
        success = false;
    }

    // A cancel request may have come in while ffmpeg was running. The killed
    // process looks like a normal failure here, so check the task file first.
    var finalStatus  = success ? "completed" : "failed";
    var latestTask   = readTaskObject(taskId);
    var wasCancelled = (latestTask !== null && latestTask.status === "cancelled");
    if (wasCancelled) {
        finalStatus = "cancelled";
        errMsg      = "Cancelled by user";
    }

    if (filelib.fileExists(taskFileOf(taskId))) {
        // Update task file with final status
        taskObj.status = finalStatus;
        taskObj.error  = errMsg;
        filelib.writeFile(taskFileOf(taskId), JSON.stringify(taskObj));
    } else {
        // The task was dismissed while ffmpeg was still running: do not recreate
        // its files, and drop the progress file the conversion just rewrote.
        if (filelib.fileExists(progressVpath)) {
            filelib.deleteFile(progressVpath);
        }
    }

    sendJSONResp(JSON.stringify({
        success:   success && !wasCancelled,
        cancelled: wasCancelled,
        taskId:    taskId,
        output:    outputVpath,
        error:     errMsg
    }));
}