import assert from 'node:assert';
import BoxError from './boxerror.js';
import debugModule from 'debug';
import fs from 'node:fs';
import locks from './locks.js';
import path from 'node:path';
import paths from './paths.js';
import safe from 'safetydance';
import scheduler from './scheduler.js';
import tasks from './tasks.js';

const debug = debugModule('box:apptaskmanager');


const gActiveTasks = {}; // indexed by app id
const gPendingTasks = [];
let gStarted = false;

const TASK_CONCURRENCY = 3;
const DRAIN_TIMER_SECS = 1000;

let gDrainTimerId = null;

async function drain() {
    debug(`drain: ${gPendingTasks.length} apptasks pending`);

    for (let i = 0; i < gPendingTasks.length; i++) {
        const space = Object.keys(gActiveTasks).length - TASK_CONCURRENCY;
        if (space == 0) {
            debug('At concurrency limit, cannot drain anymore');
            break;
        }

        const { appId, taskId, options, onFinished }  = gPendingTasks[i];

        // acquire lock _before_ the task. this prevents the task failing if it can't get a lock
        const [lockError] = await safe(locks.acquire(`${locks.TYPE_APP_TASK_PREFIX}${appId}`));
        if (lockError) continue;

        gPendingTasks.splice(i, 1);
        gActiveTasks[appId] = {};

        const logFile = path.join(paths.LOG_DIR, appId, 'apptask.log');

        if (!fs.existsSync(path.dirname(logFile))) safe.fs.mkdirSync(path.dirname(logFile)); // ensure directory

        scheduler.suspendAppJobs(appId);

        // background
        let taskError = null, taskResult = null;
        tasks.startTask(taskId, Object.assign(options, { logFile }))
            .then((result) => { taskResult = result; })
            .catch((error) => { taskError = error; })
            .finally(async () => {
                delete gActiveTasks[appId];
                await safe(onFinished(taskError, taskResult), { debug }); // hasPendingTasks() can now return false
                await locks.release(`${locks.TYPE_APP_TASK_PREFIX}${appId}`);
                await locks.releaseByTaskId(taskId);
                scheduler.resumeAppJobs(appId);
            });
    }

    gDrainTimerId = null;
    if (gPendingTasks.length) gDrainTimerId = setTimeout(drain, DRAIN_TIMER_SECS); // check for released locks
}

async function start() {
    assert.strictEqual(gDrainTimerId, null);
    assert.strictEqual(gStarted, false);

    debug('started');
    gStarted = true;

    if (gPendingTasks.length) gDrainTimerId = setTimeout(drain, DRAIN_TIMER_SECS);
}

function scheduleTask(appId, taskId, options, onFinished) {
    assert.strictEqual(typeof appId, 'string');
    assert.strictEqual(typeof taskId, 'string');
    assert.strictEqual(typeof options, 'object');
    assert.strictEqual(typeof onFinished, 'function');

    if (appId in gActiveTasks) {
        onFinished(new BoxError(BoxError.CONFLICT, `Task for ${appId} is already active`));
        return;
    }

    tasks.update(taskId, { percent: 1, message: gStarted ? 'Queued' : 'Waiting for platform to initialize' });
    gPendingTasks.push({ appId, taskId, options, onFinished });

    if (gStarted && !gDrainTimerId) gDrainTimerId = setTimeout(drain, DRAIN_TIMER_SECS);
}

function hasPendingTasks() {
    return Object.keys(gActiveTasks).length > 0 || gPendingTasks.length > 0;
}

export default {
    start,
    scheduleTask,
    hasPendingTasks
};