// ==UserScript==
// @name        SoundCloud Restore Playback
// @description Saves/restores playback position on SoundCloud.com
// @namespace   https://github.com/crabvk
// @version     0.3.2
// @author      Vyacheslav Konovalov
// @match       https://soundcloud.com/*
// @license     MIT
// @noframes
// @grant       GM_getValue
// @grant       GM_setValue
// @grant       GM_deleteValue
// @downloadURL https://raw.githubusercontent.com/crabvk/userscripts/master/soundcloud-restore-playback.user.js
// @homepageURL https://github.com/crabvk/userscripts
// ==/UserScript==

/**
 * Finds the last array element that matches the condition.
 *
 * @param {Array} array Any array.
 * @param {number} cond Condition to match against each array element.
 */
const findLast = (array, cond) => {
    let i = array.length - 1
    for (; i >= 0; i--) {
        if (cond(array[i])) {
            return array[i]
        }
    }
}

/**
 * Clicks on the timeline according to factor.
 *
 * @param {number} factor Current position divided by track duration.
 * @param {number} wrapper The timeline wrapper element on which to click.
 */
const restorePlayback = (factor, wrapper) => {
    const rect = wrapper.getBoundingClientRect()
    const args = {
        view: unsafeWindow,
        bubbles: true,
        clientX: rect.x + Math.floor(rect.width * factor),
        clientY: rect.y + 10
    }
    wrapper.dispatchEvent(new MouseEvent('mousedown', args))
    wrapper.dispatchEvent(new MouseEvent('mouseup', args))
}

const observeProgress = player => {
    let isInit = true
    let isRestore = false
    let lastKey, lastPosition
    const cond = m => isInit ? m.attributeName === 'aria-valuemax' : m.attributeName === 'aria-valuenow'

    new MutationObserver(mutations => {
        const mutation = findLast(mutations, m => m.type === 'attributes' && cond(m))
        if (mutation === undefined) {
            return
        }

        const duration = parseInt(mutation.target.getAttribute('aria-valuemax'))
        // Skip tracks shorter than 10 minutes
        if (duration < 600) {
            return
        }

        const key = player.querySelector('.playbackSoundBadge__titleLink').getAttribute('href')
        let position

        if (!isInit && key === lastKey) {
            // Ignore position change triggered by restorePlayback function
            if (isRestore) {
                isRestore = false
                return
            }
            position = parseInt(mutation.target.getAttribute('aria-valuenow'))
            if (position > 0 && position % 5 === 0 || Math.abs(lastPosition - position) > 4) {
                GM_setValue(key, position)
            }
        } else {
            isInit = false
            position = GM_getValue(key) || 0
            if (position > 0) {
                // Do not restore position from last 30 seconds of the track
                if (position < duration - 30) {
                    isRestore = true
                    restorePlayback(position / duration, mutation.target)
                } else {
                    GM_deleteValue(key)
                }
            }
        }

        lastKey = key
        lastPosition = position
    }).observe(player.querySelector('.playbackTimeline__progressWrapper'), { attributes: true })
}

const player = document.body.querySelector('#app .playControls')
observeProgress(player)