path: root/background/storage.js

/**
 * Hachette storage manager
 *
 * Copyright (C) 2021 Wojtek Kosior
 * Redistribution terms are gathered in the `copyright' file.
 */

/*
 * IMPORTS_START
 * IMPORT TYPE_PREFIX
 * IMPORT TYPE_NAME
 * IMPORT list_prefixes
 * IMPORT make_lock
 * IMPORT lock
 * IMPORT unlock
 * IMPORT make_once
 * IMPORT browser
 * IMPORT is_chrome
 * IMPORT observables
 * IMPORTS_END
 */

var exports = {};

/* We're yet to decide how to handle errors... */

/* Here are some basic wrappers for storage API functions */

async function get(key)
{
    try {
	/* Fix for fact that Chrome does not use promises here */
	let promise = is_chrome ?
	    new Promise((resolve, reject) =>
			chrome.storage.local.get(key,
						 val => resolve(val))) :
	    browser.storage.local.get(key);

	return (await promise)[key];
    } catch (e) {
	console.log(e);
    }
}

async function set(key, value)
{
    try {
	return browser.storage.local.set({[key]: value});
    } catch (e) {
	console.log(e);
    }
}

async function setn(keys_and_values)
{
    let obj = Object();
    while (keys_and_values.length > 1) {
	let value = keys_and_values.pop();
	let key = keys_and_values.pop();
	obj[key] = value;
    }

    try {
	return browser.storage.local.set(obj);
    } catch (e) {
	console.log(e);
    }
}

async function set_var(name, value)
{
    return set(TYPE_PREFIX.VAR + name, value);
}

async function get_var(name)
{
    return get(TYPE_PREFIX.VAR + name);
}

/*
 * A special case of persisted variable is one that contains list
 * of items.
 */

async function get_list_var(name)
{
    let list = await get_var(name);

    return list === undefined ? [] : list;
}

/* We maintain in-memory copies of some stored lists. */

async function list(prefix)
{
    let name = TYPE_NAME[prefix] + "s"; /* Make plural. */
    let map = new Map();

    for (let item of await get_list_var(name))
	map.set(item, await get(prefix + item));

    return {map, prefix, name, observable: observables.make(),
	    lock: make_lock()};
}

var list_by_prefix = {};

async function init()
{
    for (let prefix of list_prefixes)
	list_by_prefix[prefix] = await list(prefix);

    return exports;
}

/*
 * Facilitate listening to changes
 */

exports.add_change_listener = function (cb, prefixes=list_prefixes)
{
    if (typeof(prefixes) === "string")
	prefixes = [prefixes];

    for (let prefix of prefixes)
	observables.subscribe(list_by_prefix[prefix].observable, cb);
}

exports.remove_change_listener = function (cb, prefixes=list_prefixes)
{
    if (typeof(prefixes) === "string")
	prefixes = [prefixes];

    for (let prefix of prefixes)
	observables.unsubscribe(list_by_prefix[prefix].observable, cb);
}

/* Prepare some hepler functions to get elements of a list */

function list_items_it(list, with_values=false)
{
    return with_values ? list.map.entries() : list.map.keys();
}

function list_entries_it(list)
{
    return list_items_it(list, true);
}

function list_items(list, with_values=false)
{
    let array = [];

    for (let item of list_items_it(list, with_values))
	array.push(item);

    return array;
}

function list_entries(list)
{
    return list_items(list, true);
}

/*
 * Below we make additional effort to update map of given kind of items
 * every time an item is added/removed to keep everything coherent.
 */
async function set_item(item, value, list)
{
    await lock(list.lock);
    let result = await _set_item(...arguments);
    unlock(list.lock)
    return result;
}
async function _set_item(item, value, list)
{
    let key = list.prefix + item;
    let old_val = list.map.get(item);
    if (old_val === undefined) {
	let items = list_items(list);
	items.push(item);
	await setn([key, value, "_" + list.name, items]);
    } else {
	await set(key, value);
    }

    list.map.set(item, value)

    let change = {
	prefix : list.prefix,
	item,
	old_val,
	new_val : value
    };

    observables.broadcast(list.observable, change);

    return old_val;
}

// TODO: The actual idea to set value to undefined is good - this way we can
//       also set a new list of items in the same API call. But such key
//       is still stored in the storage. We need to somehow remove it later.
//       For that, we're going to have to store 1 more list of each kind.
async function remove_item(item, list)
{
    await lock(list.lock);
    let result = await _remove_item(...arguments);
    unlock(list.lock)
    return result;
}
async function _remove_item(item, list)
{
    let old_val = list.map.get(item);
    if (old_val === undefined)
	return;

    let key = list.prefix + item;
    let items = list_items(list);
    let index = items.indexOf(item);
    items.splice(index, 1);

    await setn([key, undefined, "_" + list.name, items]);

    list.map.delete(item);

    let change = {
	prefix : list.prefix,
	item,
	old_val,
	new_val : undefined
    };

    observables.broadcast(list.observable, change);

    return old_val;
}

// TODO: same as above applies here
async function replace_item(old_item, new_item, list, new_val=undefined)
{
    await lock(list.lock);
    let result = await _replace_item(...arguments);
    unlock(list.lock)
    return result;
}
async function _replace_item(old_item, new_item, list, new_val=undefined)
{
    let old_val = list.map.get(old_item);
    if (new_val === undefined) {
	if (old_val === undefined)
	    return;
	new_val = old_val
    } else if (new_val === old_val && new_item === old_item) {
	return old_val;
    }

    if (old_item === new_item || old_val === undefined) {
	await _set_item(new_item, new_val, list);
	return old_val;
    }

    let new_key = list.prefix + new_item;
    let old_key = list.prefix + old_item;
    let items = list_items(list);
    let index = items.indexOf(old_item);
    items[index] = new_item;
    await setn([old_key, undefined, new_key, new_val,
		"_" + list.name, items]);

    list.map.delete(old_item);

    let change = {
	prefix : list.prefix,
	item : old_item,
	old_val,
	new_val : undefined
    };

    observables.broadcast(list.observable, change);

    list.map.set(new_item, new_val);

    change.item = new_item;
    change.old_val = undefined;
    change.new_val = new_val;

    observables.broadcast(list.observable, change);

    return old_val;
}

/*
 * For scripts, item name is chosen by user, data should be
 * an object containing:
 * - script's url and hash or
 * - script's text or
 * - all three
 */

/*
 * For bags, item name is chosen by user, data is an array of 2-element
 * arrays with type prefix and script/bag names.
 */

/*
 * For pages data argument is an object with properties `allow'
 * and `components'. Item name is url.
 */

exports.set = async function (prefix, item, data)
{
    return set_item(item, data, list_by_prefix[prefix]);
}

exports.get = function (prefix, item)
{
    return list_by_prefix[prefix].map.get(item);
}

exports.remove = async function (prefix, item)
{
    return remove_item(item, list_by_prefix[prefix]);
}

exports.replace = async function (prefix, old_item, new_item,
				  new_data=undefined)
{
    return replace_item(old_item, new_item, list_by_prefix[prefix],
			new_data);
}

exports.get_all_names = function (prefix)
{
    return list_items(list_by_prefix[prefix]);
}

exports.get_all_names_it = function (prefix)
{
    return list_items_it(list_by_prefix[prefix]);
}

exports.get_all = function (prefix)
{
    return list_entries(list_by_prefix[prefix]);
}

exports.get_all_it = function (prefix)
{
    return list_entries_it(list_by_prefix[prefix]);
}

/* Finally, a quick way to wipe all the data. */
// TODO: maybe delete items in such order that none of them ever references
// an already-deleted one?
exports.clear = async function ()
{
    let lists = list_prefixes.map((p) => list_by_prefix[p]);

    for (let list of lists)
	await lock(list.lock);

    for (let list of lists) {

	let change = {
	    prefix : list.prefix,
	    new_val : undefined
	};

	for (let [item, val] of list_entries_it(list)) {
	    change.item = item;
	    change.old_val = val;
	    observables.broadcast(list.observable, change);
	}

	list.map = new Map();
    }

    await browser.storage.local.clear();

    for (let list of lists)
	unlock(list.lock);
}

const get_storage = make_once(init);

/*
 * EXPORTS_START
 * EXPORT get_storage
 * EXPORTS_END
 */