/**
* Myext scripts and bundles usage index
*
* Copyright (C) 2021 Wojtek Kosior
*
* Dual-licensed under:
*   - 0BSD license
*   - GPLv3 or (at your option) any later version
*/

"use strict";

/*
 * We want to count referenes to scripts and bundles in order to know,
 * for example, whether one can be safely deleted.
 */

(() => {
    const TYPE_PREFIX = window.TYPE_PREFIX;
    const get_storage = window.get_storage;
    const make_once = window.make_once;

    var component_uses = new Map();
    var storage;

    function add_use_info_by_item(prefix, item, components)
    {
	for (let component of components) {
	    component = component.join("");

	    let used_by_info = component_uses.get(component);

	    if (used_by_info === undefined) {
		used_by_info = {};
		component_uses.set(component, used_by_info);
	    }

	    if (used_by_info[prefix] === undefined)
		used_by_info[prefix] = new Set();

	    used_by_info[prefix].add(item);
	}
    }

    function remove_use_info_by_item(prefix, item, components)
    {
	for (let component of components) {
	    used_by_info = component_uses.get(component.join(""));
	    if (used_by_info === undefined ||
		used_by_info[prefix] === undefined)
		return;

	    used_by_info[prefix].delete(item);
	}
    }

    function build_reverse_uses_info(entries_it, type_prefix)
    {
	for (let [item, components] of storage.get_all_it(type_prefix))
	    add_use_info_by_item(type_prefix, item, components);
    }

    function handle_change(change)
    {
	if (change.old_val !== undefined)
	    remove_use_info_by_item(change.prefix, change.item, change.old_val);

	if (change.new_val !== undefined)
	    add_use_info_by_item(change.prefix, change.item, change.new_val);
    }

    function get_uses(arg1, arg2=undefined)
    {
	let [prefix, item] = [arg1, arg2];

	if (arg2 === undefined)
	    [prefix, item] = arg1;

	return component_uses.get(prefix + item);
    }

    async function init()
    {
	storage = await get_storage();

	prefixes = [TYPE_PREFIX.PAGE, TYPE_PREFIX.BUNDLE];
	for (let prefix of prefixes)
	    build_reverse_uses_info(prefix);

	storage.add_change_listener(handle_change, prefixes);

	return get_uses;
    }

    window.get_reverse_use_info = make_once(init);
})();