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

import TYPE_PREFIX from '/common/stored_types.mjs';
import get_storage from './storage.mjs';
import make_once from '/common/once.mjs';

"use strict";

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

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;
}

export default make_once(init);