path: root/common/patterns_query_tree.js

/**
 * This file is part of Haketilo.
 *
 * Function: Data structure to query items by URL patterns.
 *
 * Copyright (C) 2021 Wojtek Kosior
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * As additional permission under GNU GPL version 3 section 7, you
 * may distribute forms of that code without the copy of the GNU
 * GPL normally required by section 4, provided you include this
 * license notice and, in case of non-source distribution, a URL
 * through which recipients can access the Corresponding Source.
 * If you modify file(s) with this exception, you may extend this
 * exception to your version of the file(s), but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * As a special exception to the GPL, any HTML file which merely
 * makes function calls to this code, and for that purpose
 * includes it by reference shall be deemed a separate work for
 * copyright law purposes. If you modify this code, you may extend
 * this exception to your version of the code, but you are not
 * obligated to do so. If you do not wish to do so, delete this
 * exception statement from your version.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * I, Wojtek Kosior, thereby promise not to sue for violation of this file's
 * license. Although I request that you do not make use this code in a
 * proprietary program, I am not going to enforce this in court.
 */

/*
 * IMPORTS_START
 * IMPORT deconstruct_url
 * IMPORTS_END
 */

/* "Pattern Tree" is how we refer to the data structure used for querying
 * Haketilo patterns. Those look like 'https://*.example.com/ab/***'. The goal
 * is to make it possible for given URL to quickly retrieve all known patterns
 * that match it.
 */
function empty_node() {
    return {
	wildcard_matches: [null, null, null],
	literal_match:    null,
	children:         {}
    };
}

function is_empty_node(tree_node) {
    const children = tree_node.children;
    for (const key in children) {
	if (children.hasOwnProperty(key))
	    return false;
    }

    if (Array.reduce(tree_node.wildcard_matches, (a, b) => b && a !== null, 1))
	return false;

    return tree_node.literal_match === null;
}

const is_wildcard = segment => ["*", "**", "***"].lastIndexOf(segment) >= 0;

/*
 * Yields all matches of this segments sequence against the tree that starts at
 * this node. Results are produces in order from greatest to lowest pattern
 * specificity.
 */
function* search_sequence(tree_node, segments)
{
    const nodes = [tree_node];

    for (const segment of segments) {
	const next_node = nodes[nodes.length - 1].children[segment];
	if (next_node === undefined)
	    break;

	nodes.push(next_node);
    }

    const nsegments = segments.length;

    const conds = [
	/* literal pattern match */
	() => nodes.length     == nsegments,
	/* wildcard pattern matches */
	() => nodes.length + 1 == nsegments && segments[nsegments - 1] != "*",
	() => nodes.length + 1 <  nsegments,
	() => nodes.length + 1 != nsegments || segments[nsegments - 1] != "***"
    ];

    while (nodes.length) {
	const node = nodes.pop();
	const items = [node.literal_match, ...node.wildcard_matches];

	for (let i = 0; i < 4; i++) {
	    if (items[i] !== null && conds[i]())
		yield items[i];
	}
    }
}

/*
 * Make item queryable through (this branch of) the Pattern Tree or remove its
 * path from there.
 *
 * item_modifier should be a function that accepts 1 argument, the item stored
 * in the tree (or `null` if there wasn't any item there), and returns an item
 * that should be used in place of the first one. It is also legal for it to
 * return the same item modifying it first. If it returns `null`, it means the
 * item should be deleted from the Tree.
 *
 * If there was not yet any item associated with the tree path designated by
 * segments and value returned by item_modifier is not `null`, make the value
 * queryable by this path.
 */
function modify_sequence(tree_node, segments, item_modifier)
{
    const nodes = [tree_node];
    let removed = true;

    for (var current_segment of segments) {
	wildcards = tree_node.wildcard_matches;

	const child = tree_node.children[current_segment] || empty_node();
	tree_node.children[current_segment] = child;
	tree_node = child;
	nodes.push(tree_node);
    }

    tree_node.literal_match = item_modifier(tree_node.literal_match);
    if (tree_node.literal_match !== null)
	removed = false;

    let i = segments.length;

    if (is_wildcard(current_segment)) {
	const asterisks = current_segment.length - 1;
	const wildcards = nodes[i - 1].wildcard_matches;
	wildcards[asterisks] = item_modifier(wildcards[asterisks]);
	if (wildcards[asterisks] !== null)
	    removed = false;
    }

    while (!removed)
	return;

    while (i > 0) {
	tree_node = nodes[i--];
	if (is_empty_node(tree_node))
	    delete nodes[i].children[segments[i]];
    }
}

/* Helper function for modify_tree(). */
function modify_path(tree_node, deco, item_modifier)
{
    tree_node = tree_node || empty_node();
    modify_sequence(tree_node, deco.path, item_modifier);
    return is_empty_node(tree_node) ? null : tree_node;
}

/* Helper function for modify_tree(). */
function modify_domain(tree_node, deco, item_modifier)
{
    const path_modifier = branch => modify_path(branch, deco, item_modifier);
    tree_node = tree_node || empty_node();
    /* We need an array of domain labels ordered most-significant-first. */
    modify_sequence(tree_node, [...deco.domain].reverse(), path_modifier);
    return is_empty_node(tree_node) ? null : tree_node;
}

/* Helper function for pattern_tree_register() and pattern_tree_deregister(). */
function modify_tree(patterns_by_proto, pattern, item_modifier)
{
    /*
     * We pass 'false' to disable length limits on URL parts. Length limits are
     * mostly useful in case of iteration over all patterns matching given URL.
     * Here we don't do that.
     */
    const deco = deconstruct_url(pattern, false);

    let tree_for_proto = patterns_by_proto[deco.proto];

    tree_for_proto = deco.domain === undefined ?
	modify_path(tree_for_proto, deco, item_modifier) :
	modify_domain(tree_for_proto, deco, item_modifier);

    patterns_by_proto[deco.proto] = tree_for_proto;
    if (tree_for_proto === null)
	delete patterns_by_proto[deco.proto];
}

/*
 * Make item queryable through the Pattern Tree that starts with the protocols
 * dictionary object passed in the first argument.
 */
function pattern_tree_register(patterns_by_proto, pattern, item_name, item)
{
    const key_prefix = pattern[pattern.length - 1] === '/' ? '/' : '_';
    item_name = key_prefix + item_name;
    const add_item = obj => Object.assign(obj || {}, {[item_name]: item});
    modify_tree(patterns_by_proto, pattern, add_item);
}

/* Helper function for pattern_tree_deregister(). */
function _remove_item(obj, item_name)
{
    obj = obj || {};
    delete obj[item_name];
    for (const key in obj)
	return obj;
    return null;
}

/*
 * Remove registered item from the Pattern Tree that starts with the protocols
 * dictionary object passed in the first argument. The remaining 2 arguments
 * should be pattern and name that have been earlier passed to
 * pattern_tree_register().
 */
function pattern_tree_deregister(patterns_by_proto, pattern, item_name)
{
    const key_prefix = pattern[pattern.length - 1] === '/' ? '/' : '_';
    item_name = key_prefix + item_name;
    const remove_item = obj => _remove_item(obj, item_name);
    modify_tree(patterns_by_proto, pattern, remove_item);
}

/*
 * Yield registered items that match url. Each yielded value is an object with
 * key being matched item names and values being the items. One such object
 * shall contain all items matched with given pattern specificity. Objects are
 * yielded in order from greatest to lowest pattern specificity.
 */
function* pattern_tree_search(patterns_by_proto, url)
{
    const deco = deconstruct_url(url, false);

    const tree_for_proto = patterns_by_proto[deco.proto] || empty_node();
    let by_path = [tree_for_proto];

    /* We need an array of domain labels ordered most-significant-first. */
    if (deco.domain !== undefined)
	by_path = search_sequence(tree_for_proto, [...deco.domain].reverse());

    for (const path_tree of by_path) {
	for (const match_obj of search_sequence(path_tree, deco.path)) {
	    let result_obj_slash    = null;
	    let result_obj_no_slash = null;

	    for (const [key, item] of Object.entries(match_obj)) {
		if (deco.trailing_slash && key[0] === '/') {
		    result_obj_slash = result_obj_slash || {};
		    result_obj_slash[key.substring(1)] = item;
		} else if (key[0] !== '/') {
		    result_obj_no_slash = result_obj_no_slash || {};
		    result_obj_no_slash[key.substring(1)] = item;
		}
	    }

	    if (deco.trailing_slash && result_obj_slash)
		yield result_obj_slash;

	    if (result_obj_no_slash)
		yield result_obj_no_slash;
	}
    }
}

const pattern_tree = {
    make:       () => ({}),
    register:   pattern_tree_register,
    deregister: pattern_tree_deregister,
    search:     pattern_tree_search
}

/*
 * EXPORTS_START
 * EXPORT pattern_tree
 * EXPORTS_END
 */