Haketilo

/**

 * 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

 */

/*

 * This is a javascript rewrite of Python implementation of the algorithm here:

 * https://git.koszko.org/pydrilla/tree/src/pydrilla/pydrilla.py?id=f4edcbe7f4739d6f82a2e1bb180960b003b30862#n205

 */

/* "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 make_tree_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] || make_tree_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]];

    }

}

/*

 * 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)

{

    /*

     * 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);

    const tree = patterns_by_proto[deco.proto] || make_tree_node();

    patterns_by_proto[deco.proto] = tree;

    let path_trees;

    if (deco.proto === "file") {

	path_trees = [tree];

    } else {

	/* We need an aray of domain labels ordered most-significant-first. */

	const domain = [...deco.domain].reverse();

	path_trees = add_sequence(tree, domain, make_tree_node);

    }

    for (const path_tree of path_trees) {

        for (const match_obj of add_sequence(path_tree, deco.path, () => {}))

            match_obj[item_name] = item;

    }

}

// /*

//  * 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 deco = deconstruct_url(pattern, false);

//     const tree = patterns_by_proto[deco.proto] || make_tree_node();

//     patterns_by_proto[deco.proto] = tree;

//     let path_trees;

//     if (deco.proto === "file") {

// 	path_trees = [tree];

//     } else {

// 	/* We need an aray of domain labels ordered most-significant-first. */

// 	const domain = [...deco.domain].reverse();

// 	..........................

// 	path_trees = add_sequence(tree, domain, make_tree_node);

//     }

// }

/*

 * Yield registered items (as [item_name, item] arrays) that match url. For

 * cosistent behavior, please don't modify the pattern tree while iterating over

 * the results.

 */

function* pattern_tree_search(patterns_by_proto, url)

{

    const deco = deconstruct_url(url, false);

    tree = patterns_by_proto[deco.proto] || make_tree_node();

    let path_trees;

    if (deco.proto === "file") {

	path_trees = [tree];

    } else {

	/* We need an aray of domain labels ordered most-significant-first. */

	const domain = [...deco.domain].reverse();

	path_trees = search_sequence(tree, domain);

    }

    for (const path_tree of path_trees) {

	for (const match_obj of search_sequence(path_tree, deco.path)) {

	    for (const entry of Object.entries(match_obj))

		yield entry;

	}

    }

}

const pattern_tree = {

    make: () => {},

    register: pattern_tree_register,

    // deregister: pattern_tree_deregister,

    search: pattern_tree_search

}

/*

 * EXPORTS_START

 * EXPORT pattern_tree

 * EXPORTS_END

 */