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+/**
+ * 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:         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. If there was
+ * not yet any item associated with the tree path designated by segments, create
+ * a new one using item_instantiator() function. Return all items matching this
+ * path (both the ones that existed and the ones just created).
+ */
+function add_sequence(tree_node, segments, item_instantiator)
+{
+    let wildcards;
+
+    for (var segment of segments) {
+	wildcards = tree_node.wildcard_matches;
+
+	const child = tree_node.children[segment] || make_tree_node();
+	tree_node.children[segment] = child;
+	tree_node = child;
+    }
+
+    if (tree_node.literal_match === null)
+	tree_node.literal_match = item_instantiator();
+
+    if (!is_wildcard(segment))
+	return [tree_node.literal_match];
+
+    if (wildcards[segment.length - 1] === null)
+	wildcards[segment.length - 1] = item_instantiator();
+
+    return [tree_node.literal_match, wildcards[segment.length - 1]];
+}
+
+/*
+ * Can be used to remove item from (this branch of) the Pattern Tree.
+ * item_modifier should be a function that accepts 1 argument, the item stored
+ * in the tree, 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 `undefined`, it means the item should be deleted from the Tree.
+ *
+ * item_modifier() will be called with all items in (this branch of) the Pattern
+ * Tree that correspond to the path designated by segments. The Tree will be
+ * updated accordingly.
+ */
+function modify_sequence(tree_node, segments, item_modifier)
+{
+    const nodes = [tree_node];
+
+    for (const segment of segments) {
+	const next_node = nodes[nodes.length - 1].children[segment];
+	nodes.push(next_node);
+    }
+
+    const nsegments = segments.length;
+    let i = segments.length - 1;
+
+    if (nsegments > 0 && is_wildcard(segments[i])) {
+	const node = nodes[nodes.length - 2];
+	const asterisks = segments[i].length;
+    }
+
+    ............................
+
+    for (let i = segments.length - 1; i >= 0; i--) {
+
+	if (i
+    }
+
+    segments
+
+    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 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 patterns_tree = {
+    make: () => {},
+    register: patterns_tree_register,
+    search: patterns_tree_search
+}
+
+/*
+ * EXPORTS_START
+ * EXPORT patterns_tree
+ * EXPORTS_END
+ */