/**
 * GoingsOn — Query State Helper
 *
 * Phase 7 Tier 4 — every filter / sort / view-mode setting that changes what
 * the user sees must be mirrored to `location.search` so reload, deep-link,
 * and back-button preserve the state (see docs/design-system.md § Filter &
 * view state in the URL). One helper, one set of conventions.
 *
 * Conventions:
 * - Writes use `history.replaceState` so each filter change doesn't push a
 *   new history entry. The back button still works for view navigation
 *   (which uses router.js's pushState).
 * - Empty values are removed from the URL — defaults render as a clean path.
 * - On view-switch, `router.js#navigate(path)` writes only the new path,
 *   wiping the previous view's query. Each view restores its own state on
 *   load via `read(name)`.
 */

(function() {
    'use strict';

    /**
     * Read a single query-string value by name. Returns null if absent or empty.
     */
    function read(name) {
        const v = new URLSearchParams(location.search).get(name);
        return v == null || v === '' ? null : v;
    }

    /**
     * Read multiple keys at once. Returns an object; absent keys are omitted.
     */
    function readMany(names) {
        const params = new URLSearchParams(location.search);
        const out = {};
        for (const n of names) {
            const v = params.get(n);
            if (v != null && v !== '') out[n] = v;
        }
        return out;
    }

    /**
     * Write a single value. Removes the key when value is null / undefined / empty / false.
     * Uses replaceState — does not push history.
     */
    function write(name, value) {
        const params = new URLSearchParams(location.search);
        if (value == null || value === '' || value === false) {
            params.delete(name);
        } else if (value === true) {
            params.set(name, '1');
        } else {
            params.set(name, String(value));
        }
        const qs = params.toString();
        const path = location.pathname + (qs ? '?' + qs : '');
        try {
            history.replaceState({ path }, '', path);
        } catch (_) { /* ignore — file:// or sandboxed contexts */ }
    }

    /**
     * Batch-write. Same key removal rules as `write`.
     */
    function writeMany(obj) {
        const params = new URLSearchParams(location.search);
        for (const [name, value] of Object.entries(obj)) {
            if (value == null || value === '' || value === false) {
                params.delete(name);
            } else if (value === true) {
                params.set(name, '1');
            } else {
                params.set(name, String(value));
            }
        }
        const qs = params.toString();
        const path = location.pathname + (qs ? '?' + qs : '');
        try {
            history.replaceState({ path }, '', path);
        } catch (_) { /* ignore */ }
    }

    /**
     * Remove a list of keys.
     */
    function clear(names) {
        const params = new URLSearchParams(location.search);
        for (const n of names) params.delete(n);
        const qs = params.toString();
        const path = location.pathname + (qs ? '?' + qs : '');
        try {
            history.replaceState({ path }, '', path);
        } catch (_) { /* ignore */ }
    }

    GoingsOn.queryState = { read, readMany, write, writeMany, clear };
})();