const routes = [];
let currentCleanup = null;

/** @returns {{ regex: RegExp, paramNames: string[] }} */
export function compileRoute(pattern) {
    const paramNames = [];
    const parts = pattern.replace(/\/:([^/]+)/g, (_, name) => {
        paramNames.push(name);
        return '/([^/]+)';
    });
    return { regex: new RegExp('^' + parts + '$'), paramNames };
}

/** Match a path against a string route pattern; returns params or null. */
export function matchRoute(pattern, path) {
    const { regex, paramNames } = compileRoute(pattern);
    const match = path.match(regex);
    if (!match) {
        return null;
    }
    const params = {};
    paramNames.forEach((name, i) => {
        params[name] = decodeURIComponent(match[i + 1]);
    });
    return params;
}

export function addRoute(pattern, handler) {
    let regex;
    let paramNames = [];
    if (pattern instanceof RegExp) {
        regex = pattern;
    } else {
        ({ regex, paramNames } = compileRoute(pattern));
    }
    routes.push({ regex, paramNames, handler });
}

export function navigate(hash) {
    window.location.hash = hash;
}

export function currentHash() {
    return window.location.hash.slice(1) || '/';
}

async function resolve() {
    if (typeof currentCleanup === 'function') {
        currentCleanup();
        currentCleanup = null;
    }

    const path = currentHash();
    for (const route of routes) {
        const match = path.match(route.regex);
        if (match) {
            const params = {};
            route.paramNames.forEach((name, i) => {
                params[name] = decodeURIComponent(match[i + 1]);
            });
            try {
                currentCleanup = await route.handler(params) || null;
            } catch (e) {
                console.error('Route handler error:', e);
            }
            return;
        }
    }
    // fallback: dashboard
    navigate('#/');
}

export function startRouter() {
    window.addEventListener('hashchange', resolve);
    resolve();
}