<?php

namespace Sharkk\Router;

class Router
{
	private array $routes = [];

	/**
	 * Add a route to the route tree. The route must be a URI path, and contain dynamic segments
	 * using a colon prefix. (:id, :slug, etc)
	 *
	 * Example:
	 * `$r->add('GET', '/posts/:id', function($id) { echo "Viewing post $id"; });`
	 */
	public function add(string $method, string $route, callable $handler): Router
	{
		// expand the route into segments and make dynamic segments into a common placeholder
		$segments = array_map(function($segment) {
			return str_starts_with($segment, ':') ? ':x' : $segment;
		}, explode('/', trim($route, '/')));

		// push each segment into the routes array as a node, except if this is the root node
		$node = &$this->routes;
		foreach ($segments as $segment) {
			// skip an empty segment, which allows us to register handlers for the root node
			if ($segment === '') continue;
			$node = &$node[$segment]; // build the node tree as we go
		}

		// Add the handler to the last node
		$node[$method] = $handler;

		return $this;
	}

	/**
	 * Perform a lookup in the route tree for a given method and URI. Returns an array with a result code,
	 * a handler if found, and any dynamic parameters. Codes are 200 for success, 404 for not found, and
	 * 405 for method not allowed.
	 *
	 * @return array ['code', 'handler', 'params']
	 */
	public function lookup(string $method, string $uri): array
	{
		// normalize uri to be tolerant of trailing slashes
		$uri = '/' . trim($uri, '/');

		// node is a reference to our current location in the node tree
		$node = $this->routes;

		// init the response array
		$res = ['code' => 0, 'handler' => null, 'params' => []];

		// if the URI is just a slash, we can return the handler for the root node
		if ($uri === '/') {
			if (!$this->checkForHandlers($node)) {
				$res['code'] = 404;
				return $res;
			}

			if (isset($node[$method])) {
				$res['code'] = 200;
				$res['handler'] = $node[$method];
			} else {
				$res['code'] = 405;
			}

			return $res;
		}

		// we'll split up the URI into segments and traverse the node tree
		foreach (explode('/', trim($uri, '/')) as $segment) {
			// check that the next segment is an array (not a callable) and exists, then move to it
			if (isset($node[$segment]) && is_array($node[$segment])) {
				$node = $node[$segment];
				continue;
			}

			// if there is a dynamic segment, move to it and store the value
			if (isset($node[':x'])) {
				$res['params'][] = $segment;
				$node = $node[':x'];
				continue;
			}

			// if we can't find a node for this segment, return 404
			$res['code'] = 404;
			return $res;
		}

		// if no handlers exist at this node, it's not a valid endpoint - return 404
		if (!$this->checkForHandlers($node)) {
			$res['code'] = 404;
			return $res;
		}

		// if we found a handler for the method, return it and any params. if not, return a 405
		if (isset($node[$method])) {
			$res['code'] = 200;
			$res['handler'] = $node[$method];
		} else {
			$res['code'] = 405;
		}

		return $res;
	}

	/**
	 * Clear all routes from the router.
	 */
	public function clear(): Router
	{
		$this->routes = [];
		return $this;
	}

	/**
	 * Dump the route tree as an array.
	 */
	public function dump(): array
	{
		return $this->routes;
	}

	/**
	 * Check if a given node has any method handlers.
	 */
	private function checkForHandlers(array $node): bool
	{
		foreach (['GET', 'POST', 'PUT', 'PATCH', 'DELETE', 'HEAD', 'OPTIONS'] as $m)
			if (isset($node[$m]))
				return true;

		return false;
	}

	/**
	 * Register a GET route.
	 */
	public function get(string $route, callable $handler): Router
	{
		return $this->add('GET', $route, $handler);
	}

	/**
	 * Register a POST route.
	 */
	public function post(string $route, callable $handler): Router
	{
		return $this->add('POST', $route, $handler);
	}

	/**
	 * Register a PUT route.
	 */
	public function put(string $route, callable $handler): Router
	{
		return $this->add('PUT', $route, $handler);
	}

	/**
	 * Register a PATCH route.
	 */
	public function patch(string $route, callable $handler): Router
	{
		return $this->add('PATCH', $route, $handler);
	}

	/**
	 * Register a DELETE route.
	 */
	public function delete(string $route, callable $handler): Router
	{
		return $this->add('DELETE', $route, $handler);
	}

	/**
	 * Register a HEAD route.
	 */
	public function head(string $route, callable $handler): Router
	{
		return $this->add('HEAD', $route, $handler);
	}
}