<?php
/**
 * Generates /.well-known/mcp.json for MCP Server Discovery.
 *
 * Allows AI agents to discover MCP (Model Context Protocol) servers
 * available on this WordPress site.
 *
 * @since 4.2.0
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

class AIREWP_MCP_JSON {

    public function __construct() {
        // Generation triggered by main plugin
    }

    /**
     * Write mcp.json, or remove it when there is nothing to publish.
     *
     * A file left behind after the last server was removed would keep being
     * served, and by the web server directly, without ever asking PHP.
     */
    public static function generate( array $settings ): void {
        $file = AI_Ready_WP::get_well_known_dir() . 'mcp.json';

        if ( ! self::is_active( $settings ) ) {
            AI_Ready_WP::delete_file( $file );
            return;
        }

        AI_Ready_WP::write_file(
            $file,
            wp_json_encode( self::build( $settings ), JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE )
        );
    }

    /**
     * Serve mcp.json straight from memory, without touching the filesystem.
     *
     * With no servers listed the URL answers 404. A manifest that says "here
     * are my servers" and lists none is not discovery, it is a file that
     * looks like one, and until 4.4.2 the plugin published exactly that as
     * soon as the feature was switched on.
     */
    public static function serve(): void {
        $settings = AI_Ready_WP::get_settings();

        if ( ! self::is_active( $settings ) ) {
            AIREWP_Rewrite::send_json(
                [
                    'error'   => 'not_found',
                    'message' => 'No MCP servers are published on this site.',
                ],
                404
            );
        }

        AIREWP_Rewrite::send_json( self::build( $settings ) );
    }

    /**
     * Whether there is a manifest to publish: the feature is on and at least
     * one server is listed.
     */
    public static function is_active( array $settings ): bool {
        return ! empty( $settings['enable_mcp_json'] ) && [] !== self::get_servers( $settings );
    }

    /**
     * Build the mcp.json data structure.
     *
     * Shared by the written file and the dynamic response so the two cannot
     * drift apart, filters included.
     */
    public static function build( array $settings ): array {
        $servers = self::get_servers( $settings );

        $mcp_json = [
            'schema_version' => '1.0.0',
            'name'           => sprintf( '%s MCP Servers', $settings['company_name'] ),
            'description'    => sprintf(
                'MCP servers available on %s',
                home_url()
            ),
            'homepage'       => home_url(),
            'servers'        => $servers,
            'metadata'       => [
                'generatedBy' => 'AI-Ready WP ' . AIREWP_VERSION,
                'generatedAt' => gmdate( 'c' ),
                'siteUrl'     => home_url(),
            ],
        ];

        /**
         * Filter the complete mcp.json output.
         *
         * @since 4.2.0
         *
         * @param array $mcp_json The mcp.json data.
         * @param array $settings Plugin settings.
         */
        $mcp_json = apply_filters( 'airewp_mcp_json', $mcp_json, $settings );

        return $mcp_json;
    }

    /**
     * Get configured MCP servers.
     *
     * @return array<array{name: string, description: string, transport: string, url: string}>
     */
    public static function get_servers( array $settings ): array {
        $servers = [];

        // Parse custom MCP servers from settings (JSON format)
        $custom_servers = $settings['mcp_servers'] ?? '';
        if ( ! empty( $custom_servers ) ) {
            $parsed = json_decode( $custom_servers, true );
            if ( is_array( $parsed ) ) {
                foreach ( $parsed as $server ) {
                    if ( ! empty( $server['name'] ) && ! empty( $server['url'] ) ) {
                        $servers[] = [
                            'name'        => sanitize_text_field( $server['name'] ),
                            'description' => sanitize_text_field( $server['description'] ?? '' ),
                            'transport'   => sanitize_text_field( $server['transport'] ?? 'streamable-http' ),
                            'url'         => esc_url_raw( $server['url'] ),
                        ];
                    }
                }
            }
        }

        /**
         * Filter the MCP servers list.
         *
         * Allows themes and plugins to register their own MCP servers.
         *
         * @since 4.2.0
         *
         * @param array $servers  Current servers list.
         * @param array $settings Plugin settings.
         */
        $servers = apply_filters( 'airewp_mcp_servers', $servers, $settings );

        return is_array( $servers ) ? array_values( $servers ) : [];
    }
}