<?php
/**
 * Metrics collector class.
 *
 * @package WP_Prometheus
 */

namespace Magdev\WpPrometheus\Metrics;

use Prometheus\CollectorRegistry;
use Prometheus\Storage\InMemory;
use Prometheus\RenderTextFormat;

// Prevent direct file access.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

/**
 * Collector class.
 *
 * Collects and manages Prometheus metrics.
 */
class Collector {

    /**
     * Prometheus collector registry.
     *
     * @var CollectorRegistry
     */
    private CollectorRegistry $registry;

    /**
     * Metric namespace.
     *
     * @var string
     */
    private string $namespace = 'wordpress';

    /**
     * Constructor.
     */
    public function __construct() {
        $this->registry = new CollectorRegistry( new InMemory() );
    }

    /**
     * Get the collector registry.
     *
     * @return CollectorRegistry
     */
    public function get_registry(): CollectorRegistry {
        return $this->registry;
    }

    /**
     * Get the metric namespace.
     *
     * @return string
     */
    public function get_namespace(): string {
        return $this->namespace;
    }

    /**
     * Collect all enabled metrics.
     *
     * @return void
     */
    public function collect(): void {
        $enabled_metrics = get_option( 'wp_prometheus_enabled_metrics', array() );

        // Always collect WordPress info.
        if ( in_array( 'wordpress_info', $enabled_metrics, true ) ) {
            $this->collect_wordpress_info();
        }

        // Collect user metrics.
        if ( in_array( 'wordpress_users_total', $enabled_metrics, true ) ) {
            $this->collect_users_total();
        }

        // Collect posts metrics.
        if ( in_array( 'wordpress_posts_total', $enabled_metrics, true ) ) {
            $this->collect_posts_total();
        }

        // Collect comments metrics.
        if ( in_array( 'wordpress_comments_total', $enabled_metrics, true ) ) {
            $this->collect_comments_total();
        }

        // Collect plugins metrics.
        if ( in_array( 'wordpress_plugins_total', $enabled_metrics, true ) ) {
            $this->collect_plugins_total();
        }

        // Collect runtime metrics (HTTP requests, DB queries).
        $this->collect_runtime_metrics( $enabled_metrics );

        /**
         * Fires after default metrics are collected.
         *
         * @param Collector $collector The metrics collector instance.
         */
        do_action( 'wp_prometheus_collect_metrics', $this );
    }

    /**
     * Render metrics in Prometheus text format.
     *
     * @return string
     */
    public function render(): string {
        $this->collect();

        $renderer = new RenderTextFormat();
        return $renderer->render( $this->registry->getMetricFamilySamples() );
    }

    /**
     * Collect WordPress info metric.
     *
     * @return void
     */
    private function collect_wordpress_info(): void {
        $gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            'info',
            'WordPress installation information',
            array( 'version', 'php_version', 'multisite' )
        );

        $gauge->set(
            1,
            array(
                get_bloginfo( 'version' ),
                PHP_VERSION,
                is_multisite() ? 'yes' : 'no',
            )
        );
    }

    /**
     * Collect total users metric.
     *
     * @return void
     */
    private function collect_users_total(): void {
        $gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            'users_total',
            'Total number of WordPress users',
            array( 'role' )
        );

        $user_count = count_users();
        foreach ( $user_count['avail_roles'] as $role => $count ) {
            $gauge->set( $count, array( $role ) );
        }
    }

    /**
     * Collect total posts metric.
     *
     * @return void
     */
    private function collect_posts_total(): void {
        $gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            'posts_total',
            'Total number of posts by type and status',
            array( 'post_type', 'status' )
        );

        $post_types = get_post_types( array( 'public' => true ) );
        foreach ( $post_types as $post_type ) {
            $counts = wp_count_posts( $post_type );
            foreach ( get_object_vars( $counts ) as $status => $count ) {
                if ( $count > 0 ) {
                    $gauge->set( (int) $count, array( $post_type, $status ) );
                }
            }
        }
    }

    /**
     * Collect total comments metric.
     *
     * @return void
     */
    private function collect_comments_total(): void {
        $gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            'comments_total',
            'Total number of comments by status',
            array( 'status' )
        );

        $comments = wp_count_comments();
        $statuses = array(
            'approved'       => $comments->approved,
            'moderated'      => $comments->moderated,
            'spam'           => $comments->spam,
            'trash'          => $comments->trash,
            'total_comments' => $comments->total_comments,
        );

        foreach ( $statuses as $status => $count ) {
            $gauge->set( (int) $count, array( $status ) );
        }
    }

    /**
     * Collect total plugins metric.
     *
     * @return void
     */
    private function collect_plugins_total(): void {
        if ( ! function_exists( 'get_plugins' ) ) {
            require_once ABSPATH . 'wp-admin/includes/plugin.php';
        }

        $gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            'plugins_total',
            'Total number of plugins by status',
            array( 'status' )
        );

        $all_plugins    = get_plugins();
        $active_plugins = get_option( 'active_plugins', array() );

        $gauge->set( count( $all_plugins ), array( 'installed' ) );
        $gauge->set( count( $active_plugins ), array( 'active' ) );
        $gauge->set( count( $all_plugins ) - count( $active_plugins ), array( 'inactive' ) );
    }

    /**
     * Collect runtime metrics from stored data.
     *
     * @param array $enabled_metrics List of enabled metrics.
     * @return void
     */
    private function collect_runtime_metrics( array $enabled_metrics ): void {
        $runtime_collector = RuntimeCollector::get_instance();
        $stored_metrics    = $runtime_collector->get_stored_metrics();

        // HTTP requests total counter.
        if ( in_array( 'wordpress_http_requests_total', $enabled_metrics, true ) && ! empty( $stored_metrics['counters'] ) ) {
            foreach ( $stored_metrics['counters'] as $counter_data ) {
                if ( 'http_requests_total' !== $counter_data['name'] ) {
                    continue;
                }

                $counter = $this->registry->getOrRegisterCounter(
                    $this->namespace,
                    'http_requests_total',
                    'Total number of HTTP requests',
                    array( 'method', 'status', 'endpoint' )
                );

                $counter->incBy(
                    (int) $counter_data['value'],
                    array(
                        $counter_data['labels']['method'] ?? 'GET',
                        $counter_data['labels']['status'] ?? '200',
                        $counter_data['labels']['endpoint'] ?? 'unknown',
                    )
                );
            }
        }

        // HTTP request duration histogram.
        if ( in_array( 'wordpress_http_request_duration_seconds', $enabled_metrics, true ) && ! empty( $stored_metrics['histograms'] ) ) {
            foreach ( $stored_metrics['histograms'] as $histogram_data ) {
                if ( 'http_request_duration_seconds' !== $histogram_data['name'] ) {
                    continue;
                }

                // For histograms, we expose as a gauge with pre-aggregated bucket counts.
                // This is a workaround since we can't directly populate histogram buckets.
                $this->expose_histogram_as_gauges(
                    'http_request_duration_seconds',
                    'HTTP request duration in seconds',
                    $histogram_data,
                    array( 'method', 'endpoint' )
                );
            }
        }

        // Database queries total counter.
        if ( in_array( 'wordpress_db_queries_total', $enabled_metrics, true ) && ! empty( $stored_metrics['counters'] ) ) {
            foreach ( $stored_metrics['counters'] as $counter_data ) {
                if ( 'db_queries_total' !== $counter_data['name'] ) {
                    continue;
                }

                $counter = $this->registry->getOrRegisterCounter(
                    $this->namespace,
                    'db_queries_total',
                    'Total number of database queries',
                    array( 'endpoint' )
                );

                $counter->incBy(
                    (int) $counter_data['value'],
                    array(
                        $counter_data['labels']['endpoint'] ?? 'unknown',
                    )
                );
            }
        }

        // Database query duration histogram (if SAVEQUERIES is enabled).
        if ( in_array( 'wordpress_db_queries_total', $enabled_metrics, true ) && ! empty( $stored_metrics['histograms'] ) ) {
            foreach ( $stored_metrics['histograms'] as $histogram_data ) {
                if ( 'db_query_duration_seconds' !== $histogram_data['name'] ) {
                    continue;
                }

                $this->expose_histogram_as_gauges(
                    'db_query_duration_seconds',
                    'Database query duration in seconds',
                    $histogram_data,
                    array( 'endpoint' )
                );
            }
        }
    }

    /**
     * Expose pre-aggregated histogram data as gauge metrics.
     *
     * Since we store histogram data externally, we expose it using gauges
     * that follow Prometheus histogram naming conventions.
     *
     * @param string $name          Metric name.
     * @param string $help          Metric description.
     * @param array  $histogram_data Stored histogram data.
     * @param array  $label_names   Label names.
     * @return void
     */
    private function expose_histogram_as_gauges( string $name, string $help, array $histogram_data, array $label_names ): void {
        $label_values = array();
        foreach ( $label_names as $label_name ) {
            $label_values[] = $histogram_data['labels'][ $label_name ] ?? 'unknown';
        }

        // Expose bucket counts.
        $bucket_gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            $name . '_bucket',
            $help . ' (bucket)',
            array_merge( $label_names, array( 'le' ) )
        );

        $cumulative_count = 0;
        foreach ( $histogram_data['buckets'] as $le => $count ) {
            $cumulative_count += $count;
            $bucket_gauge->set(
                $cumulative_count,
                array_merge( $label_values, array( $le ) )
            );
        }

        // Expose sum.
        $sum_gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            $name . '_sum',
            $help . ' (sum)',
            $label_names
        );
        $sum_gauge->set( $histogram_data['sum'], $label_values );

        // Expose count.
        $count_gauge = $this->registry->getOrRegisterGauge(
            $this->namespace,
            $name . '_count',
            $help . ' (count)',
            $label_names
        );
        $count_gauge->set( $histogram_data['count'], $label_values );
    }

    /**
     * Register a custom gauge metric.
     *
     * @param string $name   Metric name.
     * @param string $help   Metric description.
     * @param array  $labels Label names.
     * @return \Prometheus\Gauge
     */
    public function register_gauge( string $name, string $help, array $labels = array() ): \Prometheus\Gauge {
        return $this->registry->getOrRegisterGauge(
            $this->namespace,
            $name,
            $help,
            $labels
        );
    }

    /**
     * Register a custom counter metric.
     *
     * @param string $name   Metric name.
     * @param string $help   Metric description.
     * @param array  $labels Label names.
     * @return \Prometheus\Counter
     */
    public function register_counter( string $name, string $help, array $labels = array() ): \Prometheus\Counter {
        return $this->registry->getOrRegisterCounter(
            $this->namespace,
            $name,
            $help,
            $labels
        );
    }

    /**
     * Register a custom histogram metric.
     *
     * @param string     $name    Metric name.
     * @param string     $help    Metric description.
     * @param array      $labels  Label names.
     * @param array|null $buckets Histogram buckets.
     * @return \Prometheus\Histogram
     */
    public function register_histogram( string $name, string $help, array $labels = array(), ?array $buckets = null ): \Prometheus\Histogram {
        return $this->registry->getOrRegisterHistogram(
            $this->namespace,
            $name,
            $help,
            $labels,
            $buckets
        );
    }
}