<?php
/**
 * Plugin logger.
 *
 * @package Rahkar\WP
 */

declare( strict_types = 1 );

namespace Rahkar\WP\Support;

defined( 'ABSPATH' ) || exit;

/**
 * Buffered, level-filtered logging into the plugin's own table.
 *
 * Writes are buffered until `shutdown` and flushed as a single multi-row insert,
 * so a checkout that logs six lines costs one query rather than six. On a busy
 * store that difference shows up directly in checkout response time.
 *
 * The table is created by {@see \Rahkar\WP\Database\Schema}; if it is missing —
 * activation half-finished, table dropped by hand — logging degrades to
 * `error_log()` rather than throwing.
 */
final class Logger {

	public const EMERGENCY = 0;
	public const ERROR     = 1;
	public const WARNING   = 2;
	public const INFO      = 3;
	public const DEBUG     = 4;

	/**
	 * Level names for display.
	 *
	 * @var array<int, string>
	 */
	public const LEVELS = [
		self::EMERGENCY => 'emergency',
		self::ERROR     => 'error',
		self::WARNING   => 'warning',
		self::INFO      => 'info',
		self::DEBUG     => 'debug',
	];

	/**
	 * Rows waiting to be written.
	 *
	 * @var list<array{level:int, channel:string, message:string, context:string, created_at:string}>
	 */
	private static array $buffer = [];

	/**
	 * Whether the end-of-request flush has been hooked yet.
	 *
	 * @var bool
	 */
	private static bool $flushHooked = false;

	/**
	 * Highest level that gets written, resolved once per request.
	 *
	 * @var int|null
	 */
	private static ?int $threshold = null;

	/**
	 * Log an error.
	 *
	 * @param string              $channel Subsystem, e.g. `queue` or `sms`.
	 * @param string              $message Human-readable message.
	 * @param array<string,mixed> $context Structured detail.
	 */
	public static function error( string $channel, string $message, array $context = [] ): void {
		self::log( self::ERROR, $channel, $message, $context );
	}

	/**
	 * Log a warning.
	 *
	 * @param string              $channel Subsystem.
	 * @param string              $message Human-readable message.
	 * @param array<string,mixed> $context Structured detail.
	 */
	public static function warning( string $channel, string $message, array $context = [] ): void {
		self::log( self::WARNING, $channel, $message, $context );
	}

	/**
	 * Log an informational event.
	 *
	 * @param string              $channel Subsystem.
	 * @param string              $message Human-readable message.
	 * @param array<string,mixed> $context Structured detail.
	 */
	public static function info( string $channel, string $message, array $context = [] ): void {
		self::log( self::INFO, $channel, $message, $context );
	}

	/**
	 * Log a debug event.
	 *
	 * @param string              $channel Subsystem.
	 * @param string              $message Human-readable message.
	 * @param array<string,mixed> $context Structured detail.
	 */
	public static function debug( string $channel, string $message, array $context = [] ): void {
		self::log( self::DEBUG, $channel, $message, $context );
	}

	/**
	 * Buffer a log line.
	 *
	 * @param int                 $level   One of the level constants.
	 * @param string              $channel Subsystem.
	 * @param string              $message Human-readable message.
	 * @param array<string,mixed> $context Structured detail.
	 */
	public static function log( int $level, string $channel, string $message, array $context = [] ): void {
		if ( $level > self::threshold() ) {
			return;
		}

		self::$buffer[] = [
			'level'      => $level,
			'channel'    => substr( $channel, 0, 32 ),
			'message'    => substr( $message, 0, 500 ),
			'context'    => self::encodeContext( $context ),
			'created_at' => current_time( 'mysql', true ),
		];

		if ( ! self::$flushHooked ) {
			self::$flushHooked = true;

			add_action( 'shutdown', [ self::class, 'flush' ], 100 );
		}
	}

	/**
	 * Write the buffer as one insert.
	 *
	 * @internal Hooked callback.
	 */
	public static function flush(): void {
		if ( [] === self::$buffer ) {
			return;
		}

		$rows = self::$buffer;

		// Cleared before the write so a failure cannot cause a retry loop.
		self::$buffer = [];

		global $wpdb;

		$table = $wpdb->prefix . 'rahkar_logs';

		$placeholders = [];
		$values       = [];

		foreach ( $rows as $row ) {
			$placeholders[] = '(%d, %s, %s, %s, %s)';

			array_push( $values, $row['level'], $row['channel'], $row['message'], $row['context'], $row['created_at'] );
		}

		$sql = "INSERT INTO `{$table}` (`level`, `channel`, `message`, `context`, `created_at`) VALUES "
			. implode( ', ', $placeholders );

		// phpcs:disable WordPress.DB.PreparedSQL.NotPrepared, WordPress.DB.DirectDatabaseQuery, PluginCheck.Security.DirectDB.UnescapedDBParameter
		$wpdb->suppress_errors( true );
		$written = $wpdb->query( $wpdb->prepare( $sql, $values ) );
		$wpdb->suppress_errors( false );
		// phpcs:enable, PluginCheck.Security.DirectDB.UnescapedDBParameter

		if ( false === $written ) {
			self::fallback( $rows );
		}
	}

	/**
	 * Resolve the active log level.
	 *
	 * Read from the plugin's own settings rather than `WP_DEBUG` so a site can run
	 * with debug off and still keep an audit trail of SMS sends and queue failures
	 * — which is usually what a store actually needs.
	 */
	private static function threshold(): int {
		if ( null !== self::$threshold ) {
			return self::$threshold;
		}

		$configured = Settings::get( 'core.log_level' );

		if ( null === $configured ) {
			$configured = ( defined( 'WP_DEBUG' ) && WP_DEBUG ) ? self::DEBUG : self::INFO;
		}

		self::$threshold = (int) $configured;

		return self::$threshold;
	}

	/**
	 * JSON-encode context, keeping the column bounded.
	 *
	 * @param array<string,mixed> $context Structured detail.
	 */
	private static function encodeContext( array $context ): string {
		if ( [] === $context ) {
			return '';
		}

		$json = wp_json_encode( $context, JSON_UNESCAPED_UNICODE | JSON_PARTIAL_OUTPUT_ON_ERROR );

		if ( ! is_string( $json ) ) {
			return '';
		}

		return substr( $json, 0, 2000 );
	}

	/**
	 * Last resort when the log table is unavailable.
	 *
	 * @param list<array{level:int, channel:string, message:string, context:string, created_at:string}> $rows Buffered rows.
	 */
	private static function fallback( array $rows ): void {
		foreach ( $rows as $row ) {
			$level = self::LEVELS[ $row['level'] ] ?? 'info';

			// phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
			error_log( sprintf( '[rahkar-wp][%s][%s] %s %s', $level, $row['channel'], $row['message'], $row['context'] ) );
		}
	}
}