<?php
if (!defined('ABSPATH')) {
    exit; // Exit if accessed directly
}

class AFFLLogService {

    public function get_logs(string $log_file_name = 'error.log') {
        // Prioritize logs from the uploads folder because it has persistence
        $uploads_log_file = AFFILILABS_UPLOADS_LOG_PATH . $log_file_name;
        if (file_exists($uploads_log_file)) {
            return $this->tail($uploads_log_file);
        }

        // Fallback
        $local_log_file = AFFILILABS_LOG_PATH . $log_file_name;
        if (file_exists($local_log_file)) {
            return $this->tail($local_log_file);
        }

        return esc_html__('No logs found.', 'affililabs');
    }

    public function get_general_log() {
        if (!defined('WP_CONTENT_DIR')) {
            return esc_html__('WP_CONTENT_DIR is not defined. Cannot locate general log file.', 'affililabs');
        }

        $general_log_file = WP_CONTENT_DIR . '/debug.log';

        if (file_exists($general_log_file)) {
            return $this->tail($general_log_file);
        }

        return esc_html__('No general WordPress/PHP logs found.', 'affililabs');
    }

    /**
     * Reads the last N lines of a file efficiently.
     *
     * @param string $filepath Path to the file.
     * @param int $lines Number of lines to retrieve.
     * @return string|false The last N lines or false on failure.
     */
    private function tail($filepath, $lines = 1000) {
        if (!file_exists($filepath) || !is_readable($filepath)) {
            return false;
        }

        $f = fopen($filepath, 'rb');
        if ($f === false) {
            return false;
        }

        $chunk = 4096;
        fseek($f, 0, SEEK_END);
        $pos = ftell($f);
        
        // Failsafe: Prevent memory exhaustion on files with no newlines
        // E.g., Stop reading after 10MB backward
        $max_bytes_to_read = 100 * 1024 * 1024; 
        $bytes_read = 0;

        $line_count = 0;
        $chunks = [];

        // Read backward in chunks until we have enough lines
        while ($pos > 0 && $line_count <= $lines && $bytes_read < $max_bytes_to_read) {
            $read_size = min($pos, $chunk);
            $pos -= $read_size;
            fseek($f, $pos);
            
            $data = fread($f, $read_size);
            $bytes_read += $read_size;
            
            // Count both \n and \r to handle Unix, Windows, and Mac line endings safely
            $line_count += substr_count($data, "\n");
            if (strpos($data, "\n") === false) {
                $line_count += substr_count($data, "\r");
            }
            
            $chunks[] = $data;
        }

        fclose($f);

        // Reassemble the read chunks efficiently
        $output = implode('', array_reverse($chunks));

        // Normalize line endings to \n for clean splitting
        $output = str_replace("\r\n", "\n", $output);
        $output = str_replace("\r", "\n", $output);

        $output_lines = explode("\n", $output);
        
        if (end($output_lines) === '') {
            array_pop($output_lines);
        }

        if (count($output_lines) > $lines) {
            $output_lines = array_slice($output_lines, -$lines);
        }

        return implode("\n", $output_lines);
    }
}