<?php
// +----------------------------------------------------------------------
// | YwxApp [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2026-2036 http://ywxapp.cn All rights reserved.
// +----------------------------------------------------------------------
// | Author: ywxapp<admin@ywxapp.cn>
// +----------------------------------------------------------------------
// | 流式文件下载响应（避免 ThinkPHP download() 助手将整文件读入内存导致大文件/慢网络截断）
// +----------------------------------------------------------------------

namespace ywxapp\library;

use think\Response;

/**
 * 流式输出二进制文件（zip 等）的下载响应。
 *
 * 相对 ThinkPHP 内置 download() 助手的优势：
 *  - 用 fread 分块输出（非 file_get_contents 整文件入内存），大文件不再吃爆 memory_limit；
 *  - 构造函数内 set_time_limit(0)，慢网络下不会被 Web 端默认执行时限截断；
 *  - 支持 HTTP Range（Accept-Ranges: bytes），客户端可断点续传，进一步抵御下载中断；
 *  - 正确回吐 Content-Length，便于客户端做字节数完整性校验。
 *
 * 用法：return new StreamZipResponse($absPath, $downloadName);
 */
class StreamZipResponse extends Response
{
    protected $filePath;
    protected $dlName;
    protected $contentType = 'application/octet-stream';

    public function __construct(string $filePath, string $dlName, int $code = 200)
    {
        $this->filePath = $filePath;
        $this->dlName   = $dlName;
        $this->code     = $code;
        $this->header   = [];

        // 取消脚本执行时间限制：防止大文件 / 慢网络下被 PHP 默认 max_execution_time 截断
        @set_time_limit(0);
        @ignore_user_abort(false);
    }

    public function send(): void
    {
        while (ob_get_level() > 0) {
            ob_end_clean();
        }

        if (!is_file($this->filePath)) {
            if (!headers_sent()) {
                http_response_code(404);
            }
            return;
        }

        $size = filesize($this->filePath);
        $name = rawurlencode($this->dlName);

        // 解析 Range（断点续传）
        $range = $this->parseRange($size);
        $isRange = $range !== null;
        $start   = $range['start'] ?? 0;
        $end     = $range['end']   ?? ($size - 1);

        if (!headers_sent()) {
            http_response_code($isRange ? 206 : 200);
            header('Pragma: public');
            header('Accept-Ranges: bytes');
            header('Content-Type: ' . $this->contentType);
            header('Cache-control: max-age=360');
            header('Content-Disposition: attachment; filename="' . $name . '"; filename* = UTF-8\'\'' . $name);
            header('Content-Transfer-Encoding: binary');
            header('Expires: ' . gmdate('D, d M Y H:i:s', time() + 360) . ' GMT');
            if ($isRange) {
                header('Content-Range: bytes ' . $start . '-' . $end . '/' . $size);
                header('Content-Length: ' . ($end - $start + 1));
            } else {
                header('Content-Length: ' . $size);
            }
        }

        $this->outputRange($this->filePath, $start, $end);

        if (function_exists('fastcgi_finish_request')) {
            fastcgi_finish_request();
        }
    }

    /**
     * 解析 HTTP Range 头，返回 [start, end] 或 null（不支持/非法）
     */
    protected function parseRange(int $size): ?array
    {
        $rangeHeader = $this->header['range'] ?? ($_SERVER['HTTP_RANGE'] ?? '');
        if ($rangeHeader === '' || !preg_match('/bytes=(\d*)-(\d*)/i', (string) $rangeHeader, $m)) {
            return null;
        }
        $start = $m[1] === '' ? 0 : (int) $m[1];
        $end   = $m[2] === '' ? ($size - 1) : (int) $m[2];
        if ($start < 0 || $end >= $size || $start > $end) {
            return null;
        }
        return ['start' => $start, 'end' => $end];
    }

    /**
     * 分块输出指定区间内容
     */
    protected function outputRange(string $path, int $start, int $end): void
    {
        $fp = fopen($path, 'rb');
        if ($fp === false) {
            return;
        }
        if ($start > 0) {
            fseek($fp, $start);
        }
        $remaining = $end - $start + 1;
        $chunk     = 8192;
        while ($remaining > 0 && !feof($fp)) {
            $read = $remaining > $chunk ? $chunk : $remaining;
            echo fread($fp, $read);
            $remaining -= $read;
            if (connection_status() !== 0) {
                break;
            }
        }
        fclose($fp);
    }
}