<?php

namespace app\service;

/**
 * 从常见文档格式提取纯文本，供 Dify 等不支持 file 附件的接口使用。
 */
class DocumentTextService
{
    private const MAX_CHARS = 12000;

    /** @var string|null 最近一次 extract 失败原因（供上层展示） */
    private static ?string $lastFailure = null;

    public static function extract(string $path, string $mime = '', string $filename = ''): ?string
    {
        self::$lastFailure = null;

        if (!is_file($path) || !is_readable($path)) {
            self::$lastFailure = 'file_unreadable';
            return null;
        }

        $ext = strtolower(pathinfo($filename ?: $path, PATHINFO_EXTENSION));
        $mime = strtolower($mime);

        $text = match (true) {
            in_array($ext, ['txt', 'md'], true) || str_starts_with($mime, 'text/') => self::readPlainText($path),
            $ext === 'docx' || str_contains($mime, 'wordprocessingml') => self::extractDocx($path),
            $ext === 'pdf' || str_contains($mime, 'pdf') => self::extractPdf($path),
            default => null,
        };

        if ($text === null) {
            return null;
        }

        $text = self::normalize($text);

        if ($text === '') {
            if (self::$lastFailure === null) {
                self::$lastFailure = 'empty_content';
            }
            return null;
        }

        return mb_substr($text, 0, self::MAX_CHARS);
    }

    public static function unsupportedReason(string $filename, string $mime = ''): string
    {
        $ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));

        if (self::$lastFailure === 'exec_disabled') {
            return 'PHP 禁用了 exec 函数，无法调用 pdftotext。请在 php.ini 的 disable_functions 中移除 exec';
        }

        if (self::$lastFailure === 'pdftotext_missing') {
            return '未找到 pdftotext 命令。请在**运行 PHP 的服务器**（不是 Dify 容器）执行：apt install poppler-utils';
        }

        if (self::$lastFailure === 'pdftotext_failed') {
            return 'pdftotext 执行失败，请检查 PDF 是否损坏或 uploads 目录是否可读';
        }

        if (self::$lastFailure === 'empty_content' && ($ext === 'pdf' || str_contains($mime, 'pdf'))) {
            return 'PDF 未提取到文字，可能是扫描版图片 PDF，请改用可复制文字的 PDF 或粘贴文字';
        }

        if ($ext === 'doc' || str_contains($mime, 'msword')) {
            return '旧版 .doc 暂不支持自动解析，请另存为 .docx 或复制文字发送';
        }

        if ($ext === 'pdf' || str_contains($mime, 'pdf')) {
            return 'PDF 文字提取失败，请在运行 PHP 的服务器安装 poppler-utils（pdftotext）';
        }

        if (!class_exists(\ZipArchive::class) && ($ext === 'docx' || str_contains($mime, 'wordprocessingml'))) {
            return 'PHP 未启用 zip 扩展，无法解析 .docx，请安装 php-zip';
        }

        return '未能提取文档文字，请改用 .txt / .docx 或粘贴文字内容';
    }

    private static function readPlainText(string $path): ?string
    {
        $content = @file_get_contents($path);
        if ($content === false) {
            return null;
        }

        if (!mb_check_encoding($content, 'UTF-8')) {
            $content = mb_convert_encoding($content, 'UTF-8', 'GB18030,UTF-8,ASCII');
        }

        return $content;
    }

    private static function extractDocx(string $path): ?string
    {
        if (!class_exists(\ZipArchive::class)) {
            return null;
        }

        $zip = new \ZipArchive();
        if ($zip->open($path) !== true) {
            return null;
        }

        $xml = $zip->getFromName('word/document.xml');
        $zip->close();

        if (!$xml) {
            return null;
        }

        $xml = preg_replace('/<w:tab[^>]*\/>/', "\t", $xml);
        $xml = preg_replace('/<\/w:p>/', "\n", $xml);
        $xml = preg_replace('/<\/w:tr>/', "\n", $xml);

        $text = strip_tags($xml);

        return html_entity_decode($text, ENT_QUOTES | ENT_XML1, 'UTF-8');
    }

    private static function extractPdf(string $path): ?string
    {
        if (!function_exists('exec')) {
            self::$lastFailure = 'exec_disabled';
            return null;
        }

        $binary = self::resolvePdftotextBinary();
        if ($binary === null) {
            self::$lastFailure = 'pdftotext_missing';
            return null;
        }

        $out = tempnam(sys_get_temp_dir(), 'pdftxt_');
        if (!$out) {
            self::$lastFailure = 'pdftotext_failed';
            return null;
        }

        $cmd = escapeshellarg($binary) . ' -enc UTF-8 -layout '
            . escapeshellarg($path) . ' ' . escapeshellarg($out) . ' 2>&1';
        exec($cmd, $_, $code);

        $text = ($code === 0 && is_file($out)) ? @file_get_contents($out) : false;
        @unlink($out);

        if ($text === false) {
            self::$lastFailure = 'pdftotext_failed';
            return null;
        }

        return $text;
    }

    /**
     * PHP-FPM 进程的 PATH 常不含 /usr/bin，需显式探测可执行文件路径。
     */
    private static function resolvePdftotextBinary(): ?string
    {
        $candidates = [
            '/usr/bin/pdftotext',
            '/usr/local/bin/pdftotext',
            'pdftotext',
        ];

        foreach ($candidates as $bin) {
            if (str_starts_with($bin, '/')) {
                if (is_executable($bin)) {
                    return $bin;
                }
                continue;
            }

            if (self::commandExists($bin)) {
                return $bin;
            }
        }

        return null;
    }

    private static function commandExists(string $command): bool
    {
        if (!function_exists('exec')) {
            return false;
        }

        $check = stripos(PHP_OS, 'WIN') === 0 ? 'where' : 'command -v';
        exec($check . ' ' . escapeshellarg($command) . ' 2>/dev/null', $output, $code);

        return $code === 0 && !empty($output);
    }

    private static function normalize(string $text): string
    {
        $text = str_replace(["\r\n", "\r"], "\n", $text);
        $text = preg_replace("/[ \t]+\n/", "\n", $text);
        $text = preg_replace("/\n{3,}/", "\n\n", $text);

        return trim($text);
    }
}