<?php

namespace app\common;

use think\Env;

/**
 * Unpaywall OA PDF 定位
 * @see https://unpaywall.org/products/api
 */
class UnpaywallService
{
    private $email;
    private $timeout = 20;

    public function __construct()
    {
        $this->email = trim((string)Env::get('unpaywall_email', Env::get('pubmed_email', '')));
    }

    /**
     * @return string PDF 直链，找不到返回空
     */
    public function findOaPdfUrl($doi)
    {
        $doi = trim((string)$doi);
        if ($doi === '' || $this->email === '') {
            return '';
        }

        $url = 'https://api.unpaywall.org/v2/' . rawurlencode($doi) . '?' . http_build_query([
            'email' => $this->email,
        ]);

        $ch = curl_init();
        curl_setopt_array($ch, [
            CURLOPT_URL            => $url,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_TIMEOUT        => $this->timeout,
            CURLOPT_SSL_VERIFYPEER => false,
            CURLOPT_HTTPHEADER     => ['User-Agent: TMRjournals-Unpaywall/1.0'],
        ]);
        $raw = curl_exec($ch);
        curl_close($ch);
        if (!is_string($raw) || $raw === '') {
            return '';
        }

        $json = json_decode($raw, true);
        if (!is_array($json)) {
            return '';
        }

        $best = $json['best_oa_location'] ?? [];
        if (!is_array($best)) {
            return '';
        }

        foreach (['url_for_pdf', 'url'] as $key) {
            $candidate = trim((string)($best[$key] ?? ''));
            if ($candidate !== '' && $this->looksLikePdfUrl($candidate)) {
                return $candidate;
            }
        }

        return '';
    }

    private function looksLikePdfUrl($url)
    {
        if (stripos($url, '.pdf') !== false) {
            return true;
        }
        return (bool)preg_match('#/(pdf|download|content/pdf)#i', $url);
    }
}