// ==UserScript==
// @name         jjg-pdf-downloader
// @namespace    https://jjg.spc.org.cn/
// @version      1.0.0
// @description  Intercept online-reading PDF and download via Ctrl+S
// @match        https://jjg.spc.org.cn/resmea/view/stdonline
// @run-at       document-start
// @grant        none
// @license      AGPL-3.0-or-later
// ==/UserScript==

(() => {
  'use strict';

  /** @type {string|null} */
  let currentObjectUrl = null;

  /** @type {HTMLDivElement|null} */
  let toastContainer = null;

  /**
   * Create toast container lazily
   * @returns {HTMLDivElement}
   */
  const ensureToastContainer = () => {
    if (toastContainer) {
      return toastContainer;
    }

    toastContainer = document.createElement('div');

    Object.assign(toastContainer.style, {
      position: 'fixed',
      top: '16px',
      left: '50%',
      transform: 'translateX(-50%)',
      zIndex: '2147483647',
      display: 'flex',
      flexDirection: 'column',
      gap: '10px',
      pointerEvents: 'none',
    });

    document.documentElement.appendChild(toastContainer);

    return toastContainer;
  };

  /**
   * Lightweight toast
   * @param {string} message
   * @param {'success'|'warning'|'error'|'info'} [type]
   */
  const toast = (message, type = 'info') => {
    const container = ensureToastContainer();

    const el = document.createElement('div');

    const theme = {
      success: {
        bg: '#16a34a',
        border: '#15803d',
      },
      warning: {
        bg: '#d97706',
        border: '#b45309',
      },
      error: {
        bg: '#dc2626',
        border: '#b91c1c',
      },
      info: {
        bg: '#2563eb',
        border: '#1d4ed8',
      },
    }[type];

    el.textContent = message;

    Object.assign(el.style, {
      minWidth: '240px',
      maxWidth: '420px',
      padding: '12px 16px',
      borderRadius: '12px',
      background: theme.bg,
      border: `1px solid ${theme.border}`,
      color: '#fff',
      fontSize: '14px',
      fontFamily:
        'system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif',
      boxShadow:
        '0 10px 30px rgba(0,0,0,0.18)',
      backdropFilter: 'blur(8px)',
      opacity: '0',
      transform: 'translateY(-8px)',
      transition:
        'opacity 160ms ease, transform 160ms ease',
      userSelect: 'none',
    });

    container.appendChild(el);

    requestAnimationFrame(() => {
      el.style.opacity = '1';
      el.style.transform = 'translateY(0)';
    });

    setTimeout(() => {
      el.style.opacity = '0';
      el.style.transform = 'translateY(-8px)';

      setTimeout(() => {
        el.remove();

        if (!container.childElementCount) {
          container.remove();
          toastContainer = null;
        }
      }, 180);
    }, 3000);
  };

  /**
   * Revoke previous ObjectURL
   */
  const revokeCurrentUrl = () => {
    if (!currentObjectUrl) {
      return;
    }

    URL.revokeObjectURL(currentObjectUrl);

    currentObjectUrl = null;
  };

  /**
   * Save PDF blob as downloadable URL
   * @param {Blob} blob
   */
  const savePdfBlob = (blob) => {
    revokeCurrentUrl();

    currentObjectUrl = URL.createObjectURL(blob);

    toast(
      'PDF 已准备好，可按 Ctrl+S 下载',
      'success'
    );
  };

  /**
   * Check target endpoint
   * @param {string} url
   * @returns {boolean}
   */
  const isOnlineReadingRequest = (url) => {
    try {
      const parsed = new URL(url, location.href);

      return parsed.pathname.endsWith('/onlinereading');
    } catch {
      return false;
    }
  };

  const originalOpen = XMLHttpRequest.prototype.open;

  /**
   * Safe XHR observation
   *
   * IMPORTANT:
   * - DO NOT modify responseType
   * - DO NOT modify response
   * - DO NOT override onload
   * - Only observe existing behavior
   */
  XMLHttpRequest.prototype.open = function (...args) {
    const [, url] = args;

    if (
      typeof url === 'string' &&
      isOnlineReadingRequest(url)
    ) {
      this.addEventListener('load', () => {
        try {
          if (
            this.status < 200 ||
            this.status >= 300
          ) {
            return;
          }

          const response = this.response;

          if (!(response instanceof Blob)) {
            return;
          }

          if (
            response.type &&
            response.type !== 'application/pdf'
          ) {
            return;
          }

          savePdfBlob(response);
        } catch (err) {
          console.error(
            '[jjg-pdf-downloader]',
            err
          );

          toast(
            'PDF 捕获失败',
            'error'
          );
        }
      });
    }

    return originalOpen.apply(this, args);
  };

  /**
   * Trigger PDF download
   */
  const triggerDownload = () => {
    if (!currentObjectUrl) {
      toast(
        '当前没有可下载的 PDF',
        'warning'
      );

      return;
    }

    const a = document.createElement('a');

    a.href = currentObjectUrl;
    a.download = 'document.pdf';

    document.body.appendChild(a);

    a.click();

    a.remove();

    toast(
      'PDF 下载已触发',
      'success'
    );
  };

  /**
   * Ctrl+S handler
   */
  document.addEventListener(
    'keydown',
    (event) => {
      const isSaveShortcut =
        (event.ctrlKey || event.metaKey) &&
        event.key.toLowerCase() === 's';

      if (!isSaveShortcut) {
        return;
      }

      event.preventDefault();
      event.stopPropagation();

      triggerDownload();
    },
    true
  );

  /**
   * Cleanup
   */
  window.addEventListener(
    'beforeunload',
    revokeCurrentUrl
  );
})();