import React, { useEffect } from 'react';

function FontSwitcherButton() {
  useEffect(() => {
    // 等待导航栏渲染完成后，插入按钮
    const insertButton = () => {
      const navbar = document.querySelector('.navbar__items--right');
      if (navbar && !document.querySelector('.font-switcher-btn')) {
        // 读取当前字体偏好
        const saved = localStorage.getItem('font-preference') || 'system';
        const isCustom = saved !== 'system';

        const btn = document.createElement('button');
        btn.className = 'font-switcher-btn';
        btn.style.cssText = `
          background: none;
          border: none;
          cursor: pointer;
          padding: 4px 6px;
          display: inline-flex;
          align-items: center;
          justify-content: center;
          opacity: 0.7;
          transition: opacity 0.2s;
          border-radius: 4px;
          color: var(--ifm-navbar-link-color);
        `;
        btn.onmouseenter = () => btn.style.opacity = '1';
        btn.onmouseleave = () => btn.style.opacity = '0.7';

        // 渲染 SVG 滑块（isCustom: true=绿色右侧，false=灰色左侧）
        const renderSVG = (custom) => {
          return `
            <svg width="34" height="20" viewBox="0 0 34 20" style="display:block;">
              <rect
                x="0" y="0" width="34" height="20" rx="10"
                fill="${custom ? '#4CAF50' : '#ccc'}"
                style="transition: fill 0.25s ease;"
              />
              <circle
                cx="${custom ? '25' : '9'}"
                cy="10"
                r="7"
                fill="white"
                style="transition: cx 0.25s cubic-bezier(0.34, 1.56, 0.64, 1); box-shadow: 0 1px 4px rgba(0,0,0,0.15);"
              />
            </svg>
          `;
        };

        btn.innerHTML = renderSVG(isCustom);
        btn.title = isCustom ? '切换到系统字体' : '切换到自定义字体';

        // 交互逻辑：左键切换 + 右键/长按/双击弹出菜单
        let pressTimer = null;
        let clickTimer = null;

        // 动态获取字体列表
        const getFontList = () => {
          const fonts = [];
          const seenKeys = new Set();
          fonts.push({ key: 'system', label: '系统字体' });
          seenKeys.add('system');

          for (const sheet of document.styleSheets) {
            try {
              const rules = sheet.cssRules || sheet.rules;
              if (!rules) continue;
              for (const rule of rules) {
                if (rule.selectorText && rule.selectorText.includes('[data-theme-font=')) {
                  const match = rule.selectorText.match(/\[data-theme-font="([^"]+)"\]/);
                  if (match && match[1]) {
                    const key = match[1];
                    if (seenKeys.has(key)) continue;
                    seenKeys.add(key);
                    const fontFamily = rule.style.getPropertyValue('--ifm-font-family-base');
                    let label = key;
                    if (fontFamily) {
                      const names = fontFamily.split(',').map(s => s.replace(/['"]/g, '').trim());
                      label = names[0] || key;
                    }
                    fonts.push({ key, label });
                  }
                }
              }
            } catch (e) {
              continue;
            }
          }
          return fonts;
        };

        // 菜单功能
        const showFontMenu = (x, y) => {
          const existingMenu = document.querySelector('.font-switcher-menu');
          if (existingMenu) existingMenu.remove();

          const fonts = getFontList();
          if (fonts.length === 0) {
            fonts.push(
              { key: 'system', label: '系统字体' },
              { key: 'pixel', label: '像素字体' }
            );
          }

          const menu = document.createElement('div');
          menu.className = 'font-switcher-menu';
          menu.style.cssText = `
            position: fixed;
            top: ${Math.min(y, window.innerHeight - 120)}px;
            left: ${Math.min(x, window.innerWidth - 140)}px;
            background: var(--ifm-background-surface-color, #fff);
            border-radius: 8px;
            box-shadow: 0 8px 24px rgba(0,0,0,0.15);
            padding: 6px 0;
            z-index: 9999;
            min-width: 120px;
            border: 1px solid var(--ifm-color-emphasis-200, #e0e0e0);
            font-size: 0.9rem;
          `;

          const current = document.documentElement.getAttribute('data-theme-font') || 'system';

          fonts.forEach((font) => {
            const item = document.createElement('div');
            item.textContent = font.label;
            const isActive = font.key === current;
            item.style.cssText = `
              padding: 6px 16px;
              cursor: pointer;
              transition: background 0.15s;
              color: var(--ifm-font-color-base, #333);
              ${isActive ? 'font-weight: bold; background: var(--ifm-color-emphasis-100, #f0f0f0);' : ''}
            `;
            item.onmouseenter = () => item.style.background = 'var(--ifm-color-emphasis-100, #f0f0f0)';
            item.onmouseleave = () => {
              if (!isActive) item.style.background = 'transparent';
              else item.style.background = 'var(--ifm-color-emphasis-100, #f0f0f0)';
            };
            item.onclick = () => {
              document.documentElement.setAttribute('data-theme-font', font.key);
              localStorage.setItem('font-preference', font.key);
              if (font.key !== 'system') {
                localStorage.setItem('last-custom-font', font.key);
              }
              updateSliderUI(font.key !== 'system');
              menu.remove();
            };
            menu.appendChild(item);
          });

          const closeMenu = (e) => {
            if (!menu.contains(e.target)) {
              menu.remove();
              document.removeEventListener('click', closeMenu);
            }
          };
          setTimeout(() => document.addEventListener('click', closeMenu), 10);

          document.body.appendChild(menu);
        };

        // 更新滑块 UI
        const updateSliderUI = (isCustom) => {
          const svg = btn.querySelector('svg');
          if (svg) {
            const rect = svg.querySelector('rect');
            const circle = svg.querySelector('circle');
            if (rect) rect.setAttribute('fill', isCustom ? '#4CAF50' : '#ccc');
            if (circle) circle.setAttribute('cx', isCustom ? '25' : '9');
          }
          btn.title = isCustom ? '切换到系统字体' : '切换到自定义字体';
        };

        // 1. 左键点击：快速切换
        btn.onclick = (e) => {
          if (clickTimer) {
            clearTimeout(clickTimer);
            clickTimer = null;
            return;
          }

          const current = document.documentElement.getAttribute('data-theme-font') || 'system';
          const lastCustom = localStorage.getItem('last-custom-font') || 'pixel';
          const next = current === 'system' ? lastCustom : 'system';
          const nextIsCustom = next !== 'system';

          document.documentElement.setAttribute('data-theme-font', next);
          localStorage.setItem('font-preference', next);
          updateSliderUI(nextIsCustom);
        };

        // 2. 右键点击：弹出菜单
        btn.oncontextmenu = (e) => {
          e.preventDefault();
          showFontMenu(e.clientX, e.clientY);
        };

        // 3. 长按（≥500ms）：弹出菜单
        btn.onmousedown = (e) => {
          if (e.button !== 0) return;
          pressTimer = setTimeout(() => {
            showFontMenu(e.clientX, e.clientY);
            pressTimer = null;
          }, 500);
        };
        btn.onmouseup = () => {
          if (pressTimer) {
            clearTimeout(pressTimer);
            pressTimer = null;
          }
        };
        btn.onmouseleave = () => {
          if (pressTimer) {
            clearTimeout(pressTimer);
            pressTimer = null;
          }
        };

        // 4. 双击：弹出菜单
        btn.ondblclick = (e) => {
          e.preventDefault();
          if (clickTimer) {
            clearTimeout(clickTimer);
            clickTimer = null;
          }
          showFontMenu(e.clientX, e.clientY);
        };

        // 防双击的单击处理
        btn.addEventListener('click', (e) => {
          if (clickTimer) {
            clearTimeout(clickTimer);
            clickTimer = null;
            return;
          }
          clickTimer = setTimeout(() => {
            clickTimer = null;
          }, 300);
        });

        // 初始化 UI 状态
        const savedState = localStorage.getItem('font-preference') || 'system';
        updateSliderUI(savedState !== 'system');

        // 插入到深色模式按钮之前
        navbar.insertBefore(btn, navbar.lastElementChild);
      }
    };

    // 初次插入
    insertButton();

    // 监听路由变化，重新插入（Docusaurus 是 SPA）
    const observer = new MutationObserver(() => insertButton());
    observer.observe(document.body, { childList: true, subtree: true });

    return () => observer.disconnect();
  }, []);

  return null;
}

export default function Root({ children }) {
  return (
    <>
      <FontSwitcherButton />
      {children}
    </>
  );
}