描述一个调用汇率 API 的货币换算器：显示汇率更新时间、支持大量币种并保存换算历史。
使用 HTML5、CSS3、JavaScript 和可靠的汇率 API 开发一个全面的货币转换器。创建一个简洁、直观的界面，配备醒目的输入字段和货币选择器。实现带时间戳指示器的实时汇率，以显示数据的新鲜度。支持 170 多种全球货币（包括加密货币），并正确显示相应货币符号与格式化。维护包含时间戳和汇率信息的转换历史日志。允许用户收藏常用货币对以便快速访问。生成可交互的历史汇率图表，并支持自定义日期范围。利用缓存的汇率实现离线功能，并提供清晰的过期状态指示器。内置计算器，支持复杂换算及算术运算。创建目标汇率提醒功能，并支持可选的通知。在可用时，提供不同服务商汇率的并排对比。支持以多种格式（PDF、CSV、JSON）打印和导出换算结果。
Develop a comprehensive currency converter using HTML5, CSS3, JavaScript and a reliable Exchange Rate API. Create a clean, intuitive interface with prominent input fields and currency selectors. Implement real-time exchange rates with timestamp indicators showing data freshness. Support 170+ global currencies including crypto with appropriate symbols and formatting. Maintain a conversion history log with timestamps and rate information. Allow users to bookmark favorite currency pairs for quick access. Generate interactive historical rate charts with customizable date ranges. Implement offline functionality using cached exchange rates with clear staleness indicators. Add a built-in calculator for complex conversions and arithmetic operations. Create rate alerts for target exchange rates with optional notifications. Include side-by-side comparison of different provider rates when available. Support printing and exporting conversion results in multiple formats (PDF, CSV, JSON).