为 Typecho 的 Code Block 添加 Copy 按钮

<script>
    // 在代码块右上角添加复制按钮
    document.addEventListener('DOMContentLoaded', initCodeCopyButton);
    function initCodeCopyButton() {
        function initCSS(callback) {
            const css = `
                .btn-code-copy {
                    position: absolute;
                    line-height: .6em;
                    top: .2em;
                    right: .2em;
                    color: rgb(87, 87, 87);
                }
                .btn-code-copy:hover {
                    color: rgb(145, 145, 145);
                    cursor: pointer;
                }
                `;
            const styleId = btoa('btn-code-copy').replace(/[=+\/]/g, '');
            const head = document.getElementsByTagName('head')[0];
            if (!head.querySelector('#' + styleId)) {
                const style = document.createElement('style');
                style.id = styleId;
                if (style.styleSheet) {
                    style.styleSheet.cssText = css;
                } else {
                    style.appendChild(document.createTextNode(css));
                }
                head.appendChild(style);
            }
            callback();
        };
        function copyTextContent(source) {
            let result = false;
            const target = document.createElement('pre');
            target.style.opacity = '0';
            target.textContent = source.textContent;
            document.body.appendChild(target);
            try {
                const range = document.createRange();
                range.selectNode(target);
                window.getSelection().removeAllRanges();
                window.getSelection().addRange(range);
                document.execCommand('copy');
                window.getSelection().removeAllRanges();
                result = true;
            } catch (e) { console.log('copy failed.'); }
            document.body.removeChild(target);
            return result;
        };
        function initButton(pre) {
            const code = pre.querySelector('code');
            if (code) {
                const preParent = pre.parentElement;
                const newPreParent = document.createElement('div');
                newPreParent.style = 'position: relative';
                preParent.insertBefore(newPreParent, pre);
                const copyBtn = document.createElement('div');
                copyBtn.innerHTML = 'copy';
                copyBtn.className = 'btn-code-copy';
                copyBtn.addEventListener('click', () => {
                    copyBtn.innerHTML = copyTextContent(code) ? 'success' : 'failure';
                    setTimeout(() => copyBtn.innerHTML = 'copy', 250);
                });
                newPreParent.appendChild(copyBtn);
                newPreParent.appendChild(pre);
            }
        };
        const pres = document.querySelectorAll('pre');
        if (pres.length !== 0) {
            initCSS(() => pres.forEach(pre => initButton(pre)));
        }
    };
</script>