"use client";

import {
  useMemo,
  useRef,
  useState,
  useEffect,
  type HTMLAttributes,
  type ReactNode,
  type ReactElement,
} from "react";
import { Check, Copy, ChevronDown, ChevronUp } from "lucide-react";
import { toast } from "@/lib/toast";

const COLLAPSE_LINE_THRESHOLD = 5;
/** 约 5 行代码高度（含行高） */
const COLLAPSED_MAX_HEIGHT = "7.75rem";

type MdCodeBlockProps = HTMLAttributes<HTMLPreElement> & {
  children?: ReactNode;
};

function isReactElement(
  node: ReactNode
): node is ReactElement<{ children?: ReactNode; className?: string }> {
  return !!node && typeof node === "object" && "props" in node;
}

/** 按 data-line / 块级结构补换行，避免行间文本被拼成一行 */
function extractText(node: ReactNode): string {
  if (node == null || typeof node === "boolean") return "";
  if (typeof node === "string" || typeof node === "number") return String(node);
  if (Array.isArray(node)) {
    return node
      .map((child, i) => {
        const text = extractText(child);
        if (
          i < node.length - 1 &&
          isReactElement(child) &&
          hasLineMarker(child)
        ) {
          return text.endsWith("\n") ? text : `${text}\n`;
        }
        return text;
      })
      .join("");
  }
  if (isReactElement(node)) {
    return extractText(node.props.children);
  }
  return "";
}

function hasLineMarker(node: ReactElement): boolean {
  const props = node.props as Record<string, unknown>;
  return (
    props["data-line"] != null ||
    (typeof props.className === "string" &&
      /\bline\b/.test(props.className))
  );
}

function countLines(pre: HTMLElement | null, fallbackText: string): number {
  if (pre) {
    // pretty-code / shiki：一行一个 [data-line] 或 .line，挂在 code 直下
    const direct = pre.querySelectorAll(":scope > code > [data-line], :scope > code > .line");
    if (direct.length > 0) return direct.length;
  }
  const text = fallbackText.replace(/\n$/, "");
  if (!text) return 0;
  return text.split("\n").length;
}

function readLanguage(
  el: HTMLElement | null,
  className?: string,
  dataLanguage?: string
): string {
  const fromData = dataLanguage || el?.getAttribute("data-language") || "";
  if (fromData) return fromData;
  const cls = [className, el?.className].filter(Boolean).join(" ");
  const m = cls.match(/language-([\w+-]+)/);
  if (m?.[1]) return m[1];
  // react-markdown：语言在子 code 上
  const childCode = el?.querySelector(":scope > code");
  const childCls = childCode?.className || "";
  const m2 = childCls.match(/language-([\w+-]+)/);
  return m2?.[1] || "";
}

function readProp(
  rest: Record<string, unknown>,
  key: string
): string | undefined {
  const v = rest[key];
  return typeof v === "string" ? v : undefined;
}

/** Markdown 代码块：语言标签、复制、>5 行默认折叠；客户端仅在未 SSR 高亮时补色 */
export default function MdCodeBlock({ children, className, ...rest }: MdCodeBlockProps) {
  const rootRef = useRef<HTMLDivElement>(null);
  const hostRef = useRef<HTMLDivElement>(null);

  const restMap = rest as Record<string, unknown>;
  const dataLanguage = readProp(restMap, "data-language");
  const dataTheme = readProp(restMap, "data-theme");

  const plainText = useMemo(() => extractText(children), [children]);
  const approxLines = useMemo(() => countLines(null, plainText), [plainText]);

  // rehype-pretty-code 会去掉 pre 上的 shiki class，但会保留 data-theme / data-language
  const serverHighlighted =
    (typeof className === "string" && className.includes("shiki")) ||
    !!dataTheme ||
    !!dataLanguage;

  const [copied, setCopied] = useState(false);
  const [expanded, setExpanded] = useState(false);
  const [lineCount, setLineCount] = useState(approxLines);
  const [language, setLanguage] = useState(() =>
    readLanguage(null, className, dataLanguage)
  );
  const [clientHtml, setClientHtml] = useState<string | null>(null);

  useEffect(() => {
    const host = hostRef.current;
    const pre = host?.querySelector("pre") ?? null;
    setLineCount(countLines(pre, plainText));
    setLanguage(readLanguage(pre, className, dataLanguage));
  }, [plainText, className, dataLanguage, clientHtml]);

  // 仅客户端预览（无 SSR 高亮）时动态补双主题；切勿覆盖服务端已渲染内容
  useEffect(() => {
    if (serverHighlighted || !plainText.trim()) return;
    const lang = readLanguage(null, className, dataLanguage) || "plaintext";
    let cancelled = false;
    (async () => {
      try {
        const { codeToHtml } = await import("shiki");
        const html = await codeToHtml(plainText.replace(/\n$/, ""), {
          lang: lang === "text" ? "plaintext" : lang,
          themes: {
            light: "github-light",
            dark: "github-dark-dimmed",
          },
          defaultColor: false,
        });
        if (!cancelled) setClientHtml(html);
      } catch {
        // 未知语言：保持纯文本
      }
    })();
    return () => {
      cancelled = true;
    };
  }, [plainText, className, dataLanguage, serverHighlighted]);

  const effectiveLines = lineCount > 0 ? lineCount : approxLines;
  const canCollapse = effectiveLines > COLLAPSE_LINE_THRESHOLD;
  const collapsed = canCollapse && !expanded;

  const onCopy = async () => {
    const pre = hostRef.current?.querySelector("pre");
    const text =
      pre?.innerText?.replace(/\n$/, "") || plainText.replace(/\n$/, "");
    if (!text) return;
    try {
      await navigator.clipboard.writeText(text);
      setCopied(true);
      window.setTimeout(() => setCopied(false), 1600);
    } catch {
      toast("复制失败，请手动选择文本");
    }
  };

  const toggleFold = () => {
    if (expanded) {
      setExpanded(false);
      // 收起后滚到该代码块顶部（含工具栏），便于继续往下读
      requestAnimationFrame(() => {
        rootRef.current?.scrollIntoView({ block: "start", behavior: "smooth" });
      });
    } else {
      setExpanded(true);
    }
  };

  const preClass = ["md-code-pre", className].filter(Boolean).join(" ");

  return (
    <div className="md-code-block" ref={rootRef}>
      <div className="md-code-toolbar">
        <span className="md-code-lang">{language || "text"}</span>
        <button
          type="button"
          className="md-code-copy"
          onClick={onCopy}
          aria-label={copied ? "已复制" : "复制代码"}
        >
          {copied ? <Check size={14} /> : <Copy size={14} />}
          <span>{copied ? "已复制" : "复制"}</span>
        </button>
      </div>
      <div
        ref={hostRef}
        className={`md-code-body${collapsed ? " md-code-collapsed" : ""}`}
        style={collapsed ? { maxHeight: COLLAPSED_MAX_HEIGHT } : undefined}
      >
        {clientHtml ? (
          <div
            className="md-code-shiki-host"
            dangerouslySetInnerHTML={{ __html: clientHtml }}
          />
        ) : (
          <pre className={preClass} {...rest}>
            {children}
          </pre>
        )}
        {collapsed && <div className="md-code-fade" aria-hidden="true" />}
      </div>
      {canCollapse && (
        <button type="button" className="md-code-fold" onClick={toggleFold}>
          {expanded ? (
            <>
              <ChevronUp size={14} />
              收起
            </>
          ) : (
            <>
              <ChevronDown size={14} />
              展开全部（{effectiveLines} 行）
            </>
          )}
        </button>
      )}
    </div>
  );
}