import type { Components } from "react-markdown";
import type { ReactElement } from "react";
import { Fragment, jsx, jsxs } from "react/jsx-runtime";
import { toJsxRuntime } from "hast-util-to-jsx-runtime";
import { unified } from "unified";
import remarkParse from "remark-parse";
import remarkGfm from "remark-gfm";
import remarkRehype from "remark-rehype";
import rehypePrettyCode, { type Options as PrettyCodeOptions } from "rehype-pretty-code";
import type { Root } from "hast";
import type { Root as MdastRoot } from "mdast";
import { visit } from "unist-util-visit";
import { mergeMarkdownComponents } from "./mergeComponents";
import {
  getPrettyCodeHighlighter,
  resolveShikiLang,
  SHIKI_THEMES,
} from "./shikiHighlighter";

/**
 * 将代码围栏语言归一到白名单（未知 → plaintext），
 * 避免 rehype-pretty-code 对未装载语言 loadLanguage 失败。
 */
function remarkNormalizeCodeLang() {
  return (tree: MdastRoot) => {
    visit(tree, "code", (node) => {
      node.lang = resolveShikiLang(node.lang);
    });
  };
}

export const prettyCodeOptions: PrettyCodeOptions = {
  theme: {
    light: SHIKI_THEMES.light,
    dark: SHIKI_THEMES.dark,
  },
  keepBackground: false,
  defaultLang: "plaintext",
  // HighlighterCore 与 pretty-code 期望的 Highlighter 在运行时兼容
  getHighlighter: getPrettyCodeHighlighter as unknown as PrettyCodeOptions["getHighlighter"],
  // 空行在 display:grid 下会塌缩成 0 高，补一个空格撑住行高
  onVisitLine(element) {
    if (element.children.length === 0) {
      element.children = [{ type: "text", value: " " }];
    }
  },
};

/** 服务端异步管线：GFM + Shiki 双主题高亮 → React 树 */
export async function renderMarkdownToReact(
  content: string,
  overrides?: Components
): Promise<ReactElement> {
  const processor = unified()
    .use(remarkParse)
    .use(remarkGfm)
    .use(remarkNormalizeCodeLang)
    .use(remarkRehype)
    .use(rehypePrettyCode, { ...prettyCodeOptions });

  const mdast = processor.parse(content || "");
  const hast = (await processor.run(mdast)) as Root;

  return toJsxRuntime(hast, {
    Fragment,
    jsx,
    jsxs,
    components: mergeMarkdownComponents(overrides) as Record<
      string,
      React.ElementType
    >,
  }) as ReactElement;
}