/** 匹配以 --- 开头/结尾的 YAML front matter（全文开头） */
const FRONT_MATTER_RE = /^---[\t ]*\r?\n([\s\S]*?)\r?\n---[\t ]*(?:\r?\n|$)([\s\S]*)$/

export function splitFrontMatter(markdown: string): { front: string | null; body: string } {
  const s = markdown.replace(/^\uFEFF/, "")
  const m = FRONT_MATTER_RE.exec(s)
  if (!m) {
    return { front: null, body: markdown }
  }
  return { front: m[1].trim(), body: m[2] }
}

/** 正文渲染用：去掉 front matter，避免把元数据块排进 HTML */
export function stripFrontMatter(markdown: string): string {
  return splitFrontMatter(markdown).body
}

function pickYamlScalar(block: string, key: string): string {
  const lines = block.split(/\r?\n/)
  const prefix = `${key}:`
  for (const line of lines) {
    const t = line.trim()
    if (!t.startsWith(prefix)) {
      continue
    }
    let v = t.slice(prefix.length).trim()
    if (!v) {
      return ""
    }
    if (
      (v.startsWith('"') && v.endsWith('"')) ||
      (v.startsWith("'") && v.endsWith("'"))
    ) {
      return v.slice(1, -1)
    }
    return v
  }
  return ""
}

/** 列表摘要：优先 `desc`，其次 `description`（简单标量行） */
export function extractFrontMatterDesc(markdown: string): string {
  const { front } = splitFrontMatter(markdown)
  if (!front) {
    return ""
  }
  const d = pickYamlScalar(front, "desc") || pickYamlScalar(front, "description")
  return d.trim()
}

export function listCardSummaryFromPostBody(bodyMarkdown: string, dbExcerpt: string): string {
  const fromFm = extractFrontMatterDesc(bodyMarkdown)
  if (fromFm) {
    return fromFm
  }
  return (dbExcerpt ?? "").trim()
}