const SECTION_HEADINGS = [
  "Added",
  "Changed",
  "Fixed",
  "Removed",
  "Deprecated",
  "Security",
] as const;

export type ChangelogSectionTitle = (typeof SECTION_HEADINGS)[number];

export type ChangelogSection = {
  title: ChangelogSectionTitle;
  items: string[];
};

export type ChangelogRelease = {
  version: string;
  date: string;
  major: number;
  minor: number;
  patch: number;
  /** Categorized release notes. */
  sections: ChangelogSection[];
  /** Optional paragraph summary for major or initial releases. */
  summary?: string;
};

export const CHANGELOG_SECTION_LABELS: Record<ChangelogSectionTitle, string> = {
  Added: "Added",
  Changed: "Improved",
  Fixed: "Fixed",
  Removed: "Removed",
  Deprecated: "Deprecated",
  Security: "Security",
};

export function parseChangelog(markdown: string): ChangelogRelease[] {
  const releases: ChangelogRelease[] = [];
  const lines = markdown.split("\n");
  let i = 0;

  while (i < lines.length) {
    const versionMatch = lines[i].match(/^## \[([\d.]+)\] - (.+)$/);
    if (!versionMatch) {
      i++;
      continue;
    }

    const version = versionMatch[1];
    const date = versionMatch[2];
    const [major = 0, minor = 0, patch = 0] = version.split(".").map(Number);

    i++;
    const sections: ChangelogSection[] = [];

    while (i < lines.length && !lines[i].match(/^## \[/)) {
      const sectionMatch = lines[i].match(/^### (.+)$/);
      if (
        sectionMatch &&
        SECTION_HEADINGS.includes(sectionMatch[1] as ChangelogSectionTitle)
      ) {
        const title = sectionMatch[1] as ChangelogSectionTitle;
        i++;
        const items: string[] = [];
        while (i < lines.length && lines[i].startsWith("- ")) {
          items.push(lines[i].slice(2).trim());
          i++;
        }
        if (items.length > 0) {
          sections.push({ title, items });
        }
        continue;
      }

      i++;
    }

    releases.push({ version, date, major, minor, patch, sections });
  }

  return releases;
}