export interface CodexFileCitationLink {
  readonly path: string;
  readonly href: string;
  readonly label: string;
  readonly lineRangeStart?: number;
}

export type CodexFileCitationAttributes = Readonly<Record<string, string | null | undefined>>;

function positiveInteger(value: string | null | undefined): number | undefined {
  if (value === null || value === undefined || value.trim().length === 0) return undefined;
  const parsed = Number(value);
  return Number.isSafeInteger(parsed) && parsed > 0 ? parsed : undefined;
}

function citationLabel(path: string): string {
  const normalized = path.replaceAll("\\", "/").replace(/\/+$/, "");
  return normalized.slice(normalized.lastIndexOf("/") + 1) || normalized || "File";
}

function markdownDestinationPath(path: string): string {
  return path.replaceAll("%", "%25").replaceAll("#", "%23").replaceAll("?", "%3F");
}

export function resolveCodexFileCitationLink(
  attributes: CodexFileCitationAttributes | null | undefined,
): CodexFileCitationLink | null {
  const path = attributes?.path?.trim();
  if (!path) return null;

  const lineRangeStart = positiveInteger(attributes?.line_range_start);
  const destinationPath = markdownDestinationPath(path);
  return {
    path,
    href: lineRangeStart === undefined ? destinationPath : `${destinationPath}#L${lineRangeStart}`,
    label: citationLabel(path),
    ...(lineRangeStart === undefined ? {} : { lineRangeStart }),
  };
}

function markdownLabel(value: string): string {
  return value.replace(/[\\[\]*_`<&]/g, "\\$&");
}

function markdownDestination(value: string): string {
  return value
    .replaceAll("<", "%3C")
    .replaceAll(">", "%3E")
    .replaceAll("\r", "%0D")
    .replaceAll("\n", "%0A");
}

export function codexFileCitationMarkdown(citation: CodexFileCitationLink): string {
  return `[${markdownLabel(citation.label)}](<${markdownDestination(citation.href)}>)`;
}