/**
 * Markdown text extraction → canonical text + gap-free offset map.
 *
 * Implements ADR-0003 for the `markdown-rendered` representation. Markup is
 * stripped to plain text before `normalize()` is applied.
 */

import { normalize, type OffsetMap } from "@citation-evidence/engine/shared";
import { buildWholeTextOffsetMap } from "../shared/offset-map";

const FENCED_CODE = /```[\s\S]*?```/g;
const INLINE_CODE = /`([^`]+)`/g;
const IMAGE = /!\[([^\]]*)\]\([^)]+\)/g;
const LINK = /\[([^\]]+)\]\([^)]+\)/g;
const HEADING = /^#{1,6}\s+/gm;
const BLOCKQUOTE = /^>\s?/gm;
const LIST_MARKER = /^[\s]*[-*+]\s+/gm;
const ORDERED_LIST = /^[\s]*\d+\.\s+/gm;
const EMPHASIS = /(\*\*|__)(.*?)\1/g;
const ITALIC = /(\*|_)([^*_]+)\1/g;
const STRIKETHROUGH = /~~(.*?)~~/g;
const HORIZONTAL_RULE = /^[-*_]{3,}\s*$/gm;

export interface MarkdownExtractionResult {
  readonly canonicalText: string;
  readonly offsetMap: OffsetMap;
}

export function extractMarkdown(source: string): MarkdownExtractionResult {
  const rawText = markdownToPlainText(source);
  const canonicalText = normalize(rawText).text;
  return {
    canonicalText,
    offsetMap: buildWholeTextOffsetMap(canonicalText),
  };
}

function markdownToPlainText(source: string): string {
  let text = source;
  text = text.replace(FENCED_CODE, "\n\n");
  text = text.replace(INLINE_CODE, "$1");
  text = text.replace(IMAGE, "$1");
  text = text.replace(LINK, "$1");
  text = text.replace(HEADING, "");
  text = text.replace(BLOCKQUOTE, "");
  text = text.replace(LIST_MARKER, "");
  text = text.replace(ORDERED_LIST, "");
  text = text.replace(EMPHASIS, "$2");
  text = text.replace(ITALIC, "$2");
  text = text.replace(STRIKETHROUGH, "$1");
  text = text.replace(HORIZONTAL_RULE, "\n\n");
  return text;
}