import { EventTimelineSet, MatrixEvent } from 'matrix-js-sdk';
import { getEventEdits, trimReplyFromBody } from './room';
import { DiffToken, wordDiff } from './wordDiff';

const isPlainText = (content: Record<string, unknown> | undefined): content is { body: string } =>
  !!content &&
  typeof content.body === 'string' &&
  content.format === undefined &&
  content.formatted_body === undefined;

/**
 * [Gitea #144] Word diff of the *last* edit to `mEvent`: the newest edit's body
 * against the one it replaced (an earlier edit, or the original). Only for
 * plain-text bodies — formatted edits return `undefined` and the caller falls
 * back to the history viewer.
 */
export function getLastEditDiff(
  mEvent: MatrixEvent,
  timelineSet: EventTimelineSet,
): DiffToken[] | undefined {
  const eventId = mEvent.getId();
  if (!eventId) return undefined;
  const relations = getEventEdits(timelineSet, eventId, mEvent.getType());
  if (!relations) return undefined;
  const edits = relations
    .getRelations()
    .filter((e) => e.getSender() === mEvent.getSender())
    .sort((m1, m2) => m2.getTs() - m1.getTs());
  const latest = edits[0];
  if (!latest) return undefined;
  const after = latest.getContent()['m.new_content'] as Record<string, unknown> | undefined;
  const before = (edits[1]?.getContent()['m.new_content'] ?? mEvent.getContent()) as
    | Record<string, unknown>
    | undefined;
  if (!isPlainText(after) || !isPlainText(before)) return undefined;
  return wordDiff(trimReplyFromBody(before.body), trimReplyFromBody(after.body));
}