// #876 top-bar "today's journal" shortcut falls back to the most recent existing day when today's summary is missing.
// Backtracks YYYY → MM → DD.md so an empty 2026/05/ still finds 2026/04. Bounded I/O: O(years × months) worst case.

import path from "node:path";
import fsp from "node:fs/promises";
import { isEnoent } from "../../utils/files/safe.js";
import { summariesRoot, DAILY_DIR } from "./paths.js";

export interface LatestDailyResult {
  /** Workspace-relative path, e.g. "conversations/summaries/daily/2026/04/26.md" */
  path: string;
  /** ISO-ish date "YYYY-MM-DD" matching the file's location. */
  isoDate: string;
}

const YEAR_RE = /^\d{4}$/;
const MONTH_RE = /^\d{2}$/;
const DAY_FILE_RE = /^(\d{2})\.md$/;

async function listSorted(dir: string, pattern: RegExp): Promise<string[]> {
  let entries: string[];
  try {
    entries = await fsp.readdir(dir);
  } catch (err) {
    if (isEnoent(err)) return [];
    throw err;
  }
  return entries
    .filter((name) => pattern.test(name))
    .sort()
    .reverse();
}

export async function findLatestDaily(workspaceRoot: string): Promise<LatestDailyResult | null> {
  const dailyRoot = path.join(summariesRoot(workspaceRoot), DAILY_DIR);
  const years = await listSorted(dailyRoot, YEAR_RE);
  for (const year of years) {
    const months = await listSorted(path.join(dailyRoot, year), MONTH_RE);
    for (const month of months) {
      const days = await listSorted(path.join(dailyRoot, year, month), DAY_FILE_RE);
      const [dayFile] = days;
      if (dayFile === undefined) continue;
      const day = DAY_FILE_RE.exec(dayFile)?.[1];
      if (day === undefined) continue;
      const relPath = path.posix.join("conversations", "summaries", DAILY_DIR, year, month, dayFile);
      return { path: relPath, isoDate: `${year}-${month}-${day}` };
    }
  }
  return null;
}