import type { MonthStat } from '@/api/stats'

/**
 * Pure derived-stat helpers for the Stats page (Task 6).
 *
 * Extracted from {@link Stats.vue} so the two pieces of trivia that are easy
 * to get wrong — (1) finding the current month's count in a DESC-ordered list
 * and (2) flipping that list to chronological ASC for the line chart — are
 * unit-testable without mounting the component or stubbing ECharts.
 */

/**
 * Look up the inquiry count for a given `YYYY-MM` month in the `monthly` list.
 *
 * Used by Stats.vue for the "本月新增" card: it passes
 * `dayjs().format('YYYY-MM')` and we return the matching count, or `0` when
 * there's no data for the current month yet (the backend omits zero-count
 * months entirely, and a fresh month may not have appeared in the trailing
 * 12-month window at all).
 *
 * The lookup is by value equality on `ym`, so input order (DESC vs ASC) is
 * irrelevant. Returns `0` for an empty list — graceful fallback for an empty
 * DB / new install.
 */
export function currentMonthCount(
  monthly: readonly MonthStat[],
  ym: string,
): number {
  // `find` rather than indexing `[0]` — the current month is not guaranteed to
  // be the first entry (DESC newest-first only covers months that have data,
  // and a brand-new month may be ABSENT from the trailing 12-month window).
  const hit = monthly.find((m) => m.ym === ym)
  return hit?.count ?? 0
}

/**
 * Return a new array of monthly stats sorted **ascending** by `ym`
 * (chronological order — what the trend line chart needs).
 *
 * The backend returns `monthly` **DESC** (newest first). The line chart's X
 * axis wants oldest → newest, so this flips the order. A fresh copy is always
 * returned (the input is never mutated), even when the input is already ASC —
 * callers can safely pass a `readonly` slice from the API response.
 *
 * String comparison on `YYYY-MM` is lexicographically correct (zero-padded
 * fixed-width format), so no Date parsing is needed.
 */
export function sortMonthlyAsc(monthly: readonly MonthStat[]): MonthStat[] {
  // Slice first so `.sort` cannot reorder the caller's array — important
  // because `monthly` may be the live API response object.
  return monthly.slice().sort((a, b) => {
    if (a.ym !== b.ym) return a.ym < b.ym ? -1 : 1
    return 0
  })
}