/**
 * Outage detection for the ride detail page's Today chart.
 *
 * An outage is a contiguous run of samples with `isOpen === false`. We number
 * them chronologically (1-based) and report their duration so the chart can
 * render `<ReferenceArea>` bands with hover tooltips like "Outage #4 — 1h 28m".
 *
 * Pure module — no DOM, no Recharts — so it's cheap to unit test.
 */

export interface OutageSample {
  recordedAt: string; // ISO 8601 UTC
  isOpen: boolean;
}

export interface Outage {
  n: number;
  startISO: string;
  endISO: string;
  /** Formatted HH:MM in the viewer's local timezone — matches the chart X-axis labels. */
  startTimeLabel: string;
  endTimeLabel: string;
  durationMin: number;
}

const TIME_FMT = new Intl.DateTimeFormat([], {
  hour: "2-digit",
  minute: "2-digit",
  hour12: false,
});

/**
 * Walk samples in chronological order and produce one Outage per contiguous
 * run of `!isOpen`. If the day ends mid-outage, the last sample becomes the
 * outage's `endISO` (still in progress).
 */
export function computeOutages(samples: OutageSample[]): Outage[] {
  const outages: Outage[] = [];
  let i = 0;
  let n = 0;
  while (i < samples.length) {
    if (samples[i].isOpen) { i++; continue; }
    const startSample = samples[i];
    while (i < samples.length && !samples[i].isOpen) i++;
    // i now points at the first open sample after the run, or samples.length.
    const endSample = i < samples.length ? samples[i] : samples[samples.length - 1];
    const startMs = Date.parse(startSample.recordedAt);
    const endMs = Date.parse(endSample.recordedAt);
    const durationMin = Math.max(0, Math.round((endMs - startMs) / 60_000));
    n += 1;
    outages.push({
      n,
      startISO: startSample.recordedAt,
      endISO: endSample.recordedAt,
      startTimeLabel: TIME_FMT.format(new Date(startSample.recordedAt)),
      endTimeLabel: TIME_FMT.format(new Date(endSample.recordedAt)),
      durationMin,
    });
  }
  return outages;
}

/**
 * Format a minute count as "47m" / "1h 28m" / "2h".
 */
export function formatOutageDuration(min: number): string {
  if (min < 60) return `${min}m`;
  const h = Math.floor(min / 60);
  const m = min % 60;
  return m === 0 ? `${h}h` : `${h}h ${m}m`;
}

/**
 * Build a lookup from time-label (HH:MM) → outage for each closed sample.
 * The chart uses this to attach outage metadata to each data point so the
 * custom tooltip can render outage-aware text without re-scanning.
 */
export function outageLookup(
  samples: OutageSample[],
  outages: Outage[],
): Map<string, Outage> {
  const byTime = new Map<string, Outage>();
  let oIdx = 0;
  let runStart: number | null = null;
  for (let i = 0; i < samples.length; i++) {
    const s = samples[i];
    if (!s.isOpen) {
      if (runStart === null) runStart = i;
      const outage = outages[oIdx];
      if (outage) byTime.set(TIME_FMT.format(new Date(s.recordedAt)), outage);
    } else if (runStart !== null) {
      runStart = null;
      oIdx += 1;
    }
  }
  return byTime;
}