const RANGES = Object.freeze({
  bp_systolic: { min: 60, max: 260, unit: 'mmHg' },
  bp_diastolic: { min: 40, max: 160, unit: 'mmHg' },
  hr: { min: 30, max: 200, unit: 'bpm' },
  spo2: { min: 50, max: 100, unit: '%' },
  temperature: { min: 33, max: 43, unit: 'celsius' },
  weight: { min: 20, max: 250, unit: 'kg' },
  sleep_minutes: { min: 0, max: 16 * 60, unit: 'min' },
});

export const HEALTH_CONTEXTS = Object.freeze(['morning', 'evening', 'other']);

export function inferBloodPressureContext(observedAt, { now = new Date(), timeZone = 'Asia/Shanghai' } = {}) {
  const date = observedAt instanceof Date ? observedAt : new Date(observedAt ?? now);
  if (Number.isNaN(date.getTime())) return 'other';
  const hourText = new Intl.DateTimeFormat('en-GB', {
    hour: '2-digit',
    hourCycle: 'h23',
    timeZone,
  }).format(date);
  const hour = Number(hourText);
  if (hour < 10) return 'morning';
  if (hour >= 18) return 'evening';
  return 'other';
}

export function validateMetricValue(metricType, value) {
  const range = RANGES[metricType];
  if (!range) {
    return { ok: false, error: 'unknown_metric' };
  }
  const num = Number(value);
  if (!Number.isFinite(num)) {
    return { ok: false, error: 'not_numeric' };
  }
  if (num < range.min || num > range.max) {
    return { ok: false, error: 'out_of_range', range };
  }
  return { ok: true, value: num, unit: range.unit };
}

export function validateBloodPressurePair(systolic, diastolic) {
  const sys = validateMetricValue('bp_systolic', systolic);
  const dia = validateMetricValue('bp_diastolic', diastolic);
  if (!sys.ok) return { ok: false, field: 'bp_systolic', ...sys };
  if (!dia.ok) return { ok: false, field: 'bp_diastolic', ...dia };
  if (sys.value <= dia.value) {
    return { ok: false, error: 'systolic_not_greater', field: 'pair' };
  }
  return { ok: true, systolic: sys.value, diastolic: dia.value };
}

export function markSuspectVsBaseline(value, baselineMean, { ratio = 0.5 } = {}) {
  const mean = Number(baselineMean);
  const num = Number(value);
  if (!Number.isFinite(mean) || mean <= 0 || !Number.isFinite(num)) {
    return { qualityFlag: 'ok', suspect: false };
  }
  const deviation = Math.abs(num - mean) / mean;
  if (deviation >= ratio) {
    return { qualityFlag: 'suspect', suspect: true, deviation };
  }
  return { qualityFlag: 'ok', suspect: false, deviation };
}

export function resolveQualityAfterConfirm({ suspect = false, userCorrected = false } = {}) {
  if (userCorrected) return 'user_corrected';
  if (suspect) return 'ok';
  return 'ok';
}

export function observationDedupKey({ metricType, observedAt, sourceRef } = {}) {
  if (!sourceRef) return null;
  return `${metricType}|${observedAt}|${sourceRef}`;
}