import {
  isValidObservationForBaseline,
  resolveBaselineMaturity,
} from './health-baseline-maturity.mjs';

const WINDOWS = Object.freeze([7, 30, 90]);

function withinWindow(observedAt, windowDays, now = Date.now()) {
  const ts = Number(observedAt);
  if (!Number.isFinite(ts)) return false;
  const start = now - windowDays * 24 * 60 * 60 * 1000;
  return ts >= start && ts <= now;
}

function mean(values) {
  if (!values.length) return null;
  return values.reduce((sum, v) => sum + v, 0) / values.length;
}

function stddev(values, avg) {
  if (values.length < 2) return 0;
  const m = avg ?? mean(values);
  const variance = values.reduce((sum, v) => sum + (v - m) ** 2, 0) / values.length;
  return Math.sqrt(variance);
}

export function computeMetricBaseline(
  observations = [],
  {
    metricType,
    context = 'any',
    windowDays = 30,
    now = Date.now(),
  } = {},
) {
  const rows = observations.filter((row) => {
    if (!isValidObservationForBaseline(row)) return false;
    if (row.metricType !== metricType) return false;
    if (row.valueNum == null) return false;
    if (context !== 'any' && row.context !== context) return false;
    return withinWindow(row.observedAt, windowDays, now);
  });
  const values = rows.map((row) => Number(row.valueNum)).filter(Number.isFinite);
  const sampleCount = values.length;
  const avg = mean(values);
  return {
    metricType,
    context,
    windowDays,
    sampleCount,
    maturity: resolveBaselineMaturity(sampleCount),
    mean: avg == null ? null : Number(avg.toFixed(2)),
    stddev: avg == null ? null : Number(stddev(values, avg).toFixed(2)),
    min: values.length ? Math.min(...values) : null,
    max: values.length ? Math.max(...values) : null,
  };
}

export function computeHealthBaselines(observations = [], { now = Date.now() } = {}) {
  const metricContexts = [
    { metricType: 'bp_systolic', context: 'morning' },
    { metricType: 'bp_diastolic', context: 'morning' },
    { metricType: 'bp_systolic', context: 'evening' },
    { metricType: 'bp_diastolic', context: 'evening' },
    { metricType: 'hr', context: 'any' },
    { metricType: 'weight', context: 'any' },
    { metricType: 'spo2', context: 'any' },
    { metricType: 'sleep_minutes', context: 'any' },
  ];
  const baselines = [];
  for (const windowDays of WINDOWS) {
    for (const spec of metricContexts) {
      baselines.push(computeMetricBaseline(observations, { ...spec, windowDays, now }));
    }
  }
  return baselines;
}

export function deviationFromBaseline(value, baselineMean) {
  const num = Number(value);
  const mean = Number(baselineMean);
  if (!Number.isFinite(num) || !Number.isFinite(mean) || mean === 0) return null;
  return Number((((num - mean) / mean) * 100).toFixed(1));
}