import { bucketForBristolType } from './domain.js';

export const PATTERN_WINDOW_DAYS = 28;
// Two logs are an anecdote. Below this the summary is required to say so instead of describing a trend.
export const MIN_WINDOW_LOGS = 3;

const DAY_MS = 86400000;

// The summary may only describe what the user recorded. No cause, no health verdict, no food ruling.
const BOUNDARY = 'Built only from your own confirmed records in this window. Timmy reports what you logged and when — not why, and never a verdict on your health or your food.';

function inWindowRecords(entries, now, windowDays) {
  const startedAt = now - windowDays * DAY_MS;
  return (Array.isArray(entries) ? entries : [])
    .map(entry => ({ entry, at: new Date(entry?.occurredAt).getTime() }))
    .filter(({ at }) => Number.isFinite(at) && at <= now && at >= startedAt)
    .sort((left, right) => left.at - right.at)
    .map(({ entry, at }) => ({
      id: String(entry?.id ?? ''),
      occurredAt: new Date(at).toISOString(),
      bristolType: Number(entry?.bristolType),
      bucket: bucketForBristolType(entry?.bristolType),
    }));
}

export function buildPatternSummary(entries = [], { now = Date.now(), windowDays = PATTERN_WINDOW_DAYS } = {}) {
  const records = inWindowRecords(entries, now, windowDays);
  const window = {
    days: windowDays,
    label: `last ${windowDays} days`,
    start: new Date(now - windowDays * DAY_MS).toISOString(),
    end: new Date(now).toISOString(),
  };

  if (records.length < MIN_WINDOW_LOGS) {
    return {
      window,
      records,
      insufficient: true,
      statements: [],
      boundary: BOUNDARY,
      copy: `Not enough confirmed logs in this window yet — ${records.length} of ${MIN_WINDOW_LOGS} needed before Timmy describes a pattern.`,
    };
  }

  const frequency = {
    id: 'frequency',
    text: `${records.length} confirmed log${records.length === 1 ? '' : 's'} in the ${window.label}.`,
    entryIds: records.map(record => record.id),
  };

  const buckets = new Map();
  for (const record of records) {
    if (!buckets.has(record.bucket)) buckets.set(record.bucket, []);
    buckets.get(record.bucket).push(record.id);
  }
  const bucketLine = (bucket, label) => ({
    id: bucket === 'constipation' ? 'firm' : bucket,
    text: `${label}: ${buckets.get(bucket).length} of ${records.length} confirmed log${records.length === 1 ? '' : 's'}.`,
    entryIds: buckets.get(bucket),
  });
  const formLines = [
    ['constipation', 'Firm side (Type 1–2)'],
    ['typical', 'Typical range (Type 3–4)'],
    ['loose', 'Loose side (Type 5–7)'],
  ].filter(([bucket]) => buckets.has(bucket)).map(([bucket, label]) => bucketLine(bucket, label));
  // Both ends in one window is not a trend, and the summary has to say so out loud rather than
  // picking whichever side is marginally larger.
  const mixedLine = buckets.has('constipation') && buckets.has('loose') ? [{
    id: 'mixed',
    text: `Firm and loose logs both appear in the ${window.label} (${buckets.get('constipation').length} firm, ${buckets.get('loose').length} loose), which is a mixed pattern and not one trend.`,
    entryIds: records.filter(record => record.bucket === 'constipation' || record.bucket === 'loose').map(record => record.id),
  }] : [];

  return { window, records, insufficient: false, statements: [frequency, ...formLines, ...mixedLine], copy: '', boundary: BOUNDARY };
}