/**
 * ─────────────────────────────────────────────
 *  SPB Git — Personal Git Platform
 * ─────────────────────────────────────────────
 *  Author  : Simon-Pierre Boucher
 *  Contact : contact@spboucher.ai
 *  File    : src/stats/activity.mjs
 *  Purpose : Contribution heatmap (52 weeks) + commit calendar data
 *  License : MIT © Simon-Pierre Boucher
 * ─────────────────────────────────────────────
 */

const DAY_MS = 86400000;
const WEEKS = 52;
const MONTHS = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];

/**
 * Bucket unix commit timestamps (seconds) into per-day counts.
 * @param {number[]} timestamps
 * @returns {Map<string, number>} ISO date (YYYY-MM-DD) → count
 */
export function bucketByDay(timestamps) {
  const days = new Map();
  for (const ts of timestamps) {
    const iso = new Date(ts * 1000).toISOString().slice(0, 10);
    days.set(iso, (days.get(iso) ?? 0) + 1);
  }
  return days;
}

/**
 * Build the GitHub-style contribution calendar grid for the last 52 weeks.
 * @param {Map<string, number>} dayCounts
 * @param {Date} [today] injection point for tests
 * @returns {{weeks: Array<Array<{date: string, count: number, level: 0|1|2|3|4}|null>>, months: Array<{index: number, label: string}>, total: number, max: number}}
 */
export function buildCalendar(dayCounts, today = new Date()) {
  const end = new Date(Date.UTC(today.getUTCFullYear(), today.getUTCMonth(), today.getUTCDate()));
  // Grid ends on the current day; columns are weeks starting Sunday.
  const endDow = end.getUTCDay();
  const start = new Date(end.getTime() - ((WEEKS - 1) * 7 + endDow) * DAY_MS);

  let max = 0;
  let total = 0;
  const weeks = [];
  const months = [];
  let lastMonth = -1;
  for (let w = 0; w < WEEKS; w += 1) {
    const week = [];
    for (let d = 0; d < 7; d += 1) {
      const date = new Date(start.getTime() + (w * 7 + d) * DAY_MS);
      if (date.getTime() > end.getTime()) {
        week.push(null);
        continue;
      }
      const iso = date.toISOString().slice(0, 10);
      const count = dayCounts.get(iso) ?? 0;
      total += count;
      if (count > max) max = count;
      week.push({ date: iso, count });
      if (d === 0) {
        const month = date.getUTCMonth();
        if (month !== lastMonth) {
          months.push({ index: w, label: MONTHS[month] });
          lastMonth = month;
        }
      }
    }
    weeks.push(week);
  }
  // Quantize to 5 levels the way GitHub does (quartiles of the max).
  for (const week of weeks) {
    for (const day of week) {
      if (!day) continue;
      day.level = day.count === 0 ? 0 : Math.min(4, Math.ceil((day.count / Math.max(1, max)) * 4));
    }
  }
  // Drop a leading month label crammed against the second one.
  if (months.length >= 2 && months[1].index - months[0].index < 3) months.shift();
  return { weeks, months, total, max };
}

/**
 * Render the contribution calendar as an accessible SVG.
 * @param {ReturnType<typeof buildCalendar>} calendar
 * @returns {string} SVG markup
 */
export function calendarSvg(calendar) {
  const cell = 11;
  const gap = 3;
  const left = 30;
  const top = 20;
  const width = left + WEEKS * (cell + gap) + 4;
  const height = top + 7 * (cell + gap) + 4;
  const parts = [];
  parts.push(
    `<svg xmlns="http://www.w3.org/2000/svg" class="heatmap-svg" viewBox="0 0 ${width} ${height}" width="${width}" height="${height}" role="img" aria-label="Commit activity, last 52 weeks">`,
  );
  for (const month of calendar.months) {
    parts.push(
      `<text x="${left + month.index * (cell + gap)}" y="12" class="heatmap-label">${month.label}</text>`,
    );
  }
  const dayLabels = [
    [1, 'Mon'],
    [3, 'Wed'],
    [5, 'Fri'],
  ];
  for (const [row, label] of dayLabels) {
    parts.push(
      `<text x="0" y="${top + row * (cell + gap) + cell - 2}" class="heatmap-label">${label}</text>`,
    );
  }
  calendar.weeks.forEach((week, w) => {
    week.forEach((day, d) => {
      if (!day) return;
      const x = left + w * (cell + gap);
      const y = top + d * (cell + gap);
      const plural = day.count === 1 ? 'commit' : 'commits';
      parts.push(
        `<rect x="${x}" y="${y}" width="${cell}" height="${cell}" rx="2" class="heatmap-cell" data-level="${day.level}"><title>${day.count} ${plural} on ${day.date}</title></rect>`,
      );
    });
  });
  parts.push('</svg>');
  return parts.join('');
}

/**
 * Aggregate commit timestamps across every repo, then build calendar + SVG.
 * Cached globally, refreshed on push.
 * @param {{repos: object, cache: object}} ctx
 * @returns {Promise<{svg: string, total: number}>}
 */
export async function contributionCalendar(ctx) {
  const cachePath = ctx.cache.path('global', 'heatmap.json');
  const cached = ctx.cache.getJSON(cachePath);
  if (cached) return cached;
  const all = [];
  for (const name of ctx.repos.list()) {
    const stamps = await ctx.repos.commitTimestamps(name);
    all.push(...stamps);
  }
  const calendar = buildCalendar(bucketByDay(all));
  const result = { svg: calendarSvg(calendar), total: calendar.total };
  ctx.cache.setJSON(cachePath, result);
  return result;
}