leetcode/apps/api/src/stats.ts

/**
 * GET /api/stats — the one JSON document behind the docs progress page.
 * Read-only aggregation over D1; shape is the page's contract, change both
 * together. A problem counts as "done" once it entered the ladder
 * (stage != 'new').
 */
import {
  CAMPAIGN_DAYS,
  CAMPAIGN_START,
  addDays,
  campaignDay,
  campaignWeek,
  isoWeek,
  STAGES,
  streak,
} from "./srs.ts";

const PHASE_NAMES: Record<number, string> = {
  1: "I — Linear",
  2: "II — Nodal & Grid",
  3: "III — Hierarchical",
  4: "IV — Relational",
  5: "V — Decision Space",
};

export async function buildStats(db: D1Database, today: string): Promise<object> {
  const { results: phaseRows } = await db
    .prepare(
      `SELECT t.milestone AS milestone, p.set_label AS set_label,
              COUNT(*) AS total,
              SUM(CASE WHEN p.stage != 'new' THEN 1 ELSE 0 END) AS done
       FROM problems p JOIN topics t ON t.issue = p.topic_issue
       WHERE t.milestone IS NOT NULL
       GROUP BY t.milestone, p.set_label
       ORDER BY t.milestone`,
    )
    .all<{ milestone: number; set_label: string; total: number; done: number }>();
  const phases = new Map<
    number,
    { milestone: number; name: string } & Record<string, number | string>
  >();
  for (const row of phaseRows) {
    const phase =
      phases.get(row.milestone) ??
      ({
        milestone: row.milestone,
        name: PHASE_NAMES[row.milestone] ?? `Phase ${row.milestone}`,
        core_done: 0,
        core_total: 0,
        optional_done: 0,
        optional_total: 0,
        deferred_done: 0,
        deferred_total: 0,
      } as { milestone: number; name: string } & Record<string, number | string>);
    phase[`${row.set_label}_done`] = row.done;
    phase[`${row.set_label}_total`] = row.total;
    phases.set(row.milestone, phase);
  }

  const { results: ladderRows } = await db
    .prepare("SELECT stage, COUNT(*) AS n FROM problems GROUP BY stage")
    .all<{ stage: string; n: number }>();
  // Every rung is present even at zero: the page's bar list is this object.
  const ladder: Record<string, number> = Object.fromEntries(STAGES.map((s) => [s, 0]));
  for (const row of ladderRows) ladder[row.stage] = row.n;

  // gates rows are keyed by ISO week (that's the digest/gate contract), but
  // the page speaks campaign weeks. The campaign never crosses a year
  // boundary, so a plain offset converts safely.
  const isoWeekOffset = isoWeek(CAMPAIGN_START) - 1;
  const { results: gateRows } = await db
    .prepare("SELECT week, issue, pass_rate, closed_on FROM gates ORDER BY week")
    .all<{ week: number; issue: number | null; pass_rate: number | null; closed_on: string | null }>();
  const gates = gateRows.map((g) => ({ ...g, week: g.week - isoWeekOffset }));

  // Review-queue depth for the next 14 days: everything due by that day.
  const queue: { date: string; due: number }[] = [];
  for (let i = 0; i < 14; i++) {
    const date = addDays(today, i);
    const row = await db
      .prepare(
        `SELECT COUNT(*) AS n FROM problems
         WHERE stage != 'retired' AND next_review IS NOT NULL AND next_review <= ?1
           AND (defer_until IS NULL OR defer_until <= ?1)`,
      )
      .bind(date)
      .first<{ n: number }>();
    queue.push({ date, due: row?.n ?? 0 });
  }

  const recent: { date: string; attempts: number; passes: number }[] = [];
  for (let i = 6; i >= 0; i--) {
    const date = addDays(today, -i);
    const row = await db
      .prepare(
        `SELECT COUNT(*) AS attempts,
                SUM(CASE WHEN result = 'pass' THEN 1 ELSE 0 END) AS passes
         FROM attempts WHERE date = ?`,
      )
      .bind(date)
      .first<{ attempts: number; passes: number | null }>();
    recent.push({ date, attempts: row?.attempts ?? 0, passes: row?.passes ?? 0 });
  }

  return {
    generated: new Date().toISOString(),
    campaign: { day: campaignDay(today), week: campaignWeek(today), start: CAMPAIGN_START, days: CAMPAIGN_DAYS },
    phases: [...phases.values()],
    ladder,
    gates,
    streak: await streak(db, today),
    queue,
    recent,
  };
}