/**
 * Nightly GitHub → D1 catalog reconcile. GitHub issues own the catalog
 * (topics, problems, set/diff labels, milestones); this recomputes desired
 * rows from scratch on every run — re-runs are no-ops. SRS-owned columns
 * (stage, next_review) are NEVER overwritten; defer_until is set once, on
 * first sight of a deferred problem. The Worker never invents catalog rows.
 *
 * Difficulty and set come from the `diff:*` / `set:*` LABELS, never from the
 * issue title — the title carries only the LC number and the problem's name,
 * so relabelling a problem is enough to move it and titles stay readable.
 * The `problem` label is what marks a sub-issue as curriculum.
 */
import { workingDay } from "./srs.ts";
import type { GitHub } from "./github.ts";

const TITLE_RE = /^LC (\d+) · (.+)$/;

const DIFFICULTIES = ["easy", "medium", "hard"] as const;
const SETS = ["core", "optional", "deferred"] as const;

/** Deferred Hards enter the queue from this date, two per working day. */
const DEFER_FROM = "2026-09-28";

export interface ReconcileReport {
  topics: number;
  problems: number;
}

/** Label names on one issue payload, narrowed with guards rather than cast. */
function labelNames(value: object): string[] {
  if (!("labels" in value) || !Array.isArray(value.labels)) return [];
  const names: string[] = [];
  for (const label of value.labels) {
    if (label && typeof label === "object" && "name" in label && typeof label.name === "string") {
      names.push(label.name);
    }
  }
  return names;
}

export async function reconcileCatalog(db: D1Database, gh: GitHub): Promise<ReconcileReport> {
  interface TopicIssue {
    number: number;
    title: string;
    milestone: number | null;
  }
  const topics: TopicIssue[] = [];
  for await (const raw of gh.list(`/repos/${gh.repo}/issues?labels=topic&state=all`)) {
    if (!raw || typeof raw !== "object") continue;
    if ("pull_request" in raw) continue;
    if (!("number" in raw) || typeof raw.number !== "number") continue;
    if (!("title" in raw) || typeof raw.title !== "string") continue;
    let milestone: number | null = null;
    if (
      "milestone" in raw &&
      raw.milestone &&
      typeof raw.milestone === "object" &&
      "number" in raw.milestone &&
      typeof raw.milestone.number === "number"
    ) {
      milestone = raw.milestone.number;
    }
    topics.push({ number: raw.number, title: raw.title, milestone });
  }

  const statements: D1PreparedStatement[] = [];
  for (const t of topics) {
    statements.push(
      db
        .prepare(
          `INSERT INTO topics (issue, name, milestone) VALUES (?1, ?2, ?3)
           ON CONFLICT(issue) DO UPDATE SET name = ?2, milestone = ?3`,
        )
        .bind(t.number, t.title.replace(/^Topic \d+ — /, ""), t.milestone),
    );
  }

  let problems = 0;
  let deferredSeen = 0;
  for (const t of topics) {
    for await (const raw of gh.list(`/repos/${gh.repo}/issues/${t.number}/sub_issues`)) {
      if (!raw || typeof raw !== "object") continue;
      if (!("number" in raw) || typeof raw.number !== "number") continue;
      if (!("title" in raw) || typeof raw.title !== "string") continue;
      const labels = labelNames(raw);
      if (!labels.includes("problem")) continue; // non-curriculum sub-issue
      const m = raw.title.match(TITLE_RE);
      if (!m) {
        console.warn(`catalog: #${raw.number} is a problem but not titled "LC <n> · <name>"`);
        continue;
      }
      const difficulty = DIFFICULTIES.find((d) => labels.includes(`diff:${d}`));
      const set = SETS.find((s) => labels.includes(`set:${s}`));
      if (!difficulty || !set) {
        console.warn(`catalog: #${raw.number} is missing a diff:/set: label — skipped`);
        continue;
      }
      const lc = Number(m[1]);
      // Two deferred Hards per WORKING day from DEFER_FROM, in catalog walk
      // order — applied only when the row is first created (SRS owns it
      // afterwards). Sunday is skipped like every other scheduled date.
      const defer = set === "deferred" ? workingDay(DEFER_FROM, Math.floor(deferredSeen / 2)) : null;
      if (set === "deferred") deferredSeen++;
      statements.push(
        db
          .prepare(
            `INSERT INTO problems (lc_number, issue, topic_issue, title, difficulty, set_label, defer_until, next_review)
             VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?7)
             ON CONFLICT(lc_number) DO UPDATE SET
               issue = ?2, topic_issue = ?3, title = ?4, difficulty = ?5, set_label = ?6`,
          )
          .bind(lc, raw.number, t.number, m[2]!, difficulty, set, defer),
      );
      problems++;
    }
  }

  // D1 batches are transactional; chunk to stay under statement limits.
  for (let i = 0; i < statements.length; i += 50) {
    await db.batch(statements.slice(i, i + 50));
  }
  return { topics: topics.length, problems };
}