/**
 * The work/ layout: one directory per spaced-repetition window.
 *
 *   work/1/<Difficulty>/<Category>/<num>.<slug>.<ext>   first solve
 *   work/3/<Difficulty>/<Category>/<num>.<slug>.<ext>   3-day blind re-solve
 *   work/7/<Difficulty>/<Category>/<num>.<slug>.<ext>   7-day blind re-solve
 *
 * The bucket name is the review window in days — the same +3/+7 windows the
 * campaign's `Spaced Repetition — <date>` issues use (WINDOWS in
 * spaced-repetition.ts). Below the bucket the layout is leetcode-cli's own
 * `workDir/Difficulty/Category/` shape, so a re-solve lands beside its first
 * solve under a different bucket.
 *
 * A window is *owed* when the first solve is at least that many days old and
 * the bucket has no file for that problem yet. Reconciled from the filesystem
 * on every run the way close-solved.ts reconciles issues: no state file, no
 * bookkeeping, and a re-solve closes its window just by existing — presence,
 * not content, so a stub in work/3 counts as done the same way `bun run pick`
 * treats a scaffold under work/1 as picked. The first solve is the one place
 * content is read: an empty scaffold in work/1 owes nothing, it is simply
 * unsolved (isImplemented() in source.ts, the same gate close-solved.ts uses
 * before it closes an issue).
 *
 * "First solve" is the ET date of the commit that first added the problem's
 * work/ file — the same push that closes its problem issue and therefore
 * starts the campaign's +3/+7 windows. An uncommitted solution has no date and
 * is never owed a review yet: you just solved it. ET dates and the date
 * arithmetic come from apps/api/src/srs.ts so the local picker and D1 cannot
 * disagree about what day it is.
 *
 * Library: side-effect-free on import — nothing scans or shells out until a
 * function is called.
 */
import { readFileSync } from "node:fs";
import { join } from "node:path";
import { WINDOWS, type Window, daysBetween } from "../api/src/srs.ts";
import { isImplemented } from "./source.ts";

export const ROOT = join(import.meta.dir, "..", "..");
export const WORK = join(ROOT, "work");

// The windows are the SRS ladder's rungs: srs.ts defines them once and the
// bucket directories are named after them. Re-exported so the picker needs
// only this module to know the work/ layout.
export { WINDOWS, type Window };

/** work/1 is the first solve, the rest are the review windows. */
export const BUCKETS = [1, ...WINDOWS] as const;
export type Bucket = (typeof BUCKETS)[number];
const BUCKET_BY_DIR: Record<string, Bucket> = { "1": 1, "3": 3, "7": 7 };

export function bucketDir(bucket: Bucket): string {
  return join(WORK, String(bucket));
}

export interface WorkFile {
  lc: number;
  slug: string;
  bucket: Bucket;
  /** Path relative to work/, bucket included. */
  rel: string;
  difficulty: string;
  category: string;
}

/** `<num>.<slug>.<ext>` — the only file name the campaign scripts parse. */
function parseName(name: string): { lc: number; slug: string } | null {
  const m = name.match(/^(\d+)\.(.+)\.[A-Za-z0-9]+$/);
  return m ? { lc: Number(m[1]), slug: m[2]! } : null;
}

/** Parse `1/Medium/Array/15.3sum.py` — null for anything off-layout. */
export function parseWorkPath(rel: string): WorkFile | null {
  const parts = rel.split("/");
  const name = parts.pop();
  const bucket = BUCKET_BY_DIR[parts[0] ?? ""];
  if (name === undefined || bucket === undefined) return null;
  const parsed = parseName(name);
  if (!parsed) return null;
  return { ...parsed, bucket, rel, difficulty: parts[1] ?? "", category: parts[2] ?? "" };
}

/** LC number -> its files in that bucket (a problem may have both js and py). */
export function scanBucket(bucket: Bucket): Map<number, WorkFile[]> {
  const files = new Map<number, WorkFile[]>();
  for (const name of new Bun.Glob("**/*.*").scanSync({ cwd: bucketDir(bucket) })) {
    const file = parseWorkPath(`${bucket}/${name}`);
    if (!file) continue;
    const found = files.get(file.lc);
    if (found) found.push(file);
    else files.set(file.lc, [file]);
  }
  return files;
}

/**
 * LC number -> ET date of the commit that first added a work/ file for it.
 *
 * One `git log` over the whole of work/, oldest commit first, so the first
 * date seen for a problem wins. Keyed by LC number rather than by path, which
 * makes every past reshuffle of the directory layout — including the move into
 * work/1 — irrelevant: the original add still counts. TZ + `format-local`
 * put the dates on the ET calendar srs.ts speaks.
 */
export function firstSolved(): Map<number, string> {
  const git = Bun.spawnSync(
    [
      "git",
      "log",
      "--reverse",
      "--no-merges",
      "--diff-filter=A",
      "--date=format-local:%Y-%m-%d",
      "--format=%ad",
      "--name-only",
      "--",
      "work",
    ],
    { cwd: ROOT, env: { ...process.env, TZ: "America/New_York" } },
  );
  if (git.exitCode !== 0) {
    throw new Error(`git log failed: ${git.stderr.toString().trim()}`);
  }

  const dates = new Map<number, string>();
  let date = "";
  for (const line of git.stdout.toString().split("\n")) {
    if (/^\d{4}-\d{2}-\d{2}$/.test(line)) {
      date = line;
      continue;
    }
    const parsed = line === "" ? null : parseName(line.slice(line.lastIndexOf("/") + 1));
    if (parsed && !dates.has(parsed.lc)) dates.set(parsed.lc, date);
  }
  return dates;
}

export interface Owed extends WorkFile {
  /** ET date of the first solve. */
  solved: string;
  /** Days since the first solve — at least the window. */
  days: number;
}

/**
 * Both review windows for `today`, oldest solve first.
 *
 * Uncapped, unlike the review issue's WINDOW_CAP: the issue is one day's
 * assignment, this is everything still owed. A window skipped for a day stays
 * on the list until its file exists.
 */
export function reviewQueues(today: string): Map<Window, Owed[]> {
  const dates = firstSolved();

  // An empty scaffold under work/1 is a problem still unsolved, not one owing
  // a review — the same call close-solved.ts makes before it closes an issue.
  const solved: { file: WorkFile; date: string }[] = [];
  for (const files of scanBucket(1).values()) {
    const date = dates.get(files[0]!.lc);
    if (date === undefined) continue; // uncommitted: you only just solved it
    const file = files.find((f) =>
      isImplemented(readFileSync(join(WORK, f.rel), "utf8"), f.rel.endsWith(".py") ? "py" : "js"),
    );
    if (file) solved.push({ file, date });
  }

  const queues = new Map<Window, Owed[]>();
  for (const window of WINDOWS) {
    const done = scanBucket(window);
    const owed: Owed[] = [];
    for (const { file, date } of solved) {
      if (done.has(file.lc)) continue;
      const days = daysBetween(date, today);
      if (days >= window) owed.push({ ...file, solved: date, days });
    }
    owed.sort((a, b) => b.days - a.days || a.lc - b.lc);
    queues.set(window, owed);
  }
  return queues;
}