#!/usr/bin/env bun
/**
 * Fuzzy-pick a problem and scaffold it via leetcode-cli, in one of the three
 * work/ buckets (see work.ts): a first solve under work/1, or the 3-day and
 * 7-day blind re-solves under work/3 and work/7. Tab cycles the sections.
 *
 * The problem index lives in the local SQLite cache (see db.ts), refreshed at
 * most once per 24h; campaign problem descriptions from README.md are
 * backfilled into the same db on the way. The new-problem section hides
 * anything that already has a numbered file under work/1 — re-picking it would
 * only clobber the existing scaffold — and each review section hides whatever
 * its own bucket already holds, so a finished re-solve leaves the list.
 */
import { autocomplete, cancel, isCancel, log, spinner } from "@clack/prompts";
import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
import { homedir } from "node:os";
import { join } from "node:path";
import { styleText } from "node:util";
import { etDate } from "../api/src/srs.ts";
import { fetchDescription, problemDb, readmeSlugs } from "./db";
import { ROOT, WINDOWS, bucketDir, reviewQueues, scanBucket, type Bucket } from "./work";

const db = problemDb();

// ── problem index (24h TTL) ──────────────────────────────────────

if (db.indexStale()) {
  const s = spinner();
  s.start("Fetching problem index from leetcode.com");
  try {
    s.stop(`Indexed ${await db.refreshIndex()} problems`);
  } catch (err) {
    if (db.all().length === 0) {
      s.error(`Fetch failed: ${err}`);
      process.exit(1);
    }
    s.stop(`Index refresh failed (${err}) — using cached copy`);
  }
}

// ── description backfill for the campaign problems in README.md ──

const missing = db.missingDescriptions(readmeSlugs(await Bun.file(join(ROOT, "README.md")).text()));
if (missing.length > 0) {
  const s = spinner();
  s.start(`Caching ${missing.length} problem descriptions`);
  let fetched = 0;
  let failed = 0;
  await Promise.all(
    Array.from({ length: 6 }, async () => {
      for (let slug = missing.shift(); slug; slug = missing.shift()) {
        try {
          const html = await fetchDescription(slug);
          if (html !== null) db.saveDescription(slug, html);
          s.message(`Caching problem descriptions (${++fetched})`);
        } catch {
          failed++; // left NULL — retried on the next run
        }
      }
    }),
  );
  s.stop(failed ? `Cached ${fetched} descriptions (${failed} failed, will retry next run)` : `Cached ${fetched} problem descriptions`);
}

// ── the three sections ───────────────────────────────────────────

/** What Enter scaffolds: this problem, into this bucket. */
interface Choice {
  bucket: Bucket;
  lc: number;
  slug: string;
}

interface Section {
  label: string;
  options: { value: Choice; label: string; hint: string }[];
}

const first = scanBucket(1);
const problems = db.all();
const titles = new Map(problems.map((p) => [p.id, p.title] as const));
db.close();

const queues = reviewQueues(etDate(new Date()));

const sections: Section[] = [
  {
    label: "new",
    options: problems
      .filter((p) => !first.has(p.id))
      .map((p) => ({
        value: { bucket: 1 as Bucket, lc: p.id, slug: p.slug },
        label: `${p.id}. ${p.title}`,
        hint: p.paidOnly ? `${p.difficulty} 🔒 premium` : p.difficulty,
      })),
  },
  ...WINDOWS.map((window) => ({
    label: `${window}-day`,
    options: queues.get(window)!.map((owed) => ({
      value: { bucket: window as Bucket, lc: owed.lc, slug: owed.slug },
      label: `${owed.lc}. ${titles.get(owed.lc) ?? owed.slug}`,
      hint: `${owed.difficulty} · ${owed.category} · solved ${owed.solved}, ${owed.days}d ago`,
    })),
  })),
];

let active = 0;

/**
 * The slice of clack's AutocompletePrompt this picker drives. @clack/prompts
 * re-exports neither the class nor its type, and apps/cli does not depend on
 * @clack/core directly, so the contract is spelled out structurally.
 */
interface Autocomplete {
  userInput: string;
  on(event: "key", cb: (char: string | undefined, key: { name?: string }) => void): void;
  emit(event: "userInput", input: string): void;
}

/** Search text that cannot match any option — see refresh() below. */
const NO_MATCH = "\u0000";

let hooked = false;

/**
 * Bind Tab to the section switch, once per prompt.
 *
 * clack has no hook for extra keys, but it calls `options` with the prompt as
 * `this`, which is all a subscription needs. Switching sections also has to
 * re-filter the list, and the prompt only recomputes `filteredOptions` when
 * the search text *changes* — hence the pair of userInput events: an
 * unmatchable string, then the real one, which recomputes against the new
 * section, resets the cursor onto its first match and leaves the typed query
 * on screen untouched. clack repaints as soon as the key handlers return.
 *
 * No `placeholder` is passed to the prompt on purpose: clack's own Tab binding
 * (fill the input with the placeholder) is inert without one.
 */
function hookTab(prompt: Autocomplete): void {
  if (hooked) return;
  hooked = true;
  prompt.on("key", (_char, key) => {
    if (key.name !== "tab") return;
    active = (active + 1) % sections.length;
    prompt.emit("userInput", NO_MATCH);
    prompt.emit("userInput", prompt.userInput);
  });
}

// Widened, not asserted: clack resolves `undefined` when Enter lands on an
// empty list, which its own types do not admit.
const picked: Choice | symbol | undefined = await autocomplete<Choice>({
  // Getter, not a string: clack reads `message` on every repaint, so the tab
  // bar tracks the active section.
  get message(): string {
    const bar = sections
      .map((section, i) => {
        const text = `${section.label} (${section.options.length})`;
        return i === active ? styleText("cyan", `▸ ${text}`) : styleText("dim", text);
      })
      .join(styleText("dim", "  ·  "));
    return `Pick a problem   ${bar}   ${styleText("dim", "Tab: next section")}`;
  },
  maxItems: 12,
  options(this: Autocomplete) {
    hookTab(this);
    return sections[active]!.options;
  },
  filter: (search, option) => {
    const haystack = option.label!.toLowerCase();
    return search
      .toLowerCase()
      .split(/\s+/)
      .every((token) => haystack.includes(token));
  },
});

if (isCancel(picked)) {
  cancel("Nothing picked.");
  process.exit(0);
}
if (picked === undefined) {
  // Enter on an empty section: nothing was focused, so there is nothing to do.
  cancel(`Nothing owed in the ${sections[active]!.label} section.`);
  process.exit(0);
}

// ── scaffold into the picked bucket ──────────────────────────────

// The active workspace names the config file; everything else about it belongs
// to leetcode-cli.
const registry = join(homedir(), ".leetcode", "workspaces.json");
let workspace = "default";
if (existsSync(registry)) {
  const parsed: unknown = JSON.parse(readFileSync(registry, "utf8"));
  if (parsed && typeof parsed === "object" && "active" in parsed && typeof parsed.active === "string") {
    workspace = parsed.active || workspace;
  }
}
const configPath = join(homedir(), ".leetcode", "workspaces", workspace, "config.json");
if (!existsSync(configPath)) {
  log.error(`No leetcode-cli config at ${configPath} — run \`leetcode config -i\` once.`);
  process.exit(1);
}

/**
 * Point leetcode-cli at one bucket. It reads its output directory from the
 * active workspace config and from nowhere else — no flag, no environment
 * override — so `workDir` is the whole handover.
 *
 * Each write MERGES the file as it is on disk at that moment; a saved copy is
 * never played back. The CLI owns this file too (theme, language, whatever a
 * `leetcode login` adds), and replaying stale bytes over it would silently
 * undo what it wrote while the child ran. After the pick, `workDir` is set to
 * work/1 instead of to whatever it was before: the first-solve bucket is the
 * one resting value that is always right, so even a killed run leaves a bare
 * `leetcode pick` on-layout.
 */
function setWorkDir(target: string): void {
  const raw: unknown = JSON.parse(readFileSync(configPath, "utf8"));
  if (raw === null || typeof raw !== "object") {
    log.error(`${configPath} holds no JSON object — run \`leetcode config -i\` to rewrite it.`);
    process.exit(1);
  }
  // 2-space JSON with a trailing newline: leetcode-cli's own format.
  writeFileSync(configPath, `${JSON.stringify({ ...raw, workDir: target }, null, 2)}\n`);
}

const dir = bucketDir(picked.bucket);
mkdirSync(dir, { recursive: true });
setWorkDir(dir);

let code: number;
try {
  const proc = Bun.spawn(
    // bun installs workspace-dep bins into this package's node_modules, not the root's
    [join(import.meta.dir, "node_modules", ".bin", "leetcode"), "pick", picked.slug],
    { cwd: ROOT, stdio: ["inherit", "inherit", "inherit"] },
  );
  code = await proc.exited;
} finally {
  setWorkDir(bucketDir(1));
}

// leetcode-cli exits 0 even when it wrote nothing (an expired session only
// prints a warning), so the scaffold itself is the acceptance test: without a
// file for this problem in the bucket, the pick failed.
if (!scanBucket(picked.bucket).has(picked.lc)) {
  log.error(
    `leetcode-cli scaffolded nothing for LC ${picked.lc} under work/${picked.bucket}/.\n` +
      "If it printed “Session expired”, run `leetcode login` and pick again.",
  );
  process.exit(code === 0 ? 1 : code);
}
process.exit(code);