#!/usr/bin/env bun
/**
 * Sync work/ leetcode solutions into docs/solutions/ pages.
 *
 * - New problems get a full page (frontmatter, badge, warning, examples,
 *   constraints, solution) in the gold-standard format.
 * - Already-ported pages only get their `## Solution` section regenerated,
 *   so hand-curated prose is never touched.
 * - When a problem is solved in both JavaScript and Python the solution
 *   renders as a <CodeGroup> (Python first); single-language solutions
 *   render as a plain fence.
 */
import { mkdir, rename } from "node:fs/promises";
import { basename, join } from "node:path";

const ROOT = join(import.meta.dir, "..");
const WORK = join(ROOT, "work");
const DOCS = join(ROOT, "docs", "solutions");

type Lang = "js" | "py";

interface Example {
  input: string;
  output: string;
  explanation: string[]; // [] = none; 1 entry = inline; >1 = bullet list
}

interface Header {
  num: number;
  title: string;
  difficulty: string;
  statement: string[]; // unwrapped paragraphs
  examples: Example[];
  constraints: string[];
  followUp: string;
}

interface Solution {
  num: number;
  slug: string;
  category: string;
  header: Header;
  code: Partial<Record<Lang, string>>;
}

// ── work/ parsing ────────────────────────────────────────────────

/** Split a source file into (header comment text, code). */
function splitSource(src: string, lang: Lang): { header: string; code: string } {
  let header: string, code: string;
  if (lang === "js") {
    const end = src.indexOf("*/");
    if (!src.trimStart().startsWith("/*") || end === -1) throw new Error("missing /* header */");
    header = src
      .slice(src.indexOf("/*") + 2, end)
      .split("\n")
      .map((l) => l.replace(/^\s*\* ?/, ""))
      .join("\n");
    code = src.slice(end + 2);
  } else {
    const open = src.indexOf('"""');
    const close = src.indexOf('"""', open + 3);
    if (open === -1 || close === -1) throw new Error('missing """ header """');
    header = src.slice(open + 3, close);
    code = src.slice(close + 3);
  }
  return { header, code: code.replace(/^\s*\n/, "").trimEnd() };
}

/** Unwrap hard-wrapped lines into logical paragraphs / bullets. */
function paragraphs(lines: string[]): string[] {
  const out: string[] = [];
  let cur = "";
  const flush = () => {
    if (cur) out.push(cur);
    cur = "";
  };
  for (const raw of lines) {
    const line = raw.replace(/\t/g, " ").trimEnd();
    const text = line.trim();
    if (!text || /^[─-]{3,}$/.test(text)) {
      flush();
      continue;
    }
    if (/^([•-] |Input:|Output:|Explanation:|Example \d+:|Constraints:|Follow[- ]?ups?:)/.test(text)) {
      flush();
      cur = text;
    } else {
      cur = cur ? `${cur} ${text}` : text;
    }
  }
  flush();
  return out;
}

function parseHeader(header: string): Header {
  const lines = header.split("\n");
  const titleLine = lines.find((l) => /^\s*\d+\.\s/.test(l))?.trim();
  if (!titleLine) throw new Error("missing '<num>. <title>' line");
  const num = Number.parseInt(titleLine, 10);
  const title = titleLine.replace(/^\d+\.\s*/, "");
  const difficulty =
    lines.find((l) => l.trim().startsWith("Difficulty:"))?.split(":")[1]?.trim() ?? "";

  // Body: everything after the ───── separator.
  const sep = lines.findIndex((l) => /^[─]{3,}/.test(l.trim()));
  const paras = paragraphs(lines.slice(sep + 1));

  const statement: string[] = [];
  const examples: Example[] = [];
  const constraints: string[] = [];
  let followUp = "";
  let section: "statement" | "example" | "constraints" = "statement";
  let ex: Example | null = null;

  for (const p of paras) {
    if (/^Example \d+:?$/.test(p)) {
      if (ex) examples.push(ex);
      ex = { input: "", output: "", explanation: [] };
      section = "example";
      continue;
    }
    if (/^Constraints:$/.test(p)) {
      if (ex) examples.push(ex);
      ex = null;
      section = "constraints";
      continue;
    }
    const fu = p.match(/^Follow[- ]?ups?:\s*(.*)$/i);
    if (fu) {
      followUp = fu[1]!;
      continue;
    }
    if (section === "statement") statement.push(p.replace(/^• /, ""));
    else if (section === "constraints") constraints.push(p.replace(/^• /, ""));
    else if (ex) {
      // Example paragraphs: Input/Output/Explanation, wrapped arbitrarily.
      // A paragraph may fuse "Input: … Output: …" only across real lines,
      // but source always keeps them on separate wrapped paragraphs.
      if (p.startsWith("Input:")) ex.input = p.slice(6).trim();
      else if (p.startsWith("Output:")) ex.output = p.slice(7).trim();
      else if (p.startsWith("Explanation:")) {
        const rest = p.slice(12).trim();
        if (rest) ex.explanation.push(rest);
      } else if (p.startsWith("- ")) ex.explanation.push(p.slice(2));
      else if (ex.explanation.length)
        ex.explanation[ex.explanation.length - 1] += ` ${p}`;
      else ex.explanation.push(p);
    }
  }
  if (ex) examples.push(ex);
  return { num, title, difficulty, statement, examples, constraints, followUp };
}

// ── README topic map ─────────────────────────────────────────────

const TOPIC_ALIASES: Record<string, string> = {
  "Hash-Based Lookup": "Hash Table",
};

async function readmeTopics(): Promise<Map<number, string>> {
  const md = await Bun.file(join(ROOT, "README.md")).text();
  const map = new Map<number, string>();
  let topic = "";
  for (const line of md.split("\n")) {
    const t = line.match(/<strong>\d+\.\s*([^<]+)<\/strong>/);
    if (t) topic = TOPIC_ALIASES[t[1]!.trim()] ?? t[1]!.trim();
    if (!topic) continue;
    const n = line.match(/<td align="center">(\d+)<\/td>/);
    if (n) map.set(Number(n[1]), topic);
  }
  return map;
}

// ── inline-code formatting heuristics ────────────────────────────

/** Identifiers worth backticking in prose, harvested from the code. */
function identifiers(sol: Solution): Set<string> {
  const ids = new Set<string>(["n", "m", "k"]);
  for (const code of Object.values(sol.code)) {
    for (const m of code.matchAll(/@param\s*\{[^}]*\}\s*(\w+)/g)) ids.add(m[1]!);
    for (const m of code.matchAll(/def \w+\(self,?\s*([^)]*)\)/g))
      for (const arg of m[1]!.split(","))
        if (arg.trim()) ids.add(arg.split(":")[0]!.trim());
    for (const m of code.matchAll(/(?:var|const|let) (\w+) = function\s*\(([^)]*)\)/g))
      for (const arg of m[2]!.split(","))
        if (arg.trim()) ids.add(arg.trim());
  }
  return ids;
}

function formatConstraint(c: string, ids: Set<string>): string {
  if (/<=|>=|==|!=|<|>/.test(c)) return `\`${c}\``;
  // Prose constraint: backtick identifier-ish tokens only.
  return c
    .split(" ")
    .map((word) => {
      const m = word.match(/^([\w.]+(?:\[[^\]]*\])?)([.,;:]?)$/);
      if (!m) return word;
      const [, tok, punct] = m;
      if (/\[[^\]]*\]/.test(tok!) || ids.has(tok!)) return `\`${tok}\`${punct}`;
      return word;
    })
    .join(" ");
}

/** Wrap value literals / expressions in an explanation sentence. */
function backtickify(text: string, ids: Set<string>): string {
  const words = text.split(" ");
  type Tok = { pre: string; core: string; post: string; codey: boolean };
  const toks: Tok[] = words.map((w) => {
    const m = w.match(/^([("']*)(.*?)([)"'.,;:!?]*)$/)!;
    const core = m[2]!;
    const codey =
      /^-?\d+(\.\d+)?([+\-*/]-?\d+(\.\d+)?)*$/.test(core) || // number / compact arithmetic
      /^\[[^\]]*\]$/.test(core) || // array literal
      /^[a-zA-Z_]\w*\[[^\]]*\]$/.test(core) || // indexed identifier
      /^[+\-*/=%]$/.test(core) || // operator
      ids.has(core);
    return { pre: m[1]!, core, post: m[3]!, codey };
  });

  const out: string[] = [];
  let i = 0;
  while (i < toks.length) {
    if (!toks[i]!.codey || /^[+\-*/=%]$/.test(toks[i]!.core)) {
      out.push(words[i]!); // prose, or an operator with no codey run to its left
      i++;
      continue;
    }
    // Extend a run of codey tokens; only unbroken by punctuation.
    let j = i;
    while (
      j + 1 < toks.length &&
      toks[j + 1]!.codey &&
      !toks[j]!.post && // punctuation after a token ends the run
      !toks[j + 1]!.pre.includes('"')
    )
      j++;
    // Trim trailing operators from the run (e.g. "5 and" keeps "and" out anyway).
    while (j > i && /^[+\-*/=%]$/.test(toks[j]!.core)) j--;
    const span = toks
      .slice(i, j + 1)
      .map((tok, idx, arr) => (idx === arr.length - 1 ? `${tok.pre}${tok.core}` : `${tok.pre}${tok.core}${tok.post}`))
      .join(" ");
    out.push(`\`${span}\`${toks[j]!.post}`);
    i = j + 1;
  }
  return out.join(" ");
}

// ── page rendering ───────────────────────────────────────────────

const FENCE: Record<Lang, { info: string; label: string }> = {
  py: { info: "py", label: "Python" },
  js: { info: "js", label: "JavaScript" },
};

function solutionSection(sol: Solution): string {
  const langs = (["py", "js"] as const).filter((l) => sol.code[l]);
  const fence = (l: Lang, titled: boolean) =>
    `\`\`\`${FENCE[l].info}${titled ? ` ${FENCE[l].label}` : ""}\n${sol.code[l]}\n\`\`\``;
  if (langs.length === 1) return `## Solution\n\n${fence(langs[0]!, false)}\n`;
  return `## Solution\n\n<CodeGroup>\n\n${langs.map((l) => fence(l, true)).join("\n\n")}\n\n</CodeGroup>\n`;
}

function warningText(h: Header): string {
  if (h.followUp) return h.followUp;
  return (
    h.statement
      .slice(1)
      .find((p) => /^(You must|Your solution must|Your algorithm|Notice that|Could you)/.test(p)) ?? ""
  );
}

function renderPage(sol: Solution, topic: string): string {
  const h = sol.header;
  const ids = identifiers(sol);
  const description = h.statement[0]?.replace(/\.\s*$/, "") ?? "";
  const parts: string[] = [];

  parts.push(
    "---",
    `title: '${h.num}. ${h.title.replaceAll("'", "''")}'`,
    /[:#]/.test(description) ? `description: '${description.replaceAll("'", "''")}'` : `description: ${description}`,
    "sidebar:",
    `  label: '${h.title.replaceAll("'", "''")}'`,
    `  badge: '${h.difficulty}'`,
    "---",
    "",
    `<Badge variant="accent">${topic}</Badge>`,
    "",
  );

  const warning = warningText(h);
  if (warning) parts.push("::::warning", warning, "::::", "");

  h.examples.forEach((ex, i) => {
    parts.push(`### Example ${i + 1}:`);
    parts.push(`- Input: \`${ex.input}\``);
    parts.push(`- Output: \`${ex.output}\``);
    if (ex.explanation.length === 1)
      parts.push(`- Explanation: ${backtickify(ex.explanation[0]!, ids)}`);
    else if (ex.explanation.length > 1) {
      parts.push("- Explanation:");
      for (const item of ex.explanation) parts.push(`  - ${backtickify(item, ids)}`);
    }
    parts.push("");
  });

  parts.push("### Constraints:", "");
  for (const c of h.constraints) parts.push(`- ${formatConstraint(c, ids)}`);
  parts.push("", solutionSection(sol));

  return parts.join("\n");
}

// ── main ─────────────────────────────────────────────────────────

const solutions = new Map<number, Solution>();
for await (const rel of new Bun.Glob("**/*.{js,py}").scan(WORK)) {
  const lang = rel.endsWith(".py") ? "py" : ("js" as Lang);
  const file = basename(rel);
  const m = file.match(/^(\d+)\.(.+)\.(?:js|py)$/);
  if (!m) {
    console.warn(`skip (unrecognized name): work/${rel}`);
    continue;
  }
  const num = Number(m[1]);
  const slug = m[2]!;
  const { header, code } = splitSource(await Bun.file(join(WORK, rel)).text(), lang);
  const parsed = parseHeader(header);
  const existing = solutions.get(num);
  if (existing) {
    existing.code[lang] = code;
    if (lang === "js") existing.header = parsed; // js header wins when both exist
  } else {
    solutions.set(num, {
      num,
      slug,
      category: rel.split("/")[1] ?? "",
      header: parsed,
      code: { [lang]: code },
    });
  }
}

const topics = await readmeTopics();

/** Insert a number-free `sidebar.label` into existing frontmatter when missing. */
function ensureLabel(page: string, h: Header): string {
  const fm = page.match(/^---\n[\s\S]*?\n---/);
  if (!fm || /^ {2}label: /m.test(fm[0])) return page;
  const label = `  label: '${h.title.replaceAll("'", "''")}'`;
  return page.replace(/^sidebar:$/m, `sidebar:\n${label}`);
}

// Existing docs pages, keyed by leetcode number from the frontmatter title.
const pages = new Map<number, string>(); // num -> path relative to DOCS
for (const rel of (await Array.fromAsync(new Bun.Glob("**/*.mdx").scan(DOCS))).sort()) {
  const text = await Bun.file(join(DOCS, rel)).text();
  const t = text.match(/^title: '(\d+)\./m);
  if (t) pages.set(Number(t[1]), rel);
}

const report: [string, string, string][] = [];
const ordered = [...solutions.values()].sort((a, b) => a.num - b.num);

for (const sol of ordered) {
  const langs = Object.keys(sol.code).sort().join("+");
  const workRef = `${sol.num}.${sol.slug} (${langs})`;
  // (category) group folder + leetcode-number prefix: numeric sidebar order, both stripped from the URL.
  const group = `(${sol.category.toLowerCase().replaceAll(" ", "-")})`;
  const name = `${group}/${sol.num}-${sol.slug}.mdx`;
  const existing = pages.get(sol.num);
  await mkdir(join(DOCS, group), { recursive: true });

  if (existing) {
    const page = await Bun.file(join(DOCS, existing)).text();
    const at = page.indexOf("## Solution");
    if (at === -1) {
      report.push([workRef, existing, "ERROR: no '## Solution' heading"]);
      continue;
    }
    const next = ensureLabel(page.slice(0, at) + solutionSection(sol), sol.header);
    const actions: string[] = [];
    if (existing !== name) {
      await rename(join(DOCS, existing), join(DOCS, name));
      actions.push("moved");
    }
    if (next !== page) {
      await Bun.write(join(DOCS, name), next);
      actions.push("updated");
    }
    report.push([workRef, name, actions.join(" + ") || "skipped (in sync)"]);
  } else {
    const topic = topics.get(sol.num) ?? sol.category;
    await Bun.write(join(DOCS, name), renderPage(sol, topic));
    report.push([workRef, name, "created"]);
  }
}

const w0 = Math.max(...report.map((r) => r[0].length), 9);
const w1 = Math.max(...report.map((r) => r[1].length), 9);
console.log(`${"work file".padEnd(w0)}  ${"docs page".padEnd(w1)}  status`);
console.log(`${"─".repeat(w0)}  ${"─".repeat(w1)}  ${"─".repeat(20)}`);
for (const [a, b, c] of report) console.log(`${a.padEnd(w0)}  ${b.padEnd(w1)}  ${c}`);