import { sql } from "kysely";
import type { WorkHint } from "@sttracker/plugin-sdk/types";
import type { Db } from "@sttracker/db/db";
import { newId, nowIso } from "@sttracker/db/ids";
import {
  createWorkIn,
  finalWorkId,
  findWorkByExternalIdsIn,
  normalizePosition,
  resolveAliasIn,
  toWork,
  updateWorkFromHintIn,
  type K,
} from "./works.ts";

export interface FuzzyInput {
  title: string;
  year?: number | null;
  creators?: { name: string }[];
}

function normalize(s: string): string {
  return s
    .normalize("NFD")
    .replace(/\p{M}+/gu, "")
    .toLowerCase()
    .replace(/[^\p{L}\p{N}]+/gu, " ")
    .trim()
    .replace(/^(the|a|an)\s+/, "");
}

function tokens(s: string): string[] {
  return normalize(s).split(" ").filter(Boolean);
}

/**
 * 0..1 similarity. Title token-set Jaccard weighs 0.7; year 0.2 (±1 year counts half); any shared
 * creator 0.1. A component missing on either side is left out and the weights renormalised, so a
 * title-only comparison can still reach 1.
 */
export function fuzzyScore(a: FuzzyInput, b: FuzzyInput): number {
  const ta = new Set(tokens(a.title));
  const tb = new Set(tokens(b.title));
  let inter = 0;
  for (const t of ta) if (tb.has(t)) inter++;
  const union = ta.size + tb.size - inter;
  const jaccard = union === 0 ? 0 : inter / union;
  let score = jaccard * 0.7;
  let weight = 0.7;
  if (a.year != null && b.year != null) {
    const d = Math.abs(a.year - b.year);
    score += d === 0 ? 0.2 : d === 1 ? 0.1 : 0;
    weight += 0.2;
  }
  const ca = new Set((a.creators ?? []).map((c) => normalize(c.name)).filter(Boolean));
  const cb = (b.creators ?? []).map((c) => normalize(c.name)).filter(Boolean);
  if (ca.size > 0 && cb.length > 0) {
    if (cb.some((n) => ca.has(n))) score += 0.1;
    weight += 0.1;
  }
  return score / weight;
}

interface Resolved {
  workId: string;
  created: boolean;
  draft: boolean;
}

async function resolve(k: K, userId: string | null, hint: WorkHint, actor: string): Promise<Resolved> {
  // 1. Any external ID on a work this user may see (parents resolve with userId null: shared only).
  const byId = await findWorkByExternalIdsIn(k, hint.externalIds, userId);
  if (byId) {
    await updateWorkFromHintIn(k, byId, hint, actor);
    const workId = userId ? await resolveAliasIn(k, userId, byId) : byId;
    const owner = await k.selectFrom("works").select("owner_user_id").where("id", "=", workId).executeTakeFirstOrThrow();
    return { workId, created: false, draft: owner.owner_user_id !== null };
  }

  // 2. Parent + position.
  const parentId = hint.parent ? (await resolve(k, null, hint.parent, actor)).workId : null;
  const position = normalizePosition(hint.position);
  if (parentId && position) {
    const child = await k
      .selectFrom("works")
      .select("id")
      .where("parent_id", "=", parentId)
      .where("position", "=", position)
      .where("owner_user_id", "is", null)
      .executeTakeFirst();
    if (child) {
      // A merged tombstone still holds its (parent_id, position) slot: follow it to the surviving work.
      const workId = await finalWorkId(k, child.id);
      await updateWorkFromHintIn(k, workId, hint, actor);
      return { workId, created: false, draft: false };
    }
    return { workId: await createWorkIn(k, { hint, parentId }, actor), created: true, draft: false };
  }

  // 3. External IDs but no match: new shared work.
  if (Object.keys(hint.externalIds).length > 0) {
    return { workId: await createWorkIn(k, { hint, parentId }, actor), created: true, draft: false };
  }

  if (userId === null) {
    // Parent of a shared child: reuse an identical shared work, else create one.
    let q = k
      .selectFrom("works")
      .select("id")
      .where("owner_user_id", "is", null)
      .where("merged_into_id", "is", null)
      .where("media_type", "=", hint.mediaType)
      .where(sql<boolean>`lower(title) = ${hint.title.toLowerCase()}`);
    q = hint.year === undefined ? q : q.where("year", "=", hint.year);
    q = parentId ? q.where("parent_id", "=", parentId) : q.where("parent_id", "is", null);
    const same = await q.executeTakeFirst();
    if (same) return { workId: same.id, created: false, draft: false };
    return { workId: await createWorkIn(k, { hint, parentId }, actor), created: true, draft: false };
  }

  // 4. Private draft plus fuzzy suggestions.
  const workId = await createWorkIn(k, { hint, ownerUserId: userId }, actor);
  await suggest(k, userId, workId, hint);
  return { workId, created: true, draft: true };
}

async function suggest(k: K, userId: string, draftId: string, hint: WorkHint): Promise<void> {
  // Bound the candidate set with LIKE on the significant title tokens (OR), so "The Expanse: Leviathan
  // Wakes" still finds "Leviathan Wakes". Tokens of 3+ chars, first five; falls back to the first token.
  const all = tokens(hint.title);
  const sig = all.filter((t) => t.length >= 3).slice(0, 5);
  const likeTokens = sig.length > 0 ? sig : all.slice(0, 1);
  if (likeTokens.length === 0) return;
  const rows = await k
    .selectFrom("works")
    .selectAll()
    .where("merged_into_id", "is", null)
    .where("id", "!=", draftId)
    .where((eb) =>
      eb.or([
        eb.and([eb("owner_user_id", "is", null), eb("media_type", "=", hint.mediaType)]),
        eb("owner_user_id", "=", userId),
      ]),
    )
    .where((eb) =>
      eb.or(likeTokens.map((t) => eb(sql<string>`lower(title)`, "like", `%${t}%`))),
    )
    .limit(200)
    .execute();
  const scored = rows
    .map(toWork)
    .map((w) => ({ id: w.id, score: fuzzyScore(hint, w) }))
    .filter((c) => c.score >= 0.6)
    .sort((a, b) => b.score - a.score)
    .slice(0, 5);
  const now = nowIso();
  for (const c of scored) {
    await k
      .insertInto("match_suggestions")
      .values({ id: newId(), user_id: userId, work_id: draftId, candidate_work_id: c.id, score: c.score, status: "pending", created_at: now })
      .execute();
  }
}

const MAX_ATTEMPTS = 3;

/** SQLite "UNIQUE constraint failed", or Postgres SQLSTATE 23505, anywhere in the cause chain. */
export function isUniqueViolation(err: unknown): boolean {
  for (let e: unknown = err, depth = 0; e && typeof e === "object" && depth < 5; e = (e as { cause?: unknown }).cause, depth++) {
    const { code, errno, message } = e as { code?: unknown; errno?: unknown; message?: unknown };
    if (code === "23505" || errno === "23505") return true;
    if (typeof message === "string" && (message.includes("UNIQUE constraint failed") || message.includes("duplicate key"))) {
      return true;
    }
  }
  return false;
}

/**
 * Resolve a hint to a work per spec §8.4. Never auto-links on fuzzy matches; those become suggestions.
 * A concurrent match may create the same work first (unique external id or parent+position); the losing
 * transaction is discarded and the whole resolve re-run, which then finds the winner's rows.
 */
export async function matchWork(db: Db, userId: string, hint: WorkHint, actor: string): Promise<Resolved> {
  for (let attempt = 1; ; attempt++) {
    try {
      return await db.k.transaction().execute((tx) => resolve(tx, userId, hint, actor));
    } catch (err) {
      if (attempt >= MAX_ATTEMPTS || !isUniqueViolation(err)) throw err;
    }
  }
}