import {
  APIErrorCode,
  APIException,
  type Category,
  type CreateCategoryRequest,
  type Dump,
  type UpdateCategoryRequest,
} from "../model/interfaces.ts";
import {
  categoryRowToApi,
  db,
  DUMP_SELECT_COLUMNS_ALIASED as SELECT_COLS_ALIASED,
  dumpRowToApi,
  isCategoryRow,
  isDumpRow,
} from "../model/db.ts";
import { isReservedSlug, isValidSlugFormat } from "../lib/reserved-slugs.ts";
import { VALIDATION } from "../config.ts";

function validateSlug(slug: string): void {
  if (!isValidSlugFormat(slug)) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      "Slug must be lowercase letters, numbers and hyphens",
    );
  }
  if (slug.length > VALIDATION.CATEGORY_SLUG_MAX) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      `Slug must be at most ${VALIDATION.CATEGORY_SLUG_MAX} characters`,
    );
  }
  if (isReservedSlug(slug)) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      `Slug "${slug}" is reserved`,
    );
  }
}

function requireName(name: string): string {
  const trimmed = name.trim();
  if (!trimmed) {
    throw new APIException(APIErrorCode.BAD_REQUEST, 400, "Name is required");
  }
  if (trimmed.length > VALIDATION.CATEGORY_NAME_MAX) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      `Name must be at most ${VALIDATION.CATEGORY_NAME_MAX} characters`,
    );
  }
  return trimmed;
}

// Maps SQLite UNIQUE violations to a friendly 409 naming the offending field.
function uniqueConflict(err: unknown, slug: string, name: string): never {
  const msg = err instanceof Error ? err.message : String(err);
  if (msg.includes("categories.name")) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      409,
      `Name "${name}" is already in use`,
    );
  }
  if (msg.includes("UNIQUE") || msg.includes("unique")) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      409,
      `Slug "${slug}" is already in use`,
    );
  }
  throw err as Error;
}

export function getCategoryById(id: string): Category {
  const row = db.prepare(`SELECT * FROM categories WHERE id = ?;`).get(id);
  if (!row || !isCategoryRow(row)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "Category not found");
  }
  return categoryRowToApi(row);
}

export function getCategoryBySlug(slug: string): Category {
  const row = db.prepare(`SELECT * FROM categories WHERE slug = ?;`).get(slug);
  if (!row || !isCategoryRow(row)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "Category not found");
  }
  return categoryRowToApi(row);
}

/** Resolve a slug to its category id, or undefined if no such category. */
export function getCategoryIdBySlug(slug: string): string | undefined {
  const row = db.prepare(`SELECT id FROM categories WHERE slug = ?;`).get(slug);
  return row && typeof (row as { id?: unknown }).id === "string"
    ? (row as { id: string }).id
    : undefined;
}

export function listCategories(): Category[] {
  const rows = db.prepare(
    `SELECT * FROM categories ORDER BY position ASC, slug ASC;`,
  ).all();
  return rows.filter(isCategoryRow).map(categoryRowToApi);
}

export function createCategory(req: CreateCategoryRequest): Category {
  validateSlug(req.slug);
  const name = requireName(req.name);

  const id = crypto.randomUUID();
  const createdAt = new Date();
  try {
    db.prepare(
      `INSERT INTO categories (id, slug, name, position, created_at)
       VALUES (?, ?, ?, ?, ?);`,
    ).run(
      id,
      req.slug,
      name,
      req.position ?? 0,
      createdAt.toISOString(),
    );
  } catch (err) {
    uniqueConflict(err, req.slug, name);
  }

  return {
    id,
    slug: req.slug,
    name,
    position: req.position ?? 0,
    createdAt,
  };
}

export function updateCategory(
  id: string,
  req: UpdateCategoryRequest,
): Category {
  const existing = getCategoryById(id);

  const newSlug = req.slug ?? existing.slug;
  if (req.slug !== undefined && req.slug !== existing.slug) {
    validateSlug(req.slug);
  }
  const newName = req.name !== undefined ? requireName(req.name) : existing.name;
  const newPosition = req.position ?? existing.position;
  const now = new Date();

  try {
    db.prepare(
      `UPDATE categories SET slug = ?, name = ?, position = ?, updated_at = ? WHERE id = ?;`,
    ).run(
      newSlug,
      newName,
      newPosition,
      now.toISOString(),
      id,
    );
  } catch (err) {
    uniqueConflict(err, newSlug, newName);
  }

  return {
    ...existing,
    slug: newSlug,
    name: newName,
    position: newPosition,
    updatedAt: now,
  };
}

export function deleteCategory(id: string): void {
  const result = db.prepare(`DELETE FROM categories WHERE id = ?;`).run(id);
  if (result.changes === 0) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "Category not found");
  }
}

/**
 * Replace the set of categories a dump belongs to. Unknown category ids are
 * rejected. An empty list clears all category assignments.
 */
export function setDumpCategories(
  dumpId: string,
  categoryIds: string[],
): void {
  const unique = [...new Set(categoryIds)];

  if (unique.length > 0) {
    const placeholders = unique.map(() => "?").join(", ");
    const found = db.prepare(
      `SELECT COUNT(*) as count FROM categories WHERE id IN (${placeholders});`,
    ).get(...unique) as { count: number } | undefined;
    if ((found?.count ?? 0) !== unique.length) {
      throw new APIException(
        APIErrorCode.BAD_REQUEST,
        400,
        "One or more categories do not exist",
      );
    }
  }

  db.prepare(`DELETE FROM dump_categories WHERE dump_id = ?;`).run(dumpId);
  const insert = db.prepare(
    `INSERT INTO dump_categories (dump_id, category_id) VALUES (?, ?);`,
  );
  for (const categoryId of unique) {
    insert.run(dumpId, categoryId);
  }
}

/** Fill `categoryIds` on each dump with a single batched lookup. */
export function attachCategoryIds(dumps: Dump[]): void {
  if (dumps.length === 0) return;
  const ids = dumps.map((d) => d.id);
  const placeholders = ids.map(() => "?").join(", ");
  const rows = db.prepare(
    `SELECT dump_id, category_id FROM dump_categories WHERE dump_id IN (${placeholders});`,
  ).all(...ids) as Array<{ dump_id: string; category_id: string }>;

  const byDump = new Map<string, string[]>();
  for (const { dump_id, category_id } of rows) {
    const list = byDump.get(dump_id) ?? [];
    list.push(category_id);
    byDump.set(dump_id, list);
  }
  for (const dump of dumps) {
    dump.categoryIds = byDump.get(dump.id) ?? [];
  }
}

export function listDumpsByCategory(
  slug: string,
  page: number,
  limit: number,
  requestingUserId?: string,
): { items: Dump[]; total: number } {
  const category = getCategoryBySlug(slug);
  const offset = (page - 1) * limit;

  const privacyClause = requestingUserId
    ? "(d.is_private = 0 OR d.user_id = ?)"
    : "d.is_private = 0";
  const privacyParams = requestingUserId ? [requestingUserId] : [];

  const rows = db.prepare(
    `SELECT ${SELECT_COLS_ALIASED}
     FROM dumps d
     INNER JOIN dump_categories dc ON dc.dump_id = d.id
     WHERE dc.category_id = ? AND ${privacyClause}
     ORDER BY d.created_at DESC LIMIT ? OFFSET ?;`,
  ).all(category.id, ...privacyParams, limit, offset);

  const totalRow = db.prepare(
    `SELECT COUNT(*) as count
     FROM dumps d
     INNER JOIN dump_categories dc ON dc.dump_id = d.id
     WHERE dc.category_id = ? AND ${privacyClause};`,
  ).get(category.id, ...privacyParams) as { count: number } | undefined;

  const items = rows.filter(isDumpRow).map(dumpRowToApi);
  attachCategoryIds(items);
  return { items, total: totalRow?.count ?? 0 };
}