import { and, asc, eq } from 'drizzle-orm';

import { db } from '@/lib/db';
import { documentFolders, type DocumentFolder } from '@/lib/db/schema/documents';
import { ConflictError, NotFoundError, ValidationError } from '@/lib/errors';

/**
 * Returns true if the error is a Postgres unique-violation (SQLSTATE 23505)
 * raised specifically on the sibling-name unique index. Narrowing to this
 * constraint prevents swallowing unrelated unique violations.
 */
function isSiblingNameConflict(err: unknown): boolean {
  if (!err || typeof err !== 'object') return false;
  const e = err as {
    code?: unknown;
    constraint_name?: unknown;
    constraint?: unknown;
    cause?: { code?: unknown; constraint_name?: unknown; constraint?: unknown };
  };
  const code = e.code ?? e.cause?.code;
  if (code !== '23505') return false;
  const constraint =
    e.constraint_name ?? e.constraint ?? e.cause?.constraint_name ?? e.cause?.constraint;
  return constraint === 'uniq_document_folders_sibling_name';
}

export interface FolderNode extends DocumentFolder {
  children: FolderNode[];
}

/**
 * Returns the entire folder tree for a port, nested under their
 * parents. Roots come back at the top level. Order is alphabetical
 * (case-insensitive) within each parent — matches the sibling-uniqueness
 * index ordering and gives reps a stable browsing experience.
 *
 * Uses a single SELECT + JS nesting rather than a recursive CTE; the
 * folder tree is small (UI gates depth; thousands of folders would be
 * a misuse) so the in-memory build is cheaper than a CTE round-trip.
 */
export async function listTree(portId: string): Promise<FolderNode[]> {
  const rows = await db
    .select()
    .from(documentFolders)
    .where(eq(documentFolders.portId, portId))
    .orderBy(asc(documentFolders.name));

  const byId = new Map<string, FolderNode>();
  for (const row of rows) byId.set(row.id, { ...row, children: [] });

  const roots: FolderNode[] = [];
  for (const node of byId.values()) {
    if (node.parentId === null) {
      roots.push(node);
    } else {
      const parent = byId.get(node.parentId);
      if (parent) parent.children.push(node);
      // Orphan rows (parentId pointing nowhere) are dropped from the
      // tree but stay in the DB. Surface via a separate maintenance
      // query if needed; never silently re-parent.
    }
  }
  return roots;
}

interface CreateFolderInput {
  name: string;
  parentId: string | null;
}

/**
 * Creates a folder under the given parent. Throws ConflictError when
 * a sibling with the same case-insensitive name already exists (the
 * DB unique index is the authoritative guard; this maps the Postgres
 * 23505 to the typed error). Throws ValidationError when `parentId`
 * doesn't belong to this port (cross-port leakage guard).
 */
export async function createFolder(
  portId: string,
  userId: string,
  data: CreateFolderInput,
): Promise<DocumentFolder> {
  const trimmed = data.name.trim();
  if (!trimmed) throw new ValidationError('Folder name cannot be empty');
  if (trimmed.length > 200) throw new ValidationError('Folder name cannot exceed 200 chars');

  if (data.parentId !== null) {
    const parent = await db.query.documentFolders.findFirst({
      where: and(eq(documentFolders.id, data.parentId), eq(documentFolders.portId, portId)),
    });
    if (!parent) throw new ValidationError('Invalid parent folder');
  }

  try {
    const [row] = await db
      .insert(documentFolders)
      .values({
        portId,
        parentId: data.parentId,
        name: trimmed,
        createdBy: userId,
      })
      .returning();
    if (!row) throw new NotFoundError('Folder');
    return row;
  } catch (err) {
    if (isSiblingNameConflict(err)) {
      throw new ConflictError(`A folder named "${trimmed}" already exists here`);
    }
    throw err;
  }
}