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

import { db } from '@/lib/db';
import { documentFolders, documents, type DocumentFolder } from '@/lib/db/schema/documents';
import { createAuditLog } from '@/lib/audit';
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;
  }
}

/**
 * Renames a folder. Throws ConflictError if a sibling with the same
 * case-insensitive name already exists. Throws NotFoundError if the
 * folder doesn't belong to the given port (cross-port leakage guard).
 */
export async function renameFolder(
  portId: string,
  folderId: string,
  newName: string,
): Promise<DocumentFolder> {
  const trimmed = newName.trim();
  if (!trimmed) throw new ValidationError('Folder name cannot be empty');
  if (trimmed.length > 200) throw new ValidationError('Folder name cannot exceed 200 chars');

  const existing = await db.query.documentFolders.findFirst({
    where: and(eq(documentFolders.id, folderId), eq(documentFolders.portId, portId)),
  });
  if (!existing) throw new NotFoundError('Folder');

  try {
    const [updated] = await db
      .update(documentFolders)
      .set({ name: trimmed, updatedAt: new Date() })
      .where(eq(documentFolders.id, folderId))
      .returning();
    if (!updated) throw new NotFoundError('Folder');
    return updated;
  } catch (err) {
    if (isSiblingNameConflict(err)) {
      throw new ConflictError(`A folder named "${trimmed}" already exists here`);
    }
    throw err;
  }
}

/**
 * Moves a folder to a new parent (or to root with newParentId=null).
 * Walks the destination's ancestor chain to detect cycles before
 * writing. Throws ValidationError for cycle/invalid-parent, NotFoundError
 * for cross-port access.
 */
export async function moveFolder(
  portId: string,
  folderId: string,
  newParentId: string | null,
): Promise<DocumentFolder> {
  if (newParentId === folderId) {
    throw new ValidationError('Cannot move a folder under itself (cycle)');
  }

  const folder = await db.query.documentFolders.findFirst({
    where: and(eq(documentFolders.id, folderId), eq(documentFolders.portId, portId)),
  });
  if (!folder) throw new NotFoundError('Folder');

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

    // Cycle check: walk the destination's ancestor chain. If we hit
    // folderId, the destination is a descendant of the folder being
    // moved — moving would create a cycle.
    let cursor: string | null = newParent.parentId;
    const seen = new Set<string>([newParent.id]);
    while (cursor) {
      if (cursor === folderId) {
        throw new ValidationError('Cannot move a folder under one of its descendants (cycle)');
      }
      if (seen.has(cursor)) break; // defensive — pre-existing cycle, bail
      seen.add(cursor);
      const next = await db.query.documentFolders.findFirst({
        where: eq(documentFolders.id, cursor),
        columns: { parentId: true },
      });
      cursor = next?.parentId ?? null;
    }
  }

  try {
    const [updated] = await db
      .update(documentFolders)
      .set({ parentId: newParentId, updatedAt: new Date() })
      .where(eq(documentFolders.id, folderId))
      .returning();
    if (!updated) throw new NotFoundError('Folder');
    return updated;
  } catch (err) {
    if (isSiblingNameConflict(err)) {
      throw new ConflictError('A folder with that name already exists in the destination');
    }
    throw err;
  }
}

/**
 * Soft-rescue delete: re-parent every child folder + every linked
 * document to the deleted folder's parent (or to root if the deleted
 * folder is at root). Audit-logged. Wrapped in a transaction so
 * partial failures don't leave dangling rows.
 */
export async function deleteFolderSoftRescue(
  portId: string,
  folderId: string,
  userId: string,
): Promise<void> {
  await db.transaction(async (tx) => {
    const folder = await tx.query.documentFolders.findFirst({
      where: and(eq(documentFolders.id, folderId), eq(documentFolders.portId, portId)),
    });
    if (!folder) throw new NotFoundError('Folder');

    const newParent = folder.parentId; // null = re-parent to root

    await tx
      .update(documentFolders)
      .set({ parentId: newParent, updatedAt: new Date() })
      .where(
        and(
          eq(documentFolders.parentId, folderId),
          eq(documentFolders.portId, portId),
        ),
      );

    await tx
      .update(documents)
      .set({ folderId: newParent, updatedAt: new Date() })
      .where(and(eq(documents.folderId, folderId), eq(documents.portId, portId)));

    await tx.delete(documentFolders).where(eq(documentFolders.id, folderId));

    void createAuditLog({
      userId,
      portId,
      action: 'delete',
      entityType: 'document_folder',
      entityId: folderId,
      oldValue: { name: folder.name, parentId: folder.parentId },
      metadata: { rescuedTo: newParent },
    });
  });
}