import {
  BadRequestException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import * as crypto from 'node:crypto';
import * as fs from 'node:fs/promises';
import * as path from 'node:path';
import { PrismaService } from '../prisma/prisma.service';
import { AuditLogService } from '../audit/audit-log.service';
import { matchesFileSignature } from '../common/file-signature';
import { Document, DocumentEntityType } from '../../generated/prisma';
import { ALLOWED_DOCUMENT_MIME_TYPES } from './document-mime-types';
import { UpdateDocumentDto } from './dto/update-document.dto';

export type DocumentSummary = Omit<Document, 'storagePath'>;

function storageRoot(): string {
  return process.env.DOCUMENTS_STORAGE_PATH ?? './uploads';
}

function toSummary(document: Document): DocumentSummary {
  return {
    id: document.id,
    entityType: document.entityType,
    entityId: document.entityId,
    fileName: document.fileName,
    mimeType: document.mimeType,
    sizeBytes: document.sizeBytes,
    uploadedByUserId: document.uploadedByUserId,
    createdAt: document.createdAt,
  };
}

@Injectable()
export class DocumentsService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly auditLog: AuditLogService,
  ) {}

  async findAll(
    entityType: DocumentEntityType,
    entityId: string,
  ): Promise<DocumentSummary[]> {
    const documents = await this.prisma.document.findMany({
      where: { entityType, entityId },
      orderBy: { createdAt: 'desc' },
    });
    return documents.map(toSummary);
  }

  private async assertEntityExists(
    entityType: DocumentEntityType,
    entityId: string,
  ): Promise<void> {
    const exists = await (() => {
      switch (entityType) {
        case 'APIARY':
          return this.prisma.apiary.findUnique({ where: { id: entityId } });
        case 'COLONY':
          return this.prisma.colony.findUnique({ where: { id: entityId } });
        case 'QUEEN':
          return this.prisma.queen.findUnique({ where: { id: entityId } });
        case 'INSPECTION':
          return this.prisma.inspection.findUnique({
            where: { id: entityId },
          });
        case 'HONEY_BATCH':
          return this.prisma.honeyBatch.findUnique({
            where: { id: entityId },
          });
        default:
          return Promise.resolve(null);
      }
    })();
    if (!exists) {
      throw new NotFoundException(`${entityType} ${entityId} not found`);
    }
  }

  async create(
    file: Express.Multer.File,
    entityType: DocumentEntityType,
    entityId: string,
    actingUserId: string,
  ): Promise<DocumentSummary> {
    if (!(file.mimetype in ALLOWED_DOCUMENT_MIME_TYPES)) {
      throw new BadRequestException('Nicht unterstützter Dateityp');
    }
    if (!matchesFileSignature(file.buffer, file.mimetype)) {
      throw new BadRequestException(
        'Datei entspricht nicht dem angegebenen Format',
      );
    }
    await this.assertEntityExists(entityType, entityId);

    const extension = ALLOWED_DOCUMENT_MIME_TYPES[file.mimetype];
    const storageFileName = `${crypto.randomUUID()}${extension}`;
    const directory = path.join(storageRoot(), entityType.toLowerCase());
    await fs.mkdir(directory, { recursive: true });
    const storagePath = path.join(directory, storageFileName);
    await fs.writeFile(storagePath, file.buffer);

    const document = await this.prisma.document.create({
      data: {
        entityType,
        entityId,
        fileName: file.originalname,
        mimeType: file.mimetype,
        sizeBytes: file.size,
        storagePath,
        uploadedByUserId: actingUserId,
      },
    });
    await this.auditLog.record({
      entityType: 'Document',
      entityId: document.id,
      action: 'CREATE',
      userId: actingUserId,
      afterData: toSummary(document),
    });
    return toSummary(document);
  }

  async readFile(
    id: string,
  ): Promise<{ buffer: Buffer; fileName: string; mimeType: string }> {
    const document = await this.prisma.document.findUnique({
      where: { id },
    });
    if (!document) {
      throw new NotFoundException('Document not found');
    }
    const buffer = await fs.readFile(document.storagePath);
    return {
      buffer,
      fileName: document.fileName,
      mimeType: document.mimeType,
    };
  }

  /**
   * Re-links a document to a different record or corrects its display name.
   * The stored file is untouched - replacing the content means uploading a
   * new document.
   */
  async update(
    id: string,
    dto: UpdateDocumentDto,
    actingUserId: string,
  ): Promise<DocumentSummary> {
    const before = await this.prisma.document.findUnique({ where: { id } });
    if (!before) {
      throw new NotFoundException('Document not found');
    }
    const entityType = dto.entityType ?? before.entityType;
    const entityId = dto.entityId ?? before.entityId;
    if (entityType !== before.entityType || entityId !== before.entityId) {
      await this.assertEntityExists(entityType, entityId);
    }
    const document = await this.prisma.document.update({
      where: { id },
      data: { entityType, entityId, fileName: dto.fileName },
    });
    await this.auditLog.record({
      entityType: 'Document',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
      beforeData: toSummary(before),
      afterData: toSummary(document),
    });
    return toSummary(document);
  }

  async delete(id: string, actingUserId: string): Promise<void> {
    const document = await this.prisma.document.findUnique({
      where: { id },
    });
    if (!document) {
      throw new NotFoundException('Document not found');
    }
    await this.prisma.document.delete({ where: { id } });
    await fs.unlink(document.storagePath).catch(() => undefined);
    await this.auditLog.record({
      entityType: 'Document',
      entityId: id,
      action: 'DELETE',
      userId: actingUserId,
      beforeData: toSummary(document),
    });
  }
}