import { randomUUID } from 'node:crypto';
import type { Readable } from 'node:stream';

import {
  BadRequestException,
  Injectable,
  NotFoundException,
  PayloadTooLargeException,
} from '@nestjs/common';
import {
  ATTACHMENT_EXTENSION_MIME_TYPES,
  AttachmentListItemView,
  AttachmentView,
  PondFilesView,
  SVG_MIME_TYPE,
  fileExtension,
  isImageMimeType,
} from '@dorfteich/shared';
import { Attachment, User } from '@prisma/client';
import { PinoLogger } from 'nestjs-pino';

import { PrismaService } from '../prisma/prisma.service';
import { QuotaService } from '../quotas/quota.service';
import { InstanceSettingsService } from '../settings/instance-settings.service';

import { FileStorageService } from './file-storage.service';
import { looksLikeSvg, sniffImageMimeType } from './magic-bytes';
import { sanitizeSvg } from './svg-sanitize';

export interface FileDownload {
  attachment: Attachment;
  stream: Readable;
  /** Raster images render inline (they are embedded in pages); everything
   * else — office files, PDFs, and SVG — is always sent as a download so it
   * can never execute inline (ADR 0011, security.md §Uploads). */
  inline: boolean;
}

/** What the upload bytes resolved to after allowlist + SVG handling. */
interface ResolvedUpload {
  mimeType: string;
  /** The bytes to store — identical to the input except for a sanitized SVG. */
  buffer: Buffer;
}

/** File storage, upload, and attachment listing API (issue #27, #61, ADR 0011). */
@Injectable()
export class FilesService {
  constructor(
    private readonly prisma: PrismaService,
    private readonly quotas: QuotaService,
    private readonly storage: FileStorageService,
    private readonly settings: InstanceSettingsService,
    private readonly logger: PinoLogger,
  ) {
    this.logger.setContext(FilesService.name);
  }

  viewOf(attachment: Attachment): AttachmentView {
    return {
      id: attachment.id,
      pondId: attachment.pondId,
      pageId: attachment.pageId,
      fileName: attachment.fileName,
      mimeType: attachment.mimeType,
      sizeBytes: attachment.sizeBytes,
      createdAt: attachment.createdAt.toISOString(),
    };
  }

  /**
   * Decide the served MIME type and the bytes to persist. Raster images pass
   * the magic-byte sniff and are always allowed. An SVG is sanitized (its
   * scripts/handlers stripped) or rejected per the instance policy. Anything
   * else is admitted only if its extension is on the configurable allowlist;
   * its bytes are never trusted to be inert, but it is only ever downloaded,
   * never rendered.
   */
  private async resolveUpload(fileName: string, buffer: Buffer): Promise<ResolvedUpload> {
    const rasterMime = sniffImageMimeType(buffer);
    if (rasterMime) return { mimeType: rasterMime, buffer };

    if (looksLikeSvg(buffer)) {
      const policy = await this.settings.get('upload.svgPolicy');
      if (policy === 'reject') {
        throw new BadRequestException({ code: 'upload_type_not_allowed' });
      }
      let clean: string;
      try {
        clean = sanitizeSvg(buffer.toString('utf8'));
      } catch {
        throw new BadRequestException({ code: 'upload_type_not_allowed' });
      }
      return { mimeType: SVG_MIME_TYPE, buffer: Buffer.from(clean, 'utf8') };
    }

    const ext = fileExtension(fileName);
    const allowed = await this.settings.get('upload.allowedExtensions');
    if (!ext || !allowed.includes(ext)) {
      throw new BadRequestException({
        code: 'upload_type_not_allowed',
        details: { allowed },
      });
    }
    return { mimeType: ATTACHMENT_EXTENSION_MIME_TYPES[ext] ?? 'application/octet-stream', buffer };
  }

  /**
   * Store an upload against a pond, optionally linked to a page. `pageId` is
   * set for a page attachment (uploaded from the page's attachments section)
   * so it is listed there and purged with the page; image pastes leave it null
   * and the collab persistence hook links them to whichever page embeds them.
   */
  async upload(
    user: User,
    pondId: string,
    file: { buffer: Buffer; size: number; originalname: string },
    pageId?: string,
  ): Promise<AttachmentView> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
    if (!pond) throw new NotFoundException();

    const maxFileBytes = await this.quotas.getEffective('max_file_bytes', {
      userId: pond.ownerId,
      pondId: pond.id,
    });
    if (file.size > maxFileBytes) {
      throw new PayloadTooLargeException({
        code: 'file_too_large',
        details: { limitBytes: maxFileBytes },
      });
    }

    const resolved = await this.resolveUpload(file.originalname, file.buffer);
    // Account for what actually lands on the volume (a sanitized SVG is
    // usually smaller than the upload) so pond_usage matches disk exactly.
    const sizeBytes = resolved.buffer.length;

    const id = randomUUID();
    // Consume the storage budget before touching the disk so a race never
    // leaves bytes written without a matching reservation.
    await this.quotas.checkAndConsume(pond.id, pond.ownerId, sizeBytes);

    try {
      await this.storage.save(pond.id, id, resolved.buffer);
      const attachment = await this.prisma.attachment.create({
        data: {
          id,
          pondId: pond.id,
          pageId: pageId ?? null,
          fileName: file.originalname,
          mimeType: resolved.mimeType,
          sizeBytes,
          storagePath: `${pond.id}/${id}`,
          uploadedBy: user.id,
        },
      });
      this.logger.info(
        { attachmentId: id, pondId: pond.id, pageId: pageId ?? null, userId: user.id },
        'audit: file uploaded',
      );
      return this.viewOf(attachment);
    } catch (error) {
      // Roll back the reservation and any bytes already written so usage
      // never drifts from what is actually on the volume/in the database.
      await this.quotas.release(pond.id, sizeBytes);
      await this.storage.delete(pond.id, id);
      throw error;
    }
  }

  /**
   * Point a set of just-uploaded attachments at the page that now embeds them
   * (issue #63 import). The import worker stores a document's media before the
   * page exists (the page's Yjs state references their ids), then calls this so
   * they list under the page and are purged with it (#31), the same invariant
   * the collab persistence hook maintains for pasted images.
   */
  async linkAttachmentsToPage(attachmentIds: string[], pageId: string): Promise<void> {
    if (attachmentIds.length === 0) return;
    await this.prisma.attachment.updateMany({
      where: { id: { in: attachmentIds } },
      data: { pageId },
    });
  }

  /** Upload against the pond of `pageId`, linked to that page (#61). */
  async uploadToPage(
    user: User,
    pageId: string,
    file: { buffer: Buffer; size: number; originalname: string },
  ): Promise<AttachmentView> {
    const page = await this.prisma.page.findFirst({ where: { id: pageId } });
    if (!page) throw new NotFoundException();
    return this.upload(user, page.pondId, file, page.id);
  }

  async download(_user: User | null, id: string): Promise<FileDownload> {
    const attachment = await this.prisma.attachment.findFirst({ where: { id } });
    if (!attachment) throw new NotFoundException();
    return {
      attachment,
      stream: this.storage.createReadStream(attachment.pondId, attachment.id),
      inline: isImageMimeType(attachment.mimeType),
    };
  }

  /** Attachments linked to a page, for its attachments section (#61). */
  async listForPage(pageId: string): Promise<AttachmentListItemView[]> {
    const rows = await this.prisma.attachment.findMany({
      where: { pageId, deletedAt: null },
      orderBy: { createdAt: 'desc' },
      include: { uploader: true, page: true },
    });
    return rows.map((row) => this.listItemOf(row));
  }

  /** Every file in a pond, for the Pond Admin file manager (#61). */
  async listForPond(pondId: string): Promise<PondFilesView> {
    const [rows, usage, storageBytesLimit] = await Promise.all([
      this.prisma.attachment.findMany({
        where: { pondId, deletedAt: null },
        orderBy: { createdAt: 'desc' },
        include: { uploader: true, page: true },
      }),
      this.prisma.pondUsage.findUnique({ where: { pondId } }),
      this.pondStorageLimit(pondId),
    ]);
    return {
      files: rows.map((row) => this.listItemOf(row)),
      storageBytesUsed: Number(usage?.storageBytesUsed ?? 0n),
      storageBytesLimit,
    };
  }

  private async pondStorageLimit(pondId: string): Promise<number> {
    const pond = await this.prisma.pond.findUnique({ where: { id: pondId } });
    if (!pond) throw new NotFoundException();
    return this.quotas.getEffective('storage_bytes', { userId: pond.ownerId, pondId });
  }

  private listItemOf(
    row: Attachment & { uploader: User; page: { title: string } | null },
  ): AttachmentListItemView {
    return {
      ...this.viewOf(row),
      uploaderName: row.uploader.displayName,
      pageTitle: row.page?.title ?? null,
    };
  }

  async remove(user: User, id: string): Promise<void> {
    const attachment = await this.prisma.attachment.findFirst({ where: { id } });
    if (!attachment) throw new NotFoundException();

    await this.prisma.attachment.delete({ where: { id: attachment.id } });
    await this.storage.delete(attachment.pondId, attachment.id);
    await this.quotas.release(attachment.pondId, attachment.sizeBytes);
    this.logger.info(
      { attachmentId: id, pondId: attachment.pondId, userId: user.id },
      'audit: file deleted',
    );
  }
}