import { createHash } from 'node:crypto';
import { readFile } from 'node:fs/promises';
import { join } from 'node:path';

import { BadRequestException, Injectable, NotFoundException } from '@nestjs/common';
import {
  BrandingAsset,
  BrandingView,
  FAVICON_SIZES,
  FaviconSize,
  LOGO_VARIANTS,
  LogoVariant,
  PondBranding,
  pondSettingsSchema,
  MAX_BRANDING_BYTES,
  MAX_LOGO_EDGE,
  hasPngMagic,
  looksLikeSvg,
  pngDimensions,
} from '@dorfteich/shared';
import { User } from '@prisma/client';

import { AuditService } from '../audit/audit.service';
import { PrismaService } from '../prisma/prisma.service';
import { QuotaService } from '../quotas/quota.service';
import { InstanceSettingsService } from '../settings/instance-settings.service';
import { BrandingStorageService } from './branding-storage.service';

/** The settings key each instance asset's metadata lives under. */
const INSTANCE_KEYS = {
  logoLight: 'instance.logo',
  logoDark: 'instance.logoDark',
  favicon: 'instance.favicon',
} as const;

/**
 * Instance branding (issue #306): the logo shown at the top of the sidebar and
 * the favicon served to the browser.
 *
 * The api stores and serves bytes; it never decodes them. Validation is the
 * PNG signature, the IHDR dimensions and the size cap — see
 * `packages/shared/src/branding.ts` for why that line is drawn there.
 */
@Injectable()
export class BrandingService {
  constructor(
    private readonly settings: InstanceSettingsService,
    private readonly storage: BrandingStorageService,
    private readonly audit: AuditService,
    private readonly prisma: PrismaService,
    private readonly quotas: QuotaService,
  ) {}

  static logoKey(variant: LogoVariant): string {
    return `instance-logo-${variant}`;
  }

  static faviconKey(size: FaviconSize): string {
    return `instance-favicon-${size}`;
  }

  /** Pond assets share the directory and the naming rules (issue #307); the
   *  pond id keeps them apart and makes purge a prefix delete. */
  static pondLogoKey(pondId: string, variant: LogoVariant): string {
    return `pond-${pondId}-logo-${variant}`;
  }

  static pondFaviconKey(pondId: string, size: FaviconSize): string {
    return `pond-${pondId}-favicon-${size}`;
  }

  /** Every branding file a pond can own — the purge deletes exactly this set
   *  (issue #307). The purge standard is absolute: after it, nothing
   *  referencing the pond survives, rows or files. */
  static pondKeys(pondId: string): string[] {
    return [
      ...LOGO_VARIANTS.map((variant) => BrandingService.pondLogoKey(pondId, variant)),
      ...FAVICON_SIZES.map((size) => BrandingService.pondFaviconKey(pondId, size)),
    ];
  }

  /**
   * Rejects anything that is not a PNG within the caps, before a byte is
   * written. SVG gets its own message: an operator who tried one deserves to
   * learn that it is refused on purpose, not that "the file is broken".
   */
  private assertUsablePng(bytes: Buffer, maxEdge: number): { width: number; height: number } {
    if (bytes.length === 0) throw new BadRequestException({ code: 'branding_file_empty' });
    if (bytes.length > MAX_BRANDING_BYTES) {
      throw new BadRequestException({ code: 'branding_file_too_large' });
    }
    if (looksLikeSvg(bytes)) throw new BadRequestException({ code: 'branding_svg_rejected' });
    if (!hasPngMagic(bytes)) throw new BadRequestException({ code: 'branding_not_a_png' });
    const size = pngDimensions(bytes);
    if (!size) throw new BadRequestException({ code: 'branding_not_a_png' });
    if (size.width > maxEdge || size.height > maxEdge) {
      throw new BadRequestException({ code: 'branding_image_too_large' });
    }
    return size;
  }

  /**
   * Reserve the pond's storage for a branding asset, releasing what the asset
   * it replaces occupied. Doing it in that order means replacing a logo with
   * one of the same size costs nothing — otherwise every re-upload would eat
   * the quota again, which is how "a pond admin fills the disk with logos"
   * happens.
   */
  private async chargeQuota(
    pond: { id: string; ownerId: string },
    bytes: number,
    previous: BrandingAsset | null,
  ): Promise<void> {
    if (previous?.byteSize) await this.quotas.release(pond.id, previous.byteSize);
    try {
      await this.quotas.checkAndConsume(pond.id, pond.ownerId, bytes);
    } catch (error) {
      // Put the released reservation back: a refused upload must not leave
      // the pond with MORE room than before.
      if (previous?.byteSize) {
        await this.quotas.checkAndConsume(pond.id, pond.ownerId, previous.byteSize);
      }
      throw error;
    }
  }

  private assetOf(bytes: Buffer, size: { width: number; height: number }): BrandingAsset {
    return {
      // Short digest: it only has to change when the bytes change, and it
      // travels in every logo URL.
      hash: createHash('sha256').update(bytes).digest('hex').slice(0, 16),
      byteSize: bytes.length,
      ...size,
    };
  }

  async view(): Promise<BrandingView> {
    const [logo, logoDark, favicon, instanceName] = await Promise.all([
      this.settings.get(INSTANCE_KEYS.logoLight),
      this.settings.get(INSTANCE_KEYS.logoDark),
      this.settings.get(INSTANCE_KEYS.favicon),
      this.settings.get('instance.name'),
    ]);
    return { logo, logoDark, favicon, instanceName };
  }

  async setLogo(admin: User, variant: LogoVariant, bytes: Buffer): Promise<BrandingView> {
    const size = this.assertUsablePng(bytes, MAX_LOGO_EDGE);
    await this.storage.save(BrandingService.logoKey(variant), bytes);
    await this.settings.set(
      variant === 'dark' ? INSTANCE_KEYS.logoDark : INSTANCE_KEYS.logoLight,
      this.assetOf(bytes, size),
      admin.id,
    );
    await this.record(admin, variant === 'dark' ? 'logoDark' : 'logo', 'set');
    return this.view();
  }

  async clearLogo(admin: User, variant: LogoVariant): Promise<BrandingView> {
    await this.storage.remove(BrandingService.logoKey(variant));
    await this.settings.set(
      variant === 'dark' ? INSTANCE_KEYS.logoDark : INSTANCE_KEYS.logoLight,
      null,
      admin.id,
    );
    await this.record(admin, variant === 'dark' ? 'logoDark' : 'logo', 'cleared');
    return this.view();
  }

  /**
   * Both favicon sizes arrive together: the browser produced them from one
   * source on the same canvas, and the api cannot resize. Storing them as a
   * pair keeps the tab icon and the home-screen icon from ever showing two
   * different images.
   */
  async setFavicon(admin: User, files: Record<FaviconSize, Buffer>): Promise<BrandingView> {
    const sizes = Object.entries(files).map(([declared, bytes]) => {
      const size = this.assertUsablePng(bytes, 512);
      const expected = Number(declared);
      if (size.width !== expected || size.height !== expected) {
        throw new BadRequestException({ code: 'branding_favicon_not_square' });
      }
      return { expected: expected as FaviconSize, bytes, size };
    });
    for (const entry of sizes) {
      await this.storage.save(BrandingService.faviconKey(entry.expected), entry.bytes);
    }
    // The 32px variant identifies the pair — it is what the tab shows.
    const small = sizes.find((entry) => entry.expected === 32)!;
    await this.settings.set(INSTANCE_KEYS.favicon, this.assetOf(small.bytes, small.size), admin.id);
    await this.record(admin, 'favicon', 'set');
    return this.view();
  }

  async clearFavicon(admin: User): Promise<BrandingView> {
    await this.storage.remove(BrandingService.faviconKey(32));
    await this.storage.remove(BrandingService.faviconKey(180));
    await this.settings.set(INSTANCE_KEYS.favicon, null, admin.id);
    await this.record(admin, 'favicon', 'cleared');
    return this.view();
  }

  /** The bytes to serve for a logo variant, or null when none is stored. */
  logoBytes(variant: LogoVariant): Promise<Buffer | null> {
    return this.storage.read(BrandingService.logoKey(variant));
  }

  /**
   * The favicon bytes: the uploaded one, else the shipped default. The
   * `<link rel="icon">` in index.html is static, so this route must always
   * answer with an image — a 404 there would leave the browser's generic
   * icon for good.
   */
  async faviconBytes(size: FaviconSize): Promise<{ bytes: Buffer; uploaded: boolean }> {
    const stored = await this.storage.read(BrandingService.faviconKey(size));
    if (stored) return { bytes: stored, uploaded: true };
    const bytes = await readFile(join(__dirname, '../../assets', `default-favicon-${size}.png`));
    return { bytes, uploaded: false };
  }

  /** The pond's own branding, defaulted — one place reads the settings blob. */
  async pondBranding(pondId: string): Promise<PondBranding> {
    const pond = await this.prisma.pond.findUnique({
      where: { id: pondId },
      select: { settings: true },
    });
    if (!pond) throw new NotFoundException();
    return pondSettingsSchema.parse(pond.settings ?? {}).branding;
  }

  private async writePondBranding(
    actor: User,
    pondId: string,
    next: PondBranding,
    asset: 'logo' | 'logoDark' | 'favicon',
    change: 'set' | 'cleared',
  ): Promise<PondBranding> {
    const pond = await this.prisma.pond.findUniqueOrThrow({
      where: { id: pondId },
      select: { settings: true },
    });
    const settings = pondSettingsSchema.parse(pond.settings ?? {});
    await this.prisma.pond.update({
      where: { id: pondId },
      data: { settings: { ...settings, branding: next } as object },
    });
    await this.audit.record({
      action: 'branding.changed',
      actorId: actor.id,
      targetType: 'pond',
      targetId: pondId,
      details: { scope: 'pond', pondId, asset, change },
    });
    return next;
  }

  /**
   * A pond logo, charged to the pond's storage quota (issue #307).
   *
   * Without the charge, branding would be a way around the quota — and
   * replacing a logo repeatedly would let a pond admin consume disk with no
   * ceiling. Charged BEFORE the write, like attachments, so a race never
   * leaves bytes on the volume without a reservation; the bytes a replaced
   * asset frees are released first, so re-uploading the same logo is free
   * rather than cumulative.
   */
  async setPondLogo(
    actor: User,
    pond: { id: string; ownerId: string },
    variant: LogoVariant,
    bytes: Buffer,
  ): Promise<PondBranding> {
    const size = this.assertUsablePng(bytes, MAX_LOGO_EDGE);
    const current = await this.pondBranding(pond.id);
    const previous = variant === 'dark' ? current.logoDark : current.logo;
    await this.chargeQuota(pond, bytes.length, previous);
    await this.storage.save(BrandingService.pondLogoKey(pond.id, variant), bytes);
    const asset = this.assetOf(bytes, size);
    return this.writePondBranding(
      actor,
      pond.id,
      variant === 'dark' ? { ...current, logoDark: asset } : { ...current, logo: asset },
      variant === 'dark' ? 'logoDark' : 'logo',
      'set',
    );
  }

  async clearPondLogo(
    actor: User,
    pond: { id: string; ownerId: string },
    variant: LogoVariant,
  ): Promise<PondBranding> {
    const current = await this.pondBranding(pond.id);
    const previous = variant === 'dark' ? current.logoDark : current.logo;
    await this.storage.remove(BrandingService.pondLogoKey(pond.id, variant));
    if (previous?.byteSize) await this.quotas.release(pond.id, previous.byteSize);
    return this.writePondBranding(
      actor,
      pond.id,
      variant === 'dark' ? { ...current, logoDark: null } : { ...current, logo: null },
      variant === 'dark' ? 'logoDark' : 'logo',
      'cleared',
    );
  }

  async setPondFavicon(
    actor: User,
    pond: { id: string; ownerId: string },
    files: Record<FaviconSize, Buffer>,
  ): Promise<PondBranding> {
    const checked = Object.entries(files).map(([declared, bytes]) => {
      const size = this.assertUsablePng(bytes, 512);
      const expected = Number(declared);
      if (size.width !== expected || size.height !== expected) {
        throw new BadRequestException({ code: 'branding_favicon_not_square' });
      }
      return { expected: expected as FaviconSize, bytes, size };
    });
    const current = await this.pondBranding(pond.id);
    const total = checked.reduce((sum, entry) => sum + entry.bytes.length, 0);
    await this.chargeQuota(pond, total, current.favicon);
    for (const entry of checked) {
      await this.storage.save(BrandingService.pondFaviconKey(pond.id, entry.expected), entry.bytes);
    }
    const small = checked.find((entry) => entry.expected === 32)!;
    // The pair is charged together, so the stored size is the pair's — that
    // is what a later release has to give back.
    const asset = { ...this.assetOf(small.bytes, small.size), byteSize: total };
    return this.writePondBranding(actor, pond.id, { ...current, favicon: asset }, 'favicon', 'set');
  }

  async clearPondFavicon(
    actor: User,
    pond: { id: string; ownerId: string },
  ): Promise<PondBranding> {
    const current = await this.pondBranding(pond.id);
    for (const size of FAVICON_SIZES) {
      await this.storage.remove(BrandingService.pondFaviconKey(pond.id, size));
    }
    if (current.favicon?.byteSize) await this.quotas.release(pond.id, current.favicon.byteSize);
    return this.writePondBranding(
      actor,
      pond.id,
      { ...current, favicon: null },
      'favicon',
      'cleared',
    );
  }

  /** Bytes for a pond asset — null when the pond has none at that slot, which
   *  is what makes the caller fall back to the instance level. */
  pondLogoBytes(pondId: string, variant: LogoVariant): Promise<Buffer | null> {
    return this.storage.read(BrandingService.pondLogoKey(pondId, variant));
  }

  pondFaviconBytes(pondId: string, size: FaviconSize): Promise<Buffer | null> {
    return this.storage.read(BrandingService.pondFaviconKey(pondId, size));
  }

  /** Removes every branding file of a pond (issue #307's purge obligation). */
  async removePondAssets(pondId: string): Promise<void> {
    for (const key of BrandingService.pondKeys(pondId)) await this.storage.remove(key);
  }

  private record(
    admin: User,
    asset: 'logo' | 'logoDark' | 'favicon',
    action: 'set' | 'cleared',
  ): Promise<unknown> {
    // `scope` is here from the start so the pond-level change (#307) is the
    // same event with a different scope, not a second id in the catalogue.
    return this.audit.record({
      action: 'branding.changed',
      actorId: admin.id,
      targetType: 'setting',
      targetId: `instance.${asset}`,
      details: { scope: 'instance', asset, change: action },
    });
  }
}