import {
  BadRequestException,
  ForbiddenException,
  HttpException,
  HttpStatus,
  Injectable,
  Logger,
  NotFoundException,
} from '@nestjs/common';
import { createHash, randomBytes, randomInt } from 'node:crypto';
import { PrismaService } from '../prisma/prisma.service';
import { AuditLogService } from '../audit/audit-log.service';
import { ApiKey } from '../../generated/prisma';
import { CreateApiKeyDto } from './dto/create-api-key.dto';
import {
  ApiKeyScope,
  combinesReadAndWrite,
  isApiKeyScope,
} from './api-key-scopes';
import { UpdateApiKeyDto } from './dto/update-api-key.dto';
import { isIpAllowed, normalizeAllowlistEntry } from './ip-allowlist';
import { PermissionResolverService } from '../auth/permissions/permission-resolver.service';
import {
  API_KEY_FAILURE_LIMIT,
  FailedAttemptLimiter,
} from './failed-attempt-limiter';
import { rateLimitSubject } from '../common/throttler/rate-limit-subject';

function normalizeAllowlist(entries: readonly string[] | undefined): string[] {
  return [
    ...new Set(
      (entries ?? [])
        .map(normalizeAllowlistEntry)
        .filter((entry): entry is string => entry !== null),
    ),
  ];
}

// ack_<8 lowercase chars>_<32 random bytes, base64url>
const TOKEN_PATTERN = /^ack_[a-z0-9]{8}_[A-Za-z0-9_-]{43}$/;
const PREFIX_ALPHABET = 'abcdefghijklmnopqrstuvwxyz0123456789';
// lastUsedAt is informational; writing it on every request would turn each
// read into a write for no benefit.
const LAST_USED_RESOLUTION_MS = 5 * 60 * 1000;
// "ack_" plus the 8-character prefix: identifies a key in logs without
// revealing its secret part.
const LOGGABLE_PREFIX_LENGTH = 12;

type RejectReason = 'unknown' | 'revoked' | 'expired';

/** What a request authenticated by an API key may do - it is not a user. */
export interface ApiKeyPrincipal {
  id: string;
  scopes: ApiKeyScope[];
}

/** An API key as shown in the admin UI - never the hash or the key itself. */
export type ApiKeySummary = Omit<ApiKey, 'keyHash'>;

export interface CreatedApiKey {
  apiKey: ApiKeySummary;
  /** The only time the plain key exists outside the caller's system. */
  token: string;
}

function hashToken(token: string): string {
  return createHash('sha256').update(token).digest('hex');
}

function randomPrefix(): string {
  let prefix = '';
  for (let i = 0; i < 8; i++) {
    prefix += PREFIX_ALPHABET[randomInt(PREFIX_ALPHABET.length)];
  }
  return `ack_${prefix}`;
}

function toSummary(apiKey: ApiKey): ApiKeySummary {
  const { keyHash, ...summary } = apiKey;
  void keyHash;
  return summary;
}

@Injectable()
export class ApiKeysService {
  private readonly logger = new Logger(ApiKeysService.name);

  constructor(
    private readonly prisma: PrismaService,
    private readonly auditLog: AuditLogService,
    private readonly permissionResolver: PermissionResolverService,
    // Counters shared by all api pods (ThrottlerHit), not process memory.
    private readonly failures: FailedAttemptLimiter,
  ) {}

  async findAll(): Promise<ApiKeySummary[]> {
    const keys = await this.prisma.apiKey.findMany({
      orderBy: { createdAt: 'desc' },
    });
    return keys.map(toSummary);
  }

  async create(
    dto: CreateApiKeyDto,
    actingUserId: string,
  ): Promise<CreatedApiKey> {
    // One scope per new key: a leaked read key cannot book, a leaked booking
    // key cannot read, and each connected system gets its own key.
    // Existing multi-scope keys stay valid (ARCHITECTURE.md, Annahme 14).
    if (combinesReadAndWrite(dto.scopes)) {
      throw new BadRequestException(
        'Lese- und Buchungsrecht bitte als getrennte Schlüssel anlegen',
      );
    }
    if (new Set(dto.scopes).size > 1) {
      throw new BadRequestException(
        'Je Schlüssel nur eine Berechtigung - bitte getrennte Schlüssel anlegen',
      );
    }
    // Nobody hands a machine more than they may do themselves.
    const callerPermissions =
      await this.permissionResolver.getPermissions(actingUserId);
    const missing = dto.scopes.filter((scope) => !callerPermissions.has(scope));
    if (missing.length > 0) {
      throw new ForbiddenException(
        `Diese Berechtigung haben Sie selbst nicht: ${missing.join(', ')}`,
      );
    }
    const prefix = randomPrefix();
    // 32 random bytes: a plain hash of it is safe to store without a slow
    // KDF - there is nothing guessable to brute-force.
    const token = `${prefix}_${randomBytes(32).toString('base64url')}`;
    const expiresAt =
      dto.expiresInDays !== undefined
        ? new Date(Date.now() + dto.expiresInDays * 24 * 60 * 60 * 1000)
        : null;

    const apiKey = await this.prisma.apiKey.create({
      data: {
        name: dto.name.trim(),
        prefix,
        keyHash: hashToken(token),
        scopes: [...new Set(dto.scopes)],
        allowedIps: normalizeAllowlist(dto.allowedIps),
        expiresAt,
        createdByUserId: actingUserId,
      },
    });
    const summary = toSummary(apiKey);
    await this.auditLog.record({
      entityType: 'ApiKey',
      entityId: apiKey.id,
      action: 'CREATE',
      userId: actingUserId,
      afterData: summary,
    });
    return { apiKey: summary, token };
  }

  /** Changes where a key may be used from, without issuing a new one. */
  async updateAllowedIps(
    id: string,
    dto: UpdateApiKeyDto,
    actingUserId: string,
  ): Promise<ApiKeySummary> {
    const before = await this.prisma.apiKey.findUnique({ where: { id } });
    if (!before) {
      throw new NotFoundException('API-Schlüssel nicht gefunden');
    }
    const updated = await this.prisma.apiKey.update({
      where: { id },
      data: { allowedIps: normalizeAllowlist(dto.allowedIps) },
    });
    await this.auditLog.record({
      entityType: 'ApiKey',
      entityId: id,
      action: 'UPDATE',
      userId: actingUserId,
      beforeData: toSummary(before),
      afterData: toSummary(updated),
    });
    return toSummary(updated);
  }

  async revoke(id: string, actingUserId: string): Promise<ApiKeySummary> {
    const before = await this.prisma.apiKey.findUnique({ where: { id } });
    if (!before) {
      throw new NotFoundException('API-Schlüssel nicht gefunden');
    }
    if (before.revokedAt) {
      return toSummary(before);
    }
    const revoked = await this.prisma.apiKey.update({
      where: { id },
      data: { revokedAt: new Date() },
    });
    await this.auditLog.record({
      entityType: 'ApiKey',
      entityId: id,
      action: 'DEACTIVATE',
      userId: actingUserId,
      beforeData: toSummary(before),
      afterData: toSummary(revoked),
    });
    return toSummary(revoked);
  }

  /**
   * Resolves a presented key to what it may do, or null for anything that
   * must not pass: malformed, unknown, revoked or expired.
   *
   * The key is found by the SHA-256 of the presented token through a unique
   * index - never by comparing secrets byte by byte, so response timing says
   * nothing about the stored key. Order matters: the lookup comes first, and
   * only an invalid key counts against (or is stopped by) the failure limit
   * of the client network. A malformed token is not a guess at a key and is
   * refused without lookup and without counting.
   */
  async authenticate(
    token: string,
    clientIp?: string,
  ): Promise<ApiKeyPrincipal | null> {
    if (!TOKEN_PATTERN.test(token)) {
      return null;
    }
    const apiKey = await this.prisma.apiKey.findUnique({
      where: { keyHash: hashToken(token) },
    });
    const now = new Date();
    const reason = rejectReason(apiKey, now);
    if (reason === null && apiKey) {
      return this.accept(apiKey, clientIp, now);
    }
    await this.recordRejection(token, reason ?? 'unknown', clientIp);
    return null;
  }

  /** Counts an invalid key; 429 once the client network is over the limit. */
  private async recordRejection(
    token: string,
    reason: RejectReason,
    clientIp: string | undefined,
  ): Promise<void> {
    // Counted per client network like the throttler (IPv6 /64), so rotating
    // addresses inside one's own prefix does not reset the budget.
    const subject = clientIp ? rateLimitSubject(clientIp) : 'unknown';
    const verdict = await this.failures.recordFailure(subject);
    if (verdict.blocked) {
      // Same body shape as the built-in 4xx exceptions (JSON object, not a
      // bare string), so clients can read `message` uniformly.
      throw new HttpException(
        {
          statusCode: HttpStatus.TOO_MANY_REQUESTS,
          error: 'Too Many Requests',
          message:
            'Zu viele Fehlversuche mit API-Schlüsseln - bitte später erneut versuchen',
        },
        HttpStatus.TOO_MANY_REQUESTS,
      );
    }
    // Only the public prefix is ever logged, never the key itself.
    this.logger.warn(
      `API key rejected (${reason}): ${token.slice(0, LOGGABLE_PREFIX_LENGTH)} from ${clientIp ?? 'unknown'}`,
    );
    if (verdict.limitReached) {
      this.logger.warn(
        `Invalid API keys from ${subject} reached ${API_KEY_FAILURE_LIMIT.maxFailures} failures - further invalid keys get 429 for ${API_KEY_FAILURE_LIMIT.windowMs / 60_000} minutes`,
      );
    }
  }

  private async accept(
    apiKey: ApiKey,
    clientIp: string | undefined,
    now: Date,
  ): Promise<ApiKeyPrincipal> {
    if (!isIpAllowed(clientIp, apiKey.allowedIps)) {
      // The key itself is right: say so, so the admin finds the cause - a
      // thief learns nothing new, they already hold the key.
      this.logger.warn(
        `API key ${apiKey.prefix} used from ${clientIp ?? 'unknown'}, not in its allowlist`,
      );
      throw new ForbiddenException(
        'API-Schlüssel ist für diese IP-Adresse nicht freigegeben',
      );
    }
    if (
      !apiKey.lastUsedAt ||
      now.getTime() - apiKey.lastUsedAt.getTime() > LAST_USED_RESOLUTION_MS ||
      apiKey.lastUsedIp !== (clientIp ?? null)
    ) {
      await this.prisma.apiKey.update({
        where: { id: apiKey.id },
        data: { lastUsedAt: now, lastUsedIp: clientIp ?? null },
      });
    }
    // Intersect with today's allowlist: narrowing it later also narrows
    // keys issued before.
    return { id: apiKey.id, scopes: apiKey.scopes.filter(isApiKeyScope) };
  }
}

function rejectReason(apiKey: ApiKey | null, now: Date): RejectReason | null {
  if (!apiKey) return 'unknown';
  if (apiKey.revokedAt) return 'revoked';
  if (apiKey.expiresAt && apiKey.expiresAt <= now) return 'expired';
  return null;
}

/** The key from an `Authorization: Bearer ack_…` header, or null. */
export function extractApiKeyToken(
  authorization: string | undefined,
): string | null {
  if (!authorization?.startsWith('Bearer ack_')) {
    return null;
  }
  return authorization.slice('Bearer '.length).trim();
}