import {
  BadRequestException,
  Inject,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { customAlphabet } from 'nanoid';
import type Redis from 'ioredis';
import { VALKEY } from '../valkey.provider';

// URL-safe, unambiguous-ish alphabet (no 0/O/1/I/l). 8 chars = 38^8 ≈ 4.4e12 codes.
const nanoid = customAlphabet(
  '23456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnpqrstuvwxyz',
  8,
);

const MAX_BYTES = 16 * 1024; // 16 KB cap per shared build
const TTL_SECONDS = 60 * 60 * 24 * 365; // 1 year

@Injectable()
export class BuildsService {
  constructor(@Inject(VALKEY) private readonly redis: Redis) {}

  async save(payload: unknown): Promise<{ code: string }> {
    const json = JSON.stringify(payload);
    if (!json || json === 'null') {
      throw new BadRequestException('empty build');
    }
    if (Buffer.byteLength(json, 'utf8') > MAX_BYTES) {
      throw new BadRequestException(`build too large (>${MAX_BYTES} bytes)`);
    }
    // Up to 5 retries on collision.
    for (let i = 0; i < 5; i++) {
      const code = nanoid();
      const key = `build:${code}`;
      const ok = await this.redis.set(key, json, 'EX', TTL_SECONDS, 'NX');
      if (ok === 'OK') return { code };
    }
    throw new BadRequestException('failed to allocate code');
  }

  async load(code: string): Promise<unknown> {
    if (!/^[2-9A-HJ-NP-Za-km-z]{8}$/.test(code)) {
      throw new BadRequestException('invalid code');
    }
    const json = await this.redis.get(`build:${code}`);
    if (!json) throw new NotFoundException('build not found');
    // refresh TTL so popular builds stay alive
    await this.redis.expire(`build:${code}`, TTL_SECONDS);
    try {
      return JSON.parse(json);
    } catch {
      throw new BadRequestException('corrupt build');
    }
  }
}