import { randomBytes } from 'node:crypto';
import { promises as fs } from 'node:fs';
import { join, resolve } from 'node:path';
import { Injectable, Logger, OnModuleDestroy, OnModuleInit } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { LessThan, Repository } from 'typeorm';
import { StoredFile } from '../entities/stored-file.entity.js';

const DAY_MS = 24 * 60 * 60 * 1000;
const CLEANUP_INTERVAL_MS = 60 * 60 * 1000; // hourly

@Injectable()
export class FilesService implements OnModuleInit, OnModuleDestroy {
  private readonly log = new Logger('FilesService');
  private timer: NodeJS.Timeout | null = null;

  // Storage root; the guild operator may relocate / resize this freely.
  readonly dir = resolve(
    process.env.FABRIC_BACKEND_GUILD_FILE_DIR ?? join(process.cwd(), '.data', 'files'),
  );
  // 0 / unset => no cap (default per product: 100MB, operator-configurable).
  readonly maxBytes = Number(
    process.env.FABRIC_BACKEND_GUILD_FILE_MAX_BYTES ?? 100 * 1024 * 1024,
  );
  readonly ttlDays = Number(process.env.FABRIC_BACKEND_GUILD_FILE_TTL_DAYS ?? 7);

  constructor(
    @InjectRepository(StoredFile)
    private readonly repo: Repository<StoredFile>,
  ) {}

  async onModuleInit(): Promise<void> {
    await fs.mkdir(this.dir, { recursive: true });
    this.log.log(
      `files dir=${this.dir} maxBytes=${this.maxBytes} ttlDays=${this.ttlDays}`,
    );
    // sweep on boot, then hourly
    void this.cleanup();
    this.timer = setInterval(() => void this.cleanup(), CLEANUP_INTERVAL_MS);
    this.timer.unref?.();
  }

  onModuleDestroy(): void {
    if (this.timer) clearInterval(this.timer);
    this.timer = null;
  }

  async store(input: {
    channelId: string | null;
    uploaderUserId: string;
    originalName: string;
    mimeType: string;
    buffer: Buffer;
  }): Promise<StoredFile> {
    const fileId = randomBytes(18).toString('base64url');
    const storagePath = fileId; // flat layout, opaque name
    await fs.writeFile(join(this.dir, storagePath), input.buffer);
    const row = this.repo.create({
      fileId,
      channelId: input.channelId,
      uploaderUserId: input.uploaderUserId,
      originalName: input.originalName.slice(0, 255),
      mimeType: (input.mimeType || 'application/octet-stream').slice(0, 150),
      sizeBytes: input.buffer.length,
      storagePath,
      expiresAt: new Date(Date.now() + this.ttlDays * DAY_MS),
    });
    return this.repo.save(row);
  }

  async find(fileId: string): Promise<StoredFile | null> {
    const row = await this.repo.findOne({ where: { fileId } });
    if (!row) return null;
    if (row.expiresAt.getTime() <= Date.now()) return null; // treat as gone
    return row;
  }

  async readBlob(row: StoredFile): Promise<Buffer> {
    return fs.readFile(join(this.dir, row.storagePath));
  }

  // Purge every row past its retention deadline together with its blob.
  async cleanup(): Promise<number> {
    const expired = await this.repo.find({ where: { expiresAt: LessThan(new Date()) } });
    let removed = 0;
    for (const row of expired) {
      try {
        await fs.rm(join(this.dir, row.storagePath), { force: true });
      } catch {
        /* best effort: drop the row regardless */
      }
      await this.repo.delete({ id: row.id });
      removed++;
    }
    if (removed) this.log.log(`retention sweep removed ${removed} expired file(s)`);
    return removed;
  }
}