import { mkdir, readFile, rename, stat, writeFile } from "node:fs/promises";
import { dirname, join, resolve } from "node:path";
import { zstdCompressSync, zstdDecompressSync } from "node:zlib";
import { sha256 } from "@websensor/core";

/**
 * Content-addressed blob store for snapshots and diffs. Identical content is stored once
 * (`sha256/ab/cd/<hash>.zst`). The interface is storage-agnostic so an S3/MinIO driver can
 * be added without touching callers.
 */
export interface BlobStore {
  put(data: Buffer | string, meta?: { contentType?: string }): Promise<{ key: string; bytes: number; deduplicated: boolean }>;
  get(key: string): Promise<Buffer>;
  getText(key: string): Promise<string>;
  exists(key: string): Promise<boolean>;
}

export class FsBlobStore implements BlobStore {
  constructor(private readonly root: string) {}

  private pathFor(key: string): string {
    return join(this.root, key + ".zst");
  }

  static keyFor(hash: string): string {
    return `sha256/${hash.slice(0, 2)}/${hash.slice(2, 4)}/${hash}`;
  }

  async put(data: Buffer | string): Promise<{ key: string; bytes: number; deduplicated: boolean }> {
    const buf = typeof data === "string" ? Buffer.from(data, "utf8") : data;
    const key = FsBlobStore.keyFor(sha256(buf));
    const p = this.pathFor(key);
    try {
      const s = await stat(p);
      if (s.size > 0) return { key, bytes: buf.length, deduplicated: true };
    } catch {
      // not present
    }
    await mkdir(dirname(p), { recursive: true });
    const tmp = `${p}.${process.pid}.${Date.now()}.tmp`;
    await writeFile(tmp, zstdCompressSync(buf));
    await rename(tmp, p);
    return { key, bytes: buf.length, deduplicated: false };
  }

  async get(key: string): Promise<Buffer> {
    const raw = await readFile(this.pathFor(key));
    return zstdDecompressSync(raw);
  }

  async getText(key: string): Promise<string> {
    return (await this.get(key)).toString("utf8");
  }

  async exists(key: string): Promise<boolean> {
    try {
      await stat(this.pathFor(key));
      return true;
    } catch {
      return false;
    }
  }
}

let store: BlobStore | null = null;
export function getBlobStore(): BlobStore {
  if (!store) store = new FsBlobStore(resolve(process.env.BLOB_STORE_DIR ?? "./data/blobs"));
  return store;
}