/**
 * AES-256-GCM encryption at rest (messaging credentials and customer contact details) and keyed
 * hashes ("blind indexes") for exact-match lookups on encrypted values.
 * APP_ENCRYPTION_KEY = 32 random bytes, base64 (`openssl rand -base64 32`).
 */
import { createCipheriv, createDecipheriv, createHmac, randomBytes } from "node:crypto";

let cached: { raw: string; enc: Buffer; idx: Buffer } | null = null;
function keys() {
  const raw = process.env.APP_ENCRYPTION_KEY ?? "";
  if (cached?.raw === raw) return cached;
  const enc = Buffer.from(raw, "base64");
  if (enc.length !== 32) throw new Error("APP_ENCRYPTION_KEY must be 32 bytes (base64)");
  // A separate key for hashing, derived so one secret covers both uses.
  const idx = createHmac("sha256", enc).update("datewise:blind-index:v1").digest();
  cached = { raw, enc, idx };
  return cached;
}

export function encrypt(plain: string): string {
  const iv = randomBytes(12);
  const c = createCipheriv("aes-256-gcm", keys().enc, iv);
  const enc = Buffer.concat([c.update(plain, "utf8"), c.final()]);
  return [iv, c.getAuthTag(), enc].map((b) => b.toString("base64url")).join(".");
}

export function decrypt(blob: string): string {
  const [iv, tag, enc] = blob.split(".").map((p) => Buffer.from(p, "base64url"));
  const d = createDecipheriv("aes-256-gcm", keys().enc, iv);
  d.setAuthTag(tag);
  return Buffer.concat([d.update(enc), d.final()]).toString("utf8");
}

/** Marks sealed column values so rows written before encryption (plain text) still read correctly. */
const PREFIX = "enc1:";

export function seal(plain: string | null | undefined): string | null | undefined {
  if (plain == null || plain === "" || plain.startsWith(PREFIX)) return plain;
  return PREFIX + encrypt(plain);
}

export function unseal(value: string | null | undefined): string | null {
  if (value == null) return null;
  return value.startsWith(PREFIX) ? decrypt(value.slice(PREFIX.length)) : value;
}

/** Keyed hash of a normalised email or phone, for exact-match queries. Never reversible. */
export function blindIndex(value: string | null | undefined, kind: "email" | "phone"): string | null {
  if (!value) return null;
  const norm = kind === "email" ? value.trim().toLowerCase() : value.replace(/[^\d+]/g, "");
  if (!norm) return null;
  return createHmac("sha256", keys().idx).update(`${kind}:${norm}`).digest("hex");
}