/**
 * PrivacyPort — V0 noop stub for Vauban Privacy Protocol (VPP) integration.
 *
 * Implements S0 port #10 (PrivacyPort): placeholder interface for privacy-preserving
 * operations. Phase 2+ will implement full Stwo+ML-KEM+viewing-key+SMT+cross-domain
 * functionality per draft-vauban-privacy-protocol-00 (target IETF submission 2026-06-29,
 * sprint-490 active 78%).
 *
 * V0 design: all operations return identity or noop stubs. Enables code to pass type
 * checks while VPP integration is deferred. No Side effects, no cryptographic guarantees.
 *
 * Reference: S0 § cross-spec invariants X-1 (isolation), X-3 (crypto-shredding);
 * VPP Phase roadmap: draft-vauban-privacy-protocol-00 + integration plan TBD.
 */

// ─── Privacy revelation mask types ────────────────────────────────────────────

/**
 * RevelationMask — declarative specification of which fields should be exposed
 * during a privacy-respecting operation.
 */
export interface RevelationMask {
  readonly public_fields: string[]; // fields always visible
  readonly private_fields: string[]; // fields always hidden
  readonly conditional?: Array<{
    readonly field: string;
    readonly condition: string; // e.g., "user_role == 'admin'"
  }>;
}

// ─── Zero-knowledge proof types ────────────────────────────────────────────────

export interface ZkProofInput {
  readonly proof_data: unknown; // opaque proof bytes / object
  readonly public_inputs: unknown; // public circuit inputs
  readonly scheme?: string; // e.g., "stwo", "starknet_stone"
}

export interface VerifyResult {
  readonly valid: boolean;
  readonly reason?: string; // why invalid (e.g., 'noop_v0', 'invalid_proof')
  readonly confidence?: number; // 0-1 confidence score (V0 always 0)
}

// ─── Sparse merkle tree commitment types ───────────────────────────────────────

export interface Commitment {
  readonly value: unknown; // commitment hash or object
  readonly salt?: string; // optional salt for hiding value
  readonly index?: number; // position in tree
}

export interface SmtResult {
  readonly smt_root: string; // hex-encoded root hash (V0: deterministic mock)
  readonly leaf_index: number; // position of committed value
  readonly version: number; // SMT version/epoch (V0: 0)
  readonly proof?: unknown; // merkle path (V0: omitted)
}

// ─── Privacy context ──────────────────────────────────────────────────────────

export interface PrivacyContext {
  readonly user_id?: string;
  readonly tenant_id?: string;
  readonly role?: string; // 'user', 'admin', 'operator'
  readonly jurisdiction?: string; // e.g., 'FR.v1', 'EU.v1'
  readonly metadata?: Record<string, unknown>;
}

// ─── PrivacyPort interface ────────────────────────────────────────────────────

/**
 * PrivacyPort — V0 noop stub.
 *
 * All methods return identity values or noop results. Replaced by full VPP
 * implementation in Phase 2 (Stwo+ML-KEM+viewing-key+SMT+cross-domain).
 *
 * Usage:
 *   const priv = new NoopPrivacyAdapter();
 *   const revealed = await priv.applyMask(data, mask, ctx); // data unchanged V0
 *   const vk = await priv.verifyZkProof(proof, ctx); // {valid: false, reason: 'noop_v0'}
 */
export interface PrivacyPort {
  /**
   * Apply a revelation mask to payload (V0: returns payload unchanged).
   *
   * Phase 2+: will implement field-level hiding via ZK commitments or viewing keys.
   *
   * @param payload input object or data structure
   * @param mask specification of which fields are public/private/conditional
   * @param ctx privacy context (user, tenant, role, jurisdiction)
   * @returns masked payload (V0: unchanged)
   */
  applyMask(
    payload: unknown,
    mask: RevelationMask,
    ctx: PrivacyContext
  ): Promise<unknown>;

  /**
   * Verify a zero-knowledge proof (V0: always returns invalid with 'noop_v0' reason).
   *
   * Phase 2+: will implement Stwo proof verification against public inputs.
   *
   * @param proof ZK proof object (scheme TBD, likely Stwo)
   * @param ctx privacy context
   * @returns { valid: false, reason: 'noop_v0' } in V0
   */
  verifyZkProof(
    proof: ZkProofInput,
    ctx: PrivacyContext
  ): Promise<VerifyResult>;

  /**
   * Commit value to sparse merkle tree (V0: returns deterministic mock root).
   *
   * Phase 2+: will implement full SMT with Poseidon hashing and viewing keys.
   *
   * @param commitment value or hash to commit
   * @param ctx privacy context
   * @returns mock SMT root (V0: deterministic, no cryptographic guarantee)
   */
  commitToSmt(commitment: Commitment, ctx: PrivacyContext): Promise<SmtResult>;
}

// ─── Noop implementation (V0 stub) ────────────────────────────────────────────

/**
 * NoopPrivacyAdapter — V0 stub implementation of PrivacyPort.
 *
 * All methods return identity values or noop results. Enables type-safe code
 * while VPP integration is deferred to Phase 2.
 *
 * Documentation: "V0 stub — replaced by VPP integration in Phase 2
 * (Stwo+ML-KEM+viewing key+SMT+cross-domain)."
 *
 * Usage:
 *   const adapter = new NoopPrivacyAdapter();
 *   const data = { secret: 'hidden', public: 'visible' };
 *   const masked = await adapter.applyMask(data, mask, ctx);
 *   // masked === data (unchanged in V0)
 */
export class NoopPrivacyAdapter implements PrivacyPort {
  async applyMask(
    payload: unknown,
    _mask: RevelationMask,
    _ctx: PrivacyContext
  ): Promise<unknown> {
    // V0: identity function — return input unchanged
    return payload;
  }

  async verifyZkProof(
    _proof: ZkProofInput,
    _ctx: PrivacyContext
  ): Promise<VerifyResult> {
    // V0: always invalid with noop marker
    return {
      valid: false,
      reason: "noop_v0",
      confidence: 0,
    };
  }

  async commitToSmt(
    commitment: Commitment,
    _ctx: PrivacyContext
  ): Promise<SmtResult> {
    // V0: return deterministic mock root based on commitment value
    // In real Phase 2+, would compute Poseidon hash and maintain SMT state
    const mockRoot = this.computeMockRoot(commitment);
    return {
      smt_root: mockRoot,
      leaf_index: commitment.index ?? 0,
      version: 0, // V0 version
    };
  }

  /**
   * Compute a deterministic mock SMT root (V0 only).
   * Purely for testing — no cryptographic guarantee.
   */
  private computeMockRoot(commitment: Commitment): string {
    // Simple deterministic hash for V0: stringify commitment and hash
    const str = JSON.stringify(commitment);
    let hash = 0;
    for (let i = 0; i < str.length; i++) {
      hash = (hash << 5) - hash + str.charCodeAt(i);
      hash = hash & hash; // keep it as 32-bit int
    }
    return "0x" + Math.abs(hash).toString(16).padStart(64, "0");
  }
}

// ─── Informational warning (not thrown) ─────────────────────────────────────

/**
 * PrivacyNoopWarning — logged when V0 noop operations are used.
 * Not thrown as an exception (non-blocking), but logged for observability.
 */
export class PrivacyNoopWarning extends Error {
  constructor(message: string, public readonly operation: string) {
    super(message);
    this.name = "PrivacyNoopWarning";
    Object.setPrototypeOf(this, new.target.prototype);
  }
}
