syntax = "proto3";
package stemedb.sync.v1;

// SyncService enables node-to-node replication for StemeDB.
//
// The service supports two sync patterns:
// 1. Gossip: Push new assertions to peers immediately after ingestion
// 2. Anti-Entropy: Periodic Merkle root exchange and diff-based sync
service SyncService {
  // Gossip pushes a new assertion to a peer.
  // Called immediately after local ingestion to propagate data quickly.
  rpc Gossip(GossipRequest) returns (GossipResponse);

  // ExchangeRoots compares Merkle roots to detect divergence.
  // If roots differ, the caller should fetch missing assertions.
  rpc ExchangeRoots(RootExchangeRequest) returns (RootExchangeResponse);

  // FetchAssertions retrieves assertion data by hash.
  // Used after ExchangeRoots to pull missing assertions.
  rpc FetchAssertions(FetchRequest) returns (FetchResponse);

  // Ping checks if a peer is alive and returns basic metadata.
  rpc Ping(PingRequest) returns (PingResponse);

  // GetLeaves returns all Merkle tree leaf hashes.
  // Used for computing the diff during anti-entropy sync.
  rpc GetLeaves(GetLeavesRequest) returns (GetLeavesResponse);
}

// GossipRequest pushes a single assertion to a peer.
message GossipRequest {
  // BLAKE3 hash of the assertion (32 bytes)
  bytes assertion_hash = 1;

  // Serialized assertion data (rkyv format)
  bytes assertion_data = 2;

  // HLC timestamp components for causal ordering
  uint64 hlc_time = 3;
  uint32 hlc_counter = 4;
  bytes hlc_node_id = 5;  // 16 bytes
}

message GossipResponse {
  // True if the assertion was accepted (stored or already existed)
  bool accepted = 1;

  // Error message if rejected (e.g., validation failure)
  string error = 2;
}

// RootExchangeRequest initiates Merkle root comparison.
message RootExchangeRequest {
  // Local Merkle root hash (32 bytes)
  bytes merkle_root = 1;

  // Number of assertions in local tree
  uint64 assertion_count = 2;
}

message RootExchangeResponse {
  // Remote Merkle root hash (32 bytes)
  bytes merkle_root = 1;

  // Number of assertions in remote tree
  uint64 assertion_count = 2;

  // True if roots match (trees are identical)
  bool roots_match = 3;
}

// FetchRequest asks for assertion data by hash.
message FetchRequest {
  // List of assertion hashes to fetch (max 1000 per request)
  repeated bytes hashes = 1;
}

message FetchResponse {
  // Retrieved assertions (may be fewer than requested if not found)
  repeated AssertionData assertions = 1;
}

// AssertionData pairs a hash with its serialized data.
message AssertionData {
  // BLAKE3 hash of the assertion (32 bytes)
  bytes hash = 1;

  // Serialized assertion data (rkyv format)
  bytes data = 2;
}

// PingRequest is a health check with node identity.
message PingRequest {
  // Sender's node ID (16 bytes)
  bytes node_id = 1;
}

message PingResponse {
  // Responder's node ID (16 bytes)
  bytes node_id = 1;

  // Number of assertions on this node
  uint64 assertion_count = 2;
}

// GetLeavesRequest requests all Merkle tree leaf hashes.
message GetLeavesRequest {
  // Maximum number of leaves to return (0 = no limit, but capped at 10000)
  uint64 max_leaves = 1;
}

// GetLeavesResponse returns Merkle tree leaf hashes.
message GetLeavesResponse {
  // All leaf hashes (each 32 bytes)
  repeated bytes leaves = 1;

  // True if there are more leaves than max_leaves
  bool truncated = 2;
}