syntax = "proto3";

package chat;

option go_package = "git.be.kaien.ru/l-ai/l-ai-chat-proto/proto";

import "google/protobuf/timestamp.proto";

// ChatService is the canonical API of the l-ai-chat Live Chat service.
// Chat Service is the single source of truth for messages; clients (Web UI,
// Telegram bot, agents) send and read messages through it.
service ChatService {
  // ListTopics returns all topics in stable (creation) order.
  rpc ListTopics(ListTopicsRequest) returns (ListTopicsResponse);

  // GetTopic returns one topic by id or slug.
  rpc GetTopic(GetTopicRequest) returns (Topic);

  // CreateTopic creates a new topic. Slug must be unique.
  rpc CreateTopic(CreateTopicRequest) returns (Topic);

  // UpdateTopic renames a topic (display_name). The slug is a stable
  // identifier and cannot be changed. Topics are persistent in the MVP:
  // there is no delete API.
  rpc UpdateTopic(UpdateTopicRequest) returns (Topic);

  // PostMessage appends a message to a topic. NOTE: this RPC is fail-closed
  // until the human-authentication stage: there is no trusted way to fill
  // author_id/author_type/source yet, so any call currently returns
  // Unimplemented. Agents MUST use AgentPostMessage (the server derives the
  // identity from the service token). The internal canonical-message path is
  // re-exposed after human auth lands.
  rpc PostMessage(PostMessageRequest) returns (PostMessageResponse);

  // AgentPostMessage posts a message as the authenticated agent. The server
  // derives every server-owned field: author_id (deterministic UUID of the
  // authenticated identity), author_type=AGENT, source=AGENT, sequence,
  // root_message_id, reply_depth, created_at. Clients cannot spoof them.
  // idempotency_key is mandatory: retries with the same key return the
  // original message (duplicated=true).
  rpc AgentPostMessage(AgentPostMessageRequest) returns (PostMessageResponse);

  // GetMessage returns a single message by id.
  rpc GetMessage(GetMessageRequest) returns (Message);

  // History returns messages of a topic, paginated by sequence (no offset
  // pagination). Use before_sequence for newest-first backward paging or
  // after_sequence for oldest-first forward paging; at most one may be set.
  rpc History(HistoryRequest) returns (HistoryResponse);

  // Subscribe opens the delivery stream of a topic for the authenticated
  // consumer. Delivery is durable at-least-once: PostgreSQL (messages +
  // per-(consumer, topic) delivery cursor) is the source of correctness;
  // the stream is a live projection. Exactly one active subscription is
  // admitted per (consumer, topic): a new Subscribe for the same pair
  // replaces the previous one, which terminates with Aborted. Every
  // DeliveryMessage carries the opaque subscription_id the consumer must
  // echo in Acknowledge. Messages are delivered in ascending sequence
  // order; gaps between sequences of one topic are normal (other topics
  // consume global sequence values).
  rpc Subscribe(SubscribeRequest) returns (stream DeliveryMessage);

  // Acknowledge advances the durable delivery cursor of the CURRENT active
  // subscription of the authenticated consumer in a topic. Cumulative:
  // last_ack_sequence = highest sequence the consumer has fully processed.
  // The ACK is validated against the active subscription: the sequence must
  // not exceed the highest sequence this subscription actually delivered,
  // and a stale/old subscription_id is rejected. The cursor is monotonic —
  // it never moves backwards. Cursor changes ONLY here; delivery itself
  // never persists cursor state.
  rpc Acknowledge(AcknowledgeRequest) returns (AcknowledgeResponse);
}

// AuthorType is the kind of identity a message author has. HUMAN covers
// internal users (the same author_id across Web and Telegram), AGENT covers
// l-ai agents, SYSTEM covers service-internal messages, INTEGRATION covers
// bridge/external systems.
enum AuthorType {
  AUTHOR_TYPE_UNSPECIFIED = 0;
  AUTHOR_TYPE_HUMAN = 1;
  AUTHOR_TYPE_AGENT = 2;
  AUTHOR_TYPE_SYSTEM = 3;
  AUTHOR_TYPE_INTEGRATION = 4;
}

// MessageSource is the channel through which a message entered the system.
enum MessageSource {
  MESSAGE_SOURCE_UNSPECIFIED = 0;
  MESSAGE_SOURCE_WEB = 1;
  MESSAGE_SOURCE_TELEGRAM = 2;
  MESSAGE_SOURCE_AGENT = 3;
  MESSAGE_SOURCE_SYSTEM = 4;
}

message Topic {
  string id = 1; // UUID
  string slug = 2; // stable, unique, e.g. "security"
  string display_name = 3; // e.g. "Security"
  google.protobuf.Timestamp created_at = 4;
}

message Message {
  string id = 1; // UUID, canonical message id
  int64 sequence = 2; // server-assigned monotonic sequence (ordering + durable cursor)
  string topic_id = 3; // UUID
  string author_id = 4; // stable identity of the author (UUID)
  AuthorType author_type = 5;
  MessageSource source = 6;
  string content = 7;
  optional string reply_to_message_id = 8; // parent message when this is a reply
  string root_message_id = 9; // root of the reply chain (== id for non-replies)
  int32 reply_depth = 10; // 0 for non-replies, parent depth + 1 for replies; hard max 20
  google.protobuf.Timestamp created_at = 11; // original creation time; age = now - created_at
}

message ListTopicsRequest {}

message ListTopicsResponse {
  repeated Topic topics = 1;
}

message GetTopicRequest {
  oneof selector {
    string id = 1;
    string slug = 2;
  }
}

message CreateTopicRequest {
  string slug = 1;
  string display_name = 2;
}

message UpdateTopicRequest {
  string id = 1; // UUID
  string display_name = 2; // new display name (required, full replace)
}

message PostMessageRequest {
  string topic_id = 1;
  string author_id = 2;
  AuthorType author_type = 3;
  MessageSource source = 4;
  string content = 5;
  optional string reply_to_message_id = 6;
  // Idempotency key: retrying PostMessage with the same author_id and key
  // returns the original message instead of creating a duplicate.
  string idempotency_key = 7;
}

message AgentPostMessageRequest {
  string topic_id = 1;
  string content = 2;
  optional string reply_to_message_id = 3;
  // Mandatory: retrying with the same key returns the original message
  // (duplicated=true) instead of creating a duplicate.
  string idempotency_key = 4;
}

message PostMessageResponse {
  Message message = 1;
  bool duplicated = 2; // true when an idempotent replay returned an existing message
}

message GetMessageRequest {
  string message_id = 1;
}

message HistoryRequest {
  string topic_id = 1;
  // Backward paging: return messages with sequence < before_sequence,
  // newest first. Mutually exclusive with after_sequence.
  int64 before_sequence = 2;
  // Forward paging: return messages with sequence > after_sequence,
  // oldest first. Mutually exclusive with before_sequence.
  int64 after_sequence = 3;
  // Maximum number of messages to return (server may cap it).
  int32 limit = 4;
}

message HistoryResponse {
  repeated Message messages = 1;
  // true when more messages exist in the requested direction.
  bool has_more = 2;
}

message SubscribeRequest {
  string topic_id = 1;
  // The consumer identity is NOT a request field: it is derived from the
  // authenticated service credential, so one agent cannot subscribe as
  // another.
}

// DeliveryMessage wraps one delivered message with delivery metadata.
// message.created_at is always the original creation time; replay + the
// timestamp let the SDK decide how to treat a delivery.
message DeliveryMessage {
  Message message = 1;
  // true when the message was committed BEFORE this subscription started
  // (backlog catch-up after connect/reconnect); false for messages committed
  // while this subscription is live.
  bool replay = 2;
  // Opaque id of the current subscription, generated by the server per
  // Subscribe stream. MUST be echoed in Acknowledge; a stale id (from a
  // replaced/closed stream) is rejected.
  string subscription_id = 3;
}

message AcknowledgeRequest {
  string topic_id = 1;
  // Highest sequence fully processed by the consumer (cumulative ack).
  int64 last_ack_sequence = 2;
  // The subscription_id of the stream that delivered the message. Must be
  // the CURRENT active subscription of this consumer in this topic.
  string subscription_id = 3;
}

message AcknowledgeResponse {
  int64 last_ack_sequence = 1; // the cursor as stored (never lower than before)
}