// SPDX-License-Identifier: MIT
// Copyright © 2021 The Tvix Authors
syntax = "proto3";

package tvix.proto.v1;

service EvaluatorService {
  rpc Evaluate(stream EvaluateRequest) returns (stream EvaluateResponse) {}
}

//
// Message types for EvaluateRequest
//

message EvaluateFile {
  // Absolute path at which the evaluator can find the file to be
  // evaluated.
  string file_path = 1;

  // Optional attribute that should be evaluated within the file,
  // assuming that the value it evaluates to is an attribute set.
  optional string attribute = 2;

  // Additional arguments to pass into the evaluation, with which the
  // file's top-level function will be auto-called.
  map<string, NixValue> arguments = 3;
}

message EvaluateExpression {
  // Literal Nix expression to evaluate.
  string expression = 1;

  // Working directory in which the expression should be evaluated.
  string working_directory = 2;
}

message BuildResultChunk {
  string drv_hash = 1;
  string output = 2;
  bytes data = 3;

  // This field may be set on the first build result chunk returned
  // to the evaluator, indicating the total size of the output that
  // is going to be streamed in bytes.
  //
  // If set, the evaluator can use this to appropriately allocate a
  // buffer for the output.
  optional int64 output_size = 4;
}

// Indicates that a single build has completed successfully. In case
// that the build outputs were required by the evaluator this also
// indicates that the output has been returned completely.
message BuildSuccess {
  string drv_hash = 1;
  string output = 2;
}

// Describes an error that occured during a single build.
//
// TODO: We might want a more sophisticated error type.
message BuildError {
  string drv_hash = 1;
  string output = 2;
  string error = 3;
}

message BuildResult {
  oneof build_result {
    BuildSuccess build_success = 1;
    BuildError build_error = 2;
  }
}


/// Messages sent to the evaluator by the build coordinator.
message EvaluateRequest {
  oneof message {
    // Ask the evaluator to evaluate the specified file, and
    // optionally attribute within that file. Must be the first
    // message.
    EvaluateFile evaluate_file = 1;

    // Ask the evaluator to evaluate the specified Nix expression.
    // Must be the first message.
    EvaluateExpression evaluate_expression = 2;

    // Send the chunks of a build result, in response to a
    // BuildRequest.
    //
    // Note: This message might change as the store protocol is
    // designed, as it is possible that mechanisms for transferring
    // files might be reused between the protocols.
    BuildResultChunk build_result_chunk = 3;

    // Indicate the result of a single build. See the documentation
    // for the message types defined above for semantic details.
    BuildResult build_result = 4;
  }
}

//
// Message types for EvaluateResponse
//

// TODO: Placeholder type.
message Derivation {
  string drv = 1;
}

// TODO: Placeholder type.
message NixValue {
  string value = 1;
}

// TODO: Placeholder type.
message NixError {
  string value = 1;
}

message BuildRequest {
  Derivation drv = 1;
  string output = 2;
}

// Messages returned to the coordinator by the evaluator.
message EvaluateResponse {
  oneof message {
    // A derivation that was instantiated while reducing the graph,
    // and whose output is not required by the evaluator.
    Derivation derivation = 1;

    // A derivation that was instantiated while reducing the graph,
    // and whose output is required by the evaluator (IFD).
    BuildRequest build_request = 2;

    // The final value yielded by the evaluation. Stream is closed
    // after this.
    NixValue done = 3;

    // Evaluation error. Stream is closed after this.
    NixError error = 4;
  }
}