gp4/Sources/P4Runtime/Parser.swift

// p4rse, Copyright 2026, Will Hawkins
//
// This file is part of p4rse.
//
// This file is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

import Common
import P4Lang

extension ParserAssignmentStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    let updated_execution = execution
    //let result = self.value.evaluate(execution: updated_execution)
    let result = updated_execution.evaluator.EvaluateExpression(
      self.value, inExecution: updated_execution)
    guard case (.Ok(let value), let updated_execution) = result else {
      return (ControlFlow.Error, execution.setError(error: result.0.error()!))
    }

    let maybe_updated_scopes = self.lvalue.set(
      to: value, inScopes: execution.scopes, duringExecution: updated_execution)
    guard case Result.Ok(let updated_scopes) = maybe_updated_scopes else {
      return (ControlFlow.Error, execution.setError(error: maybe_updated_scopes.error()!))
    }
    execution.scopes = updated_scopes.0

    return (ControlFlow.Next, updated_execution)
  }
}

extension ParserStateDirectTransitionValue: EvaluatableParserState {
  public func execute(
    program: Common.ProgramExecution
  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
    var program = program.enter_scope()

    let (control_flow, next_execution) = program.evaluator.ExecuteStatements(
      self.state.statements, inExecution: program)

    switch control_flow {
    case .Next: program = next_execution
    case .Error: return (reject, next_execution.exit_scope())
    default:
      return (
        reject,
        next_execution.exit_scope().setError(
          error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
      )
    }

    return (self.next_state as! EvaluatableParserState, program.exit_scope())
  }

  public func done() -> Bool {
    return false
  }

  public func state() -> P4Lang.ParserState {
    return self.state
  }
}

extension ParserStateNoTransitionValue: EvaluatableParserState {
  public func execute(
    program: Common.ProgramExecution
  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
    return (self, program)
  }

  public func done() -> Bool {
    return true
  }

  public func state() -> P4Lang.ParserState {
    return self.state
  }
}

extension ParserStateSelectTransitionValue: EvaluatableParserState {
  public func execute(
    program: Common.ProgramExecution
  ) -> (any EvaluatableParserState, Common.ProgramExecution) {
    var program = program.enter_scope()

    let (control_flow, next_execution) = program.evaluator.ExecuteStatements(
      self.state.statements, inExecution: program)
    switch control_flow {
    case .Next: program = next_execution
    case .Error: return (reject, next_execution.exit_scope())
    default:
      return (
        reject,
        next_execution.exit_scope().setError(
          error: Error(withMessage: "Invalid control flow (\(control_flow) in parser)"))
      )
    }

    switch program.evaluator.EvaluateExpression(self.te, inExecution: program) {
    case (.Ok(let value), let program):
      if AnyParserState.eq(rhs: value.type().baseType()) {
        return (value.dataValue() as! EvaluatableParserState, program.exit_scope())
      } else {
        return (
          self,
          program.setError(
            error: Error(withMessage: "Select transition transitioned to a none state"))
        )
      }
    case (.Error(let e), let program): return (self, program.setError(error: e).exit_scope())
    }
  }

  public func done() -> Bool {
    return false
  }

  public func state() -> P4Lang.ParserState {
    return self.state
  }
}

extension ParserValue: LibraryCallable {
  public typealias T = InstantiatedParserState
  public func call(
    execution: Common.ProgramExecution, arguments: ArgumentList
  ) -> (P4Lang.InstantiatedParserState, Common.ProgramExecution) {
    var execution = execution.enter_scope()

    execution = execution.declare(
      identifier: accept.state().getName(),
      withValue: P4Value(accept, P4QualifiedType.ReadOnly(accept.type())))
    execution = execution.declare(
      identifier: reject.state().getName(),
      withValue: P4Value(reject, P4QualifiedType.ReadOnly(reject.type())))

    // Add initial values to the global scope
    for (name, value) in execution.getGlobalValues() {
      execution = execution.declare(identifier: name, withValue: value)
    }

    // First, add every state to the scope!
    for state in self.tipe.states.states {
      guard let instantiated_state = state.instantiate(state.getName()) else {
        return (
          reject,
          execution.setError(error: Error(withMessage: "Could not instantiate \(state.getName())"))
        )
      }
      execution = execution.declare(
        identifier: state.getName(), withValue: P4Value(instantiated_state))
    }

    guard let _current_state = self.tipe.findStartState(),
      var current_state = _current_state.instantiate(Identifier(name: "start"))
        as? EvaluatableParserState
    else {
      return (
        reject, execution.setError(error: Error(withMessage: "Could not find the start state"))
      )
    }

    let call_body: (ProgramExecution) -> (Result<P4Value>, ProgramExecution) = {
      (execution: ProgramExecution) in
      var current_execution = execution
      // Evaluate until the state is either accept or reject.
      while !current_state.done() && !current_execution.hasError() {
        (current_state, current_execution) = current_state.execute(program: current_execution)
      }
      return (.Ok(P4Value((current_state))), current_execution)
    }

    return
      switch Call(
        body: call_body, withArguments: arguments, withParameters: self.tipe.parameters,
        inExecution: execution)
    {
    case (.Ok(let value), let updated_execution):
      (value.dataValue() as! InstantiatedParserState, updated_execution)
    case (.Error(let e), let updated_execution):
      (reject, updated_execution.setError(error: Error(withMessage: "Cannot call parser: \(e)")))
    }
  }
}