gp4/Sources/P4Runtime/Statements.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 BlockStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    var execution = execution
    for s in self.statements {
      let (control_flow, next_execution) = s.evaluate(execution: execution)
      switch control_flow {
      case ControlFlow.Return(let value): return (ControlFlow.Return(value), next_execution)
      case ControlFlow.Next: execution = next_execution
      case ControlFlow.Error: return (ControlFlow.Error, next_execution)
      default:
        return (
          ControlFlow.Next,
          next_execution.setError(
            error: Error(withMessage: "Invalid control flow \(control_flow) in block statement"))
        )
      }
    }
    return (ControlFlow.Next, execution)
  }
}

extension VariableDeclarationStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    guard case .Ok(let initial_value) = self.initializer.evaluate(execution: execution) else {
      return (
        ControlFlow.Error,
        execution.setError(error: Error(withMessage: "Could not evaluate \(self.initializer)"))
      )
    }
    let new_scopes = execution.scopes.declare(identifier: self.identifier, withValue: initial_value)
    execution.scopes = new_scopes
    return (ControlFlow.Next, execution)
  }
}

extension ConditionalStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    guard case .Ok(let evaluated_condition) = self.condition.evaluate(execution: execution) else {
      return (
        ControlFlow.Error,
        execution.setError(error: Error(withMessage: "Could not evaluate \(self.condition)"))
      )
    }

    if !evaluated_condition.type().eq(rhs: P4Boolean()) {
      return (
        ControlFlow.Error,
        execution.setError(error: Error(withMessage: "Condition expression is not a Boolean"))
      )
    }

    if evaluated_condition.eq(rhs: P4BooleanValue.init(withValue: true)) {
      let execution = execution.enter_scope()
      switch self.thenn.evaluate(execution: execution) {
      case (ControlFlow.Next, let result): return (ControlFlow.Next, result.exit_scope())
      case (ControlFlow.Error, let result): return (ControlFlow.Error, result.exit_scope())
      case (let cf, let result):
        return (
          ControlFlow.Next,
          result.setError(
            error: Error(withMessage: "Invalid control flow \(cf) in conditional statement"))
        )
      }
    } else if let elss = self.elss {
      let execution = execution.enter_scope()
      switch elss.evaluate(execution: execution) {
      case (ControlFlow.Next, let result): return (ControlFlow.Next, result.exit_scope())
      case (ControlFlow.Error, let result): return (ControlFlow.Error, result.exit_scope())
      case (let cf, let result):
        return (
          ControlFlow.Next,
          result.setError(
            error: Error(withMessage: "Invalid control flow \(cf) in conditional statement"))
        )
      }
    }
    return (ControlFlow.Next, execution)
  }
}

extension ExpressionStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    // TODO: Should this do something? Side effects?
    return (ControlFlow.Next, execution)
  }
}

extension ReturnStatement: EvaluatableStatement {
  public func evaluate(execution: ProgramExecution) -> (ControlFlow, ProgramExecution) {
    return switch self.value.evaluate(execution: execution) {
      case .Ok(let v): (ControlFlow.Return(v), execution)
      case .Error(let e): (ControlFlow.Error, execution.setError(error: e))
    }
  }
}