gp4/Sources/P4Lang/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

public struct LocalElements {}

public struct LocalElement {}

public struct ParserAssignmentStatement {
  public let lvalue: EvaluatableLValueExpression
  public let value: EvaluatableExpression

  public init(
    withLValue lvalue: EvaluatableLValueExpression, withValue value: EvaluatableExpression
  ) {
    self.lvalue = lvalue
    self.value = value
  }
}

/// A P4 Parser State
///
/// Note: A P4 Parser State is both a type and a value.
/// This "bare" parser state represents the state more as a type than a value.
public class ParserState: P4Type, Equatable, CustomStringConvertible {
  let name: Identifier
  public let statements: [EvaluatableStatement]

  public static func == (lhs: ParserState, rhs: ParserState) -> Bool {
    return lhs.eq(rhs: rhs)
  }

  public func eq(rhs: any Common.P4Type) -> Bool {
    return switch rhs {
    case let rrhs as ParserState: self.name == rrhs.name
    default: false
    }
  }

  public var description: String {
    return "Parser State named \(self.name)"
  }

  public func getName() -> Identifier {
    return self.name
  }

  public func getStatements() -> [EvaluatableStatement] {
    return self.statements
  }

  /// Construct a ParserState
  public init(_ name: Identifier, _ statements: [EvaluatableStatement] = Array()) {
    self.name = name
    self.statements = statements
  }

  public func def() -> P4DataValue? {
    return .none
  }

  public func instantiate(_ name: Identifier) -> InstantiatedParserState? {
    return .none
  }
}

public class _AnyParserState: ParserState {
  public override func eq(rhs: any Common.P4Type) -> Bool {
    return switch rhs {
    case is ParserState: true
    default: false
    }
  }
}

nonisolated(unsafe) public let AnyParserState = _AnyParserState(Identifier(name: "AnyParserState"))

public struct TransitionStatement {}

public class ParserStateDirectTransition: ParserState {

  public let next_state: InstantiatedParserState?
  public let next_state_identifier: Identifier?

  /// Construct a ParserState
  public init(
    name: Identifier, withNextState next_state: InstantiatedParserState,
    withStatements stmts: [EvaluatableStatement] = Array(),
  ) {
    self.next_state = next_state
    self.next_state_identifier = .none
    super.init(name, stmts)
  }

  public init(
    name: Identifier, withNextStateIdentifier next_state_id: Identifier,
    withStatements stmts: [EvaluatableStatement] = Array(),
  ) {
    self.next_state = .none
    self.next_state_identifier = next_state_id
    super.init(name, stmts)
  }

  public override func instantiate(_ name: Identifier) -> InstantiatedParserState? {
    return if let next_state = self.next_state {
      ParserStateDirectTransitionValue(name: name, withState: self, withNextState: next_state)
    } else {
      ParserStateDirectTransitionValue(
        name: name, withState: self, withNextStateIdentifier: self.next_state_identifier!)
    }
  }
}

public class ParserStateNoTransition: ParserState {
  /// Construct a ParserState
  public init(
    name: Identifier, withStatements stmts: [EvaluatableStatement] = Array(),
  ) {
    super.init(name, stmts)
  }

  public override func instantiate(_ name: Identifier) -> InstantiatedParserState? {
    return ParserStateNoTransitionValue(name: name, withState: self)
  }
}

public class ParserStateSelectTransition: ParserState {

  public let te: SelectExpression

  public init(
    name: Identifier, withTransitionExpression te: SelectExpression,
    withStatements stmts: [EvaluatableStatement] = Array()
  ) {
    self.te = te
    super.init(name, stmts)
  }

  public override func instantiate(_ name: Identifier) -> InstantiatedParserState? {
    return ParserStateSelectTransitionValue(name: name, withState: self, withSelectExpression: te)
  }
}

/// Instantiated Parser State
///
public class InstantiatedParserState: P4DataValue {
  public static func == (lhs: InstantiatedParserState, rhs: InstantiatedParserState) -> Bool {
    return lhs.state == rhs.state
  }

  public func type() -> any Common.P4Type {
    return self.state
  }

  public func eq(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let other as InstantiatedParserState: self.state == other.state
    default: false
    }
  }

  public func lt(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let other as InstantiatedParserState: self.state.getName() < other.state.getName()
    default: false
    }
  }

  public func lte(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let other as InstantiatedParserState: self.state.getName() <= other.state.getName()
    default: false
    }
  }

  public func gt(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let other as InstantiatedParserState: self.state.getName() > other.state.getName()
    default: false
    }
  }

  public func gte(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let other as InstantiatedParserState: self.state.getName() >= other.state.getName()
    default: false
    }
  }

  public private(set) var state: ParserState
  public private(set) var name: Identifier

  public var description: String {
    return "Instance of state of type \(state) named \(name)"
  }

  public init(_ name: Identifier, _ state: ParserState) {
    self.name = name
    self.state = state
  }
}

public class ParserStateDirectTransitionValue: InstantiatedParserState {
  public let next_state: InstantiatedParserState?
  public let next_state_identifier: Identifier?

  public init(
    name: Identifier, withState state: ParserStateDirectTransition,
    withNextState next_state: InstantiatedParserState
  ) {
    self.next_state = next_state
    self.next_state_identifier = .none
    super.init(name, state)
  }

  public init(
    name: Identifier, withState state: ParserStateDirectTransition,
    withNextStateIdentifier next_state_id: Identifier
  ) {
    self.next_state = .none
    self.next_state_identifier = next_state_id
    super.init(name, state)
  }
}

public class ParserStateNoTransitionValue: InstantiatedParserState {
  public init(name: Identifier, withState state: ParserStateNoTransition) {
    super.init(name, state)
  }
}

public class ParserStateSelectTransitionValue: InstantiatedParserState {
  public let te: SelectExpression
  public init(
    name: Identifier, withState state: ParserStateSelectTransition,
    withSelectExpression te: SelectExpression
  ) {
    self.te = te
    super.init(name, state)
  }
}

nonisolated(unsafe) private let accept_type = ParserStateNoTransition(
  name: Identifier(name: "accept"), withStatements: [])
nonisolated(unsafe) private let reject_type = ParserStateNoTransition(
  name: Identifier(name: "reject"), withStatements: [])

nonisolated(unsafe) public let accept = ParserStateNoTransitionValue(
  name: Identifier(name: "accept"), withState: accept_type)
nonisolated(unsafe) public let reject = ParserStateNoTransitionValue(
  name: Identifier(name: "reject"), withState: reject_type)

public struct ParserStates {
  public var states: [ParserState] = Array()

  public func count() -> Int {
    return states.count
  }

  public func find(withIdentifier id: Identifier) -> ParserState? {
    for state in states {
      if state.getName() == id {
        return .some(state)
      }
    }
    return .none
  }

  public init(_ states: [ParserState] = Array()) {
    self.states = states
  }

  public func append(state: ParserState) -> ParserStates {
    var new_states = self.states
    new_states.append(state)
    return ParserStates(new_states)
  }
}

/// A P4 Parser
///
/// Note: A Parser is a type
public struct Parser: P4Type {
  public var states: ParserStates

  public var name: Identifier
  public var parameters: ParameterList

  public init(withName name: Identifier) {
    self.states = ParserStates()
    self.parameters = ParameterList()
    self.name = name
  }

  public init(withName name: Identifier, withParameters parameters: ParameterList) {
    self.states = ParserStates()
    self.parameters = parameters
    self.name = name
  }

  public func findStartState() -> ParserState? {
    return self.states.find(withIdentifier: Identifier(name: "start"))
  }

  public var description: String {
    return "Parser \(self.name) with parameters: \(parameters) and states: \(self.states)"
  }

  public func def() -> P4DataValue? {
    return .none
  }

  public func eq(rhs: any Common.P4Type) -> Bool {
    return switch rhs {
    case let parser_rhs as Parser: self.name == parser_rhs.name
    default: false
    }
  }

  public func instantiate(_ name: Identifier) -> ParserValue {
    return ParserValue(self, name)
  }
}

/// A instance of a P4 Parser
///
public struct ParserValue: P4DataValue {
  public func type() -> P4Type {
    return self.tipe
  }

  public func eq(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let rrhs as ParserValue: rrhs.type().eq(rhs: self.type()) && self.name == rrhs.name
    default: false
    }
  }

  public func lt(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let rrhs as ParserValue: rrhs.type().eq(rhs: self.type()) && self.name < rrhs.name
    default: false
    }
  }

  public func lte(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let rrhs as ParserValue: rrhs.type().eq(rhs: self.type()) && self.name <= rrhs.name
    default: false
    }
  }

  public func gt(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let rrhs as ParserValue: rrhs.type().eq(rhs: self.type()) && self.name > rrhs.name
    default: false
    }
  }

  public func gte(rhs: any Common.P4DataValue) -> Bool {
    return switch rhs {
    case let rrhs as ParserValue: rrhs.type().eq(rhs: self.type()) && self.name >= rrhs.name
    default: false
    }
  }

  public var tipe: Parser
  public var name: Identifier

  public init(_ tipe: Parser, _ name: Identifier) {
    self.tipe = tipe
    self.name = name
  }

  public var description: String {
    return "Parser \(self.name) of type \(self.tipe)"
  }

  public func def() -> P4DataValue? {
    return self.tipe.def()
  }

}