gp4/Sources/P4Parser/Visitor.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 CSTVisitorDriver {
  public init() {}

  public func visit<T>(
    _ elem: any CST.Categories.LanguageElement, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {
    return switch elem {
    case let elem as CST.Categories.Expression:
      visit(expression: elem, visitor: visitor, context: context)
    case let elem as CST.Categories.Statement:
      visit(statement: elem, visitor: visitor, context: context)
    case let elem as CST.Categories.State: visit(state: elem, visitor: visitor, context: context)
    case let elem as CST.Categories.Declaration:
      visit(declaration: elem, visitor: visitor, context: context)
    default: .Error(Error(withMessage: "AST Language Element (\(elem)) Is Not Visitable"))
    }
  }

  func visit<T>(
    declaration: any CST.Categories.Declaration, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {
    return switch declaration {
    case let elem as CST.Control: visitor.visit(node: elem, driver: self, context: context)
    case let elem as CST.ExternDeclaration:
      visitor.visit(node: elem, driver: self, context: context)
    case let elem as CST.FunctionDeclaration:
      visitor.visit(node: elem, driver: self, context: context)
    case let elem as CST.StructDeclaration:
      visitor.visit(node: elem, driver: self, context: context)
    case let elem as CST.Parser: visitor.visit(node: elem, driver: self, context: context)
    default: .Error(Error(withMessage: "AST Declaration Element (\(declaration)) Is Not Visitable"))
    }
  }

  func visit<T>(
    expression: any CST.Categories.Expression, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {
    return switch expression {
    case let s as CST.Identifier:
      visitor.visit(node: s, driver: self, context: context)
    case let s as CST.KeysetExpression:
      visitor.visit(node: s, driver: self, context: context)
    case let s as CST.SelectCaseExpression:
      visitor.visit(node: s, driver: self, context: context)
    case let e as CST.SelectExpression:
      visitor.visit(node: e, driver: self, context: context)
    case let e as CST.BinaryOperatorExpression:
      visitor.visit(node: e, driver: self, context: context)
    case let e as CST.Literal: visitor.visit(node: e, driver: self, context: context)
    default: .Error(Error(withMessage: "AST Expression Element (\(expression)) Is Not Visitable"))
    }
  }

  func visit<T>(
    state: any CST.Categories.State, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {
    return switch state {
    case let s as CST.ParserStateDirectTransition:
      visitor.visit(node: s, driver: self, context: context)
    case let s as CST.ParserStateNoTransition:
      visitor.visit(node: s, driver: self, context: context)
    case let s as CST.ParserStateSelectTransition:
      visitor.visit(node: s, driver: self, context: context)
    default: .Error(Error(withMessage: "AST State Element (\(state)) Is Not Visitable"))
    }
  }

  func visit<T>(
    statement: any CST.Categories.Statement, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {
    return switch statement {
    case let s as CST.Statements: visitor.visit(node: s, driver: self, context: context)
    case let s as CST.ExpressionStatement: visitor.visit(node: s, driver: self, context: context)
    case let s as CST.VariableDeclarationStatement:
      visitor.visit(node: s, driver: self, context: context)
    case let s as CST.Parser: visitor.visit(node: s, driver: self, context: context)
    default: .Error(Error(withMessage: "AST Statement Element (\(statement)) Is Not Visitable"))
    }
  }

  public func start<T>(
    program: CST.Program, visitor: any CSTVisitor<T>, context: T
  ) -> Result<T> {

    var context = context
    switch visit(statement: program.statements, visitor: visitor, context: context) {
    case .Ok(let c): context = c
    case .Error(let e): return .Error(e)
    }

    return .Ok(context)
  }
}