gp4/Sources/Parser/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 P4
import SwiftTreeSitter
import TreeSitterP4

extension MutableTree {
    public func isError(lang: Language) -> Bool {
        guard
            let parser_error_query = try? SwiftTreeSitter.Query(
                language: lang,
                data: String(
                    "(ERROR)"
                ).data(using: String.Encoding.utf8)!)
        else {
            return false
        }

        let error_qr = parser_error_query.execute(in: self)
        for _ in error_qr {
            return true
        }
        return false
    }
}

let p4lang = Language(tree_sitter_p4())

public protocol ParseableParserStatement {
    static func Parse(node: Node, inTree tree: MutableTree) -> Result<P4.ParserStatement?>
}

extension P4.ExpressionStatement: ParseableParserStatement {
    public static func Parse(node: Node, inTree tree: MutableTree) -> Result<P4.ParserStatement?> {
        guard
            let parser_state_query = try? SwiftTreeSitter.Query(
                language: p4lang,
                data: String(
                    "(expressionStatement (expression) @expression)"
                ).data(using: String.Encoding.utf8)!)
        else {
            return Result.Ok(.none)
        }

        let qr = parser_state_query.execute(node: node, in: tree)
        let query_result = qr.next()!
        let expression_capture = query_result.captures(named: "expression")
        if !expression_capture.isEmpty {
            // TODO: Actually create an ExpressionStatement
            return Result.Ok(P4.ExpressionStatement())
        }

        return Result.Ok(.none)

    }
}

extension P4.VariableDeclarationStatement: ParseableParserStatement {
    public static func Parse(node: Node, inTree tree: MutableTree) -> Result<P4.ParserStatement?> {
        guard
            let parser_state_query = try? SwiftTreeSitter.Query(
                language: p4lang,
                data: String(
                    "((annotations)? (typeRef) @type-name variable_name: (identifier) @identifier)"
                ).data(using: String.Encoding.utf8)!)
        else {
            return Result.Ok(.none)
        }

        let qr = parser_state_query.execute(node: node, in: tree)
        let parser_declaration = qr.next()!

        let type_name_capture = parser_declaration.captures(named: "type-name")
        let variable_name_capture = parser_declaration.captures(named: "identifier")

        // There must be a state name and there must be a transition statement.
        guard !type_name_capture.isEmpty,
            !variable_name_capture.isEmpty,
            let variable_name = variable_name_capture[0].node.text
        else {
            return Result.Error(Error(withMessage: "Could not parse a parser declaration"))
        }

        return Result.Ok(
            // TODO: Add support for parsing the value.
            P4.VariableDeclarationStatement(
                withIdentifier: Identifier(
                    name: variable_name, withValue: Value(withValue: ValueType.Boolean(true)))))
    }
}

public struct Parser {
    static func ParserLocalElements(capture: [QueryCapture], inTree tree: MutableTree) -> Result<
        [P4.ParserStatement]
    > {
        let localElementsParsers: [ParseableParserStatement.Type] = [
            P4.VariableDeclarationStatement.self
        ]

        var localElements: [P4.ParserStatement] = Array()

        for raw_le_statement in capture {
            var parsed_le_statement: P4.ParserStatement? = .none

            for le_parser in localElementsParsers {
                if case Result.Ok(.some(let parsed)) = le_parser.Parse(node: raw_le_statement.node, inTree: tree) {
                    parsed_le_statement = parsed
                    break
                }
            }

            if let le_statement = parsed_le_statement {
                localElements.append(le_statement)
            } else {
                // There were no parseable statements.
                return Result.Error(
                    Error(withMessage: "Failed to parse a local element: \(raw_le_statement)"))
            }
        }

        return Result.Ok(localElements)
    }

    static func ParserStatements(capture: [QueryCapture], inTree tree: MutableTree) -> Result<
        [P4.ParserStatement]
    > {
        let statementParsers: [ParseableParserStatement.Type] = [
            P4.ExpressionStatement.self, P4.VariableDeclarationStatement.self,
        ]

        var statements: [P4.ParserStatement] = Array()

        for raw_statement in capture {
            var parsed_statement: P4.ParserStatement? = .none

            // Iterate through statement parsers and give each one a chance.
            for parser in statementParsers {
                if case Result.Ok(.some(let parsed)) = parser.Parse(node: raw_statement.node, inTree: tree) {
                    parsed_statement = parsed
                    break
                }
            }

            if let statement = parsed_statement {
                statements.append(statement)
            } else {
                // There were no parseable statements.
                return Result.Error(
                    Error(withMessage: "Failed to parse a statement element: \(raw_statement)"))
            }
        }
        return Result.Ok(statements)
    }

    static func ParserTransitionStatement(node: Node, inTree tree: MutableTree) -> P4
        .ParserTransitionStatement?
    {
        return P4.ParserTransitionStatement()
    }

    static func ParserState(node: Node, inTree tree: MutableTree) -> Result<P4.ParserState> {
        guard
            let parser_state_query = try? SwiftTreeSitter.Query(
                language: p4lang,
                data: String(
                    "(parserState (state) (identifier) @state-name (parserLocalElements)? @state-local-elements (parserStatements)? @state-statements (parserTransitionStatement) @transition)"
                ).data(using: String.Encoding.utf8)!)
        else {
            return Result.Error(Error(withMessage: "Could not compile the tree sitter query"))
        }

        let qr = parser_state_query.execute(node: node, in: tree)

        let parser_declaration = qr.next()!

        let transition_capture = parser_declaration.captures(named: "transition")
        let state_name_capture = parser_declaration.captures(named: "state-name")
        let state_le_capture = parser_declaration.captures(named: "state-local-elements")
        let statements_capture = parser_declaration.captures(named: "state-statements")

        // There must be a state name and there must be a transition statement.
        guard !state_name_capture.isEmpty,
            !transition_capture.isEmpty,
            let parsed_state_name = state_name_capture[0].node.text,
            let transition_statement = ParserTransitionStatement(
                node: transition_capture[0].node, inTree: tree)
        else {
            return Result.Error(Error(withMessage: "Could not parse a parser declaration"))
        }

        let maybe_parsed_les =
            if !state_le_capture.isEmpty {
                ParserLocalElements(capture: state_le_capture, inTree: tree)
            } else {
                Result.Ok([P4.ParserStatement]())
            }

        guard case Result<[P4.ParserStatement]>.Ok(let parsed_les) = maybe_parsed_les else {
            return Result.Error(maybe_parsed_les.error()!)
        }

        let maybe_parsed_statements =
            if !statements_capture.isEmpty {
                ParserStatements(capture: statements_capture, inTree: tree)
            } else {
                Result.Ok([P4.ParserStatement]())
            }
        guard case Result<[P4.ParserStatement]>.Ok(let parsed_statements) = maybe_parsed_statements
        else {
            return Result.Error(maybe_parsed_statements.error()!)
        }

        // TODO: Validate that there is only one!
        return Result.Ok(
            P4.ParserState(
                name: parsed_state_name, withLocalElements: parsed_les,
                withStatements: parsed_statements,
                withTransition: transition_statement))
    }

    static func Parser(node: Node, inTree tree: MutableTree) -> Result<P4.Parser> {
        guard
            let parser_state_query = try? SwiftTreeSitter.Query(
                language: p4lang,
                data: String(
                    "(parserStates) @parser-states"
                ).data(using: String.Encoding.utf8)!)
        else {
            return Result.Error(
                Error(withMessage: "Could not compile the parser state tree sitter query"))
        }

        var parser = P4.Parser()

        // Build a state from each one listed.
        for parser_states in parser_state_query.execute(node: node, in: tree) {
            switch ParserState(node: parser_states.nodes[0], inTree: tree) {
            case Result.Ok(let state): parser.states.append(state)
            case Result.Error(let error): return Result.Error(error)
            }
        }
        return Result.Ok(parser)
    }

    public static func Program(_ source: String) -> Result<P4.Program> {

        let p = SwiftTreeSitter.Parser.init()

        do {
            try p.setLanguage(p4lang)
        } catch {
            return Result.Error(Error(withMessage: "Could not configure the P4 parser"))
        }

        let result = p.parse(source)
        guard let tree = result,
            !tree.isError(lang: p4lang)
        else {
            return Result.Error(Error(withMessage: "Could not compile the P4 program"))
        }

        guard
            let parser_declaration_query = try? SwiftTreeSitter.Query(
                language: p4lang,
                data: String(
                    "(parserDeclaration (parserType) (parserStates) @parser-states)"
                ).data(using: String.Encoding.utf8)!)
        else {
            return Result.Error(
                Error(withMessage: "Could not compile the parser declaration tree sitter query"))
        }

        var program: P4.Program = P4.Program()

        let parser_qc = parser_declaration_query.execute(in: tree)

        for parser_declaration in parser_qc {
            switch Parser(node: parser_declaration.nodes[0], inTree: tree) {
            case Result.Ok(let parser): program.parsers.append(parser)
            case Result.Error(let error): return Result.Error(error)
            }
        }

        return Result.Ok(program)
    }
}