PureYAML/Sources/Parsing/Parser.Events.swift

extension PureYAML.Parsing.Parser {
    func parseEvents(_ yaml: String) throws -> [PureYAML.Parsing.Event] {
        let events: [PureYAML.Parsing.Event]
        do {
            var parser = try PureYAML.Parsing.LibYAML.Parser(yaml)
            events = try parser.parse().map { $0.bumpingMark() }
        } catch let error as PureYAML.Parsing.LibYAML.ScannerError {
            throw PureYAML.Parsing.ParseError(translating: error)
        } catch let error as PureYAML.Parsing.LibYAML.ParserError {
            throw PureYAML.Parsing.ParseError(translating: error)
        }
        try enforceNestingLimit(events)
        return events
    }

    /// The deepest collection nesting the value/event composers will build. The
    /// ported parser produces events iteratively without recursion, but the
    /// composers, equality, hashing, and `Model/Value` teardown all recurse with
    /// the nesting depth, so the event stream is bounded here before any recursive
    /// consumer runs. 64 accepts every realistic document yet rejects pathological
    /// input well before it can overflow the stack.
    static var maxNestingDepth: Int {
        64
    }

    /// Reject an event stream that nests collections past ``maxNestingDepth`` with
    /// a ``ParseError/nestingTooDeep(line:column:)`` so deeply nested input fails
    /// cleanly instead of overflowing a recursive consumer's stack.
    private func enforceNestingLimit(_ events: [PureYAML.Parsing.Event]) throws {
        var depth = 0
        for event in events {
            switch event {
            case .sequenceStart, .mappingStart:
                depth += 1
                if depth > Self.maxNestingDepth {
                    throw PureYAML.Parsing.ParseError.nestingTooDeep(line: event.mark.line, column: event.mark.column)
                }
            case .sequenceEnd, .mappingEnd:
                depth -= 1
            default:
                break
            }
        }
    }

    func parseStreaming(_ yaml: String) throws -> PureYAML.Model.Value {
        var composer = PureYAML.Parsing.EventStreamComposer(
            scalarParser: self,
            mode: .singleDocument,
        )
        for event in try parseEvents(yaml) {
            try composer.consume(event)
        }
        return try composer.composedValue()
    }

    func parseStreamStreaming(_ yaml: String) throws -> [PureYAML.Stream.Document] {
        var composer = PureYAML.Parsing.EventStreamComposer(
            scalarParser: self,
            mode: .stream,
        )
        for event in try parseEvents(yaml) {
            try composer.consume(event)
        }
        return try composer.composedStream()
    }

    func parseLocatedStreaming(_ yaml: String) throws -> PureYAML.Model.LocatedValue {
        var composer = PureYAML.Parsing.EventStreamComposer(
            scalarParser: self,
            mode: .singleDocument,
            tracksLocations: true,
        )
        for event in try parseEvents(yaml) {
            try composer.consume(event)
        }
        return try composer.composedLocated()
    }

    func parseStreamLocatedStreaming(_ yaml: String) throws -> [PureYAML.Model.LocatedValue] {
        var composer = PureYAML.Parsing.EventStreamComposer(
            scalarParser: self,
            mode: .stream,
            tracksLocations: true,
        )
        for event in try parseEvents(yaml) {
            try composer.consume(event)
        }
        return try composer.composedLocatedStream()
    }
}