PureYAML/Sources/Parsing/LibYAML.Parser.Node.swift

extension PureYAML.Parsing.LibYAML.Parser {
    typealias NodeProperties = PureYAML.Parsing.LibYAML.NodeProperties

    /// Port of `yaml_parser_parse_node`. An ALIAS is emitted directly; otherwise
    /// the node's anchor/tag properties are consumed, the tag is resolved, and the
    /// content token selects a scalar, a flow/block collection start, or an empty
    /// scalar standing in for a property-only node.
    mutating func parseNode(block: Bool, indentlessSequence: Bool) throws -> Event {
        let token = peekToken()
        if case let .alias(name) = token.type {
            state = states.removeLast()
            skipToken()
            return .alias(anchor: name, mark: token.startMark)
        }
        let props = consumeNodeProperties()
        let tag = try props.tagHandle.map {
            try resolveTag(handle: $0, suffix: props.tagSuffix ?? "", startMark: props.startMark, tagMark: props.tagMark)
        }
        return try dispatchNodeContent(block: block, indentlessSequence: indentlessSequence, props: props, tag: tag)
    }

    /// Consume `properties ::= TAG ANCHOR? | ANCHOR TAG?` ahead of the content.
    private mutating func consumeNodeProperties() -> NodeProperties {
        var token = peekToken()
        var props = NodeProperties(anchor: nil, tagHandle: nil, tagSuffix: nil, startMark: token.startMark, tagMark: token.startMark)
        if case let .anchor(name) = token.type {
            props.anchor = name
            skipToken()
            token = peekToken()
            if case let .tag(handle, suffix) = token.type {
                props.tagHandle = handle
                props.tagSuffix = suffix
                props.tagMark = token.startMark
                skipToken()
            }
        } else if case let .tag(handle, suffix) = token.type {
            props.tagHandle = handle
            props.tagSuffix = suffix
            props.tagMark = token.startMark
            skipToken()
            token = peekToken()
            if case let .anchor(name) = token.type {
                props.anchor = name
                skipToken()
            }
        }
        return props
    }

    /// Select the event for the content token following a node's properties.
    private mutating func dispatchNodeContent(block: Bool, indentlessSequence: Bool, props: NodeProperties, tag: String?) throws -> Event {
        let token = peekToken()
        if indentlessSequence, case .blockEntry = token.type {
            state = .indentlessSequenceEntry
            return .sequenceStart(anchor: props.anchor, tag: tag, style: .block, mark: props.startMark)
        }
        if let event = contentEvent(token: token, block: block, props: props, tag: tag) {
            return event
        }
        return try emptyNodeOrError(token: token, block: block, props: props, tag: tag)
    }

    /// A scalar or a flow/block collection start, or nil if the token is neither.
    private mutating func contentEvent(token: Token, block: Bool, props: NodeProperties, tag: String?) -> Event? {
        switch token.type {
        case let .scalar(value, style):
            state = states.removeLast()
            skipToken()
            return .scalar(value: value, anchor: props.anchor, tag: tag, style: style, mark: props.startMark, endMark: token.endMark)
        case .flowSequenceStart:
            state = .flowSequenceFirstEntry
            return .sequenceStart(anchor: props.anchor, tag: tag, style: .flow, mark: props.startMark)
        case .flowMappingStart:
            state = .flowMappingFirstKey
            return .mappingStart(anchor: props.anchor, tag: tag, style: .flow, mark: props.startMark)
        case .blockSequenceStart where block:
            state = .blockSequenceFirstEntry
            return .sequenceStart(anchor: props.anchor, tag: tag, style: .block, mark: props.startMark)
        case .blockMappingStart where block:
            state = .blockMappingFirstKey
            return .mappingStart(anchor: props.anchor, tag: tag, style: .block, mark: props.startMark)
        default:
            return nil
        }
    }

    /// An empty scalar when the node carried only properties, else a parse error.
    private mutating func emptyNodeOrError(token: Token, block: Bool, props: NodeProperties, tag: String?) throws -> Event {
        if props.anchor != nil || tag != nil {
            state = states.removeLast()
            return .scalar(value: "", anchor: props.anchor, tag: tag, style: .plain, mark: props.startMark, endMark: props.startMark)
        }
        throw ParserError(
            context: block ? "while parsing a block node" : "while parsing a flow node",
            problem: "did not find expected node content",
            mark: token.startMark,
        )
    }
}