PureYAML/Tests/LibYAMLParserTests.swift

@testable import PureYAML
import Testing

/// End-to-end event production through the ported parser state machine. Events are
/// rendered to the YAML test-suite "yeast" format (mark-independent) so the
/// expectations read like the canonical `test.event` files.
@Suite("LibYAML Parser")
struct LibYAMLParserTests {
    private func events(_ input: String) throws -> [String] {
        var parser = try PureYAML.Parsing.LibYAML.Parser(input)
        return try parser.parse().map(render)
    }

    private func render(_ event: PureYAML.Parsing.Event) -> String {
        switch event {
        case .streamStart:
            "+STR"
        case .streamEnd:
            "-STR"
        case let .documentStart(explicit, _):
            explicit ? "+DOC ---" : "+DOC"
        case let .documentEnd(explicit, _):
            explicit ? "-DOC ..." : "-DOC"
        case let .sequenceStart(anchor, tag, style, _):
            "+SEQ" + (style == .flow ? " []" : "") + properties(anchor, tag)
        case .sequenceEnd:
            "-SEQ"
        case let .mappingStart(anchor, tag, style, _):
            "+MAP" + (style == .flow ? " {}" : "") + properties(anchor, tag)
        case .mappingEnd:
            "-MAP"
        case let .scalar(value, anchor, tag, style, _):
            "=VAL" + properties(anchor, tag) + " " + styleChar(style) + escape(value)
        case let .alias(anchor, _):
            "=ALI *" + anchor
        }
    }

    private func properties(_ anchor: String?, _ tag: String?) -> String {
        (anchor.map { " &" + $0 } ?? "") + (tag.map { " <" + $0 + ">" } ?? "")
    }

    private func styleChar(_ style: PureYAML.Parsing.ScalarStyle) -> String {
        switch style {
        case .plain: ":"
        case .singleQuoted: "'"
        case .doubleQuoted: "\""
        case .literal: "|"
        case .folded: ">"
        }
    }

    private func escape(_ value: String) -> String {
        var output = ""
        for scalar in value.unicodeScalars {
            switch scalar {
            case "\\": output += "\\\\"
            case "\n": output += "\\n"
            case "\t": output += "\\t"
            case "\r": output += "\\r"
            default: output.unicodeScalars.append(scalar)
            }
        }
        return output
    }

    @Test("a bare root scalar")
    func test_rootScalar() throws {
        #expect(try events("x\n") == ["+STR", "+DOC", "=VAL :x", "-DOC", "-STR"])
    }

    @Test("a block sequence")
    func test_blockSequence() throws {
        #expect(try events("- a\n- b\n") == [
            "+STR", "+DOC", "+SEQ", "=VAL :a", "=VAL :b", "-SEQ", "-DOC", "-STR",
        ])
    }

    @Test("a block mapping")
    func test_blockMapping() throws {
        #expect(try events("a: b\n") == [
            "+STR", "+DOC", "+MAP", "=VAL :a", "=VAL :b", "-MAP", "-DOC", "-STR",
        ])
    }

    @Test("a mapping nested in a sequence entry with an empty value")
    func test_nestedMappingEmptyValue() throws {
        // The original block-mapping bug: `- a:` / `  b: c` is {a: null, b: c}.
        #expect(try events("- a:\n  b: c\n") == [
            "+STR", "+DOC", "+SEQ", "+MAP",
            "=VAL :a", "=VAL :",
            "=VAL :b", "=VAL :c",
            "-MAP", "-SEQ", "-DOC", "-STR",
        ])
    }

    @Test("a flow sequence")
    func test_flowSequence() throws {
        #expect(try events("[a, b]\n") == [
            "+STR", "+DOC", "+SEQ []", "=VAL :a", "=VAL :b", "-SEQ", "-DOC", "-STR",
        ])
    }

    @Test("a flow mapping")
    func test_flowMapping() throws {
        #expect(try events("{a: b}\n") == [
            "+STR", "+DOC", "+MAP {}", "=VAL :a", "=VAL :b", "-MAP", "-DOC", "-STR",
        ])
    }

    @Test("an anchor and an alias")
    func test_anchorAlias() throws {
        #expect(try events("a: &x 1\nb: *x\n") == [
            "+STR", "+DOC", "+MAP",
            "=VAL :a", "=VAL &x :1",
            "=VAL :b", "=ALI *x",
            "-MAP", "-DOC", "-STR",
        ])
    }

    @Test("a shorthand tag resolves against the default !! handle")
    func test_shorthandTag() throws {
        #expect(try events("!!str x\n") == [
            "+STR", "+DOC", "=VAL <tag:yaml.org,2002:str> :x", "-DOC", "-STR",
        ])
    }

    @Test("a custom %TAG directive resolves a shorthand")
    func test_tagDirective() throws {
        #expect(try events("%TAG !e! tag:example.com,2000:\n---\n!e!foo x\n") == [
            "+STR", "+DOC ---", "=VAL <tag:example.com,2000:foo> :x", "-DOC", "-STR",
        ])
    }

    @Test("a version directive opens an explicit document")
    func test_versionDirective() throws {
        #expect(try events("%YAML 1.2\n---\nx\n") == [
            "+STR", "+DOC ---", "=VAL :x", "-DOC", "-STR",
        ])
    }

    @Test("multiple explicit documents")
    func test_multipleDocuments() throws {
        #expect(try events("---\na\n---\nb\n") == [
            "+STR",
            "+DOC ---", "=VAL :a", "-DOC",
            "+DOC ---", "=VAL :b", "-DOC",
            "-STR",
        ])
    }

    @Test("a quoted scalar is not plain-implicit")
    func test_quotedScalar() throws {
        #expect(try events("\"x\"\n") == [
            "+STR", "+DOC", "=VAL \"x", "-DOC", "-STR",
        ])
    }
}