import Foundation
import Testing
@testable import PureYAMLStreaming

/// Differential proof that the token-driven `ResumableDocumentScanner` emits
/// byte-identical document splits to the retired line-based heuristic on every
/// input where that heuristic was correct: the existing fixture corpus,
/// generated multi-document streams, and handwritten benign shapes. Inputs
/// where the heuristic was wrong (directives, grammar-internal `---` lines,
/// input ending on a `---` line without a newline) are covered by
/// `DocumentScannerTests` instead, which pins the corrected behavior.
@Suite("Document scanner differential")
struct DocumentScannerDifferentialTests {
    /// Streams the line-based heuristic split correctly: newline-terminated,
    /// directive-free, and with every column-zero `---` a real boundary.
    static let benignInputs: [String] = [
        "---\na: 1\n---\nb: 2\n",
        "name: only\n",
        "# note\n---\na: 1\n",
        "---\na: 1\n# trailing\n---\nb: 2\n",
        "a: 1\n--- # comment\nb: 2\n",
        "a: 1\n...\nb: 2\n",
        "---\na: 1\n...\n---\nb: 2\n",
        "---\n---\n",
        "a: 1\r\n---\r\nb: 2\r\n",
        "# only comments\n\n",
        "",
    ]

    @Test("matches the line-based reference on benign streams", arguments: benignInputs)
    func matchesReferenceOnBenignStreams(input: String) throws {
        for chunkSize in [1, 2, 3, 7, 64, max(input.unicodeScalars.count, 1)] {
            let rewired = try rewiredSegments(input, chunkSize: chunkSize)
            let reference = try referenceSegments(input, chunkSize: chunkSize)
            #expect(rewired == reference, "chunk size \(chunkSize) diverged for: \(input.debugDescription)")
            #expect(rewired.joined() == input)
        }
    }

    @Test("matches the line-based reference on a generated multi-document stream")
    func matchesReferenceOnGeneratedStream() throws {
        var input = ""
        for index in 0 ..< 300 {
            input += """
            ---
            name: doc-\(index)
            enabled: \(index.isMultiple(of: 2) ? "true" : "false")
            nested:
              index: \(index)
              tags:
                - real
                - streaming
                - chunk-\(index % 17)

            """
        }

        for chunkSize in [7, 31, 4096] {
            let rewired = try rewiredSegments(input, chunkSize: chunkSize)
            let reference = try referenceSegments(input, chunkSize: chunkSize)
            #expect(rewired.count == 300)
            #expect(rewired == reference, "chunk size \(chunkSize) diverged on the generated stream")
            #expect(rewired.joined() == input)
        }
    }

    @Test("matches the line-based reference across the Geekbench corpus")
    func matchesReferenceAcrossCorpus() throws {
        let fixtureRoot = URL(fileURLWithPath: #filePath)
            .deletingLastPathComponent()
            .deletingLastPathComponent()
            .deletingLastPathComponent()
            .deletingLastPathComponent()
            .appendingPathComponent("PureYAMLGeekbench")
            .appendingPathComponent("Fixtures")
            .appendingPathComponent("real-yaml")
        guard FileManager.default.fileExists(atPath: fixtureRoot.path) else {
            return
        }

        let files = try FileManager.default.contentsOfDirectory(
            at: fixtureRoot,
            includingPropertiesForKeys: nil
        ).filter { url in
            url.pathExtension == "yaml" || url.pathExtension == "yml"
        }
        #expect(files.count >= 100)

        for file in files {
            let input = try String(decoding: Data(contentsOf: file), as: UTF8.self)
            for chunkSize in [31, 4097] {
                let rewired = try rewiredSegments(input, chunkSize: chunkSize)
                let reference = try referenceSegments(input, chunkSize: chunkSize)
                #expect(rewired == reference, "chunk size \(chunkSize) diverged for \(file.lastPathComponent)")
                #expect(rewired.joined() == input, "segments lost bytes for \(file.lastPathComponent)")
            }
        }
    }
}