import Foundationimport Testing@testable import CodexBarCore @Suite(.serialized)struct CostUsageJsonlPerformanceTests {    @Test    func `scanner benchmark beats front buffer baseline`() throws {        let root = FileManager.default.temporaryDirectory.appendingPathComponent(            "codexbar-cost-usage-bench-\(UUID().uuidString)",            isDirectory: true)        try FileManager.default.createDirectory(at: root, withIntermediateDirectories: true)        defer { try? FileManager.default.removeItem(at: root) }         let fileURL = root.appendingPathComponent("scanner-benchmark.jsonl", isDirectory: false)        let lineCount = 20000        let line = #"{"type":"assistant","message":{"usage":{"input_tokens":1,"output_tokens":2}}}"#        let fixture = makeBenchmarkFixture(line: line, lineCount: lineCount)        try fixture.write(to: fileURL)         let maxLineBytes = 8192        let prefixBytes = 8192         let currentSummary = try summarizeScan(            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: CostUsageJsonl.scan)        let baselineSummary = try summarizeScan(            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: scanWithFrontBufferBaseline)         #expect(currentSummary == baselineSummary)        #expect(currentSummary.lineCount == lineCount)        #expect(currentSummary.truncatedCount == 0)         // Warm up both code paths before timing.        _ = try summarizeScan(            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: CostUsageJsonl.scan)        _ = try summarizeScan(            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: scanWithFrontBufferBaseline)         let currentFastest = try fastestScanDurationNanoseconds(            runs: 3,            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: CostUsageJsonl.scan)        let baselineFastest = try fastestScanDurationNanoseconds(            runs: 3,            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: scanWithFrontBufferBaseline)         let speedup = Double(baselineFastest) / Double(currentFastest)        print(            "Cost usage JSONL scanner benchmark: current=\(currentFastest)ns " +                "baseline=\(baselineFastest)ns speedup=\(String(format: "%.2f", speedup))x")        #expect(currentFastest < baselineFastest)    }} private struct JsonlScanSummary: Equatable {    let lineCount: Int    let truncatedCount: Int    let payloadByteCount: Int    let endOffset: Int64} private typealias JsonlScanner = (    _ fileURL: URL,    _ offset: Int64,    _ maxLineBytes: Int,    _ prefixBytes: Int,    _ onLine: (CostUsageJsonl.Line) -> Void) throws -> Int64 private func makeBenchmarkFixture(line: String, lineCount: Int) -> Data {    let lineBytes = Data(line.utf8)    var data = Data()    data.reserveCapacity((lineBytes.count + 1) * lineCount)    for _ in 0..<lineCount {        data.append(lineBytes)        data.append(0x0A)    }    return data} private func summarizeScan(    fileURL: URL,    maxLineBytes: Int,    prefixBytes: Int,    scanner: JsonlScanner) throws -> JsonlScanSummary{    var lineCount = 0    var truncatedCount = 0    var payloadByteCount = 0     let endOffset = try scanner(fileURL, 0, maxLineBytes, prefixBytes) { line in        lineCount += 1        payloadByteCount += line.bytes.count        if line.wasTruncated {            truncatedCount += 1        }    }     return JsonlScanSummary(        lineCount: lineCount,        truncatedCount: truncatedCount,        payloadByteCount: payloadByteCount,        endOffset: endOffset)} private func fastestScanDurationNanoseconds(    runs: Int,    fileURL: URL,    maxLineBytes: Int,    prefixBytes: Int,    scanner: JsonlScanner) throws -> UInt64{    var fastest = UInt64.max    for _ in 0..<runs {        let startedAt = DispatchTime.now().uptimeNanoseconds        _ = try summarizeScan(            fileURL: fileURL,            maxLineBytes: maxLineBytes,            prefixBytes: prefixBytes,            scanner: scanner)        let elapsed = DispatchTime.now().uptimeNanoseconds - startedAt        fastest = min(fastest, elapsed)    }    return fastest} @discardableResultprivate func scanWithFrontBufferBaseline(    fileURL: URL,    offset: Int64 = 0,    maxLineBytes: Int,    prefixBytes: Int,    onLine: (CostUsageJsonl.Line) -> Void) throws    -> Int64{    let handle = try FileHandle(forReadingFrom: fileURL)    defer { try? handle.close() }     let startOffset = max(0, offset)    if startOffset > 0 {        try handle.seek(toOffset: UInt64(startOffset))    }     var buffer = Data()    buffer.reserveCapacity(64 * 1024)     var current = Data()    current.reserveCapacity(4 * 1024)    var lineBytes = 0    var truncated = false    var bytesRead: Int64 = 0     func flushLine() {        guard lineBytes > 0 else { return }        onLine(.init(bytes: current, wasTruncated: truncated))        current.removeAll(keepingCapacity: true)        lineBytes = 0        truncated = false    }     while true {        let chunk = try handle.read(upToCount: 256 * 1024) ?? Data()        if chunk.isEmpty {            flushLine()            break        }         bytesRead += Int64(chunk.count)        buffer.append(chunk)         while true {            guard let nl = buffer.firstIndex(of: 0x0A) else { break }            let linePart = buffer[..<nl]            buffer.removeSubrange(...nl)             lineBytes += linePart.count            if !truncated {                if lineBytes > maxLineBytes || lineBytes > prefixBytes {                    truncated = true                    current.removeAll(keepingCapacity: true)                } else {                    current.append(contentsOf: linePart)                }            }             flushLine()        }    }     return startOffset + bytesRead}