package gotool

import (
	"bytes"
	"io"
	"testing"
)

const performanceDiagnosticSize = 8 << 20

func BenchmarkPerformanceCombinedOutput(b *testing.B) {
	for _, testCase := range []struct {
		name      string
		size      int
		chunkSize int
	}{
		{name: "modest", size: 4 << 10, chunkSize: 4 << 10},
		{name: "diagnostic-8MiB", size: performanceDiagnosticSize, chunkSize: performanceDiagnosticSize},
		{name: "diagnostic-8MiB-32KiB-chunks", size: performanceDiagnosticSize, chunkSize: 32 << 10},
	} {
		input := bytes.Repeat([]byte("go tool diagnostic output\n"), (testCase.size+25)/26)
		input = input[:testCase.size]
		b.Run(testCase.name+"/discard-forwarding", func(b *testing.B) {
			// Verify capture and forwarding for this workload outside the measurement.
			var forwarded bytes.Buffer
			verification := &combinedWriter{output: &forwarded}
			for offset := 0; offset < len(input); offset += testCase.chunkSize {
				chunk := input[offset:min(offset+testCase.chunkSize, len(input))]
				if written, err := verification.Write(chunk); err != nil || written != len(chunk) {
					b.Fatalf("verify output write = %d, err %v; want %d bytes", written, err, len(chunk))
				}
			}
			if !bytes.Equal(verification.take(), input) || !bytes.Equal(forwarded.Bytes(), input) {
				b.Fatal("captured and forwarded output must equal the complete input")
			}
			b.ReportAllocs()
			b.SetBytes(int64(len(input)))
			b.ResetTimer()
			b.ReportMetric(float64(len(input)), "bytes/op")
			for i := 0; i < b.N; i++ {
				writer := &combinedWriter{output: io.Discard}
				for offset := 0; offset < len(input); offset += testCase.chunkSize {
					chunk := input[offset:min(offset+testCase.chunkSize, len(input))]
					if written, err := writer.Write(chunk); err != nil || written != len(chunk) {
						b.Fatalf("write captured output = %d, err %v; want %d bytes", written, err, len(chunk))
					}
				}
				captured := writer.take()
				if len(captured) != len(input) {
					b.Fatalf("captured output = %d bytes, want %d", len(captured), len(input))
				}
			}
		})
	}
}