package gotool

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

const performanceDiagnosticSize = 8 << 20

func BenchmarkPerformanceCombinedOutput(b *testing.B) {
	for _, testCase := range []struct {
		name string
		size int
	}{
		{name: "modest", size: 4 << 10},
		{name: "diagnostic-8MiB", size: performanceDiagnosticSize},
	} {
		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) {
			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}
				if written, err := writer.Write(input); err != nil || written != len(input) {
					b.Fatalf("write captured output = %d, err %v; want %d bytes", written, err, len(input))
				}
				captured := writer.take()
				if len(captured) != len(input) {
					b.Fatalf("captured output = %d bytes, want %d", len(captured), len(input))
				}
			}
		})
	}
}