// Copyright 2026 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//go:build vm_histogram

package promutil

import (
	"bytes"
	"testing"

	"github.com/stretchr/testify/require"
)

func TestMetricsResponseWriterPreservesChunkedLines(t *testing.T) {
	var buf bytes.Buffer
	writer := &metricsResponseWriter{Writer: &buf}

	_, err := writer.Write([]byte(`test_metric{label="foo"`))
	require.NoError(t, err)
	_, err = writer.Write([]byte("} 1\n"))
	require.NoError(t, err)

	require.Equal(t, "test_metric{label=\"foo\"} 1\n", buf.String())
}

func TestMetricsResponseWriterEnsureTrailingNewline(t *testing.T) {
	var buf bytes.Buffer
	writer := &metricsResponseWriter{Writer: &buf}

	_, err := writer.Write([]byte("test_metric 1"))
	require.NoError(t, err)
	require.NoError(t, writer.ensureTrailingNewline())
	require.NoError(t, writer.ensureTrailingNewline())

	require.Equal(t, "test_metric 1\n", buf.String())
}

func TestMetricsResponseWriterKeepsExistingTrailingNewline(t *testing.T) {
	var buf bytes.Buffer
	writer := &metricsResponseWriter{Writer: &buf}

	_, err := writer.Write([]byte("test_metric 1\n"))
	require.NoError(t, err)
	require.NoError(t, writer.ensureTrailingNewline())

	require.Equal(t, "test_metric 1\n", buf.String())
}