// Copyright 2025 The Prometheus Authors
// 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.

package main

import (
	"io"
	"net/http"
	"net/http/httptest"
	"net/url"
	"os"
	"testing"
	"time"

	remoteapi "github.com/prometheus/client_golang/exp/api/remote"
	"github.com/stretchr/testify/require"
)

func TestPushMetrics(t *testing.T) {
	tests := []struct {
		name        string
		metricsData string
	}{
		{
			name: "successful push with gauge metrics",
			metricsData: `# HELP test_metric A test metric
# TYPE test_metric gauge
test_metric{label="value1"} 42.0
test_metric{label="value2"} 43.0
`,
		},
		{
			name: "successful push with counter metrics",
			metricsData: `# HELP test_counter A test counter
# TYPE test_counter counter
test_counter 100
`,
		},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			// Create test server using client_golang's remote write handler.
			store := &mockStorage{}
			handler := remoteapi.NewWriteHandler(
				store,
				remoteapi.MessageTypes{remoteapi.WriteV1MessageType},
			)

			server := httptest.NewServer(handler)
			defer server.Close()

			serverURL, err := url.Parse(server.URL)
			require.NoError(t, err)

			// Create a temp file with metrics data.
			tmpFile := t.TempDir() + "/metrics.txt"
			err = os.WriteFile(tmpFile, []byte(tc.metricsData), 0o644)
			require.NoError(t, err)

			// Call PushMetrics.
			status := PushMetrics(
				serverURL,
				http.DefaultTransport,
				map[string]string{},
				30*time.Second,
				map[string]string{"job": "test"},
				tmpFile,
			)

			require.Equal(t, successExitCode, status)
			// Verify that the handler received and processed the request.
			require.True(t, store.called, "Handler should have been called")
			require.NoError(t, store.lastErr, "Handler should not have returned an error")

			// Verify proper data propagation.
			require.NotEmpty(t, store.receivedData, "Request should contain data (compression and decompression successful)")
			require.Contains(t, store.receivedContentType, "application/x-protobuf", "Content-Type should be protobuf")
		})
	}
}

// mockStorage is a simple mock for testing the remote write handler.
type mockStorage struct {
	called              bool
	lastErr             error
	receivedData        []byte
	receivedContentType string
}

func (m *mockStorage) Store(req *http.Request, _ remoteapi.WriteMessageType) (*remoteapi.WriteResponse, error) {
	m.called = true

	// Capture content-type header.
	m.receivedContentType = req.Header.Get("Content-Type")

	if req.Body != nil {
		data, err := io.ReadAll(req.Body)
		if err == nil {
			m.receivedData = data
		}
	}

	if m.lastErr != nil {
		return nil, m.lastErr
	}
	resp := remoteapi.NewWriteResponse()
	resp.SetStatusCode(http.StatusNoContent)
	return resp, nil
}