// Copyright 2024 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 config

import (
	"os"
	"path/filepath"
	"testing"

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

func TestGenerateChecksum(t *testing.T) {
	// Create a temporary directory to hold the test files.
	tmpDir, err := os.MkdirTemp("", "checksum_test")
	require.NoError(t, err)
	defer os.RemoveAll(tmpDir) // Clean up.

	// Define paths for the temporary files.
	yamlFilePath := filepath.Join(tmpDir, "test.yml")
	ruleFilePath := filepath.Join(tmpDir, "rule_file.yml")
	scrapeConfigFilePath := filepath.Join(tmpDir, "scrape_config.yml")

	// Define initial and modified content for the files.
	originalRuleContent := "groups:\n- name: example\n  rules:\n  - alert: ExampleAlert"
	modifiedRuleContent := "groups:\n- name: example\n  rules:\n  - alert: ModifiedAlert"

	originalScrapeConfigContent := "scrape_configs:\n- job_name: example"
	modifiedScrapeConfigContent := "scrape_configs:\n- job_name: modified_example"

	// Define YAML content referencing the rule and scrape config files.
	yamlContent := `
rule_files:
  - rule_file.yml
scrape_config_files:
  - scrape_config.yml
`

	// Write initial content to files.
	require.NoError(t, os.WriteFile(ruleFilePath, []byte(originalRuleContent), 0o644))
	require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(originalScrapeConfigContent), 0o644))
	require.NoError(t, os.WriteFile(yamlFilePath, []byte(yamlContent), 0o644))

	// Generate the original checksum.
	originalChecksum := calculateChecksum(t, yamlFilePath)

	t.Run("Rule File Change", func(t *testing.T) {
		// Modify the rule file.
		require.NoError(t, os.WriteFile(ruleFilePath, []byte(modifiedRuleContent), 0o644))

		// Checksum should change.
		modifiedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, modifiedChecksum)

		// Revert the rule file.
		require.NoError(t, os.WriteFile(ruleFilePath, []byte(originalRuleContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Scrape Config Change", func(t *testing.T) {
		// Modify the scrape config file.
		require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(modifiedScrapeConfigContent), 0o644))

		// Checksum should change.
		modifiedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, modifiedChecksum)

		// Revert the scrape config file.
		require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(originalScrapeConfigContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Rule File Deletion", func(t *testing.T) {
		// Delete the rule file.
		require.NoError(t, os.Remove(ruleFilePath))

		// Checksum should change.
		deletedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, deletedChecksum)

		// Restore the rule file.
		require.NoError(t, os.WriteFile(ruleFilePath, []byte(originalRuleContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Scrape Config Deletion", func(t *testing.T) {
		// Delete the scrape config file.
		require.NoError(t, os.Remove(scrapeConfigFilePath))

		// Checksum should change.
		deletedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, deletedChecksum)

		// Restore the scrape config file.
		require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(originalScrapeConfigContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Main File Change", func(t *testing.T) {
		// Modify the main YAML file.
		modifiedYamlContent := `
global:
  scrape_interval: 3s
rule_files:
  - rule_file.yml
scrape_config_files:
  - scrape_config.yml
`
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(modifiedYamlContent), 0o644))

		// Checksum should change.
		modifiedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, modifiedChecksum)

		// Revert the main YAML file.
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(yamlContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Rule File Removed from YAML Config", func(t *testing.T) {
		// Modify the YAML content to remove the rule file.
		modifiedYamlContent := `
scrape_config_files:
  - scrape_config.yml
`
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(modifiedYamlContent), 0o644))

		// Checksum should change.
		modifiedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, modifiedChecksum)

		// Revert the YAML content.
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(yamlContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Scrape Config Removed from YAML Config", func(t *testing.T) {
		// Modify the YAML content to remove the scrape config file.
		modifiedYamlContent := `
rule_files:
  - rule_file.yml
`
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(modifiedYamlContent), 0o644))

		// Checksum should change.
		modifiedChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, modifiedChecksum)

		// Revert the YAML content.
		require.NoError(t, os.WriteFile(yamlFilePath, []byte(yamlContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Empty Rule File", func(t *testing.T) {
		// Write an empty rule file.
		require.NoError(t, os.WriteFile(ruleFilePath, []byte(""), 0o644))

		// Checksum should change.
		emptyChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, emptyChecksum)

		// Restore the rule file.
		require.NoError(t, os.WriteFile(ruleFilePath, []byte(originalRuleContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})

	t.Run("Empty Scrape Config File", func(t *testing.T) {
		// Write an empty scrape config file.
		require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(""), 0o644))

		// Checksum should change.
		emptyChecksum := calculateChecksum(t, yamlFilePath)
		require.NotEqual(t, originalChecksum, emptyChecksum)

		// Restore the scrape config file.
		require.NoError(t, os.WriteFile(scrapeConfigFilePath, []byte(originalScrapeConfigContent), 0o644))

		// Checksum should return to the original.
		revertedChecksum := calculateChecksum(t, yamlFilePath)
		require.Equal(t, originalChecksum, revertedChecksum)
	})
}

// calculateChecksum generates a checksum for the given YAML file path.
func calculateChecksum(t *testing.T, yamlFilePath string) string {
	checksum, err := GenerateChecksum(yamlFilePath)
	require.NoError(t, err)
	require.NotEmpty(t, checksum)
	return checksum
}