package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
)

type Result struct {
	FilteredChanges []string `json:"filteredChanges"`
	NextVersion     string   `json:"nextVersion"`
}

func main() {
	// Parse command-line arguments
	var patterns patternList
	var depth int

	flag.Var(&patterns, "p", "Path pattern to filter changed files (can be specified multiple times)")
	flag.Var(&patterns, "pattern", "Path pattern to filter changed files (can be specified multiple times)")
	flag.IntVar(&depth, "d", 2, "Depth of changeset (default is 2)")
	flag.IntVar(&depth, "depth", 2, "Depth of changeset (default is 2)")
	help := flag.Bool("h", false, "Display this help message")
	helpLong := flag.Bool("help", false, "Display this help message")
	flag.Parse()

	if *help || *helpLong {
		flag.Usage()
		os.Exit(1)
	}

	if len(patterns) == 0 {
		fmt.Println("Error: At least one path pattern must be specified.")
		flag.Usage()
		os.Exit(1)
	}

	// Get the current commit SHA
	currentSHA := getCurrentSHA()

	// Get parent commits
	parentSHAs := getParentSHAs(currentSHA)

	if len(parentSHAs) == 0 {
		fmt.Println("Single commit with no parents. Listing all changes.")
		parentSHAs = append(parentSHAs, currentSHA+"~1")
	}

	// Collect all changed files from all parents
	changedFiles := make(map[string]struct{})
	for _, parentSHA := range parentSHAs {
		files := getChangedFiles(parentSHA, currentSHA)
		for _, file := range files {
			changedFiles[file] = struct{}{}
		}
	}

	// Filter and process changed files
	filteredChanges := filterAndProcessFiles(changedFiles, patterns, depth)

	// Get the next semantic version using git-sv
	nextVersion := getNextVersion()

	// Prepare the result
	result := Result{
		FilteredChanges: uniqueStrings(filteredChanges),
		NextVersion:     nextVersion,
	}

	// Output results as JSON
	output, err := json.Marshal(result)
	if err != nil {
		log.Fatalf("Error marshaling JSON: %v", err)
	}

	fmt.Println(string(output))
}

// Custom flag type for multiple patterns
type patternList []string

func (p *patternList) String() string {
	return strings.Join(*p, ", ")
}

func (p *patternList) Set(value string) error {
	*p = append(*p, value)
	return nil
}

// Helper functions
func getCurrentSHA() string {
	output, err := exec.Command("git", "rev-parse", "HEAD").Output()
	if err != nil {
		log.Fatalf("Error getting current SHA: %v", err)
	}
	return strings.TrimSpace(string(output))
}

func getParentSHAs(commitSHA string) []string {
	output, err := exec.Command("git", "rev-list", "--parents", "-n", "1", commitSHA).Output()
	if err != nil {
		log.Fatalf("Error getting parent SHAs: %v", err)
	}
	parts := strings.Fields(string(output))
	if len(parts) > 1 {
		return parts[1:] // Exclude the current commit SHA
	}
	return []string{}
}

func getChangedFiles(parentSHA, currentSHA string) []string {
	output, err := exec.Command("git", "diff", "--name-only", parentSHA, currentSHA).Output()
	if err != nil {
		log.Fatalf("Error getting changed files: %v", err)
	}
	lines := strings.Split(strings.TrimSpace(string(output)), "\n")
	if len(lines) == 1 && lines[0] == "" {
		return []string{}
	}
	return lines
}

func filterAndProcessFiles(changedFiles map[string]struct{}, patterns []string, depth int) []string {
	var filtered []string
	for file := range changedFiles {
		for _, pattern := range patterns {
			matched, err := regexp.MatchString(pattern, file)
			if err != nil {
				log.Fatalf("Invalid regex pattern: %v", err)
			}
			if matched {
				processedFile := processFilePath(file, depth)
				filtered = append(filtered, processedFile)
				break // Stop checking other patterns for this file
			}
		}
	}
	return filtered
}

func processFilePath(filePath string, depth int) string {
	parts := strings.Split(filePath, string(os.PathSeparator))
	if len(parts) > depth {
		parts = parts[:depth]
	}
	return filepath.Join(parts...)
}

func uniqueStrings(input []string) []string {
	uniqueMap := make(map[string]struct{})
	for _, item := range input {
		uniqueMap[item] = struct{}{}
	}
	var result []string
	for item := range uniqueMap {
		result = append(result, item)
	}
	return result
}

func getNextVersion() string {
	// Ensure that git-sv is available
	if _, err := exec.LookPath("git-sv"); err != nil {
		log.Fatalf("Error: git-sv is not installed or not in PATH.")
	}
	output, err := exec.Command("git-sv", "next-version").Output()
	if err != nil {
		log.Fatalf("Error getting next version: %v", err)
	}
	nextVersion := strings.TrimSpace(string(output))
	return nextVersion
}