package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
)

// applyStandardModifications applies standard modifications
func applyStandardModifications(targetFilePath string, modifications []string) error {
	// Open the target file
	targetFile, err := os.Open(targetFilePath)
	if err != nil {
		return fmt.Errorf("failed to open target file: %v", err)
	}
	defer targetFile.Close()

	// Prepare a temporary file for output
	tempFilePath := targetFilePath + ".tmp"
	tempFile, err := os.Create(tempFilePath)
	if err != nil {
		return fmt.Errorf("failed to create temp file: %v", err)
	}
	defer tempFile.Close()

	scanner := bufio.NewScanner(targetFile)
	var targetLines []string
	for scanner.Scan() {
		targetLines = append(targetLines, scanner.Text())
	}

	if err := scanner.Err(); err != nil {
		return fmt.Errorf("failed to read target file: %v", err)
	}

	// Apply the modifications
	updatedLines, err := applyModifications(targetLines, modifications)
	if err != nil {
		return err
	}

	// Write the updated lines to the temporary file
	for _, line := range updatedLines {
		_, err := fmt.Fprintln(tempFile, line)
		if err != nil {
			return fmt.Errorf("failed to write to temp file: %v", err)
		}
	}

	// Replace the original file with the updated file
	err = os.Rename(tempFilePath, targetFilePath)
	if err != nil {
		return fmt.Errorf("failed to replace target file: %v", err)
	}

	return nil
}

// applyModifications applies the changes from the patch file to the target lines
func applyModifications(targetLines, modifications []string) ([]string, error) {
	var result []string
	i := 0

	for _, mod := range modifications {
		switch {
		case strings.HasPrefix(mod, "-"): // Delete or replace
			mod = strings.TrimPrefix(mod, "-")
			for i < len(targetLines) {
				if strings.TrimSpace(targetLines[i]) == strings.TrimSpace(mod) {
					i++ // Skip this line (delete)
					break
				}
				result = append(result, targetLines[i])
				i++
			}
		case strings.HasPrefix(mod, "+"): // Add or replace
			mod = strings.TrimPrefix(mod, "+")
			result = append(result, mod)
		default: // Keep existing lines
			if i < len(targetLines) {
				result = append(result, targetLines[i])
				i++
			}
		}
	}

	// Append remaining lines from the original file
	for i < len(targetLines) {
		result = append(result, targetLines[i])
		i++
	}

	return result, nil
}