package fileops

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

type ReplaceResult struct {
	File         string
	ChangedLines []int
}

// ReplaceInFile replaces all occurrences of from with to in the file at path.
// Returns the 1-indexed line numbers that were changed. If dryRun is true,
// the file is not written.
func ReplaceInFile(path, from, to string, dryRun bool) (ReplaceResult, error) {
	result := ReplaceResult{File: path}

	f, err := os.Open(path)
	if err != nil {
		return result, err
	}

	var lines []string
	scanner := bufio.NewScanner(f)
	lineNum := 0
	for scanner.Scan() {
		lineNum++
		line := scanner.Text()
		replaced := strings.ReplaceAll(line, from, to)
		if replaced != line {
			result.ChangedLines = append(result.ChangedLines, lineNum)
		}
		lines = append(lines, replaced)
	}
	f.Close()
	if err := scanner.Err(); err != nil {
		return result, err
	}

	if len(result.ChangedLines) == 0 || dryRun {
		return result, nil
	}

	return result, atomicWrite(path, strings.Join(lines, "\n")+trailingNewline(lines))
}

// ReplaceInFileRegex replaces regex matches of pattern with repl in the file at path.
func ReplaceInFileRegex(path, pattern, repl string, dryRun bool) (ReplaceResult, error) {
	result := ReplaceResult{File: path}

	f, err := os.Open(path)
	if err != nil {
		return result, err
	}

	re, err := compilePattern(pattern)
	if err != nil {
		f.Close()
		return result, err
	}

	var lines []string
	scanner := bufio.NewScanner(f)
	lineNum := 0
	for scanner.Scan() {
		lineNum++
		line := scanner.Text()
		replaced := re.ReplaceAllString(line, repl)
		if replaced != line {
			result.ChangedLines = append(result.ChangedLines, lineNum)
		}
		lines = append(lines, replaced)
	}
	f.Close()
	if err := scanner.Err(); err != nil {
		return result, err
	}

	if len(result.ChangedLines) == 0 || dryRun {
		return result, nil
	}

	return result, atomicWrite(path, strings.Join(lines, "\n")+trailingNewline(lines))
}

func PrintReplaceResults(results []ReplaceResult) {
	total := 0
	for _, r := range results {
		if len(r.ChangedLines) == 0 {
			continue
		}
		total++
		nums := formatLineNums(r.ChangedLines)
		fmt.Printf("%s: lines %s\n", r.File, nums)
	}
	fmt.Printf("%d file(s) modified.\n", total)
}

func atomicWrite(path, content string) error {
	tmp, err := os.CreateTemp(filepath.Dir(path), ".text-shark-*")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	if _, err := tmp.WriteString(content); err != nil {
		tmp.Close()
		os.Remove(tmpName)
		return err
	}
	if err := tmp.Close(); err != nil {
		os.Remove(tmpName)
		return err
	}
	return os.Rename(tmpName, path)
}

func trailingNewline(lines []string) string {
	if len(lines) > 0 {
		return "\n"
	}
	return ""
}

func formatLineNums(nums []int) string {
	parts := make([]string, len(nums))
	for i, n := range nums {
		parts[i] = fmt.Sprintf("%d", n)
	}
	return strings.Join(parts, ", ")
}