package main

import(
	"os"
	"bufio"
	"errors"
	"fmt"
)

func main() {
	wordlist, err := getWordlistFrom("wordlist.txt")
	if err != nil {
		fmt.Println(err)
		return
	}

	start, end, err := getUserInput()
	if err != nil {
		fmt.Println(err)
		return
	}

	ladder, err := getWordLadder(start, end, wordlist)
	if err != nil {
		fmt.Println(err)
		return
	}

	for _, word := range ladder {
		println(word)
	}
}

func getWordLadder(start, end string, wordlist []string) ([]string, error) {
	ladder := []string{start}

	for step := 1; step <= 4; step++ {
		next := ""

		for _, word := range wordlist {
			matchesWithStart := getMatchingCharsBetweenStrings(start, word)
			matchesWithEnd := getMatchingCharsBetweenStrings(end, word)

			if matchesWithStart == len(start) - step && matchesWithEnd == step {
				next = word
				break
			}
		}

		if len(next) == 0 {
			return nil, errors.New("Word ladder not possible with current wordlist")
		}

		ladder = append(ladder, next)
	}

	ladder = append(ladder, end)

	return ladder, nil
}

func getUserInput() (string, string, error) {
	if len(os.Args) != 3 {
		return "", "", errors.New("Invalid number of arguments")
	}

	return os.Args[1], os.Args[2], nil
}

func getWordlistFrom(path string) ([]string, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}

	defer file.Close()

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

	return lines, scanner.Err()
}

func getMatchingCharsBetweenStrings(a, b string) (matches int) {
	for _, charA := range a {
		for _, charB := range b {
			if charA == charB {
				matches++
			}
		}
	}

	return
}