package main

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

/*

	@Ref: https://livebook.manning.com/book/go-in-practice/chapter-3/65
	1. --reac flag is able to do the race detection
	2. How to use scanner to split the word in a file
	3. sync.Mutex usage
*/

func main() {

	wg := sync.WaitGroup{}

	w := newWords()
	for _, file := range os.Args[1:] {
		wg.Add(1)
		go func(filename string) {
			tallyWords(filename, w)
			wg.Done()
		}(file)

	}

	wg.Wait()

	fmt.Println("Words that appear more than once:")
	for word, count := range w.found {
		if count > 1 {
			fmt.Printf("%s: %d\n", word, count)
		}
	}
}

type words struct {
	sync.Mutex
	found map[string]int
}

func newWords() *words {
	return &words{found: make(map[string]int)}
}

func (w *words) add(word string, n int) {
	w.Lock()
	defer w.Unlock()

	count, ok := w.found[word]
	if !ok {
		w.found[word] = n
		return
	}
	w.found[word] = count + n
}

func tallyWords(filename string, dist *words) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}

	defer file.Close()

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanWords)
	for scanner.Scan() {
		word := strings.ToLower(scanner.Text())
		dist.add(word, 1)
	}
	return scanner.Err()
}