// Package letter is for counting letters.
package letter
import (
	"sync"
)
// FreqMap records the frequency of each rune in a given text.
type FreqMap map[rune]int
// Frequency counts the frequency of each rune in a given text and returns this
// data as a FreqMap.
func Frequency(s string) FreqMap {
	m := FreqMap{}
	for _, r := range s {
		m[r]++
	}
	return m
}
// ConcurrentFrequency concurrently calls Frequency on each of input slice elementst,
// returns with the union of each FreqMap.
func ConcurrentFrequency(input []string) FreqMap {
	freqs := make(chan FreqMap)
	wg := new(sync.WaitGroup)
	for _, st := range input {
		wg.Add(1)
		go func(st string) {
			mp := Frequency(st)
			freqs <- mp
		}(st)
	}
	go func() {
		wg.Wait()
		close(freqs)
	}()
	out := FreqMap{}
	for mp := range freqs {
		wg.Done()
		for k, v := range mp {
			out[k] += v
		}
	}
	return out
}