package main

import (
	"bufio"
	"fmt"
	"log"
	"math"
	"math/rand"
	"os"
	"runtime"
	"time"
)

const (
	randomMin  = 0
	randomMax  = 9999999999999999
	numSamples = 10000000
)

func main() {

	results := [9]int{} // There are 9 possible leading digits and 0 does not count, offset by 1 for index to actual value. Examples: To access 1 use [0].  To access 5 use [4].  To access 9 use [8].
	currentSample := 0

	statusTicker := time.NewTicker(time.Second)
	go func() {
		for {
			<-statusTicker.C
			percentCompleted := (currentSample * 100) / numSamples
			log.Printf("%d %% completed generating and analyzing samples", percentCompleted)
		}
	}()

	log.Printf("generating numbers...")

	rand.Seed(time.Now().UnixNano())
	generatedNumbers := make(chan int, 1024)
	for i := 0; i < runtime.NumCPU(); i++ {
		go generatorWorker(generatedNumbers)
	}

	for currentSample = 0; currentSample < numSamples; currentSample++ {
		results[firstDigit(<-generatedNumbers)-1]++
	}

	statusTicker.Stop()
	log.Printf("done.")

	// output results
	for digitMinusOne, count := range results {
		fmt.Printf("%d: %d\n", digitMinusOne+1, count)
	}

	fmt.Print("Press 'Enter' to continue...")
	bufio.NewReader(os.Stdin).ReadBytes('\n')
}

func generatorWorker(returnChannel chan int) {
	for {
		returnChannel <- rand.Intn(randomMax-randomMin+1) + randomMin // We must use Intn instead of Int because from Base10's perspective, integers cut off at a really weird spot
	}
}

func firstDigit(x int) int {
	return int(math.Abs(float64(x)) / math.Pow(10, float64(numDigits(x)-1)))
}

func numDigits(x int) int {
	if x == 0 {
		return 1
	}
	return int(math.Floor(math.Log10(math.Abs(float64(x))))) + 1
}