// 0008.go contains some functions to solve ProjectEuler.net's Problem #8
// https://projecteuler.net/problem=8
package main

import (
	"fmt"
	"strings"
	"strconv"
)

// StringToIntArray converts a number string to an int array, assuming all
// elements in the string array were numbers to begin with.
func StringToIntArray(numberString string) []int {
	// Create int array
	intArray := make([]int, len(numberString))
	// Strip whitespace in numberString and convert to string array
	stringArray := strings.Split(strings.Join(strings.Fields(numberString), ""), "")

	for i, s := range stringArray {
		// Convert string to int and add to int array
		intArray[i], _ = strconv.Atoi(s)
	}

	// Return result
	return intArray
}

// AdjacentProduct returns the highest product in an array given the number
// of consecutive digits and the int array.
func AdjacentProduct(digits int, intArray []int) int {
	// Initialise variables
	maxProduct := 0
	length := len(intArray)-digits
	var currentProduct int

	OUTER:
	for i := 0; i<length; i++ {
		currentProduct = 1

		for j := 0; j < digits; j++ {
			if intArray[i+j] == 0 {
				// Anything * 0 is equal to 0, and irrelevant
				i += digits-1
				continue OUTER
			}

			// Calculate product
			currentProduct *= intArray[i+j]
		}

		if currentProduct > maxProduct {
			// Get highest possible product
			maxProduct = currentProduct
		}
	}

	return maxProduct
}

func main(){
	// Answer the problem
	number := `73167176531330624919225119674426574742355349194934
	96983520312774506326239578318016984801869478851843
	85861560789112949495459501737958331952853208805511
	12540698747158523863050715693290963295227443043557
	66896648950445244523161731856403098711121722383113
	62229893423380308135336276614282806444486645238749
	30358907296290491560440772390713810515859307960866
	70172427121883998797908792274921901699720888093776
	65727333001053367881220235421809751254540594752243
	52584907711670556013604839586446706324415722155397
	53697817977846174064955149290862569321978468622482
	83972241375657056057490261407972968652414535100474
	82166370484403199890008895243450658541227588666881
	16427171479924442928230863465674813919123162824586
	17866458359124566529476545682848912883142607690042
	24219022671055626321111109370544217506941658960408
	07198403850962455444362981230987879927244284909188
	84580156166097919133875499200524063689912560717606
	05886116467109405077541002256983155200055935729725
	71636269561882670428252483600823257530420752963450`

	numberArray := StringToIntArray(number)

	fmt.Println(AdjacentProduct(13, numberArray))
}