// Package allyourbase converts numbers between various bases.
package allyourbase
import (
	"fmt"
	"math"
)
// ConvertToBase converts ibase based input to obase based output.
func ConvertToBase(ibase int, input []int, obase int) ([]int, error) {
	if ibase < 2 {
		return nil, fmt.Errorf("input base must be >= 2")
	}
	if obase < 2 {
		return nil, fmt.Errorf("output base must be >= 2")
	}
	value, err := countValue(ibase, input)
	if err != nil {
		return nil, err
	}
	return createValue(value, obase), nil
}
func countValue(ibase int, input []int) (int, error) {
	value := 0
	for i, v := range input {
		if v < 0 || v >= ibase {
			return 0, fmt.Errorf("all digits must satisfy 0 <= d < input base")
		}
		value += v * int(math.Pow(float64(ibase), float64(len(input)-1-i)))
	}
	return value, nil
}
func createValue(value, obase int) []int {
	// calculate maximal place value needed for representing value
	var p int
	for sum := 0; sum <= value; p++ {
		sum += (obase - 1) * int(math.Pow(float64(obase), float64(p)))
	}
	// generate obase representation of value
	out := make([]int, p)
	for i := p - 1; value != 0; i-- {
		for j := obase - 1; j >= 0; j-- {
			cand := j * int(math.Pow(float64(obase), float64(i)))
			if cand <= value {
				value -= cand
				out[len(out)-1-i] = j
				break
			}
		}
	}
	return out
}