/*
Package scale is for calculating music scales.
*/
package scale
import (
	"errors"
	"fmt"
	"os"
	"strings"
)
var (
	sharpScale = []string{"A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#"}
	flatScale  = []string{"A", "Bb", "B", "C", "Db", "D", "Eb", "E", "F", "Gb", "G", "Ab"}
	sharps     = []string{"a", "C", "G", "D", "A", "E", "B", "F#", "e", "b", "f#", "c#", "g#", "d#"} // a minor and C major is here just for the tests
	flats      = []string{"F", "Bb", "Eb", "Ab", "Db", "Gb", "d", "g", "c", "f", "bb", "eb"}
)
// setScale sets the scale to sharp or flat based on tonic
func setScale(tonic string) (scale []string, err error) {
	for _, v := range sharps {
		if v == tonic {
			return sharpScale, nil
		}
	}
	for _, v := range flats {
		if v == tonic {
			return flatScale, nil
		}
	}
	return nil, errors.New("tonic has not found: neither in sharps, nor in flats")
}
// genChromatic generates the choromatic scale starting with the given tonic
func genChromatic(scale []string, tonic string) (chr []string) {
	for k, v := range scale {
		if strings.ToLower(v) == strings.ToLower(tonic) {
			chr = scale[k:]
			chr = append(chr, scale[:k]...)
			break
		}
	}
	return
}
// genDiatonic generates the diatonic scale based on intervals
func genDiatonic(scale []string, interval string) (diat []string) {
	act := 0
	diat = append(diat, scale[0])
	for k := 0; k < len(interval)-1; k++ {
		switch {
		case interval[k] == 'm':
			act += 1
		case interval[k] == 'M':
			act += 2
		case interval[k] == 'A':
			act += 3
		}
		if act >= len(scale) {
			act = act - len(scale)
		}
		diat = append(diat, scale[act])
	}
	return
}
// Scale gives back the proper scale for the given tonic and intervals.
func Scale(tonic, interval string) (s []string) {
	scale, err := setScale(tonic)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	s = genChromatic(scale, tonic)
	if len(interval) == 0 {
		return
	}
	s = genDiatonic(s, interval)
	return
}