/**
 * file: types/tag.go
 * author: Theo Technicguy
 * license: Apache 2.0
 *
 * Tag type and functions
 */

package types

import (
	"crypto/sha1"
	"encoding/binary"
	"errors"
)

const (
	colorBase = 0xff
	colorRage = colorBase*colorBase*colorBase + 1
)

var (
	ErrTagNameEmpty     = errors.New("tag name is empty")
	ErrTagHasColor      = errors.New("tag has valid color")
	ErrTagInvalidCollor = errors.New("tag has invalid color")
)

// A Tag is a simple structure used to categorize products.
// Tag names are unique. Tag colors are base 10 RGB notation.
type Tag struct {
	Id    uint   `json:"id"`
	Name  string `json:"name"`
	Color uint   `json:"color"`
}

// GenerateColor generates a random tag color using the tag's
// name's SHA1.
func (t *Tag) GenerateColor() error {
	if t.Name == "" {
		return ErrTagNameEmpty
	}
	if t.ValidColor() {
		return ErrTagHasColor
	}

	hash := sha1.Sum([]byte(t.Name))
	t.Color = uint(binary.BigEndian.Uint64(hash[:])) % colorRage

	return nil
}

// RGB converts the base 10 RGB color in an array of color values.
func (t *Tag) RGB() ([]uint, error) {
	if !t.ValidColor() {
		return nil, ErrTagInvalidCollor
	}
	c := t.Color
	colors := []uint{}

	for c > 0 {
		colors = append(colors, c%colorBase)
		c = c / colorBase
	}

	return colors, nil
}

// ValidColor verifies that the tag's color is valid.
func (t *Tag) ValidColor() bool {
	return t.Color < colorRage
}

// ValidName verifies that the tag has a name.
// Uniqueness verification is the data source's job.
func (t *Tag) ValidName() bool {
	return t.Name != ""
}

// Valid verifies that the tag is valid.
// A valid tag has a valid color and a name.
func (t *Tag) Valid() bool {
	return t.ValidColor() && t.ValidName()
}