hexmap/server/state/color.go

package state

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

// Color is an internal representation of an RGBA8888 color.
type Color struct {
	// R is the red component of the color.
	R uint8
	// G is the green component of the color.
	G uint8
	// B is the blue component of the color.
	B uint8
	// A is the alpha component of the color.
	A uint8
}

var TransparentColor = Color{R: 0, G: 0, B: 0, A: 0}
var ErrInvalidColorString = errors.New("color strings must start with # and be followed by 3, 4, 6, or 8 hex digits")

func ColorFromString(s string) (Color, error) {
	if !strings.HasPrefix(s, "#") {
		return TransparentColor, ErrInvalidColorString
	}
	hex := s[1:]
	v, err := strconv.ParseUint(hex, 16, 64)
	if err != nil {
		return TransparentColor, ErrInvalidColorString
	}
	switch len(hex) {
	case 3:
		return ColorFromRGBA4444(uint16(v<<4 | 0xF)), nil
	case 4:
		return ColorFromRGBA4444(uint16(v)), nil
	case 6:
		return ColorFromRGBA8888(uint32(v<<8 | 0xFF)), nil
	case 8:
		return ColorFromRGBA8888(uint32(v)), nil
	default:
		return TransparentColor, ErrInvalidColorString
	}
}

// String prints the Color in an abbreviated notation.
// Specifically, short form is used when possible (i.e., when all components are evenly divisible by 0x11).
// The alpha component is left out if it's 0xFF.
func (c Color) String() string {
	if c.R%0x11 == 0 && c.G%0x11 == 0 && c.B%0x11 == 0 && c.A%0x11 == 0 {
		// Short form works.
		if c.A == 0xFF {
			// It's great when it's easy!
			return fmt.Sprintf("#%01X%01X%01X", c.R/0x11, c.G/0x11, c.B/0x11)
		} else {
			// Just need to add the alpha.
			return fmt.Sprintf("#%01X%01X%01X%01X", c.R/0x11, c.G/0x11, c.B/0x11, c.A/0x11)
		}
	} else {
		// Gotta use long form.
		if c.A == 0xFF {
			// Can skip the alpha channel, though.
			return fmt.Sprintf("#%02X%02X%02X", c.R, c.G, c.B)
		} else {
			// Doing things the hard way.
			return fmt.Sprintf("#%02X%02X%02X%02X", c.R, c.G, c.B, c.A)
		}
	}
}