feat: Add dynamic icon generation

go.mod

@@ -6,6 +6,7 @@ require (
 	fyne.io/systray v1.11.0
 	github.com/Masterminds/sprig/v3 v3.2.3
 	github.com/emersion/go-autostart v0.0.0-20210130080809-00ed301c8e9a
+	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0
 	github.com/hhsnopek/etag v0.0.0-20171206181245-aea95f647346
 	github.com/knadh/koanf/providers/file v1.1.0
 	github.com/knadh/koanf/providers/rawbytes v0.1.0
@@ -19,6 +20,7 @@ require (
 	github.com/skratchdot/open-golang v0.0.0-20200116055534-eef842397966
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.9.0
+	golang.org/x/image v0.18.0
 )
 
 require (
@@ -44,7 +46,6 @@ require (
 	github.com/spf13/cast v1.3.1 // indirect
 	github.com/tj/assert v0.0.3 // indirect
 	golang.org/x/crypto v0.17.0 // indirect
-	golang.org/x/image v0.18.0 // indirect
 	golang.org/x/sys v0.22.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -24,6 +24,8 @@ github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1 h1:TQcrn6Wq+sKGkpyPvppOz99zsM
 github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
 github.com/godbus/dbus/v5 v5.1.0 h1:4KLkAxT3aOY8Li4FRJe/KvhoNFFxo0m6fNuFUO8QJUk=
 github.com/godbus/dbus/v5 v5.1.0/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 h1:DACJavvAHhabrF08vX0COfcOBJRhZ8lUbR+ZWIs0Y5g=
+github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0/go.mod h1:E/TSTwGwJL78qG/PmXZO1EjYhfJinVAhrmmHX6Z8B9k=
 github.com/google/uuid v1.1.1 h1:Gkbcsh/GbpXz7lPftLA3P6TYMwjCLYm83jiFQZF/3gY=
 github.com/google/uuid v1.1.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/hhsnopek/etag v0.0.0-20171206181245-aea95f647346 h1:Odeq5rB6OZSkib5gqTG+EM1iF0bUVjYYd33XB1ULv00=

internal/config/color.go

@@ -0,0 +1,67 @@
+package config
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"image/color"
+	"strconv"
+)
+
+var (
+	ErrMissingPrefix = errors.New(`hex code missing "#" prefix`)
+	ErrInvalidLength = errors.New("hex code should be 4 or 7 characters")
+)
+
+type HexColor color.RGBA
+
+func (h HexColor) MarshalText() ([]byte, error) {
+	shorthand := h.R>>4 == h.R&0xF && h.G>>4 == h.G&0xF && h.B>>4 == h.B&0xF
+	if shorthand {
+		return []byte(fmt.Sprintf("#%x%x%x", h.R&0xF, h.G&0xF, h.B&0xF)), nil
+	}
+	return []byte(fmt.Sprintf("#%02x%02x%02x", h.R, h.G, h.B)), nil
+}
+
+func (h *HexColor) UnmarshalText(text []byte) error {
+	if !bytes.HasPrefix(text, []byte("#")) {
+		return ErrMissingPrefix
+	}
+	switch len(text) {
+	case 4, 7:
+	default:
+		return ErrInvalidLength
+	}
+
+	parsed, err := strconv.ParseUint(string(text[1:]), 16, 32)
+	if err != nil {
+		return err
+	}
+
+	if parsed > 0xFFF {
+		h.R = uint8(parsed >> 16 & 0xFF)
+		h.G = uint8(parsed >> 8 & 0xFF)
+		h.B = uint8(parsed & 0xFF)
+	} else {
+		h.R = uint8(parsed >> 8 & 0xF)
+		h.R |= h.R << 4
+		h.G = uint8(parsed >> 4 & 0xF)
+		h.G |= h.G << 4
+		h.B = uint8(parsed & 0xF)
+		h.B |= h.B << 4
+	}
+	h.A = 0xFF
+	return nil
+}
+
+func (h HexColor) RGBA() color.RGBA {
+	return color.RGBA(h)
+}
+
+func White() HexColor {
+	return HexColor{R: 0xFF, G: 0xFF, B: 0xFF, A: 0xFF}
+}
+
+func Black() HexColor {
+	return HexColor{A: 0xFF}
+}

internal/config/color_test.go

@@ -0,0 +1,69 @@
+package config
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHexColor_MarshalText(t *testing.T) {
+	t.Parallel()
+	type fields struct {
+		HexColor HexColor
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		want    []byte
+		wantErr require.ErrorAssertionFunc
+	}{
+		{"white", fields{HexColor{R: 0xFF, G: 0xFF, B: 0xFF}}, []byte("#fff"), require.NoError},
+		{"black", fields{HexColor{}}, []byte("#000"), require.NoError},
+		{"red", fields{HexColor{R: 0xFF}}, []byte("#f00"), require.NoError},
+		{"green", fields{HexColor{G: 0xFF}}, []byte("#0f0"), require.NoError},
+		{"blue", fields{HexColor{B: 0xFF}}, []byte("#00f"), require.NoError},
+		{"blue-gray", fields{HexColor{R: 0x60, G: 0x7D, B: 0x8B}}, []byte("#607d8b"), require.NoError},
+		{"increment", fields{HexColor{R: 1, G: 2, B: 3}}, []byte("#010203"), require.NoError},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			h := tt.fields.HexColor
+			got, err := h.MarshalText()
+			tt.wantErr(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestHexColor_UnmarshalText(t *testing.T) {
+	t.Parallel()
+	type args struct {
+		text []byte
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    HexColor
+		wantErr require.ErrorAssertionFunc
+	}{
+		{"white", args{[]byte("#fff")}, HexColor{R: 0xFF, G: 0xFF, B: 0xFF, A: 0xFF}, require.NoError},
+		{"black", args{[]byte("#000")}, HexColor{A: 0xFF}, require.NoError},
+		{"red", args{[]byte("#f00")}, HexColor{R: 0xFF, A: 0xFF}, require.NoError},
+		{"green", args{[]byte("#0f0")}, HexColor{G: 0xFF, A: 0xFF}, require.NoError},
+		{"blue", args{[]byte("#00f")}, HexColor{B: 0xFF, A: 0xFF}, require.NoError},
+		{"blue-gray", args{[]byte("#607d8b")}, HexColor{R: 0x60, G: 0x7D, B: 0x8B, A: 0xFF}, require.NoError},
+		{"missing-prefix", args{[]byte("fff")}, HexColor{}, require.Error},
+		{"too-long", args{[]byte("#fffffff")}, HexColor{}, require.Error},
+		{"too-short", args{[]byte("#fffff")}, HexColor{}, require.Error},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			h := HexColor{}
+			tt.wantErr(t, h.UnmarshalText(tt.args.text))
+			assert.Equal(t, tt.want, h)
+		})
+	}
+}

internal/config/config.go

@@ -13,14 +13,22 @@ type Config struct {
 	Flags     *pflag.FlagSet `toml:"-"`
 	callbacks []func()       `toml:"-"`
 
-	Title     string    `toml:"title" comment:"Tray title."`
-	URL       string    `toml:"url" comment:"Nightscout URL. (required)"`
-	Token     string    `toml:"token" comment:"Nightscout token. Using an access token is recommended instead of the API secret."`
-	Units     string    `toml:"units" comment:"Blood sugar unit. (one of: mg/dL, mmol/L)"`
-	Arrows    Arrows    `toml:"arrows" comment:"Customize the arrows."`
-	LocalFile LocalFile `toml:"local-file" comment:"Enables writing the latest blood sugar to a local temporary file."`
-	Log       Log       `toml:"log" comment:"Log configuration"`
-	Advanced  Advanced  `toml:"advanced" comment:"Advanced settings."`
+	Title       string      `toml:"title" comment:"Tray title."`
+	URL         string      `toml:"url" comment:"Nightscout URL. (required)"`
+	Token       string      `toml:"token" comment:"Nightscout token. Using an access token is recommended instead of the API secret."`
+	Units       string      `toml:"units" comment:"Blood sugar unit. (one of: mg/dL, mmol/L)"`
+	DynamicIcon DynamicIcon `toml:"dynamic_icon" comment:"Makes the tray icon show the current blood sugar reading."`
+	Arrows      Arrows      `toml:"arrows" comment:"Customize the arrows."`
+	LocalFile   LocalFile   `toml:"local-file" comment:"Enables writing the latest blood sugar to a local temporary file."`
+	Log         Log         `toml:"log" comment:"Log configuration"`
+	Advanced    Advanced    `toml:"advanced" comment:"Advanced settings."`
+}
+
+type DynamicIcon struct {
+	Enabled     bool     `toml:"enabled"`
+	FontColor   HexColor `toml:"font_color" comment:"Hex code used to render text."`
+	FontFile    string   `toml:"font_file" comment:"If left blank, an embedded font will be used."`
+	MaxFontSize float64  `toml:"max_font_size" comment:"Maximum font size in points."`
 }
 
 type Arrows struct {

internal/config/default.go

@@ -3,6 +3,7 @@ package config
 import (
 	"log/slog"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"time"
 
@@ -15,6 +16,11 @@ func New() *Config {
 	conf := &Config{
 		Title: "Nightscout",
 		Units: UnitsMgdl,
+		DynamicIcon: DynamicIcon{
+			Enabled:     true,
+			FontColor:   White(),
+			MaxFontSize: 40,
+		},
 		Arrows: Arrows{
 			DoubleUp:      "⇈",
 			SingleUp:      "↑",
@@ -40,6 +46,13 @@ func New() *Config {
 		},
 	}
 
+	switch runtime.GOOS {
+	case "darwin":
+		conf.DynamicIcon.Enabled = false
+	case "windows":
+		conf.DynamicIcon.FontColor = Black()
+	}
+
 	conf.Flags = flag.NewFlagSet("", flag.ContinueOnError)
 	conf.RegisterFlags()
 

internal/config/load.go

@@ -9,6 +9,7 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"slices"
 	"time"
 
 	"github.com/knadh/koanf/providers/file"
@@ -145,8 +146,13 @@ func (conf *Config) Watch(ctx context.Context) error {
 	})
 }
 
-func (conf *Config) AddCallback(fn func()) {
+func (conf *Config) AddCallback(fn func()) int {
 	conf.callbacks = append(conf.callbacks, fn)
+	return len(conf.callbacks) - 1
+}
+
+func (conf *Config) RemoveCallback(idx int) {
+	conf.callbacks = slices.Delete(conf.callbacks, idx, idx+1)
 }
 
 func migrateConfig(k *koanf.Koanf) error {

internal/dynamicicon/dynamicicon.go

@@ -0,0 +1,119 @@
+package dynamicicon
+
+import (
+	"bytes"
+	_ "embed"
+	"errors"
+	"image"
+	"image/draw"
+	"log/slog"
+	"os"
+	"sync"
+
+	"github.com/gabe565/nightscout-menu-bar/internal/config"
+	"github.com/gabe565/nightscout-menu-bar/internal/nightscout"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+const (
+	width, height   = 32, 32
+	widthF, heightF = fixed.Int26_6(width << 6), fixed.Int26_6(height << 6)
+)
+
+//go:embed Inconsolata_Condensed-Black.ttf
+var defaultFont []byte
+
+type DynamicIcon struct {
+	config *config.Config
+	mu     sync.Mutex
+
+	font *truetype.Font
+	img  *image.RGBA
+}
+
+func New(conf *config.Config) *DynamicIcon {
+	d := &DynamicIcon{
+		config: conf,
+		img:    image.NewRGBA(image.Rectangle{Max: image.Point{X: width, Y: height}}),
+	}
+	return d
+}
+
+var ErrFontSize = errors.New("unable to determine the correct font size")
+
+func (d *DynamicIcon) Generate(p *nightscout.Properties) ([]byte, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if d.font == nil {
+		var b []byte
+		if d.config.DynamicIcon.FontFile == "" {
+			b = defaultFont
+		} else {
+			var err error
+			if b, err = os.ReadFile(d.config.DynamicIcon.FontFile); err != nil {
+				return nil, err
+			}
+		}
+
+		f, err := truetype.Parse(b)
+		if err != nil {
+			return nil, err
+		}
+
+		d.font = f
+	}
+
+	bgnow := p.Bgnow.DisplayBg(d.config.Units)
+
+	var face font.Face
+	defer func() {
+		if face != nil {
+			_ = face.Close()
+		}
+	}()
+
+	drawer := &font.Drawer{
+		Dst: d.img,
+		Src: image.NewUniform(d.config.DynamicIcon.FontColor.RGBA()),
+	}
+
+	fontSize := d.config.DynamicIcon.MaxFontSize
+	for {
+		face = truetype.NewFace(d.font, &truetype.Options{
+			Size: fontSize,
+		})
+		drawer.Face = face
+
+		if textWidth := drawer.MeasureString(bgnow); textWidth <= widthF {
+			break
+		}
+
+		_ = face.Close()
+		if fontSize <= 1 {
+			return nil, ErrFontSize
+		}
+		fontSize -= 0.5
+	}
+
+	metrics := face.Metrics()
+
+	draw.Draw(d.img, d.img.Bounds(), image.Transparent, image.Point{}, draw.Src)
+	drawer.Dot.X = (widthF - drawer.MeasureString(bgnow)) / 2
+	drawer.Dot.Y = (heightF + metrics.Ascent - metrics.Descent) / 2
+	slog.Debug("Generating dynamic icon",
+		"font_size", fontSize,
+		"dot", drawer.Dot,
+		"value", bgnow,
+	)
+	drawer.DrawString(bgnow)
+
+	var buf bytes.Buffer
+	if err := encode(&buf, d.img); err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}

internal/dynamicicon/encode.go

@@ -0,0 +1,13 @@
+//go:build !windows
+
+package dynamicicon
+
+import (
+	"image"
+	"image/png"
+	"io"
+)
+
+func encode(w io.Writer, img image.Image) error {
+	return png.Encode(w, img)
+}