money notation

.gitignore

@@ -0,0 +1,19 @@
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories
+vendor/
+
+# Editor settings
+.vscode
+.idea

finance.go

@@ -0,0 +1,46 @@
+package humanize
+
+import (
+	"fmt"
+)
+
+func Finance(f float64) string {
+	switch n := f; {
+	case n >= 1_000_000_000_000_000:
+		s := fmt.Sprintf("%.f", f)
+		s = insertAt(1, '.', []rune(s[:4]))
+		return fmt.Sprintf("$%sQ", s)
+
+	case n >= 1_000_000_000_000:
+		s := fmt.Sprintf("%.f", f)
+		s = insertAt(1, '.', []rune(s[:4]))
+		return fmt.Sprintf("$%sT", s)
+
+	case n >= 1_000_000_000:
+		s := fmt.Sprintf("%.f", f)
+		s = insertAt(1, '.', []rune(s[:4]))
+		return fmt.Sprintf("$%sB", s)
+
+	case n >= 1_000_000:
+		s := fmt.Sprintf("%.f", f)
+		s = insertAt(1, '.', []rune(s[:4]))
+		return fmt.Sprintf("$%sM", s)
+
+	case n >= 1_000:
+		s := fmt.Sprintf("%.f", f)
+		s = insertAt(1, '.', []rune(s[:4]))
+		return fmt.Sprintf("$%sK", s)
+
+	case n < 1_000:
+		return fmt.Sprintf("$%.f", f)
+
+	default:
+		return "NaN"
+	}
+}
+
+func insertAt(index int, elem rune, slice []rune) string {
+	copy(slice[index+1:], slice[index:])
+	slice[index] = elem
+	return string(slice)
+}

finance_test.go

@@ -0,0 +1,30 @@
+package humanize
+
+import (
+	"math"
+	"testing"
+)
+
+func TestFinance(t *testing.T) {
+	tests := []struct {
+		name string
+		arg  float64
+		want string
+	}{
+		{"Quadrillions", 2_475_260_494_216_000, "$2.47Q"},
+		{"Trillions", 2_475_260_494_216, "$2.47T"},
+		{"Billions", 2_475_260_494, "$2.47B"},
+		{"Millions", 2_475_260, "$2.47M"},
+		{"Thousands", 2_475, "$2.47K"},
+		{"Hundreds", 247, "$247"},
+		{"Tens", 24, "$24"},
+		{"NaN", math.NaN(), "NaN"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := Finance(tt.arg); got != tt.want {
+				t.Errorf("Finance() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}