refactor: change project structure and package name

pkg/chart/first_value_annotation.go

@@ -0,0 +1,37 @@
+package chart
+
+import "fmt"
+
+// FirstValueAnnotation returns an annotation series of just the first value of a value provider as an annotation.
+func FirstValueAnnotation(innerSeries ValuesProvider, vfs ...ValueFormatter) AnnotationSeries {
+	var vf ValueFormatter
+	if len(vfs) > 0 {
+		vf = vfs[0]
+	} else if typed, isTyped := innerSeries.(ValueFormatterProvider); isTyped {
+		_, vf = typed.GetValueFormatters()
+	} else {
+		vf = FloatValueFormatter
+	}
+
+	var firstValue Value2
+	if typed, isTyped := innerSeries.(FirstValuesProvider); isTyped {
+		firstValue.XValue, firstValue.YValue = typed.GetFirstValues()
+		firstValue.Label = vf(firstValue.YValue)
+	} else {
+		firstValue.XValue, firstValue.YValue = innerSeries.GetValues(0)
+		firstValue.Label = vf(firstValue.YValue)
+	}
+
+	var seriesName string
+	var seriesStyle Style
+	if typed, isTyped := innerSeries.(Series); isTyped {
+		seriesName = fmt.Sprintf("%s - First Value", typed.GetName())
+		seriesStyle = typed.GetStyle()
+	}
+
+	return AnnotationSeries{
+		Name:        seriesName,
+		Style:       seriesStyle,
+		Annotations: []Value2{firstValue},
+	}
+}