feat: add ResolveOrExtracDecFromHeaders to internal/utils module in @…

…observerly/skysolve

feat: add ResolveOrExtracDecFromHeaders to internal/utils module in @observerly/skysolve

internal/utils/headers.go

@@ -47,3 +47,32 @@ func ResolveOrExtractRAFromHeaders(value float32, header fits.FITSHeader) (float
 }
 
 /*****************************************************************************************************************/
+
+func ResolveOrExtractDecFromHeaders(value float32, header fits.FITSHeader) (float32, error) {
+	// First, pick a candidate Dec (v):
+	v := value
+
+	// If the candidate Dec (v) is NaN, try to get it from the header:
+	if math.IsNaN(float64(v)) {
+		dec, exists := header.Floats["DEC"]
+		if !exists {
+			return float32(math.NaN()), fmt.Errorf("dec header not found in the supplied FITS file")
+		}
+		v = dec.Value
+	}
+
+	// Validate the candidate Dec (v) is a valid float32:
+	if math.IsNaN(float64(v)) {
+		return float32(math.NaN()), fmt.Errorf("dec value needs to be a valid float32")
+	}
+
+	// Validate the candidate Dec (v) is within the range [-90, 90]:
+	if v < -90 || v > 90 {
+		return float32(math.NaN()), fmt.Errorf("dec value is out of range: %f", v)
+	}
+
+	// Return the candidate Dec (v):
+	return v, nil
+}
+
+/*****************************************************************************************************************/

internal/utils/headers_test.go

@@ -32,6 +32,19 @@ func newFITSHeaderWithRA(ra float32) fits.FITSHeader {
 	}
 }
 
+// newFITSHeaderWithDec is a helper that returns a fits.FITSHeader
+// populated with an Dec value.
+func newFITSHeaderWithDec(dec float32) fits.FITSHeader {
+	return fits.FITSHeader{
+		Floats: map[string]fits.FITSHeaderFloat{
+			"DEC": {
+				Value:   dec,
+				Comment: "Right Ascension",
+			},
+		},
+	}
+}
+
 /*****************************************************************************************************************/
 
 // newFITSHeaderNoRA is a helper that returns a fits.FITSHeader
@@ -42,6 +55,14 @@ func newFITSHeaderNoRA() fits.FITSHeader {
 	}
 }
 
+// newFITSHeaderNoDec is a helper that returns a fits.FITSHeader
+// with no Dec entry in the Floats map.
+func newFITSHeaderNoDec() fits.FITSHeader {
+	return fits.FITSHeader{
+		Floats: map[string]fits.FITSHeaderFloat{},
+	}
+}
+
 /*****************************************************************************************************************/
 
 func TestRAValueIsNotNaNAndWithinRange(t *testing.T) {
@@ -150,3 +171,110 @@ func TestRAValueIsNaNAndRAHeaderNaN(t *testing.T) {
 }
 
 /*****************************************************************************************************************/
+
+func TestDecValueIsNotNaNAndWithinRange(t *testing.T) {
+	value := float32(45.0) // well within -90..+90
+	header := newFITSHeaderNoDec()
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	if got != value {
+		t.Errorf("Expected %f, got %f", value, got)
+	}
+}
+
+func TestDecValueIsNotNaNAndOutOfRangeNegative(t *testing.T) {
+	value := float32(-91.0)
+	header := newFITSHeaderNoDec()
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error for Dec < -90, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN for out-of-range Dec, got %f", got)
+	}
+}
+
+func TestDecValueIsNotNaNAndOutOfRangePositive(t *testing.T) {
+	value := float32(91.0)
+	header := newFITSHeaderNoDec()
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error for Dec > +90, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN for out-of-range Dec, got %f", got)
+	}
+}
+
+func TestDecValueIsNaNAndDecHeaderFoundAndValid(t *testing.T) {
+	value := float32(math.NaN())
+	header := newFITSHeaderWithDec(30.0) // valid Dec
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err != nil {
+		t.Fatalf("Unexpected error when Dec is pulled from header: %v", err)
+	}
+	expected := float32(30.0)
+	if got != expected {
+		t.Errorf("Expected Dec = %f, got %f", expected, got)
+	}
+}
+
+func TestDecValueIsNaNAndDecHeaderMissing(t *testing.T) {
+	value := float32(math.NaN())
+	header := newFITSHeaderNoDec()
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error when Dec header is missing, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN when Dec header is missing, got %f", got)
+	}
+}
+
+func TestDecValueIsNaNAndDecHeaderOutOfRangeNegative(t *testing.T) {
+	value := float32(math.NaN())
+	header := newFITSHeaderWithDec(-95.0)
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error for Dec < -90, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN for out-of-range Dec, got %f", got)
+	}
+}
+
+func TestDecValueIsNaNAndDecHeaderOutOfRangePositive(t *testing.T) {
+	value := float32(math.NaN())
+	header := newFITSHeaderWithDec(100.0)
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error for Dec > +90, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN for out-of-range Dec, got %f", got)
+	}
+}
+
+func TestDecValueIsNaNAndDecHeaderNaN(t *testing.T) {
+	value := float32(math.NaN())
+	header := newFITSHeaderWithDec(float32(math.NaN()))
+
+	got, err := ResolveOrExtractDecFromHeaders(value, header)
+	if err == nil {
+		t.Fatalf("Expected an error for Dec=NaN in header, but got none")
+	}
+	if !math.IsNaN(float64(got)) {
+		t.Errorf("Expected NaN when Dec=NaN in header, got %f", got)
+	}
+}
+
+/*****************************************************************************************************************/