Internal state persistence (#27)

Allow us to generate year over year reports without having to rerun everything from the beginning.

Co-authored-by: Natercio Moniz <[email protected]>

internal/filler_test.go

@@ -271,3 +271,47 @@ func TestFillerQueue_AdjustForSplit_NilReceiver(t *testing.T) {
 	var fq *FillerQueue
 	fq.AdjustForSplit(decimal.NewFromFloat(5)) // must not panic
 }
+
+func TestNewFillerFromState(t *testing.T) {
+	// The underlying Record reports very different values; NewFillerFromState
+	// must ignore them and use the caller-supplied overrides instead.
+	rec := &testRecord{
+		quantity: decimal.NewFromFloat(999),
+		price:    decimal.NewFromFloat(999),
+	}
+
+	qty := decimal.NewFromFloat(50)
+	price := decimal.NewFromFloat(20)
+	filled := qty // fully filled on load
+
+	f := NewFillerFromState(rec, qty, price, filled)
+
+	if !f.Quantity().Equal(qty) {
+		t.Errorf("want quantity %v but got %v", qty, f.Quantity())
+	}
+	if !f.Price().Equal(price) {
+		t.Errorf("want price %v but got %v", price, f.Price())
+	}
+	if !f.IsFilled() {
+		t.Errorf("want IsFilled() to be true when filled == quantity")
+	}
+
+	// Partially filled: filled < quantity => IsFilled must be false.
+	partial := NewFillerFromState(rec, qty, price, decimal.NewFromFloat(10))
+	if partial.IsFilled() {
+		t.Errorf("want IsFilled() to be false when filled < quantity")
+	}
+	if !partial.Quantity().Equal(qty) {
+		t.Errorf("want quantity %v but got %v", qty, partial.Quantity())
+	}
+	if !partial.Price().Equal(price) {
+		t.Errorf("want price %v but got %v", price, partial.Price())
+	}
+
+	// Filled from Fill() on a restored lot must work correctly against the
+	// restored (not Record-derived) quantity/price.
+	_, done := partial.Fill(decimal.NewFromFloat(40))
+	if !done {
+		t.Errorf("after filling the remaining 40, IsFilled() should be true")
+	}
+}