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.go

@@ -22,10 +22,26 @@ func NewFiller(r Record) *Filler {
 	}
 }
 
+// NewFillerFromState constructs a Filler from a previously persisted state.
+// It bypasses the Record-derived defaults so callers can restore a lot that
+// may have been split-adjusted or partially filled since the Record was first
+// created.
+func NewFillerFromState(record Record, quantity, price, filled decimal.Decimal) *Filler {
+	return &Filler{
+		Record:   record,
+		filled:   filled,
+		quantity: quantity,
+		price:    price,
+	}
+}
+
 func (f *Filler) Quantity() decimal.Decimal { return f.quantity }
 
 func (f *Filler) Price() decimal.Decimal { return f.price }
 
+// Filled returns how much of the Filler's quantity has already been consumed.
+func (f *Filler) Filled() decimal.Decimal { return f.filled }
+
 // Fill accrues some quantity. Returns how mutch was accrued in the 1st return value and whether
 // it was filled or not on the 2nd return value.
 func (f *Filler) Fill(quantity decimal.Decimal) (decimal.Decimal, bool) {
@@ -70,8 +86,8 @@ func (fq *FillerQueue) Push(f *Filler) {
 	fq.l.PushBack(f)
 }
 
-// Pop removes and returns the first Filler of the queue in the 1st return value. If the list is
-// empty returns false on the 2nd return value, true otherwise.
+// Pop removes and returns the first Filler of the queue in the 1st return value if there is one. If
+// the queue is already empty returns false on the 2nd return value, otherwise returns true.
 func (fq *FillerQueue) Pop() (*Filler, bool) {
 	el := fq.frontElement()
 	if el == nil {