Add money and head handling functions

Created types to manage the cannonical coinage of DnD.
First pass at computing computing values for heads.

1 files changed, 138 insertions, 0 deletions

diff --git a/economy/coins.go b/economy/coins.go
new file mode 100644
index 0000000..e2d3531
--- /dev/null
+++ b/economy/coins.go
@@ -0,0 +1,138 @@
+package economy
+
+import (
+	"fmt"
+	"strings"
+)
+
+type Coin float64
+
+const (
+	CopperPiece   Coin = 1
+	SilverPiece   Coin = 10
+	ElectrumPiece Coin = 50
+	GoldPiece     Coin = 100
+	PlatinumPiece Coin = 1000
+)
+
+type Money struct {
+	Copper   Coin
+	Silver   Coin
+	Electrum Coin
+	Gold     Coin
+	Platinum Coin
+}
+
+func abs[T int | int32 | int64](x T) T {
+	if x < 0 {
+		return -x
+	}
+
+	return x
+}
+
+// Computes sign(a) * (abs(a) % b)
+func safeMod(dividend int, divisor uint) int {
+	absMod := abs(dividend) % int(divisor)
+	if dividend < 0 {
+		return -absMod
+	}
+	return absMod
+}
+
+func (a *Money) Add(b Money) {
+	a.Copper += b.Copper
+	a.Silver += b.Silver
+	a.Electrum += b.Electrum
+	a.Gold += b.Gold
+	a.Platinum += b.Platinum
+}
+
+func (a *Money) Subtract(b Money) {
+	a.Copper -= b.Copper
+	a.Silver -= b.Silver
+	a.Electrum -= b.Electrum
+	a.Gold -= b.Gold
+	a.Platinum -= b.Platinum
+}
+
+func (a *Money) Multiply(b Money) {
+	a.Copper *= b.Copper
+	a.Silver *= b.Silver
+	a.Electrum *= b.Electrum
+	a.Gold *= b.Gold
+	a.Platinum *= b.Platinum
+}
+
+// Converts coins Money to the smallest amount of largest denomination possible
+func (m *Money) Simplify() {
+	totalValue := m.Value()
+
+	totalCopper := int(totalValue)
+
+	if abs(totalCopper) > int(PlatinumPiece) {
+		m.Platinum = Coin(totalCopper / int(PlatinumPiece))
+		totalCopper = safeMod(totalCopper, uint(PlatinumPiece))
+	}
+	if abs(totalCopper) > int(GoldPiece) {
+		m.Gold = Coin(totalCopper / int(GoldPiece))
+		totalCopper = safeMod(totalCopper, uint(GoldPiece))
+	}
+	if abs(totalCopper) > int(ElectrumPiece) {
+		m.Electrum = Coin(totalCopper / int(ElectrumPiece))
+		totalCopper = safeMod(totalCopper, uint(ElectrumPiece))
+	}
+	if abs(totalCopper) > int(SilverPiece) {
+		m.Silver = Coin(totalCopper / int(SilverPiece))
+		totalCopper = safeMod(totalCopper, uint(SilverPiece))
+	}
+	m.Copper = Coin(totalCopper)
+}
+
+func (m Money) Value() Coin {
+	var value Coin = 0.0
+
+	value += m.Copper
+	value += m.Silver * SilverPiece
+	value += m.Electrum * ElectrumPiece
+	value += m.Gold * GoldPiece
+	value += m.Platinum * PlatinumPiece
+
+	return value
+}
+
+func (m Money) String() string {
+	var b strings.Builder
+
+	if m.Copper != 0 {
+		fmt.Fprintf(&b, "%.2fcp", m.Copper)
+	}
+
+	if m.Silver != 0 {
+		fmt.Fprintf(&b, "%.2fsp", m.Silver)
+	}
+
+	if m.Electrum != 0 {
+		fmt.Fprintf(&b, "%.2fep", m.Electrum)
+	}
+
+	if m.Gold != 0 {
+		fmt.Fprintf(&b, "%.2fgp", m.Gold)
+	}
+
+	if m.Platinum != 0 {
+		fmt.Fprintf(&b, "%.2fpp", m.Platinum)
+	}
+
+	return b.String()
+}
+
+func Sum(amounts []Money) Money {
+	total := Money{}
+
+	for _, amount := range amounts {
+		total.Add(amount)
+	}
+
+	return total
+}