1 files changed, 136 insertions, 0 deletions
diff --git a/internal/casino/house_edge_craps.go b/internal/casino/house_edge_craps.go
new file mode 100644
index 0000000..06a6629
--- /dev/null
+++ b/internal/casino/house_edge_craps.go
@@ -0,0 +1,136 @@
+package casino
+
+import (
+	"strconv"
+	"strings"
+)
+
+func crapsHouseEdge(cfg TableConfig, bet string) HouseEdge {
+	c := cfg.Craps.Normalize()
+	switch bet {
+	case "pass", "come", "dontpass", "dontcome":
+		return edge(-crapsContractEV(c, bet, 0))
+	case "odds pass", "odds come <n>", "odds dontpass", "odds dontcome <n>":
+		return edge(0)
+	case "buy <n>", "lay <n>":
+		e := HouseEdge{Note: "5% commission on wins, before upward credit rounding; small stakes cost more"}
+		for _, n := range []int{2, 3, 4, 5, 6, 8, 9, 10, 11, 12} {
+			if !c.number(n) {
+				continue
+			}
+			// Buy: 5% of stake times P(number before 7).
+			// Lay: 5% of true-odds profit times P(7 before number).
+			// Both reduce to .05 * ways(number)/(ways(number)+6).
+			w := float64(diceWays(n))
+			e.Parts = append(e.Parts, EdgePart{strconv.Itoa(n), .05 * w / (w + 6)})
+		}
+		return e
+	case "hard 4 / hard 10":
+		return edge(-crapsResolvedEV(c, "hard", 4))
+	case "hard 6 / hard 8":
+		return edge(-crapsResolvedEV(c, "hard", 6))
+	case "eleven / ace-deuce":
+		return edge(-crapsResolvedEV(c, "eleven", 0))
+	case "aces / boxcars":
+		return edge(-crapsResolvedEV(c, "aces", 0))
+	case "hop <a> <b>":
+		return HouseEdge{Parts: []EdgePart{{"unequal dice", -crapsResolvedEV(c, "hop", 12)}, {"doubles", -crapsResolvedEV(c, "hop", 11)}}}
+	case "small / tall":
+		return edge(1 - 35*crapsCollectProbability([]int{2, 3, 4, 5, 6}))
+	case "all":
+		return edge(1 - 176*crapsCollectProbability([]int{2, 3, 4, 5, 6, 8, 9, 10, 11, 12}))
+	case "fire":
+		return edge(1 - crapsFireReturn())
+	case "field", "seven", "craps", "horn":
+		return edge(-crapsResolvedEV(c, bet, 0))
+	}
+	if strings.HasPrefix(bet, "place ") {
+		n, err := strconv.Atoi(strings.TrimPrefix(bet, "place "))
+		if err == nil && c.number(n) {
+			return edge(-crapsResolvedEV(c, "place", n))
+		}
+	}
+	return unknownEdge("unrecognized craps target")
+}
+
+func diceWays(n int) int {
+	if n < 2 || n > 12 {
+		return 0
+	}
+	if n > 7 {
+		return 13 - n
+	}
+	return n - 1
+}
+
+// Enumerate the actual outcome function, skipping neutral rolls. Off-on-
+// come-out wagers have the same eventual EV when left working to resolution.
+func crapsResolvedEV(c CrapsConfig, kind string, n int) float64 {
+	sum, resolved := 0.0, 0.0
+	for a := 1; a <= 6; a++ {
+		for b := 1; b <= 6; b++ {
+			ok, x, y := c.outcome(kind, n, a, b, 6)
+			if ok {
+				sum += float64(x) / float64(y)
+				resolved++
+			}
+		}
+	}
+	return sum / resolved
+}
+
+// A contract starts at n=0 and travels once to its personal point. Self
+// loops (neutral dice or high-point come-out 2/3) are eliminated exactly.
+func crapsContractEV(c CrapsConfig, kind string, n int) float64 {
+	sum, effective := 0.0, 0.0
+	for a := 1; a <= 6; a++ {
+		for b := 1; b <= 6; b++ {
+			if c.variant() == "die_rich" && b != 1 {
+				continue
+			}
+			bb := b
+			if c.variant() == "die_rich" {
+				bb = 0
+			}
+			ok, x, y := c.outcome(kind, n, a, bb, 6)
+			if ok {
+				sum += float64(x) / float64(y)
+				effective++
+				continue
+			}
+			if n == 0 && c.pointNumber(a+bb) {
+				sum += crapsContractEV(c, kind, a+bb)
+				effective++
+			}
+		}
+	}
+	return sum / effective
+}
+
+// Probability of collecting all listed totals before ANY seven. All other
+// rolls are self loops. This also accounts for duplicate rolls correctly.
+func crapsCollectProbability(numbers []int) float64 {
+	full := (1 << len(numbers)) - 1
+	memo := make(map[int]float64)
+	var visit func(int) float64
+	visit = func(mask int) float64 {
+		if mask == full {
+			return 1
+		}
+		if p, ok := memo[mask]; ok {
+			return p
+		}
+		numerator, denominator := 0.0, 6.0
+		for i, n := range numbers {
+			if mask&(1<<i) != 0 {
+				continue
+			}
+			w := float64(diceWays(n))
+			numerator += w * visit(mask|(1<<i))
+			denominator += w
+		}
+		memo[mask] = numerator / denominator
+		return memo[mask]
+	}
+	return visit(0)
+}