Add examples catalog with subcommand dispatch

- Extract game engine from package main to engine/ library package
- Create examples/ package with registry, Entry type, and BuilderDeps
- Register default world as an example (moved from main())
- Add combat example: two teams of units facing each other
- Rewrite main.go as thin dispatch: go run . example [name]
- Update README with examples catalog one-liner

1 files changed, 41 insertions, 0 deletions

diff --git a/engine/order.go b/engine/order.go
new file mode 100644
index 0000000..8aa991b
--- /dev/null
+++ b/engine/order.go
@@ -0,0 +1,41 @@
+package engine
+
+import (
+	"log/slog"
+
+	"age_of_empires/ecs"
+	"age_of_empires/monad"
+	"age_of_empires/physics"
+)
+
+type OrderKind int
+
+const (
+	OrderKindNone OrderKind = iota
+	OrderKindPatrol
+	OrderKindGather
+)
+
+func MainAction(g *Game, mainEntity ecs.Entity, target physics.Point, moveMap physics.MoveMap) {
+	mask := g.Mask[mainEntity]
+	targetEntity := g.entityAt(target)
+	gatherTargetRequired := ecs.CM_ResourceSource
+	mainGatherRequired := ecs.CM_ResourceGatherer | ecs.CM_Move
+	if targetEntity >= 0 && (g.Mask[targetEntity]&gatherTargetRequired == gatherTargetRequired) && (mask&mainGatherRequired == mainGatherRequired) {
+		Gather(g.GetMoveMap(), g.Position[mainEntity], &g.Move[mainEntity], &g.Order[mainEntity], &g.ResourceGatherer[mainEntity], targetEntity, g.Position[targetEntity])
+		return
+	}
+	moveRequired := ecs.CM_Move | ecs.CM_Position
+	if mask&moveRequired == moveRequired {
+		position := g.Position[mainEntity]
+		g.Order[mainEntity] = OrderKindNone
+		g.Move[mainEntity] = physics.NewMove(position, target, moveMap)
+		return
+	}
+	if mask&ecs.CM_Spawn == ecs.CM_Spawn {
+		slog.Info("Setting spawn target")
+		spawn := &g.Spawn[mainEntity]
+		spawn.SpawnTarget = monad.Some(target)
+		return
+	}
+}