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, 80 insertions, 0 deletions

diff --git a/engine/gather_order.go b/engine/gather_order.go
new file mode 100644
index 0000000..e0c71fb
--- /dev/null
+++ b/engine/gather_order.go
@@ -0,0 +1,80 @@
+package engine
+
+import (
+	"math"
+	"time"
+
+	"age_of_empires/ecs"
+	"age_of_empires/physics"
+
+	"golang.org/x/exp/slog"
+)
+
+func UpdateGatherSystem(g *Game, now time.Time, moveMap physics.MoveMap, masks []ecs.Mask, orders []OrderKind, positions []physics.Point, moves []physics.Move, gatherers []ResourceGatherer) {
+	required := ecs.CM_ResourceGatherer | ecs.CM_Position | ecs.CM_Move | ecs.CM_Order
+	for i, mask := range masks {
+		if mask&required == required {
+			order := &orders[i]
+			position := positions[i]
+			move := &moves[i]
+			gatherer := &gatherers[i]
+			if *order == OrderKindGather {
+				if gatherer.CurrentVolume == gatherer.MaxCapacity {
+					updateGathererFull(g, getAllStorageDockings(g), moveMap, gatherer, order, move, position)
+				} else if physics.Distance(position, g.Position[gatherer.Source]) <= 100 {
+					updateGathering(now, gatherer, &g.ResourceSource[gatherer.Source])
+				} else if !move.IsActive {
+					startMoveToSource(moveMap, gatherer, move, order, position, g.Position[gatherer.Source])
+				}
+			}
+		}
+	}
+}
+
+func updateGathering(now time.Time, gatherer *ResourceGatherer, source *ResourceSource) {
+	if gatherer.CurrentVolume >= gatherer.MaxCapacity || gatherer.LastPickupTime.Add(200*time.Millisecond).After(now) {
+		return
+	}
+	gatherer.LastPickupTime = now
+	gatherer.CurrentVolume += 1
+	source.Remaining -= 1
+}
+
+func updateGathererFull(g *Game, storageDockings []physics.Point, moveMap physics.MoveMap, gatherer *ResourceGatherer, order *OrderKind, move *physics.Move, position physics.Point) {
+	if move.IsActive {
+		return
+	}
+	destination, distance := physics.Closest(position, storageDockings, moveMap)
+	if distance == math.MaxInt {
+		slog.Info("no accessible storage, canceling gather order")
+		*order = OrderKindNone
+		return
+	}
+	slog.Info("storage target", slog.String("storage", destination.String()), slog.Int("distance", distance))
+	if distance > 1 {
+		slog.Info("moving to storage", slog.String("storage", destination.String()))
+		*move = physics.NewMove(position, destination, moveMap)
+		return
+	}
+	g.ResourceAmount += gatherer.CurrentVolume
+	gatherer.CurrentVolume = 0
+	startMoveToSource(moveMap, gatherer, move, order, position, g.Position[gatherer.Source])
+}
+
+func startMoveToSource(moveMap physics.MoveMap, gatherer *ResourceGatherer, move *physics.Move, order *OrderKind, position physics.Point, sourcePosition physics.Point) {
+	sourceDockings := physics.AdjacentPoints(sourcePosition)
+	destination, distance := physics.Closest(position, sourceDockings, moveMap)
+	if distance == math.MaxInt {
+		slog.Info("no accessible storage, canceling gather order")
+		*order = OrderKindNone
+		return
+	}
+	*move = physics.NewMove(position, destination, moveMap)
+}
+
+func Gather(moveMap physics.MoveMap, position physics.Point, move *physics.Move, order *OrderKind, gatherer *ResourceGatherer, source ecs.Entity, sourcePosition physics.Point) {
+	slog.Info("gathering from", slog.String("source", sourcePosition.String()))
+	*order = OrderKindGather
+	gatherer.Source = source
+	startMoveToSource(moveMap, gatherer, move, order, position, sourcePosition)
+}