2 files changed, 78 insertions, 1 deletions
diff --git a/src/simulation/actions.js b/src/simulation/actions.js
index 62a8395..6497917 100644
--- a/src/simulation/actions.js
+++ b/src/simulation/actions.js
@@ -159,7 +159,50 @@ const unfreeze = {
 };
 
 
+const take_flag = {
+  size: 1,
+  propose: (world, agent, head) => {
+    if (head[0] < threshold) { return []; }
+    else {
+      const dx = { n: 0, e: 1, s: 0, w: -1 }[agent.flags.orientation];
+      const dy = { n: -1, e: 0, s: 1, w: 0 }[agent.flags.orientation];
+      const target = world.agents.filter(
+        a => a.x === agent.x+dx && a.y === agent.y+dy
+      )[0];
+      if (target === undefined || !target.flags.flag) {
+        return [
+          { 
+            lattice_changes: [{
+              x: agent.x + dx, y: agent.y + dy,
+              from: 'flag', to: 'empty',
+              flags: { emit: [ 0, 0, 1, 0, 0, 0, 0, 0 ] },
+            }],
+            agent_changes: [{
+              agent_id: agent.id,
+              flags: { flag: true },
+            }],
+          }
+        ];
+      } else {
+        return [{
+          agent_changes: [
+            {
+              agent_id: target.id,
+              flags: { flag: false },
+            },
+            {
+              agent_id: agent.id,
+              flags: { flag: true },
+            },
+          ],
+        }];
+      }
+    }
+  },
+};
+
+
 export const actions = [
   move_forward, move_backward, turn_left, turn_right, 
-  place, trigger, pretend_frozen, unfreeze,
+  place, trigger, pretend_frozen, unfreeze, take_flag,
 ];
diff --git a/src/simulation/actions.test.js b/src/simulation/actions.test.js
index c5f35be..e0b29dc 100644
--- a/src/simulation/actions.test.js
+++ b/src/simulation/actions.test.js
@@ -8,6 +8,7 @@ const [
   turn_left, turn_right,
   place, trigger,
   pretend_frozen, unfreeze,
+  take_flag,
   ...rest
 ] = actions;
 
@@ -246,3 +247,36 @@ test("unfreeze", () => {
 
   expect(unfreeze.propose({agents}, agent1, [0])).toEqual([]);
 });
+
+
+test("take flag", () => {
+  const agent = { id: 0, x: 0, y: 0, flags: { orientation: 'n' } };
+  const other1 = { id: 1, x: 0, y: -1, flags: { flag: true } };
+  const other2 = { id: 2, x: 0, y: 1, flags: { flag: false } };
+
+  const world = { agents: [ agent, other1, other2 ] };
+
+  expect(take_flag.propose(world, agent, [1])).toEqual([
+    { agent_changes: [
+      { agent_id: 1, flags: { flag: false } },
+      { agent_id: 0, flags: { flag: true  } },
+    ]},
+  ]);
+
+  agent.flags.orientation = 's';
+  expect(take_flag.propose(world, agent, [1])).toEqual([
+    { 
+      lattice_changes: [
+        { 
+          x: 0, y: 1, from: 'flag', to: 'empty',
+          flags: { emit: [ 0, 0, 1, 0, 0, 0, 0, 0 ] },
+        },
+      ],
+      agent_changes: [
+        { agent_id: 0, flags: { flag: true  } },
+      ]
+    },
+  ]);
+
+  expect(take_flag.propose(world, agent, [0])).toEqual([]);
+});