From 6b34565a2aeeb03dfe7d5297f3d63ee8de893c5d Mon Sep 17 00:00:00 2001
From: Mike <mike@prime31.com>
Date: Sat, 13 Jun 2020 14:29:13 -0700
Subject: [PATCH] entity iterator

---
 zig-ecs/src/ecs/handles.zig     | 50 +++++++++++++++++++++++++--------
 zig-ecs/src/ecs/registry.zig    |  7 ++++-
 zig-ecs/tests/registry_test.zig |  3 ++
 3 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/zig-ecs/src/ecs/handles.zig b/zig-ecs/src/ecs/handles.zig
index cbf71d1..567aeb9 100644
--- a/zig-ecs/src/ecs/handles.zig
+++ b/zig-ecs/src/ecs/handles.zig
@@ -21,6 +21,28 @@ pub fn Handles(comptime HandleType: type, comptime IndexType: type, comptime Ver
 
         const invalid_id = std.math.maxInt(IndexType);
 
+        pub const Iterator = struct {
+            hm: Self,
+            index: usize = 0,
+
+            pub fn init(hm: Self) @This() {
+                return .{ .hm = hm };
+            }
+
+            pub fn next(self: *@This()) ?HandleType {
+                if (self.index == self.hm.append_cursor) return null;
+
+                for (self.hm.handles[self.index..self.hm.append_cursor]) |h| {
+                    self.index += 1;
+                    if (self.hm.alive(h)) {
+                        return h;
+                    }
+                }
+
+                return null;
+            }
+        };
+
         pub fn init(allocator: *std.mem.Allocator) Self {
             return initWithCapacity(allocator, 32);
         }
@@ -88,10 +110,14 @@ pub fn Handles(comptime HandleType: type, comptime IndexType: type, comptime Ver
             self.last_destroyed = id;
         }
 
-        pub fn isAlive(self: Self, handle: HandleType) bool {
+        pub fn alive(self: Self, handle: HandleType) bool {
             const id = self.extractId(handle);
             return id < self.append_cursor and self.handles[id] == handle;
         }
+
+        pub fn iterator(self: Self) Iterator {
+            return Iterator.init(self);
+        }
     };
 }
 
@@ -103,33 +129,33 @@ test "handles" {
     const e1 = hm.create();
     const e2 = hm.create();
 
-    std.debug.assert(hm.isAlive(e0));
-    std.debug.assert(hm.isAlive(e1));
-    std.debug.assert(hm.isAlive(e2));
+    std.debug.assert(hm.alive(e0));
+    std.debug.assert(hm.alive(e1));
+    std.debug.assert(hm.alive(e2));
 
     hm.remove(e1) catch unreachable;
-    std.debug.assert(!hm.isAlive(e1));
+    std.debug.assert(!hm.alive(e1));
 
     std.testing.expectError(error.RemovedInvalidHandle, hm.remove(e1));
 
     var e_tmp = hm.create();
-    std.debug.assert(hm.isAlive(e_tmp));
+    std.debug.assert(hm.alive(e_tmp));
 
     hm.remove(e_tmp) catch unreachable;
-    std.debug.assert(!hm.isAlive(e_tmp));
+    std.debug.assert(!hm.alive(e_tmp));
 
     hm.remove(e0) catch unreachable;
-    std.debug.assert(!hm.isAlive(e0));
+    std.debug.assert(!hm.alive(e0));
 
     hm.remove(e2) catch unreachable;
-    std.debug.assert(!hm.isAlive(e2));
+    std.debug.assert(!hm.alive(e2));
 
     e_tmp = hm.create();
-    std.debug.assert(hm.isAlive(e_tmp));
+    std.debug.assert(hm.alive(e_tmp));
 
     e_tmp = hm.create();
-    std.debug.assert(hm.isAlive(e_tmp));
+    std.debug.assert(hm.alive(e_tmp));
 
     e_tmp = hm.create();
-    std.debug.assert(hm.isAlive(e_tmp));
+    std.debug.assert(hm.alive(e_tmp));
 }
diff --git a/zig-ecs/src/ecs/registry.zig b/zig-ecs/src/ecs/registry.zig
index b07d91d..a6c8e0d 100644
--- a/zig-ecs/src/ecs/registry.zig
+++ b/zig-ecs/src/ecs/registry.zig
@@ -250,7 +250,7 @@ pub const Registry = struct {
     }
 
     pub fn valid(self: *Registry, entity: Entity) bool {
-        return self.handles.isAlive(entity);
+        return self.handles.alive(entity);
     }
 
     /// Returns the entity identifier without the version
@@ -275,6 +275,11 @@ pub const Registry = struct {
         self.handles.remove(entity) catch unreachable;
     }
 
+    /// returns an interator that iterates all live entities
+    pub fn entities(self: Registry) EntityHandles.Iterator {
+        return self.handles.iterator();
+    }
+
     pub fn add(self: *Registry, entity: Entity, value: var) void {
         assert(self.valid(entity));
         self.assure(@TypeOf(value)).add(entity, value);
diff --git a/zig-ecs/tests/registry_test.zig b/zig-ecs/tests/registry_test.zig
index b2b7ea8..dd8144b 100644
--- a/zig-ecs/tests/registry_test.zig
+++ b/zig-ecs/tests/registry_test.zig
@@ -24,6 +24,9 @@ test "Registry" {
     std.testing.expect(reg.has(Position, e1));
     std.testing.expect(reg.has(BigOne, e1));
 
+    var iter = reg.entities();
+    while (iter.next()) |e| std.testing.expectEqual(e1, e);
+
     reg.remove(Empty, e1);
     std.testing.expect(!reg.has(Empty, e1));
 }