Use a modification safe observers list

1 files changed, 71 insertions, 0 deletions

diff --git a/src/observers.hh b/src/observers.hh
new file mode 100644
index 0000000..3e56e6b
--- /dev/null
+++ b/src/observers.hh
@@ -0,0 +1,71 @@
+#ifndef OBSERVERS_HH
+#define OBSERVERS_HH
+
+#include <memory>
+#include <vector>
+
+template<typename T>
+class Observers {
+public:
+  Observers()
+    : current_(0), protected_(0), removed_(0) {
+  }
+
+  void add(T* observer) {
+    if (!observer) return;
+    for (auto it = observers_.begin(); it != observers_.end(); ++it) {
+      if (*it == observer) return;
+    }
+    observers_.push_back(observer);
+  }
+
+  void remove(T* observer) {
+    if (!observer) return;
+    size_t index = 0;
+    for (; index < observers_.size(); ++index) {
+      if (observers_[index] == observer) {
+        if (index < protected_) {
+          observers_[index] = nullptr;
+          ++removed_;
+        } else {
+          observers_.erase(observers_.begin() + index);
+        }
+        break;
+      }
+    }
+  }
+
+  T* first() {
+    if (protected_) return nullptr;
+    if (observers_.empty()) return nullptr;
+    protected_ = observers_.size();
+    return observers_[current_];
+  }
+
+  T* next() {
+    if (current_ >= protected_) return nullptr;
+    ++current_;
+    if (current_ >= protected_) {
+      if (removed_) {
+        for (size_t i = protected_; i > 0; --i) {
+          if (!observers_[i - 1]) {
+            observers_.erase(observers_.begin() + i - 1);
+            if (--removed_ == 0) break;
+          }
+        }
+      }
+      protected_ = current_ = 0;
+      return nullptr;
+    }
+    auto ret = observers_[current_];
+    return ret ? ret : next();
+  }
+
+private:
+  size_t current_;
+  size_t protected_;
+  size_t removed_;
+  std::vector<T*> observers_;
+};
+
+#endif  // OBSERVERS_HH