From 8e18c643bda15cb6e6ffd743d8267a52d60fe22b Mon Sep 17 00:00:00 2001
From: Eugene Dubovoy <eugene.dubovoy@gmail.com>
Date: Fri, 28 Oct 2016 19:51:17 +0300
Subject: [PATCH] Add Blackboard pattern

---
 blackboard.py | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 blackboard.py

diff --git a/blackboard.py b/blackboard.py
new file mode 100644
index 0000000..1c9fa1d
--- /dev/null
+++ b/blackboard.py
@@ -0,0 +1,127 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+@author: Eugene Duboviy <eugene.dubovoy@gmail.com> | github.com/duboviy
+
+In Blackboard pattern several specialised sub-systems (knowledge sources)
+assemble their knowledge to build a possibly partial or approximate solution.
+In this way, the sub-systems work together to solve the problem,
+where the solution is the sum of its parts.
+
+https://en.wikipedia.org/wiki/Blackboard_system
+"""
+
+import abc
+import random
+
+
+class Blackboard(object):
+
+    def __init__(self):
+        self.experts = []
+        self.common_state = {
+            'problems': 0,
+            'suggestions': 0,
+            'contributions': [],
+            'progress': 0   # percentage, if 100 -> task is finished
+        }
+
+    def add_expert(self, expert):
+        self.experts.append(expert)
+
+
+class Controller(object):
+
+    def __init__(self, blackboard):
+        self.blackboard = blackboard
+
+    def run_loop(self):
+        while self.blackboard.common_state['progress'] < 100:
+            for expert in self.blackboard.experts:
+                if expert.is_eager_to_contribute:
+                    expert.contribute()
+        return self.blackboard.common_state['contributions']
+
+
+class AbstractExpert(object):
+
+    __metaclass__ = abc.ABCMeta
+
+    def __init__(self, blackboard):
+        self.blackboard = blackboard
+
+    @abc.abstractproperty
+    def is_eager_to_contribute(self):
+        raise NotImplementedError('Must provide implementation in subclass.')
+
+    @abc.abstractmethod
+    def contribute(self):
+        raise NotImplementedError('Must provide implementation in subclass.')
+
+
+class Student(AbstractExpert):
+
+    @property
+    def is_eager_to_contribute(self):
+        return True
+
+    def contribute(self):
+        self.blackboard.common_state['problems'] += random.randint(1, 10)
+        self.blackboard.common_state['suggestions'] += random.randint(1, 10)
+        self.blackboard.common_state['contributions'] += [self.__class__.__name__]
+        self.blackboard.common_state['progress'] += random.randint(1, 2)
+
+
+class Scientist(AbstractExpert):
+
+    @property
+    def is_eager_to_contribute(self):
+        return random.randint(0, 1)
+
+    def contribute(self):
+        self.blackboard.common_state['problems'] += random.randint(10, 20)
+        self.blackboard.common_state['suggestions'] += random.randint(10, 20)
+        self.blackboard.common_state['contributions'] += [self.__class__.__name__]
+        self.blackboard.common_state['progress'] += random.randint(10, 30)
+
+
+class Professor(AbstractExpert):
+
+    @property
+    def is_eager_to_contribute(self):
+        return True if self.blackboard.common_state['problems'] > 100 else False
+
+    def contribute(self):
+        self.blackboard.common_state['problems'] += random.randint(1, 2)
+        self.blackboard.common_state['suggestions'] += random.randint(10, 20)
+        self.blackboard.common_state['contributions'] += [self.__class__.__name__]
+        self.blackboard.common_state['progress'] += random.randint(10, 100)
+
+
+if __name__ == '__main__':
+    blackboard = Blackboard()
+
+    blackboard.add_expert(Student(blackboard))
+    blackboard.add_expert(Scientist(blackboard))
+    blackboard.add_expert(Professor(blackboard))
+
+    c = Controller(blackboard)
+    contributions = c.run_loop()
+
+    from pprint import pprint
+    pprint(contributions)
+
+### OUTPUT ###
+# ['Student',
+#  'Student',
+#  'Scientist',
+#  'Student',
+#  'Scientist',
+#  'Student',
+#  'Scientist',
+#  'Student',
+#  'Scientist',
+#  'Student',
+#  'Scientist',
+#  'Professor']