implementation of the revenue sharing model

Signed-off-by: Loïc Dachary <loic@dachary.org>

share.py

@@ -0,0 +1,35 @@
+# py.test-3 --log-cli-level=DEBUG -v -k test_share_income share.py
+
+EXPENSE = 1
+
+#
+# For a given income, return a list of the members who will not be paid in full
+# and how much will remain in their expense balance.
+#
+# See https://forum.hostea.org/t/decision-revenue-sharing-model/92
+#
+def share_income(income, members):
+    if income <= 0:
+        return members
+    if income < len(members):
+        share = 1
+        count = income
+    else:
+        share = min(int(income / len(members)), min(members, key=lambda m: m[EXPENSE])[EXPENSE])
+        count = len(members)
+    remaining = []
+    for i in range(count):
+        m = members[i]
+        m[EXPENSE] -= share
+        if m[EXPENSE] > 0:
+            remaining.append(m)
+    remaining.extend(members[count:])
+    return share_income(income - share * count, remaining)
+
+def test_share_income():
+    assert share_income(1, [['a', 1], ['b', 1]]) == [['b', 1]]
+    assert share_income(5, [['a', 10], ['b', 2]]) == [['a', 7]]
+    assert share_income(5, [['a', 2], ['b', 10], ['c', 1]]) == [['b', 8]]
+    assert share_income(5, [['a', 2], ['b', 10], ['c', 1], ['d', 40]]) == [['b', 9], ['d', 39]]
+    assert share_income(5, [['a', 2], ['b', 10], ['c', 1], ['d', 40], ['e', 3]]) == [['a', 1], ['b', 9], ['d', 39], ['e', 2]]
+    assert share_income(5, [['a', 2], ['b', 10], ['c', 1], ['d', 40], ['e', 3], ['f', 1]]) == [['a', 1], ['b', 9], ['d', 39], ['e', 2], ['f', 1]]