Finish markov chain generation impl

* Markov chains will train and generate chains correctly now
* Implement Markov.save_chains/0
* Add a couple more utils that help accomplish the above

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

test/contrib/markov/chain_test.exs

@@ -9,6 +9,32 @@ defmodule MarkovChainTest do
       {["bar", "baz"], %{nil => 1}},
       {["foo", "bar"], %{"baz" => 1}},
     ]
+
+    chain = chain |> Chain.train(~w(foo bar baz))
+
+    assert chain.chain == [
+      {["bar", "baz"], %{nil => 2}},
+      {["foo", "bar"], %{"baz" => 2}},
+    ]
+
+    chain = chain |> Chain.train(~w(baz bar foo))
+
+    assert chain.chain == [
+      {["bar", "foo"], %{nil => 1}},
+      {["baz", "bar"], %{"foo" => 1}},
+      {["bar", "baz"], %{nil => 2}},
+      {["foo", "bar"], %{"baz" => 2}},
+    ]
+
+    chain = chain |> Chain.train(~w(a b c))
+    assert chain.chain == [
+      {["b", "c"], %{nil => 1}},
+      {["a", "b"], %{"c" => 1}},
+      {["bar", "foo"], %{nil => 1}},
+      {["baz", "bar"], %{"foo" => 1}},
+      {["bar", "baz"], %{nil => 2}},
+      {["foo", "bar"], %{"baz" => 2}},
+    ]
   end
 
   test "chain add_weight works correctly" do
@@ -28,5 +54,17 @@ defmodule MarkovChainTest do
     assert chain.chain == [
       {["foo", "bar"], %{"baz" => 3, "qux" => 1}}
     ]
+
+    chain = chain |> Chain.add_weight(["bar", "baz"], "qux")
+    assert chain.chain == [
+      {["bar", "baz"], %{"qux" => 1}},
+      {["foo", "bar"], %{"baz" => 3, "qux" => 1}},
+    ]
+
+    chain = chain |> Chain.add_weight(["bar", "baz"], nil)
+    assert chain.chain == [
+      {["bar", "baz"], %{"qux" => 1, nil => 1}},
+      {["foo", "bar"], %{"baz" => 3, "qux" => 1}},
+    ]
   end
 end