Change `PluginAction` type to `Message -> String`

Have `PluginAction` functions take a Message type instead of a plain
string. This gives us access to additional fields on the message:
channel and nick.

sorbot.cabal:
Add `Message` to `exposed-modules` in order to be able to use it when
building.

Lib.hs:
Change our test message to be a `Message` data type to conform to the new
`PluginAction` interface.

Plugin.hs:
Use `Message` where appropriate. When calling `perform`, pass it a
`Message` instead of a `String`. This means we have to match the regex
within the plugin in order to get the match data. The benefit of that
change is that now we have access to the full message in the plugin if
we need it, not just the regex-filtered part.

GitHubCommit.hs:
Do a regex match against the Message text in order to get the SHA we
want from the message.

2 files changed, 8 insertions, 2 deletions

diff --git a/src/Plugin/Base.hs b/src/Plugin/Base.hs
index 329c21a..c85f53a 100644
--- a/src/Plugin/Base.hs
+++ b/src/Plugin/Base.hs
@@ -4,7 +4,9 @@ module Plugin.Base
     , Plugin(..)
     ) where
 
-type PluginAction = String -> String
+import Message
+
+type PluginAction = Message -> String
 
 data Plugin = Plugin
     { matchRegex :: String
diff --git a/src/Plugin/GitHubCommit.hs b/src/Plugin/GitHubCommit.hs
index 24c4831..8fa8d0a 100644
--- a/src/Plugin/GitHubCommit.hs
+++ b/src/Plugin/GitHubCommit.hs
@@ -2,6 +2,9 @@ module Plugin.GitHubCommit
     ( gitHubCommit
     ) where
 
+import Text.Regex.TDFA
+
+import qualified Message as M
 import Plugin.Base
 
 gitHubCommit = Plugin
@@ -10,4 +13,5 @@ gitHubCommit = Plugin
     }
 
 gitHubCommitAction :: PluginAction
-gitHubCommitAction match = "https://github.com/" ++ match
+gitHubCommitAction message =
+    "https://github.com/" ++ M.text message =~ matchRegex gitHubCommit