Connect plugins to the database

The GitHub Commit plugin needs access to the database in order to work
properly. Include 'sqlite-simple' to give us access to the database and
have it transform rows into Haskell objects.

This change has the unfortunate effect of forcing us to make
`PluginAction` an IO type. This means we'll need to make all our plugin
action functions use IO, even the pure ones. `PluginAction` now takes a
database connection as a second argument, and returns an `IO String`.

I don't like the fact that the database argument is effectively
hard-coded. Thus the TODO note to try to make a type class to replace it
so we can pass a null database connection when it isn't needed.
Eventually, if more things like this need to be passed into the
function, we might consider making a new struct type for the purpose.

In order to be able to use the `query_` function, which takes a
String-like `Query`, we have to declare `OverloadedStrings`. Now in
`gitHubCommitAction` we take the database connection as an argument,
select a row (for now it's always the first one to test this out), and
send back a GitHub commit URL (if a record matched, otherwise return an
empty string). Eventually we'll want to make this more real by selecting
the row corresponding to the channel in `message`. Also, instead of
returning an empty string, we should be returning an `Either`, so the
error state is clear.

Update the `ChannelRepoUrl` data constructor to use record syntax so we
can name its fields.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/Plugin/Base.hs b/src/Plugin/Base.hs
index c85f53a..b752fd1 100644
--- a/src/Plugin/Base.hs
+++ b/src/Plugin/Base.hs
@@ -4,9 +4,12 @@ module Plugin.Base
     , Plugin(..)
     ) where
 
+import Database.SQLite.Simple
+
 import Message
 
-type PluginAction = Message -> String
+-- TODO: Replace Connection with a type class
+type PluginAction = Message -> Connection -> IO String
 
 data Plugin = Plugin
     { matchRegex :: String