1 files changed, 56 insertions, 1 deletions
diff --git a/src/Settlr/Storage.hs b/src/Settlr/Storage.hs
index d646134..53c29b7 100644
--- a/src/Settlr/Storage.hs
+++ b/src/Settlr/Storage.hs
@@ -1,2 +1,57 @@
-module Settlr.Storage(
+module Settlr.Storage
+  ( Group(..)
+  , Member(..)
+  , Money(..)
+  , Currency(..)
+  , GroupMetadata(..)
+  , getMetadata
+  , createGroup
+  , deleteGroup
+  , Expense(..)
+  , getExpenses
+  , getSaldo
+  , addExpense
   ) where
+
+import Data.Text (Text)
+import Data.Map (Map)
+
+-- Identifier of a group.
+newtype Group = Group Text
+
+-- Identifier of a group member.
+newtype Member = Member Text
+
+-- An amount of money in a particular currency (usually, the smallest unit for the currency).
+newtype Money = Money Int
+
+data Currency = CurrencyEUR | CurrencyUSD
+
+data GroupMetadata = GroupMetadata
+  { grpName     :: !Text
+  , grpMembers  :: ![Member]
+  , grpCurrency :: !Currency
+  }
+
+getMetadata :: Group -> IO GroupMetadata
+getMetadata = undefined
+
+createGroup :: GroupMetadata -> IO Group
+createGroup = undefined
+
+deleteGroup :: Group -> IO ()
+deleteGroup = undefined
+
+data Expense = Expense
+  { expCreditor :: !Member
+  , expDebtors  :: !(Map Member Money)
+  }
+
+getExpenses :: Group -> IO [Expense]
+getExpenses = undefined
+
+getSaldo :: Group -> Member -> IO Money
+getSaldo = undefined
+
+addExpense :: Group -> Expense -> IO ()
+addExpense = undefined