{- This file is part of Vervis.
 -
 - Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
 -
 - ♡ Copying is an act of love. Please copy, reuse and share.
 -
 - The author(s) have dedicated all copyright and related and neighboring
 - rights to this software to the public domain worldwide. This software is
 - distributed without any warranty.
 -
 - You should have received a copy of the CC0 Public Domain Dedication along
 - with this software. If not, see
 - <http://creativecommons.org/publicdomain/zero/1.0/>.
 -}

module Vervis.Migration
    ( migrateDB
    )
where

import Prelude

import Control.Monad.IO.Class (MonadIO)
import Control.Monad.Trans.Reader (ReaderT, runReaderT)
import Data.Maybe (fromMaybe)
import Database.Persist
import Database.Persist.Sql (SqlBackend, toSqlKey)

import Database.Persist.Schema
import Database.Persist.Schema.PostgreSQL (schemaBackend)

import Vervis.Model

key :: SchemaVersionId
key = toSqlKey 1

getDbSchemaVersion :: MonadIO m => ReaderT SqlBackend m (Maybe Int)
getDbSchemaVersion = fmap schemaVersionNumber <$> get key

setDbSchemaVersion :: MonadIO m => Int -> ReaderT SqlBackend m ()
setDbSchemaVersion v = update key [SchemaVersionNumber =. v]

-- | Run the migration system. The second parameter is the list of migration
-- actions in chronological order. The migration process is:
--
-- * Check the schema version of the DB
-- * Compare to the schema version of the app, which is the length of the list
-- * If any migrations are required, run them
-- * Update the schema version in the DB
runMigrations
    :: MonadIO m
    => SchemaBackend SqlBackend
    -> [SchemaT SqlBackend m ()]
    -> ReaderT SqlBackend m ()
runMigrations sb migrations = do
    dver <- fromMaybe 0 <$> getDbSchemaVersion
    let aver = length migrations
    case compare aver dver of
        LT -> error "Older app version running with newer DB schema version"
        EQ -> return ()
        GT -> do
            let migs = drop dver migrations
            runReaderT (sequence migs) sb
            setDbSchemaVersion aver

changes :: MonadIO m => [SchemaT SqlBackend m ()]
changes =
    [
    ]

migrateDB :: MonadIO m => ReaderT SqlBackend m ()
migrateDB = runMigrations schemaBackend changes