/datum/migration_controller
	var/list/db_states[0]
	var/list/packages[0]

	var/TABLE_NAME = "_migrations"
	var/id = ""

/datum/migration_controller/proc/setup()
	return FALSE
/datum/migration_controller/proc/createMigrationTable()
	return FALSE

/datum/migration_controller/New()
	if(!setup())
		world.log << "\[Migrations] ([id]): Setup() returned false, will not run migrations for this DBMS."
	else
		if(!hasTable(TABLE_NAME))
			world.log << "\[Migrations] ([id]): Creating [TABLE_NAME]"
			createMigrationTable()

		for(var/list/row in query("SELECT pkgID, version FROM [TABLE_NAME]"))
			if(id=="mysql")
				db_states[row[1]] = text2num(row[2])
			else
				db_states[row["pkgID"]] = text2num(row["version"])

		var/list/newpacks[0]
		for(var/mtype in typesof(/datum/migration)-list(/datum/migration))
			var/datum/migration/M = new mtype(src)
			if(M.package == "" || M.name == "" || M.dbms != id)
				continue
			if(!(M.package in newpacks))
				newpacks[M.package]=list()
			var/list/pack = newpacks[M.package]
			pack += M
		for(var/pkgID in newpacks)
			if(!(pkgID in packages))
				packages[pkgID]=list()
			var/list/prepack = newpacks[pkgID]
			var/list/pack[prepack.len]
			for(var/datum/migration/M in newpacks[pkgID])
				pack[M.id] = M
				//world.log << "\[Migrations] [pkgID]#[M.id] = [M.type] - [M.name]"
			packages[pkgID]=pack
			world.log << "\[Migrations] Loaded [pack.len] [id] DB migrations from package [pkgID]."
		//VersionCheck()
		UpdateAll()

/datum/migration_controller/proc/getCurrentVersion(var/pkgID)
	if(pkgID in db_states)
		return db_states[pkgID]
	else
		return 0

/datum/migration_controller/proc/VersionCheck()
	for(var/pkgID in packages)
		var/currentVersion = getCurrentVersion(pkgID)
		var/latestVersionAvail = 0
		for(var/datum/migration/M in packages[pkgID])
			if(M.id > latestVersionAvail)
				latestVersionAvail = M.id
		//world.log << "\[Migrations] Package [pkgID]: Current: [currentVersion], Avail: [latestVersionAvail]"
		if(latestVersionAvail > currentVersion)
			world.log << "\[Migrations] *** [pkgID] is behind [latestVersionAvail-currentVersion] versions!"

/datum/migration_controller/proc/UpdateAll()
	for(var/pkgID in packages)
		var/latestVersionAvail = 0
		for(var/datum/migration/M in packages[pkgID])
			if(M.id > latestVersionAvail)
				latestVersionAvail = M.id
		if(latestVersionAvail > getCurrentVersion())
			UpdatePackage(pkgID, latestVersionAvail)
	VersionCheck()

/datum/migration_controller/proc/UpdatePackage(var/pkgID, var/to_version=-1)
	var/list/package = packages[pkgID]
	var/from_version = getCurrentVersion(pkgID)
	if(to_version==-1)
		for(var/datum/migration/M in packages[pkgID])
			if(M.id > to_version)
				to_version = M.id
	if(from_version == to_version)
		world.log << "\[Migrations] [pkgID] is up to date."
		return
	world.log << "\[Migrations] Updating [pkgID] from [from_version] to [to_version]..."
	for(var/datum/migration/M in package)
		if(M.id > from_version && M.id <= to_version)
			if(!M.up())
//				to_chat(world, "[log_text] <span style='font-weight:bold;color:red;'>FAIL</span><br>Failed to process migration [pkgID] #[M.id]!")
				world.log << "Failed to process migration [pkgID] #[M.id]"
				return FALSE
			else
				M.execute("REPLACE INTO [TABLE_NAME] (pkgID,version) VALUES ('[pkgID]',[M.id])") // SQLite also supports REPLACE.
				world.log << "\[Migrations] Successfully applied [pkgID]#[M.id] ([M.name])"
	world.log << "\[Migrations] Done!"
	return TRUE

/datum/migration_controller/proc/query(var/sql)
	var/DBQuery/query = execute(sql)

	var/list/rows=list()
	while(query.NextRow())
		rows += list(query.item)
	return rows

/datum/migration_controller/proc/hasResult(var/sql)
	return FALSE

/datum/migration_controller/proc/execute(var/sql)
	return list()

/datum/migration_controller/proc/hasTable(var/tableName)
	return FALSE