refactor: repositories (#28)

* cleanup unnecessary mocks

* refactor document storage location

* remove unused function

* move ownership to document types to repo package

* move types and mappers to repo package

* refactor sets to own package

backend/internal/repo/map_helpers.go

@@ -0,0 +1,52 @@
+package repo
+
+// mapTErrFunc is a factory function that returns a mapper function that
+// wraps the given mapper function but first will check for an error and
+// return the error if present.
+//
+// Helpful for wrapping database calls that return both a value and an error
+func mapTErrFunc[T any, Y any](fn func(T) Y) func(T, error) (Y, error) {
+	return func(t T, err error) (Y, error) {
+		if err != nil {
+			var zero Y
+			return zero, err
+		}
+
+		return fn(t), nil
+	}
+}
+
+// TODO: Future Usage
+// func mapEachFunc[T any, Y any](fn func(T) Y) func([]T) []Y {
+// 	return func(items []T) []Y {
+// 		result := make([]Y, len(items))
+// 		for i, item := range items {
+// 			result[i] = fn(item)
+// 		}
+
+// 		return result
+// 	}
+// }
+
+func mapTEachErrFunc[T any, Y any](fn func(T) Y) func([]T, error) ([]Y, error) {
+	return func(items []T, err error) ([]Y, error) {
+		if err != nil {
+			return nil, err
+		}
+
+		result := make([]Y, len(items))
+		for i, item := range items {
+			result[i] = fn(item)
+		}
+
+		return result, nil
+	}
+}
+
+func mapEach[T any, U any](items []T, fn func(T) U) []U {
+	result := make([]U, len(items))
+	for i, item := range items {
+		result[i] = fn(item)
+	}
+	return result
+}