userUpdate.sml

fragment realworld {
	"std" 1.0
	"url/url" 1.0
}

NoChange = struct{}

# userUpdate is analogous to "PUT /api/user" resolving a mutation
# causing a permanent mutation of the t:User entity identified by
# p:username in case of success
userUpdate = (
	# username identifies the user to be updated
	username Username,
	
	# newUsername doesn't change User.email when not given
	newUsername ?Username,

	# newEmail doesn't change User.email when not given
	newEmail ?EmailAddress,

	# newBio resets User.bio to unset when not given,
	# use NoChange to leave User.bio unchanged
	newBio ?(String or NoChange),

	# newImage resets User.image to unset when not given,
	# use NoChange to leave User.image unchanged
	newImage ?(url::Url or NoChange),
) -> (
	std::Mutation<UserResolver> or
	ErrUnauth or
	ErrUserNotFound or
	ErrUsernameReserved or
	ErrEmailReserved
) => {
	user = entity<User>(predicate: (u) => u.username == username)
	userByNewUsername = entity<User>(predicate: (u) => u.username == newUsername)
	userByNewEmail = entity<User>(predicate: (u) => u.email == newEmail)

	& = match {
		// Ensure the profile exists
		user == Nil then ErrUserNotFound

		// Ensure only the owner is allowed to update a profile
		!isOwner(owner: User from user) then ErrUnauth

		// Ensure username uniqueness
		userByNewUsername != Nil then ErrUsernameReserved

		// Ensure email uniqueness
		userByNewEmail != Nil then ErrEmailReserved

		else {
			user = User from user

			updatedProfile = User{
				username: newUsername as v {
					Username then v
					else user.username
				},
				email: newEmail as v {
					EmailAddress then v
					else user.email
				},
				bio: newBio as v {
					NoChange then user.bio
					String then v
					else Nil
				},
				image: newImage as v {
					NoChange then user.image
					url::Url then v
					else Nil
				},
				..user,
			}

			& = std::Mutation{
				effects: {
					// Update the profile
					std::mutated(user, updatedProfile),
				},
				data: UserResolver{user: updatedProfile},
			}
		}
	}
}