#load "extLib.cma"

open Printf

(* Record changes and report changes *)
module HasChanged =
	struct
		type change_rec = { fn: string ; ov:  string ; nv:  string ; }

		let create () = DynArray.create () ;;
		let to_list changes = DynArray.to_list changes ;;

		let change fn ov nv = {fn=fn; ov=ov; nv=nv;}
		let add_maybe changes fn ov nv =
			if ov != nv then DynArray.add changes (change fn ov nv) ;;
		let field_names a b =
			if String.length a > 0
				then a ^ "," ^ b.fn
				else b.fn ;;
		let field_values a b =
			if String.length a > 0
				then a ^ ",'" ^ b.nv ^ "'"
				else "'" ^ b.nv ^ "'";;
		let field_name_value_pair a b =
			if String.length a > 0
				then a ^ "," ^ b.fn ^ "='" ^ b.nv ^ "'"
				else b.fn ^ "='" ^ b.nv ^ "'" ;;
end ;;

let update_stmt table id changes =
	let vp = List.fold_left HasChanged.field_name_value_pair "" changes in
		sprintf "UPDATE %s SET %s WHERE id=%i" table vp id ;;

let add_callback v f = DynArray.add v f ;;

(*  This entire module will be auto-generated based on table information *)
module User =
	struct
		type user = {
			mutable id: int ;
			mutable code: string ;
			mutable password: string ;
			mutable first_name: string ;
			mutable last_name: string ;
			mutable version: int ;
			mutable original: user option ; }

		let before_create = DynArray.create ()
		let before_update = DynArray.create ()
		let before_insert = DynArray.create ()

		let create id code password first_name last_name version =
			{ id=id; code=code; password=password; first_name=first_name;
			  last_name=last_name; version=0; original=None; }

		let empty = create 0 "" "" "" "" 0

		let changes u =
			let do_change_compare u1 u2 =
				let changes = HasChanged.create () in
					HasChanged.add_maybe changes "id" (string_of_int u1.id) (string_of_int u2.id) ;
					HasChanged.add_maybe changes "code" u1.code u2.code ;
					HasChanged.add_maybe changes "password" u1.password u2.password ;
					HasChanged.add_maybe changes "first_name" u1.first_name u2.first_name ;
					HasChanged.add_maybe changes "last_name" u1.last_name u2.last_name ;
					HasChanged.add_maybe changes "version" (string_of_int u1.version) (string_of_int u2.version) ;
					HasChanged.to_list changes
			in
				match u.original with
				| Some orig -> do_change_compare orig u
				| None -> do_change_compare empty u ;;

		let clear_changes u =
			u.original <- (Some (create u.id u.code u.password u.first_name u.last_name u.version))

		let insert u =
			DynArray.iter (fun f -> f u) before_insert;
			let stmt = sprintf ("INSERT INTO users (code,password,first_name,last_name,version) VALUES ('%s','%s','%s','%s',%i)")
						u.code u.password u.first_name u.last_name u.version in
				u.id <- 10 ;
				clear_changes u ;
				stmt ;;

		let update u =
			DynArray.iter (fun f -> f u) before_update;
			let stmt = update_stmt "users" u.id (changes u) in
				clear_changes u ;
				stmt ;;

		let save u = if u.id == 0 then insert u else update u ;;
end ;;

(* Methods that I use to extend the base functionality of the auto-generated
	User module *)
let user_cb_set_defaults u = u.User.version <- 1 ;;
let user_cb_increment_version u = u.User.version <- u.User.version + 1 ;;
let user_full_name u = sprintf "%s %s" u.User.first_name u.User.last_name ;;
let user_blinded_name u = sprintf "%s %c." u.User.first_name (String.get u.User.last_name 0) ;;

(* Simple callback interface *)
add_callback User.before_insert user_cb_set_defaults ;;
add_callback User.before_update user_cb_increment_version ;;

(* Play around a bit *)
let u=User.create 0 "john" "doe" "John" "Doe" 0 in
	printf "%s\n" (User.save u) ;
	u.User.first_name <- "Jane" ;
	u.User.last_name <- "Smith" ;
	printf "%s\n" (user_blinded_name u) ;
	u.User.code <- "jsmith" ;
	printf "%s\n" (User.save u) ;;