exception Bad_selector

let make_digests (arr:string array) = 
	Array.map (fun str -> Digest.string str) arr

let file_is_safe requested_file dig_list =
	let dig = Digest.string requested_file in
	Array.fold_left 
			(fun acc digest -> if Digest.compare dig digest = 0 then true else acc)
			false
			dig_list

let read_in_and_print ic =
	try
		while true do
			print_endline (input_line ic);
		done
	with 
		| End_of_file -> ()
		| Sys_error e -> Printf.fprintf stderr "%s\n" e


let get_real_file rootdir basename =
	Stdlib.Filename.concat rootdir (Stdlib.Filename.basename basename)

let check_exists full_path =
	Sys.file_exists full_path && Sys.is_regular_file full_path

let validate_file_path rootdir path =
	check_exists (get_real_file rootdir path)

let read_safe_root_digests rootdir =
	try 
		Sys.readdir rootdir |> make_digests
	with Sys_error e -> Printf.fprintf stderr "%s\n" e; [||]

let rec get_dir_from_selector selector dirpairs =
	match dirpairs with
	| [] -> None
	| hd :: tl -> match hd with
				| (tuple_selector, dir) when selector = tuple_selector -> Some dir
				| _ -> get_dir_from_selector selector tl

let read_selector_and_filename () =
	let selector = read_line () and filename = read_line() in
	(selector, filename)

let validate_and_print rootdir filename =
	let digests = read_safe_root_digests rootdir in
	if Array.length digests = 0 then false
	else begin
		match file_is_safe filename digests with
		| true -> begin match validate_file_path rootdir filename with
			| true -> begin try
						In_channel.with_open_bin (get_real_file rootdir filename) read_in_and_print; true
					with  Sys_error e -> false
				end
			| false -> false
			end
		| false -> false
	end

let program selector dirpairs filename = 
	validate_and_print (match (get_dir_from_selector selector dirpairs) with
		| None -> (Printf.fprintf stderr "No directory found for selector '%s'\n" selector; raise Bad_selector)
		| Some dir -> dir
	) filename 


.