Look up book author, title, and publisher by isbn in Amazon web services

amz_lookup

-module (amz_lookup).
-export([http_by_isbn/1]).

% -compile(export_all).

-include_lib("xmerl/include/xmerl.hrl").

% NOTE: Macros blocked out to protect the innocent. Use your own.

-define(ASSOC_TAG, "AAAAAAAA").
-define(ACCESS_KEY, "XXXXXXXXX").
-define(SECRET_KEY, "YYYYYYYYYYYYYYYYYYYY")


%% Look up book author, title, and publisher by isbn  in Amazon web services db.
%% http://docs.aws.amazon.com/AWSECommerceService/latest/DG/EX_LookupbyISBN.html
%% http://docs.aws.amazon.com/AWSECommerceService/latest/DG/rest-signature.html

%% Compute timestamp

pad_date(Int) when Int < 10 ->
   "0" ++ integer_to_list(Int);

pad_date(Int)               ->
   integer_to_list(Int).

timestamp() ->
   [{{Year, Month, Day},{Hour, Minute, Second}}] =
       calendar:local_time_to_universal_time_dst(calendar:local_time()),
   S =  integer_to_list(Year) ++
        "-" ++
        pad_date(Month) ++
        "-" ++
        pad_date(Day) ++
        "T" ++
        pad_date(Hour) ++
        ":" ++
        pad_date(Minute) ++
        ":" ++
        pad_date(Second) ++
        "Z",
    http_uri:encode(S).


%% Test: > book_request:timestamp().
%% "2015-04-13T22%3A08%3A16Z"

%% List parameters

parameters(ISBN) ->
   [
    {"Service=AWSECommerceService"},
    {"Operation=ItemLookup"},
    {"ResponseGroup=Small"},
    {"SearchIndex=All"},
    {"IdType=ISBN"},
    {"ItemId=" ++ ISBN},
    {"AWSAccessKeyId=" ++ ?ACCESS_KEY},
    {"AssociateTag=" ++ ?ASSOC_TAG},
    {"Timestamp=" ++ timestamp()}
   ].

%% Test: > book_request:parameters("9780982589205").
%% [{"Service=AWSECommerceService"},
%% {"Operation=ItemLookup"},
%% {"ResponseGroup=Small"},
%% {"SearchIndex=All"},
%% {"IdType=ISBN"},
%% {"ItemId=9780982589205"},
%% {"AWSAccessKeyId=[My secret key]},
%% {"AssociateTag=[My associate tag]"},
%% {"Timestamp=2015-04-13T22%3A11%3A54Z"}]

%% Compute signature and request
%% See: http://docs.aws.amazon.com/AWSECommerceService/latest/DG/rest-signature.html

by_isbn(ISBN) ->
     % Compute request
   Http = "http://webservices.amazon.com/onca/xml?",
   A = parameters(ISBN),
   B = lists:flatten([element(1, X) ++ "&" || X <- A]),
   C = string:substr(B, 1, length(B) - 1),
   Request = Http ++ C,
      %  io:format("~nREQUEST: ~n~s~n~n", [Request]),
      % Compute signature
      % http://docs.aws.amazon.com/AWSECommerceService/latest/DG/rest-signature.html
   D = lists:sort(A),
   E = [element(1,X) ++ "&" || X <- D],
   F = lists:flatten(E),
   G = string:substr(F, 1, length(F) -1 ),
      % io:format("STEPS 3, 4, 5 - Split and sort parameters, join with ampersands: ~n~s~n~n", [G]),
   H = "GET\nwebservices.amazon.com\n/onca/xml\n" ++ G,
      %  io:format("STEP 6 & 7 - Prepend method; String to sign: ~n~s~n~n",[H]),
   Signature = base64:encode_to_string(crypto:hmac(sha256, ?SECRET_KEY, H)),
      %  io:format("STEP 8 - Calculate HMAC: ~n~s~n~n",[Signature]),
      %  io:format("STEP 9 - uri encode HMAC"),
   Request ++ "&Signature=" ++ http_uri:encode(Signature).

%% Fetch author, title, publisher via http

http_by_isbn(ISBN) ->
   {ok, {_Status, _Headers, Body}} = httpc:request(by_isbn(ISBN)),
   {Xml, _Rest} =  xmerl_scan:string(Body),
   [ #xmlText{value=Author}] = xmerl_xpath:string("//Author/text()", Xml),
   [ #xmlText{value=Title}] = xmerl_xpath:string("//Title/text()", Xml),
   [ #xmlText{value=Publisher}] = xmerl_xpath:string("//Manufacturer/text()", Xml),
   {Author, Title, Publisher}.