-module(logic_email).
-export([send_verification_email/2, send_specialist_invite/2, send_password_reset/2,
         send_booking_reminder/4, send_waitlist_promoted/3]).

%% Email transport (Spec#8 / stage outbound :25 blocked):
%%   EMAIL_TRANSPORT = smtp | http_api | log | auto (default auto)
%%   auto: EMAIL_API_KEY set → http_api; else SMTP_HOST set → smtp; else log
%% SMTP: SMTP_HOST, SMTP_PORT, SMTP_USER, SMTP_PASS, SMTP_FROM, SMTP_TLS
%% HTTP API: EMAIL_API_KEY, EMAIL_API_PROVIDER=resend|brevo (default resend),
%%   optional EMAIL_API_URL; SMTP_FROM as sender
%% Tests: smtp_deliver / email_http_deliver app env mocks

-spec send_verification_email(binary(), binary()) -> ok.
send_verification_email(Email, Token) ->
  send_kind(verify, Email, abs_url(<<"/verify?token=">>, Token)).

-spec send_specialist_invite(binary(), binary()) -> ok.
send_specialist_invite(Email, Token) ->
  send_kind(invite, Email, abs_url(<<"/invites?token=">>, Token)).

-spec send_password_reset(binary(), binary()) -> ok.
send_password_reset(Email, Token) ->
  send_kind(reset, Email, abs_url(<<"/reset-password?token=">>, Token)).

-spec send_booking_reminder(binary(), binary(), calendar:datetime(), binary()) -> ok.
send_booking_reminder(Email, EventTitle, StartTime, EventPath) ->
  Url = abs_path(EventPath),
  WhenText = format_utc(StartTime),
  {Subject, Plain, Html} =
    logic_email_templates:render_reminder(Url, to_bin(EventTitle), WhenText),
  send(to_bin(Email), Subject, Plain, Html).

-spec send_waitlist_promoted(binary(), binary(), binary()) -> ok.
send_waitlist_promoted(Email, EventTitle, EventPath) ->
  Url = abs_path(EventPath),
  {Subject, Plain, Html} =
    logic_email_templates:render_waitlist_promoted(Url, to_bin(EventTitle)),
  send(to_bin(Email), Subject, Plain, Html).

send_kind(Kind, To0, Url) ->
  {Subject, Plain, Html} = logic_email_templates:render(Kind, Url),
  send(to_bin(To0), Subject, Plain, Html).

send(To, Subject, Plain, Html) ->
  case transport() of
    log ->
      logger:info(#{what => email_log_only, to => To, subject => Subject}),
      ok;
    smtp ->
      send_smtp(To, Subject, Plain, Html);
    http_api ->
      send_http_api(To, Subject, Plain, Html)
  end.

transport() ->
  case env_bin("EMAIL_TRANSPORT", <<>>) of
    <<"smtp">> -> smtp;
    <<"http_api">> -> http_api;
    <<"log">> -> log;
    <<"auto">> -> transport_auto();
    <<>> ->
      case application:get_env(eventhub, email_transport) of
        {ok, smtp} -> smtp;
        {ok, http_api} -> http_api;
        {ok, log} -> log;
        _ -> transport_auto()
      end;
    _ ->
      transport_auto()
  end.

transport_auto() ->
  case application:get_env(eventhub, email_transport) of
    {ok, smtp} -> smtp;
    {ok, http_api} -> http_api;
    {ok, log} -> log;
    _ ->
      case api_key() of
        <<>> ->
          case smtp_relay() of
            undefined -> log;
            _ -> smtp
          end;
        _ ->
          http_api
      end
  end.

%%%-------------------------------------------------------------------
%%% SMTP
%%%-------------------------------------------------------------------

send_smtp(To, Subject, Plain, Html) ->
  case smtp_relay() of
    undefined ->
      logger:info(#{what => email_log_only, to => To, subject => Subject}),
      ok;
    Relay ->
      From = from_addr(),
      Raw = rfc822(From, To, Subject, Plain, Html),
      Opts = smtp_opts(Relay),
      safe_smtp_deliver(From, To, Raw, Opts)
  end.

safe_smtp_deliver(From, To, Raw, Opts) ->
  Fun = smtp_deliver_fun(),
  try Fun(From, To, Raw, Opts) of
    {ok, _} -> ok;
    ok -> ok;
    {error, Reason} ->
      logger:warning(#{what => smtp_send_error, to => To, reason => Reason}),
      ok;
    Other ->
      logger:warning(#{what => smtp_send_unexpected, to => To, result => Other}),
      ok
  catch
    Class:Reason:Stack ->
      logger:warning(#{what => smtp_send_crash, to => To,
                       class => Class, reason => Reason, stack => Stack}),
      ok
  end.

smtp_deliver_fun() ->
  case application:get_env(eventhub, smtp_deliver) of
    {ok, Fun} when is_function(Fun, 4) -> Fun;
    _ -> fun default_smtp_deliver/4
  end.

default_smtp_deliver(From, To, Raw, Opts) ->
  gen_smtp_client:send({From, [To], Raw}, Opts).

smtp_relay() ->
  case app_or_env(smtp_host, "SMTP_HOST") of
    <<>> -> undefined;
    Host -> binary_to_list(Host)
  end.

smtp_opts(Relay) ->
  Port = env_int("SMTP_PORT", 587),
  Tls = tls_mode(env_bin("SMTP_TLS", <<"if_available">>)),
  Base = [
    {relay, Relay},
    {port, Port},
    {tls, Tls},
    {hostname, "calentiq.com"}
  ],
  User = env_bin("SMTP_USER", <<>>),
  Pass = env_bin("SMTP_PASS", <<>>),
  case User of
    <<>> -> Base;
    _ ->
      [{username, binary_to_list(User)},
       {password, binary_to_list(Pass)},
       {auth, always} | Base]
  end.

tls_mode(<<"always">>) -> always;
tls_mode(<<"never">>) -> never;
tls_mode(_) -> if_available.

%%%-------------------------------------------------------------------
%%% HTTP API (HTTPS transactional — no outbound :25/:587)
%%% Providers: resend (default/canon), brevo (optional)
%%%-------------------------------------------------------------------

send_http_api(To, Subject, Plain, Html) ->
  case api_key() of
    <<>> ->
      logger:warning(#{what => email_api_missing_key, to => To}),
      ok;
    Key ->
      From = from_addr(),
      safe_http_deliver(Key, From, To, Subject, Plain, Html)
  end.

safe_http_deliver(Key, From, To, Subject, Plain, Html) ->
  Fun = http_deliver_fun(),
  try Fun(Key, From, To, Subject, Plain, Html) of
    ok -> ok;
    {ok, _} -> ok;
    {error, Reason} ->
      logger:warning(#{what => email_api_error, to => To, reason => Reason}),
      ok;
    Other ->
      logger:warning(#{what => email_api_unexpected, to => To, result => Other}),
      ok
  catch
    Class:Reason:Stack ->
      logger:warning(#{what => email_api_crash, to => To,
                       class => Class, reason => Reason, stack => Stack}),
      ok
  end.

http_deliver_fun() ->
  case application:get_env(eventhub, email_http_deliver) of
    {ok, Fun} when is_function(Fun, 6) -> Fun;
    _ -> fun default_http_deliver/6
  end.

default_http_deliver(Key, From, To, Subject, Plain, Html) ->
  _ = application:ensure_all_started(inets),
  _ = application:ensure_all_started(ssl),
  Provider = api_provider(),
  {Url, Headers, Body} = http_api_request(Provider, Key, From, To, Subject, Plain, Html),
  Request = {binary_to_list(Url), Headers, "application/json", Body},
  HttpOpts = [{timeout, 15000}, {ssl, [{verify, verify_peer},
                                       {cacerts, public_key:cacerts_get()}]}],
  case httpc:request(post, Request, HttpOpts, [{body_format, binary}]) of
    {ok, {{_, Code, _}, _, _Resp}} when Code >= 200, Code < 300 ->
      ok;
    {ok, {{_, Code, _}, _, Resp}} ->
      {error, {http_status, Code, Resp}};
    {error, Reason} ->
      {error, Reason}
  end.

http_api_request(resend, Key, From, To, Subject, Plain, Html) ->
  Url = case env_bin("EMAIL_API_URL", <<>>) of
    <<>> -> <<"https://api.resend.com/emails">>;
    U -> U
  end,
  FromLine = <<"CalenTIQ <", From/binary, ">">>,
  Body = jsx:encode(#{
    <<"from">> => FromLine,
    <<"to">> => [To],
    <<"subject">> => Subject,
    <<"html">> => Html,
    <<"text">> => Plain
  }),
  Headers = [
    {"authorization", "Bearer " ++ binary_to_list(Key)},
    {"accept", "application/json"},
    {"content-type", "application/json"}
  ],
  {Url, Headers, Body};
http_api_request(brevo, Key, From, To, Subject, Plain, Html) ->
  Url = case env_bin("EMAIL_API_URL", <<>>) of
    <<>> -> <<"https://api.brevo.com/v3/smtp/email">>;
    U -> U
  end,
  Body = jsx:encode(#{
    <<"sender">> => #{
      <<"name">> => <<"CalenTIQ">>,
      <<"email">> => From
    },
    <<"to">> => [#{<<"email">> => To}],
    <<"subject">> => Subject,
    <<"htmlContent">> => Html,
    <<"textContent">> => Plain
  }),
  Headers = [
    {"api-key", binary_to_list(Key)},
    {"accept", "application/json"},
    {"content-type", "application/json"}
  ],
  {Url, Headers, Body}.

api_provider() ->
  case env_bin("EMAIL_API_PROVIDER", <<"resend">>) of
    <<"resend">> -> resend;
    <<"brevo">> -> brevo;
    <<"sendinblue">> -> brevo;
    Other ->
      case application:get_env(eventhub, email_api_provider) of
        {ok, resend} -> resend;
        {ok, brevo} -> brevo;
        _ when Other =:= <<>> -> resend;
        _ ->
          logger:warning(#{what => email_api_unknown_provider, provider => Other}),
          resend
      end
  end.

api_key() ->
  case application:get_env(eventhub, email_api_key) of
    {ok, K} when is_binary(K), K =/= <<>> -> K;
    {ok, K} when is_list(K), K =/= "" -> unicode:characters_to_binary(K);
    _ -> env_bin("EMAIL_API_KEY", <<>>)
  end.

%%%-------------------------------------------------------------------
%%% Shared
%%%-------------------------------------------------------------------

from_addr() ->
  env_bin("SMTP_FROM", <<"noreply@calentiq.com">>).

abs_url(PathPrefix, Token) ->
  Base = strip_slash(env_bin("PUBLIC_APP_URL", <<"https://stage.calentiq.com">>)),
  TokenB = to_bin(Token),
  <<Base/binary, PathPrefix/binary, TokenB/binary>>.

abs_path(Path0) ->
  Base = strip_slash(env_bin("PUBLIC_APP_URL", <<"https://stage.calentiq.com">>)),
  Path = case to_bin(Path0) of
    <<$/, Rest/binary>> -> <<$/, Rest/binary>>;
    Rest -> <<$/, Rest/binary>>
  end,
  <<Base/binary, Path/binary>>.

format_utc({{Y, Mo, D}, {H, Mi, _S}}) ->
  iolist_to_binary(io_lib:format("~4..0B-~2..0B-~2..0B ~2..0B:~2..0B",
                                 [Y, Mo, D, H, Mi])).

strip_slash(Url) ->
  case binary:last(Url) of
    $/ -> binary:part(Url, 0, byte_size(Url) - 1);
    _ -> Url
  end.

rfc822(From, To, Subject, Plain, Html) ->
  Bound = <<"eh-alt-01">>,
  iolist_to_binary([
    <<"From: CalenTIQ <">>, From, <<">\r\n">>,
    <<"To: ">>, To, <<"\r\n">>,
    <<"Subject: ">>, encode_subject(Subject), <<"\r\n">>,
    <<"MIME-Version: 1.0\r\n">>,
    <<"Content-Type: multipart/alternative; boundary=\"">>, Bound, <<"\"\r\n">>,
    <<"\r\n">>,
    <<"--">>, Bound, <<"\r\n">>,
    <<"Content-Type: text/plain; charset=utf-8\r\n">>,
    <<"Content-Transfer-Encoding: 8bit\r\n\r\n">>,
    Plain, <<"\r\n">>,
    <<"--">>, Bound, <<"\r\n">>,
    <<"Content-Type: text/html; charset=utf-8\r\n">>,
    <<"Content-Transfer-Encoding: 8bit\r\n\r\n">>,
    Html, <<"\r\n">>,
    <<"--">>, Bound, <<"--\r\n">>
  ]).

app_or_env(AppKey, EnvName) ->
  case application:get_env(eventhub, AppKey) of
    {ok, Val} when Val =/= undefined, Val =/= <<>>, Val =/= "" -> to_bin(Val);
    _ -> env_bin(EnvName, <<>>)
  end.

env_bin(Name, Default) ->
  case os:getenv(Name) of
    false -> Default;
    "" -> Default;
    S -> unicode:characters_to_binary(S)
  end.

env_int(Name, Default) ->
  case os:getenv(Name) of
    false -> Default;
    "" -> Default;
    S ->
      try list_to_integer(S) of
        N -> N
      catch
        _:_ -> Default
      end
  end.

to_bin(B) when is_binary(B) -> B;
to_bin(L) when is_list(L) -> unicode:characters_to_binary(L).

encode_subject(Bin) ->
  <<"=?UTF-8?B?", (base64:encode(Bin))/binary, "?=">>.