% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
%   http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.

-module(couch_replicator_api_wrap).

% This module wraps the native erlang API, and allows for performing
% operations on a remote vs. local databases via the same API.
%
% Notes:
% Many options and apis aren't yet supported here, they are added as needed.

-include_lib("couch/include/couch_db.hrl").
-include_lib("couch_mrview/include/couch_mrview.hrl").
-include("couch_replicator_api_wrap.hrl").

-export([
    db_open/1,
    db_open/3,
    db_close/1,
    get_db_info/1,
    get_pending_count/2,
    get_view_info/3,
    update_doc/3,
    update_doc/4,
    update_docs/3,
    update_docs/4,
    ensure_full_commit/1,
    get_missing_revs/2,
    bulk_get/3,
    open_doc/3,
    open_doc_revs/6,
    changes_since/5,
    db_uri/1,
    normalize_db/1
]).

-import(couch_replicator_httpc, [
    send_req/3
]).

-import(couch_util, [
    encode_doc_id/1,
    get_value/2,
    get_value/3
]).

-define(MAX_WAIT, 5 * 60 * 1000).

-define(MAX_URL_LEN, 7000).
-define(MIN_URL_LEN, 200).

db_uri(#httpdb{url = Url}) ->
    couch_util:url_strip_password(Url).

db_open(Db) ->
    db_open(Db, false, []).

db_open(#httpdb{} = Db1, Create, CreateParams) ->
    {ok, Db} = couch_replicator_httpc:setup(Db1),
    try
        case Create of
            false ->
                ok;
            true ->
                Db2 = maybe_append_create_query_params(Db, CreateParams),
                send_req(
                    Db2,
                    [{method, put}],
                    fun
                        (401, _, _) ->
                            throw({unauthorized, ?l2b(db_uri(Db2))});
                        (403, _, _) ->
                            throw({forbidden, ?l2b(db_uri(Db2))});
                        (_, _, _) ->
                            ok
                    end
                )
        end,
        send_req(
            Db,
            [{method, get}],
            fun
                (200, _, {Props}) ->
                    UpdateSeq = get_value(<<"update_seq">>, Props),
                    InstanceStart = get_value(<<"instance_start_time">>, Props),
                    case {UpdateSeq, InstanceStart} of
                        {undefined, _} ->
                            throw({db_not_found, ?l2b(db_uri(Db))});
                        {_, undefined} ->
                            throw({db_not_found, ?l2b(db_uri(Db))});
                        _ ->
                            {ok, Db}
                    end;
                (200, _, _Body) ->
                    throw({db_not_found, ?l2b(db_uri(Db))});
                (401, _, _) ->
                    throw({unauthorized, ?l2b(db_uri(Db))});
                (403, _, _) ->
                    throw({forbidden, ?l2b(db_uri(Db))});
                (_, _, _) ->
                    throw({db_not_found, ?l2b(db_uri(Db))})
            end
        )
    catch
        throw:Error ->
            db_close(Db),
            throw(Error);
        error:Error ->
            db_close(Db),
            erlang:error(Error);
        exit:Error ->
            db_close(Db),
            erlang:exit(Error)
    end.

db_close(#httpdb{httpc_pool = Pool} = HttpDb) ->
    couch_replicator_auth:cleanup(HttpDb),
    unlink(Pool),
    ok = couch_replicator_httpc_pool:stop(Pool).

get_db_info(#httpdb{} = Db) ->
    send_req(
        Db,
        [],
        fun(200, _, {Props}) ->
            {ok, Props}
        end
    ).

get_pending_count(#httpdb{} = Db, Seq) when is_number(Seq) ->
    % Source looks like Apache CouchDB and not Cloudant so we fall
    % back to using update sequence differences.
    send_req(Db, [], fun(200, _, {Props}) ->
        case get_value(<<"update_seq">>, Props) of
            UpdateSeq when is_number(UpdateSeq) ->
                {ok, UpdateSeq - Seq};
            _ ->
                {ok, null}
        end
    end);
get_pending_count(#httpdb{} = Db, Seq) ->
    EncodedSeq = couch_replicator_utils:seq_encode(Seq),
    Options = [{path, "_changes"}, {qs, [{"since", EncodedSeq}, {"limit", "0"}]}],
    send_req(Db, Options, fun(200, _, {Props}) ->
        {ok, couch_util:get_value(<<"pending">>, Props, null)}
    end).

get_view_info(#httpdb{} = Db, DDocId, ViewName) ->
    Path = io_lib:format("~s/_view/~s/_info", [DDocId, ViewName]),
    send_req(
        Db,
        [{path, Path}],
        fun(200, _, {Props}) ->
            {VInfo} = couch_util:get_value(<<"view_index">>, Props, {[]}),
            {ok, VInfo}
        end
    ).

ensure_full_commit(#httpdb{} = Db) ->
    send_req(
        Db,
        [
            {method, post},
            {path, "_ensure_full_commit"},
            {headers, [{"Content-Type", "application/json"}]}
        ],
        fun
            (201, _, {Props}) ->
                {ok, get_value(<<"instance_start_time">>, Props)};
            (_, _, {Props}) ->
                {error, get_value(<<"error">>, Props)}
        end
    ).

get_missing_revs(#httpdb{} = Db, IdRevs) ->
    JsonBody = {[{Id, couch_doc:revs_to_strs(Revs)} || {Id, Revs} <- IdRevs]},
    send_req(
        Db,
        [
            {method, post},
            {path, "_revs_diff"},
            {body, ?JSON_ENCODE(JsonBody)},
            {headers, [{"Content-Type", "application/json"}]}
        ],
        fun
            (200, _, {Props}) ->
                ConvertToNativeFun = fun({Id, {Result}}) ->
                    MissingRevs = couch_doc:parse_revs(
                        get_value(<<"missing">>, Result)
                    ),
                    PossibleAncestors = couch_doc:parse_revs(
                        get_value(<<"possible_ancestors">>, Result, [])
                    ),
                    {Id, MissingRevs, PossibleAncestors}
                end,
                {ok, lists:map(ConvertToNativeFun, Props)};
            (ErrCode, _, ErrMsg) when is_integer(ErrCode) ->
                {error, {revs_diff_failed, ErrCode, ErrMsg}}
        end
    ).

bulk_get(#httpdb{} = Db, #{} = IdRevs, Options) ->
    FoldFun = fun({Id, Rev}, PAs, Acc) -> [{Id, Rev, PAs} | Acc] end,
    ReqDocsList = lists:sort(maps:fold(FoldFun, [], IdRevs)),
    MapFun = fun({Id, Rev, PAs}) ->
        #{
            <<"id">> => Id,
            <<"rev">> => couch_doc:rev_to_str(Rev),
            <<"atts_since">> => couch_doc:revs_to_strs(PAs)
        }
    end,
    ReqDocsMaps = lists:map(MapFun, ReqDocsList),
    % We are also sending request parameters in the doc body with the hopes
    % that at some point in the future we could make that the default, instead
    % of having to send query parameters with a POST request as we do today
    Body = options_to_json_map(Options, #{<<"docs">> => ReqDocsMaps}),
    Req = [
        {method, post},
        {path, "_bulk_get"},
        {qs, options_to_query_args(Options, [])},
        {body, ?JSON_ENCODE(Body)},
        {headers, [
            {"Content-Type", "application/json"},
            {"Accept", "application/json"}
        ]}
    ],
    try
        send_req(Db, Req, fun
            (200, _, {[{<<"results">>, Res}]}) when is_list(Res) ->
                Zip = lists:zipwith(fun bulk_get_zip/2, ReqDocsList, Res),
                {ok, maps:from_list(Zip)};
            (200, _, _) ->
                {error, {bulk_get_failed, invalid_results}};
            (ErrCode, _, _) when is_integer(ErrCode) ->
                % On older Apache CouchDB instances where _bulk_get is not
                % implemented we would hit the POST db/doc form uploader
                % handler. When that fails the request body is not consumed and
                % we'd end up recycling a worker with an unsent body in the
                % connection stream. Instead of waiting for it to blow up
                % eventually and consuming an extra retry attempt, proactively
                % advise httpc logic to stop this worker and not return back to
                % the pool.
                couch_replicator_httpc:stop_http_worker(),
                {error, {bulk_get_failed, ErrCode}}
        end)
    catch
        exit:{http_request_failed, _, _, {error, {code, ErrCode}}} ->
            % We are being a bit more tolerant of _bulk_get errors as we can
            % always fallback to individual fetches
            {error, {bulk_get_failed, ErrCode}}
    end.

bulk_get_zip({Id, Rev, _}, {[_ | _] = Props}) ->
    Docs = couch_util:get_value(<<"docs">>, Props),
    ResId = couch_util:get_value(<<"id">>, Props),
    % "docs" is a one item list, either [{"ok": Doc}] or [{"error": Error}]
    case Docs of
        [{[{<<"ok">>, {[_ | _]} = Doc}]}] when ResId =:= Id ->
            {{Id, Rev}, couch_doc:from_json_obj(Doc)};
        [{[{<<"error">>, {[_ | _] = Err}}]}] when ResId =:= Id ->
            Tag = couch_util:get_value(<<"error">>, Err),
            Reason = couch_util:get_value(<<"reason">>, Err),
            couch_log:debug("~p bulk_get zip error ~p:~p", [?MODULE, Tag, Reason]),
            {{Id, Rev}, {error, {Tag, Reason}}};
        Other ->
            couch_log:debug("~p bulk_get zip other error:~p", [?MODULE, Other]),
            {{Id, Rev}, {error, {unexpected_bulk_get_response, Other}}}
    end.

-spec open_doc_revs(#httpdb{}, binary(), list(), list(), function(), any()) -> no_return().
open_doc_revs(#httpdb{retries = 0} = HttpDb, Id, Revs, Options, _Fun, _Acc) ->
    Path = encode_doc_id(Id),
    QS = options_to_query_args(HttpDb, Path, [revs, {open_revs, Revs} | Options]),
    Url = couch_util:url_strip_password(
        couch_replicator_httpc:full_url(HttpDb, [{path, Path}, {qs, QS}])
    ),
    couch_log:error("Replication crashing because GET ~s failed", [Url]),
    exit(kaboom);
open_doc_revs(#httpdb{} = HttpDb, Id, Revs, Options, Fun, Acc) ->
    Path = encode_doc_id(Id),
    QS = options_to_query_args(HttpDb, Path, [revs, {open_revs, Revs} | Options]),
    {Pid, Ref} = spawn_monitor(fun() ->
        Self = self(),
        Callback = fun
            (200, Headers, StreamDataFun) ->
                remote_open_doc_revs_streamer_start(Self),
                {<<"--">>, _, _} = couch_httpd:parse_multipart_request(
                    header_value("Content-Type", Headers),
                    StreamDataFun,
                    fun mp_parse_mixed/1
                );
            (414, _, _) ->
                exit(request_uri_too_long)
        end,
        Streamer = spawn_link(fun() ->
            Params = [
                {path, Path},
                {qs, QS},
                {ibrowse_options, [{stream_to, {self(), once}}]},
                {headers, [{"Accept", "multipart/mixed"}]}
            ],
            % We're setting retries to 0 here to avoid the case where the
            % Streamer retries the request and ends up jumbling together two
            % different response bodies.  Retries are handled explicitly by
            % open_doc_revs itself.
            send_req(HttpDb#httpdb{retries = 0}, Params, Callback)
        end),
        % If this process dies normally we can leave
        % the Streamer process hanging around keeping an
        % HTTP connection open. This is a bit of a
        % hammer approach to making sure it releases
        % that connection back to the pool.
        spawn(fun() ->
            Ref = erlang:monitor(process, Self),
            receive
                {'DOWN', Ref, process, Self, normal} ->
                    exit(Streamer, {streamer_parent_died, Self});
                {'DOWN', Ref, process, Self, _} ->
                    ok
            end
        end),
        receive
            {started_open_doc_revs, Ref} ->
                Ret = receive_docs_loop(Streamer, Fun, Id, Revs, Ref, Acc),
                exit({exit_ok, Ret})
        end
    end),
    receive
        {'DOWN', Ref, process, Pid, {exit_ok, Ret}} ->
            Ret;
        {'DOWN', Ref, process, Pid, {{nocatch, missing_doc}, _}} ->
            throw(missing_doc);
        {'DOWN', Ref, process, Pid, {{nocatch, {missing_stub, _} = Stub}, _}} ->
            throw(Stub);
        {'DOWN', Ref, process, Pid, {http_request_failed, _, _, max_backoff}} ->
            exit(max_backoff);
        {'DOWN', Ref, process, Pid, request_uri_too_long} ->
            NewMaxLen = get_value(max_url_len, Options, ?MAX_URL_LEN) div 2,
            case NewMaxLen < ?MIN_URL_LEN of
                true ->
                    throw(request_uri_too_long);
                false ->
                    couch_log:info(
                        "Reducing url length to ~B because of"
                        " 414 response",
                        [NewMaxLen]
                    ),
                    Options1 = lists:keystore(
                        max_url_len,
                        1,
                        Options,
                        {max_url_len, NewMaxLen}
                    ),
                    open_doc_revs(HttpDb, Id, Revs, Options1, Fun, Acc)
            end;
        {'DOWN', Ref, process, Pid, Else} ->
            Url = couch_util:url_strip_password(
                couch_replicator_httpc:full_url(HttpDb, [{path, Path}, {qs, QS}])
            ),
            #httpdb{retries = Retries, wait = Wait0} = HttpDb,
            Wait = 2 * erlang:min(Wait0 * 2, ?MAX_WAIT),
            couch_log:notice(
                "Retrying GET to ~s in ~p seconds due to error ~w",
                [Url, Wait / 1000, error_reason(Else)]
            ),
            ok = timer:sleep(Wait),
            RetryDb = HttpDb#httpdb{
                retries = Retries - 1,
                wait = Wait
            },
            open_doc_revs(RetryDb, Id, Revs, Options, Fun, Acc)
    end.

error_reason({http_request_failed, "GET", _Url, {error, timeout}}) ->
    timeout;
error_reason({http_request_failed, "GET", _Url, {error, {_, req_timedout}}}) ->
    req_timedout;
error_reason({http_request_failed, "GET", _Url, Error}) ->
    Error;
error_reason(Else) ->
    Else.

open_doc(#httpdb{} = Db, Id, Options) ->
    send_req(
        Db,
        [{path, encode_doc_id(Id)}, {qs, options_to_query_args(Options, [])}],
        fun
            (200, _, Body) ->
                {ok, couch_doc:from_json_obj(Body)};
            (_, _, {Props}) ->
                {error, get_value(<<"error">>, Props)}
        end
    ).

update_doc(Db, Doc, Options) ->
    update_doc(Db, Doc, Options, ?INTERACTIVE_EDIT).

update_doc(#httpdb{} = HttpDb, #doc{id = DocId} = Doc, Options, Type) ->
    QArgs =
        case Type of
            ?REPLICATED_CHANGES ->
                [{"new_edits", "false"}];
            _ ->
                []
        end ++ options_to_query_args(Options, []),
    Boundary = couch_uuids:random(),
    JsonBytes = ?JSON_ENCODE(
        couch_doc:to_json_obj(
            Doc, [revs, attachments, follows, att_encoding_info | Options]
        )
    ),
    {ContentType, Len} = couch_doc:len_doc_to_multi_part_stream(
        Boundary,
        JsonBytes,
        Doc#doc.atts,
        true
    ),
    Headers =
        case lists:member(delay_commit, Options) of
            true ->
                [{"X-Couch-Full-Commit", "false"}];
            false ->
                []
        end ++ [{"Content-Type", ?b2l(ContentType)}, {"Content-Length", Len}],
    Body = {fun stream_doc/1, {JsonBytes, Doc#doc.atts, Boundary, Len}},
    send_req(
        % A crash here bubbles all the way back up to run_user_fun inside
        % open_doc_revs, which will retry the whole thing.  That's the
        % appropriate course of action, since we've already started streaming
        % the response body from the GET request.
        HttpDb#httpdb{retries = 0},
        [
            {method, put},
            {path, encode_doc_id(DocId)},
            {qs, QArgs},
            {headers, Headers},
            {body, Body}
        ],
        fun
            (Code, _, {Props}) when Code =:= 200 orelse Code =:= 201 orelse Code =:= 202 ->
                {ok, couch_doc:parse_rev(get_value(<<"rev">>, Props))};
            (409, _, _) ->
                throw(conflict);
            (Code, _, {Props}) ->
                case {Code, get_value(<<"error">>, Props)} of
                    {401, <<"unauthorized">>} ->
                        throw({unauthorized, get_value(<<"reason">>, Props)});
                    {403, <<"forbidden">>} ->
                        throw({forbidden, get_value(<<"reason">>, Props)});
                    {412, <<"missing_stub">>} ->
                        throw({missing_stub, get_value(<<"reason">>, Props)});
                    {413, _} ->
                        {error, request_body_too_large};
                    {_, Error} ->
                        {error, Error}
                end
        end
    ).

update_docs(Db, DocList, Options) ->
    update_docs(Db, DocList, Options, ?INTERACTIVE_EDIT).

update_docs(_Db, [], _Options, _UpdateType) ->
    {ok, []};
update_docs(#httpdb{} = HttpDb, DocList, Options, UpdateType) ->
    FullCommit = atom_to_list(not lists:member(delay_commit, Options)),
    Prefix =
        case UpdateType of
            ?REPLICATED_CHANGES ->
                <<"{\"new_edits\":false,\"docs\":[">>;
            ?INTERACTIVE_EDIT ->
                <<"{\"docs\":[">>
        end,
    Suffix = <<"]}">>,
    % Note: nginx and other servers don't like PUT/POST requests without
    % a Content-Length header, so we can't do a chunked transfer encoding
    % and JSON encode each doc only before sending it through the socket.
    {Docs, Len} = lists:mapfoldl(
        fun
            (#doc{} = Doc, Acc) ->
                Json = ?JSON_ENCODE(couch_doc:to_json_obj(Doc, [revs, attachments])),
                {Json, Acc + iolist_size(Json)};
            (Doc, Acc) ->
                {Doc, Acc + iolist_size(Doc)}
        end,
        byte_size(Prefix) + byte_size(Suffix) + length(DocList) - 1,
        DocList
    ),
    BodyFun = fun
        (eof) ->
            eof;
        ([]) ->
            {ok, Suffix, eof};
        ([prefix | Rest]) ->
            {ok, Prefix, Rest};
        ([Doc]) ->
            {ok, Doc, []};
        ([Doc | RestDocs]) ->
            {ok, [Doc, ","], RestDocs}
    end,
    Headers = [
        {"Content-Length", Len},
        {"Content-Type", "application/json"},
        {"X-Couch-Full-Commit", FullCommit}
    ],
    send_req(
        HttpDb,
        [
            {method, post},
            {path, "_bulk_docs"},
            {body, {BodyFun, [prefix | Docs]}},
            {headers, Headers}
        ],
        fun
            (201, _, Results) when is_list(Results) ->
                {ok, bulk_results_to_errors(Results)};
            (413, _, _) ->
                {error, request_body_too_large};
            (417, _, Results) when is_list(Results) ->
                {ok, bulk_results_to_errors(Results)};
            (ErrCode, _, ErrMsg) when is_integer(ErrCode) ->
                {error, {bulk_docs_failed, ErrCode, ErrMsg}}
        end
    ).

changes_since(
    #httpdb{headers = Headers1, timeout = InactiveTimeout} = HttpDb,
    Style,
    StartSeq,
    UserFun,
    Options
) ->
    Timeout = erlang:max(1000, InactiveTimeout div 3),
    EncodedSeq = couch_replicator_utils:seq_encode(StartSeq),
    BaseQArgs =
        case get_value(continuous, Options, false) of
            false ->
                [{"feed", "normal"}];
            true ->
                [{"feed", "continuous"}]
        end ++
            [
                {"style", atom_to_list(Style)},
                {"since", EncodedSeq},
                {"timeout", integer_to_list(Timeout)}
            ],
    DocIds = get_value(doc_ids, Options),
    Selector = get_value(selector, Options),
    {QArgs, Method, Body, Headers} =
        case {DocIds, Selector} of
            {undefined, undefined} ->
                QArgs1 = maybe_add_changes_filter_q_args(BaseQArgs, Options),
                {QArgs1, get, [], Headers1};
            {undefined, _} when is_tuple(Selector) ->
                Headers2 = [{"Content-Type", "application/json"} | Headers1],
                JsonSelector = ?JSON_ENCODE({[{<<"selector">>, Selector}]}),
                {[{"filter", "_selector"} | BaseQArgs], post, JsonSelector, Headers2};
            {_, undefined} when is_list(DocIds) ->
                Headers2 = [{"Content-Type", "application/json"} | Headers1],
                JsonDocIds = ?JSON_ENCODE({[{<<"doc_ids">>, DocIds}]}),
                {[{"filter", "_doc_ids"} | BaseQArgs], post, JsonDocIds, Headers2}
        end,
    try
        send_req(
            HttpDb,
            [
                {method, Method},
                {path, "_changes"},
                {qs, QArgs},
                {headers, Headers},
                {body, Body},
                {ibrowse_options, [{stream_to, {self(), once}}]}
            ],
            fun
                (200, _, DataStreamFun) ->
                    parse_changes_feed(Options, UserFun, DataStreamFun);
                (405, _, _) when is_list(DocIds) ->
                    % CouchDB versions < 1.1.0 don't have the builtin
                    % _changes feed filter "_doc_ids" neither support POST
                    send_req(
                        HttpDb,
                        [
                            {method, get},
                            {path, "_changes"},
                            {qs, BaseQArgs},
                            {headers, Headers1},
                            {ibrowse_options, [{stream_to, {self(), once}}]}
                        ],
                        fun(200, _, DataStreamFun2) ->
                            UserFun2 = fun
                                (#doc_info{id = Id} = DocInfo) ->
                                    case lists:member(Id, DocIds) of
                                        true ->
                                            UserFun(DocInfo);
                                        false ->
                                            ok
                                    end;
                                (LastSeq) ->
                                    UserFun(LastSeq)
                            end,
                            parse_changes_feed(
                                Options,
                                UserFun2,
                                DataStreamFun2
                            )
                        end
                    );
                (ErrCode, _, ErrMsg) when is_integer(ErrCode) ->
                    throw({retry_limit, {changes_req_failed, ErrCode, ErrMsg}})
            end
        )
    catch
        exit:{http_request_failed, _, _, max_backoff} ->
            exit(max_backoff);
        exit:{http_request_failed, _, _, {error, {connection_closed, mid_stream}}} ->
            throw(retry_no_limit);
        exit:{http_request_failed, _, _, _} = Error ->
            throw({retry_limit, Error})
    end.

% internal functions

maybe_add_changes_filter_q_args(BaseQS, Options) ->
    case get_value(filter, Options) of
        undefined ->
            BaseQS;
        FilterName ->
            %% get list of view attributes
            ViewFields0 = [atom_to_list(F) || F <- record_info(fields, mrargs)],
            ViewFields = ["key" | ViewFields0],

            {Params} = get_value(query_params, Options, {[]}),
            [
                {"filter", ?b2l(FilterName)}
                | lists:foldl(
                    fun({K, V}, QSAcc) ->
                        Ks = couch_util:to_list(K),
                        case lists:keymember(Ks, 1, QSAcc) of
                            true ->
                                QSAcc;
                            false when FilterName =:= <<"_view">> ->
                                V1 =
                                    case lists:member(Ks, ViewFields) of
                                        true -> ?JSON_ENCODE(V);
                                        false -> couch_util:to_list(V)
                                    end,
                                [{Ks, V1} | QSAcc];
                            false ->
                                [{Ks, couch_util:to_list(V)} | QSAcc]
                        end
                    end,
                    BaseQS,
                    Params
                )
            ]
    end.

parse_changes_feed(Options, UserFun, DataStreamFun) ->
    case get_value(continuous, Options, false) of
        true ->
            continuous_changes(DataStreamFun, UserFun);
        false ->
            EventFun = fun(Ev) ->
                changes_ev1(Ev, fun(DocInfo, _) -> UserFun(DocInfo) end, [])
            end,
            json_stream_parse:events(DataStreamFun, EventFun)
    end.

options_to_query_args(HttpDb, Path, Options0) ->
    case lists:keytake(max_url_len, 1, Options0) of
        false ->
            MaxLen = ?MAX_URL_LEN,
            Options = Options0;
        {value, {max_url_len, MaxLen}, Options} ->
            ok
    end,
    case lists:keytake(atts_since, 1, Options) of
        false ->
            options_to_query_args(Options, []);
        {value, {atts_since, []}, Options2} ->
            options_to_query_args(Options2, []);
        {value, {atts_since, PAs}, Options2} ->
            QueryArgs1 = options_to_query_args(Options2, []),
            FullUrl = couch_replicator_httpc:full_url(
                HttpDb, [{path, Path}, {qs, QueryArgs1}]
            ),
            RevList = atts_since_arg(
                length("GET " ++ FullUrl ++ " HTTP/1.1\r\n") +
                    % +6 = % encoded [ and ]
                    length("&atts_since=") + 6,
                PAs,
                MaxLen,
                []
            ),
            [{"atts_since", ?b2l(iolist_to_binary(?JSON_ENCODE(RevList)))} | QueryArgs1]
    end.

options_to_query_args([], Acc) ->
    lists:reverse(Acc);
options_to_query_args([ejson_body | Rest], Acc) ->
    options_to_query_args(Rest, Acc);
options_to_query_args([delay_commit | Rest], Acc) ->
    options_to_query_args(Rest, Acc);
options_to_query_args([revs | Rest], Acc) ->
    options_to_query_args(Rest, [{"revs", "true"} | Acc]);
options_to_query_args([{open_revs, all} | Rest], Acc) ->
    options_to_query_args(Rest, [{"open_revs", "all"} | Acc]);
options_to_query_args([latest | Rest], Acc) ->
    options_to_query_args(Rest, [{"latest", "true"} | Acc]);
options_to_query_args([{open_revs, Revs} | Rest], Acc) ->
    JsonRevs = ?b2l(iolist_to_binary(?JSON_ENCODE(couch_doc:revs_to_strs(Revs)))),
    options_to_query_args(Rest, [{"open_revs", JsonRevs} | Acc]);
options_to_query_args([{attachments, Bool} | Rest], Acc) when is_atom(Bool) ->
    BoolStr = atom_to_list(Bool),
    options_to_query_args(Rest, [{"attachments", BoolStr} | Acc]).

options_to_json_map([], #{} = Acc) ->
    Acc;
options_to_json_map([latest | Rest], #{} = Acc) ->
    options_to_json_map(Rest, Acc#{<<"latest">> => true});
options_to_json_map([revs | Rest], #{} = Acc) ->
    options_to_json_map(Rest, Acc#{<<"revs">> => true});
options_to_json_map([{attachments, Bool} | Rest], #{} = Acc) when is_atom(Bool) ->
    options_to_json_map(Rest, Acc#{<<"attachments">> => Bool}).

atts_since_arg(_UrlLen, [], _MaxLen, Acc) ->
    lists:reverse(Acc);
atts_since_arg(UrlLen, [PA | Rest], MaxLen, Acc) ->
    RevStr = couch_doc:rev_to_str(PA),
    NewUrlLen =
        case Rest of
            [] ->
                % plus 2 double quotes (% encoded)
                UrlLen + size(RevStr) + 6;
            _ ->
                % plus 2 double quotes and a comma (% encoded)
                UrlLen + size(RevStr) + 9
        end,
    case NewUrlLen >= MaxLen of
        true ->
            lists:reverse(Acc);
        false ->
            atts_since_arg(NewUrlLen, Rest, MaxLen, [RevStr | Acc])
    end.

% TODO: A less verbose, more elegant and automatic restart strategy for
%       the exported open_doc_revs/6 function. The restart should be
%       transparent to the caller like any other Couch API function exported
%       by this module.
receive_docs_loop(Streamer, Fun, Id, Revs, Ref, Acc) ->
    try
        % Left only for debugging purposes via an interactive or remote shell
        erlang:put(open_doc_revs, {Id, Revs, Ref, Streamer}),
        receive_docs(Streamer, Fun, Ref, Acc)
    catch
        error:{restart_open_doc_revs, NewRef} ->
            receive_docs_loop(Streamer, Fun, Id, Revs, NewRef, Acc)
    end.

receive_docs(Streamer, UserFun, Ref, UserAcc) ->
    Streamer ! {get_headers, Ref, self()},
    receive
        {started_open_doc_revs, NewRef} ->
            restart_remote_open_doc_revs(Ref, NewRef);
        {headers, Ref, Headers} ->
            case header_value("content-type", Headers) of
                {"multipart/related", _} = ContentType ->
                    % Skip document body and attachment size limits validation here
                    % since these should be validated by the replication target
                    case
                        couch_doc:doc_from_multi_part_stream(
                            ContentType,
                            fun() -> receive_doc_data(Streamer, Ref) end,
                            Ref,
                            _ValidateDocLimits = false
                        )
                    of
                        {ok, Doc, WaitFun, Parser} ->
                            case run_user_fun(UserFun, {ok, Doc}, UserAcc, Ref) of
                                {ok, UserAcc2} ->
                                    ok;
                                {skip, UserAcc2} ->
                                    couch_httpd_multipart:abort_multipart_stream(Parser)
                            end,
                            WaitFun(),
                            receive_docs(Streamer, UserFun, Ref, UserAcc2)
                    end;
                {"application/json", []} ->
                    Doc = couch_doc:from_json_obj(
                        ?JSON_DECODE(receive_all(Streamer, Ref, []))
                    ),
                    {_, UserAcc2} = run_user_fun(UserFun, {ok, Doc}, UserAcc, Ref),
                    receive_docs(Streamer, UserFun, Ref, UserAcc2);
                {"application/json", [{"error", "true"}]} ->
                    {ErrorProps} = ?JSON_DECODE(receive_all(Streamer, Ref, [])),
                    Rev = get_value(<<"missing">>, ErrorProps),
                    Result = {{not_found, missing}, couch_doc:parse_rev(Rev)},
                    {_, UserAcc2} = run_user_fun(UserFun, Result, UserAcc, Ref),
                    receive_docs(Streamer, UserFun, Ref, UserAcc2)
            end;
        {done, Ref} ->
            {ok, UserAcc}
    end.

run_user_fun(UserFun, Arg, UserAcc, OldRef) ->
    {Pid, Ref} = spawn_monitor(fun() ->
        try UserFun(Arg, UserAcc) of
            Resp ->
                exit({exit_ok, Resp})
        catch
            throw:Reason ->
                exit({exit_throw, Reason});
            error:Reason ->
                exit({exit_error, Reason});
            exit:Reason ->
                exit({exit_exit, Reason})
        end
    end),
    receive
        {started_open_doc_revs, NewRef} ->
            erlang:demonitor(Ref, [flush]),
            exit(Pid, kill),
            restart_remote_open_doc_revs(OldRef, NewRef);
        {'DOWN', Ref, process, Pid, {exit_ok, Ret}} ->
            Ret;
        {'DOWN', Ref, process, Pid, {exit_throw, Reason}} ->
            throw(Reason);
        {'DOWN', Ref, process, Pid, {exit_error, Reason}} ->
            erlang:error(Reason);
        {'DOWN', Ref, process, Pid, {exit_exit, Reason}} ->
            erlang:exit(Reason)
    end.

restart_remote_open_doc_revs(Ref, NewRef) ->
    receive
        {body_bytes, Ref, _} ->
            restart_remote_open_doc_revs(Ref, NewRef);
        {body_done, Ref} ->
            restart_remote_open_doc_revs(Ref, NewRef);
        {done, Ref} ->
            restart_remote_open_doc_revs(Ref, NewRef);
        {headers, Ref, _} ->
            restart_remote_open_doc_revs(Ref, NewRef)
    after 0 ->
        erlang:error({restart_open_doc_revs, NewRef})
    end.

remote_open_doc_revs_streamer_start(Parent) ->
    receive
        {get_headers, _Ref, Parent} ->
            remote_open_doc_revs_streamer_start(Parent);
        {next_bytes, _Ref, Parent} ->
            remote_open_doc_revs_streamer_start(Parent)
    after 0 ->
        Parent ! {started_open_doc_revs, make_ref()}
    end.

receive_all(Streamer, Ref, Acc) ->
    Streamer ! {next_bytes, Ref, self()},
    receive
        {started_open_doc_revs, NewRef} ->
            restart_remote_open_doc_revs(Ref, NewRef);
        {body_bytes, Ref, Bytes} ->
            receive_all(Streamer, Ref, [Bytes | Acc]);
        {body_done, Ref} ->
            lists:reverse(Acc)
    end.

mp_parse_mixed(eof) ->
    receive
        {get_headers, Ref, From} ->
            From ! {done, Ref}
    end;
mp_parse_mixed({headers, H}) ->
    receive
        {get_headers, Ref, From} ->
            From ! {headers, Ref, H}
    end,
    fun mp_parse_mixed/1;
mp_parse_mixed({body, Bytes}) ->
    receive
        {next_bytes, Ref, From} ->
            From ! {body_bytes, Ref, Bytes}
    end,
    fun mp_parse_mixed/1;
mp_parse_mixed(body_end) ->
    receive
        {next_bytes, Ref, From} ->
            From ! {body_done, Ref};
        {get_headers, Ref, From} ->
            self() ! {get_headers, Ref, From}
    end,
    fun mp_parse_mixed/1.

receive_doc_data(Streamer, Ref) ->
    Streamer ! {next_bytes, Ref, self()},
    receive
        {body_bytes, Ref, Bytes} ->
            {Bytes, fun() -> receive_doc_data(Streamer, Ref) end};
        {body_done, Ref} ->
            {<<>>, fun() -> receive_doc_data(Streamer, Ref) end}
    end.

changes_ev1(object_start, UserFun, UserAcc) ->
    fun(Ev) -> changes_ev2(Ev, UserFun, UserAcc) end.

changes_ev2({key, <<"results">>}, UserFun, UserAcc) ->
    fun(Ev) -> changes_ev3(Ev, UserFun, UserAcc) end;
changes_ev2(_, UserFun, UserAcc) ->
    fun(Ev) -> changes_ev2(Ev, UserFun, UserAcc) end.

changes_ev3(array_start, UserFun, UserAcc) ->
    fun(Ev) -> changes_ev_loop(Ev, UserFun, UserAcc) end.

changes_ev_loop(object_start, UserFun, UserAcc) ->
    fun(Ev) ->
        json_stream_parse:collect_object(
            Ev,
            fun(Obj) ->
                UserAcc2 = UserFun(json_to_doc_info(Obj), UserAcc),
                fun(Ev2) -> changes_ev_loop(Ev2, UserFun, UserAcc2) end
            end
        )
    end;
changes_ev_loop(array_end, _UserFun, _UserAcc) ->
    fun(_Ev) -> changes_ev_done() end.

changes_ev_done() ->
    fun(_Ev) -> changes_ev_done() end.

continuous_changes(DataFun, UserFun) ->
    {DataFun2, _, Rest} = json_stream_parse:events(
        DataFun,
        fun(Ev) -> parse_changes_line(Ev, UserFun) end
    ),
    continuous_changes(fun() -> {Rest, DataFun2} end, UserFun).

parse_changes_line(object_start, UserFun) ->
    fun(Ev) ->
        json_stream_parse:collect_object(
            Ev,
            fun(Obj) -> UserFun(json_to_doc_info(Obj)) end
        )
    end.

json_to_doc_info({Props}) ->
    case get_value(<<"changes">>, Props) of
        undefined ->
            {last_seq, get_value(<<"last_seq">>, Props)};
        Changes ->
            RevsInfo0 = lists:map(
                fun({Change}) ->
                    Rev = couch_doc:parse_rev(get_value(<<"rev">>, Change)),
                    Del = couch_replicator_utils:is_deleted(Change),
                    #rev_info{rev = Rev, deleted = Del}
                end,
                Changes
            ),

            RevsInfo =
                case get_value(<<"removed">>, Props) of
                    true ->
                        [_ | RevsInfo1] = RevsInfo0,
                        RevsInfo1;
                    _ ->
                        RevsInfo0
                end,

            #doc_info{
                id = get_value(<<"id">>, Props),
                high_seq = get_value(<<"seq">>, Props),
                revs = RevsInfo
            }
    end.

bulk_results_to_errors(Results) ->
    lists:reverse(
        lists:foldl(
            fun({Props}, Acc) ->
                case get_value(<<"error">>, Props, get_value(error, Props)) of
                    undefined ->
                        Acc;
                    Error ->
                        Id = get_value(<<"id">>, Props, get_value(id, Props)),
                        Rev = get_value(<<"rev">>, Props, get_value(rev, Props)),
                        Reason = get_value(<<"reason">>, Props, get_value(reason, Props)),
                        [
                            {[
                                {id, Id},
                                {rev, rev_to_str(Rev)},
                                {error, Error},
                                {reason, Reason}
                            ]}
                            | Acc
                        ]
                end
            end,
            [],
            Results
        )
    ).

rev_to_str({_Pos, _Id} = Rev) ->
    couch_doc:rev_to_str(Rev);
rev_to_str(Rev) ->
    Rev.

write_fun() ->
    fun(Data) ->
        receive
            {get_data, Ref, From} ->
                From ! {data, Ref, Data}
        end
    end.

stream_doc({JsonBytes, Atts, Boundary, Len}) ->
    case erlang:erase({doc_streamer, Boundary}) of
        Pid when is_pid(Pid) ->
            unlink(Pid),
            exit(Pid, kill);
        _ ->
            ok
    end,
    DocStreamer = spawn_link(
        couch_doc,
        doc_to_multi_part_stream,
        [Boundary, JsonBytes, Atts, write_fun(), true]
    ),
    erlang:put({doc_streamer, Boundary}, DocStreamer),
    {ok, <<>>, {Len, Boundary}};
stream_doc({0, Id}) ->
    erlang:erase({doc_streamer, Id}),
    eof;
stream_doc({LenLeft, Id}) when LenLeft > 0 ->
    Ref = make_ref(),
    erlang:get({doc_streamer, Id}) ! {get_data, Ref, self()},
    receive
        {data, Ref, Data} ->
            {ok, Data, {LenLeft - iolist_size(Data), Id}}
    end.

header_value(Key, Headers) ->
    header_value(Key, Headers, undefined).

header_value(Key, Headers, Default) ->
    Headers1 = [{string:to_lower(K), V} || {K, V} <- Headers],
    case lists:keyfind(string:to_lower(Key), 1, Headers1) of
        {_, Value} ->
            Value;
        _ ->
            Default
    end.

% Normalize an #httpdb{} or #db{} record such that it can be used for
% comparisons. This means remove things like pids and also sort options / props.
normalize_db(#httpdb{} = HttpDb) ->
    #httpdb{
        url = HttpDb#httpdb.url,
        auth_props = lists:sort(HttpDb#httpdb.auth_props),
        headers = lists:keysort(1, HttpDb#httpdb.headers),
        timeout = HttpDb#httpdb.timeout,
        ibrowse_options = lists:keysort(1, HttpDb#httpdb.ibrowse_options),
        retries = HttpDb#httpdb.retries,
        http_connections = HttpDb#httpdb.http_connections
    };
normalize_db(<<DbName/binary>>) ->
    DbName.

maybe_append_create_query_params(Db, []) ->
    Db;
maybe_append_create_query_params(Db, CreateParams) ->
    NewUrl = Db#httpdb.url ++ "?" ++ mochiweb_util:urlencode(CreateParams),
    Db#httpdb{url = NewUrl}.

-ifdef(TEST).

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

normalize_http_db_test() ->
    HttpDb = #httpdb{
        url = "http://host/db",
        auth_props = [{"key", "val"}],
        headers = [{"k2", "v2"}, {"k1", "v1"}],
        timeout = 30000,
        ibrowse_options = [{k2, v2}, {k1, v1}],
        retries = 10,
        http_connections = 20
    },
    Expected = HttpDb#httpdb{
        headers = [{"k1", "v1"}, {"k2", "v2"}],
        ibrowse_options = [{k1, v1}, {k2, v2}]
    },
    ?assertEqual(Expected, normalize_db(HttpDb)),
    ?assertEqual(<<"local">>, normalize_db(<<"local">>)).

-endif.