%%% Copyright (c) 2014, NORDUnet A/S.
%%% See LICENSE for licensing information.

-module(db).
-behaviour(gen_server).

%% API.
-export([start_link/0, stop/0]).
-export([add/4, add/2, add_entryhash/2, add_index/2, set_treesize/1, size/0]).
-export([get_by_index/1, get_by_indices/3, get_by_leaf_hash/1, get_by_entry_hash/1, entry_for_leafhash/1, leafhash_for_index/1]).
%% gen_server callbacks.
-export([init/1, handle_call/3, terminate/2, handle_cast/2, handle_info/2,
         code_change/3]).

-include_lib("stdlib/include/qlc.hrl").
-include("db.hrl").

size() ->
    binary_to_integer(atomic:readfile(treesize_path())).

init(_Args) ->
    {ok, []}.

start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

stop() ->
    gen_server:call(?MODULE, stop).

%%%%%%%%%%%%%%%%%%%%
%% Public API.

-spec add(binary(), binary(), binary(), non_neg_integer()) -> ok.
add(LeafHash, EntryHash, Data, Index) ->
    gen_server:call(?MODULE, {add, {LeafHash, EntryHash, Data, Index}}).

-spec add(binary(), binary()) -> ok.
add(LeafHash, Data) ->
    gen_server:call(?MODULE, {add, {LeafHash, Data}}).

-spec add_entryhash(binary(), binary()) -> ok.
add_entryhash(LeafHash, EntryHash) ->
    gen_server:call(?MODULE, {add_entryhash, {LeafHash, EntryHash}}).

-spec add_index(binary(), non_neg_integer()) -> ok.
add_index(LeafHash, Index) ->
    gen_server:call(?MODULE, {add_index, {LeafHash, Index}}).

-spec set_treesize(non_neg_integer()) -> ok.
set_treesize(Size) ->
    gen_server:call(?MODULE, {set_treesize, Size}).

-spec get_by_indices(integer(), integer(), {sorted, true|false}) ->
                            [{non_neg_integer(), binary(), binary()}].
get_by_indices(Start, End, {sorted, Sorted}) ->
    gen_server:call(?MODULE, {get_by_indices, {Start, End, Sorted}}).

-spec get_by_index(binary()) -> notfound |
                                {non_neg_integer(), binary(), binary()}.
get_by_index(Index) ->
    gen_server:call(?MODULE, {get_by_index, Index}).

-spec get_by_leaf_hash(binary()) -> notfound |
                                    {non_neg_integer(), binary(), binary()}.
get_by_leaf_hash(LeafHash) ->
    gen_server:call(?MODULE, {get_by_leaf_hash, LeafHash}).

-spec get_by_entry_hash(binary()) -> notfound |
                                     {non_neg_integer(), binary(), binary()}.
get_by_entry_hash(EntryHash) ->
    gen_server:call(?MODULE, {get_by_entry_hash, EntryHash}).

%%%%%%%%%%%%%%%%%%%%
%% gen_server callbacks.

handle_cast(_Request, State) ->
    {noreply, State}.

handle_info(_Info, State) ->
    {noreply, State}.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

terminate(_Reason, _State) ->
    io:format("~p terminating~n", [?MODULE]),
    ok.

%%%%%%%%%%%%%%%%%%%%
%% The meat.

% Table for Leaf hash -> Entry
entry_root_path() ->
    {ok, Value} = application:get_env(plop, entry_root_path),
    Value.

% Table for Leaf hash -> Entry
indexforhash_root_path() ->
    {ok, Value} = application:get_env(plop, indexforhash_root_path),
    Value.

% Table for Index -> Leaf hash
index_path() ->
    {ok, Value} = application:get_env(plop, index_path),
    Value.

% Table for Entry hash -> Leaf hash
entryhash_root_path() ->
    {ok, Value} = application:get_env(plop, entryhash_root_path),
    Value.

% File that stores tree size
treesize_path() ->
    {ok, Value} = application:get_env(plop, treesize_path),
    Value.


entry_for_leafhash(LeafHash) ->
    perm:readfile(entry_root_path(), LeafHash).

index_for_leafhash(LeafHash) ->
    case perm:readfile(indexforhash_root_path(), LeafHash) of
        noentry ->
            noentry;
        Index ->
            binary_to_integer(Index)
    end.

leafhash_for_index(Index) ->
    index:get(index_path(), Index).

leafhash_for_entryhash(EntryHash) ->
    perm:readfile(entryhash_root_path(), EntryHash).

get_by_indices_helper(Start, _End) when Start < 0 ->
    [];
get_by_indices_helper(Start, End) ->
    EndBound = min(End, size() - 1),
    case Start =< EndBound of
        true ->
            lists:map(fun (Index) ->
                              LeafHash = leafhash_for_index(Index),
                              Entry = entry_for_leafhash(LeafHash),
                              {Index, LeafHash, Entry}
                      end, lists:seq(Start, EndBound));
        false ->
            []
    end.

handle_call(stop, _From, State) ->
    {stop, normal, stopped, State};

handle_call({add, {LeafHash, EntryHash, Data, Index}}, _From, State) ->
    ok = perm:ensurefile(entry_root_path(), LeafHash, Data),
    ok = perm:ensurefile(entryhash_root_path(), EntryHash, LeafHash),
    ok = perm:ensurefile(indexforhash_root_path(),
                         LeafHash, integer_to_binary(Index)),
    ok = index:add(index_path(), Index, LeafHash),
    ok = atomic:replacefile(treesize_path(), integer_to_list(Index+1)),
    {reply, ok, State};

handle_call({add, {LeafHash, Data}}, _From, State) ->
    lager:debug("add leafhash ~p", [LeafHash]),
    ok = perm:ensurefile(entry_root_path(), LeafHash, Data),
    lager:debug("leafhash ~p added", [LeafHash]),
    {reply, ok, State};

handle_call({add_entryhash, {LeafHash, EntryHash}}, _From, State) ->
    ok = perm:ensurefile(entryhash_root_path(), EntryHash, LeafHash),
    {reply, ok, State};

handle_call({add_index, {LeafHash, Index}}, _From, State) ->
    ok = perm:ensurefile(indexforhash_root_path(),
                         LeafHash, integer_to_binary(Index)),
    ok = index:add(index_path(), Index, LeafHash),
    {reply, ok, State};

handle_call({set_treesize, Size}, _From, State) ->
    ok = atomic:replacefile(treesize_path(), integer_to_list(Size)),
    {reply, ok, State};

handle_call({get_by_indices, {Start, End, _Sorted}}, _From, State) ->
    {reply, get_by_indices_helper(Start, End), State};

handle_call({get_by_index, Index}, _From, State) ->
    LeafHash = leafhash_for_index(Index),
    Entry = entry_for_leafhash(LeafHash),
    R = {Index, LeafHash, Entry},
    {reply, R, State};

handle_call({get_by_leaf_hash, LeafHash}, _From, State) ->
    R = case entry_for_leafhash(LeafHash) of
            noentry ->
                notfound;
            Entry ->
                case index_for_leafhash(LeafHash) of
                    noentry ->
                        notfound;
                    Index ->
                        {Index, LeafHash, Entry}
                end
        end,
    {reply, R, State};

handle_call({get_by_entry_hash, EntryHash}, _From, State) ->
    R = case leafhash_for_entryhash(EntryHash) of
            noentry ->
                notfound;
            LeafHash ->
                Entry = entry_for_leafhash(LeafHash),
                %% Don't fetch index, isn't used and might not exist
                {notfetched, LeafHash, Entry}
        end,
    {reply, R, State}.