EP Exercise 5-1: A Database Server

-module(db_server).
-export([start/0,stop/0,upgrade/1,code_upgrade/0]).
-export([write/2,read/1,delete/1]).
-export([init/0,loop/1]).
-vsn(1.0).

start() ->
    register(deb_server, spawn(db_server, init, [])).

stop() ->
    db_server ! stop.

upgrade(Data) ->
    db_server ! {upgrade, Data}.

write(Key, Data) ->
    db_server ! {write, Key, Data}.

read(Key) ->
    db_server ! {read, self(), Key},
    receive Reply ->
             Reply end.

delete(Key) ->
    db_server ! {delete, Key}.

code_upgrade(Data) ->
    db_server ! {code_upgrade, Data}.

init() ->
    loop(db:new()).

loop(Db) ->
    receive
        {write, Key, Data} ->
            loop(db:write(Key, Data, Db));
        {read, Pid, Key} ->
            Pid ! db:read(Key, Db),
            loop(Db);
        {delete, Key} ->
            loop(db:delete(Key, Db));
        {upgrade, Data} ->
            NewDb = db:convert(Data, Db),
            db_server:loop(NewDb);
        code_upgrade ->
            loop(db:code_upgrade(Data));
        stop ->
            db:destroy(Db)
    end.

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