%% ===== 属性声明（文件头）=====
-module(my_module).
-author("Developer").
-vsn("1.0.0").

%% ===== 编译选项 =====
-compile(export_all).  %% 仅在开发时使用

%% ===== 行为声明 =====
-behaviour(gen_server).

%% ===== 头文件包含 =====
-include_lib("eunit/include/eunit.hrl").

%% ===== 宏定义 =====
-define(TIMEOUT, 5000).
-define(LOG(Level, Msg), logger:log(Level, Msg)).

%% ===== 类型定义 =====
-type user() :: #{name := string(), age := integer()}.
-export_type([user/0]).

%% ===== 导出声明 =====
%% API
-export([start_link/0, get_user/1]).

%% Behaviour callbacks
-export([init/1, handle_call/3, handle_cast/2]).

%% ===== 记录定义 =====
-record(state, {
    users = #{} :: #{integer() => user()},
    last_id = 0 :: non_neg_integer()
}).

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

%% ===== Callback 实现 =====
init([]) ->
    {ok, #state{}}.

%% ===== 内部函数 =====

%% 4 空格缩进（不是 Tab）
my_function(Arg1, Arg2) ->
    case Arg1 of
        pattern1 ->
            do_something(Arg2);
        pattern2 ->
            do_another_thing(Arg2)
    end.

%% 长函数调用换行
some_long_function(
    VeryLongArgument1,
    VeryLongArgument2,
    VeryLongArgument3
).

%% 条件表达式
if
    Condition1 -> Result1;
    Condition2 -> Result2;
    true -> DefaultResult
end.

%% 列表推导
Result = [
    transform(Item)
    || Item <- List,
       is_valid(Item)
].

%% ✅ 好的 API：简洁明确
-module(user_service).
-export([create/1, get/1, update/2, delete/1]).

-spec create(#{name := string(), age := integer()}) -> {ok, user()} | {error, term()}.
create(#{name := _, age := _} = Params) ->
    gen_server:call(?MODULE, {create, Params}).

-spec get(integer()) -> {ok, user()} | {error, not_found}.
get(Id) ->
    gen_server:call(?MODULE, {get, Id}).

%% ❌ 不好的 API：模糊、职责不清
-export([do_stuff/2, handle/3, process/4]).

%% 使用 OTP 21+ 的 logger 模块
-include_lib("kernel/include/logger.hrl").

%% 不同级别的日志
?LOG_DEBUG("Debug message: ~p", [Data]).
?LOG_INFO("User ~p logged in", [UserId]).
?LOG_WARNING("High memory usage: ~p%", [Usage]).
?LOG_ERROR("Database connection failed: ~p", [Reason]).

%% logger 配置
%% config/sys.config
[
    {kernel, [
        {logger, [
            {handler, default, logger_std_h, 
             #{level => info,
               config => #{file => "log/app.log"}}},
            {handler, error_log, logger_std_h,
             #{level => error,
               config => #{file => "log/error.log"}}}
        ]}
    ]}
].

%% ✅ 好的错误处理：明确的错误类型
-spec divide(number(), number()) -> {ok, float()} | {error, division_by_zero}.
divide(_, 0) -> {error, division_by_zero};
divide(A, B) -> {ok, A / B}.

%% ✅ 使用 try/catch 处理外部调用
safe_file_read(Path) ->
    try file:read_file(Path) of
        {ok, Data} -> {ok, Data};
        {error, Reason} -> {error, {file_error, Reason}}
    catch
        C:E -> {error, {exception, C, E}}
    end.

%% ❌ 不要忽略错误
{ok, Data} = file:read_file("config.txt").  %% 失败时崩溃

%% 集中配置模块
-module(app_config).
-export([get/1, get/2]).

get(Key) ->
    application:get_env(my_app, Key).

get(Key, Default) ->
    application:get_env(my_app, Key, Default).

%% 使用
Port = app_config:get(http_port, 8080).

%% 进程监控
%% 1. 使用 Observer
observer:start().

%% 2. 进程内存监控
-spec check_process_memory() -> [{pid(), integer()}].
check_process_memory() ->
    Procs = [{P, process_info(P, memory)} || P <- erlang:processes()],
    [{P, M} || {P, {_, M}} <- Procs, M > 100000000].  %% > 100MB

%% 3. 消息队列监控
-spec check_mailboxes() -> [{pid(), integer()}].
check_mailboxes() ->
    Procs = [{P, process_info(P, message_queue_len)} || P <- erlang:processes()],
    [{P, L} || {P, {_, L}} <- Procs, L > 1000].

%% 4. 定期检查
start_monitor() ->
    spawn_link(fun() -> monitor_loop() end).

monitor_loop() ->
    timer:sleep(60000),  %% 每分钟
    case check_mailboxes() of
        [] -> ok;
        Blocked ->
            logger:warning("Processes with high mailbox: ~p", [Blocked])
    end,
    monitor_loop().

## 项目初始化模板
rebar3 new release my_project

## 添加常用依赖
## rebar.config
{deps, [
    {cowboy, "2.12.0"},     %% HTTP
    {jsx, "3.1.0"},         %% JSON
    {gun, "2.1.0"},         %% HTTP 客户端
    {jiffy, "1.1.1"},       %% JSON (NIF)
    {poolboy, "1.5.2"},     %% 连接池
    {meck, "0.9.2"},        %% Mock (test)
    {proper, "1.4.0"}       %% Property test (test)
]}.

## 常用命令
rebar3 compile          %% 编译
rebar3 eunit            %% 单元测试
rebar3 ct               %% 集成测试
rebar3 dialyzer         %% 类型检查
rebar3 as prod release  %% 生产构建
rebar3 shell            %% 开发 Shell