%% 创建元组
Point = {10, 20}.
Person = {person, "Alice", 25, "Beijing"}.

%% 元素访问（1-indexed）
element(1, Point).         %% 10
element(2, Point).         %% 20
element(3, Person).        %% 25

%% 替换元素（返回新元组）
NewPoint = setelement(1, Point, 100).  %% {100, 20}
Point.  %% 仍然是 {10, 20}

%% 元组大小
tuple_size(Point).         %% 2
tuple_size(Person).        %% 4

%% 转换为列表
tuple_to_list(Person).     %% [person, "Alice", 25, "Beijing"]

%% 从列表创建
list_to_tuple([1, 2, 3]).  %% {1, 2, 3}

%% 追加元素（O(n)）
erlang:append_element(Point, 30).  %% {10, 20, 30}

%% 基本解构
{X, Y} = {10, 20}.  %% X=10, Y=20

%% 标签元组模式（Erlang 传统风格）
{person, Name, Age, City} = Person.
%% Name="Alice", Age=25, City="Beijing"

%% 嵌套解构
{point, {X, Y}, {W, H}} = {point, {10, 20}, {100, 200}}.
%% X=10, Y=20, W=100, H=200

%% 通配符
{person, Name, _, _} = Person.
%% Name="Alice"

%% 用元组表示用户
User = {user, "Alice", 25, "alice@example.com"}.

%% 提取字段
{user, Name, Age, Email} = User.

%% 用元组表示结果
ok = {ok, Value}.           %% 成功结果
error = {error, Reason}.    %% 错误结果

%% 常见模式
case file:read_file("data.txt") of
    {ok, Data} -> process(Data);
    {error, Reason} -> io:format("Error: ~p~n", [Reason])
end.

%% 在头文件中定义 record
%% include/user.hrl
-record(user, {
    name = "",           %% 默认值
    age = 0,
    email = "",
    active = true
}).

%% 或在模块中定义
-module(my_module).
-record(person, {
    name,
    age,
    city = "unknown"
}).

%% 需要先包含头文件或在模块中定义
-include("user.hrl").

%% 使用默认值创建
U1 = #user{}.
%% {user, "", 0, "", true}

%% 指定字段创建
U2 = #user{name = "Alice", age = 25, email = "alice@example.com"}.
%% {user, "Alice", 25, "alice@example.com", true}

%% 指定部分字段（其他用默认值）
U3 = #user{name = "Bob"}.
%% {user, "Bob", 0, "", true}

%% 使用 #record.field 语法
Name = U2#user.name.       %% "Alice"
Age = U2#user.age.         %% 25

%% 模式匹配
#user{name = Name, age = Age} = U2.
%% Name="Alice", Age=25

%% 部分匹配
#user{name = Name} = U2.
%% Name="Alice"

%% 更新字段（创建新记录，原记录不变）
U4 = U2#user{age = 26, city = "Beijing"}.
%% {user, "Alice", 26, "alice@example.com", true}

%% U2 不变
U2#user.age.  %% 25

%% Record -> Map
record_to_map(#user{} = U) ->
    #{
        name => U#user.name,
        age => U#user.age,
        email => U#user.email,
        active => U#user.active
    }.

%% Map -> Record
map_to_record(#{name := N, age := A, email := E, active := Act}) ->
    #user{name = N, age = A, email = E, active = Act}.

%% Map 字面量（使用 => 操作符）
M1 = #{name => "Alice", age => 25}.
M2 = #{1 => "one", 2 => "two", 3 => "three"}.

%% 混合键类型
M3 = #{atom_key => 1, "string_key" => 2, 42 => 3}.

%% 空 Map
Empty = #{}.
map_size(Empty).  %% 0

%% 使用 maps 模块
M4 = maps:from_list([{name, "Alice"}, {age, 25}]).
%% #{name => "Alice", age => 25}

M = #{name => "Alice", age => 25, city => "Beijing"}.

%% 语法一：#{} 操作符（不存在会崩溃）
Val = M#{name}.     %% "Alice"
M#{height}.         %% 错误！key not found

%% 语法二：maps:get/2（不存在会崩溃）
maps:get(name, M).          %% "Alice"

%% 语法三：maps:get/3（带默认值）
maps:get(height, M, 0).     %% 0（不存在时返回默认值）

%% 语法四：maps:find/2（返回 {ok, Val} 或 error）
maps:find(name, M).         %% {ok, "Alice"}
maps:find(height, M).       %% error

%% 语法五：maps:is_key/2（检查是否存在）
maps:is_key(name, M).       %% true
maps:is_key(height, M).     %% false

M = #{name => "Alice", age => 25}.

%% 添加/更新字段（=> 用于 put 操作）
M2 = M#{city => "Beijing"}.
%% #{name => "Alice", age => 25, city => "Beijing"}

%% 更新已存在的字段（:= 用于 update 操作）
M3 = M#{age := 26}.
%% #{name => "Alice", age => 26}

%% ❌ 错误：用 := 更新不存在的字段
M#{height := 170}.  %% 错误！key not found

%% ✅ 正确：用 => 添加新字段
M#{height => 170}.

%% maps:put/3
M4 = maps:put(age, 26, M).

%% maps:remove/2
M5 = maps:remove(age, M).
%% #{name => "Alice"}

%% maps:merge/2
M6 = maps:merge(#{a => 1}, #{b => 2, a => 3}).
%% #{a => 3, b => 2}（第二个 map 优先）

M = #{name => "Alice", age => 25, city => "Beijing"}.

%% 部分匹配（只需要匹配你关心的 key）
#{name := Name} = M.                    %% Name = "Alice"
#{name := Name, age := Age} = M.        %% Name="Alice", Age=25

%% 函数参数中的 Map 匹配
greet(#{name := Name}) ->
    io:format("Hello, ~s!~n", [Name]).

handle_request(#{method := get, path := "/users"}) ->
    list_users();
handle_request(#{method := post, path := "/users", body := Body}) ->
    create_user(Body);
handle_request(#{method := _, path := Path}) ->
    {error, {not_found, Path}}.

%% 注意：=> 用于创建/put，:= 用于匹配/update
%% #{key => value}     创建 map 或添加字段
%% #{key := Value}     模式匹配或更新已有字段

M = #{a => 1, b => 2, c => 3}.

%% 方式一：maps:foreach/2（遍历，无返回值）
maps:foreach(fun(K, V) ->
    io:format("~p => ~p~n", [K, V])
end, M).

%% 方式二：maps:fold/3（折叠，有返回值）
Sum = maps:fold(fun(_K, V, Acc) -> V + Acc end, 0, M).
%% 6

%% 方式三：转列表后操作
[{K, V} || {K, V} := M].
%% [{a,1},{b,2},{c,3}]

%% 方式四：使用 maps:iterator（高效遍历大 Map）
Iter = maps:iterator(M),
遍历(Iter) ->
    case maps:next(Iter) of
        {K, V, NextIter} ->
            io:format("~p => ~p~n", [K, V]),
            遍历(NextIter);
        none ->
            done
    end.

%% user_manager.erl
-module(user_manager).
-export([new/0, add_user/4, get_user/2, update_user/3,
         remove_user/2, list_active/1, find_by_city/2]).

-type user() :: #{
    id := integer(),
    name := string(),
    age := integer(),
    city := string(),
    active := boolean()
}.
-type user_db() :: #{integer() => user()}.

-spec new() -> user_db().
new() -> #{}.

-spec add_user(integer(), string(), integer(), string()) -> fun((user_db()) -> user_db()).
add_user(Id, Name, Age, City) ->
    fun(Db) ->
        User = #{id => Id, name => Name, age => Age, city => City, active => true},
        Db#{Id => User}
    end.

-spec get_user(integer(), user_db()) -> {ok, user()} | {error, not_found}.
get_user(Id, Db) ->
    case maps:find(Id, Db) of
        {ok, User} -> {ok, User};
        error -> {error, not_found}
    end.

-spec update_user(integer(), map(), user_db()) -> user_db().
update_user(Id, Updates, Db) ->
    case maps:find(Id, Db) of
        {ok, User} ->
            UpdatedUser = maps:merge(User, Updates),
            Db#{Id => UpdatedUser};
        error ->
            Db
    end.

-spec remove_user(integer(), user_db()) -> user_db().
remove_user(Id, Db) ->
    maps:remove(Id, Db).

-spec list_active(user_db()) -> [user()].
list_active(Db) ->
    maps:fold(fun(_Id, #{active := true} = User, Acc) -> [User | Acc];
                 (_Id, _, Acc) -> Acc
              end, [], Db).

-spec find_by_city(string(), user_db()) -> [user()].
find_by_city(City, Db) ->
    [User || {_Id, #{city := C} = User} := Db, C =:= City].

$ erl
1> c(user_manager).
{ok, user_manager}
2> Db0 = user_manager:new().
#{}
3> Db1 = (user_manager:add_user(1, "Alice", 25, "Beijing"))(Db0).
4> Db2 = (user_manager:add_user(2, "Bob", 30, "Shanghai"))(Db1).
5> {ok, User} = user_manager:get_user(1, Db2).
{ok,#{active => true,age => 25,city => "Beijing",id => 1,name => "Alice"}}
6> user_manager:find_by_city("Beijing", Db2).
[#{active => true,age => 25,city => "Beijing",id => 1,name => "Alice"}]

%% config.erl
-module(config).
-export([load/1, get/2, get/3, set/3, to_list/1]).

-type config() :: #{atom() => term()}.

-spec load([{atom(), term()}]) -> config().
load(Defaults) ->
    maps:from_list(Defaults).

-spec get(atom(), config()) -> term().
get(Key, Config) ->
    maps:get(Key, Config).

-spec get(atom(), config(), term()) -> term().
get(Key, Config, Default) ->
    maps:get(Key, Config, Default).

-spec set(atom(), term(), config()) -> config().
set(Key, Value, Config) ->
    Config#{Key => Value}.

-spec to_list(config()) -> [{atom(), term()}].
to_list(Config) ->
    maps:to_list(Config).

%% 二进制模式匹配与元组结合
<<A:16/little, B:16/big>> = <<1, 0, 0, 2>>.
%% A = 1（小端序）, B = 2（大端序）

%% 解析结构化二进制数据
parse_record(<<Type:8, Length:16, Data:Length/binary, _CRC:32>>) ->
    #{type => Type, data => Data}.