glimit

-module(glimit).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch, inline]).
-define(FILEPATH, "src/glimit.gleam").
-export([new/0, per_second/2, per_second_fn/2, burst_limit/2, burst_limit_fn/2, on_limit_exceeded/2, identifier/2, build/1, apply_built/2, apply/2, apply2/2, apply3/2, apply4/2]).
-export_type([rate_limiter/3, rate_limiter_builder/3]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

?MODULEDOC(
    " This module provides a rate limiter that can be used to limit the number of\n"
    " requests or function calls per second for a given identifier.\n"
    "\n"
    " A single rate limiter actor stores all token bucket state. Each hit is a single\n"
    " message to the rate limiter, which performs the Token Bucket calculation inline.\n"
    " A periodic sweep removes idle (full) buckets to reduce memory usage. The\n"
    " rate limiter fails open — if the rate limiter actor is unavailable, requests are\n"
    " allowed through.\n"
    "\n"
    " The rate limits are configured using the following two options:\n"
    "\n"
    " - `per_second`: The rate of new available tokens per second. Think of this\n"
    "   as the steady state rate limit.\n"
    " - `burst_limit`: The maximum number of available tokens. Think of this as\n"
    "   the burst rate limit. The default value is the `per_second` rate limit.\n"
    "\n"
    " The rate limiter can be applied to a function or handler using the `apply`\n"
    " function, which returns a new function that checks the rate limit before\n"
    " calling the original function.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.burst_limit(100)\n"
    "   |> glimit.identifier(fn(request) { request.ip })\n"
    "   |> glimit.on_limit_exceeded(fn(_request) { \"Rate limit reached\" })\n"
    "\n"
    " let handler =\n"
    "   fn(_request) { \"Hello, world!\" }\n"
    "   |> glimit.apply(limiter)\n"
    " ```\n"
    "\n"
    " # Multi-argument functions\n"
    "\n"
    " `apply` wraps a single-argument function `fn(a) -> b`. To rate-limit a\n"
    " function with multiple arguments, use `apply2`, `apply3`, or `apply4`:\n"
    "\n"
    " ```gleam\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.identifier(fn(args: #(String, String)) { args.0 })\n"
    "   |> glimit.on_limit_exceeded(fn(_args) { too_many_requests() })\n"
    "\n"
    " let limited_handle =\n"
    "   handle\n"
    "   |> glimit.apply2(limiter)\n"
    "\n"
    " limited_handle(\"user_123\", \"upload\")\n"
    " ```\n"
    "\n"
).

-type rate_limiter(FYS, FYT, FYU) :: {rate_limiter,
        gleam@erlang@process:subject(glimit@rate_limiter:message(FYU)),
        fun((FYS) -> FYT),
        fun((FYS) -> FYU)}.

-type rate_limiter_builder(FYV, FYW, FYX) :: {rate_limiter_builder,
        gleam@option:option(fun((FYX) -> integer())),
        gleam@option:option(fun((FYX) -> integer())),
        gleam@option:option(fun((FYV) -> FYX)),
        gleam@option:option(fun((FYV) -> FYW))}.

-file("src/glimit.gleam", 85).
?DOC(" Create a new rate limiter builder.\n").
-spec new() -> rate_limiter_builder(any(), any(), any()).
new() ->
    {rate_limiter_builder, none, none, none, none}.

-file("src/glimit.gleam", 113).
?DOC(
    " Set the rate of new available tokens per second.\n"
    "\n"
    " Note that this is not the maximum number of requests that can be made in a single\n"
    " second, but the rate at which tokens are added to the bucket. Think of this as the\n"
    " steady state rate limit, while the `burst_limit` function sets the maximum number of\n"
    " available tokens (or the burst rate limit).\n"
    "\n"
    " This value is also used as the default value for the `burst_limit` function.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    " ```\n"
).
-spec per_second(rate_limiter_builder(FZE, FZF, FZG), integer()) -> rate_limiter_builder(FZE, FZF, FZG).
per_second(Limiter, Limit) ->
    {rate_limiter_builder,
        {some, fun(_) -> Limit end},
        erlang:element(3, Limiter),
        erlang:element(4, Limiter),
        erlang:element(5, Limiter)}.

-file("src/glimit.gleam", 135).
?DOC(
    " Set the rate limit per second, based on the identifier.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.identifier(fn(request) { request.user_id })\n"
    "   |> glimit.per_second_fn(fn(user_id) {\n"
    "     db.get_rate_limit(user_id)\n"
    "   })\n"
    " ```\n"
).
-spec per_second_fn(
    rate_limiter_builder(FZN, FZO, FZP),
    fun((FZP) -> integer())
) -> rate_limiter_builder(FZN, FZO, FZP).
per_second_fn(Limiter, Limit_fn) ->
    {rate_limiter_builder,
        {some, Limit_fn},
        erlang:element(3, Limiter),
        erlang:element(4, Limiter),
        erlang:element(5, Limiter)}.

-file("src/glimit.gleam", 158).
?DOC(
    " Set the maximum number of available tokens.\n"
    "\n"
    " The maximum number of available tokens is the maximum number of requests that can be\n"
    " made in a single second. The default value is the same as the rate limit per second.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.burst_limit(100)\n"
    " ```\n"
).
-spec burst_limit(rate_limiter_builder(FZW, FZX, FZY), integer()) -> rate_limiter_builder(FZW, FZX, FZY).
burst_limit(Limiter, Burst_limit) ->
    {rate_limiter_builder,
        erlang:element(2, Limiter),
        {some, fun(_) -> Burst_limit end},
        erlang:element(4, Limiter),
        erlang:element(5, Limiter)}.

-file("src/glimit.gleam", 181).
?DOC(
    " Set the maximum number of available tokens, based on the identifier.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.identifier(fn(request) { request.user_id })\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.burst_limit_fn(fn(user_id) {\n"
    "     db.get_burst_limit(user_id)\n"
    "   })\n"
    " ```\n"
).
-spec burst_limit_fn(
    rate_limiter_builder(GAF, GAG, GAH),
    fun((GAH) -> integer())
) -> rate_limiter_builder(GAF, GAG, GAH).
burst_limit_fn(Limiter, Burst_limit_fn) ->
    {rate_limiter_builder,
        erlang:element(2, Limiter),
        {some, Burst_limit_fn},
        erlang:element(4, Limiter),
        erlang:element(5, Limiter)}.

-file("src/glimit.gleam", 201).
?DOC(
    " Set the handler to be called when the rate limit is reached.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.on_limit_exceeded(fn(_request) { \"Rate limit reached\" })\n"
    " ```\n"
).
-spec on_limit_exceeded(rate_limiter_builder(GAO, GAP, GAQ), fun((GAO) -> GAP)) -> rate_limiter_builder(GAO, GAP, GAQ).
on_limit_exceeded(Limiter, On_limit_exceeded) ->
    {rate_limiter_builder,
        erlang:element(2, Limiter),
        erlang:element(3, Limiter),
        erlang:element(4, Limiter),
        {some, On_limit_exceeded}}.

-file("src/glimit.gleam", 220).
?DOC(
    " Set the identifier function to be used to identify the rate limit.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " import glimit\n"
    "\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.identifier(fn(request) { request.ip })\n"
    " ```\n"
).
-spec identifier(rate_limiter_builder(GAX, GAY, GAZ), fun((GAX) -> GAZ)) -> rate_limiter_builder(GAX, GAY, GAZ).
identifier(Limiter, Identifier) ->
    {rate_limiter_builder,
        erlang:element(2, Limiter),
        erlang:element(3, Limiter),
        {some, Identifier},
        erlang:element(5, Limiter)}.

-file("src/glimit.gleam", 236).
?DOC(
    " Build the rate limiter.\n"
    "\n"
    " Note that using `apply` will already build the rate limiter, so this function is\n"
    " only useful if you want to build the rate limiter manually and apply it to multiple\n"
    " functions.\n"
    "\n"
    " To apply the resulting rate limiter to a function or handler, use the `apply_built`\n"
    " function.\n"
).
-spec build(rate_limiter_builder(GBG, GBH, GBI)) -> {ok,
        rate_limiter(GBG, GBH, GBI)} |
    {error, binary()}.
build(Config) ->
    gleam@result:'try'(case erlang:element(2, Config) of
            {some, Per_second} ->
                {ok, Per_second};

            none ->
                {error, <<"`per_second` rate limit is required"/utf8>>}
        end, fun(Per_second@1) ->
            Burst_limit@1 = case erlang:element(3, Config) of
                {some, Burst_limit} ->
                    Burst_limit;

                none ->
                    Per_second@1
            end,
            gleam@result:'try'(case erlang:element(4, Config) of
                    {some, Identifier} ->
                        {ok, Identifier};

                    none ->
                        {error, <<"`identifier` function is required"/utf8>>}
                end, fun(Identifier@1) ->
                    gleam@result:'try'(case erlang:element(5, Config) of
                            {some, On_limit_exceeded} ->
                                {ok, On_limit_exceeded};

                            none ->
                                {error,
                                    <<"`on_limit_exceeded` function is required"/utf8>>}
                        end, fun(On_limit_exceeded@1) ->
                            gleam@result:'try'(
                                begin
                                    _pipe = glimit@rate_limiter:new(
                                        Per_second@1,
                                        Burst_limit@1
                                    ),
                                    gleam@result:map_error(
                                        _pipe,
                                        fun(_) ->
                                            <<"Failed to start rate limiter"/utf8>>
                                        end
                                    )
                                end,
                                fun(Rate_limiter_actor) ->
                                    {ok,
                                        {rate_limiter,
                                            Rate_limiter_actor,
                                            On_limit_exceeded@1,
                                            Identifier@1}}
                                end
                            )
                        end)
                end)
        end).

-file("src/glimit.gleam", 288).
?DOC(
    " Apply the rate limiter to a request handler or function.\n"
    "\n"
    " This function is useful if you want to build the rate limiter manually using the\n"
    " `build` function.\n"
).
-spec apply_built(fun((GBX) -> GBY), rate_limiter(GBX, GBY, any())) -> fun((GBX) -> GBY).
apply_built(Func, Limiter) ->
    fun(Input) ->
        Identifier = (erlang:element(4, Limiter))(Input),
        case glimit@rate_limiter:hit(erlang:element(2, Limiter), Identifier) of
            {ok, nil} ->
                Func(Input);

            {error, rate_limited} ->
                (erlang:element(3, Limiter))(Input);

            {error, unavailable} ->
                Func(Input)
        end
    end.

-file("src/glimit.gleam", 272).
?DOC(
    " Apply the rate limiter to a request handler or function.\n"
    "\n"
    " Panics if the rate limiter cannot be started or if the `identifier`\n"
    " function or `on_limit_exceeded` function is missing.\n"
).
-spec apply(fun((GBR) -> GBS), rate_limiter_builder(GBR, GBS, any())) -> fun((GBR) -> GBS).
apply(Func, Config) ->
    Limiter@1 = case build(Config) of
        {ok, Limiter} ->
            Limiter;

        {error, Message} ->
            erlang:error(#{gleam_error => panic,
                    message => Message,
                    file => <<?FILEPATH/utf8>>,
                    module => <<"glimit"/utf8>>,
                    function => <<"apply"/utf8>>,
                    line => 278})
    end,
    apply_built(Func, Limiter@1).

-file("src/glimit.gleam", 322).
?DOC(
    " Apply the rate limiter to a 2-argument function.\n"
    "\n"
    " The config's `identifier` and `on_limit_exceeded` receive a `#(a, b)` tuple.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.identifier(fn(args: #(String, String)) { args.0 })\n"
    "   |> glimit.on_limit_exceeded(fn(_) { \"Rate limited\" })\n"
    "\n"
    " let limited =\n"
    "   handle\n"
    "   |> glimit.apply2(limiter)\n"
    "\n"
    " limited(\"user_123\", \"upload\")\n"
    " ```\n"
).
-spec apply2(
    fun((GCD, GCE) -> GCF),
    rate_limiter_builder({GCD, GCE}, GCF, any())
) -> fun((GCD, GCE) -> GCF).
apply2(Func, Config) ->
    Wrapped = begin
        _pipe = fun(Args) ->
            Func(erlang:element(1, Args), erlang:element(2, Args))
        end,
        apply(_pipe, Config)
    end,
    fun(A, B) -> Wrapped({A, B}) end.

-file("src/glimit.gleam", 352).
?DOC(
    " Apply the rate limiter to a 3-argument function.\n"
    "\n"
    " The config's `identifier` and `on_limit_exceeded` receive a `#(a, b, c)` tuple.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.identifier(fn(args: #(String, String, Int)) { args.0 })\n"
    "   |> glimit.on_limit_exceeded(fn(_) { \"Rate limited\" })\n"
    "\n"
    " let limited =\n"
    "   handle\n"
    "   |> glimit.apply3(limiter)\n"
    "\n"
    " limited(\"user_123\", \"upload\", 42)\n"
    " ```\n"
).
-spec apply3(
    fun((GCK, GCL, GCM) -> GCN),
    rate_limiter_builder({GCK, GCL, GCM}, GCN, any())
) -> fun((GCK, GCL, GCM) -> GCN).
apply3(Func, Config) ->
    Wrapped = begin
        _pipe = fun(Args) ->
            Func(
                erlang:element(1, Args),
                erlang:element(2, Args),
                erlang:element(3, Args)
            )
        end,
        apply(_pipe, Config)
    end,
    fun(A, B, C) -> Wrapped({A, B, C}) end.

-file("src/glimit.gleam", 382).
?DOC(
    " Apply the rate limiter to a 4-argument function.\n"
    "\n"
    " The config's `identifier` and `on_limit_exceeded` receive a `#(a, b, c, d)` tuple.\n"
    "\n"
    " # Example\n"
    "\n"
    " ```gleam\n"
    " let limiter =\n"
    "   glimit.new()\n"
    "   |> glimit.per_second(10)\n"
    "   |> glimit.identifier(fn(args: #(String, String, Int, Bool)) { args.0 })\n"
    "   |> glimit.on_limit_exceeded(fn(_) { \"Rate limited\" })\n"
    "\n"
    " let limited =\n"
    "   handle\n"
    "   |> glimit.apply4(limiter)\n"
    "\n"
    " limited(\"user_123\", \"upload\", 42, True)\n"
    " ```\n"
).
-spec apply4(
    fun((GCS, GCT, GCU, GCV) -> GCW),
    rate_limiter_builder({GCS, GCT, GCU, GCV}, GCW, any())
) -> fun((GCS, GCT, GCU, GCV) -> GCW).
apply4(Func, Config) ->
    Wrapped = begin
        _pipe = fun(Args) ->
            Func(
                erlang:element(1, Args),
                erlang:element(2, Args),
                erlang:element(3, Args),
                erlang:element(4, Args)
            )
        end,
        apply(_pipe, Config)
    end,
    fun(A, B, C, D) -> Wrapped({A, B, C, D}) end.