-module(fio@observer).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch, inline]).
-define(FILEPATH, "src/fio/observer.gleam").
-export([emit/5, trace/4, trace_bytes/4, format/1, fan_out/2, noop_sink/1]).
-export_type([event/0]).

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

-type event() :: {event,
        binary(),
        binary(),
        {ok, nil} | {error, fio@error:fio_error()},
        gleam@option:option(integer())}.

-file("src/fio/observer.gleam", 100).
?DOC(
    " Emit an `Event` to `sink` after `result` is produced, then return `result`\n"
    " unchanged.\n"
    "\n"
    " This is the lowest-level building block. Use `trace` when you do not have\n"
    " a byte count to report.\n"
    "\n"
    " ```gleam\n"
    " fio.read_bits(\"data.bin\")\n"
    " |> observer.emit(\"read_bits\", \"data.bin\", option.None, my_sink)\n"
    " ```\n"
).
-spec emit(
    {ok, FBF} | {error, fio@error:fio_error()},
    binary(),
    binary(),
    gleam@option:option(integer()),
    fun((event()) -> nil)
) -> {ok, FBF} | {error, fio@error:fio_error()}.
emit(Result, Op, Path, Bytes, Sink) ->
    Outcome = gleam@result:map(Result, fun(_) -> nil end),
    Sink({event, Op, Path, Outcome, Bytes}),
    Result.

-file("src/fio/observer.gleam", 125).
?DOC(
    " Like `emit` but without a byte count (`bytes` is always `None`).\n"
    "\n"
    " Use this for operations where byte count is not meaningful (delete, rename,\n"
    " touch, create_directory, etc.):\n"
    "\n"
    " ```gleam\n"
    " fio.delete(\"old.txt\")\n"
    " |> observer.trace(\"delete\", \"old.txt\", my_sink)\n"
    " ```\n"
).
-spec trace(
    {ok, FBL} | {error, fio@error:fio_error()},
    binary(),
    binary(),
    fun((event()) -> nil)
) -> {ok, FBL} | {error, fio@error:fio_error()}.
trace(Result, Op, Path, Sink) ->
    emit(Result, Op, Path, none, Sink).

-file("src/fio/observer.gleam", 141).
?DOC(
    " Like `trace` but automatically infers the byte count from the result when\n"
    " the operation returns a `BitArray` (e.g. `fio.read_bits`).\n"
    "\n"
    " ```gleam\n"
    " fio.read_bits(\"archive.tar.gz\")\n"
    " |> observer.trace_bytes(\"read_bits\", \"archive.tar.gz\", my_sink)\n"
    " ```\n"
).
-spec trace_bytes(
    {ok, bitstring()} | {error, fio@error:fio_error()},
    binary(),
    binary(),
    fun((event()) -> nil)
) -> {ok, bitstring()} | {error, fio@error:fio_error()}.
trace_bytes(Result, Op, Path, Sink) ->
    Bytes = case Result of
        {ok, Data} ->
            {some, erlang:byte_size(Data)};

        {error, _} ->
            none
    end,
    emit(Result, Op, Path, Bytes, Sink).

-file("src/fio/observer.gleam", 166).
?DOC(
    " Format an `Event` as a human-readable string.\n"
    " Useful when building simple logging sinks.\n"
    "\n"
    " ```gleam\n"
    " fn log_sink(event: Event) -> Nil {\n"
    "   io.println(observer.format(event))\n"
    " }\n"
    " ```\n"
).
-spec format(event()) -> binary().
format(Event) ->
    Status = case erlang:element(4, Event) of
        {ok, _} ->
            <<"ok"/utf8>>;

        {error, E} ->
            <<<<"err("/utf8, (fio@error:describe(E))/binary>>/binary, ")"/utf8>>
    end,
    Bytes_str = case erlang:element(5, Event) of
        none ->
            <<""/utf8>>;

        {some, N} ->
            <<" bytes="/utf8, (erlang:integer_to_binary(N))/binary>>
    end,
    <<<<<<<<<<<<"[fio] "/utf8, (erlang:element(2, Event))/binary>>/binary,
                        " "/utf8>>/binary,
                    (erlang:element(3, Event))/binary>>/binary,
                " -> "/utf8>>/binary,
            Status/binary>>/binary,
        Bytes_str/binary>>.

-file("src/fio/observer.gleam", 186).
?DOC(
    " Combine two sinks into one: both receive every event in order.\n"
    "\n"
    " Useful for fan-out — log to stdout AND record in a test buffer:\n"
    "\n"
    " ```gleam\n"
    " let combined = observer.fan_out(log_sink, test_recorder_sink)\n"
    " fio.write(\"out.txt\", data) |> observer.trace(\"write\", \"out.txt\", combined)\n"
    " ```\n"
).
-spec fan_out(fun((event()) -> nil), fun((event()) -> nil)) -> fun((event()) -> nil).
fan_out(First, Second) ->
    fun(Event) ->
        First(Event),
        Second(Event)
    end.

-file("src/fio/observer.gleam", 203).
?DOC(
    " A no-op sink that discards all events.\n"
    " Useful as a default/placeholder argument when observability is optional.\n"
    "\n"
    " ```gleam\n"
    " pub fn copy(src, dest, sink: observer.Sink) {\n"
    "   fio.copy(src, dest) |> observer.trace(\"copy\", src, sink)\n"
    " }\n"
    " // caller passes observer.noop_sink when not interested\n"
    " copy(\"a.txt\", \"b.txt\", observer.noop_sink)\n"
    " ```\n"
).
-spec noop_sink(event()) -> nil.
noop_sink(_) ->
    nil.