First logger

Logging...
  console: [WRN] orders Stock for AX-7 is low: 3 left
  console: [ERR] orders Could not archive the order | EInOutError: Disk quota exceeded
Memory sink:
  ok: 26 events reached the memory sink, the debug event included
  ok: the template filled its holes and kept them as properties
  ok: the failure kept the exception apart from the message
  ok: the timer named the scope and reported its duration
  ok: no sink failed
Text file C:\Users\you\AppData\Local\Temp\AtlasLogFirstLogger\app.log:
  ok: full files were rolled into 2 archives
  ok: all 25 events at info and above are in the text files, the debug event is not
  ok: empty tokens leave no double spaces
  ok: category, scope and properties are on the line
  ok: the exception follows the message
  ok: the newest line is last in the active file
    [INF] [import] Imported row 17 of 20 {row=17, rows=20}
    [INF] [import] Imported row 18 of 20 {row=18, rows=20}
    [INF] [import] Imported row 19 of 20 {row=19, rows=20}
    [INF] [import] Imported row 20 of 20 {row=20, rows=20}
    [INF] [import] import finished in 2 ms {scope=import, elapsed_ms=2}
JSON file C:\Users\you\AppData\Local\Temp\AtlasLogFirstLogger\app.jsonl:
  ok: one JSON object per event
    {"ts":"2026-09-22T01:37:43.606Z","seq":3,"level":"info","category":"orders","thread":52800,"scope":"checkout","msg":"Order 1042 placed by Contoso for 1250.5","template":"Order {id} placed by {customer} for {total}","props":{"id":"1042","customer":"Contoso","total":"1250.5"}}
  ok: the JSON object keeps message, template, scope and properties apart, with a UTC time
  ok: the exception is a nested object
All checks passed.

program FirstLogger;

// Atlas Log quick start. One logger writes to a memory ring buffer, the
// console (warnings and above), the debugger, a size-rotated text file and a
// JSON-lines file, both files in a temporary folder. The program logs with
// message templates, a channel, a scope, a failure and a timer, reads its own
// output back, checks it, and deletes the folder. Exit code 0 means every
// check passed.

{$APPTYPE CONSOLE}

uses
  System.SysUtils, System.Classes, System.IOUtils, System.JSON,
  Atlas.Log, Atlas.LogSinks;

procedure Check(Condition: Boolean; const What: string);
begin
  if not Condition then raise Exception.Create('Check failed: ' + What);
  Writeln('  ok: ', What);
end;

// The file sink keeps its file open and denies other writers, not readers.
function ReadLines(const FileName: string): TArray<string>;
var
  Stream: TFileStream;
  Bytes: TBytes;
begin
  Stream := TFileStream.Create(FileName, fmOpenRead or fmShareDenyNone);
  try
    SetLength(Bytes, Stream.Size);
    if Length(Bytes) > 0 then Stream.ReadBuffer(Bytes[0], Length(Bytes));
  finally
    Stream.Free;
  end;
  Result := TEncoding.UTF8.GetString(Bytes).Split([sLineBreak], TStringSplitOptions.ExcludeEmpty);
end;

procedure Run(const Folder: string);
var
  Log: TAtlasLogger;
  Memory: TAtlasMemorySink;
  Console: TAtlasConsoleSink;
  Debugger: TAtlasDebugSink;
  Plain, Json: TAtlasFileSink;
  Orders: TAtlasLogChannel;
  Scope, Timer: IInterface;
  Events: TArray<TAtlasLogEvent>;
  Lines: TArray<string>;
  Name: string;
  Parsed: TJSONValue;
  I, Archive, Archives: Integer;
begin
  Log := TAtlasLogger.Create(nil);
  try
    Log.MinLevel := llDebug;

    // Sinks owned by the logger are freed with it.
    Memory := TAtlasMemorySink.Create(Log);
    Memory.Capacity := 100;
    Memory.Logger := Log;

    Console := TAtlasConsoleSink.Create(Log);
    Console.MinLevel := llWarning;
    Console.Pattern := '  console: [{level:short}] {category} {message}{exception}';
    Console.Logger := Log;

    Debugger := TAtlasDebugSink.Create(Log);
    Debugger.Logger := Log;

    Plain := TAtlasFileSink.Create(Log);
    Plain.FileName := TPath.Combine(Folder, 'app.log');
    Plain.Pattern := '[{level:short}] {category} {scope} {message}{exception}{props}';
    Plain.MinLevel := llInfo;
    Plain.MaxBytes := 512;
    Plain.MaxFiles := 5;
    Plain.Logger := Log;

    Json := TAtlasFileSink.Create(Log);
    Json.FileName := TPath.Combine(Folder, 'app.jsonl');
    Json.Layout := loJson;
    Json.Logger := Log;

    Writeln('Logging...');
    Log.Info('Application started');
    Log.Debug('Settings read from {file}', ['settings.json']);

    Orders := Log.Channel('orders');
    Scope := Log.BeginScope('checkout');
    Orders.Info('Order {id} placed by {customer} for {total}', [1042, 'Contoso', 1250.5]);
    Orders.Warning('Stock for {sku} is low: {left} left', ['AX-7', 3]);
    Scope := nil;

    try
      raise EInOutError.Create('Disk quota exceeded');
    except
      on E: Exception do Orders.Failure(E, 'Could not archive the order');
    end;

    Timer := Log.Time('import');
    for I := 1 to 20 do Log.Info('Imported row {row} of {rows}', [I, 20]);
    Timer := nil;
    Log.Flush;

    Writeln('Memory sink:');
    Events := Memory.Snapshot;
    Check(Length(Events) = 26, '26 events reached the memory sink, the debug event included');
    Check((Events[2].Message = 'Order 1042 placed by Contoso for 1250.5') and (Events[2].Category = 'orders') and
      (Events[2].Scope = 'checkout') and (Events[2].PropertyValue('customer') = 'Contoso') and
      (Events[2].Template = 'Order {id} placed by {customer} for {total}'), 'the template filled its holes and kept them as properties');
    Check((Events[4].Level = llError) and (Events[4].ExceptionClass = 'EInOutError') and
      (Events[4].ExceptionMessage = 'Disk quota exceeded'), 'the failure kept the exception apart from the message');
    Check((Events[5].Scope = 'import') and (Events[25].Message.StartsWith('import finished in ')) and
      (StrToIntDef(Events[25].PropertyValue('elapsed_ms'), -1) >= 0), 'the timer named the scope and reported its duration');
    for I := 1 to High(Events) do
      if Events[I].Sequence <> Events[I - 1].Sequence + 1 then Check(False, 'sequence numbers increase by one');
    Check(Log.SinkErrors = 0, 'no sink failed');

    Writeln('Text file ', Plain.ActiveFileName, ':');
    // Oldest archive first, then the active file.
    Lines := nil;
    Archives := 0;
    for Archive := Plain.MaxFiles downto 1 do
    begin
      Name := TPath.Combine(Folder, Format('app.%d.log', [Archive]));
      if not TFile.Exists(Name) then Continue;
      Inc(Archives);
      if TFile.GetSize(Name) > Plain.MaxBytes then Check(False, Name + ' stays within MaxBytes');
      Lines := Lines + ReadLines(Name);
    end;
    Lines := Lines + ReadLines(Plain.ActiveFileName);
    Check(Archives >= 1, Format('full files were rolled into %d archives', [Archives]));
    Check(Length(Lines) = 25, 'all 25 events at info and above are in the text files, the debug event is not');
    Check(Lines[0] = '[INF] Application started', 'empty tokens leave no double spaces');
    Check(Lines[1] = '[INF] orders [checkout] Order 1042 placed by Contoso for 1250.5 {id=1042, customer=Contoso, total=1250.5}',
      'category, scope and properties are on the line');
    Check(Lines[3] = '[ERR] orders Could not archive the order | EInOutError: Disk quota exceeded', 'the exception follows the message');
    Check(Lines[24].StartsWith('[INF] [import] import finished in '), 'the newest line is last in the active file');
    for I := 20 to 24 do Writeln('    ', Lines[I]);

    Writeln('JSON file ', Json.ActiveFileName, ':');
    Lines := ReadLines(Json.ActiveFileName);
    Check(Length(Lines) = 26, 'one JSON object per event');
    for I := 0 to High(Lines) do
    begin
      Parsed := TJSONObject.ParseJSONValue(Lines[I]);
      if not (Parsed is TJSONObject) then Check(False, 'every line parses as a JSON object');
      Parsed.Free;
    end;
    Writeln('    ', Lines[2]);
    Parsed := TJSONObject.ParseJSONValue(Lines[2]);
    try
      Check((Parsed.GetValue<string>('msg') = 'Order 1042 placed by Contoso for 1250.5') and
        (Parsed.GetValue<string>('category') = 'orders') and (Parsed.GetValue<string>('scope') = 'checkout') and
        (Parsed.GetValue<string>('template') = 'Order {id} placed by {customer} for {total}') and
        (Parsed.GetValue<string>('props.total') = '1250.5') and Parsed.GetValue<string>('ts').EndsWith('Z'),
        'the JSON object keeps message, template, scope and properties apart, with a UTC time');
    finally
      Parsed.Free;
    end;
    Parsed := TJSONObject.ParseJSONValue(Lines[4]);
    try
      Check((Parsed.GetValue<string>('level') = 'error') and (Parsed.GetValue<string>('exception.type') = 'EInOutError'),
        'the exception is a nested object');
    finally
      Parsed.Free;
    end;
  finally
    // Frees the sinks too, which closes the files.
    Log.Free;
  end;
end;

var
  Folder: string;
begin
  Folder := TPath.Combine(TPath.GetTempPath, 'AtlasLogFirstLogger');
  try
    try
      if TDirectory.Exists(Folder) then TDirectory.Delete(Folder, True);
      Run(Folder);
      Writeln('All checks passed.');
    finally
      if TDirectory.Exists(Folder) then TDirectory.Delete(Folder, True);
    end;
  except
    on E: Exception do
    begin
      Writeln(E.ClassName, ': ', E.Message);
      ExitCode := 1;
    end;
  end;
end.