Add StringScanner.pas

Components/StringScanner.pas

@@ -0,0 +1,123 @@
+unit StringScanner;
+
+{
+  Inno Setup
+  Copyright (C) 1997-2025 Jordan Russell
+  Portions by Martijn Laan
+  For conditions of distribution and use, see LICENSE.TXT.
+
+  TStringScanner
+}
+
+interface
+
+uses
+  SysUtils;
+
+type
+  TStringScanner = record
+  strict private
+    FStr: String;
+    FPosition: Integer;
+    function GetReachedEnd: Boolean;
+    function GetRemainingCount: Integer;
+  public
+    class function Init(const AString: String): TStringScanner; static;
+    function Consume(const C: Char): Boolean; overload;
+    function Consume(const S: String): Boolean; overload;
+    function ConsumeMulti(const C: TSysCharSet; const AMinChars: Integer = 1;
+      const AMaxChars: Integer = Maxint): Integer;
+    function ConsumeMultiToString(const C: TSysCharSet;
+      var ACapturedString: String; const AMinChars: Integer = 1;
+      const AMaxChars: Integer = Maxint): Integer;
+    property ReachedEnd: Boolean read GetReachedEnd;
+    property RemainingCount: Integer read GetRemainingCount;
+    property Str: String read FStr;
+  end;
+
+implementation
+
+{$ZEROBASEDSTRINGS OFF}
+
+{ TStringScanner }
+
+class function TStringScanner.Init(const AString: String): TStringScanner;
+begin
+  Result.FPosition := 1;
+  Result.FStr := AString;
+end;
+
+function TStringScanner.Consume(const C: Char): Boolean;
+begin
+  Result := (GetRemainingCount > 0) and (FStr[FPosition] = C);
+  if Result then
+    Inc(FPosition);
+end;
+
+function TStringScanner.Consume(const S: String): Boolean;
+begin
+  const SLen = Length(S);
+  if SLen > GetRemainingCount then
+    Exit(False);
+
+  for var I := 0 to SLen-1 do
+    if FStr[FPosition + I] <> S[I+1] then
+      Exit(False);
+
+  Inc(FPosition, SLen);
+  Result := True;
+end;
+
+function TStringScanner.ConsumeMulti(const C: TSysCharSet;
+  const AMinChars: Integer = 1; const AMaxChars: Integer = Maxint): Integer;
+begin
+  if (AMinChars <= 0) or (AMinChars > AMaxChars) then
+    raise Exception.Create('TStringScanner.ConsumeMulti: Invalid parameter');
+
+  const Remain = GetRemainingCount;
+  if Remain < AMinChars then
+    Exit(0);
+
+  Result := 0;
+  while (Result < AMaxChars) and (Result < Remain) and
+     CharInSet(FStr[FPosition + Result], C) do
+    Inc(Result);
+
+  if Result < AMinChars then
+    Result := 0
+  else
+    Inc(FPosition, Result);
+end;
+
+function TStringScanner.ConsumeMultiToString(const C: TSysCharSet;
+  var ACapturedString: String; const AMinChars: Integer = 1;
+  const AMaxChars: Integer = Maxint): Integer;
+begin
+  const StartPos = FPosition;
+  Result := ConsumeMulti(C, AMinChars, AMaxChars);
+  if Result > 0 then
+    ACapturedString := Copy(FStr, StartPos, Result)
+  else
+    ACapturedString := '';
+end;
+
+function TStringScanner.GetReachedEnd: Boolean;
+begin
+  Result := (GetRemainingCount = 0);
+end;
+
+function TStringScanner.GetRemainingCount: Integer;
+begin
+  { The "<= 0" check exists to protect against OOB reads in case someone calls
+    into an instance that was never properly initialized (via Init).
+    Inside TStringScanner, FStr[FPosition] must not be accessed unless
+    GetRemainingCount is called first and returns a nonzero value. }
+
+  const Len = Length(FStr);
+  if (FPosition <= 0) or (FPosition > Len) then
+    Result := 0
+  else
+    Result := Len - FPosition + 1;
+end;
+
+end.