unit rectangles;

{$MODE OBJFPC}

// this could be used a lot more.

interface

type
  TCoordinate = Integer;

  TRectangleP = ^TRectangle;
  TRectangle = object
    LeftTop : record
      X : TCoordinate;
      Y : TCoordinate;
    end;
    RightBottom : record
      X : TCoordinate;
      Y : TCoordinate;
    end;

    constructor Init;
    function Intersect(const bRectangle : TRectangle) : TRectangleP;
    procedure IntersectM(const bRectangle : TRectangle);
    procedure AssignFrom(const bRectangle : TRectangle);
  end;

implementation

function Max(aA, aB : TCoordinate) : TCoordinate; inline;
begin
  if aA < aB then
    Result := aA
  else
    Result := aB;
end;

function Min(aA, aB : TCoordinate) : TCoordinate; inline;
begin
  if aA > aB then
    Result := aA
  else
    Result := aB;
end;

constructor TRectangle.Init;
begin
  LeftTop.X := 0;
  LeftTop.Y := 0;
  RightBottom.X := 0;
  RightBottom.Y := 0;
end;

function TRectangle.Intersect(const bRectangle : TRectangle) : TRectangleP;
begin
  Result := New(TRectangleP, Init);
  Result^.AssignFrom(Self);
  Result^.IntersectM(bRectangle);
end;

procedure TRectangle.IntersectM(const bRectangle : TRectangle);
begin
  Self.LeftTop.X := Max(Self.LeftTop.X, bRectangle.LeftTop.X);
  Self.LeftTop.Y := Max(Self.LeftTop.Y, bRectangle.LeftTop.Y);
  Self.RightBottom.X := Min(Self.RightBottom.X, bRectangle.RightBottom.Y);
  Self.RightBottom.Y := Min(Self.RightBottom.Y, bRectangle.RightBottom.Y);
end;

procedure TRectangle.AssignFrom(const bRectangle : TRectangle);
begin
  Self.LeftTop.X := bRectangle.LeftTop.X;
  Self.LeftTop.Y := bRectangle.LeftTop.Y;
  Self.RightBottom.X := bRectangle.RightBottom.X;
  Self.RightBottom.Y := bRectangle.RightBottom.Y;
end;


end.