date_handling.adb

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;

package body Date_Handling is
   function Previous_Date (D : in Date_Type) return Date_Type is
      Prev : Date_Type := D;
   begin
      if D.Month = 1 and D.Day = 1 then
     Prev.Year := D.Year - 1;
     Prev.Month := 12;
     Prev.Day := 31;
      elsif D.Month = 3 and D.Day = 1 then
     Prev.Month := 2;
     Prev.Day := 28;
      elsif (D.Month = 5 or D.Month = 7 or D.Month = 10 or D.Month = 12) and D.Day = 1 then
     Prev.Month := D.Month - 1;
     Prev.Day := 30;
      elsif D.Day = 1 then
     Prev.Month := D.Month - 1;
     Prev.Day := 31;
      else
     Prev.Day := D.Day - 1;
      end if;
      return Prev;
   end Previous_Date;

   function Next_Date (D : in Date_Type) return Date_Type is
      Next : Date_Type := D;
   begin
      if D.Month = 12 and D.Day = 31 then
     Next.Year := D.Year + 1;
     Next.Month := 1;
     Next.Day := 1;
      elsif D.Month = 2 and D.Day = 28 then
     Next.Month := 3;
     Next.Day := 1;
      elsif (D.Month = 4 or D.Month = 6 or D.Month = 9 or D.Month = 11) and D.Day = 30 then
     Next.Month := D.Month + 1;
     Next.Day := 1;
      elsif D.Day = 31 then
     Next.Month := D.Month + 1;
     Next.Day := 1;
      else
     Next.Day := D.Day + 1;
      end if;
      return Next;
   end Next_Date;

   function "<" (A, B : in Date_Type) return Boolean is
   begin
      if A.Year < B.Year or (A.Year = B.Year and A.Month < B.Month) or (A.Year = B.Year and A.Month = B.Month and A.Day < B.Day) then
     return True;
      else
     return False;
      end if;
   end "<";

   function ">" (A, B : in Date_Type) return Boolean is
   begin
      if A.Year > B.Year or (A.Year = B.Year and A.Month > B.Month) or (A.Year = B.Year and A.Month = B.Month and A.Day > B.Day) then
     return True;
      else
     return False;
      end if;
   end ">";

   function "=" (A, B : in Date_Type) return Boolean is
   begin
      if A.Year = B.Year and A.Month = B.Month and A.Day = B.Day then
     return True;
      else
     return False;
      end if;
   end "=";

   procedure Get(D : in out Date_Type) is
      C : Character;
      D_28 : Integer range 1..28;
      D_30 : Integer range 1..30;
   begin
      loop
     begin
        begin
           Get(D.Year);
        exception
           when others =>
          raise Year_Error;
        end;

        Get(C);

        begin
           Get(D.Month);
        exception
           when others =>
          raise Month_Error;
        end;

        Get(C);

        begin
           if D.Month = 2 then
          Get(D_28);
          D.Day := D_28;
           elsif D.Month = 4 or D.Month = 6 or D.Month = 9 then
          Get(D_30);
          D.Day := D_30;
           else
          Get(D.Day);
           end if;
        exception
           when others =>
          raise Day_Error;
        end;

        exit;

     exception
        when Year_Error =>
           Put_Line("Ogiltigt år.");
           Skip_Line;
        when Month_Error =>
           Put_Line("Ogiltig månad.");
           Skip_Line;
        when Day_Error =>
           Put_Line("Ogiltig dag.");
           Skip_Line;
     end;
      end loop;
   end Get;

   procedure Put(D : in Date_Type) is
   begin
      if D.Year < 10 then
     Put("000");
      elsif D.Year < 100 then
     Put("00");
      elsif D.Year < 1000 then
     Put("0");
      end if;
      Put(D.Year, 0);
      Put('-');
      if D.Month < 10 then
     Put(0, 0);
      end if;
      Put(D.Month, 0);
      Put('-');
      if D.Day < 10 then
     Put(0, 0);
      end if;
      Put(D.Day, 0);
   end Put;

end Date_Handling;