{
  Solutions to the Advent Of Code.
  Copyright (C) 2023  Stefan Müller

  This program is free software: you can redistribute it and/or modify it under
  the terms of the GNU General Public License as published by the Free Software
  Foundation, either version 3 of the License, or (at your option) any later
  version.

  This program is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  this program.  If not, see <http://www.gnu.org/licenses/>.
}

unit UGearRatios;

{$mode ObjFPC}{$H+}

interface

uses
  Classes, SysUtils, USolver;

const
  CDigitChars = ['0'..'9'];
  CNonSymbolChars = ['0'..'9', '.'];

type

  { TGearRatios }

  TGearRatios = class(TSolver)
  private
    FPreviousLine, FLine: string;
    procedure ProcessDataLineTriplet(const APreviousLine, ALine, ANextLine: string);
  public
    procedure ProcessDataLine(const ALine: string); override;
    procedure Finish; override;
    function GetDataFileName: string; override;
    function GetPuzzleName: string; override;
  end;

implementation

{ TGearRatios }

procedure TGearRatios.ProcessDataLineTriplet(const APreviousLine, ALine, ANextLine: string);
var
  i, numberStart, numberLength, partNumber: Integer;
  inNumber, isPartNumber: Boolean;
begin
  inNumber := False;

  for i := 1 to ALine.Length do
  begin
    // Checks if number starts.
    if not inNumber and (ALine[i] in CDigitChars) then
    begin
      inNumber := True;
      numberStart := i;

      // Checks for a symbol in the column before the first digit.
      isPartNumber := (i > 1) and
        (not (APreviousLine[i - 1] in CNonSymbolChars)
        or not (ALine[i - 1] in CNonSymbolChars)
        or not (ANextLine[i - 1] in CNonSymbolChars));
    end;

    // Checks for a symbol in the column of the current digit.
    if inNumber and not isPartNumber and
      (not (APreviousLine[i] in CNonSymbolChars)
      or not (ANextLine[i] in CNonSymbolChars)) then
    begin
      isPartNumber := True;
    end;

    // Checks if number ends.
    if inNumber and (not (ALine[i] in CDigitChars) or (i = ALine.Length)) then
    begin
      inNumber := False;

      // Checks for a symbol in the column after the last digit.
      if not (APreviousLine[i] in CNonSymbolChars)
        or not (ALine[i] in CNonSymbolChars)
        or not (ANextLine[i] in CNonSymbolChars) then
      begin
        isPartNumber := True;
      end;

      // Counts if it is a part number.
      if isPartNumber then
      begin
        numberLength := i - numberStart;
        if ALine[i] in CDigitChars then
          Inc(numberLength);
        partNumber := StrToInt(Copy(ALine, numberStart, numberLength));
        Inc(FPart1, partNumber);
      end;
    end;
  end;
end;

procedure TGearRatios.ProcessDataLine(const ALine: string);
begin
  if not (FLine = '') then
  begin
    // Processes lines 2 to n - 1 in calls for lines 3 to n.
    ProcessDataLineTriplet(FPreviousLine, FLine, ALine);
    FPreviousLine := FLine;
    FLine := ALine;
  end
  else if not (FPreviousLine = '') then
  begin
    // Processes line 1 in call for line 2.
    FLine := ALine;
    // Duplicates the first line for the algorithm because it does not influence the result.
    ProcessDataLineTriplet(FPreviousLine, FPreviousLine, FLine);
  end
  else
    // Processes nothing in call for line 1.
    FPreviousLine := ALine;
end;

procedure TGearRatios.Finish;
begin
  // Processes line n.
  // Duplicates the last line for the algorithm because it does not influence the result.
  if FLine = '' then
    FLine := FPreviousLine;
  ProcessDataLineTriplet(FPreviousLine, FLine, FLine);
end;

function TGearRatios.GetDataFileName: string;
begin
  Result := 'gear_ratios.txt';
end;

function TGearRatios.GetPuzzleName: string;
begin
  Result := 'Day 3: Gear Ratios';
end;

end.