{
  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 UGiveSeedFertilizer;

{$mode ObjFPC}{$H+}

interface

uses
  Classes, SysUtils, fgl, USolver;

type

  { TAlmanacMapRange }

  TAlmanacMapRange = class
  private
    FDestinationStart, FSourceStart, FSourceEnd, FDifference1, FDifference2: Cardinal;
  public
    constructor Create(const ALine: string);
    constructor Create(const ADestinationStart, ASourceStart, ALength: Cardinal);
    function TryConvert(const AInput: Cardinal; out OOutput: Cardinal): Boolean;
  end;

  { TGiveSeedFertilizer }

  TGiveSeedFertilizer = class(TSolver)
  private
    FNew, FConverted, FProcessedIndices: specialize TFPGList<Cardinal>;
    procedure ProcessSeeds(const ALine: string);
    procedure ProcessMapRange(const ALine: string);
    procedure FinishMap;
  public
    constructor Create;
    destructor Destroy; override;
    procedure ProcessDataLine(const ALine: string); override;
    procedure Finish; override;
    function GetDataFileName: string; override;
    function GetPuzzleName: string; override;
  end;

implementation

{ TAlmanacMapRange }

constructor TAlmanacMapRange.Create(const ALine: string);
var
  split: TStringArray;
begin
  split := ALine.Split(' ');
  Create(StrToDWord(split[0]), StrToDWord(split[1]), StrToDWord(split[2]));
end;

constructor TAlmanacMapRange.Create(const ADestinationStart, ASourceStart, ALength: Cardinal);
begin
  FDestinationStart := ADestinationStart;
  FSourceStart := ASourceStart;

  // All input values are within Cardinal range, but the calculations might not be.
  if ASourceStart <= Cardinal.MaxValue - ALength then
    FSourceEnd := ASourceStart + ALength
  else
    FSourceEnd := Cardinal.MaxValue;

  if ADestinationStart >= ASourceStart then
  begin
    FDifference1 := ADestinationStart - ASourceStart;
    FDifference2 := 0;
  end
  else begin
    FDifference1 := 0;
    FDifference2 := ASourceStart - ADestinationStart;
  end;
end;

function TAlmanacMapRange.TryConvert(const AInput: Cardinal; out OOutput: Cardinal): Boolean;
begin
  if (FSourceStart <= AInput) and (AInput < FSourceEnd) then
  begin
    if FDifference1 > 0 then
      OOutput := AInput + FDifference1
    else
      OOutput := AInput - FDifference2;
    Result := True;
  end
  else begin
    OOutput := 0;
    Result := False;
  end;
end;

{ TGiveSeedFertilizer }

procedure TGiveSeedFertilizer.ProcessSeeds(const ALine: string);
var
  split: TStringArray;
  i: Integer;
begin
  split := Aline.Split(' ');
  for i := 1 to Length(split) - 1 do
  begin
    FNew.Add(StrToDWord(split[i]));
  end;
end;

procedure TGiveSeedFertilizer.ProcessMapRange(const ALine: string);
var
  range: TAlmanacMapRange;
  i: Integer;
  converted: Cardinal;
begin
  // Converts all "new" values that fall into this mapping range.
  range := TAlmanacMapRange.Create(ALine);
  for i := 0 to FNew.Count - 1 do
  begin
    if range.TryConvert(FNew[i], converted) then
    begin
      FConverted.Add(converted);
      FProcessedIndices.Add(i);
    end;
  end;
  range.Free;

  // Forgets the converted values.
  for i := FProcessedIndices.Count - 1 downto 0 do
  begin
    FNew.Delete(FProcessedIndices[i]);
  end;
  FProcessedIndices.Clear;
end;

procedure TGiveSeedFertilizer.FinishMap;
var
  value: Cardinal;
begin
  // Resets the lists for the next map, remaining values stay unconverted.
  for value in FConverted do
  begin
    FNew.Add(value);
  end;
  FConverted.Clear;
end;

constructor TGiveSeedFertilizer.Create;
begin
  FNew := specialize TFPGList<Cardinal>.Create;
  FConverted := specialize TFPGList<Cardinal>.Create;
  FProcessedIndices := specialize TFPGList<Cardinal>.Create;
end;

destructor TGiveSeedFertilizer.Destroy;
begin
  FNew.Free;
  FConverted.Free;
  FProcessedIndices.Free;
  inherited Destroy;
end;

procedure TGiveSeedFertilizer.ProcessDataLine(const ALine: string);
begin
  if LeftStr(ALine, 6) = 'seeds:' then
    ProcessSeeds(ALine)
  else if RightStr(ALine, 4) = 'map:' then
    FinishMap
  else if Aline <> '' then
    ProcessMapRange(ALine);
end;

procedure TGiveSeedFertilizer.Finish;
var
  value: Cardinal;
begin
  FinishMap;
  for value in FNew do
  begin
    if (FPart1 = 0) or (value < FPart1) then
      FPart1 := value;
  end;
end;

function TGiveSeedFertilizer.GetDataFileName: string;
begin
  Result := 'give_seed_fertilizer.txt';
end;

function TGiveSeedFertilizer.GetPuzzleName: string;
begin
  Result := 'Day 5: If You Give A Seed A Fertilizer';
end;

end.