{
  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 ADestinationStart, ASourceStart, ALength: Cardinal);
    function TryConvert(const AInput: Cardinal; out OOutput: Cardinal): Boolean;
  end;

  { TAlmanacMap }

  TAlmanacMap = class
  private
    FRanges: specialize TFPGObjectList<TAlmanacMapRange>;
  public
    constructor Create;
    destructor Destroy; override;
    procedure AddMapRange(const ALine: string);
    function Convert(const AInput: Cardinal): Cardinal;
  end;

  { TGiveSeedFertilizer }

  TGiveSeedFertilizer = class(TSolver)
  private
    FSeeds: specialize TFPGList<Cardinal>;
    FMaps: specialize TFPGObjectList<TAlmanacMap>;
    procedure ProcessSeeds(const ALine: string);
  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 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;

{ TAlmanacMap }

constructor TAlmanacMap.Create;
begin
  FRanges := specialize TFPGObjectList<TAlmanacMapRange>.Create;
end;

destructor TAlmanacMap.Destroy;
begin
  FRanges.Free;
  inherited Destroy;
end;

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

function TAlmanacMap.Convert(const AInput: Cardinal): Cardinal;
var
  range: TAlmanacMapRange;
begin
  for range in FRanges do
  begin
    if range.TryConvert(AInput, Result) then
      Exit;
  end;

  Result := AInput;
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
    FSeeds.Add(StrToDWord(split[i]));
  end;
end;

constructor TGiveSeedFertilizer.Create;
begin
  FSeeds := specialize TFPGList<Cardinal>.Create;
  FMaps := specialize TFPGObjectList<TAlmanacMap>.Create;
end;

destructor TGiveSeedFertilizer.Destroy;
begin
  FSeeds.Free;
  FMaps.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
    FMaps.Add(TAlmanacMap.Create)
  else if Aline <> '' then
    FMaps.Last.AddMapRange(ALine);
end;

procedure TGiveSeedFertilizer.Finish;
var
  seed, value: Cardinal;
  map: TAlmanacMap;
begin
  for seed in FSeeds do
  begin
    value := seed;
    for map in FMaps do
    begin
      value := map.Convert(value);
    end;
    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.