{ lib, utils, ... }:
with lib;
with builtins;
with utils;
let
  disk = map toIntBase10 (stringToCharacters (head (readLines ./input)));
  files = genList (id:
    let baseIndex = id * 2;
    in {
      size = elemAt disk baseIndex;
      freeAfter = if (baseIndex + 1) < (length disk) then
        elemAt disk (baseIndex + 1)
      else
        0;
      inherit id;
    }) ((length disk) / 2 + 1);

  totalSize = listSumWith (getAttr "size") files;
  # totalFree = listSumWith (getAttr "freeAfter") files;

  diskExpanded = concatLists (map
    (f: (genList (const f.id) f.size) ++ (genList (const null) f.freeAfter))
    files);
  # diskSemiExpanded = concatLists (map (f: [ (genList (const f.id) f.size) f.freeAfter ]) files);

  toMove = reverseList (filter (invert isNull) (drop totalSize diskExpanded));
  # base = take totalSize diskExpanded;

  compress = files': toMove':
    let f = head files';
    in if toMove' == [ ] then
      (genList (const f.id) f.size)
    else
      (genList (const f.id) f.size) ++ (take f.freeAfter toMove')
      ++ (compress (tail files') (drop f.freeAfter toMove'));

  compressed = take totalSize (compress files toMove);
  # compressed = compress files toMove;

  checksum = imap0 mul compressed;

in {
  # part1 = listSum checksum;
  # inherit files;
  # test = listSumLog (sublist 0 50000 checksum);
  part1 = listSumLog checksum;
  # inherit chunks;
  # inherit compressed;
  # lenCompressed = length compressed;
  # compressedHead = head compressed;
  # inherit totalSize totalFree;
  # inherit diskExpanded;
  # moveLen = length toMove;
  # nullsInBase = count isNull base;
  # inherit disk;
  # sumTest = listSumLog [1 2 3 4 5];

  diskSize = listSum disk; # TOO DAMN LARGE FOR LINEAR RECURSION!
  fileCount = length files; # TOO DAMN LARGE FOR LINEAR RECURSION!
}