#!/usr/bin/env bash

FILE=input
# Sparse sequence
read -r -a SPARSE_ARRAY <<< "$(
  INDEX=0
  FILE_ID=0
  while read -r CHAR
  do
    if [[ $(( INDEX % 2 )) -eq 0 ]]
    then
      for (( i=1; i<=CHAR; i++ )) do printf "%s " "$FILE_ID"
      done
      (( FILE_ID++ ))
    else
      for (( i=1; i<=CHAR; i++ ))
      do
        printf ". "
      done
    fi
    (( INDEX++ ))
  done <<< "$( sed -E 's/(.)/\1\n/g' "$FILE" | grep -v '^$' )"
)"
printf "%s" "${SPARSE_ARRAY[@]}"
printf "\n"
printf "Sparse array len: %s\n" "${#SPARSE_ARRAY[@]}"
SHADOW_ARRAY=( "${SPARSE_ARRAY[@]}" )

# Start by working backwards
j=$(( ${#SPARSE_ARRAY[@]} - 1 )) # Moveable index since file blocks jump
k=0 # SHADOW_ARRAY cursor
while [[ $j -ge 0 ]]
do
  if [[ ${SPARSE_ARRAY[j]} != '.' ]] 
  then

    # Get file size
    FILE_SIZE=0
    ID=${SPARSE_ARRAY[j]}
    while [[ ${SPARSE_ARRAY[j]} == "$ID" ]]
    do
      (( FILE_SIZE++ ))
      (( j-- ))
    done
    printf "File ID: %s, File size: %s\n" "$ID" "$FILE_SIZE" 2>&1

    # Search for available contiguous space
    # Search from start until the file itself
    k=0
    while [[ $k -lt $(( j - FILE_SIZE )) ]] 
    do
      CONT_SPACE=0

      # Skip ahead until first match of space
      while [[ ${SHADOW_ARRAY[k]} != "." ]]
      do
        (( k++ ))
      done

      # Space found, now get contiguous length
      while [[ ${SHADOW_ARRAY[k]} == '.' ]]
      do
        (( CONT_SPACE++ ))
        (( k++ ))
      done
      
      # Space length is ok, can proceed
      if [[ $FILE_SIZE -le $CONT_SPACE ]] ;then break; fi
    done

    # Can proceed
    if [[ $FILE_SIZE -le $CONT_SPACE ]]
    then
      # Move the file to the contiguous space
      (( k-= CONT_SPACE ))
      while [[ $FILE_SIZE -gt 0 ]]
      do
        SHADOW_ARRAY[k]=$ID
        SHADOW_ARRAY[j+FILE_SIZE]='.'
	(( k++ ))
        (( FILE_SIZE-- ))
      done
    else
      # Skip the file
      continue
    fi
  else
    (( j-- ))
  fi
done
printf "%s" "${SHADOW_ARRAY[@]}"
printf "\n"

# Generate checksum for sparse array
CHECKSUM=0
for (( i=0; i<${#SHADOW_ARRAY[@]}; i++ ))
do
  if [[ ${SHADOW_ARRAY[i]} != "." ]] ;then (( CHECKSUM += i * SHADOW_ARRAY[i] )); fi
done
printf "%s" "$CHECKSUM"