#!/usr/bin/env bash

FILE=input
MAP_WIDTH=$(( $( head -1 "$FILE" | wc -c ) -1 ))
MAP_LEN=$( < "$FILE" wc -l )
read -r -a MAP_ARRAY <<< "$( paste -s -d "" <"$FILE" | sed -E 's/(.)(.)/\1 \2 /g' )"
printf "%s " "${MAP_ARRAY[@]}"
printf "\n"

MAP_SIZE=${#MAP_ARRAY[@]}
for (( i=0; i<MAP_SIZE ; i++ ))
do
  if [[ ${MAP_ARRAY[i]} -eq 0 ]]
  then
    printf "Trailhead found at position %s\n" "$i"
    TRAILHEADS+=( "$i" )
  elif [[ ${MAP_ARRAY[i]} -eq 9 ]]
  then
    printf "Peak found at position %s\n" "$i"
    PEAKS+=( "$i" )
  fi
done
printf "%s " "${TRAILHEADS[@]}"
printf "\n"
printf "%s " "${PEAKS[@]}"
printf "\n"

get_nine () {

  # Trails are explored areas
  # Paths are areas to explore
  GET_NUM=$1
  DIRECTIONS=$2
  TRAIL=$3
  COMBINATIONS=()

  # For each direction, get multiplication of prime number
  # corresponding to each direction
  # Modulus for valid directions is 0
  # 2 : Up
  # 3 : Down
  # 7 : Left
  # 13 : Right
  if [[ $(( DIRECTIONS % 2 )) -eq 0 ]] 
  then
    INDEX=$(( TRAIL - MAP_WIDTH ))
    if [[ ${MAP_ARRAY[INDEX]} -eq $GET_NUM ]]
    then
      COMBINATIONS+=( "$INDEX" )
    fi
  fi
  if [[ $(( DIRECTIONS % 3 )) -eq 0 ]] 
  then
    INDEX=$(( TRAIL + MAP_WIDTH ))
    if [[ ${MAP_ARRAY[INDEX]} -eq $GET_NUM ]]
    then
      COMBINATIONS+=( "$INDEX" )
    fi
  fi
  if [[ $(( DIRECTIONS % 7 )) -eq 0 ]] 
  then
    INDEX=$(( TRAIL - 1 ))
    if [[ ${MAP_ARRAY[INDEX]} -eq $GET_NUM ]]
    then
      COMBINATIONS+=( "$INDEX" )
    fi
  fi
  if [[ $(( DIRECTIONS % 13 )) -eq 0 ]]
  then
    INDEX=$(( TRAIL + 1 ))
    if [[ ${MAP_ARRAY[INDEX]} -eq $GET_NUM ]]
    then
      COMBINATIONS+=( "$INDEX" )
    fi
  fi
  printf "Get: %s \n" "$GET_NUM" >&2
  printf "trail: %s \n" "$TRAIL" >&2
  printf "neighbors found : %s \n" "${COMBINATIONS[@]}" >&2

  # Check if the end has been reached
  # or no matching neighbors
  if [[ $GET_NUM -eq 9 ]] || [[ ${#COMBINATIONS[@]} -eq 0 ]]
  then
    # Exit recursion
    printf "%s" "${#COMBINATIONS[@]}"
    return
  fi

  # Recurse
  TOTAL=0
  NEXT_NUM=$(( GET_NUM+=1 ))
  for INDEX in "${COMBINATIONS[@]}"
  do
    COUNT=$( 
      get_nine \
        "$NEXT_NUM" \
	"$( get_valid_neighbors "$INDEX" )" \
	"$INDEX" 
    )
    (( TOTAL+=COUNT ))
  done
  printf "%s" "$TOTAL"
}

get_valid_neighbors () {

  IDX=$1
  NUM=1

  # Basically check for bounds
  # For each direction, get multiplication of prime number
  # corresponding to each direction
  # 2 : Up
  # 3 : Down
  # 7 : Left
  # 13 : Right
  if [[ $(( IDX / MAP_LEN )) -gt 0 ]]
  then
    (( NUM*=2 ))
  fi
  if [[ $(( IDX / MAP_LEN )) -le $MAP_LEN ]]
  then
    (( NUM*=3 ))
  fi
  if [[ $(( IDX % MAP_WIDTH )) -ne 0 ]]
  then
    (( NUM*=7 ))
  fi
  if [[ $(( IDX % MAP_WIDTH )) -ne $(( MAP_WIDTH - 1 )) ]]
  then
    (( NUM*=13 ))
  fi

  printf "%s" "$NUM"
}

PATH_COUNT=0
ITER=999999
for TRAILHEAD in "${TRAILHEADS[@]}"
do
  COUNT=$( get_nine "1" "$( get_valid_neighbors "$TRAILHEAD" )" "$TRAILHEAD" )
  (( PATH_COUNT+=COUNT ))
  (( ITER-- ))
  if [[ $ITER -eq 0 ]] ;then break; fi
done

printf "%s\n" "$PATH_COUNT"