#!/usr/bin/env bash

set -o errexit
set -o nounset
set -o pipefail
if [[ "${TRACE-0}" == "1" ]]; then
  set -o xtrace
fi

cd "$(dirname "$0")"

INPUT_FILE="$1"

get_seed_pairs ()
{
  IFS=" " read -r -a seeds <<< "$(grep seeds "${INPUT_FILE}" | cut -d ' ' -f 2-)"
  seed_count="${#seeds[@]}"
  pairs=$((seed_count/2))
  for ((i=0; i<pairs; i++)); do
    j=$((i*2))
    k=$((i*2+1))
    seed_pairs[${seeds[${j}]}]="${seeds[${k}]}"
  done
}

gen_map ()
{
  # Generates files for given index of map in input file.
  local paragraph map_name map_content
  paragraph=$(($1+1)) # number of paragraph in input file
  map_name=$(awk -v RS= "{if(NR == ${paragraph}) print}" "${INPUT_FILE}" | head -n 1 | cut -d ' ' -f 1)
  map_content=$(awk -v RS= "{if(NR == ${paragraph}) print}" "${INPUT_FILE}"| tail -n +2)
  echo "${map_content}" > "${map_name}.map"
  maps+=("${map_name}.map")
}

map_seed ()
{
  # Usage: map_seed MAP_FILE SEED_NUMBER
  # Prints the mapping of the seed number in the give map.
  local map seed dest_start source_start length diff
  map="$1"
  seed="$2"
  while read -r line; do
    dest_start=$(cut -d ' ' -f 1 <<< "${line}")
    source_start=$(cut -d ' ' -f 2 <<< "${line}")
    length=$(cut -d ' ' -f 3 <<< "${line}")
    if [[ ${seed} -ge ${source_start} && ${seed} -le $((source_start+length-1)) ]]; then
      diff=$((seed-source_start))
      echo -n $((dest_start+diff))
      return
    fi
  done < "${map}"
  echo -n "${seed}" # no mapping
}

main ()
{
  declare -A seed_pairs=()
  declare -a maps=()
  local map_count destination lowest length seed
  get_seed_pairs
  map_count=$(awk -v RS= 'END {print NR}' "${INPUT_FILE}")
  map_count=$((map_count-1)) # one of the paragraphs in the file is seeds
  for ((i=1; i<=map_count; i++)); do
    gen_map "${i}"
  done
  lowest=''
  for s in "${!seed_pairs[@]}"; do
    length=${seed_pairs[${s}]}
    echo "running from start ${s} length ${length}"
    for ((z=0; z<length; z++)); do
      y=$((s+z))
      destination=''
      for map in "${maps[@]}"; do
        if [[ -z ${destination} ]]; then
          destination=$(map_seed "${map}" "${y}")
        else
          destination=$(map_seed "${map}" "${destination}")
        fi
      done
      if [[ -z ${lowest} ]]; then
        lowest="${destination}"
      elif [[ ${destination} -lt ${lowest} ]]; then
        lowest="${destination}"
      fi
      echo "iteration ${z} seed ${y} destination ${destination}"
    done
    echo "interim lowest: ${lowest}"
  done
  echo "${lowest}"
  rm -f ./*.map
}

main