#!/usr/bin/env bash
#github.com/fsaintjacques/semver-tool

NAT='0|[1-9][0-9]*'
ALPHANUM='[0-9]*[A-Za-z-][0-9A-Za-z-]*'
IDENT="$NAT|$ALPHANUM"
FIELD='[0-9A-Za-z-]+'
SEMVER_REGEX="\
^[vV]?\
($NAT)\\.($NAT)\\.($NAT)\
(\\-(${IDENT})(\\.(${IDENT}))*)?\
(\\+${FIELD}(\\.${FIELD})*)?$"

function validate_version {
  local version=$1
  if [[ "$version" =~ $SEMVER_REGEX ]]; then
    if [ "$#" -eq "2" ]; then
      local major=${BASH_REMATCH[1]}
      local minor=${BASH_REMATCH[2]}
      local patch=${BASH_REMATCH[3]}
      local prere=${BASH_REMATCH[4]}
      local build=${BASH_REMATCH[8]}
      eval "$2=(\"$major\" \"$minor\" \"$patch\" \"$prere\" \"$build\")"
    else
      echo "$version"
    fi
  fi
}

function is_nat {
  [[ "$1" =~ ^($NAT)$ ]]
}

function is_null {
  [ -z "$1" ]
}

function order_nat {
  [ "$1" -lt "$2" ] && {
    echo -1
    return
  }
  [ "$1" -gt "$2" ] && {
    echo 1
    return
  }
  echo 0
}

function order_string {
  [[ $1 < $2 ]] && {
    echo -1
    return
  }
  [[ $1 > $2 ]] && {
    echo 1
    return
  }
  echo 0
}

function compare_fields {
  local l="$1[@]"
  local r="$2[@]"
  local leftfield=("${!l}")
  local rightfield=("${!r}")
  local left
  local right
  local i=$((-1))
  local order=$((0))
  while true; do
    [ $order -ne 0 ] && {
      echo $order
      return
    }
    : $((i++))
    left="${leftfield[$i]}"
    right="${rightfield[$i]}"

    is_null "$left" && is_null "$right" && {
      echo 0
      return
    }
    is_null "$left" && {
      echo -1
      return
    }
    is_null "$right" && {
      echo 1
      return
    }
    is_nat "$left" && is_nat "$right" && {
      order=$(order_nat "$left" "$right")
      continue
    }
    is_nat "$left" && {
      echo -1
      return
    }
    is_nat "$right" && {
      echo 1
      return
    }
    {
      order=$(order_string "$left" "$right")
      continue
    }
  done
}

# shellcheck disable=SC2206
function compare_version {
  local order
  validate_version "$1" V
  validate_version "$2" V_
  local left=("${V[0]}" "${V[1]}" "${V[2]}")
  local right=("${V_[0]}" "${V_[1]}" "${V_[2]}")

  order=$(compare_fields left right)
  [ "$order" -ne 0 ] && {
    echo "$order"
    return
  }
  local prerel="${V[3]:1}"
  local prerel_="${V_[3]:1}"
  local left=(${prerel//./ })
  local right=(${prerel_//./ })
  [ -z "$prerel" ] && [ -z "$prerel_" ] && {
    echo 0
    return
  }
  [ -z "$prerel" ] && {
    echo 1
    return
  }
  [ -z "$prerel_" ] && {
    echo -1
    return
  }
  compare_fields left right
}

function command_compare {
  local v
  local v_
  v=$(validate_version "$1")
  v_=$(validate_version "$2")
  set +u
  compare_version "$v" "$v_"
}