#!/usr/bin/env bash
set -euo pipefail

read -r INPUT

error() {
  echo "{\"error\":\"$1\"}"
  exit 0
}

A=$(echo "$INPUT" | jq -r '.a // empty')
OP=$(echo "$INPUT" | jq -r '.op // empty')
B=$(echo "$INPUT" | jq -r '.b // empty')

[[ -z "$A" || -z "$OP" || -z "$B" ]] && error "missing parameter"

is_number='^-?[0-9]+([.][0-9]+)?$'
[[ ! "$A" =~ $is_number ]] && error "a is not a number"
[[ ! "$B" =~ $is_number ]] && error "b is not a number"

case "$OP" in
  "+") RESULT=$(echo "$A + $B" | bc) ;;
  "-") RESULT=$(echo "$A - $B" | bc) ;;
  "*") RESULT=$(echo "$A * $B" | bc) ;;
  "/")
    [[ "$(echo "$B == 0" | bc)" -eq 1 ]] && error "division by zero"
    RESULT=$(echo "scale=10; $A / $B" | bc)
    ;;
  *) error "unsupported operator" ;;
esac

echo "{\"result\": $RESULT}"