require "http/client"
require "json"

module Deepl
  class ApiKeyError < Exception; end
  class RequestError < Exception; end

  class Translator
    API_ENDPOINT = "https://api-free.deepl.com/v2/translate"

    @http_headers : HTTP::Headers

    def initialize
      @http_headers = build_http_headers
    end

    def build_http_headers
      HTTP::Headers{
        "Authorization" => "DeepL-Auth-Key #{get_api_key}",
        "Content-Type"  => "application/x-www-form-urlencoded",
      }
    end

    def get_api_key
      if ENV.has_key?("DEEPL_API_KEY")
        ENV["DEEPL_API_KEY"]
      else
        raise ApiKeyError.new
      end
    end

    def request_translation(text : String, target_lang : String)
      request_payload = "text=#{URI.encode_www_form(text)}&target_lang=#{URI.encode_www_form(target_lang)}"
      send_post_request(request_payload)
    end

    def send_post_request(request_data : String)
      HTTP::Client.post(API_ENDPOINT, body: request_data, headers: @http_headers)
    rescue error
      raise RequestError.new("Error: #{error} #{error.message}")
    end

    def translate(text, target_lang)
      response = request_translation(text, target_lang)
      parsed_response = JSON.parse(response.body)
      parsed_response.dig("translations", 0, "text")
    end
  end
end

{
  "translations": [
    {
      "detected_source_language": "EN",
      "text": "Hallo, Welt!"
    }
  ]
}

input_text = ARGV[0]
target_lang = "ZH"

translator = Deepl::Translator.new
translated_text = translator.translate(input_text, target_lang)

puts translated_text

./deepl Hello.
你好。