package com.RNAppleAuthentication

import android.webkit.JavascriptInterface

/**
 * [JavascriptInterface] to be injected in a WebView (with name [NAME], see [WebView.addJavascriptInterface]) that
 * receives the "form_data" from a web page (triggered by [JS_TO_INJECT]) and analyzes the 2 expected fields from apple
 * authentication:
 * - [STATE] : a _nonce_ string set in [AuthenticationAttempt.create] that needs to match [expectedState];
 * - [CODE] : the authorization code that'll be used to authenticate the user.
 *
 * @author Khaled O. Shamieh <khaled.shamieh@gmail.com>
 */
class FormInterceptorInterface(private val expectedState: String, private val callback: (SignInWithAppleResult) -> Unit) {
  @JavascriptInterface
  fun processFormData(formData: String) {
    val values = formData.split(FORM_DATA_SEPARATOR)
    val tokenEncoded = values.find { it.startsWith(TOKEN) }
    val codeEncoded = values.find { it.startsWith(CODE) }
    val stateEncoded = values.find { it.startsWith(STATE) }
    val userEncoded = values.find { it.startsWith(USER) }

    if (stateEncoded != null && (codeEncoded != null || tokenEncoded != null || userEncoded != null)) {
      val stateValue = stateEncoded.substringAfter(KEY_VALUE_SEPARATOR)
      val codeValue = codeEncoded?.substringAfter(KEY_VALUE_SEPARATOR)
      val tokenValue = tokenEncoded?.substringAfter(KEY_VALUE_SEPARATOR)
      val userValue = userEncoded?.substringAfter(KEY_VALUE_SEPARATOR)

      if (stateValue == expectedState) {
        callback(SignInWithAppleResult.Success(codeValue ?: "", tokenValue ?: "", stateValue, userValue ?: ""))
      } else {
        callback(SignInWithAppleResult.Failure(IllegalArgumentException("state does not match")))
      }
    } else {
      // Error, couldn't find the required info.
      callback(SignInWithAppleResult.Cancel)
    }
  }

  companion object {
    const val NAME = "FormInterceptorInterface"
    private const val STATE = "state"
    private const val CODE = "code"
    private const val TOKEN = "id_token"
    private const val USER = "user"
    private const val FORM_DATA_SEPARATOR = "|"
    private const val KEY_VALUE_SEPARATOR = "="

    /**
     * This piece of Javascript code fetches all (key, value) attributes from the site's form data and concatenates
     * them in the form: "key [KEY_VALUE_SEPARATOR] value [FORM_DATA_SEPARATOR]".
     * Then, invokes the method [processFormData] on the app's side (that's exposed to Javascript) so that the form
     * data can be analyzed in the app's context.
     */
    val JS_TO_INJECT =
      """
        function parseForm(form){

            var values = '';
            for(var i=0 ; i< form.elements.length; i++){
                values +=
                    form.elements[i].name +
                    '$KEY_VALUE_SEPARATOR' +
                    form.elements[i].value +
                    '$FORM_DATA_SEPARATOR'
            }
            $NAME.processFormData(values);
        }


        for(var i=0 ; i< document.forms.length ; i++){
            parseForm(document.forms[i]);
        }
      """.trimIndent()
  }
}