package com.androidsmsretriever

import android.content.Context
import android.content.ContextWrapper
import android.content.pm.PackageManager
import android.util.Base64
import android.util.Log
import java.nio.charset.StandardCharsets
import java.security.MessageDigest
import java.security.NoSuchAlgorithmException
import java.util.*

/**
 * This is a helper class to generate your message hash to be included in your SMS message.
 *
 *
 * Without the correct hash, your app won't recieve the message callback. This only needs to be
 * generated once per app and stored. Then you can remove this helper class from your code.
 */
class AppSignatureHelper(context: Context?) :
  ContextWrapper(context) {// Get all package signatures for the current package
  // For each signature create a compatible hash
  /**
   * Get all the app signatures for the current package
   *
   * @return
   */
  @get:Throws(PackageManager.NameNotFoundException::class)
  val appSignatures: ArrayList<String>
    get() {
      val appCodes = ArrayList<String>()
      // Get all package signatures for the current package
      val packageName = packageName
      val packageManager = packageManager
      val signatures = if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.P) {
        val packageInfo = packageManager.getPackageInfo(
          packageName,
          PackageManager.GET_SIGNING_CERTIFICATES
        )
        packageInfo.signingInfo?.apkContentsSigners
      } else {
        val packageInfo = packageManager.getPackageInfo(
          packageName,
          PackageManager.GET_SIGNATURES
        )
        packageInfo.signatures
      }
      // For each signature create a compatible hash
      if (signatures != null) {
        for (signature in signatures) {
          val hash = hash(packageName, signature.toCharsString())
          if (hash != null) {
            appCodes.add(String.format("%s", hash))
          }
        }
      }
      return appCodes
    }

  companion object {
    private const val TAG = "AppSignatureHelper"
    private const val HASH_TYPE = "SHA-256"
    private const val NUM_HASHED_BYTES = 9
    private const val NUM_BASE64_CHAR = 11
    private fun hash(packageName: String, signature: String): String? {
      val appInfo = "$packageName $signature"
      try {
        val messageDigest = MessageDigest.getInstance(HASH_TYPE)
        messageDigest.update(appInfo.toByteArray(StandardCharsets.UTF_8))
        var hashSignature = messageDigest.digest()

        // truncated into NUM_HASHED_BYTES
        hashSignature = Arrays.copyOfRange(hashSignature, 0, NUM_HASHED_BYTES)
        // encode into Base64
        var base64Hash =
          Base64.encodeToString(hashSignature, Base64.NO_PADDING or Base64.NO_WRAP)
        base64Hash = base64Hash.substring(0, NUM_BASE64_CHAR)
        Log.d(TAG, String.format("pkg: %s -- hash: %s", packageName, base64Hash))
        return base64Hash
      } catch (e: NoSuchAlgorithmException) {
        Log.e(TAG, "hash:NoSuchAlgorithm", e)
      }
      return null
    }
  }
}