/*
 * Copyright 2019 Allan Wang
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.pitchedapps.frost.utils

import android.content.Context
import android.hardware.fingerprint.FingerprintManager
import android.os.Build
import androidx.biometric.BiometricPrompt
import androidx.fragment.app.FragmentActivity
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent
import ca.allanwang.kau.utils.string
import com.pitchedapps.frost.R
import com.pitchedapps.frost.prefs.Prefs
import java.util.concurrent.Executor
import java.util.concurrent.ExecutorService
import java.util.concurrent.Executors
import kotlinx.coroutines.CompletableDeferred

typealias BiometricDeferred = CompletableDeferred<BiometricPrompt.CryptoObject?>

/**
 * Container for [BiometricPrompt]
 * Inspired by coroutine's CommonPool
 */
object BiometricUtils {

    private val executor: Executor
        get() = pool ?: getOrCreatePoolSync()

    @Volatile
    private var pool: ExecutorService? = null

    private var lastUnlockTime = -1L

    private const val UNLOCK_TIME_INTERVAL = 15 * 60 * 1000

    /**
     * Checks if biometric authentication is possible
     * Currently, this means checking for enrolled fingerprints
     */
    @Suppress("DEPRECATION")
    fun isSupported(context: Context): Boolean {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) return false
        val fingerprintManager =
            context.getSystemService(FingerprintManager::class.java) ?: return false
        return fingerprintManager.isHardwareDetected && fingerprintManager.hasEnrolledFingerprints()
    }

    private fun getOrCreatePoolSync(): Executor =
        pool ?: Executors.newSingleThreadExecutor().also { pool = it }

    private fun shouldPrompt(context: Context, prefs: Prefs): Boolean {
        return prefs.biometricsEnabled && System.currentTimeMillis() - lastUnlockTime > UNLOCK_TIME_INTERVAL
    }

    /**
     * Generates a prompt dialog and attempt to return an auth object.
     * Note that the underlying request will call [androidx.fragment.app.FragmentTransaction.commit],
     * so this cannot happen after onSaveInstanceState.
     */
    fun authenticate(
        activity: FragmentActivity,
        prefs: Prefs,
        force: Boolean = false
    ): BiometricDeferred {
        val deferred: BiometricDeferred = CompletableDeferred()
        if (!force && !shouldPrompt(activity, prefs)) {
            deferred.complete(null)
            return deferred
        }
        val info = BiometricPrompt.PromptInfo.Builder()
            .setTitle(activity.string(R.string.biometrics_prompt_title))
            .setNegativeButtonText(activity.string(R.string.kau_cancel))
            .build()
        val prompt = BiometricPrompt(activity, executor, Callback(activity, deferred))
        activity.lifecycle.addObserver(object : LifecycleObserver {
            @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
            fun onPause() {
                if (!deferred.isCompleted) {
                    prompt.cancelAuthentication()
                    deferred.cancel()
                    activity.finish()
                }
                activity.lifecycle.removeObserver(this)
            }
        })
        prompt.authenticate(info)
        return deferred
    }

    private class Callback(val activity: FragmentActivity, val deferred: BiometricDeferred) :
        BiometricPrompt.AuthenticationCallback() {
        override fun onAuthenticationError(errorCode: Int, errString: CharSequence) {
            deferred.cancel()
            activity.finish()
        }

        override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
            lastUnlockTime = System.currentTimeMillis()
            deferred.complete(result.cryptoObject)
        }

        override fun onAuthenticationFailed() {
            deferred.cancel()
            activity.finish()
        }
    }

    /**
     * For completeness we provide a shutdown function.
     * In practice, we initialize the executor only when it is first used,
     * and keep it alive throughout the app lifecycle, as it will be used an arbitrary number of times,
     * with unknown frequency
     */
    @Synchronized
    fun shutdown() {
        pool?.shutdown()
        pool = null
    }
}