/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package mozilla.components.service.sync.logins

import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Deferred
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.async
import kotlinx.coroutines.launch
import mozilla.components.concept.storage.Login
import mozilla.components.concept.storage.LoginStorageDelegate
import mozilla.components.concept.storage.LoginValidationDelegate
import mozilla.components.concept.storage.LoginsStorage

/**
 * [LoginStorageDelegate] implementation.
 *
 * An abstraction that handles the persistence and retrieval of [LoginEntry]s so that Gecko doesn't
 * have to.
 *
 * In order to use this class, attach it to the active [GeckoRuntime] as its `loginStorageDelegate`.
 * It is not designed to work with other engines.
 *
 * This class is part of a complex flow integrating Gecko and Application Services code, which is
 * described here:
 *
 * - GV finds something on a page that it believes could be autofilled
 * - GV calls [onLoginFetch]
 *   - We retrieve all [Login]s with matching domains (if any) from [loginStorage]
 *   - We return these [Login]s to GV
 * - GV autofills one of the returned [Login]s into the page
 *   - GV calls [onLoginUsed] to let us know which [Login] was used
 * - User submits their credentials
 * - GV detects something that looks like a login submission
 *   - ([GeckoLoginStorageDelegate] is not involved with this step) A prompt is shown to the user,
 *   who decides whether or not to save the [Login]
 *     - If the user declines, break
 *   - GV calls [onLoginSave] with a [Login]
 *     - If this [Login] was autofilled, it is updated with new information but retains the same
 *     [Login.guid]
 *     - If this is a new [Login], its [Login.guid] will be an empty string
 *   - We [CREATE] or [UPDATE] the [Login] in [loginStorage]
 *     - If [CREATE], [loginStorage] generates a new guid for it
 */
class GeckoLoginStorageDelegate(
    private val loginStorage: Lazy<LoginsStorage>,
    private val scope: CoroutineScope = CoroutineScope(Dispatchers.IO)
) : LoginStorageDelegate {

    override fun onLoginUsed(login: Login) {
        val guid = login.guid
        // If the guid is null, we have no way of associating the login with any record in the DB
        if (guid == null || guid.isEmpty()) return
        scope.launch {
            loginStorage.value.touch(guid)
        }
    }

    override fun onLoginFetch(domain: String): Deferred<List<Login>> {
        return scope.async {
            loginStorage.value.getByBaseDomain(domain)
        }
    }

    @Synchronized
    override fun onLoginSave(login: Login) {
        val validationDelegate = DefaultLoginValidationDelegate(storage = loginStorage)
        scope.launch {
            when (val result = validationDelegate.ensureValidAsync(login).await()) {
                is LoginValidationDelegate.Result.CanBeUpdated -> {
                    loginStorage.value.update(result.foundLogin)
                }
                LoginValidationDelegate.Result.CanBeCreated -> {
                    // If an existing Login was autofilled, we want to clear its guid to
                    // avoid updating its record
                    loginStorage.value.add(login.copy(guid = null))
                }
                else -> {
                    // There was an error, do not attempt to save/update
                }
            }
        }
    }
}
