package cash.z.ecc.android.sdk.transaction

import android.content.Context
import androidx.room.Room
import androidx.room.RoomDatabase
import cash.z.ecc.android.sdk.db.PendingTransactionDao
import cash.z.ecc.android.sdk.db.PendingTransactionDb
import cash.z.ecc.android.sdk.db.entity.*
import cash.z.ecc.android.sdk.ext.twig
import cash.z.ecc.android.sdk.service.LightWalletService
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.Dispatchers.IO
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.sync.Mutex
import kotlinx.coroutines.sync.withLock
import kotlinx.coroutines.withContext
import java.io.PrintWriter
import java.io.StringWriter
import kotlin.math.max

/**
 * Facilitates persistent attempts to ensure that an outbound transaction is completed.
 *
 * @param db the database where the wallet can freely write information related to pending
 * transactions. This database effectively serves as the mempool for transactions created by this
 * wallet.
 * @property encoder responsible for encoding a transaction by taking all the inputs and returning
 * an [cash.z.ecc.android.sdk.entity.EncodedTransaction] object containing the raw bytes and transaction
 * id.
 * @property service the lightwallet service used to submit transactions.
 */
class PersistentTransactionManager(
    db: PendingTransactionDb,
    internal val encoder: TransactionEncoder,
    private val service: LightWalletService
) : OutboundTransactionManager {

    private val daoMutex = Mutex()

    /**
     * Internal reference to the dao that is only accessed after locking the [daoMutex] in order
     * to enforce DB access in both a threadsafe and coroutinesafe way.
     */
    private val _dao: PendingTransactionDao = db.pendingTransactionDao()

    /**
     * Constructor that creates the database and then executes a callback on it.
     */
    constructor(
        appContext: Context,
        encoder: TransactionEncoder,
        service: LightWalletService,
        dataDbName: String = "PendingTransactions.db"
    ) : this(
        Room.databaseBuilder(
            appContext,
            PendingTransactionDb::class.java,
            dataDbName
        ).setJournalMode(RoomDatabase.JournalMode.TRUNCATE).build(),
        encoder,
        service
    )


    //
    // OutboundTransactionManager implementation
    //

    override suspend fun initSpend(
        zatoshiValue: Long,
        toAddress: String,
        memo: String,
        fromAccountIndex: Int
    ): PendingTransaction = withContext(Dispatchers.IO) {
        twig("constructing a placeholder transaction")
        var tx = PendingTransactionEntity(
            value = zatoshiValue,
            toAddress = toAddress,
            memo = memo.toByteArray(),
            accountIndex = fromAccountIndex
        )
        try {
            safeUpdate("creating tx in DB") {
                tx = findById(create(tx))!!
                twig("successfully created TX in DB with id: ${tx.id}")
            }
        } catch (t: Throwable) {
            twig(
                "Unknown error while attempting to create and fetch pending transaction:" +
                    " ${t.message} caused by: ${t.cause}"
            )
        }

        tx
    }

    override suspend fun applyMinedHeight(pendingTx: PendingTransaction, minedHeight: Int) {
        twig("a pending transaction has been mined!")
        safeUpdate("updating mined height for pending tx id: ${pendingTx.id} to $minedHeight") {
            updateMinedHeight(pendingTx.id, minedHeight)
        }
    }

    override suspend fun encode(
        spendingKey: String,
        pendingTx: PendingTransaction
    ): PendingTransaction = withContext(Dispatchers.IO) {
        twig("managing the creation of a transaction")
        var tx = pendingTx as PendingTransactionEntity
        try {
            twig("beginning to encode transaction with : $encoder")
            val encodedTx = encoder.createTransaction(
                spendingKey,
                tx.value,
                tx.toAddress,
                tx.memo,
                tx.accountIndex
            )
            twig("successfully encoded transaction!")
            safeUpdate("updating transaction encoding") {
                updateEncoding(tx.id, encodedTx.raw, encodedTx.txId, encodedTx.expiryHeight)
            }
        } catch (t: Throwable) {
            val message = "failed to encode transaction due to : ${t.message} caused by: ${t.cause}"
            twig(message)
            safeUpdate("updating transaction error info") {
                updateError(tx.id, message, ERROR_ENCODING)
            }
        } finally {
            safeUpdate("incrementing transaction encodeAttempts (from: ${tx.encodeAttempts})") {
                updateEncodeAttempts(tx.id, max(1, tx.encodeAttempts + 1))
                tx = findById(tx.id)!!
            }
        }

        tx
    }

    override suspend fun submit(pendingTx: PendingTransaction): PendingTransaction = withContext(Dispatchers.IO) {
        // reload the tx to check for cancellation
        var tx = pendingTransactionDao { findById(pendingTx.id) }
            ?: throw IllegalStateException("Error while submitting transaction. No pending" +
                    " transaction found that matches the one being submitted. Verify that the" +
                    " transaction still exists among the set of pending transactions.")
        try {
            // do nothing if failed or cancelled
            when {
                tx.isFailedEncoding() -> twig("Warning: this transaction will not be submitted because it failed to be encoded.")
                tx.isCancelled() -> twig("Warning: ignoring cancelled transaction with id ${tx.id}. We will not submit it to the network because it has been cancelled.")
                else -> {
                    twig("submitting transaction with memo: ${tx.memo} amount: ${tx.value}")
                    val response = service.submitTransaction(tx.raw)
                    val error = response.errorCode < 0
                    twig("${if (error) "FAILURE! " else "SUCCESS!"} submit transaction completed with" +
                            " response: ${response.errorCode}: ${response.errorMessage}")

                    safeUpdate("updating submitted transaction (hadError: $error)") {
                        updateError(tx.id, if (error) response.errorMessage else null, response.errorCode)
                        updateSubmitAttempts(tx.id, max(1, tx.submitAttempts + 1))
                    }
                }
            }
        } catch (t: Throwable) {
            // a non-server error has occurred
            val message =
                "Unknown error while submitting transaction: ${t.message} caused by: ${t.cause}"
            twig(message)
            safeUpdate("updating submission failure") {
                updateError(tx.id, t.message, ERROR_SUBMITTING)
                updateSubmitAttempts(tx.id, max(1, tx.submitAttempts + 1))
            }
        } finally {
            safeUpdate("fetching latest tx info") {
                tx = findById(tx.id)!!
            }
        }

        tx
    }

    override suspend fun monitorById(id: Long): Flow<PendingTransaction> {
        return pendingTransactionDao { monitorById(id) }
    }

    override suspend fun isValidShieldedAddress(address: String) =
        encoder.isValidShieldedAddress(address)

    override suspend fun isValidTransparentAddress(address: String) =
        encoder.isValidTransparentAddress(address)

    override suspend fun cancel(pendingId: Long): Boolean {
        return pendingTransactionDao {
            val tx = findById(pendingId)
            if (tx?.isSubmitted() == true) {
                twig("Attempt to cancel transaction failed because it has already been submitted!")
                false
            } else {
                twig("Cancelling unsubmitted transaction id: $pendingId")
                cancel(pendingId)
                true
            }
        }
    }

    override suspend fun findById(id: Long) = pendingTransactionDao {
        findById(id)
    }

    override suspend fun markForDeletion(id: Long) = pendingTransactionDao {
        withContext(IO) {
            twig("[cleanup] marking pendingTx $id for deletion")
            removeRawTransactionId(id)
            updateError(id, "safe to delete", -9090)
        }
    }

    /**
     * Remove a transaction and pretend it never existed.
     *
     * @return the final number of transactions that were removed from the database.
     */
    override suspend fun abort(existingTransaction: PendingTransaction): Int {
        return pendingTransactionDao {
            twig("[cleanup] Deleting pendingTxId: ${existingTransaction.id}")
            delete(existingTransaction as PendingTransactionEntity)
        }
    }

    override fun getAll() = _dao.getAll()


    //
    // Helper functions
    //


    /**
     * Updating the pending transaction is often done at the end of a function but still should
     * happen within a try/catch block, surrounded by logging. So this helps with that while also
     * ensuring that no other coroutines are concurrently interacting with the DAO.
     */
     private suspend fun <R> safeUpdate(logMessage: String = "", block: suspend PendingTransactionDao.() -> R ): R? {
        return try {
            twig(logMessage)
            pendingTransactionDao { block() }
        } catch (t: Throwable) {
            val stacktrace = StringWriter().also { t.printStackTrace(PrintWriter(it)) }.toString()
            twig(
                "Unknown error while attempting to '$logMessage':" +
                    " ${t.message} caused by: ${t.cause} stacktrace: $stacktrace"
            )
            null
        }
    }


    private suspend fun <T> pendingTransactionDao(block: suspend PendingTransactionDao.() -> T): T {
        return daoMutex.withLock {
            withContext(IO) {
                _dao.block()
            }
        }
    }

    companion object {
        /** Error code for an error while encoding a transaction */
        const val ERROR_ENCODING = 2000
        /** Error code for an error while submitting a transaction */
        const val ERROR_SUBMITTING = 3000
    }
}