zcash-android-wallet-sdk/sdk-lib/src/main/java/cash/z/ecc/android/sdk/internal/transaction/WalletTransactionEncoder.kt

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

import cash.z.ecc.android.sdk.db.entity.EncodedTransaction
import cash.z.ecc.android.sdk.exception.TransactionEncoderException
import cash.z.ecc.android.sdk.ext.masked
import cash.z.ecc.android.sdk.internal.twig
import cash.z.ecc.android.sdk.internal.twigTask
import cash.z.ecc.android.sdk.jni.RustBackend
import cash.z.ecc.android.sdk.jni.RustBackendWelding
import cash.z.ecc.android.sdk.internal.SaplingParamTool
import cash.z.ecc.android.sdk.internal.SdkDispatchers
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.withContext

/**
 * Class responsible for encoding a transaction in a consistent way. This bridges the gap by
 * behaving like a stateless API so that callers can request [createTransaction] and receive a
 * result, even though there are intermediate database interactions.
 *
 * @property rustBackend the instance of RustBackendWelding to use for creating and validating.
 * @property repository the repository that stores information about the transactions being created
 * such as the raw bytes and raw txId.
 */
class WalletTransactionEncoder(
    private val rustBackend: RustBackendWelding,
    private val repository: TransactionRepository
) : TransactionEncoder {

    /**
     * Creates a transaction, throwing an exception whenever things are missing. When the provided
     * wallet implementation doesn't throw an exception, we wrap the issue into a descriptive
     * exception ourselves (rather than using double-bangs for things).
     *
     * @param spendingKey the key associated with the notes that will be spent.
     * @param zatoshi the amount of zatoshi to send.
     * @param toAddress the recipient's address.
     * @param memo the optional memo to include as part of the transaction.
     * @param fromAccountIndex the optional account id to use. By default, the 1st account is used.
     *
     * @return the successfully encoded transaction or an exception
     */
    override suspend fun createTransaction(
        spendingKey: String,
        zatoshi: Long,
        toAddress: String,
        memo: ByteArray?,
        fromAccountIndex: Int
    ): EncodedTransaction = withContext(SdkDispatchers.IO) {
        val transactionId = createSpend(spendingKey, zatoshi, toAddress, memo)
        repository.findEncodedTransactionById(transactionId)
            ?: throw TransactionEncoderException.TransactionNotFoundException(transactionId)
    }

    override suspend fun createShieldingTransaction(
        spendingKey: String,
        transparentSecretKey: String,
        memo: ByteArray?
    ): EncodedTransaction = withContext(SdkDispatchers.IO) {
        val transactionId = createShieldingSpend(spendingKey, transparentSecretKey, memo)
        repository.findEncodedTransactionById(transactionId)
            ?: throw TransactionEncoderException.TransactionNotFoundException(transactionId)
    }

    /**
     * Utility function to help with validation. This is not called during [createTransaction]
     * because this class asserts that all validation is done externally by the UI, for now.
     *
     * @param address the address to validate
     *
     * @return true when the given address is a valid z-addr
     */
    override suspend fun isValidShieldedAddress(address: String): Boolean = withContext(Dispatchers.IO) {
        rustBackend.isValidShieldedAddr(address)
    }

    /**
     * Utility function to help with validation. This is not called during [createTransaction]
     * because this class asserts that all validation is done externally by the UI, for now.
     *
     * @param address the address to validate
     *
     * @return true when the given address is a valid t-addr
     */
    override suspend fun isValidTransparentAddress(address: String): Boolean = withContext(Dispatchers.IO) {
        rustBackend.isValidTransparentAddr(address)
    }

    override suspend fun getConsensusBranchId(): Long {
        val height = repository.lastScannedHeight()
        if (height < rustBackend.network.saplingActivationHeight)
            throw TransactionEncoderException.IncompleteScanException(height)
        return rustBackend.getBranchIdForHeight(height)
    }

    /**
     * Does the proofs and processing required to create a transaction to spend funds and inserts
     * the result in the database. On average, this call takes over 10 seconds.
     *
     * @param spendingKey the key associated with the notes that will be spent.
     * @param zatoshi the amount of zatoshi to send.
     * @param toAddress the recipient's address.
     * @param memo the optional memo to include as part of the transaction.
     * @param fromAccountIndex the optional account id to use. By default, the 1st account is used.
     *
     * @return the row id in the transactions table that contains the spend transaction or -1 if it
     * failed.
     */
    private suspend fun createSpend(
        spendingKey: String,
        zatoshi: Long,
        toAddress: String,
        memo: ByteArray? = byteArrayOf(),
        fromAccountIndex: Int = 0
    ): Long = withContext(Dispatchers.IO) {
        twigTask(
            "creating transaction to spend $zatoshi zatoshi to" +
                " ${toAddress.masked()} with memo $memo"
        ) {
            try {
                val branchId = getConsensusBranchId()
                SaplingParamTool.ensureParams((rustBackend as RustBackend).pathParamsDir)
                twig("params exist! attempting to send with consensus branchId $branchId...")
                rustBackend.createToAddress(
                    branchId,
                    fromAccountIndex,
                    spendingKey,
                    toAddress,
                    zatoshi,
                    memo
                )
            } catch (t: Throwable) {
                twig("${t.message}")
                throw t
            }
        }.also { result ->
            twig("result of sendToAddress: $result")
        }
    }

    private suspend fun createShieldingSpend(
        spendingKey: String,
        transparentSecretKey: String,
        memo: ByteArray? = byteArrayOf()
    ): Long = withContext(Dispatchers.IO) {
        twigTask("creating transaction to shield all UTXOs") {
            try {
                SaplingParamTool.ensureParams((rustBackend as RustBackend).pathParamsDir)
                twig("params exist! attempting to shield...")
                rustBackend.shieldToAddress(
                    spendingKey,
                    transparentSecretKey,
                    memo
                )
            } catch (t: Throwable) {
                // TODO: if this error matches: Insufficient balance (have 0, need 1000 including fee)
                // then consider custom error that says no UTXOs existed to shield
                twig("Shield failed due to: ${t.message}")
                throw t
            }
        }.also { result ->
            twig("result of shieldToAddress: $result")
        }
    }
}