/*
 * This file is part of LibEuFin.
 * Copyright (C) 2023 Taler Systems S.A.
 *
 * LibEuFin is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation; either version 3, or
 * (at your option) any later version.
 *
 * LibEuFin 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 Affero General
 * Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public
 * License along with LibEuFin; see the file COPYING.  If not, see
 * <http://www.gnu.org/licenses/>
 */

package tech.libeufin.common

import com.zaxxer.hikari.HikariConfig
import com.zaxxer.hikari.HikariDataSource
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.withContext
import org.postgresql.ds.PGSimpleDataSource
import org.postgresql.jdbc.PgConnection
import org.postgresql.util.PSQLState
import org.slf4j.Logger
import org.slf4j.LoggerFactory
import java.net.URI
import java.nio.file.Path
import java.sql.PreparedStatement
import java.sql.ResultSet
import java.sql.SQLException
import kotlin.io.path.Path
import kotlin.io.path.exists
import kotlin.io.path.readText

fun getCurrentUser(): String = System.getProperty("user.name")

private val logger: Logger = LoggerFactory.getLogger("libeufin-db")

// Check GANA (https://docs.gnunet.org/gana/index.html) for numbers allowance.

/**
 * This function converts postgresql:// URIs to JDBC URIs.
 *
 * URIs that are already jdbc: URIs are passed through.
 *
 * This avoids the user having to create complex JDBC URIs for postgres connections.
 * They are especially complex when using unix domain sockets, as they're not really
 * supported natively by JDBC.
 */
fun getJdbcConnectionFromPg(pgConn: String): String {
    // Pass through jdbc URIs.
    if (pgConn.startsWith("jdbc:")) {
        return pgConn
    }
    if (!pgConn.startsWith("postgresql://") && !pgConn.startsWith("postgres://")) {
        throw Exception("Not a Postgres connection string: $pgConn")
    }
    var maybeUnixSocket = false
    val parsed = URI(pgConn)
    val hostAsParam: String? = if (parsed.query != null) {
        getQueryParam(parsed.query, "host")
    } else {
        null
    }
    /**
     * In some cases, it is possible to leave the hostname empty
     * and specify it via a query param, therefore a "postgresql:///"-starting
     * connection string does NOT always mean Unix domain socket.
     * https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING
     */
    if (parsed.host == null &&
        (hostAsParam == null || hostAsParam.startsWith('/'))
    ) {
        maybeUnixSocket = true
    }
    if (maybeUnixSocket) {
        // Check whether the database user should differ from the process user.
        var pgUser = getCurrentUser()
        if (parsed.query != null) {
            val maybeUserParam = getQueryParam(parsed.query, "user")
            if (maybeUserParam != null) pgUser = maybeUserParam
        }
        // Check whether the Unix domain socket location was given non-standard.
        val socketLocation = hostAsParam ?: "/var/run/postgresql/.s.PGSQL.5432"
        if (!socketLocation.startsWith('/')) {
            throw Exception("PG connection wants Unix domain socket, but non-null host doesn't start with slash")
        }
        return "jdbc:postgresql://localhost${parsed.path}?user=$pgUser&socketFactory=org.newsclub.net.unix." +
                "AFUNIXSocketFactory\$FactoryArg&socketFactoryArg=$socketLocation"
    }
    if (pgConn.startsWith("postgres://")) {
        // The JDBC driver doesn't like postgres://, only postgresql://.
        // For consistency with other components, we normalize the postgres:// URI
        // into one that the JDBC driver likes.
        return "jdbc:postgresql://" + pgConn.removePrefix("postgres://")
    }
    return "jdbc:$pgConn"
}

data class DatabaseConfig(
    val dbConnStr: String,
    val sqlDir: Path
)

fun pgDataSource(dbConfig: String): PGSimpleDataSource {
    val jdbcConnStr = getJdbcConnectionFromPg(dbConfig)
    logger.debug("connecting to database via JDBC string '$jdbcConnStr'")
    val pgSource = PGSimpleDataSource()
    pgSource.setUrl(jdbcConnStr)
    pgSource.prepareThreshold = 1
    return pgSource
}

fun PGSimpleDataSource.pgConnection(): PgConnection {
    val conn = connection.unwrap(PgConnection::class.java)
    // FIXME: bring the DB schema to a function argument.
    conn.execSQLUpdate("SET search_path TO libeufin_bank;")
    return conn
}

fun <R> PgConnection.transaction(lambda: (PgConnection) -> R): R {
    try {
        autoCommit = false
        val result = lambda(this)
        commit()
        autoCommit = true
        return result
    } catch (e: Exception) {
        rollback()
        autoCommit = true
        throw e
    }
}

fun <T> PreparedStatement.oneOrNull(lambda: (ResultSet) -> T): T? {
    executeQuery().use {
        return if (it.next()) lambda(it) else null
    }
}

fun <T> PreparedStatement.one(lambda: (ResultSet) -> T): T =
    requireNotNull(oneOrNull(lambda)) { "Missing result to database query" }

fun <T> PreparedStatement.all(lambda: (ResultSet) -> T): List<T> {
    executeQuery().use {
        val ret = mutableListOf<T>()
        while (it.next()) {
            ret.add(lambda(it))
        }
        return ret
    }
}

fun PreparedStatement.executeQueryCheck(): Boolean {
    executeQuery().use {
        return it.next()
    }
}

fun PreparedStatement.executeUpdateCheck(): Boolean {
    executeUpdate()
    return updateCount > 0
}

/**
 * Helper that returns false if the row to be inserted
 * hits a unique key constraint violation, true when it
 * succeeds.  Any other error (re)throws exception.
 */
fun PreparedStatement.executeUpdateViolation(): Boolean {
    return try {
        executeUpdateCheck()
    } catch (e: SQLException) {
        logger.debug(e.message)
        if (e.sqlState == PSQLState.UNIQUE_VIOLATION.state) return false
        throw e // rethrowing, not to hide other types of errors.
    }
}

fun PreparedStatement.executeProcedureViolation(): Boolean {
    val savepoint = connection.setSavepoint()
    return try {
        executeUpdate()
        connection.releaseSavepoint(savepoint)
        true
    } catch (e: SQLException) {
        connection.rollback(savepoint)
        if (e.sqlState == PSQLState.UNIQUE_VIOLATION.state) return false
        throw e // rethrowing, not to hide other types of errors.
    }
}

// TODO comment
fun PgConnection.dynamicUpdate(
    table: String,
    fields: Sequence<String>,
    filter: String,
    bind: Sequence<Any?>,
) {
    val sql = fields.joinToString()
    if (sql.isEmpty()) return
    prepareStatement("UPDATE $table SET $sql $filter").run {
        for ((idx, value) in bind.withIndex()) {
            setObject(idx + 1, value)
        }
        executeUpdate()
    }
}

/**
 * Only runs versioning.sql if the _v schema is not found.
 *
 * @param conn database connection
 * @param cfg database configuration
 */
fun maybeApplyV(conn: PgConnection, cfg: DatabaseConfig) {
    conn.transaction {
        val checkVSchema = conn.prepareStatement(
            "SELECT schema_name FROM information_schema.schemata WHERE schema_name = '_v'"
        )
        if (!checkVSchema.executeQueryCheck()) {
            logger.debug("_v schema not found, applying versioning.sql")
            val sqlVersioning = Path("${cfg.sqlDir}/versioning.sql").readText()
            conn.execSQLUpdate(sqlVersioning)
        }
    }
}

// sqlFilePrefix is, for example, "libeufin-bank" or "libeufin-nexus" (no trailing dash).
fun initializeDatabaseTables(conn: PgConnection, cfg: DatabaseConfig, sqlFilePrefix: String) {
    logger.info("doing DB initialization, sqldir ${cfg.sqlDir}")
    maybeApplyV(conn, cfg)
    conn.transaction {
        val checkStmt = conn.prepareStatement("SELECT count(*) as n FROM _v.patches where patch_name = ?")

        for (n in 1..9999) {
            val numStr = n.toString().padStart(4, '0')
            val patchName = "$sqlFilePrefix-$numStr"

            checkStmt.setString(1, patchName)
            val patchCount = checkStmt.oneOrNull { it.getInt(1) } ?: throw Exception("unable to query patches")
            if (patchCount >= 1) {
                logger.debug("patch $patchName already applied")
                continue
            }

            val path = Path("${cfg.sqlDir}/$sqlFilePrefix-$numStr.sql")
            if (!path.exists()) {
                logger.debug("path $path doesn't exist anymore, stopping")
                break
            }
            logger.info("applying patch $path")
            val sqlPatchText = path.readText()
            conn.execSQLUpdate(sqlPatchText)
        }
        val sqlProcedures = Path("${cfg.sqlDir}/$sqlFilePrefix-procedures.sql")
        if (!sqlProcedures.exists()) {
            logger.warn("no procedures.sql for the SQL collection: $sqlFilePrefix")
            return@transaction
        }
        logger.info("run procedure.sql")
        conn.execSQLUpdate(sqlProcedures.readText())
    }
}

// sqlFilePrefix is, for example, "libeufin-bank" or "libeufin-nexus" (no trailing dash).
fun resetDatabaseTables(conn: PgConnection, cfg: DatabaseConfig, sqlFilePrefix: String) {
    logger.info("reset DB, sqldir ${cfg.sqlDir}")
    val isInitialized = conn.prepareStatement(
        """
        SELECT EXISTS(SELECT 1 FROM information_schema.schemata WHERE schema_name='_v') AND
            EXISTS(SELECT 1 FROM information_schema.schemata WHERE schema_name='${sqlFilePrefix.replace("-", "_")}')
        """
    ).one{ it.getBoolean(1) }
    if (!isInitialized) {
        logger.info("versioning schema not present, not running drop sql")
        return
    }

    val sqlDrop = Path("${cfg.sqlDir}/$sqlFilePrefix-drop.sql").readText()
    conn.execSQLUpdate(sqlDrop)
}

abstract class DbPool(cfg: String, schema: String) : java.io.Closeable {
    val pgSource = pgDataSource(cfg)
    private val pool: HikariDataSource

    init {
        val config = HikariConfig()
        config.dataSource = pgSource
        config.schema = schema
        config.transactionIsolation = "TRANSACTION_SERIALIZABLE"
        pool = HikariDataSource(config)
        pool.connection.use { con ->
            val meta = con.metaData
            val majorVersion = meta.databaseMajorVersion
            val minorVersion = meta.databaseMinorVersion
            if (majorVersion < MIN_VERSION) {
                throw Exception("postgres version must be at least $MIN_VERSION.0 got $majorVersion.$minorVersion")
            }
        }
    }

    suspend fun <R> conn(lambda: suspend (PgConnection) -> R): R {
        // Use a coroutine dispatcher that we can block as JDBC API is blocking
        return withContext(Dispatchers.IO) {
            pool.connection.use { lambda(it.unwrap(PgConnection::class.java)) }
        }
    }

    suspend fun <R> serializable(lambda: suspend (PgConnection) -> R): R = conn { conn ->
        repeat(SERIALIZATION_RETRY) {
            try {
                return@conn lambda(conn)
            } catch (e: SQLException) {
                if (e.sqlState != PSQLState.SERIALIZATION_FAILURE.state)
                    throw e
            }
        }
        try {
            return@conn lambda(conn)
        } catch (e: SQLException) {
            logger.warn("Serialization failure after $SERIALIZATION_RETRY retry")
            throw e
        }
    }

    override fun close() {
        pool.close()
    }
}

fun ResultSet.getAmount(name: String, currency: String): TalerAmount {
    return TalerAmount(
        getLong("${name}_val"),
        getInt("${name}_frac"),
        currency
    )
}

fun ResultSet.getBankPayto(payto: String, name: String, ctx: BankPaytoCtx): String {
    return Payto.parse(getString(payto)).bank(getString(name), ctx)
}