package io.ktor.util.cio

import io.ktor.util.*
import kotlinx.coroutines.*
import kotlinx.coroutines.io.*
import kotlinx.io.core.*
import kotlinx.io.pool.*
import java.io.*
import java.nio.*
import java.nio.channels.*
import kotlin.coroutines.*

/**
 * Open a read channel for file and launch a coroutine to fill it.
 * Please note that file reading is blocking so if you are starting it on [Dispatchers.Unconfined] it may block
 * your async code
 */
@KtorExperimentalAPI
@UseExperimental(ExperimentalIoApi::class)
fun File.readChannel(
    start: Long = 0,
    endInclusive: Long = -1,
    coroutineContext: CoroutineContext = Dispatchers.IO
): ByteReadChannel {
    val fileLength = length()
    val file = RandomAccessFile(this@readChannel, "r")
    return CoroutineScope(coroutineContext).writer(coroutineContext, autoFlush = false) {
        require(start >= 0L) { "start position shouldn't be negative but it is $start" }
        require(endInclusive <= fileLength - 1) { "endInclusive points to the position out of the file: file size = ${file.length()}, endInclusive = $endInclusive" }

        file.use {
            val fileChannel: FileChannel = file.channel
            if (start > 0) {
                fileChannel.position(start)
            }

            if (endInclusive == -1L) {
                channel.writeSuspendSession {
                    while (true) {
                        val buffer = request(1)
                        if (buffer == null) {
                            channel.flush()
                            tryAwait(1)
                            continue
                        }

                        val rc = fileChannel.read(buffer)
                        if (rc == -1) break
                        written(rc)
                    }
                }

                return@use
            }

            var position = start
            channel.writeWhile { buffer ->
                val fileRemaining = endInclusive - position + 1
                val rc = if (fileRemaining < buffer.remaining()) {
                    val l = buffer.limit()
                    buffer.limit(buffer.position() + fileRemaining.toInt())
                    val r = fileChannel.read(buffer)
                    buffer.limit(l)
                    r
                } else {
                    fileChannel.read(buffer)
                }

                if (rc > 0) position += rc

                rc != -1 && position <= endInclusive
            }
        }
    }.channel
}

/**
 * Open a write channel for file and launch a coroutine to read from it.
 * Please note that file writing is blocking so if you are starting it on [Dispatchers.Unconfined] it may block
 * your async code
 */
@KtorExperimentalAPI
fun File.writeChannel(
    pool: ObjectPool<ByteBuffer> = KtorDefaultPool
): ByteWriteChannel = GlobalScope.reader(Dispatchers.Unconfined, autoFlush = true) {
    RandomAccessFile(this@writeChannel, "rw").use { file ->
        pool.useInstance { buffer: ByteBuffer ->
            while (!channel.isClosedForRead) {
                buffer.clear()
                channel.readAvailable(buffer)
                buffer.flip()
                file.write(buffer.array(), buffer.arrayOffset() + buffer.position(), buffer.limit())
            }
        }
    }
}.channel
