/*
Mangadex@Home
Copyright (c) 2020, MangaDex Network
This file is part of MangaDex@Home.

MangaDex@Home is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

MangaDex@Home 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with this MangaDex@Home.  If not, see <http://www.gnu.org/licenses/>.
*/
package mdnet.server

import io.micrometer.core.instrument.Timer
import io.micrometer.prometheus.PrometheusMeterRegistry
import mdnet.Constants
import mdnet.cache.CachingInputStream
import mdnet.cache.Image
import mdnet.cache.ImageMetadata
import mdnet.cache.ImageStorage
import mdnet.logging.info
import mdnet.logging.trace
import mdnet.logging.warn
import org.http4k.core.*
import org.http4k.filter.CachingFilters
import org.http4k.lens.Path
import org.slf4j.LoggerFactory
import java.io.BufferedInputStream
import java.io.BufferedOutputStream
import java.io.InputStream
import java.time.Clock
import java.util.concurrent.Executors

class ImageServer(
    private val storage: ImageStorage,
    private val upstream: HttpHandler,
    registry: PrometheusMeterRegistry
) {
    private val executor = Executors.newCachedThreadPool()
    private val cacheLookupTimer = Timer.builder("cache.lookup")
        .publishPercentiles(0.5, 0.75, 0.9, 0.99)
        .register(registry)

    // This is part of the ImageServer, and it expects `chapterHash` and `fileName` path segments.
    fun handler(dataSaver: Boolean): HttpHandler = baseHandler().then { request ->
        val chapterHash = Path.of("chapterHash")(request)
        val fileName = Path.of("fileName")(request)

        val sanitizedUri = if (dataSaver) {
            "/data-saver"
        } else {
            "/data"
        } + "/$chapterHash/$fileName"

        val imageId = if (dataSaver) {
            md5Bytes("saver$chapterHash.$fileName")
        } else {
            md5Bytes("$chapterHash.$fileName")
        }.let {
            printHexString(it)
        }

        val image: Image? = cacheLookupTimer.recordCallable { storage.loadImage(imageId) }

        if (image != null) {
            request.handleCacheHit(sanitizedUri, image)
        } else {
            request.handleCacheMiss(sanitizedUri, imageId)
        }
    }

    private fun Request.handleCacheHit(sanitizedUri: String, image: Image): Response {
        // our files never change, so it's safe to use the browser cache
        return if (this.header("If-Modified-Since") != null) {
            LOGGER.info { "Request for $sanitizedUri cached by browser" }

            val lastModified = image.data.lastModified

            Response(Status.NOT_MODIFIED)
                .header("Last-Modified", lastModified)
        } else {
            LOGGER.info { "Request for $sanitizedUri is being served from cache" }

            respondWithImage(
                BufferedInputStream(image.stream),
                image.data.size, image.data.contentType, image.data.lastModified,
                true
            )
        }
    }

    private fun Request.handleCacheMiss(sanitizedUri: String, imageId: String): Response {
        val mdResponse = upstream(Request(Method.GET, sanitizedUri))

        if (mdResponse.status != Status.OK) {
            LOGGER.warn { "Upstream query for $sanitizedUri errored with status ${mdResponse.status}" }

            mdResponse.close()
            return Response(mdResponse.status)
        }

        val contentType = mdResponse.header("Content-Type")!!
        val contentLength = mdResponse.header("Content-Length")?.toInt()
        val lastModified = mdResponse.header("Last-Modified")

        if (!contentType.isImageMimetype()) {
            LOGGER.warn { "Upstream query for $sanitizedUri returned bad mimetype $contentType" }
            mdResponse.close()
            return Response(Status.INTERNAL_SERVER_ERROR)
        }

        // bad upstream responses mean we can't cache, so bail
        if (contentLength == null || lastModified == null) {
            LOGGER.info { "Request for $sanitizedUri is being served due to upstream issues" }
            return respondWithImage(mdResponse.body.stream, contentLength, contentType, lastModified, false)
        }

        LOGGER.trace { "Upstream query for $sanitizedUri succeeded" }

        val writer = storage.storeImage(imageId, ImageMetadata(contentType, lastModified, contentLength))

        // A null writer means that this file is being written to
        // concurrently so we skip the cache process
        return if (writer != null) {
            LOGGER.info { "Request for $sanitizedUri is being cached and served" }

            val tee = CachingInputStream(
                mdResponse.body.stream,
                executor, BufferedOutputStream(writer.stream),
            ) {
                try {
                    if (writer.commit(contentLength)) {
                        LOGGER.info { "Cache download for $sanitizedUri committed" }
                    } else {
                        LOGGER.info { "Cache download for $sanitizedUri aborted" }
                    }
                } catch (e: Exception) {
                    LOGGER.warn(e) { "Cache go/no go for $sanitizedUri failed" }
                }
            }
            respondWithImage(tee, contentLength, contentType, lastModified, false)
        } else {
            LOGGER.info { "Request for $sanitizedUri is being served due to write errors" }
            respondWithImage(mdResponse.body.stream, contentLength, contentType, lastModified, false)
        }
    }

    private fun respondWithImage(input: InputStream, length: Int?, type: String, lastModified: String?, cached: Boolean): Response =
        Response(Status.OK)
            .header("Content-Type", type)
            .header("X-Content-Type-Options", "nosniff")
            .let {
                if (length != null) {
                    it.body(input, length.toLong()).header("Content-Length", length.toString())
                } else {
                    it.body(input).header("Transfer-Encoding", "chunked")
                }
            }
            .let {
                if (lastModified != null) {
                    it.header("Last-Modified", lastModified)
                } else {
                    it
                }
            }
            .header("X-Cache", if (cached) "HIT" else "MISS")

    companion object {
        private val LOGGER = LoggerFactory.getLogger(ImageServer::class.java)
        private fun String.isImageMimetype() = this.toLowerCase().startsWith("image/")

        private fun baseHandler(): Filter =
            CachingFilters.Response.MaxAge(Clock.systemUTC(), Constants.MAX_AGE_CACHE)
                .then { next: HttpHandler ->
                    { request: Request ->
                        val response = next(request)
                        response.header("access-control-allow-origin", "https://mangadex.org")
                            .header("access-control-expose-headers", "*")
                            .header("access-control-allow-methods", "GET")
                            .header("timing-allow-origin", "https://mangadex.org")
                    }
                }
    }
}