package net.lamgc.scalabot

import mu.KotlinLogging
import net.lamgc.scalabot.extension.BotExtensionCreateOptions
import net.lamgc.scalabot.extension.BotExtensionFactory
import net.lamgc.scalabot.util.getPriority
import org.eclipse.aether.artifact.Artifact
import org.telegram.telegrambots.abilitybots.api.util.AbilityExtension
import java.io.File
import java.io.FileNotFoundException
import java.net.URL
import java.net.URLClassLoader
import java.net.URLDecoder
import java.nio.charset.StandardCharsets
import java.util.*
import java.util.concurrent.atomic.AtomicInteger

/**
 * 扩展加载器.
 *
 * 扩展加载器并非负责加载扩展的 Class, 而是委派搜索器发现并获取扩展, 然后加载扩展实例.
 *
 * 注意, 扩展加载器将内置两个 Finder: [FileNameFinder] 和 [MavenMetaInformationFinder].
 *
 * @param bot 扩展加载器所负责的 ScalaBot 实例.
 * @param extensionsDataFolder 提供给扩展用于数据存储的根目录(实际目录为 `{root}/{group...}/{artifact}`).
 * @param extensionsPath 提供给 Finder 用于搜索扩展的本地扩展包存放路径.
 * @param extensionFinders 加载器所使用的搜索器集合. 加载扩展时将使用所提供的的加载器.
 */
internal class ExtensionLoader(
    private val bot: ScalaBot,
    private val extensionsDataFolder: File = AppPaths.DATA_EXTENSIONS.file,
    private val extensionsPath: File = AppPaths.EXTENSIONS.file,
    private val extensionFinders: Set<ExtensionPackageFinder> = setOf()
) {
    private val log = KotlinLogging.logger { }

    private val finders: Set<ExtensionPackageFinder> = mutableSetOf(
        FileNameFinder,
        MavenMetaInformationFinder
    ).apply { addAll(extensionFinders) }.toSet()

    /**
     * 加载扩展, 并返回扩展项.
     *
     * 调用本方法后, 将会指派提供的 Finder 搜索 ScalaBot 配置的扩展包.
     *
     * @return 返回存放了所有已加载扩展项的 Set. 可通过 [LoadedExtensionEntry] 获取扩展的有关信息.
     */
    fun getExtensions(): Set<LoadedExtensionEntry> {
        val extensionEntries = mutableSetOf<LoadedExtensionEntry>()
        for (extensionArtifact in bot.extensions) {
            val extensionFilesMap = findExtensionPackage(extensionArtifact)
            val foundedNumber = allFoundedPackageNumber(extensionFilesMap)
            if (checkConflict(extensionFilesMap)) {
                printExtensionFileConflictError(extensionArtifact, extensionFilesMap)
                continue
            } else if (foundedNumber == 0) {
                log.warn { "[Bot ${bot.botUsername}] 找不到符合的扩展包文件: $extensionArtifact" }
                continue
            }

            extensionEntries.addAll(
                getExtensionFactories(
                    extensionArtifact,
                    filterHighPriorityResult(extensionFilesMap)
                )
            )
        }
        return extensionEntries.toSet()
    }

    /**
     * 检查是否发生冲突.
     *
     * 扩展包冲突有两种情况:
     * 1. 有多个同为最高优先级的搜索器搜索到了扩展包.
     * 2. 唯一的最高优先级搜索器搜索到了多个扩展包.
     *
     * 扩展包冲突指的是**有多个具有相同构件坐标的扩展包被搜索到**,
     * 如果不顾扩展包冲突直接加载的话, 将会出现安全隐患,
     * 因此在加载器发现冲突的情况下将输出相关信息, 提示用户进行排查.
     *
     * @param foundResult 扩展包搜索结果.
     *
     * @return 如果出现冲突, 返回 `true`.
     */
    private fun checkConflict(foundResult: Map<ExtensionPackageFinder, Set<FoundExtensionPackage>>): Boolean {
        if (foundResult.isEmpty()) {
            return false
        }

        val highPriorityFinders = filterHighPriorityResult(foundResult).keys
        if (highPriorityFinders.size > 1) {
            return true
        } else {
            val finder = highPriorityFinders.firstOrNull() ?: return false
            return foundResult[finder]!!.size > 1
        }
    }

    /**
     * 从结果中过滤出由最高优先级的搜索器搜索到的扩展包.
     */
    private fun filterHighPriorityResult(foundResult: Map<ExtensionPackageFinder, Set<FoundExtensionPackage>>)
            : Map<ExtensionPackageFinder, Set<FoundExtensionPackage>> {
        val finders: List<ExtensionPackageFinder> = foundResult.keys
            .filter { checkExtensionPackageFinder(it) && (foundResult[it]?.size ?: 0) != 0 }
            .sortedBy { it.getPriority() }

        val highPriority = finders.first().getPriority()
        return foundResult.filterKeys { it.getPriority() == highPriority }
    }

    private fun getExtensionFactories(
        extensionArtifact: Artifact,
        foundResult: Map<ExtensionPackageFinder, Set<FoundExtensionPackage>>
    ): Set<LoadedExtensionEntry> {
        val foundPackage = foundResult.values.first().first()
        val extClassLoader =
            ExtensionClassLoaderCleaner.getOrCreateExtensionClassLoader(extensionArtifact, foundPackage)
        val factories = mutableSetOf<LoadedExtensionEntry>()
        for (factory in extClassLoader.serviceLoader) {
            try {
                val extension =
                    factory.createExtensionInstance(
                        bot, getExtensionDataFolder(extensionArtifact),
                        BotExtensionCreateOptions(
                            bot.accountId,
                            bot.botConfig.proxy.copy()
                        )
                    )
                if (extension == null) {
                    log.debug { "Factory ${factory::class.java} 创建插件时返回了 null, 已跳过. (BotName: ${bot.botUsername})" }
                    continue
                }
                factories.add(LoadedExtensionEntry(extensionArtifact, factory::class.java, extension))
            } catch (e: Exception) {
                log.error(e) { "创建扩展时发生异常. (ExtArtifact: `$extensionArtifact`, Factory: ${factory::class.java.name})" }
            }
        }
        return factories.toSet()
    }

    /**
     * 只是用来统计扩展包搜索结果的数量而已.
     *
     * @return 返回扩展包的数量.
     */
    private fun allFoundedPackageNumber(filesMap: Map<ExtensionPackageFinder, Set<FoundExtensionPackage>>): Int {
        var number = 0
        for (files in filesMap.values) {
            number += files.size
        }
        return number
    }

    /**
     * 搜索指定构件坐标的依赖包.
     *
     * 搜索扩展包将根据搜索器优先级从高到低依次搜索, 当某一个优先级的搜索器搜到扩展包后将停止搜索.
     * 可以根据不同优先级的搜索器, 配置扩展包的主用和备用文件.
     *
     * @return 返回各个搜索器返回的搜索结果.
     */
    private fun findExtensionPackage(
        extensionArtifact: Artifact,
    ): Map<ExtensionPackageFinder, Set<FoundExtensionPackage>> {
        val result = mutableMapOf<ExtensionPackageFinder, Set<FoundExtensionPackage>>()
        val sortedFinders = finders.sortedBy { it.getPriority() }
        var highPriority = sortedFinders.first().getPriority()

        for (finder in sortedFinders) {
            if (finder.getPriority() > highPriority && result.isNotEmpty()) {
                break
            }
            highPriority = finder.getPriority()

            if (!checkExtensionPackageFinder(finder)) {
                continue
            }
            try {
                val artifacts = finder.findByArtifact(extensionArtifact, extensionsPath)
                if (artifacts.isNotEmpty()) {
                    result[finder] = artifacts
                }
            } catch (e: Exception) {
                log.error(e) { "搜索器 ${finder::class.java.name} 在搜索扩展 `$extensionArtifact` 时发生错误." }
            }
        }
        return result
    }

    /**
     * 检查扩展包搜索器是否设置了 [FinderRules] 注解.
     * @return 如果已设置注解, 则返回 `true`.
     */
    private fun checkExtensionPackageFinder(finder: ExtensionPackageFinder): Boolean =
        finder::class.java.getDeclaredAnnotation(FinderRules::class.java) != null

    /**
     * 在日志中输出有关扩展包冲突的错误信息.
     */
    private fun printExtensionFileConflictError(
        extensionArtifact: Artifact,
        foundResult: Map<ExtensionPackageFinder, Set<FoundExtensionPackage>>
    ) {
        log.error {
            val errMessage = StringBuilder(
                """
                [Bot ${bot.botUsername}] 扩展包 $extensionArtifact 存在多个文件, 为防止安全问题, 已禁止加载该扩展包:
                """.trimIndent()
            ).append('\n')

            foundResult.forEach { (finder, files) ->
                errMessage.append("\t- 搜索器 `").append(finder::class.simpleName).append("`")
                    .append("(Priority: ${finder.getPriority()})")
                    .append(" 找到了以下扩展包: \n")
                for (file in files) {
                    errMessage.append("\t\t* ")
                        .append(URLDecoder.decode(file.getRawUrl().toString(), StandardCharsets.UTF_8)).append('\n')
                }
            }
            errMessage
        }
    }

    /**
     * 创建扩展数据目录, 并返回 [File] 对象.
     * @param extensionArtifact 扩展包构件坐标.
     * @return 返回对应的数据存储目录.
     */
    private fun getExtensionDataFolder(extensionArtifact: Artifact): File {
        val dataFolder =
            File(extensionsDataFolder, "${extensionArtifact.groupId}/${extensionArtifact.artifactId}")
        if (!dataFolder.exists()) {
            dataFolder.mkdirs()
        }
        return dataFolder
    }

    /**
     * 已加载扩展项.
     * @property extensionArtifact 扩展的构件坐标([Artifact]).
     * @property factoryClass 扩展的工厂类.
     * @property extension 扩展实例.
     */
    data class LoadedExtensionEntry(
        val extensionArtifact: Artifact,
        val factoryClass: Class<out BotExtensionFactory>,
        val extension: AbilityExtension
    )

}

/**
 * 扩展的类加载器清除器.
 *
 * 原计划是用来通过关闭 ClassLoader 来卸载扩展的, 但似乎并没有这么做.
 *
 * 该类为保留措施, 尚未启用.
 */
internal object ExtensionClassLoaderCleaner {

    private val artifactMap = mutableMapOf<Artifact, ExtensionClassLoader>()
    private val usageCountMap = mutableMapOf<ExtensionClassLoader, AtomicInteger>()

    @Synchronized
    fun getOrCreateExtensionClassLoader(
        extensionArtifact: Artifact,
        foundExtensionPackage: FoundExtensionPackage
    ): ExtensionClassLoader {
        return if (!artifactMap.containsKey(extensionArtifact)) {
            val newClassLoader = foundExtensionPackage.createClassLoader()
            artifactMap[extensionArtifact] = newClassLoader
            usageCountMap[newClassLoader] = AtomicInteger(1)
            newClassLoader
        } else {
            artifactMap[extensionArtifact]!!
        }
    }

    @Synchronized
    fun releaseExtensionClassLoader(extensionArtifacts: Set<Artifact>) {
        for (extensionArtifact in extensionArtifacts) {
            if (!artifactMap.containsKey(extensionArtifact)) {
                throw IllegalStateException("No corresponding classloader exists.")
            }

            val classLoader = artifactMap[extensionArtifact]!!
            val usageCounter = usageCountMap[classLoader]!!
            if (usageCounter.decrementAndGet() == 0) {
                cleanExtensionClassLoader(extensionArtifact)
            }
        }
    }

    private fun cleanExtensionClassLoader(extensionArtifact: Artifact) {
        if (!artifactMap.containsKey(extensionArtifact)) {
            return
        }
        val classLoader = artifactMap.remove(extensionArtifact)!!
        try {
            classLoader.close()
        } finally {
            usageCountMap.remove(classLoader)
        }
    }

}

/**
 * 扩展包搜索器.
 *
 * 通过实现该接口, 可添加一种搜索扩展包的方式, 无论其来源.
 */
internal interface ExtensionPackageFinder {
    /**
     * 在指定目录中搜索指定构件坐标的扩展包文件(夹).
     * @param extensionArtifact 欲查找的扩展包构件坐标.
     * @param extensionsPath 建议的搜索路径, 如搜索器希望通过网络来获取也可以.
     * @return 返回按搜索器的方式可以找到的所有与构件坐标有关的扩展包路径.
     */
    fun findByArtifact(extensionArtifact: Artifact, extensionsPath: File): Set<FoundExtensionPackage>

    /**
     * 获取类加载器工厂.
     *
     * 搜索器可根据需求自行实现类加载器工厂.
     * @return 返回 [ExtensionClassLoaderFactory] 实现.
     */
    fun getClassLoaderFactory(): ExtensionClassLoaderFactory = DefaultExtensionClassLoaderFactory
}

/**
 * 已找到的扩展包信息.
 * 通过实现该接口, 以寻找远端文件的 [ExtensionPackageFinder];
 * 可以在适当的时候将扩展包下载到本地, 而无需在搜索阶段下载扩展包.
 */
internal interface FoundExtensionPackage {

    /**
     * 获取扩展包的构件坐标.
     * @return 返回扩展包的构件坐标.
     */
    fun getExtensionArtifact(): Artifact

    /**
     * 获取原始的扩展 Url.
     * @return 返回扩展包所在的 Url.
     */
    fun getRawUrl(): URL

    /**
     * 获取扩展包并返回扩展包在本地的 File 对象.
     *
     * 当调用本方法时, Finder 可以将扩展包下载到本地(如果扩展包在远端服务器的话).
     * @return 返回扩展包在本地存储时指向扩展包文件的 File 对象.
     */
    fun getPackageFile(): File

    /**
     * 找到该扩展包的发现器对象.
     */
    fun getExtensionPackageFinder(): ExtensionPackageFinder

}

private fun FoundExtensionPackage.createClassLoader(): ExtensionClassLoader =
    getExtensionPackageFinder().getClassLoaderFactory().createClassLoader(this)

/**
 * 已找到的扩展包文件.
 * @param artifact 扩展包构件坐标.
 * @param file 已找到的扩展包文件.
 * @param finder 搜索到该扩展包的搜索器.
 */
internal class FileFoundExtensionPackage(
    private val artifact: Artifact,
    private val file: File,
    private val finder: ExtensionPackageFinder
) : FoundExtensionPackage {

    init {
        if (!file.exists()) {
            throw FileNotFoundException(file.canonicalPath)
        }
    }

    override fun getExtensionArtifact(): Artifact = artifact

    override fun getRawUrl(): URL = file.canonicalFile.toURI().toURL()

    override fun getPackageFile(): File = file

    override fun getExtensionPackageFinder(): ExtensionPackageFinder = finder
}

/**
 * 扩展包专属的类加载器.
 *
 * 通过为每个扩展包提供专有的加载器, 可防止意外使用其他扩展的类(希望如此).
 * @param urls 扩展包资源 Url.
 * @param dependencyLoader 依赖项的类加载器. 当扩展包含有其他依赖项时, 需将依赖项单独设置在一个类加载器中, 以确保扩展加载安全.
 */
internal class ExtensionClassLoader(urls: Array<URL>, dependencyLoader: ClassLoader = getSystemClassLoader()) :
    URLClassLoader(urls, dependencyLoader) {

    /**
     * 指定扩展包 File 来创建 ClassLoader.
     * @param extensionFile 扩展包文件.
     */
    constructor(extensionFile: File) :
            this(arrayOf(URL(getUrlString(extensionFile))))

    val serviceLoader: ServiceLoader<BotExtensionFactory> = ServiceLoader.load(BotExtensionFactory::class.java, this)

    // 为防止从非扩展包位置引入扩展的问题, 覆写了以下两个方法
    // 当寻找 BotExtensionFactory 时, 将不再遵循双亲委派原则,
    // 以免使用了不来自扩展包的机器人扩展.

    override fun getResources(name: String?): Enumeration<URL> {
        if ("META-INF/services/${BotExtensionFactory::class.java.name}" == name) {
            return findResources(name)
        }
        return super.getResources(name)
    }

    override fun getResource(name: String?): URL? {
        if ("META-INF/services/${BotExtensionFactory::class.java}" == name) {
            return findResource(name)
        }
        return super.getResource(name)
    }

    companion object {
        private fun getUrlString(extensionFile: File, defaultScheme: String = "file:///"): String {
            return when (extensionFile.extension.lowercase()) {
                "jar" -> "jar:file:///${extensionFile.canonicalPath}!/"
                else -> defaultScheme + extensionFile.canonicalPath
            }
        }
    }
}

/**
 * 扩展类加载器工厂接口.
 *
 * 可供有多依赖需求的扩展使用, 由 Finder 提供.
 */
internal interface ExtensionClassLoaderFactory {

    /**
     * 创建扩展包的类加载器.
     * @param foundExtensionPackage 已找到的扩展包信息.
     */
    fun createClassLoader(foundExtensionPackage: FoundExtensionPackage): ExtensionClassLoader

}

/**
 * 针对单文件依赖的 ClassLoader 工厂.
 */
internal object DefaultExtensionClassLoaderFactory : ExtensionClassLoaderFactory {
    override fun createClassLoader(foundExtensionPackage: FoundExtensionPackage): ExtensionClassLoader {
        return ExtensionClassLoader(foundExtensionPackage.getPackageFile())
    }
}


/**
 * 搜索器规则.
 * @property priority 搜索器优先级. 优先级从 0 (最高)开始, 相同构件坐标下将使用优先级最高的搜索器所找到的文件.
 * 如无特殊需求, 建议使用 [FinderPriority] 中已定义好的优先级.
 */
annotation class FinderRules(
    val priority: Int
)

/**
 * **建议**的搜索器优先级常量.
 */
class FinderPriority private constructor() {

    companion object {
        /**
         * 本地扩展包.
         */
        const val LOCAL = 100

        /**
         * 远端扩展包.
         */
        const val REMOTE = 200

        /**
         * 替补的扩展包.
         */
        const val ALTERNATE = 500
    }

}