commonMain.message.data.MessageKey.kt Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of mirai-core-api-common Show documentation
Mirai API module
There is a newer version: 2.12.3
Show newest version
/*
 * Copyright 2019-2021 Mamoe Technologies and contributors.
 *
 *  此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
 *  Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
 *
 *  https://github.com/mamoe/mirai/blob/master/LICENSE
 */

package net.mamoe.mirai.message.data

/**
 * 类型 Key. 由伴生对象实现, 表示一个 [Message] 对象的类型.
 *
 * 每个 [ConstrainSingle] 类型都拥有一个伴生对象来持有 [MessageKey] 以允许 `val source = chain[MessageSource]` 的用法.
 *
 * #### 用例
 * [MessageChain.get][MessageChain.get]: 允许使用数组访问操作符获取指定类型的消息元素
 * ```
 * val source: MessageSource = chain[MessageSource]
 * ```
 *
 * @param M 指代持有这个 Key 的消息类型
 */
public interface MessageKey {
    /**
     * 将一个 [SingleMessage] 强转为 [M] 类型. 在类型不符合时返回 `null`
     */
    public val safeCast: (SingleMessage) -> M?
}


/**
 * 独立的 [MessageKey] 的实现. '独立' 即 `final`, 不支持多态类型. 适用于作为最顶层的 [MessageKey], 如 [MessageSource].
 *
 * @see AbstractPolymorphicMessageKey
 */
public abstract class AbstractMessageKey(
    override val safeCast: (SingleMessage) -> M?,
) : MessageKey


/**
 * 多态 [MessageKey].
 *
 * 示例: [HummerMessage]
 * ```
 *               MessageContent
 *                     ↑
 *               HummerMessage
 *                     ↑
 *        +------------+-------------+------------+
 *        |            |             |            |
 *  PokeMessage     VipFace      FlashImage      ...
 *
 * ```
 *
 * 当 [连接][Message.plus] 一个 [VipFace] 到一个 [MessageChain] 时,
 * 由于 [VipFace] 最上层为 [MessageContent], 消息链中第一个 [MessageContent] 会被 (保留顺序地) 替换为 [VipFace], 其他所有 [MessageContent] 都会被删除.
 *
 * 如:
 * ```
 * val source: MessageSource = ...
 *
 * val result = messageChainOf(PlainText("a"), PlainText("b"), source, AtAll) + VipFace.LiuLian
 * // result 为 [VipFace.LiuLian, source]
 *
 * val result = source1 + source2
 * // result 为 [source2], 总是右侧替换左侧
 * ```
 */
public abstract class AbstractPolymorphicMessageKey(
    baseKey: MessageKey,
    safeCast: (SingleMessage) -> M?,
) : MessageKey, AbstractMessageKey(safeCast) {
    @JvmField
    internal val topmostKey: MessageKey<*> =
        if (baseKey is AbstractPolymorphicMessageKey<*, *>) baseKey.topmostKey else baseKey
}

/**
 * 尝试 [MessageKey.safeCast], 成功时返回 `true`
 */
public fun MessageKey<*>.isInstance(message: SingleMessage): Boolean = this.safeCast(message) != null

/**
 * 获取最上层 [MessageKey].
 * @see AbstractPolymorphicMessageKey
 */
public val  MessageKey.topmostKey: MessageKey<*>
    get() = when (this) {
        is AbstractPolymorphicMessageKey<*, *> -> this.topmostKey
        else -> this
    }