Make `SingleMessage` implement `CharSequence` and `Iterable<String>`

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/At.kt

@@ -29,7 +29,10 @@ import kotlin.jvm.JvmSynthetic
  * @see AtAll 全体成员
  */
 class At
-private constructor(val target: Long, val display: String) : Message, MessageContent {
+private constructor(val target: Long, val display: String) :
+    MessageContent,
+    CharSequence by display,
+    Comparable<String> by display {
 
     /**
      * 构造一个 [At] 实例. 这是唯一的公开的构造方式.
@@ -52,9 +55,9 @@ private constructor(val target: Long, val display: String) : Message, MessageCon
 
     override fun followedBy(tail: Message): CombinedMessage {
         if (tail is PlainText && tail.stringValue.startsWith(' ')) {
-            return super<MessageContent>.followedBy(tail)
+            return super.followedBy(tail)
         }
-        return super<MessageContent>.followedBy(PlainText(" ")) + tail
+        return super.followedBy(PlainText(" ")) + tail
     }
 }
 

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt

@@ -15,6 +15,8 @@ package net.mamoe.mirai.message.data
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 
+private const val display = "@全体成员"
+
 /**
  * "@全体成员".
  *
@@ -22,15 +24,20 @@ import kotlin.jvm.JvmName
  *
  * @see At at 单个群成员
  */
-object AtAll : Message, Message.Key<AtAll>, MessageContent {
-    override fun toString(): String = "@全体成员"
+object AtAll :
+    Message.Key<AtAll>,
+    MessageContent,
+    CharSequence by display,
+    Comparable<String> by display {
+
+    override fun toString(): String = display
 
     // 自动为消息补充 " "
 
     override fun followedBy(tail: Message): CombinedMessage {
         if (tail is PlainText && tail.stringValue.startsWith(' ')) {
-            return super<MessageContent>.followedBy(tail)
+            return super.followedBy(tail)
         }
-        return super<MessageContent>.followedBy(PlainText(" ")) + tail
+        return super.followedBy(PlainText(" ")) + tail
     }
 }
\ No newline at end of file

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Face.kt

@@ -18,7 +18,12 @@ import kotlin.jvm.JvmName
 /**
  * QQ 自带表情
  */
-class Face(val id: Int) : Message, MessageContent {
+class Face private constructor(val id: Int, private val stringValue: String) :
+    MessageContent,
+    CharSequence by stringValue, Comparable<String> by stringValue {
+
+    constructor(id: Int) : this(id, "[mirai:face$id]")
+
     override fun toString(): String = "[mirai:face$id]"
 
     /**

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt

@@ -44,6 +44,9 @@ interface Image : Message, MessageContent {
 }
 
 /**
+ * 通过 [Image.imageId] 构造一个 [Image] 以便发送.
+ * 这个图片必须是服务器已经存在的图片.
+ *
  * 请查看 `ExternalImageJvm` 获取更多创建 [Image] 的方法
  */
 @Suppress("FunctionName")
@@ -57,9 +60,21 @@ fun Image(imageId: String): Image = when (imageId.length) {
 
 @MiraiInternalAPI("使用 Image")
 abstract class AbstractImage internal constructor() : Image {
-    final override fun toString(): String {
-        return "[mirai:$imageId]"
-    }
+
+    private var _stringValue: String? = null
+        get() {
+            return field ?: kotlin.run {
+                field = "[mirai:$imageId]"
+                field
+            }
+        }
+    override val length: Int get() = _stringValue!!.length
+    override fun get(index: Int): Char = _stringValue!![index]
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence =
+        _stringValue!!.subSequence(startIndex, endIndex)
+
+    override fun compareTo(other: String): Int = _stringValue!!.compareTo(other)
+    final override fun toString(): String = _stringValue!!
 }
 
 // region 在线图片
@@ -120,7 +135,9 @@ suspend inline fun OfflineImage.queryOriginUrl(): String = queryUrl()
 
 
 /**
- * 群图片
+ * 群图片.
+ *
+ * [imageId] 形如 `{01E9451B-70ED-EAE3-B37C-101F1EEBF5B5}.png` (42 长度)
  */
 // CustomFace
 @OptIn(MiraiInternalAPI::class)
@@ -191,6 +208,8 @@ abstract class OnlineGroupImage : GroupImage(), OnlineImage
 
 /**
  * 好友图片
+ *
+ * [imageId] 形如 `/f8f1ab55-bf8e-4236-b55e-955848d7069f` (37 长度)
  */ // NotOnlineImage
 @OptIn(MiraiInternalAPI::class)
 sealed class FriendImage : AbstractImage() {

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt

@@ -98,6 +98,14 @@ interface Message {
         return CombinedMessage(tail, this)
     }
 
+    /**
+     * 转换为易辨识的字符串.
+     *
+     * 各个 [SingleMessage] 的转换示例:
+     * [PlainText]: "Hello"
+     * [GroupImage]: "[mirai:{01E9451B-70ED-EAE3-B37C-101F1EEBF5B5}.png]"
+     * [FriendImage]: ""
+     */
     override fun toString(): String
 
     operator fun plus(another: Message): CombinedMessage = this.followedBy(another)
@@ -121,24 +129,17 @@ fun Message.repeat(count: Int): MessageChain {
 
 inline operator fun Message.times(count: Int): MessageChain = this.repeat(count)
 
-interface SingleMessage : Message
+interface SingleMessage : Message, CharSequence, Comparable<String>
 
 /**
  * 消息元数据, 即不含内容的元素.
  * 包括: [MessageSource]
  */
 interface MessageMetadata : SingleMessage {
-    /*
-    fun iterator(): Iterator<Message> {
-        return object : Iterator<Message> {
-            var visited: Boolean = false
-            override fun hasNext(): Boolean = !visited
-            override fun next(): Message {
-                if (visited) throw NoSuchElementException()
-                return this@MessageMetadata.also { visited = true }
-            }
-        }
-    }*/
+    override val length: Int get() = 0
+    override fun get(index: Int): Char = ""[index] // produce uniform exception
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence = "".subSequence(startIndex, endIndex)
+    override fun compareTo(other: String): Int = "".compareTo(other)
 }
 
 /**

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/PlainText.kt

@@ -23,7 +23,11 @@ import kotlin.jvm.JvmSynthetic
  *
  * 一般不需要主动构造 [PlainText], [Message] 可直接与 [String] 相加. Java 用户请使用 [MessageChain.plus]
  */
-inline class PlainText(val stringValue: String) : Message, MessageContent {
+class PlainText(val stringValue: String) :
+    MessageContent,
+    Comparable<String> by stringValue,
+    CharSequence by stringValue {
+
     constructor(charSequence: CharSequence) : this(charSequence.toString())
 
     override operator fun contains(sub: String): Boolean = sub in stringValue

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/QuoteReply.kt

@@ -29,10 +29,10 @@ import kotlin.jvm.JvmName
  * 总是使用 [quote] 来构造这个实例.
  */
 open class QuoteReply
-@MiraiInternalAPI constructor(val source: MessageSource) : Message, MessageContent {
+@MiraiInternalAPI constructor(val source: MessageSource) : Message, MessageMetadata {
     companion object Key : Message.Key<QuoteReply>
 
-    override fun toString(): String = ""
+    final override fun toString(): String = ""
 }
 
 /**

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/builder.kt

@@ -7,15 +7,22 @@
  * https://github.com/mamoe/mirai/blob/master/LICENSE
  */
 
+@file:JvmMultifileClass
+@file:JvmName("MessageUtils")
+
 package net.mamoe.mirai.message.data
 
+import kotlin.jvm.JvmMultifileClass
+import kotlin.jvm.JvmName
 import kotlin.jvm.JvmOverloads
+import kotlin.jvm.JvmSynthetic
 
 /**
  * 构建一个 [MessageChain]
  *
  * @see MessageChainBuilder
  */
+@JvmSynthetic
 inline fun buildMessageChain(block: MessageChainBuilder.() -> Unit): MessageChain {
     return MessageChainBuilder().apply(block).asMessageChain()
 }
@@ -25,6 +32,7 @@ inline fun buildMessageChain(block: MessageChainBuilder.() -> Unit): MessageChai
  *
  * @see MessageChainBuilder
  */
+@JvmSynthetic
 inline fun buildMessageChain(initialSize: Int, block: MessageChainBuilder.() -> Unit): MessageChain {
     return MessageChainBuilder(initialSize).apply(block).asMessageChain()
 }
@@ -34,6 +42,7 @@ inline fun buildMessageChain(initialSize: Int, block: MessageChainBuilder.() ->
  *
  * @see MessageChainBuilder
  */
+@JvmSynthetic
 inline fun buildMessageChain(
     container: MutableCollection<Message>,
     block: MessageChainBuilder.() -> Unit