From fb8960d9779694afad90b5ee7217c5a592ba9511 Mon Sep 17 00:00:00 2001
From: Executor <exprotected@outlook.com>
Date: Sun, 14 Mar 2021 22:38:39 +0800
Subject: [PATCH] =?UTF-8?q?=E5=AE=9E=E7=8E=B0MiraiCodeReader=E3=80=82?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 Mirai-CSharp/Mirai-CSharp.csproj        |   1 +
 Mirai-CSharp/Utility/MiraiCodeReader.cs | 102 ++++++++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 Mirai-CSharp/Utility/MiraiCodeReader.cs

diff --git a/Mirai-CSharp/Mirai-CSharp.csproj b/Mirai-CSharp/Mirai-CSharp.csproj
index 993561d..87fa37f 100644
--- a/Mirai-CSharp/Mirai-CSharp.csproj
+++ b/Mirai-CSharp/Mirai-CSharp.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>net5.0;netcoreapp3.1;netstandard2.1;netstandard2.0</TargetFrameworks>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <RootNamespace>Mirai_CSharp</RootNamespace>
     <OutputType>Library</OutputType>
     <NoWin32Manifest>true</NoWin32Manifest>
diff --git a/Mirai-CSharp/Utility/MiraiCodeReader.cs b/Mirai-CSharp/Utility/MiraiCodeReader.cs
new file mode 100644
index 0000000..31759dd
--- /dev/null
+++ b/Mirai-CSharp/Utility/MiraiCodeReader.cs
@@ -0,0 +1,102 @@
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Mirai_CSharp.Utility
+{
+    //see https://github.com/mamoe/mirai/blob/dev/docs/Messages.md#mirai-%E7%A0%81
+    public ref struct MiraiCodeReader
+    {
+        public delegate void NameHandler(ReadOnlySpan<char> name);
+
+        public delegate void ArgumentHandler(ReadOnlySpan<char> argument);
+
+        private readonly ReadOnlySpan<char> _Code;
+
+        private int _Index;
+
+        private ReadOnlySpan<char> Current => GetFromIndex(_Code, _Index);
+
+        public MiraiCodeReader(ReadOnlySpan<char> code)
+        {
+            _Code = code;
+            _Index = 0;
+        }
+
+        public void Parse(NameHandler nameHandler, ArgumentHandler argumentHandler)
+        {
+            //[mirai:
+            ReadOnlySpan<char> code = Current;
+            if (code.Length < 9)
+            {
+                throw new FormatException();
+            }
+            if (!GetFromLength(code, 7).SequenceEqual("[mirai:".AsSpan()))
+            {
+                throw new FormatException();
+            }
+            if (!FindBlock(GetFromIndex(code, 7), ']', out code))
+            {
+                throw new FormatException("Missing end of char ]");
+            }
+            //[mirai:......]
+            _Index += code.Length + 7;
+            if (!FindBlock(code, ':', out ReadOnlySpan<char> result))
+            {
+                if (code.Length - 1 == 0)
+                {
+                    throw new FormatException("Missing name");
+                }
+                nameHandler(GetFromLength(code, code.Length - 1));
+                return;
+            }
+            nameHandler(GetFromLength(result, result.Length - 1));
+            while (FindBlock(code = GetFromIndex(code, result.Length), ':', out result))
+            {
+                argumentHandler(GetFromLength(result, result.Length - 1));
+            }
+            argumentHandler(GetFromLength(code, code.Length - 1)); // do not check empty argument
+        }
+
+        private static unsafe bool FindBlock(ReadOnlySpan<char> input, char seperator, out ReadOnlySpan<char> span)
+        {
+            int end = 0;
+            ReadOnlySpan<char> code;
+            do
+            {
+                code = CreateReadOnlySpan(ref Unsafe.Add(ref MemoryMarshal.GetReference(input), end), input.Length - end);
+                int result = code.IndexOf(seperator);
+                if (result == -1)
+                {
+                    span = default;
+                    return false;
+                }
+                end += result;
+            }
+            while (Unsafe.Add(ref MemoryMarshal.GetReference(code), end++ - 1) == '\\');
+            span = CreateReadOnlySpan(ref MemoryMarshal.GetReference(input), end);
+            return true;
+        }
+
+        private static unsafe ReadOnlySpan<char> GetFromIndex(ReadOnlySpan<char> span, int index)
+        {
+            return CreateReadOnlySpan(ref Unsafe.Add(ref MemoryMarshal.GetReference(span), index), span.Length - index);
+        }
+
+        private static unsafe ReadOnlySpan<char> GetFromLength(ReadOnlySpan<char> span, int length)
+        {
+            return CreateReadOnlySpan(ref MemoryMarshal.GetReference(span), length);
+        }
+#if !NETSTANDARD2_0
+        private static unsafe ReadOnlySpan<char> CreateReadOnlySpan(ref char c, int length)
+        {
+            return MemoryMarshal.CreateReadOnlySpan(ref c, length);
+        }
+#else
+        private static unsafe ReadOnlySpan<char> CreateReadOnlySpan(ref char c, int length)
+        {
+            return new ReadOnlySpan<char>(Unsafe.AsPointer(ref c), length);
+        }
+#endif
+    }
+}