From 1642aded0a998035ce12d53e7af6f92a34efb52a Mon Sep 17 00:00:00 2001
From: "diamondburned (Forefront)" <datutbrus@gmail.com>
Date: Fri, 24 Jan 2020 18:49:33 -0800
Subject: [PATCH] Fixed the emoji argument

---
 bot/error.go                       | 10 ++++++-
 bot/extras/arguments/emoji.go      | 47 +++++++++++++++++++++++-------
 bot/extras/arguments/emoji_test.go | 28 ++++++++++++++++++
 3 files changed, 73 insertions(+), 12 deletions(-)
 create mode 100644 bot/extras/arguments/emoji_test.go

diff --git a/bot/error.go b/bot/error.go
index e529c89..6662c1d 100644
--- a/bot/error.go
+++ b/bot/error.go
@@ -16,6 +16,10 @@ type ErrUnknownCommand struct {
 }
 
 func (err *ErrUnknownCommand) Error() string {
+	return UnknownCommandString(err)
+}
+
+var UnknownCommandString = func(err *ErrUnknownCommand) string {
 	var header = "Unknown command: " + err.Prefix
 	if err.Parent != "" {
 		header += err.Parent + " " + err.Command
@@ -35,10 +39,14 @@ type ErrInvalidUsage struct {
 
 	// TODO: usage generator?
 	// Here, as a reminder
-	ctx *CommandContext
+	Ctx *CommandContext
 }
 
 func (err *ErrInvalidUsage) Error() string {
+	return InvalidUsageString(err)
+}
+
+var InvalidUsageString = func(err *ErrInvalidUsage) string {
 	if err.Index == 0 {
 		return "Invalid usage, error: " + err.Err
 	}
diff --git a/bot/extras/arguments/emoji.go b/bot/extras/arguments/emoji.go
index e6fd4cd..7780d35 100644
--- a/bot/extras/arguments/emoji.go
+++ b/bot/extras/arguments/emoji.go
@@ -3,6 +3,7 @@ package arguments
 import (
 	"errors"
 	"regexp"
+	"unicode/utf16"
 )
 
 var (
@@ -54,17 +55,9 @@ func (e Emoji) URL() string {
 }
 
 func (e *Emoji) Parse(arg string) error {
-	// Check if Unicode
-	var unicode string
-
-	for _, r := range arg {
-		if r < '\U0001F600' && r > '\U0001F64F' {
-			unicode += string(r)
-		}
-	}
-
-	if unicode != "" {
-		e.ID = unicode
+	// Check if Unicode emoji
+	if stringIsEmojiOnly(arg) {
+		e.ID = arg
 		e.Custom = false
 
 		return nil
@@ -83,3 +76,35 @@ func (e *Emoji) Parse(arg string) error {
 
 	return nil
 }
+
+func stringIsEmojiOnly(emoji string) bool {
+	runes := []rune(emoji)
+	// Slice of runes is 2, since some emojis have 2 runes.
+	if len(runes) > 2 {
+		return false
+	}
+
+	return emojiRune(runes[0])
+}
+
+var surrogates = [...][2]rune{ // [0] from, [1] to
+	{utf16.DecodeRune(0xD83C, 0xD000), utf16.DecodeRune(0xD83C, 0xDFFF)},
+	{utf16.DecodeRune(0xD83E, 0xD000), utf16.DecodeRune(0xD83E, 0xDFFF)},
+	{utf16.DecodeRune(0xD83F, 0xD000), utf16.DecodeRune(0xD83F, 0xDFFF)},
+}
+
+func emojiRune(r rune) bool {
+	b := r == '\u00a9' || r == '\u00ae' ||
+		(r >= '\u2000' && r <= '\u3300')
+	if b {
+		return true
+	}
+
+	for _, surrogate := range surrogates {
+		if surrogate[0] <= r && r <= surrogate[1] {
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/bot/extras/arguments/emoji_test.go b/bot/extras/arguments/emoji_test.go
new file mode 100644
index 0000000..7fef1c2
--- /dev/null
+++ b/bot/extras/arguments/emoji_test.go
@@ -0,0 +1,28 @@
+package arguments
+
+import "testing"
+
+func TestEmojiRune(t *testing.T) {
+	var emojis = []string{
+		"🏑",
+		"❄️",
+		"🤲🏿",
+	}
+
+	var notEmojis = []string{
+		"🏃🏿🏃🏿", // dual emojis
+		"te",   // not emoji
+	}
+
+	for i, emoji := range emojis {
+		if !stringIsEmojiOnly(emoji) {
+			t.Fatal(i, "is an emoji, function returned false")
+		}
+	}
+
+	for i, not := range notEmojis {
+		if stringIsEmojiOnly(not) {
+			t.Fatal(i, "is not an emoji, function returned true")
+		}
+	}
+}