1 files changed, 111 insertions, 0 deletions
diff --git a/bot/exts/evergreen/error_handler.py b/bot/exts/evergreen/error_handler.py
new file mode 100644
index 00000000..d268dab1
--- /dev/null
+++ b/bot/exts/evergreen/error_handler.py
@@ -0,0 +1,111 @@
+import logging
+import math
+import random
+from typing import Iterable, Union
+
+from discord import Embed, Message
+from discord.ext import commands
+
+from bot.constants import Colours, ERROR_REPLIES, NEGATIVE_REPLIES
+from bot.utils.decorators import InChannelCheckFailure, InMonthCheckFailure
+from bot.utils.exceptions import BrandingError
+
+log = logging.getLogger(__name__)
+
+
+class CommandErrorHandler(commands.Cog):
+    """A error handler for the PythonDiscord server."""
+
+    def __init__(self, bot: commands.Bot):
+        self.bot = bot
+
+    @staticmethod
+    def revert_cooldown_counter(command: commands.Command, message: Message) -> None:
+        """Undoes the last cooldown counter for user-error cases."""
+        if command._buckets.valid:
+            bucket = command._buckets.get_bucket(message)
+            bucket._tokens = min(bucket.rate, bucket._tokens + 1)
+            logging.debug("Cooldown counter reverted as the command was not used correctly.")
+
+    @staticmethod
+    def error_embed(message: str, title: Union[Iterable, str] = ERROR_REPLIES) -> Embed:
+        """Build a basic embed with red colour and either a random error title or a title provided."""
+        embed = Embed(colour=Colours.soft_red)
+        if isinstance(title, str):
+            embed.title = title
+        else:
+            embed.title = random.choice(title)
+        embed.description = message
+        return embed
+
+    @commands.Cog.listener()
+    async def on_command_error(self, ctx: commands.Context, error: commands.CommandError) -> None:
+        """Activates when a command opens an error."""
+        if hasattr(ctx.command, 'on_error'):
+            logging.debug("A command error occured but the command had it's own error handler.")
+            return
+
+        error = getattr(error, 'original', error)
+        logging.debug(
+            f"Error Encountered: {type(error).__name__} - {str(error)}, "
+            f"Command: {ctx.command}, "
+            f"Author: {ctx.author}, "
+            f"Channel: {ctx.channel}"
+        )
+
+        if isinstance(error, commands.CommandNotFound):
+            return
+
+        if isinstance(error, BrandingError):
+            await ctx.send(embed=self.error_embed(str(error)))
+            return
+
+        if isinstance(error, (InChannelCheckFailure, InMonthCheckFailure)):
+            await ctx.send(embed=self.error_embed(str(error), NEGATIVE_REPLIES), delete_after=7.5)
+            return
+
+        if isinstance(error, commands.UserInputError):
+            self.revert_cooldown_counter(ctx.command, ctx.message)
+            embed = self.error_embed(
+                f"Your input was invalid: {error}\n\nUsage:\n```{ctx.prefix}{ctx.command} {ctx.command.signature}```"
+            )
+            await ctx.send(embed=embed)
+            return
+
+        if isinstance(error, commands.CommandOnCooldown):
+            mins, secs = divmod(math.ceil(error.retry_after), 60)
+            embed = self.error_embed(
+                f"This command is on cooldown:\nPlease retry in {mins} minutes {secs} seconds.",
+                NEGATIVE_REPLIES
+            )
+            await ctx.send(embed=embed, delete_after=7.5)
+            return
+
+        if isinstance(error, commands.DisabledCommand):
+            await ctx.send(embed=self.error_embed("This command has been disabled.", NEGATIVE_REPLIES))
+            return
+
+        if isinstance(error, commands.NoPrivateMessage):
+            await ctx.send(embed=self.error_embed("This command can only be used in the server.", NEGATIVE_REPLIES))
+            return
+
+        if isinstance(error, commands.BadArgument):
+            self.revert_cooldown_counter(ctx.command, ctx.message)
+            embed = self.error_embed(
+                "The argument you provided was invalid: "
+                f"{error}\n\nUsage:\n```{ctx.prefix}{ctx.command} {ctx.command.signature}```"
+            )
+            await ctx.send(embed=embed)
+            return
+
+        if isinstance(error, commands.CheckFailure):
+            await ctx.send(embed=self.error_embed("You are not authorized to use this command.", NEGATIVE_REPLIES))
+            return
+
+        log.exception(f"Unhandled command error: {str(error)}", exc_info=error)
+
+
+def setup(bot: commands.Bot) -> None:
+    """Error handler Cog load."""
+    bot.add_cog(CommandErrorHandler(bot))
+    log.info("CommandErrorHandler cog loaded")