[ButtonPoll] Improve permission checks

Closes #126

buttonpoll/buttonpoll.py

@@ -126,7 +126,6 @@ async def buttonpoll(self, ctx: commands.Context, chan: Optional[TextChannel] =
             assert isinstance(channel, (TextChannel, discord.Thread))
             assert isinstance(ctx.author, discord.Member)  # we are in a guild...
 
-        # these two checks are untested :)
         if not channel.permissions_for(ctx.author).send_messages:  # type:ignore
             return await ctx.send(
                 f"You don't have permission to send messages in {channel.mention}, so I can't "
@@ -137,6 +136,11 @@ async def buttonpoll(self, ctx: commands.Context, chan: Optional[TextChannel] =
                 f"I don't have permission to send messages in {channel.mention}, so I can't "
                 "start a poll there."
             )
+        if not channel.permissions_for(ctx.me).attach_files:  # type:ignore
+            await ctx.send(
+                "\N{WARNING SIGN}\N{VARIATION SELECTOR-16} I don't have permission to attach "
+                "files in that channel. I won't be able to send a pie chart."
+            )
 
         view = StartSetupView(author=ctx.author, channel=channel, cog=self)
         await ctx.send("Click below to start a poll!", view=view)
@@ -158,6 +162,10 @@ async def advstartpoll(self, ctx: commands.Context, *, arguments: str = ""):
 \N{WARNING SIGN}\N{VARIATION SELECTOR-16} **This command is for advanced users only.
 You should use `[p]buttonpoll` or the slash command `poll` for a more user-friendly experience.**
 
+\N{WARNING SIGN}\N{VARIATION SELECTOR-16} This command does not check for permissions. Please
+check I have permission to send messages in the channel you want to start the poll in. I'll also
+need permission to attach files if you want a pie chart.
+
 **Required arguments:**
 - `--channel ID`: The channel ID to start the poll in
 - `--question string`: The question to ask

buttonpoll/poll.py

@@ -228,10 +228,17 @@ async def finish(self):
                 )
             )
 
-            plot = await self.plot()
+            if channel.permissions_for(guild.me).attach_files:
+                plot = await self.plot()
+                embed.set_image(url="attachment://plot.png")
+                message = await channel.send(embed=embed, file=plot, view=view)
+            else:
+                message = await channel.send(embed=embed, view=view)
+                log.warning(
+                    f"Channel {self.channel_id} does not allow me to attach files. "
+                    f"I was unable to attach a pie chart to poll {self.unique_poll_id}."
+                )
 
-            embed.set_image(url="attachment://plot.png")
-            message = await channel.send(embed=embed, file=plot, view=view)
             view.stop()
 
             view2 = discord.ui.View()