feat: Proper error handling

- Bump version to 0.8.0
- Added discord error struct
- All errors now implement std::error::Error
- Implemented error handler instead of relying on default
- Fixed bug where you could send answer on a completed quest

discord/src/error.rs

@@ -0,0 +1,60 @@
+use std::fmt::Display;
+
+use poise::serenity_prelude as serenity;
+
+#[non_exhaustive]
+#[derive(Debug)]
+pub enum Error {
+    QuestNotFound(u16),
+    QuestIsPublic(u16),
+    QuestIsCompleted(u16),
+    NoContent,
+    NoChannelOrUser,
+    BothChannelAndUser,
+    SerenityError(serenity::Error),
+    SquadQuestError(squad_quest::error::Error),
+}
+
+impl From<serenity::Error> for Error {
+    fn from(value: serenity::Error) -> Self {
+        Self::SerenityError(value)
+    }
+}
+
+impl From<squad_quest::error::Error> for Error {
+    fn from(value: squad_quest::error::Error) -> Self {
+        Self::SquadQuestError(value)
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::QuestNotFound(u16) => write!(f, "quest #{u16} not found"),
+            Self::QuestIsPublic(u16) => write!(f, "quest #{u16} is already public"),
+            Self::QuestIsCompleted(u16) => write!(f, "quest #{u16} is already completed for this user"),
+            Self::NoContent => write!(f, "no text or attachment was specified"),
+            Self::NoChannelOrUser => write!(f, "no channel or user was specified"),
+            Self::BothChannelAndUser => write!(f, "both channel and user was specified"),
+            Self::SerenityError(_) => write!(f, "discord interaction error"),
+            Self::SquadQuestError(_) => write!(f, "internal logic error"),
+        }
+    }
+}
+
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::QuestNotFound(_) |
+            Self::QuestIsPublic(_) |
+            Self::QuestIsCompleted(_) |
+            Self::NoContent |
+            Self::NoChannelOrUser |
+            Self::BothChannelAndUser => None,
+            Self::SerenityError(error) => Some(error),
+            Self::SquadQuestError(error) => Some(error),
+        }
+    }
+}
+
+