//! Error enum definition wrapping potential model implementation errors.

use std::{
    error::Error as StdError,
    fmt::{
        Display,
        Formatter,
        Result as FmtResult
    }
};
use super::Permissions;

/// An error returned from the [`model`] module.
///
/// This is always wrapped within the library's [`Error::Model`] variant.
///
/// # Examples
///
/// Matching an [`Error`] with this variant would look something like the
/// following for the [`GuildId::ban`] method, which in this example is used to
/// re-ban all members with an odd discriminator:
///
/// ```rust,no_run
/// # #[cfg(all(feature = "client", feature = "model"))]
/// # use std::error::Error;
/// #
/// # #[cfg(all(feature = "client", feature = "model"))]
/// # fn try_main() -> Result<(), Box<Error>> {
/// use serenity::prelude::*;
/// use serenity::model::prelude::*;
/// use serenity::Error;
/// use serenity::model::ModelError;
/// use std::env;
///
/// struct Handler;
///
/// impl EventHandler for Handler {
///     fn guild_ban_removal(&self, context: Context, guild_id: GuildId, user: User) {
///         // If the user has an even discriminator, don't re-ban them.
///         if user.discriminator % 2 == 0 {
///             return;
///         }
///
///      match guild_id.ban(&context.http, user, &8) {
///             Ok(()) => {
///                 // Ban successful.
///             },
///             Err(Error::Model(ModelError::DeleteMessageDaysAmount(amount))) => {
///                 println!("Failed deleting {} days' worth of messages", amount);
///             },
///             Err(why) => {
///                 println!("Unexpected error: {:?}", why);
///             },
///         }
///     }
/// }
/// let token = env::var("DISCORD_BOT_TOKEN")?;
/// let mut client = Client::new(&token, Handler).unwrap();
///
/// client.start()?;
/// #     Ok(())
/// # }
/// #
/// # #[cfg(all(feature = "client", feature = "model"))]
/// # fn main() {
/// #     try_main().unwrap();
/// # }
/// #
/// # #[cfg(not(all(feature="client", feature = "model")))]
/// # fn main() { }
/// ```
///
/// [`Error`]: ../../enum.Error.html
/// [`Error::Model`]: ../../enum.Error.html#variant.Model
/// [`GuildId::ban`]: ../id/struct.GuildId.html#method.ban
/// [`model`]: ../index.html
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub enum Error {
    /// When attempting to delete below or above the minimum and maximum allowed
    /// number of messages.
    BulkDeleteAmount,
    /// When attempting to delete a number of days' worth of messages that is
    /// not allowed.
    DeleteMessageDaysAmount(u8),
    /// Indicates that the textual content of an embed exceeds the maximum
    /// length.
    EmbedTooLarge(u64),
    /// An indication that a [guild][`Guild`] could not be found by
    /// [Id][`GuildId`] in the [`Cache`].
    ///
    /// [`Guild`]: ../guild/struct.Guild.html
    /// [`GuildId`]: ../id/struct.GuildId.html
    /// [`Cache`]: ../../cache/struct.Cache.html
    GuildNotFound,
    /// An indication that a [role][`Role`] could not be found by
    /// [Id][`RoleId`] in the [`Cache`].
    ///
    /// [`Role`]: ../guild/struct.Role.html
    /// [`RoleId`]: ../id/struct.GuildId.html
    /// [`Cache`]: ../../cache/struct.Cache.html
    RoleNotFound,
    /// Indicates that there are hierarchy problems restricting an action.
    ///
    /// For example, when banning a user, if the other user has a role with an
    /// equal to or higher position, then they can not be banned.
    ///
    /// When editing a role, if the role is higher in position than the current
    /// user's highest role, then the role can not be edited.
    Hierarchy,
    /// Indicates that you do not have the required permissions to perform an
    /// operation.
    ///
    /// The provided [`Permission`]s is the set of required permissions
    /// required.
    ///
    /// [`Permission`]: ../permissions/struct.Permissions.html
    InvalidPermissions(Permissions),
    /// An indicator that the [current user] cannot perform an action.
    ///
    /// [current user]: ../user/struct.CurrentUser.html
    InvalidUser,
    /// An indicator that an item is missing from the [`Cache`], and the action
    /// can not be continued.
    ///
    /// [`Cache`]: ../../cache/struct.Cache.html
    ItemMissing,
    /// Indicates that a [`Message`]s content was too long and will not
    /// successfully send, as the length is over 2000 codepoints, or 4000 bytes.
    ///
    /// The number of bytes larger than the limit is provided.
    ///
    /// [`Message`]: ../channel/struct.Message.html
    MessageTooLong(u64),
    /// Indicates that the current user is attempting to Direct Message another
    /// bot user, which is disallowed by the API.
    MessagingBot,
    /// An indicator that the [`ChannelType`] cannot perform an action.
    ///
    /// [`ChannelType`]: ../channel/enum.ChannelType.html
    InvalidChannelType,
    #[doc(hidden)]
    __Nonexhaustive,
}

impl Display for Error {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult { f.write_str(self.description()) }
}

impl StdError for Error {
    fn description(&self) -> &str {
        match *self {
            Error::BulkDeleteAmount => "Too few/many messages to bulk delete.",
            Error::DeleteMessageDaysAmount(_) => "Invalid delete message days.",
            Error::EmbedTooLarge(_) => "Embed too large.",
            Error::GuildNotFound => "Guild not found in the cache.",
            Error::RoleNotFound => "Role not found in the cache.",
            Error::Hierarchy => "Role hierarchy prevents this action.",
            Error::InvalidChannelType => "The channel cannot perform the action.",
            Error::InvalidPermissions(_) => "Invalid permissions.",
            Error::InvalidUser => "The current user cannot perform the action.",
            Error::ItemMissing => "The required item is missing from the cache.",
            Error::MessageTooLong(_) => "Message too large.",
            Error::MessagingBot => "Attempted to message another bot user.",
            Error::__Nonexhaustive => unreachable!(),
        }
    }
}
