//! Provides common error types and associated convenience methods for TinyChain.
//!
//! This crate is a part of TinyChain: [http://github.com/haydnv/tinychain](http://github.com/haydnv/tinychain)

use std::fmt;

use destream::{en, EncodeMap, Encoder};

pub type TCResult<T> = Result<T, TCError>;

struct ErrorData {
    message: String,
    stack: Vec<String>,
}

impl<'en> en::ToStream<'en> for ErrorData {
    fn to_stream<E: Encoder<'en>>(&'en self, encoder: E) -> Result<E::Ok, E::Error> {
        if self.stack.is_empty() {
            return en::ToStream::to_stream(&self.message, encoder);
        }

        let mut map = encoder.encode_map(Some(2))?;
        map.encode_entry("message", &self.message)?;
        map.encode_entry("stack", &self.stack)?;
        map.end()
    }
}

impl<'en> en::IntoStream<'en> for ErrorData {
    fn into_stream<E: Encoder<'en>>(self, encoder: E) -> Result<E::Ok, E::Error> {
        if self.stack.is_empty() {
            return en::IntoStream::into_stream(self.message, encoder);
        }

        let mut map = encoder.encode_map(Some(2))?;
        map.encode_entry("message", self.message)?;
        map.encode_entry("stack", self.stack)?;
        map.end()
    }
}

impl<T> From<T> for ErrorData
where
    T: fmt::Display,
{
    fn from(message: T) -> Self {
        Self {
            message: message.to_string(),
            stack: vec![],
        }
    }
}

/// The category of a `TCError`.
#[derive(Clone, Copy, Eq, PartialEq)]
pub enum ErrorType {
    BadGateway,
    BadRequest,
    Conflict,
    Forbidden,
    Internal,
    MethodNotAllowed,
    NotFound,
    NotImplemented,
    Timeout,
    Unauthorized,
    Unavailable,
}

impl<'en> en::IntoStream<'en> for ErrorType {
    fn into_stream<E: Encoder<'en>>(self, encoder: E) -> Result<E::Ok, E::Error> {
        format!(
            "/error/{}",
            match self {
                Self::BadGateway => "bad_gateway",
                Self::BadRequest => "bad_request",
                Self::Conflict => "conflict",
                Self::Forbidden => "forbidden",
                Self::Internal => "internal",
                Self::MethodNotAllowed => "method_not_allowed",
                Self::NotFound => "not_found",
                Self::NotImplemented => "not_implemented",
                Self::Timeout => "timeout",
                Self::Unauthorized => "unauthorized",
                Self::Unavailable => "temporarily unavailable",
            }
        )
        .into_stream(encoder)
    }
}

impl fmt::Debug for ErrorType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

impl fmt::Display for ErrorType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str(match self {
            Self::BadGateway => "bad gateway",
            Self::BadRequest => "bad request",
            Self::Conflict => "conflict",
            Self::Forbidden => "forbidden",
            Self::Internal => "internal error",
            Self::MethodNotAllowed => "method not allowed",
            Self::NotFound => "not found",
            Self::NotImplemented => "not implemented",
            Self::Timeout => "request timeout",
            Self::Unauthorized => "unauthorized",
            Self::Unavailable => "temporarily unavailable",
        })
    }
}

/// A general error description.
pub struct TCError {
    code: ErrorType,
    data: ErrorData,
}

impl TCError {
    /// Returns a new error with the given code and message.
    pub fn new<I: fmt::Display>(code: ErrorType, message: I) -> Self {
        Self {
            code,
            data: message.into(),
        }
    }

    /// Reconstruct a [`TCError`] from its [`ErrorType`] and data.
    pub fn with_stack<I, S, SI>(code: ErrorType, message: I, stack: S) -> Self
    where
        I: fmt::Display,
        SI: fmt::Display,
        S: IntoIterator<Item = SI>,
    {
        Self {
            code,
            data: ErrorData {
                message: message.to_string(),
                stack: stack.into_iter().map(|msg| msg.to_string()).collect(),
            },
        }
    }

    /// Error indicating that the an upstream server send an invalid response.
    pub fn bad_gateway<I: fmt::Display>(cause: I) -> Self {
        Self::new(ErrorType::BadGateway, cause)
    }

    /// Error indicating that the request is badly-constructed or nonsensical.
    pub fn bad_request<M: fmt::Display, I: fmt::Display>(message: M, cause: I) -> Self {
        Self::new(ErrorType::BadRequest, format!("{}: {}", message, cause))
    }

    /// Error indicating that the request depends on a resource which is exclusively locked
    /// by another request.
    pub fn conflict<M: fmt::Display>(message: M) -> Self {
        Self::new(ErrorType::Conflict, message)
    }

    /// Error indicating that the request actor's credentials do not authorize access to some
    /// request dependencies.
    pub fn forbidden<M: fmt::Display, I: fmt::Display>(message: M, id: I) -> Self {
        Self::new(ErrorType::Forbidden, format!("{}: {}", message, id))
    }

    /// A truly unexpected error, for which the calling application cannot define any specific
    /// handling behavior.
    pub fn internal<I: fmt::Display>(info: I) -> Self {
        #[cfg(debug_assertions)]
        panic!("{}", info);

        #[cfg(not(debug_assertions))]
        Self::new(ErrorType::Internal, info)
    }

    /// Error indicating that the requested resource exists but does not support the request method.
    pub fn method_not_allowed<M: fmt::Display, S: fmt::Display, P: fmt::Display>(
        method: M,
        subject: S,
        path: P,
    ) -> Self {
        Self::new(
            ErrorType::MethodNotAllowed,
            format!("{} endpoint {} does not support {}", subject, path, method),
        )
    }

    /// Error indicating that the requested resource does not exist at the specified location.
    pub fn not_found<I: fmt::Display>(locator: I) -> Self {
        Self::new(ErrorType::NotFound, locator)
    }

    /// Error indicating that a required feature is not yet implemented.
    pub fn not_implemented<F: fmt::Display>(feature: F) -> Self {
        Self::new(ErrorType::NotImplemented, feature)
    }

    /// Error indicating that the request failed to complete in the allotted time.
    pub fn timeout<I: fmt::Display>(info: I) -> Self {
        Self::new(ErrorType::Timeout, info)
    }

    /// Error indicating that the user's credentials are missing or nonsensical.
    pub fn unauthorized<I: fmt::Display>(info: I) -> Self {
        Self::new(
            ErrorType::Unauthorized,
            format!("invalid credentials: {}", info),
        )
    }

    /// Error indicating that this host is currently overloaded
    pub fn unavailable<I: fmt::Display>(info: I) -> Self {
        Self::new(ErrorType::Unavailable, info)
    }

    /// Error indicating that the request is badly-constructed or nonsensical.
    pub fn unsupported<I: fmt::Display>(info: I) -> Self {
        Self::new(ErrorType::BadRequest, info)
    }

    pub fn code(&self) -> ErrorType {
        self.code
    }

    pub fn message(&'_ self) -> &'_ str {
        &self.data.message
    }

    pub fn consume<I: fmt::Display>(mut self, info: I) -> Self {
        self.data.stack.push(info.to_string());
        self
    }
}

impl std::error::Error for TCError {}

impl<'en> en::ToStream<'en> for TCError {
    fn to_stream<E: Encoder<'en>>(&'en self, encoder: E) -> Result<E::Ok, E::Error> {
        let mut map = encoder.encode_map(Some(1))?;
        map.encode_entry(self.code, &self.data)?;
        map.end()
    }
}

impl<'en> en::IntoStream<'en> for TCError {
    fn into_stream<E: Encoder<'en>>(self, encoder: E) -> Result<E::Ok, E::Error> {
        let mut map = encoder.encode_map(Some(1))?;
        map.encode_entry(self.code, self.data)?;
        map.end()
    }
}

impl fmt::Debug for TCError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(self, f)
    }
}

impl fmt::Display for TCError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}: {}", self.code, self.data.message)
    }
}