use std::any::type_name;
use std::borrow::Cow;
use std::error::Error as StdError;
use std::fmt::Display;
use std::io;
use std::result::Result as StdResult;

use crate::database::Database;

/// A specialized `Result` type for SQLx.
pub type Result<T> = StdResult<T, Error>;

// Convenience type alias for usage within SQLx.
pub(crate) type BoxDynError = Box<dyn StdError + 'static + Send + Sync>;

/// An unexpected `NULL` was encountered during decoding.
///
/// Returned from [`Row::get`] if the value from the database is `NULL`,
/// and you are not decoding into an `Option`.
#[derive(thiserror::Error, Debug)]
#[error("unexpected null; try decoding as an `Option`")]
pub struct UnexpectedNullError;

/// Represents all the ways a method can fail within SQLx.
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum Error {
    /// Error occurred while parsing a connection string.
    #[error("error occurred while parsing a connection string: {0}")]
    ParseConnectOptions(#[source] BoxDynError),

    /// Error returned from the database.
    #[error("error returned from database: {0}")]
    Database(Box<dyn DatabaseError>),

    /// Error communicating with the database backend.
    #[error("error communicating with the server: {0}")]
    Io(#[from] io::Error),

    /// Error occurred while attempting to establish a TLS connection.
    #[error("error occurred while attempting to establish a TLS connection: {0}")]
    Tls(#[source] BoxDynError),

    /// Unexpected or invalid data encountered while communicating with the database.
    ///
    /// This should indicate there is a programming error in a SQLx driver or there
    /// is something corrupted with the connection to the database itself.
    #[error("encountered unexpected or invalid data: {0}")]
    Protocol(String),

    /// No rows returned by a query that expected to return at least one row.
    #[error("no rows returned by a query that expected to return at least one row")]
    RowNotFound,

    /// Column index was out of bounds.
    #[error("column index out of bounds: the len is {len}, but the index is {index}")]
    ColumnIndexOutOfBounds { index: usize, len: usize },

    /// No column found for the given name.
    #[error("no column found for name: {0}")]
    ColumnNotFound(String),

    /// Error occurred while decoding a value from a specific column.
    #[error("error occurred while decoding column {index}: {source}")]
    ColumnDecode {
        index: String,

        #[source]
        source: BoxDynError,
    },

    /// Error occurred while decoding a value.
    #[error("error occurred while decoding: {0}")]
    Decode(#[source] BoxDynError),

    /// A [`Pool::acquire`] timed out due to connections not becoming available or
    /// because another task encountered too many errors while trying to open a new connection.
    ///
    /// [`Pool::acquire`]: crate::pool::Pool::acquire
    #[error("pool timed out while waiting for an open connection")]
    PoolTimedOut,

    /// [`Pool::close`] was called while we were waiting in [`Pool::acquire`].
    ///
    /// [`Pool::acquire`]: crate::pool::Pool::acquire
    /// [`Pool::close`]: crate::pool::Pool::close
    #[error("attempted to acquire a connection on a closed pool")]
    PoolClosed,
}

impl Error {
    pub fn into_database_error(self) -> Option<Box<dyn DatabaseError + 'static>> {
        match self {
            Error::Database(err) => Some(err),
            _ => None,
        }
    }

    pub fn as_database_error(&self) -> Option<&(dyn DatabaseError + 'static)> {
        match self {
            Error::Database(err) => Some(&**err),
            _ => None,
        }
    }

    #[allow(dead_code)]
    #[inline]
    pub(crate) fn protocol(err: impl Display) -> Self {
        Error::Protocol(err.to_string())
    }

    #[allow(dead_code)]
    #[inline]
    pub(crate) fn tls(err: impl StdError + Send + Sync + 'static) -> Self {
        Error::Tls(err.into())
    }
}

pub(crate) fn mismatched_types<DB: Database, T>(
    actual: &DB::TypeInfo,
    expected: &DB::TypeInfo,
) -> BoxDynError {
    let ty_name = type_name::<T>();

    format!(
        "mismatched types; Rust type `{}` (as SQL type `{}`) is not compatible with SQL type `{}`",
        ty_name, actual, expected
    )
    .into()
}

/// An error that was returned from the database.
pub trait DatabaseError: 'static + Send + Sync + StdError {
    /// The primary, human-readable error message.
    fn message(&self) -> &str;

    /// The (SQLSTATE) code for the error.
    fn code(&self) -> Option<Cow<'_, str>> {
        None
    }

    #[doc(hidden)]
    fn as_error(&self) -> &(dyn StdError + Send + Sync + 'static);

    #[doc(hidden)]
    fn as_error_mut(&mut self) -> &mut (dyn StdError + Send + Sync + 'static);

    #[doc(hidden)]
    fn into_error(self: Box<Self>) -> Box<dyn StdError + Send + Sync + 'static>;
}

impl dyn DatabaseError {
    /// Downcast a reference to this generic database error to a specific
    /// database error type.
    ///
    /// # Panics
    ///
    /// Panics if the database error type is not `E`. This is a deliberate contrast from
    /// `Error::downcast_ref` which returns `Option<&E>`. In normal usage, you should know the
    /// specific error type. In other cases, use `try_downcast_ref`.
    ///
    pub fn downcast_ref<E: DatabaseError>(&self) -> &E {
        self.try_downcast_ref().unwrap_or_else(|| {
            panic!(
                "downcast to wrong DatabaseError type; original error: {}",
                self
            )
        })
    }

    /// Downcast this generic database error to a specific database error type.
    ///
    /// # Panics
    ///
    /// Panics if the database error type is not `E`. This is a deliberate contrast from
    /// `Error::downcast` which returns `Option<E>`. In normal usage, you should know the
    /// specific error type. In other cases, use `try_downcast`.
    ///
    pub fn downcast<E: DatabaseError>(self: Box<Self>) -> Box<E> {
        self.try_downcast().unwrap_or_else(|e| {
            panic!(
                "downcast to wrong DatabaseError type; original error: {}",
                e
            )
        })
    }

    /// Downcast a reference to this generic database error to a specific
    /// database error type.
    #[inline]
    pub fn try_downcast_ref<E: DatabaseError>(&self) -> Option<&E> {
        self.as_error().downcast_ref()
    }

    /// Downcast this generic database error to a specific database error type.
    #[inline]
    pub fn try_downcast<E: DatabaseError>(self: Box<Self>) -> StdResult<Box<E>, Box<Self>> {
        if self.as_error().is::<E>() {
            Ok(self.into_error().downcast().unwrap())
        } else {
            Err(self)
        }
    }
}

impl<E> From<E> for Error
where
    E: DatabaseError,
{
    #[inline]
    fn from(error: E) -> Self {
        Error::Database(Box::new(error))
    }
}

// Format an error message as a `Protocol` error
macro_rules! err_protocol {
    ($expr:expr) => {
        $crate::error::Error::Protocol($expr.into())
    };

    ($fmt:expr, $($arg:tt)*) => {
        $crate::error::Error::Protocol(format!($fmt, $($arg)*))
    };
}