use std::{convert, result};
use std::marker::PhantomData;

use super::{Statement, Error, Result};
use types::{FromSql, FromSqlError};
use statement::StatementCrateImpl;

/// An handle for the resulting rows of a query.
pub struct Rows<'stmt> {
    stmt: Option<&'stmt Statement<'stmt>>,
}

impl<'stmt> Rows<'stmt> {
    fn reset(&mut self) {
        if let Some(stmt) = self.stmt.take() {
            stmt.reset();
        }
    }

    /// Attempt to get the next row from the query. Returns `Some(Ok(Row))` if there
    /// is another row, `Some(Err(...))` if there was an error getting the next
    /// row, and `None` if all rows have been retrieved.
    ///
    /// ## Note
    ///
    /// This interface is not compatible with Rust's `Iterator` trait, because the
    /// lifetime of the returned row is tied to the lifetime of `self`. This is a
    /// "streaming iterator". For a more natural interface, consider using `query_map`
    /// or `query_and_then` instead, which return types that implement `Iterator`.
    #[cfg_attr(feature = "cargo-clippy", allow(should_implement_trait))] // cannot implement Iterator
    pub fn next<'a>(&'a mut self) -> Option<Result<Row<'a, 'stmt>>> {
        self.stmt
            .and_then(|stmt| match stmt.step() {
                Ok(true) => {
                    Some(Ok(Row {
                        stmt,
                        phantom: PhantomData,
                    }))
                }
                Ok(false) => {
                    self.reset();
                    None
                }
                Err(err) => {
                    self.reset();
                    Some(Err(err))
                }
            })
    }
}

// TODO: This trait lets us have "pub(crate)" visibility on some methods. Remove this
// once pub(crate) is stable.
pub trait RowsCrateImpl<'stmt> {
    fn new(stmt: &'stmt Statement<'stmt>) -> Rows<'stmt>;
    fn get_expected_row<'a>(&'a mut self) -> Result<Row<'a, 'stmt>>;
}

impl<'stmt> RowsCrateImpl<'stmt> for Rows<'stmt> {
    fn new(stmt: &'stmt Statement<'stmt>) -> Rows<'stmt> {
        Rows { stmt: Some(stmt) }
    }

    fn get_expected_row<'a>(&'a mut self) -> Result<Row<'a, 'stmt>> {
        match self.next() {
            Some(row) => row,
            None => Err(Error::QueryReturnedNoRows),
        }
    }
}

impl<'stmt> Drop for Rows<'stmt> {
    fn drop(&mut self) {
        self.reset();
    }
}

/// An iterator over the mapped resulting rows of a query.
pub struct MappedRows<'stmt, F> {
    rows: Rows<'stmt>,
    map: F,
}

// TODO: This trait lets us have "pub(crate)" visibility on some methods. Remove this
// once pub(crate) is stable.
pub trait MappedRowsCrateImpl<'stmt, T, F> {
    fn new(rows: Rows<'stmt>, f: F) -> MappedRows<'stmt, F>;
}

impl<'stmt, T, F> MappedRowsCrateImpl<'stmt, T, F> for MappedRows<'stmt, F>
    where F: FnMut(&Row) -> T
{
    fn new(rows: Rows<'stmt>, f: F) -> MappedRows<'stmt, F> {
        MappedRows { rows, map: f }
    }
}

impl<'conn, T, F> Iterator for MappedRows<'conn, F>
    where F: FnMut(&Row) -> T
{
    type Item = Result<T>;

    fn next(&mut self) -> Option<Result<T>> {
        let map = &mut self.map;
        self.rows
            .next()
            .map(|row_result| row_result.map(|row| (map)(&row)))
    }
}

/// An iterator over the mapped resulting rows of a query, with an Error type
/// unifying with Error.
pub struct AndThenRows<'stmt, F> {
    rows: Rows<'stmt>,
    map: F,
}

// TODO: This trait lets us have "pub(crate)" visibility on some methods. Remove this
// once pub(crate) is stable.
pub trait AndThenRowsCrateImpl<'stmt, T, E, F> {
    fn new(rows: Rows<'stmt>, f: F) -> AndThenRows<'stmt, F>;
}

impl<'stmt, T, E, F> AndThenRowsCrateImpl<'stmt, T, E, F> for AndThenRows<'stmt, F>
    where F: FnMut(&Row) -> result::Result<T, E>
{
    fn new(rows: Rows<'stmt>, f: F) -> AndThenRows<'stmt, F> {
        AndThenRows { rows, map: f }
    }
}

impl<'stmt, T, E, F> Iterator for AndThenRows<'stmt, F>
    where E: convert::From<Error>,
          F: FnMut(&Row) -> result::Result<T, E>
{
    type Item = result::Result<T, E>;

    fn next(&mut self) -> Option<Self::Item> {
        let map = &mut self.map;
        self.rows
            .next()
            .map(|row_result| row_result.map_err(E::from).and_then(|row| (map)(&row)))
    }
}

/// A single result row of a query.
pub struct Row<'a, 'stmt> {
    stmt: &'stmt Statement<'stmt>,
    phantom: PhantomData<&'a ()>,
}

impl<'a, 'stmt> Row<'a, 'stmt> {
    /// Get the value of a particular column of the result row.
    ///
    /// ## Failure
    ///
    /// Panics if calling `row.get_checked(idx)` would return an error, including:
    ///
    ///    * If the underlying SQLite column type is not a valid type as a source for `T`
    ///    * If the underlying SQLite integral value is outside the range representable by `T`
    ///    * If `idx` is outside the range of columns in the returned query
    pub fn get<I: RowIndex, T: FromSql>(&self, idx: I) -> T {
        self.get_checked(idx).unwrap()
    }

    /// Get the value of a particular column of the result row.
    ///
    /// ## Failure
    ///
    /// Returns an `Error::InvalidColumnType` if the underlying SQLite column
    /// type is not a valid type as a source for `T`.
    ///
    /// Returns an `Error::InvalidColumnIndex` if `idx` is outside the valid column range
    /// for this row.
    ///
    /// Returns an `Error::InvalidColumnName` if `idx` is not a valid column name
    /// for this row.
    pub fn get_checked<I: RowIndex, T: FromSql>(&self, idx: I) -> Result<T> {
        let idx = try!(idx.idx(self.stmt));
        let value = self.stmt.value_ref(idx);
        FromSql::column_result(value).map_err(|err| match err {
                                                  FromSqlError::InvalidType => {
                                                      Error::InvalidColumnType(idx,
                                                                               value.data_type())
                                                  }
                                                  FromSqlError::OutOfRange(i) => {
                                                      Error::IntegralValueOutOfRange(idx, i)
                                                  }
                                                  FromSqlError::Other(err) => {
                Error::FromSqlConversionFailure(idx as usize, value.data_type(), err)
            }
                                              })
    }

    /// Return the number of columns in the current row.
    pub fn column_count(&self) -> usize {
        self.stmt.column_count()
    }
}

/// A trait implemented by types that can index into columns of a row.
pub trait RowIndex {
    /// Returns the index of the appropriate column, or `None` if no such
    /// column exists.
    fn idx(&self, stmt: &Statement) -> Result<usize>;
}

impl RowIndex for usize {
    #[inline]
    fn idx(&self, stmt: &Statement) -> Result<usize> {
        if *self >= stmt.column_count() {
            Err(Error::InvalidColumnIndex(*self))
        } else {
            Ok(*self)
        }
    }
}

impl<'a> RowIndex for &'a str {
    #[inline]
    fn idx(&self, stmt: &Statement) -> Result<usize> {
        stmt.column_index(*self)
    }
}