/*!
 * Iterators over parts of a Matrix
 *
 * # Examples
 *
 * Extending a matrix with new columns
 * ```
 * use easy_ml::matrices::Matrix;
 *
 * // we start with some matrix where the first and second columns correspond
 * // to x and y points
 * let mut matrix = Matrix::from(vec![
 *     vec![ 3.0, 4.0 ],
 *     vec![ 8.0, 1.0 ],
 *     vec![ 2.0, 9.0 ]]);
 * // insert a third column based on the formula x * y
 * matrix.insert_column_with(2, matrix.column_iter(0)
 *     // join together the x and y columns
 *     .zip(matrix.column_iter(1))
 *     // compute the values for the new column
 *     .map(|(x, y)| x * y)
 *     // Collect into a vector so we stop immutably borrowing from `matrix`.
 *     // This is only neccessary when we use the data from a Matrix to modify itself,
 *     // because the rust compiler enforces that we do not mutably and immutably borrow
 *     // something at the same time. If we used data from a different Matrix to update
 *     // `matrix` then we could stop at map and pass the iterator directly.
 *     .collect::<Vec<f64>>()
 *     // now that the Vec created owns the data for the new column and we have stopped
 *     // borrowing immutably from `matrix` we turn the vec back into an iterator and
 *     // mutably borrow `matrix` to add the new column
 *     .drain(..));
 * assert_eq!(matrix.get(0, 2), 3.0 * 4.0);
 * assert_eq!(matrix.get(1, 2), 8.0 * 1.0);
 * assert_eq!(matrix.get(2, 2), 2.0 * 9.0);
 * ```
 */

use crate::matrices::{Matrix, Row, Column};

/**
 * An iterator over a column in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * Depending on the row iterator you want to obtain,
 * can either iterate through 1, 3 or 2, 4.
 */
pub struct ColumnIterator<'a, T: Clone> {
    matrix: &'a Matrix<T>,
    column: Column,
    counter: usize,
    finished: bool,
}

impl <'a, T: Clone> ColumnIterator<'a, T> {
    /**
     * Constructs a column iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>, column: Column) -> ColumnIterator<T> {
        ColumnIterator {
            matrix,
            column,
            counter: 0,
            finished: false,
        }
    }
}

impl <'a, T: Clone> Iterator for ColumnIterator<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get(self.counter, self.column));

        if self.counter == self.matrix.rows() - 1 {
            self.finished = true;
        }

        self.counter += 1;

        value
    }
}

/**
 * An iterator over a row in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * Depending on the row iterator you want to obtain,
 * can either iterate through 1, 2 or 3, 4.
 */
pub struct RowIterator<'a, T: Clone> {
    matrix: &'a Matrix<T>,
    row: Row,
    counter: usize,
    finished: bool,
}

impl <'a, T: Clone> RowIterator<'a, T> {
    /**
     * Constructs a row iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>, row: Row) -> RowIterator<T> {
        RowIterator {
            matrix,
            row,
            counter: 0,
            finished: false,
        }
    }
}

impl <'a, T: Clone> Iterator for RowIterator<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get(self.row, self.counter));

        if self.counter == self.matrix.columns() - 1 {
            self.finished = true;
        }

        self.counter += 1;

        value
    }
}

/**
 * An column major iterator over all values in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * The elements will be iterated through as 1, 3, 2, 4
 */
pub struct ColumnMajorIterator<'a, T: Clone> {
    matrix: &'a Matrix<T>,
    column_counter: Column,
    row_counter: Row,
    finished: bool,
}

impl <'a, T: Clone> ColumnMajorIterator<'a, T> {
    /**
     * Constructs a column major iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>) -> ColumnMajorIterator<T> {
        ColumnMajorIterator {
            matrix,
            column_counter: 0,
            row_counter: 0,
            finished: false,
        }
    }
}

impl <'a, T: Clone> Iterator for ColumnMajorIterator<'a, T> {
    type Item = T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get(self.row_counter, self.column_counter));

        if self.row_counter == self.matrix.rows() - 1
                && self.column_counter == self.matrix.columns() -1 {
            // reached end of matrix for next iteration
            self.finished = true;
        }

        if self.row_counter == self.matrix.rows() - 1 {
            // reached end of a column, need to reset to first element in next column
            self.row_counter = 0;
            self.column_counter += 1;
        } else {
            // keep incrementing through this column
            self.row_counter += 1;
        }

        value
    }
}

/**
 * An iterator over references to a column in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * Depending on the row iterator you want to obtain,
 * can either iterate through &1, &3 or &2, &4.
 */
pub struct ColumnReferenceIterator<'a, T> {
    matrix: &'a Matrix<T>,
    column: Column,
    counter: usize,
    finished: bool,
}

impl <'a, T> ColumnReferenceIterator<'a, T> {
    /**
     * Constructs a column iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>, column: Column) -> ColumnReferenceIterator<T> {
        ColumnReferenceIterator {
            matrix,
            column,
            counter: 0,
            finished: false,
        }
    }
}

impl <'a, T> Iterator for ColumnReferenceIterator<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get_reference(self.counter, self.column));

        if self.counter == self.matrix.rows() - 1 {
            self.finished = true;
        }

        self.counter += 1;

        value
    }
}

/**
 * An iterator over references to a row in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * Depending on the row iterator you want to obtain,
 * can either iterate through &1, &2 or &3, &4.
 */
pub struct RowReferenceIterator<'a, T> {
    matrix: &'a Matrix<T>,
    row: Row,
    counter: usize,
    finished: bool,
}

impl <'a, T> RowReferenceIterator<'a, T> {
    /**
     * Constructs a row iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>, row: Row) -> RowReferenceIterator<T> {
        RowReferenceIterator {
            matrix,
            row,
            counter: 0,
            finished: false,
        }
    }
}

impl <'a, T> Iterator for RowReferenceIterator<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get_reference(self.row, self.counter));

        if self.counter == self.matrix.columns() - 1 {
            self.finished = true;
        }

        self.counter += 1;

        value
    }
}

/**
 * An column major iterator over references to all values in a matrix.
 *
 * For a 2x2 matrix such as `[ 1, 2; 3, 4]`: ie
 * ```ignore
 * [
 *   1, 2
 *   3, 4
 * ]
 * ```
 * The elements will be iterated through as &1, &3, &2, &4
 */
pub struct ColumnMajorReferenceIterator<'a, T> {
    matrix: &'a Matrix<T>,
    column_counter: Column,
    row_counter: Row,
    finished: bool,
}

impl <'a, T> ColumnMajorReferenceIterator<'a, T> {
    /**
     * Constructs a column major iterator over this matrix.
     */
    pub fn new(matrix: &Matrix<T>) -> ColumnMajorReferenceIterator<T> {
        ColumnMajorReferenceIterator {
            matrix,
            column_counter: 0,
            row_counter: 0,
            finished: false,
        }
    }
}

impl <'a, T> Iterator for ColumnMajorReferenceIterator<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        if self.finished {
            return None
        }

        let value = Some(self.matrix.get_reference(self.row_counter, self.column_counter));

        if self.row_counter == self.matrix.rows() - 1
                && self.column_counter == self.matrix.columns() -1 {
            // reached end of matrix for next iteration
            self.finished = true;
        }

        if self.row_counter == self.matrix.rows() - 1 {
            // reached end of a column, need to reset to first element in next column
            self.row_counter = 0;
            self.column_counter += 1;
        } else {
            // keep incrementing through this column
            self.row_counter += 1;
        }

        value
    }
}