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use std::any::{Any, TypeId};
use std::collections::HashMap;
use std::ops::Index;

use crate::{DataFrame, Header, ColumnType};

/// An opaque container for arbitrary types plucked from different [`Column`]s
///
/// `Row`s only exist derivatively from a [`DataFrame`] that holds them. They hold boxed
/// references to the values owned by [`Column`]s.
///
/// Because `Row`s exist ephemerally, the number of cells and their types can't be known at compile
/// time. The values are stored as [`Any`]s and must be downcast into the appropriate types to
/// access the interior values. `Row` allows you to access values by specifying the column name or
/// offset and supplying a type parameter which is forwarded to [`downcast_ref`] for you.
///
/// ```
/// use tubular::DataFrame;
///
/// let mut df = DataFrame::default();
/// df.push("Fruits", &["apple", "pear", "mango"]);
/// df.push("Quantity", &[16, 25, 3]);
/// df.push("Organic", &[true, true, false]);
///
/// for row in df.rows() {
///     let organic = *row.column_name::<bool>("Organic");
///     let label = if organic { "Organic" } else { "" };
///     println!("{} Fruit {} - {} available",
///         label,
///         row.column_name::<String>("Fruits"),
///         row.column_name::<i32>("Quantity")
///     );
/// }
/// ```
///
/// [`Column`]: enum.Column.html
#[derive(Default)]
pub struct Row<'d> {
    headers: Vec<&'d Header>,
    cells: HashMap<&'d Header, Box<dyn Any>>,
}

impl<'d> Row<'d> {
    /// Number of cells in this `Row`
    pub fn len(&self) -> usize {
        self.cells.len()
    }

    /// Returns the cell value by number and downcasts to `T` simultaneously.
    ///
    /// # Panics
    ///
    /// This method panics if `T` does not match the type of the value at the provided index.
    pub fn column_index<T>(&'d self, index: usize) -> &'d T
        where T: 'static + ColumnType {
        self[index].downcast_ref::<T>().unwrap()
    }

    /// Returns the cell value by column name and downcasts to `T` simultaneously.
    ///
    /// # Panics
    ///
    /// This method panics if `T` does not match the type of the value at the provided name.
    pub fn column_name<T>(&'d self, index: &'static str) -> &'d T
        where T: 'static + ColumnType {
        self[index].downcast_ref::<T>().unwrap()
    }
}

impl<'d> std::fmt::Debug for Row<'d> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let mut cell_displays = vec![];
        for i in 0..self.len() {
            let any_cell = &self[i];
            let type_id = any_cell.type_id();
            cell_displays.push(if type_id == TypeId::of::<String>() {
                any_cell.downcast_ref::<String>().unwrap().clone()
            } else if type_id == TypeId::of::<bool>() {
                format!("{}", any_cell.downcast_ref::<bool>().unwrap())
            } else if type_id == TypeId::of::<u32>() {
                format!("{}", any_cell.downcast_ref::<u32>().unwrap())
            } else {
                "?".into()
            })
        }
        write!(f, "Row[{}]", cell_displays.join(", "))
    }
}

impl<'d> Index<&'static str> for Row<'d> {
    type Output = Box<dyn Any>;

    fn index(&self, index: &'static str) -> &Self::Output {
        &self.cells[&index.to_string()]
    }
}

impl<'d> Index<String> for Row<'d> {
    type Output = Box<dyn Any>;

    fn index(&self, index: String) -> &Self::Output {
        &self.cells[&index]
    }
}

impl<'d> Index<usize> for Row<'d> {
    type Output = Box<dyn Any>;

    fn index(&self, index: usize) -> &Self::Output {
        &self.cells[&self.headers[index]]
    }
}

/// Iterator over [`Row`](struct.Row.html) made by calling [`rows()`](struct.DataFrame.html#method.rows)
#[derive(Debug, PartialEq)]
pub struct Rows<'d> {
    index: usize,
    df: &'d DataFrame,
}

impl<'d> From<&'d DataFrame> for Rows<'d> {
    fn from(df: &'d DataFrame) -> Rows<'d> {
        Rows {
            index: 0,
            df,
        }
    }
}

impl<'d> Iterator for Rows<'d> {
    type Item = Row<'d>;

    fn next(&mut self) -> Option<Row<'d>> {
        if self.index >= self.df.row_len() {
            return None;
        }

        let index = self.index;
        self.index += 1;

        let mut row = Row::default();
        for (col_index, column) in self.df.into_iter().enumerate() {
            let header: &'d Header = &self.df.headers()[col_index];
            row.cells.insert(header, column.to_any(index));
            row.headers.push(header);
        }

        Some(row)
    }
}