use anyhow::Result;
use ratatui::{
    buffer::Buffer,
    layout::{Constraint, Flex, Rect},
    style::{Color, Stylize},
    text::{Line, Text},
    widgets::{Block, Cell, Row, StatefulWidget, Table, Widget},
};

use super::{Address, Book, RangeSelection};

// TODO(zaphar): Move this to the book module.
// NOTE(zaphar): This is stolen from ironcalc but ironcalc doesn't expose it
// publically.
pub(crate) const LAST_COLUMN: usize = 16_384;
pub(crate) const LAST_ROW: usize = 1_048_576;

/// A visible column to show in our Viewport.
#[derive(Clone, Debug)]
pub struct VisibleColumn {
    pub idx: usize,
    pub length: u16,
}

impl<'a> From<&'a VisibleColumn> for Constraint {
    fn from(value: &'a VisibleColumn) -> Self {
        Constraint::Length(value.length as u16)
    }
}

#[derive(Debug, Default)]
pub struct ViewportState {
    prev_corner: Address,
}

/// A renderable viewport over a book.
pub struct Viewport<'ws> {
    pub(crate) selected: Address,
    book: &'ws Book,
    range_selection: Option<&'ws RangeSelection>,
    block: Option<Block<'ws>>,
}

pub(crate) const COLNAMES: [&'static str; 26] = [
    "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S",
    "T", "U", "V", "W", "X", "Y", "Z",
];

impl<'ws> Viewport<'ws> {
    pub fn new(book: &'ws Book, app_state: Option<&'ws RangeSelection>) -> Self {
        Self {
            book,
            range_selection: app_state,
            selected: Default::default(),
            block: None,
        }
    }

    pub fn with_selected(mut self, location: Address) -> Self {
        self.selected = location;
        self
    }

    pub(crate) fn get_visible_rows(&self, height: u16, state: &ViewportState) -> Vec<usize> {
        // NOTE(jeremy): For now the row default height is 1. We'll have
        // to adjust that if this changes.
        let mut length = 1;
        let start_row = std::cmp::min(self.selected.row, state.prev_corner.row);
        let mut start = start_row;
        let mut end = start_row;
        for row_idx in start_row..=LAST_ROW {
            let updated_length = length + 1;
            if updated_length <= height {
                length = updated_length;
                end = row_idx;
            } else if self.selected.row >= row_idx {
                start = start + 1;
                end = row_idx;
            } else {
                //dbg!(&start);
                //dbg!(&end);
                break;
            }
        }
        return (start..=end).collect();
    }

    pub(crate) fn get_visible_columns(
        &self,
        width: u16,
        state: &ViewportState,
    ) -> Result<Vec<VisibleColumn>> {
        let mut visible = Vec::new();
        // TODO(zaphar): This should be a shared constant with our first column.
        // We start out with a length of 5 already reserved
        let mut length = 5;
        let start_idx = std::cmp::min(self.selected.col, state.prev_corner.col);
        for idx in start_idx..=LAST_COLUMN {
            let size = self.book.get_col_size(idx)? as u16;
            let updated_length = length + size;
            let col = VisibleColumn { idx, length: size };
            if updated_length < width {
                length = updated_length;
                visible.push(col);
            } else if self.selected.col >= col.idx {
                // We need a sliding window now
                if let Some(first) = visible.first() {
                    // subtract the first columns size.
                    length = length - first.length;
                    // remove the first column.
                    // TODO(jwall): This is a bit inefficient. Can we do better?
                    visible = visible.into_iter().skip(1).collect();
                }
                // Add this col to the visible.
                length += size;
                visible.push(col);
                // What if the length is still too long?
                if length > width {
                    if let Some(first) = visible.first() {
                        // subtract the first columns size.
                        length = length - first.length;
                    }
                    visible = visible.into_iter().skip(1).collect();
                }
            } else {
                break;
            }
        }
        return Ok(visible);
    }

    pub fn block(mut self, block: Block<'ws>) -> Self {
        self.block = Some(block);
        self
    }

    pub(crate) fn to_table<'widget>(
        &self,
        width: u16,
        height: u16,
        state: &mut ViewportState,
    ) -> Result<Table<'widget>> {
        let visible_columns = self.get_visible_columns(width, state)?;
        let visible_rows = self.get_visible_rows(height, state);
        if let Some(vc) = visible_columns.first() {
            state.prev_corner.col = vc.idx
        }
        if let Some(vr) = visible_rows.first() {
            state.prev_corner.row = *vr;
        }
        let rows: Vec<Row> =
            visible_rows
                .into_iter()
                .map(|ri| {
                    let mut cells = vec![Cell::new(Text::from(ri.to_string()))];
                    cells.extend(visible_columns.iter().map(
                        |VisibleColumn { idx: ci, length: _ }| {
                            let content = self
                                .book
                                .get_cell_addr_rendered(&Address { row: ri, col: *ci })
                                .unwrap();
                            self.compute_cell_style(ri, *ci, Cell::new(Text::raw(content)))
                        },
                    ));
                    Row::new(cells)
                })
                .collect();
        let constraints: Vec<Constraint> = visible_columns
            .iter()
            .map(|vc| Constraint::from(vc))
            .collect();
        let end_idx = visible_columns.last().unwrap().idx;
        let mut header = Vec::with_capacity(constraints.len());
        header.push(Cell::new(""));
        header.extend((state.prev_corner.col..=end_idx).map(|i| {
            let count = if i == 26 { 1 } else { (i / 26) + 1 };
            let even = i % 2 == 0;
            Cell::new(Line::raw(COLNAMES[(i - 1) % 26].repeat(count)).centered())
                .bg(if even {
                    Color::Rgb(57, 61, 71)
                } else {
                    Color::Rgb(165, 169, 160)
                })
                .fg(if even { Color::White } else { Color::Black })
                .bold()
        }));
        let mut col_constraints = vec![Constraint::Length(5)];
        col_constraints.extend(constraints.into_iter());
        Ok(Table::new(rows, col_constraints)
            .header(Row::new(header).underlined())
            .column_spacing(0)
            .flex(Flex::Start))
    }

    fn compute_cell_style<'widget>(&self, ri: usize, ci: usize, mut cell: Cell<'widget>) -> Cell<'widget> {
        let style = self.book.get_cell_style(self.book.current_sheet, &Address { row: ri, col: ci, });
        let bg_color = map_color(style.as_ref().map(|s| s.fill.bg_color.as_ref()).flatten(), Color::Rgb(35, 33, 54));
        let fg_color = map_color(style.as_ref().map(|s| s.fill.fg_color.as_ref()).flatten(), Color::White);
        if let Some((start, end)) =
            &self.range_selection.map_or(None, |r| r.get_range())
        {
            if ri >= start.row
                && ri <= end.row
                && ci >= start.col
                && ci <= end.col
            {
                // This is a selected range
                cell = cell.fg(Color::Black).bg(Color::LightBlue)
            }
        } else {
            cell = cell.bg(bg_color).fg(fg_color);
        }
        match (self.book.location.row == ri, self.book.location.col == ci) {
            (true, true) => cell.fg(Color::White).bg(Color::Rgb(57, 61, 71)),
            // TODO(zaphar): Support ironcalc style options
            _ => cell,
        }
        .bold()
    }
}

pub(crate) fn map_color(color: Option<&String>, otherwise: Color) -> Color {
    color.map(|s| match s.to_lowercase().as_str() {
        "red" => Color::Red,
        "blue" => Color::Blue,
        "green" => Color::Green,
        "magenta" => Color::Magenta,
        "cyan" => Color::Cyan,
        "white" => Color::White,
        "yellow" => Color::Yellow,
        "black" => Color::Black,
        "gray" | "grey" => Color::Gray,
        "lightred" => Color::LightRed,
        "lightblue" => Color::LightBlue,
        "lightgreen" => Color::LightGreen,
        "lightmagenta" => Color::LightMagenta,
        "lightcyan" => Color::LightCyan,
        "lightyellow" => Color::LightYellow,
        "darkgrey" | "darkgray" => Color::DarkGray,
        candidate => {
            // TODO(jeremy): Should we support more syntaxes than hex string?
            // hsl(...) ??
            // rgb(...) ??
            if candidate.starts_with("#") {
                if let Ok(rgb) = colorsys::Rgb::from_hex_str(candidate) {
                    // Note that the colorsys rgb model clamps the f64 values to no more 
                    // than 255.0 so the below casts are safe.
                    Color::Rgb(rgb.red() as u8, rgb.green() as u8, rgb.blue() as u8)
                } else {
                    otherwise
                }
            } else {
                otherwise
            }
        }
    }).unwrap_or(otherwise)
}

impl<'ws> StatefulWidget for Viewport<'ws> {
    type State = ViewportState;

    fn render(self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
        // The block surrounding this table adds 2 additional rows and columns
        // to the available rect for rendering this table.
        let mut table = self
            .to_table(area.width - 2, area.height - 2, state)
            .expect("Failed to turn viewport into a table.");
        if let Some(block) = self.block {
            table = table.block(block);
        }
        Widget::render(table, area, buf);
    }
}