use cursive::direction::Direction;
use cursive::event::{Event, EventResult, Key};
use cursive::theme::{Effect, Style};
use cursive::view::View;
use cursive::{Printer, Vec2};

use chrono::prelude::*;
use chrono::{Duration, Local, NaiveDate};

use crate::habit::{Bit, Count, Habit, TrackEvent, ViewMode};

use crate::CONFIGURATION;

pub trait ShadowView {
    fn draw(&self, printer: &Printer);
    fn required_size(&mut self, _: Vec2) -> Vec2;
    fn take_focus(&mut self, _: Direction) -> bool;
    fn on_event(&mut self, e: Event) -> EventResult;
}

// the only way to not rewrite each View implementation for trait
// objects of Habit is to rewrite the View trait itself.
impl<T> ShadowView for T
where
    T: Habit,
    T::HabitType: std::fmt::Display,
{
    fn draw(&self, printer: &Printer) {
        let now = if self.view_month_offset() == 0 {
            Local::today()
        } else {
            Local::today()
                .checked_sub_signed(Duration::weeks(4 * self.view_month_offset() as i64))
                .unwrap()
        };
        let year = now.year();
        let month = now.month();

        let goal_reached_style = Style::from(CONFIGURATION.reached_color);
        let todo_style = Style::from(CONFIGURATION.todo_color);
        let future_style = Style::from(CONFIGURATION.future_color);

        let strikethrough = Style::from(Effect::Strikethrough);

        let goal_status =
            self.view_month_offset() == 0 && self.reached_goal(Local::now().naive_utc().date());

        printer.with_style(
            Style::merge(&[
                if goal_status {
                    strikethrough
                } else {
                    Style::none()
                },
                if !printer.focused {
                    future_style
                } else {
                    Style::none()
                },
            ]),
            |p| {
                p.print((0, 0), &format!(" {} ", self.name()));
            },
        );

        let draw_month = |printer: &Printer| {
            let days = (1..31)
                .map(|i| NaiveDate::from_ymd_opt(year, month, i))
                .flatten() // dates 28-31 may not exist, ignore them if they don't
                .collect::<Vec<_>>();
            for (week, line_nr) in days.chunks(7).zip(2..) {
                let weekly_goal = self.goal() * week.len() as u32;
                let is_this_week = week.contains(&Local::now().naive_utc().date());
                let remaining = week.iter().map(|&i| self.remaining(i)).sum::<u32>();
                let completions = weekly_goal - remaining;
                let full = CONFIGURATION.view_width - 8;
                let bars_to_fill = (completions * full as u32) / weekly_goal;
                let percentage = (completions as f64 * 100f64) / weekly_goal as f64;
                printer.with_style(future_style, |p| {
                    p.print((4, line_nr), &"―".repeat(full));
                });
                printer.with_style(goal_reached_style, |p| {
                    p.print((4, line_nr), &"―".repeat(bars_to_fill as usize));
                });
                printer.with_style(
                    if is_this_week {
                        Style::none()
                    } else {
                        future_style
                    },
                    |p| {
                        p.print((0, line_nr), &format!("{:3.0}% ", percentage));
                    },
                );
            }
        };
        let draw_day = |printer: &Printer| {
            let mut i = 1;
            while let Some(d) = NaiveDate::from_ymd_opt(year, month, i) {
                let day_style;
                if self.reached_goal(d) {
                    day_style = goal_reached_style;
                } else {
                    day_style = todo_style;
                }
                let coords: Vec2 = ((i % 7) * 3, i / 7 + 2).into();
                if let Some(c) = self.get_by_date(d) {
                    printer.with_style(day_style, |p| {
                        p.print(coords, &format!("{:^3}", c));
                    });
                } else {
                    printer.with_style(future_style, |p| {
                        p.print(coords, &format!("{:^3}", CONFIGURATION.future_chr));
                    });
                }
                i += 1;
            }
        };
        match self.view_mode() {
            ViewMode::Day => draw_day(printer),
            ViewMode::Month => draw_month(printer),
            _ => draw_day(printer),
        };
    }

    fn required_size(&mut self, _: Vec2) -> Vec2 {
        (25, 6).into()
    }

    fn take_focus(&mut self, _: Direction) -> bool {
        true
    }

    fn on_event(&mut self, e: Event) -> EventResult {
        let now = Local::now().naive_utc().date();
        match e {
            Event::Key(Key::Enter) | Event::Char('n') => {
                self.modify(now, TrackEvent::Increment);
                return EventResult::Consumed(None);
            }
            Event::Key(Key::Backspace) | Event::Char('p') => {
                self.modify(now, TrackEvent::Decrement);
                return EventResult::Consumed(None);
            }
            _ => return EventResult::Ignored,
        }
    }
}

macro_rules! auto_view_impl {
    ($struct_name:ident) => {
        impl View for $struct_name {
            fn draw(&self, printer: &Printer) {
                ShadowView::draw(self, printer);
            }
            fn required_size(&mut self, x: Vec2) -> Vec2 {
                ShadowView::required_size(self, x)
            }
            fn take_focus(&mut self, d: Direction) -> bool {
                ShadowView::take_focus(self, d)
            }
            fn on_event(&mut self, e: Event) -> EventResult {
                ShadowView::on_event(self, e)
            }
        }
    };
}

auto_view_impl!(Count);
auto_view_impl!(Bit);