use egui::{Color32, Direction, FontId, Layout, RichText, Ui};
use egui_extras::{Size, StripBuilder};
use std::time::{Duration, Instant};

use eframe::App;

#[derive(Debug, Clone, Copy)]
pub enum CountDirection {
    Up,
    Down,
}

#[derive(Debug, Clone, Copy)]
pub struct Timer {
    direction: CountDirection,
    duration: Duration,
    state: State,
}

#[derive(Debug, Clone, Copy)]
enum State {
    Unstarted,
    Paused(ChronoState),  // time remaining
    Running(ChronoState), // time remaining
}

impl PartialEq for State {
    fn eq(&self, other: &Self) -> bool {
        match (self, other) {
            (Self::Paused(_), Self::Paused(_)) => true,
            (Self::Running(_), Self::Running(_)) => true,
            (Self::Unstarted, Self::Unstarted) => true,
            _ => false,
        }
    }
}

impl Eq for State {}

#[derive(Debug, Clone, Copy)]
struct ChronoState {
    started: Instant,
    remaining: Duration,
}

impl Default for Timer {
    fn default() -> Self {
        let dur = Duration::from_secs(30);
        Self {
            direction: CountDirection::Down,
            duration: dur,
            state: State::Unstarted,
        }
    }
}

impl App for Timer {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        ctx.request_repaint_after(Duration::from_secs(1));
        egui::CentralPanel::default().show(ctx, |ui| {
            let size = ctx.used_size();
            let vsize = if size[1].is_normal() {
                size[1].abs()
            } else {
                600.0
            };

            match self.state {
                State::Unstarted => self.unstarted(ui, vsize),
                _ => self.running(ui, vsize),
            }
        });
    }
}

impl Timer {
    pub fn new(duration: Duration, direction: CountDirection, paused: bool) -> Self {
        if paused {
            Timer {
                duration,
                direction,
                state: State::Unstarted,
            }
        } else {
            let cs = ChronoState {
                remaining: duration,
                started: Instant::now(),
            };
            Timer {
                duration,
                direction,
                state: State::Running(cs),
            }
        }
    }

    fn unstarted(&mut self, ui: &mut Ui, size: f32) {
        let start = RichText::new("START")
            .font(FontId::monospace(size * 0.9))
            .color(Color32::WHITE)
            .background_color(Color32::LIGHT_GREEN);

        StripBuilder::new(ui)
            .size(Size::remainder())
            .cell_layout(Layout::centered_and_justified(egui::Direction::TopDown))
            .horizontal(|mut strip| {
                strip.cell(|ui| {
                    if ui.button(start).clicked() {
                        let dur = self.duration;
                        self.state = State::Running(ChronoState {
                            started: Instant::now(),
                            remaining: dur,
                        });
                    }
                });
            });
    }

    fn running(&mut self, ui: &mut Ui, size: f32) {
        let tsize = size * 0.3;
        let text = RichText::new("PAUSE")
            .font(FontId::monospace(tsize))
            .color(Color32::GOLD);

        let elapsed;
        let started;
        let mut is_paused;
        if let State::Running(rs) = self.state {
            elapsed = Instant::now() - rs.started;
            started = rs.started;
            is_paused = false;
        } else if let State::Paused(cs) = self.state {
            elapsed = cs.remaining;
            started = Instant::now() - (self.duration - elapsed);
            is_paused = true;
        } else {
            unreachable!()
        }

        let remaining = if is_paused {
            elapsed
        } else {
            self.duration.saturating_sub(elapsed)
        };

        StripBuilder::new(ui)
            .size(Size::relative(0.3333))
            .size(Size::remainder())
            .cell_layout(Layout::centered_and_justified(Direction::LeftToRight))
            .vertical(|mut strip| {
                if is_paused {
                    strip.strip(|pstrip| {
                        pstrip
                            .sizes(Size::remainder(), 2)
                            .cell_layout(Layout::centered_and_justified(Direction::TopDown))
                            .horizontal(|mut pstrip| {
                                pstrip.cell(|ui| {
                                    let resume = RichText::new("RESUME")
                                        .color(Color32::GREEN)
                                        .font(FontId::monospace(tsize));
                                    if ui.button(resume).clicked() {
                                        is_paused = false;
                                    }
                                });
                                pstrip.cell(|ui| {
                                    let reset = RichText::new("RESET")
                                        .color(Color32::RED)
                                        .font(FontId::monospace(tsize));
                                    if ui.button(reset).clicked() {
                                        self.state = State::Unstarted;
                                        is_paused = true;
                                    }
                                });
                            });
                    });
                } else {
                    // first the pause
                    strip.cell(|ui| {
                        if ui.button(text).clicked() {
                            is_paused = true;
                        }
                    });
                }

                let remaining = match self.direction {
                    CountDirection::Down => remaining,
                    _ => self.duration - remaining,
                };

                // now the numbers
                let hours = remaining.as_secs() / 3600;
                let minutes = (remaining.as_secs() / 60) % 60;
                let seconds = remaining.as_secs() % 60;
                let tsize = size * 0.7;
                let hours = RichText::new(format!("{:02}", hours)).font(FontId::monospace(tsize));
                let minutes =
                    RichText::new(format!("{:02}", minutes)).font(FontId::monospace(tsize));
                let seconds =
                    RichText::new(format!("{:02}", seconds)).font(FontId::monospace(tsize));
                strip.strip(|strip| {
                    strip
                        .sizes(Size::relative(0.33), 3)
                        .cell_layout(Layout::centered_and_justified(Direction::TopDown))
                        .horizontal(|mut strip| {
                            strip.cell(|ui| {
                                ui.label(hours);
                            });
                            strip.cell(|ui| {
                                ui.label(minutes);
                            });
                            strip.cell(|ui| {
                                ui.label(seconds);
                            });
                        });
                });
            });

        let cs = ChronoState { remaining, started };
        if is_paused {
            if self.state == State::Unstarted {
                return;
            }
            self.state = State::Paused(cs);
        } else {
            self.state = State::Running(cs);
        }
    }
}