//! Title screen: a turning orrery over a drifting starfield.
//!
//! Every universe seed gets its own orrery, and everything here moves as a
//! function of `ctx.ticks`, so it doubles as a check that the tick loop runs.

use std::f64::consts::TAU;

use rand::RngExt;
use ratatui::Frame;
use ratatui::buffer::Buffer;
use ratatui::crossterm::event::{KeyCode, KeyEvent};
use ratatui::layout::{Constraint, Flex, Layout, Rect};
use ratatui::style::{Color, Style, Stylize};
use ratatui::symbols::Marker;
use ratatui::text::{Line, Span};
use ratatui::widgets::Paragraph;
use ratatui::widgets::canvas::{Canvas, Points};

use super::derelict::Derelict;
use super::forge::Forge;
use super::{Scene, Transition};
use crate::app::{Ctx, TICKS_PER_SECOND};
use crate::seed;

const LOGO: [&str; 4] = [
    r"  ___    ___   ___   ___   ___  __   __",
    r" / _ \  | _ \ | _ \ | __| | _ \ \ \ / /",
    r"| (_) | |   / |   / | _|  |   /  \ V / ",
    r" \___/  |_|_\ |_|_\ |___| |_|_\   |_|  ",
];

/// Star layers: drift speed in screen-widths per second, glyph, colour.
/// Nearer layers move faster, which reads as depth.
const STAR_LAYERS: [(f64, char, Color); 3] =
    [(0.004, '.', Color::DarkGray), (0.010, '·', Color::Gray), (0.025, '*', Color::White)];

/// The orrery is seen from above at an angle, so circular orbits look like
/// ellipses this many times as tall as they are wide.
const TILT: f64 = 0.4;

const PLANET_COLOURS: [Color; 6] = [
    Color::LightRed,
    Color::LightBlue,
    Color::LightGreen,
    Color::LightMagenta,
    Color::LightCyan,
    Color::Rgb(205, 133, 63),
];

struct Star {
    x: f64,
    y: f64,
    layer: usize,
}

struct Planet {
    /// Orbit radius as a fraction of the largest orbit that fits.
    orbit: f64,
    /// Seconds per revolution.
    period: f64,
    phase: f64,
    glyph: &'static str,
    colour: Color,
}

pub struct Title {
    stars: Vec<Star>,
    planets: Vec<Planet>,
}

impl Title {
    pub fn new(ctx: &Ctx) -> Self {
        let mut rng = seed::rng(seed::derive(ctx.seed, "title", 0));
        let stars = (0..160)
            .map(|_| Star {
                x: rng.random(),
                y: rng.random(),
                layer: rng.random_range(0..STAR_LAYERS.len()),
            })
            .collect();
        let count = rng.random_range(3..=5);
        let planets = (0..count)
            .map(|i| {
                let orbit = (i as f64 + rng.random_range(0.6..1.0)) / count as f64;
                Planet {
                    orbit,
                    // Kepler's third law, roughly: outer planets are slower.
                    period: 45.0 * orbit.powf(1.5),
                    phase: rng.random_range(0.0..TAU),
                    glyph: if rng.random_bool(0.5) { "o" } else { "•" },
                    colour: PLANET_COLOURS[rng.random_range(..PLANET_COLOURS.len())],
                }
            })
            .collect();
        Title { stars, planets }
    }

    fn draw_stars(&self, buf: &mut Buffer, area: Rect, seconds: f64) {
        for star in &self.stars {
            let (speed, glyph, colour) = STAR_LAYERS[star.layer];
            let x = (star.x - speed * seconds).rem_euclid(1.0);
            let col = area.x + (x * f64::from(area.width)) as u16;
            let row = area.y + (star.y * f64::from(area.height)) as u16;
            if let Some(cell) = buf.cell_mut((col, row)) {
                cell.set_char(glyph).set_fg(colour);
            }
        }
    }

    fn draw_orrery(&self, frame: &mut Frame, area: Rect, seconds: f64) {
        // Braille gives each cell 2x4 dots. With these bounds one unit is one
        // dot, and dots are about square, so geometry here needs no aspect
        // correction (unlike plain cells, which are twice as tall as wide).
        let half_w = f64::from(area.width);
        let half_h = 2.0 * f64::from(area.height);
        let max_radius = (half_w * 0.95).min(half_h * 0.9 / TILT);

        let canvas = Canvas::default()
            .marker(Marker::Braille)
            .x_bounds([-half_w, half_w])
            .y_bounds([-half_h, half_h])
            .paint(|c| {
                for planet in &self.planets {
                    let r = planet.orbit * max_radius;
                    let steps = (r * 2.0) as usize + 16;
                    let ring: Vec<(f64, f64)> = (0..steps)
                        .map(|i| {
                            let a = TAU * i as f64 / steps as f64;
                            (r * a.cos(), r * TILT * a.sin())
                        })
                        .collect();
                    c.draw(&Points { coords: &ring, color: Color::DarkGray });
                }
                c.print(0.0, 0.0, Span::styled("☼", Style::new().fg(Color::Yellow).bold()));
                for planet in &self.planets {
                    let r = planet.orbit * max_radius;
                    let a = planet.phase + TAU * seconds / planet.period;
                    let glyph = Span::styled(planet.glyph, Style::new().fg(planet.colour).bold());
                    c.print(r * a.cos(), r * TILT * a.sin(), glyph);
                }
            });
        frame.render_widget(canvas, area);
    }
}

impl Scene for Title {
    fn key(&mut self, key: KeyEvent, ctx: &mut Ctx) -> Transition {
        match key.code {
            KeyCode::Char(c) => match c.to_ascii_lowercase() {
                'd' => {
                    ctx.boarded += 1;
                    let ship = seed::derive(ctx.seed, "derelict", ctx.boarded);
                    Transition::Push(Box::new(Derelict::new(ship)))
                }
                'n' => Transition::Push(Box::new(Forge::new(ctx))),
                'q' => Transition::Quit,
                _ => Transition::None,
            },
            KeyCode::Esc => Transition::Quit,
            _ => Transition::None,
        }
    }

    fn render(&self, frame: &mut Frame, ctx: &Ctx) {
        let seconds = ctx.ticks as f64 / f64::from(TICKS_PER_SECOND);
        let area = frame.area();
        self.draw_stars(frame.buffer_mut(), area, seconds);

        let [sky, logo, _, menu, hold, footer] = Layout::vertical([
            Constraint::Fill(1),
            Constraint::Length(LOGO.len() as u16),
            Constraint::Length(1),
            Constraint::Length(4),
            Constraint::Length(1),
            Constraint::Length(1),
        ])
        .areas(area);

        self.draw_orrery(frame, sky, seconds);

        let logo_lines: Vec<Line> = LOGO.iter().map(|l| Line::from(*l).bold()).collect();
        frame.render_widget(Paragraph::new(logo_lines).centered().fg(Color::Yellow), logo);

        let item = |key: &'static str, label: &'static str, built: bool| {
            let style = if built { Style::new() } else { Style::new().fg(Color::DarkGray) };
            let mut spans = vec![Span::styled(key, style.bold()), Span::styled(label, style)];
            if !built {
                spans.push(Span::styled("  (not yet built)", style.italic()));
            }
            Line::from(spans)
        };
        let [menu] = Layout::horizontal([Constraint::Length(46)]).flex(Flex::Center).areas(menu);
        frame.render_widget(
            Paragraph::new(vec![
                item("[d] ", "board a derelict", true),
                item("[n] ", "the name forge", true),
                item("[f] ", "fly a star system", false),
                item("[q] ", "leave", true),
            ]),
            menu,
        );

        let h = &ctx.hold;
        if !h.artifacts.is_empty() || h.scrip > 0 {
            let plural = if h.artifacts.len() == 1 { "" } else { "s" };
            let text = format!(
                "your hold: {} artifact{plural}, {} ¤ of salvage",
                h.artifacts.len(),
                h.scrip
            );
            frame.render_widget(Paragraph::new(text).centered().fg(Color::Yellow), hold);
        }

        let keys = if ctx.keyboard.key_release {
            "held keys detectable (kitty keyboard protocol)"
        } else {
            "held keys not detectable: flight will need a throttle"
        };
        frame.render_widget(
            Paragraph::new(format!("universe {}  ·  {keys}", ctx.seed)).centered().dark_gray(),
            footer,
        );
    }
}