//! Drawing space: starfields, lit planets, rocks, stations, wrecks and your
//! ship, in terminal cells.
//!
//! A local map unit is one cell across and half a cell down (cells are
//! about twice as tall as wide), so a circle of radius r spans 2r columns
//! and r rows, and looks round.

use ratatui::buffer::Buffer;
use ratatui::layout::Rect;
use ratatui::style::{Color, Modifier};

use crate::names::Culture;
use crate::seed;
use crate::space::Vec2;
use crate::space::flight::Ship;
use crate::space::system::Rgb;

pub fn rgb((r, g, b): Rgb) -> Color {
    Color::Rgb(r, g, b)
}

/// `colour` at `k` times its brightness (k from 0 to about 1.3).
pub fn shade((r, g, b): Rgb, k: f64) -> Color {
    let f = |c: u8| (f64::from(c) * k).round().clamp(0.0, 255.0) as u8;
    Color::Rgb(f(r), f(g), f(b))
}

/// Between `a` (at k = 0) and `b` (at k = 1).
pub fn mix(a: Rgb, b: Rgb, k: f64) -> Rgb {
    let k = k.clamp(0.0, 1.0);
    let f = |x: u8, y: u8| (f64::from(x) * (1.0 - k) + f64::from(y) * k).round() as u8;
    (f(a.0, b.0), f(a.1, b.1), f(a.2, b.2))
}

/// A number from 0 to 1 that's always the same for the same inputs.
pub fn hash01(seed: u64, x: i64, y: i64) -> f64 {
    let h = seed::derive(seed, "", (x as u64) << 32 ^ (y as u64 & 0xffff_ffff));
    (h >> 11) as f64 / (1u64 << 53) as f64
}

/// Where on screen a map position lands, with the camera in the middle of
/// `area`. Fractional: the cell is the floor of each coordinate.
#[derive(Clone, Copy)]
pub struct View {
    pub area: Rect,
    pub camera: Vec2,
}

impl View {
    pub fn screen(&self, p: Vec2) -> (f64, f64) {
        let a = self.area;
        let col = f64::from(a.x) + f64::from(a.width) / 2.0 + (p.x - self.camera.x);
        let row = f64::from(a.y) + f64::from(a.height) / 2.0 + (p.y - self.camera.y) / 2.0;
        (col, row)
    }

    /// The cell a map position falls in, if it's on screen.
    pub fn cell(&self, p: Vec2) -> Option<(u16, u16)> {
        let (col, row) = self.screen(p);
        cell_in(self.area, col.floor(), row.floor())
    }

    pub fn put(&self, buf: &mut Buffer, p: Vec2, ch: char, fg: Color) {
        if let Some(pos) = self.cell(p) {
            buf[pos].set_char(ch).set_fg(fg);
        }
    }
}

fn cell_in(area: Rect, col: f64, row: f64) -> Option<(u16, u16)> {
    let inside = col >= f64::from(area.x)
        && row >= f64::from(area.y)
        && col < f64::from(area.right())
        && row < f64::from(area.bottom());
    inside.then_some((col as u16, row as u16))
}

/// Writes `text` centred on a screen column, clipped to `area`.
pub fn label(buf: &mut Buffer, area: Rect, col: f64, row: f64, text: &str, fg: Color) {
    let width = text.chars().count() as f64;
    let start = (col - width / 2.0).floor();
    for (i, ch) in text.chars().enumerate() {
        if let Some(pos) = cell_in(area, start + i as f64, row.floor()) {
            buf[pos].set_char(ch).set_fg(fg);
        }
    }
}

/// Star layers: how fast each moves as the camera does, how rare its stars
/// are, glyph, and colour. Slower layers read as further away.
const STAR_LAYERS: [(f64, u32, char, Rgb); 3] = [
    (0.04, 90, '.', (70, 72, 92)),
    (0.12, 170, '·', (130, 132, 150)),
    (0.3, 420, '+', (210, 210, 225)),
];

pub fn starfield(buf: &mut Buffer, area: Rect, camera: Vec2, seed: u64) {
    for (layer, &(parallax, rarity, glyph, colour)) in STAR_LAYERS.iter().enumerate() {
        let layer_seed = seed::derive(seed, "stars", layer as u64);
        let dx = (camera.x * parallax).floor() as i64;
        let dy = (camera.y * parallax / 2.0).floor() as i64;
        for row in area.top()..area.bottom() {
            for col in area.left()..area.right() {
                let h = hash01(layer_seed, i64::from(col) + dx, i64::from(row) + dy);
                if h * f64::from(rarity) < 1.0 {
                    buf[(col, row)].set_char(glyph).set_fg(rgb(colour));
                }
            }
        }
    }
}

/// How to paint a sphere.
pub struct Surface {
    pub rgb: Rgb,
    /// Cloud bands, for giants.
    pub banded: bool,
    /// City lights on the night side.
    pub lights: bool,
    /// Glyphs from darkest to brightest.
    pub ramp: &'static [char],
    /// Varies the mottling and bands from one body to the next.
    pub seed: u64,
}

pub const PLANET_RAMP: &[char] = &['·', '░', '▒', '▓', '█'];
pub const ROCK_RAMP: &[char] = &['.', ':', '%', '#', '@'];

/// A sphere centred at screen position (`col`, `row`), `radius` columns
/// across, lit from `sun` (a unit vector on the map, y down). Returns
/// whether it covered any cell.
pub fn sphere(
    buf: &mut Buffer,
    area: Rect,
    (col, row): (f64, f64),
    radius: f64,
    sun: Vec2,
    surface: &Surface,
) -> bool {
    // Mostly from the side, a little from in front, so there's always a
    // terminator to see.
    let light = {
        let (x, y, z) = (sun.x, sun.y, 0.45);
        let len = (x * x + y * y + z * z).sqrt();
        (x / len, y / len, z / len)
    };
    let top = (row - radius / 2.0).floor() as i64;
    let bottom = (row + radius / 2.0).ceil() as i64;
    let left = (col - radius).floor() as i64;
    let right = (col + radius).ceil() as i64;
    let mut drawn = false;
    for r in top..=bottom {
        for c in left..=right {
            let nx = (c as f64 + 0.5 - col) / radius;
            let ny = (r as f64 + 0.5 - row) * 2.0 / radius;
            let d2 = nx * nx + ny * ny;
            if d2 > 1.0 {
                continue;
            }
            let Some(pos) = cell_in(area, c as f64, r as f64) else {
                continue;
            };
            drawn = true;
            let nz = (1.0 - d2).sqrt();
            let lit = (nx * light.0 + ny * light.1 + nz * light.2).max(0.0);
            let grain = |n: f64| {
                let g = hash01(surface.seed, (nx * n).floor() as i64, (ny * n).floor() as i64);
                0.86 + 0.14 * g
            };
            let mut tone = grain(5.0);
            if surface.banded {
                let phase = (surface.seed % 628) as f64 / 100.0;
                tone =
                    0.84 + 0.12 * (ny * 7.0 + phase).sin() + 0.06 * (ny * 19.0 + phase * 2.0).sin();
            }
            let cell = &mut buf[pos];
            if lit < 0.04 {
                let city = surface.lights && grain(13.0) > 0.99 - 0.08;
                if city {
                    cell.set_char('·').set_fg(Color::Rgb(255, 196, 110));
                } else {
                    cell.set_char(surface.ramp[0]).set_fg(shade(surface.rgb, 0.16 * tone));
                }
                continue;
            }
            let steps = surface.ramp.len() - 1;
            let glyph = surface.ramp[1 + ((lit * steps as f64) as usize).min(steps - 1)];
            cell.set_char(glyph).set_fg(shade(surface.rgb, (0.2 + 0.95 * lit) * tone));
        }
    }
    drawn
}

/// One glyph per eighth of a turn, for headings (0 is up, clockwise).
pub fn arrow(heading: f64) -> char {
    const ARROWS: [char; 8] = ['↑', '↗', '→', '↘', '↓', '↙', '←', '↖'];
    let eighth = (heading / std::f64::consts::TAU * 8.0).round() as i64;
    ARROWS[eighth.rem_euclid(8) as usize]
}

/// Each culture's station, drawn centred on its position.
pub fn station_art(culture: Culture) -> (&'static [&'static str], Rgb) {
    match culture {
        Culture::Qaari => (&["  .-=-.  ", "=(( o ))=", "  '-=-'  "], (232, 190, 112)),
        Culture::Cant => (&["   /\\   ", "=[|##|]=", "  |##|  ", "   \\/   "], (204, 124, 92)),
        Culture::Houses => (&["  _/^^\\_ ", " <|-<>-|>", "   \\__/  "], (206, 186, 240)),
        Culture::Drift => (&[" =o=  =o= ", "<==[  ]==>", " =o=  =o= "], (124, 212, 200)),
    }
}

pub fn draw_station(buf: &mut Buffer, view: &View, culture: Culture, ticks: u64) {
    let (art, colour) = station_art(culture);
    let (col, row) = view.screen(Vec2::ZERO);
    let top = row - art.len() as f64 / 2.0;
    for (i, line) in art.iter().enumerate() {
        let width = line.chars().count() as f64;
        let start = (col - width / 2.0).floor();
        for (j, ch) in line.chars().enumerate() {
            if ch == ' ' {
                continue;
            }
            let Some(pos) = cell_in(view.area, start + j as f64, (top + i as f64).floor()) else {
                continue;
            };
            // Running lights blink in turn.
            let light = ch == 'o' && (ticks / 15 + j as u64).is_multiple_of(3);
            let fg = if light { Color::Rgb(255, 240, 200) } else { rgb(colour) };
            buf[pos].set_char(ch).set_fg(fg);
            if light {
                buf[pos].modifier.insert(Modifier::BOLD);
            }
        }
    }
}

/// A wreck: a dark hull pointing along its heading, with a red distress
/// beacon blinking if `beacon` (there's still anything aboard, and the
/// beacon hasn't failed).
pub fn draw_wreck(
    buf: &mut Buffer,
    view: &View,
    pos: Vec2,
    heading: f64,
    beacon: bool,
    ticks: u64,
) {
    let along = Vec2::from_heading(heading);
    let hull = Color::Rgb(112, 118, 140);
    view.put(buf, pos - along * 1.5, '=', hull);
    view.put(buf, pos, '#', hull);
    view.put(buf, pos + along * 1.5, arrow(heading), hull);
    if beacon && ticks % 40 < 8 {
        view.put(buf, pos, '#', Color::Rgb(255, 70, 60));
    }
}

/// Your ship's outline, a notched dart: corners as (ahead, to the right)
/// of its position, in map units. About five and a half units long.
const HULL: [(f64, f64); 4] = [(2.75, 0.0), (-2.75, 2.1), (-0.75, 0.0), (-2.75, -2.1)];

/// Where the engine flame starts: the notch at the back of the hull.
const NOZZLE: f64 = -0.75;

/// Braille dot bits by (column, row) within a cell.
const BRAILLE: [[u32; 4]; 2] = [[0x01, 0x02, 0x04, 0x40], [0x08, 0x10, 0x20, 0x80]];

/// Your ship, turned to exactly its heading, with a flame out the back
/// while the engine is lit. Drawn in braille dots, which are half a unit
/// square (two across a cell, four down), so it turns smoothly rather than
/// snapping between eight arrows.
pub fn draw_ship(buf: &mut Buffer, view: &View, ship: &Ship, ticks: u64) {
    let ahead = Vec2::from_heading(ship.heading);
    let right = Vec2::new(-ahead.y, ahead.x);
    let local = |p: Vec2| (p.dot(ahead), p.dot(right));
    let (col, row) = view.screen(ship.pos);
    if ship.thrusting {
        // A plume, widest just behind the nozzle, flickering between short
        // and long ten times a second. Its first unit or two is mostly
        // hidden under the hull, which reads better than filling the notch.
        let length = 4.0 + 2.0 * hash01(0, (ticks / 3) as i64, 0);
        let flame = [
            (NOZZLE, 0.5),
            (NOZZLE - 1.5, 1.0),
            (NOZZLE - length, 0.0),
            (NOZZLE - 1.5, -1.0),
            (NOZZLE, -0.5),
        ];
        for ((c, r), ch) in braille(view, ship.pos, 7.0, |p| inside(&flame, local(p))) {
            // Yellow near the ship, cooling to red-orange at the tip.
            let middle = Vec2::new(f64::from(c) + 0.5 - col, (f64::from(r) + 0.5 - row) * 2.0);
            let k = (NOZZLE - local(middle).0) / length;
            let colour = mix((255, 224, 130), (240, 80, 30), (k - 0.3) / 0.7);
            buf[(c, r)].set_char(ch).set_fg(rgb(colour));
        }
    }
    // The hull goes on top: where the two share a cell, the hull wins.
    for (cell, ch) in braille(view, ship.pos, 3.5, |p| inside(&HULL, local(p))) {
        buf[cell].set_char(ch).set_fg(Color::White);
    }
}

/// The braille characters for a shape within `reach` map units of `pos`,
/// and the cells they go in. `covers` says whether a point (in map units
/// from `pos`) is inside the shape, and a dot is lit when the shape covers
/// at least 40% of it, which keeps edges clean at every angle.
fn braille(
    view: &View,
    pos: Vec2,
    reach: f64,
    covers: impl Fn(Vec2) -> bool,
) -> Vec<((u16, u16), char)> {
    // Samples per dot, each way.
    const SAMPLES: u32 = 4;
    let sub = |i: u32| (f64::from(i) + 0.5) / f64::from(SAMPLES);
    let (col, row) = view.screen(pos);
    let mut cells = Vec::new();
    for r in (row - reach / 2.0).floor() as i64..=(row + reach / 2.0).floor() as i64 {
        for c in (col - reach).floor() as i64..=(col + reach).floor() as i64 {
            let Some(cell) = cell_in(view.area, c as f64, r as f64) else {
                continue;
            };
            let mut bits = 0;
            for (dx, column) in BRAILLE.iter().enumerate() {
                for (dy, bit) in column.iter().enumerate() {
                    let mut hits = 0;
                    for sx in 0..SAMPLES {
                        for sy in 0..SAMPLES {
                            // In map units from `pos`: a column is one, a row two.
                            let x = c as f64 - col + (dx as f64 + sub(sx)) / 2.0;
                            let y = (r as f64 - row + (dy as f64 + sub(sy)) / 4.0) * 2.0;
                            hits += u32::from(covers(Vec2::new(x, y)));
                        }
                    }
                    if hits * 5 >= SAMPLES * SAMPLES * 2 {
                        bits |= bit;
                    }
                }
            }
            if let Some(ch) = char::from_u32(0x2800 + bits).filter(|_| bits != 0) {
                cells.push((cell, ch));
            }
        }
    }
    cells
}

/// Whether `point` is inside `polygon` (even-odd rule, so it may be concave).
fn inside(polygon: &[(f64, f64)], (x, y): (f64, f64)) -> bool {
    let mut odd = false;
    for (i, &(x1, y1)) in polygon.iter().enumerate() {
        let (x2, y2) = polygon[(i + 1) % polygon.len()];
        if (y1 > y) != (y2 > y) && x < x1 + (y - y1) * (x2 - x1) / (y2 - y1) {
            odd = !odd;
        }
    }
    odd
}

#[cfg(test)]
mod tests {
    use super::*;

    /// Every lit braille dot in `buf`, in map units from the centre of
    /// `view`, as (ahead, to the right) for a ship facing `heading`.
    fn ship_dots(buf: &Buffer, view: &View, heading: f64) -> Vec<(f64, f64)> {
        let ahead = Vec2::from_heading(heading);
        let right = Vec2::new(-ahead.y, ahead.x);
        let (col, row) = view.screen(view.camera);
        let mut dots = Vec::new();
        for r in 0..view.area.height {
            for c in 0..view.area.width {
                let ch = buf[(c, r)].symbol().chars().next().unwrap_or(' ');
                let bits = u32::from(ch).wrapping_sub(0x2800);
                for (dx, column) in BRAILLE.iter().enumerate() {
                    for (dy, &bit) in column.iter().enumerate() {
                        if bits <= 0xff && bits & bit != 0 {
                            let x = f64::from(c) - col + (dx as f64 + 0.5) / 2.0;
                            let y = (f64::from(r) - row + (dy as f64 + 0.5) / 4.0) * 2.0;
                            let p = Vec2::new(x, y);
                            dots.push((p.dot(ahead), p.dot(right)));
                        }
                    }
                }
            }
        }
        dots
    }

    fn ship(heading: f64, thrusting: bool) -> Ship {
        Ship { pos: Vec2::ZERO, vel: Vec2::ZERO, heading, thrusting }
    }

    #[test]
    fn the_ship_points_its_nose_along_its_heading() {
        let view = View { area: Rect::new(0, 0, 20, 10), camera: Vec2::ZERO };
        for heading in [0.0, 1.0, 1.9, 2.5, 3.6, 4.4, 5.5] {
            let mut buf = Buffer::empty(view.area);
            draw_ship(&mut buf, &view, &ship(heading, false), 0);
            let dots = ship_dots(&buf, &view, heading);
            assert!((24..=36).contains(&dots.len()), "{heading}: {} dots", dots.len());
            let front = dots.iter().filter(|d| d.0 > 1.25);
            assert!(front.clone().count() >= 2, "{heading}: a nose");
            assert!(front.clone().all(|d| d.1.abs() < 1.25), "{heading}: a narrow nose");
            let wing = |side: f64| dots.iter().any(|d| d.0 < -1.5 && d.1 * side > 1.25);
            assert!(wing(1.0) && wing(-1.0), "{heading}: wings behind, either side");
        }
    }

    #[test]
    fn a_lit_engine_trails_a_flame_out_the_back() {
        let view = View { area: Rect::new(0, 0, 24, 12), camera: Vec2::ZERO };
        for heading in [0.0, 2.0, 4.0] {
            // The flame's dots, as how far ahead of the ship each one is.
            let flame = |thrusting: bool, ticks: u64| {
                let mut buf = Buffer::empty(view.area);
                draw_ship(&mut buf, &view, &ship(heading, thrusting), ticks);
                for cell in buf.content.iter_mut().filter(|c| c.fg == Color::White) {
                    cell.reset();
                }
                ship_dots(&buf, &view, heading)
            };
            assert!(flame(false, 0).is_empty(), "{heading}: no flame with the engine off");
            let lit = flame(true, 0);
            assert!(!lit.is_empty(), "{heading}: a flame with it on");
            assert!(lit.iter().all(|d| d.0 < -1.0), "{heading}: only behind: {lit:?}");
            let sizes: Vec<usize> = (0..60).step_by(3).map(|t| flame(true, t).len()).collect();
            assert!(sizes.iter().min() < sizes.iter().max(), "{heading}: flickering");
        }
    }

    #[test]
    fn arrows_point_where_headings_do() {
        use std::f64::consts::TAU;
        assert_eq!(arrow(0.0), '↑');
        assert_eq!(arrow(TAU / 4.0), '→');
        assert_eq!(arrow(TAU - 0.1), '↑');
        assert_eq!(arrow(-TAU / 8.0), '↖');
    }

    #[test]
    fn spheres_are_round_and_lit_on_the_sunward_side() {
        let area = Rect::new(0, 0, 40, 20);
        let mut buf = Buffer::empty(area);
        let surface = Surface {
            rgb: (200, 200, 200),
            banded: false,
            lights: false,
            ramp: PLANET_RAMP,
            seed: 1,
        };
        assert!(sphere(&mut buf, area, (20.0, 10.0), 8.0, Vec2::new(1.0, 0.0), &surface));
        let row: String = (0..40).map(|c| buf[(c, 10)].symbol().chars().next().unwrap()).collect();
        let covered = row.chars().filter(|&c| c != ' ').count();
        assert!((15..=17).contains(&covered), "8 units across each way: {row:?}");
        let column: usize = (0..20).filter(|&r| buf[(20, r)].symbol() != " ").count();
        assert!((7..=9).contains(&column), "and half that many rows tall");
        assert_eq!(buf[(26, 10)].symbol(), "█", "bright to the east, where the sun is");
        assert_eq!(buf[(13, 10)].symbol(), "·", "dark to the west");
    }
}