// Touch input: turns the raw touches of macroquad into gestures.
//   one finger:  press, tap, double tap, long press, drag (start / move / end), release
//   two fingers: camera gesture (pan by the centre, pinch = zoom, twist = rotate)
// Positions are device pixels (the unit of the interface, see ui::begin_ui).

use macroquad::prelude::*;

const LONG_PRESS: f64 = 0.5; // seconds without moving
const DOUBLE_TAP: f64 = 0.3; // max. time between two taps
// touches come in device pixels; everything here works in interface units (see ui::dpr)
fn ui_pos(p: Vec2) -> Vec2 {
    p * crate::ui::dpr() / crate::ui::device_dpr()
}

const DRAG_CSS: f32 = 10.0; // movement (CSS pixels) that turns a press into a drag

#[derive(Clone, Copy, Debug)]
pub enum Gesture {
    Press(Vec2),
    Tap(Vec2),
    DoubleTap(Vec2),
    LongPress(Vec2),
    DragStart(Vec2), // start position of the drag
    DragMove(Vec2),
    DragEnd,
    Release(Vec2),
    Cancel, // a second finger arrived: abort the one-finger action
    Camera { center: Vec2, pan: Vec2, zoom: f32, rotate: f32 },
}

#[derive(Clone, Copy)]
enum St {
    Idle,
    One { id: u64, start: Vec2, pos: Vec2, t0: f64, drag: bool, long: bool },
    Two { a: u64, b: u64, center: Vec2, dist: f32, angle: f32 },
    Wait, // after a two-finger gesture: until all fingers are lifted
}

pub struct TouchInput {
    st: St,
    last_tap: Option<(Vec2, f64)>,
    pending_tap: Option<(Vec2, f64)>, // single tap held back while a double tap is possible
    pub seen: bool,                   // a touch happened since the start
}

fn ended(p: TouchPhase) -> bool {
    matches!(p, TouchPhase::Ended | TouchPhase::Cancelled)
}

impl TouchInput {
    pub fn new() -> TouchInput {
        TouchInput { st: St::Idle, last_tap: None, pending_tap: None, seen: false }
    }

    // a finger is on the screen (one-finger state)
    pub fn finger(&self) -> Option<Vec2> {
        match self.st {
            St::One { pos, .. } => Some(pos),
            _ => None,
        }
    }

    fn tap(&mut self, p: Vec2, now: f64, want_double: bool, out: &mut Vec<Gesture>) {
        let near = |a: Vec2, b: Vec2| a.distance(b) < DRAG_CSS * 3.0 * crate::ui::dpr();
        if want_double {
            if let Some((q, t)) = self.pending_tap {
                if now - t < DOUBLE_TAP && near(p, q) {
                    self.pending_tap = None;
                    out.push(Gesture::DoubleTap(p));
                    return;
                }
                out.push(Gesture::Tap(q));
            }
            self.pending_tap = Some((p, now));
        } else {
            if let Some((q, _)) = self.pending_tap.take() {
                out.push(Gesture::Tap(q));
            }
            out.push(Gesture::Tap(p));
        }
        self.last_tap = Some((p, now));
    }

    // want_double: taps are held back briefly so that a double tap can be recognised
    pub fn update(&mut self, now: f64, want_double: bool) -> Vec<Gesture> {
        let mut out = Vec::new();
        let ts = touches();
        if !ts.is_empty() {
            self.seen = true;
        }
        let find = |id: u64| ts.iter().find(|t| t.id == id);
        let active: Vec<&Touch> = ts.iter().filter(|t| !ended(t.phase)).collect();
        let drag_px = DRAG_CSS * crate::ui::dpr();

        match self.st {
            St::Idle => {
                if active.len() >= 2 {
                    self.start_two(active[0], active[1]);
                } else if let Some(t) = active.first() {
                    out.push(Gesture::Press(ui_pos(t.position)));
                    self.st = St::One { id: t.id, start: ui_pos(t.position), pos: ui_pos(t.position), t0: now, drag: false, long: false };
                } else if let Some(t) = ts.iter().find(|t| ended(t.phase)) {
                    // started and ended between two frames
                    out.push(Gesture::Press(ui_pos(t.position)));
                    self.tap(ui_pos(t.position), now, want_double, &mut out);
                    out.push(Gesture::Release(ui_pos(t.position)));
                }
            }
            St::One { id, start, t0, mut drag, mut long, .. } => {
                if active.len() >= 2 {
                    out.push(Gesture::Cancel);
                    self.start_two(active[0], active[1]);
                } else {
                    match find(id) {
                        Some(t) if !ended(t.phase) => {
                            let pos = ui_pos(t.position);
                            if !drag && pos.distance(start) > drag_px {
                                drag = true;
                                out.push(Gesture::DragStart(start));
                            }
                            if drag {
                                out.push(Gesture::DragMove(pos));
                            } else if !long && now - t0 > LONG_PRESS {
                                long = true;
                                out.push(Gesture::LongPress(pos));
                            }
                            self.st = St::One { id, start, pos, t0, drag, long };
                        }
                        other => {
                            let pos = other.map(|t| ui_pos(t.position)).unwrap_or(start);
                            if drag {
                                out.push(Gesture::DragEnd);
                            } else if !long {
                                self.tap(pos, now, want_double, &mut out);
                            }
                            out.push(Gesture::Release(pos));
                            self.st = St::Idle;
                        }
                    }
                }
            }
            St::Two { a, b, center, dist, angle } => match (find(a).filter(|t| !ended(t.phase)), find(b).filter(|t| !ended(t.phase))) {
                (Some(ta), Some(tb)) => {
                    let (c, d, an) = Self::geometry(ui_pos(ta.position), ui_pos(tb.position));
                    let mut rot = an - angle;
                    if rot > std::f32::consts::PI {
                        rot -= std::f32::consts::TAU;
                    } else if rot < -std::f32::consts::PI {
                        rot += std::f32::consts::TAU;
                    }
                    out.push(Gesture::Camera { center: c, pan: c - center, zoom: d / dist.max(1.0), rotate: rot });
                    self.st = St::Two { a, b, center: c, dist: d, angle: an };
                }
                _ => self.st = if active.is_empty() { St::Idle } else { St::Wait },
            },
            St::Wait => {
                if active.is_empty() {
                    self.st = St::Idle;
                }
            }
        }
        if let Some((p, t)) = self.pending_tap {
            if !want_double || now - t >= DOUBLE_TAP {
                self.pending_tap = None;
                out.push(Gesture::Tap(p));
            }
        }
        out
    }

    fn geometry(p: Vec2, q: Vec2) -> (Vec2, f32, f32) {
        let d = q - p;
        ((p + q) * 0.5, d.length(), d.y.atan2(d.x))
    }

    fn start_two(&mut self, a: &Touch, b: &Touch) {
        let (center, dist, angle) = Self::geometry(ui_pos(a.position), ui_pos(b.position));
        self.pending_tap = None;
        self.st = St::Two { a: a.id, b: b.id, center, dist, angle };
    }
}