use std::{
    collections::VecDeque,
    time::Instant,
};

use dioxus::prelude::*;
use freya_elements::{
    self as dioxus_elements,
    events::{
        touch::TouchPhase,
        TouchEvent,
    },
};
use futures_util::StreamExt;

/// Distance between the first tap and the second tap in [`Gesture::DoubleTap`] gesture.
const DOUBLE_TAP_DISTANCE: f64 = 100.0;

/// Maximum time between the start of the first tap and the start of the second tap in a [`Gesture::DoubleTap`] gesture.
const DOUBLE_TAP_TIMEOUT: u128 = 300; // 300ms

/// Minimum time between the end of the first time to the start of the second tap in a [`Gesture::DoubleTap`] gesture.
const DOUBLE_TAP_MIN: u128 = 40; // 40ms

/// In-memory events queue maximum size.
const MAX_EVENTS_QUEUE: usize = 20;

/// Gesture emitted by the [`GestureArea`] component.
#[derive(Debug, PartialEq, Eq)]
pub enum Gesture {
    TapUp,
    TapDown,
    DoubleTap,
}

/// Properties for the [`GestureArea`] component.
#[derive(Props, Clone, PartialEq)]
pub struct GestureAreaProps {
    /// Inner children for the GestureArea.
    pub children: Element,
    /// Handler for the `ongesture` event.
    pub ongesture: EventHandler<Gesture>,
}

type EventsQueue = VecDeque<(Instant, TouchEvent)>;

/// Detect complex touch gestures such as [`Gesture::DoubleTap`].
///
/// # Example
///
/// ```rust,no_run
/// # use freya::prelude::*;
/// fn app() -> Element {
///    let mut gesture = use_signal(|| "Tap here".to_string());
///    rsx!(
///        GestureArea {
///            ongesture: move |g| gesture.set(format!("{g:?}")),
///            label {
///                "{gesture}"
///            }
///        }
///    )
/// }
/// ```
#[allow(non_snake_case)]
pub fn GestureArea(props: GestureAreaProps) -> Element {
    let event_emitter = use_coroutine(
        |mut rx: UnboundedReceiver<(Instant, TouchEvent)>| async move {
            let mut touch_events = VecDeque::<(Instant, TouchEvent)>::new();

            while let Some(new_event) = rx.next().await {
                touch_events.push_back(new_event);

                // Keep the touch events queue under a certain size
                if touch_events.len() > MAX_EVENTS_QUEUE {
                    touch_events.pop_front();
                }

                // Find the first event with the `target_phase` that happened before the `start_time`
                let find_previous_event = |start_time: &Instant,
                                           events: &EventsQueue,
                                           target_phase: TouchPhase|
                 -> Option<(Instant, TouchEvent)> {
                    let mut start = false;
                    for (time, event) in events.iter().rev() {
                        if time == start_time {
                            start = true;
                            continue;
                        }
                        if event.phase == target_phase && start {
                            return Some((*time, event.clone()));
                        }
                    }
                    None
                };

                // Process the most recent event
                let event = touch_events.iter().last();

                if let Some((time, event)) = event {
                    let phase = event.get_touch_phase();

                    match phase {
                        TouchPhase::Started => {
                            // TapDown
                            props.ongesture.call(Gesture::TapDown);

                            let last_ended_event =
                                find_previous_event(time, &touch_events, TouchPhase::Ended);
                            let last_started_event =
                                find_previous_event(time, &touch_events, TouchPhase::Started);

                            // DoubleTap
                            if let Some(((ended_time, ended_event), (started_time, _))) =
                                last_ended_event.zip(last_started_event)
                            {
                                // Has the latest `touchend` event went too far?
                                let is_ended_close = event
                                    .get_screen_coordinates()
                                    .distance_to(ended_event.get_screen_coordinates())
                                    < DOUBLE_TAP_DISTANCE;
                                // Is the latest `touchend` mature enough?
                                let is_ended_mature =
                                    ended_time.elapsed().as_millis() >= DOUBLE_TAP_MIN;

                                // Hast the latest `touchstart` event expired?
                                let is_started_recent =
                                    started_time.elapsed().as_millis() <= DOUBLE_TAP_TIMEOUT;

                                if is_ended_close && is_ended_mature && is_started_recent {
                                    props.ongesture.call(Gesture::DoubleTap);
                                }
                            }
                        }
                        TouchPhase::Ended => {
                            // TapUp
                            props.ongesture.call(Gesture::TapUp);
                        }
                        _ => {}
                    }
                }
            }
        },
    );

    let ontouchcancel = move |e: TouchEvent| {
        event_emitter.send((Instant::now(), e));
    };

    let ontouchend = move |e: TouchEvent| {
        event_emitter.send((Instant::now(), e));
    };

    let ontouchmove = move |e: TouchEvent| {
        event_emitter.send((Instant::now(), e));
    };

    let ontouchstart = move |e: TouchEvent| {
        event_emitter.send((Instant::now(), e));
    };

    rsx!(
        rect {
            ontouchcancel: ontouchcancel,
            ontouchend: ontouchend,
            ontouchmove: ontouchmove,
            ontouchstart: ontouchstart,
            {props.children}
        }
    )
}

#[cfg(test)]
mod test {
    use std::time::Duration;

    use freya::prelude::*;
    use freya_testing::prelude::*;
    use tokio::time::sleep;

    use crate::gesture_area::DOUBLE_TAP_MIN;

    /// This test simulates a `DoubleTap` gesture in this order:
    /// 1. Touch start
    /// 2. Touch end
    /// 3. Wait 40ms
    /// 4. Touch start
    #[tokio::test]
    pub async fn double_tap() {
        fn dobule_tap_app() -> Element {
            let mut value = use_signal(|| "EMPTY".to_string());

            let ongesture = move |e: Gesture| {
                value.set(format!("{e:?}"));
            };

            rsx!(
                GestureArea {
                    ongesture,
                    rect {
                        width: "100%",
                        height: "100%",

                    }
                }
                label {
                    "{value}"
                }
            )
        }

        let mut utils = launch_test(dobule_tap_app);

        // Initial state
        utils.wait_for_update().await;

        assert_eq!(utils.root().get(1).get(0).text(), Some("EMPTY"));

        utils.push_event(PlatformEvent::Touch {
            name: EventName::TouchStart,
            location: (1.0, 1.0).into(),
            phase: TouchPhase::Started,
            finger_id: 0,
            force: None,
        });

        utils.push_event(PlatformEvent::Touch {
            name: EventName::TouchEnd,
            location: (1.0, 1.0).into(),
            phase: TouchPhase::Ended,
            finger_id: 0,
            force: None,
        });

        utils.wait_for_update().await;
        utils.wait_for_update().await;

        sleep(Duration::from_millis(DOUBLE_TAP_MIN as u64)).await;

        utils.push_event(PlatformEvent::Touch {
            name: EventName::TouchStart,
            location: (1.0, 1.0).into(),
            phase: TouchPhase::Started,
            finger_id: 0,
            force: None,
        });

        utils.wait_for_update().await;
        utils.wait_for_update().await;

        assert_eq!(utils.root().get(1).get(0).text(), Some("DoubleTap"));
    }

    /// Simulates `TapUp` and `TapDown` gestures.
    #[tokio::test]
    pub async fn tap_up_down() {
        fn tap_up_down_app() -> Element {
            let mut value = use_signal(|| "EMPTY".to_string());

            let ongesture = move |e: Gesture| {
                value.set(format!("{e:?}"));
            };

            rsx!(
                GestureArea {
                    ongesture,
                    rect {
                        width: "100%",
                        height: "100%",

                    }
                }
                label {
                    "{value}"
                }
            )
        }

        let mut utils = launch_test(tap_up_down_app);

        // Initial state
        utils.wait_for_update().await;

        assert_eq!(utils.root().get(1).get(0).text(), Some("EMPTY"));

        utils.push_event(PlatformEvent::Touch {
            name: EventName::TouchStart,
            location: (1.0, 1.0).into(),
            phase: TouchPhase::Started,
            finger_id: 0,
            force: None,
        });

        utils.wait_for_update().await;
        utils.wait_for_update().await;

        assert_eq!(utils.root().get(1).get(0).text(), Some("TapDown"));

        utils.push_event(PlatformEvent::Touch {
            name: EventName::TouchEnd,
            location: (1.0, 1.0).into(),
            phase: TouchPhase::Ended,
            finger_id: 0,
            force: None,
        });

        utils.wait_for_update().await;
        utils.wait_for_update().await;

        assert_eq!(utils.root().get(1).get(0).text(), Some("TapUp"));
    }
}