//! fighter-to-fighter pushing

use bevy::prelude::*;

use crate::{
    fighter::{
        Fighter, FighterFacingDirection, FighterRoster, FighterSurfaceState, FighterTranslation,
        manifest::FighterManifest,
    },
    game_settings::GameSettings,
    math::int::FGi32,
    stage::line::{StageCollision, StageLineID, StagePoly},
};

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
struct Pushbox {
    center: FGi32,
    radius: FGi32,
    line_id: StageLineID,
}

fn can_interact(stage: &StageCollision, first: StageLineID, second: StageLineID) -> bool {
    if first.polygon != second.polygon {
        return false;
    }
    if first.segment == second.segment {
        return true;
    }

    let Some(poly) = stage.stage_polys.get(first.polygon) else {
        return false;
    };
    adjacent_segment(poly, first.segment, second.segment)
}

fn adjacent_segment(poly: &StagePoly, first: usize, second: usize) -> bool {
    poly.get_next_segment_index(first) == Some(second)
        || poly.get_prev_segment_index(first) == Some(second)
}

fn push_delta(first: Pushbox, second: Pushbox, nudge: FGi32) -> FGi32 {
    if (first.center - second.center).abs() >= first.radius + second.radius {
        return FGi32::ZERO;
    }
    (first.center - second.center).signum() * nudge
}

fn calculate_push_deltas(
    pushboxes: &[Option<Pushbox>],
    stage: &StageCollision,
    nudge: FGi32,
) -> Vec<FGi32> {
    let mut deltas = vec![FGi32::ZERO; pushboxes.len()];
    for first in 0..pushboxes.len() {
        let Some(first_pushbox) = pushboxes[first] else {
            continue;
        };
        for second in 0..pushboxes.len() {
            if first == second {
                continue;
            }
            let Some(second_pushbox) = pushboxes[second] else {
                continue;
            };
            if can_interact(stage, first_pushbox.line_id, second_pushbox.line_id) {
                deltas[first] += push_delta(first_pushbox, second_pushbox, nudge);
            }
        }
    }
    deltas
}

pub fn apply_grounded_pushes(
    roster: Res<FighterRoster>,
    mut fighters: Query<(
        &Fighter,
        &mut FighterTranslation,
        &FighterFacingDirection,
        &FighterSurfaceState,
    )>,
    manifests: Res<Assets<FighterManifest>>,
    settings: Res<GameSettings>,
    stage: Res<StageCollision>,
) {
    let pushboxes = roster
        .0
        .iter()
        .map(|entity| {
            let Ok((fighter, translation, facing, surface)) = fighters.get(*entity) else {
                return None;
            };
            let Some(line_id) = surface.line_id() else {
                return None;
            };
            let manifest = manifests.get(&fighter.manifest)?;
            let attributes = &manifest.attributes;
            Some(Pushbox {
                center: translation.x + facing.to_sign() * attributes.pushbox_offset,
                radius: attributes.pushbox_radius,
                line_id,
            })
        })
        .collect::<Vec<_>>();
    let deltas = calculate_push_deltas(
        &pushboxes,
        &stage,
        settings.fighter_common.grounded_push_nudge,
    );

    for (entity, delta) in roster.0.iter().zip(deltas) {
        if delta == FGi32::ZERO {
            continue;
        }
        if let Ok((_, mut translation, _, _)) = fighters.get_mut(*entity) {
            translation.x += delta;
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::math::vec::FGVec2;
    use crate::stage::line::{StagePolyLineSegmentType, StagePolyType};

    fn stage() -> StageCollision {
        StageCollision {
            stage_polys: vec![StagePoly::build(
                StagePolyType::Platform,
                &[
                    (FGVec2::lit("0", "0"), StagePolyLineSegmentType::Floor),
                    (FGVec2::lit("10", "0"), StagePolyLineSegmentType::Floor),
                    (FGVec2::lit("20", "0"), StagePolyLineSegmentType::Floor),
                    (FGVec2::lit("30", "0"), StagePolyLineSegmentType::Floor),
                ],
            )],
            ..StageCollision::default()
        }
    }

    fn box_at(x: &str, segment: usize) -> Pushbox {
        Pushbox {
            center: FGi32::lit(x),
            radius: FGi32::lit("1"),
            line_id: StageLineID {
                polygon: 0,
                segment,
            },
        }
    }

    #[test]
    fn overlapping_pair_gets_opposite_fixed_nudges() {
        let deltas = calculate_push_deltas(
            &[Some(box_at("0", 0)), Some(box_at("1", 0))],
            &stage(),
            FGi32::lit("0.3"),
        );
        assert_eq!(deltas, vec![FGi32::lit("-0.3"), FGi32::lit("0.3")]);
    }

    #[test]
    fn touching_pushboxes_do_not_nudge() {
        let deltas = calculate_push_deltas(
            &[Some(box_at("0", 0)), Some(box_at("2", 0))],
            &stage(),
            FGi32::lit("0.3"),
        );
        assert_eq!(deltas, vec![FGi32::ZERO, FGi32::ZERO]);
    }

    #[test]
    fn adjacent_segments_can_push_and_unrelated_segments_cannot() {
        let adjacent = calculate_push_deltas(
            &[Some(box_at("9.5", 0)), Some(box_at("10", 1))],
            &stage(),
            FGi32::lit("0.3"),
        );
        assert_eq!(adjacent, vec![FGi32::lit("-0.3"), FGi32::lit("0.3")]);

        let unrelated = calculate_push_deltas(
            &[Some(box_at("1", 0)), Some(box_at("2", 2))],
            &stage(),
            FGi32::lit("0.3"),
        );
        assert_eq!(unrelated, vec![FGi32::ZERO, FGi32::ZERO]);
    }

    #[test]
    fn multiple_overlaps_accumulate() {
        let deltas = calculate_push_deltas(
            &[
                Some(box_at("0", 0)),
                Some(box_at("0.5", 0)),
                Some(box_at("1", 0)),
            ],
            &stage(),
            FGi32::lit("0.3"),
        );
        assert_eq!(
            deltas,
            vec![FGi32::lit("-0.6"), FGi32::ZERO, FGi32::lit("0.6")]
        );
    }

    #[test]
    fn system_parameters_initialize_without_query_conflicts() {
        let mut world = World::new();
        let mut schedule = Schedule::default();
        schedule.add_systems(apply_grounded_pushes);

        schedule.initialize(&mut world).unwrap();
    }
}