use std::collections::{BTreeMap, BTreeSet};
use std::fmt;

use anyhow::Result;
use serde::{Deserialize, Serialize};

use abstutil::MultiMap;
use geom::{Angle, Distance, PolyLine, Pt2D};

use crate::{DirectedRoadID, Direction, IntersectionID, LaneID, Map};

/// Turns are uniquely identified by their (src, dst) lanes and their parent intersection.
/// Intersection is needed to distinguish crosswalks that exist at two ends of a sidewalk.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
pub struct TurnID {
    pub parent: IntersectionID,
    /// src and dst must both belong to parent. No guarantees that src is incoming and dst is
    /// outgoing for turns between sidewalks.
    pub src: LaneID,
    pub dst: LaneID,
}

impl fmt::Display for TurnID {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "TurnID({}, {}, {})", self.src, self.dst, self.parent)
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialOrd, Ord, PartialEq, Serialize, Deserialize)]
pub enum TurnType {
    Crosswalk,
    SharedSidewalkCorner,
    // These are for vehicle turns
    Straight,
    Right,
    Left,
    UTurn,
}

// TODO This concept may be dated, now that Movements exist. Within a movement, the lane-changing
// turns should be treated as less important.
#[derive(Serialize, Deserialize, Debug, PartialEq, Clone, Copy, PartialOrd)]
pub enum TurnPriority {
    /// For stop signs: Can't currently specify this!
    /// For traffic signals: Can't do this turn right now.
    Banned,
    /// For stop signs: cars have to stop before doing this turn, and are accepted with the lowest
    /// priority.
    /// For traffic signals: Cars can do this immediately if there are no previously accepted
    /// conflicting turns.
    Yield,
    /// For stop signs: cars can do this without stopping. These can conflict!
    /// For traffic signals: Must be non-conflicting.
    Protected,
}

/// A Turn leads from the end of one Lane to the start of another. (Except for pedestrians;
/// sidewalks are bidirectional.)
#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
pub struct Turn {
    pub id: TurnID,
    pub turn_type: TurnType,
    // TODO Some turns might not actually have geometry. Currently encoded by two equal points.
    // Represent more directly?
    pub geom: PolyLine,
    /// Empty except for TurnType::Crosswalk. Usually just one other ID, except for the case of 4
    /// duplicates at a degenerate intersection.
    pub other_crosswalk_ids: BTreeSet<TurnID>,
}

impl Turn {
    pub fn conflicts_with(&self, other: &Turn) -> bool {
        if self.turn_type == TurnType::SharedSidewalkCorner
            || other.turn_type == TurnType::SharedSidewalkCorner
        {
            return false;
        }
        if self.id == other.id {
            return false;
        }
        if self.between_sidewalks() && other.between_sidewalks() {
            return false;
        }

        if self.geom.first_pt() == other.geom.first_pt() {
            return false;
        }
        if self.geom.last_pt() == other.geom.last_pt() {
            return true;
        }
        self.geom.intersection(&other.geom).is_some()
    }

    // TODO What should this be for zero-length turns? Probably src's pt1 to dst's pt2 or
    // something.
    pub fn angle(&self) -> Angle {
        self.geom.first_pt().angle_to(self.geom.last_pt())
    }

    pub fn between_sidewalks(&self) -> bool {
        self.turn_type == TurnType::SharedSidewalkCorner || self.turn_type == TurnType::Crosswalk
    }

    // TODO Maybe precompute this.
    /// penalties for (lane types, lane-changing, slow lane)
    pub fn penalty(&self, map: &Map) -> (usize, usize, usize) {
        let from = map.get_l(self.id.src);
        let to = map.get_l(self.id.dst);

        // Starting from the farthest from the center line (right in the US), where is this travel
        // lane? Filters by the lane type and ignores lanes that don't go to the target road.
        let from_idx = {
            let mut cnt = 0;
            let r = map.get_r(from.parent);
            for (l, lt) in r.children(from.dir).iter().rev() {
                if from.lane_type != *lt {
                    continue;
                }
                if map
                    .get_turns_from_lane(*l)
                    .into_iter()
                    .any(|t| map.get_l(t.id.dst).parent == to.parent)
                {
                    cnt += 1;
                    if from.id == *l {
                        break;
                    }
                }
            }
            cnt
        };

        // Starting from the farthest from the center line (right in the US), where is this travel
        // lane? Filters by the lane type.
        let to_idx = {
            let mut cnt = 0;
            let r = map.get_r(to.parent);
            for (l, lt) in r.children(to.dir).iter().rev() {
                if to.lane_type != *lt {
                    continue;
                }
                cnt += 1;
                if to.id == *l {
                    break;
                }
            }
            cnt
        };

        // TODO I thought about different cases where there are the same/more/less lanes going in
        // and out, but then actually, I think the reasonable thing in all cases is just to do
        // this.
        let lc_cost = ((from_idx as isize) - (to_idx as isize)).abs() as usize;

        // Always prefer a dedicated bike or bus lane. This takes care of entering one from a
        // driving lane and staying on one.
        // It may seem weird to have a cost for cars just sticking to driving lanes, but this cost
        // is relative to all available options. All choices for a car are the same, so it doesn't
        // matter.
        let lt_cost = if to.is_biking() || to.is_bus() { 0 } else { 1 };

        // Keep right (in the US)
        let slow_lane = if to_idx > 1 { 1 } else { 0 };

        (lt_cost, lc_cost, slow_lane)
    }
}

/// A movement is like a turn, but with less detail -- it identifies a movement from one directed
/// road to another.
/// One road usually has 4 crosswalks, each a singleton Movement. We need all of the information
/// here to keep each crosswalk separate.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
pub struct MovementID {
    pub from: DirectedRoadID,
    pub to: DirectedRoadID,
    pub parent: IntersectionID,
    pub crosswalk: bool,
}

impl MovementID {
    // TODO Expensive! Should we natively store movements everywhere?
    pub(crate) fn get(self, map: &Map) -> Result<Movement> {
        Ok(Movement::for_i(self.parent, map)?.remove(&self).unwrap())
    }
}

/// This is cheaper to store than a MovementID. It simply indexes into the list of movements.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, PartialOrd, Ord, Serialize, Deserialize)]
pub struct CompressedMovementID {
    pub i: IntersectionID,
    // There better not be any intersection with more than 256 movements...
    pub idx: u8,
}

/// A Movement groups all turns from one road to another, letting traffic signals operate at a
/// higher level of abstraction.
/// This is used for pathfinding and traffic signals currently; other places focus instead on turns.
// TODO Unclear how this plays with different lane types
#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
pub struct Movement {
    pub id: MovementID,
    pub turn_type: TurnType,
    pub members: Vec<TurnID>,
    /// The "overall" path of movement, aka, an "average" of the turn geometry
    pub geom: PolyLine,
    pub angle: Angle,
}

impl Movement {
    pub(crate) fn for_i(i: IntersectionID, map: &Map) -> Result<BTreeMap<MovementID, Movement>> {
        let mut results = BTreeMap::new();
        let mut movements: MultiMap<(DirectedRoadID, DirectedRoadID), TurnID> = MultiMap::new();
        for turn in map.get_turns_in_intersection(i) {
            let from = map.get_l(turn.id.src).get_directed_parent();
            let to = map.get_l(turn.id.dst).get_directed_parent();
            match turn.turn_type {
                TurnType::SharedSidewalkCorner => {}
                TurnType::Crosswalk => {
                    let id = MovementID {
                        from,
                        to,
                        parent: i,
                        crosswalk: true,
                    };
                    results.insert(
                        id,
                        Movement {
                            id,
                            turn_type: TurnType::Crosswalk,
                            members: vec![turn.id],
                            geom: turn.geom.clone(),
                            angle: turn.angle(),
                        },
                    );
                }
                _ => {
                    movements.insert((from, to), turn.id);
                }
            }
        }
        for ((from, to), members) in movements.consume() {
            let geom = movement_geom(
                members.iter().map(|t| &map.get_t(*t).geom).collect(),
                from,
                to,
            )?;
            let turn_types: BTreeSet<TurnType> =
                members.iter().map(|t| map.get_t(*t).turn_type).collect();
            if turn_types.len() > 1 {
                warn!(
                    "Movement between {} and {} has weird turn types! {:?}",
                    from, to, turn_types
                );
            }
            let members: Vec<TurnID> = members.into_iter().collect();
            let id = MovementID {
                from,
                to,
                parent: i,
                crosswalk: false,
            };
            results.insert(
                id,
                Movement {
                    id,
                    turn_type: *turn_types.iter().next().unwrap(),
                    angle: map.get_t(members[0]).angle(),
                    members,
                    geom,
                },
            );
        }
        if results.is_empty() {
            bail!("No Movements! Does the intersection have at least 2 roads?");
        }
        Ok(results)
    }

    /// Polyline points FROM intersection
    pub fn src_center_and_width(&self, map: &Map) -> (PolyLine, Distance) {
        let r = map.get_r(self.id.from.id);

        let mut leftmost = Distance::meters(99999.0);
        let mut rightmost = Distance::ZERO;
        let mut left = Distance::ZERO;

        for (l, _, _) in r.lanes_ltr() {
            let right = left + map.get_l(l).width;

            if self.members.iter().any(|t| t.src == l) {
                leftmost = leftmost.min(left);
                rightmost = rightmost.max(right);
            }

            left = right;
        }

        let mut pl = r
            .get_left_side(map)
            .must_shift_right((leftmost + rightmost) / 2.0);
        if self.id.from.dir == Direction::Back {
            pl = pl.reversed();
        }
        // Flip direction, so we point away from the intersection
        if !self.id.crosswalk || map.get_l(self.members[0].src).src_i != self.members[0].parent {
            pl = pl.reversed()
        };
        (pl, rightmost - leftmost)
    }

    pub fn conflicts_with(&self, other: &Movement) -> bool {
        if self.id == other.id {
            return false;
        }
        if self.turn_type == TurnType::Crosswalk && other.turn_type == TurnType::Crosswalk {
            return false;
        }

        if self.id.from == other.id.from
            && self.turn_type != TurnType::Crosswalk
            && other.turn_type != TurnType::Crosswalk
        {
            return false;
        }
        if self.id.to == other.id.to
            && self.turn_type != TurnType::Crosswalk
            && other.turn_type != TurnType::Crosswalk
        {
            return true;
        }
        // TODO If you hit a panic below, you've probably got two separate roads overlapping.
        // Fix it in OSM. Examples: https://www.openstreetmap.org/changeset/87465499,
        // https://www.openstreetmap.org/changeset/85952811
        /*if self.geom == other.geom {
            println!("*********** {:?} and {:?} have the same geom", self.id, other.id);
            return true;
        }*/
        self.geom.intersection(&other.geom).is_some()
    }
}

fn movement_geom(
    polylines: Vec<&PolyLine>,
    from: DirectedRoadID,
    to: DirectedRoadID,
) -> Result<PolyLine> {
    let num_pts = polylines[0].points().len();
    for pl in &polylines {
        if num_pts != pl.points().len() {
            // Kiiiiinda spammy
            if false {
                warn!(
                    "Movement between {} and {} can't make nice geometry",
                    from, to
                );
            }
            return Ok(polylines[0].clone());
        }
    }

    let mut pts = Vec::new();
    for idx in 0..num_pts {
        pts.push(Pt2D::center(
            &polylines
                .iter()
                .map(|pl| pl.points()[idx])
                .collect::<Vec<_>>(),
        ));
    }
    PolyLine::deduping_new(pts)
}

impl TurnID {
    pub fn to_movement(self, map: &Map) -> MovementID {
        MovementID {
            from: map.get_l(self.src).get_directed_parent(),
            to: map.get_l(self.dst).get_directed_parent(),
            parent: self.parent,
            crosswalk: map.get_l(self.src).is_walkable(),
        }
    }
}