/*
Copyright 2014 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package s2

import (
	"fmt"
	"io"
	"math"

	"github.com/golang/geo/r1"
	"github.com/golang/geo/r3"
	"github.com/golang/geo/s1"
)

// Rect represents a closed latitude-longitude rectangle.
type Rect struct {
	Lat r1.Interval
	Lng s1.Interval
}

var (
	validRectLatRange = r1.Interval{-math.Pi / 2, math.Pi / 2}
	validRectLngRange = s1.FullInterval()
)

// EmptyRect returns the empty rectangle.
func EmptyRect() Rect { return Rect{r1.EmptyInterval(), s1.EmptyInterval()} }

// FullRect returns the full rectangle.
func FullRect() Rect { return Rect{validRectLatRange, validRectLngRange} }

// RectFromLatLng constructs a rectangle containing a single point p.
func RectFromLatLng(p LatLng) Rect {
	return Rect{
		Lat: r1.Interval{p.Lat.Radians(), p.Lat.Radians()},
		Lng: s1.Interval{p.Lng.Radians(), p.Lng.Radians()},
	}
}

// RectFromCenterSize constructs a rectangle with the given size and center.
// center needs to be normalized, but size does not. The latitude
// interval of the result is clamped to [-90,90] degrees, and the longitude
// interval of the result is FullRect() if and only if the longitude size is
// 360 degrees or more.
//
// Examples of clamping (in degrees):
//   center=(80,170),  size=(40,60)   -> lat=[60,90],   lng=[140,-160]
//   center=(10,40),   size=(210,400) -> lat=[-90,90],  lng=[-180,180]
//   center=(-90,180), size=(20,50)   -> lat=[-90,-80], lng=[155,-155]
func RectFromCenterSize(center, size LatLng) Rect {
	half := LatLng{size.Lat / 2, size.Lng / 2}
	return RectFromLatLng(center).expanded(half)
}

// IsValid returns true iff the rectangle is valid.
// This requires Lat ⊆ [-π/2,π/2] and Lng ⊆ [-π,π], and Lat = ∅ iff Lng = ∅
func (r Rect) IsValid() bool {
	return math.Abs(r.Lat.Lo) <= math.Pi/2 &&
		math.Abs(r.Lat.Hi) <= math.Pi/2 &&
		r.Lng.IsValid() &&
		r.Lat.IsEmpty() == r.Lng.IsEmpty()
}

// IsEmpty reports whether the rectangle is empty.
func (r Rect) IsEmpty() bool { return r.Lat.IsEmpty() }

// IsFull reports whether the rectangle is full.
func (r Rect) IsFull() bool { return r.Lat.Equal(validRectLatRange) && r.Lng.IsFull() }

// IsPoint reports whether the rectangle is a single point.
func (r Rect) IsPoint() bool { return r.Lat.Lo == r.Lat.Hi && r.Lng.Lo == r.Lng.Hi }

// Vertex returns the i-th vertex of the rectangle (i = 0,1,2,3) in CCW order
// (lower left, lower right, upper right, upper left).
func (r Rect) Vertex(i int) LatLng {
	var lat, lng float64

	switch i {
	case 0:
		lat = r.Lat.Lo
		lng = r.Lng.Lo
	case 1:
		lat = r.Lat.Lo
		lng = r.Lng.Hi
	case 2:
		lat = r.Lat.Hi
		lng = r.Lng.Hi
	case 3:
		lat = r.Lat.Hi
		lng = r.Lng.Lo
	}
	return LatLng{s1.Angle(lat) * s1.Radian, s1.Angle(lng) * s1.Radian}
}

// Lo returns one corner of the rectangle.
func (r Rect) Lo() LatLng {
	return LatLng{s1.Angle(r.Lat.Lo) * s1.Radian, s1.Angle(r.Lng.Lo) * s1.Radian}
}

// Hi returns the other corner of the rectangle.
func (r Rect) Hi() LatLng {
	return LatLng{s1.Angle(r.Lat.Hi) * s1.Radian, s1.Angle(r.Lng.Hi) * s1.Radian}
}

// Center returns the center of the rectangle.
func (r Rect) Center() LatLng {
	return LatLng{s1.Angle(r.Lat.Center()) * s1.Radian, s1.Angle(r.Lng.Center()) * s1.Radian}
}

// Size returns the size of the Rect.
func (r Rect) Size() LatLng {
	return LatLng{s1.Angle(r.Lat.Length()) * s1.Radian, s1.Angle(r.Lng.Length()) * s1.Radian}
}

// Area returns the surface area of the Rect.
func (r Rect) Area() float64 {
	if r.IsEmpty() {
		return 0
	}
	capDiff := math.Abs(math.Sin(r.Lat.Hi) - math.Sin(r.Lat.Lo))
	return r.Lng.Length() * capDiff
}

// AddPoint increases the size of the rectangle to include the given point.
func (r Rect) AddPoint(ll LatLng) Rect {
	if !ll.IsValid() {
		return r
	}
	return Rect{
		Lat: r.Lat.AddPoint(ll.Lat.Radians()),
		Lng: r.Lng.AddPoint(ll.Lng.Radians()),
	}
}

// expanded returns a rectangle that has been expanded by margin.Lat on each side
// in the latitude direction, and by margin.Lng on each side in the longitude
// direction. If either margin is negative, then it shrinks the rectangle on
// the corresponding sides instead. The resulting rectangle may be empty.
//
// The latitude-longitude space has the topology of a cylinder. Longitudes
// "wrap around" at +/-180 degrees, while latitudes are clamped to range [-90, 90].
// This means that any expansion (positive or negative) of the full longitude range
// remains full (since the "rectangle" is actually a continuous band around the
// cylinder), while expansion of the full latitude range remains full only if the
// margin is positive.
//
// If either the latitude or longitude interval becomes empty after
// expansion by a negative margin, the result is empty.
//
// Note that if an expanded rectangle contains a pole, it may not contain
// all possible lat/lng representations of that pole, e.g., both points [π/2,0]
// and [π/2,1] represent the same pole, but they might not be contained by the
// same Rect.
//
// If you are trying to grow a rectangle by a certain distance on the
// sphere (e.g. 5km), refer to the ExpandedByDistance() C++ method implementation
// instead.
func (r Rect) expanded(margin LatLng) Rect {
	lat := r.Lat.Expanded(margin.Lat.Radians())
	lng := r.Lng.Expanded(margin.Lng.Radians())

	if lat.IsEmpty() || lng.IsEmpty() {
		return EmptyRect()
	}

	return Rect{
		Lat: lat.Intersection(validRectLatRange),
		Lng: lng,
	}
}

func (r Rect) String() string { return fmt.Sprintf("[Lo%v, Hi%v]", r.Lo(), r.Hi()) }

// PolarClosure returns the rectangle unmodified if it does not include either pole.
// If it includes either pole, PolarClosure returns an expansion of the rectangle along
// the longitudinal range to include all possible representations of the contained poles.
func (r Rect) PolarClosure() Rect {
	if r.Lat.Lo == -math.Pi/2 || r.Lat.Hi == math.Pi/2 {
		return Rect{r.Lat, s1.FullInterval()}
	}
	return r
}

// Union returns the smallest Rect containing the union of this rectangle and the given rectangle.
func (r Rect) Union(other Rect) Rect {
	return Rect{
		Lat: r.Lat.Union(other.Lat),
		Lng: r.Lng.Union(other.Lng),
	}
}

// Intersection returns the smallest rectangle containing the intersection of
// this rectangle and the given rectangle. Note that the region of intersection
// may consist of two disjoint rectangles, in which case a single rectangle
// spanning both of them is returned.
func (r Rect) Intersection(other Rect) Rect {
	lat := r.Lat.Intersection(other.Lat)
	lng := r.Lng.Intersection(other.Lng)

	if lat.IsEmpty() || lng.IsEmpty() {
		return EmptyRect()
	}
	return Rect{lat, lng}
}

// Intersects reports whether this rectangle and the other have any points in common.
func (r Rect) Intersects(other Rect) bool {
	return r.Lat.Intersects(other.Lat) && r.Lng.Intersects(other.Lng)
}

// CapBound returns a cap that countains Rect.
func (r Rect) CapBound() Cap {
	// We consider two possible bounding caps, one whose axis passes
	// through the center of the lat-long rectangle and one whose axis
	// is the north or south pole.  We return the smaller of the two caps.

	if r.IsEmpty() {
		return EmptyCap()
	}

	var poleZ, poleAngle float64
	if r.Lat.Hi+r.Lat.Lo < 0 {
		// South pole axis yields smaller cap.
		poleZ = -1
		poleAngle = math.Pi/2 + r.Lat.Hi
	} else {
		poleZ = 1
		poleAngle = math.Pi/2 - r.Lat.Lo
	}
	poleCap := CapFromCenterAngle(Point{r3.Vector{0, 0, poleZ}}, s1.Angle(poleAngle)*s1.Radian)

	// For bounding rectangles that span 180 degrees or less in longitude, the
	// maximum cap size is achieved at one of the rectangle vertices.  For
	// rectangles that are larger than 180 degrees, we punt and always return a
	// bounding cap centered at one of the two poles.
	if math.Remainder(r.Lng.Hi-r.Lng.Lo, 2*math.Pi) >= 0 && r.Lng.Hi-r.Lng.Lo < 2*math.Pi {
		midCap := CapFromPoint(PointFromLatLng(r.Center())).AddPoint(PointFromLatLng(r.Lo())).AddPoint(PointFromLatLng(r.Hi()))
		if midCap.Height() < poleCap.Height() {
			return midCap
		}
	}
	return poleCap
}

// RectBound returns itself.
func (r Rect) RectBound() Rect {
	return r
}

// Contains reports whether this Rect contains the other Rect.
func (r Rect) Contains(other Rect) bool {
	return r.Lat.ContainsInterval(other.Lat) && r.Lng.ContainsInterval(other.Lng)
}

// ContainsCell reports whether the given Cell is contained by this Rect.
func (r Rect) ContainsCell(c Cell) bool {
	// A latitude-longitude rectangle contains a cell if and only if it contains
	// the cell's bounding rectangle. This test is exact from a mathematical
	// point of view, assuming that the bounds returned by Cell.RectBound()
	// are tight. However, note that there can be a loss of precision when
	// converting between representations -- for example, if an s2.Cell is
	// converted to a polygon, the polygon's bounding rectangle may not contain
	// the cell's bounding rectangle. This has some slightly unexpected side
	// effects; for instance, if one creates an s2.Polygon from an s2.Cell, the
	// polygon will contain the cell, but the polygon's bounding box will not.
	return r.Contains(c.RectBound())
}

// ContainsLatLng reports whether the given LatLng is within the Rect.
func (r Rect) ContainsLatLng(ll LatLng) bool {
	if !ll.IsValid() {
		return false
	}
	return r.Lat.Contains(ll.Lat.Radians()) && r.Lng.Contains(ll.Lng.Radians())
}

// ContainsPoint reports whether the given Point is within the Rect.
func (r Rect) ContainsPoint(p Point) bool {
	return r.ContainsLatLng(LatLngFromPoint(p))
}

// CellUnionBound computes a covering of the Rect.
func (r Rect) CellUnionBound() []CellID {
	return r.CapBound().CellUnionBound()
}

// intersectsLatEdge reports whether the edge AB intersects the given edge of constant
// latitude. Requires the points to have unit length.
func intersectsLatEdge(a, b Point, lat s1.Angle, lng s1.Interval) bool {
	// Unfortunately, lines of constant latitude are curves on
	// the sphere. They can intersect a straight edge in 0, 1, or 2 points.

	// First, compute the normal to the plane AB that points vaguely north.
	z := Point{a.PointCross(b).Normalize()}
	if z.Z < 0 {
		z = Point{z.Mul(-1)}
	}

	// Extend this to an orthonormal frame (x,y,z) where x is the direction
	// where the great circle through AB achieves its maximium latitude.
	y := Point{z.PointCross(PointFromCoords(0, 0, 1)).Normalize()}
	x := y.Cross(z.Vector)

	// Compute the angle "theta" from the x-axis (in the x-y plane defined
	// above) where the great circle intersects the given line of latitude.
	sinLat := math.Sin(float64(lat))
	if math.Abs(sinLat) >= x.Z {
		// The great circle does not reach the given latitude.
		return false
	}

	cosTheta := sinLat / x.Z
	sinTheta := math.Sqrt(1 - cosTheta*cosTheta)
	theta := math.Atan2(sinTheta, cosTheta)

	// The candidate intersection points are located +/- theta in the x-y
	// plane. For an intersection to be valid, we need to check that the
	// intersection point is contained in the interior of the edge AB and
	// also that it is contained within the given longitude interval "lng".

	// Compute the range of theta values spanned by the edge AB.
	abTheta := s1.IntervalFromPointPair(
		math.Atan2(a.Dot(y.Vector), a.Dot(x)),
		math.Atan2(b.Dot(y.Vector), b.Dot(x)))

	if abTheta.Contains(theta) {
		// Check if the intersection point is also in the given lng interval.
		isect := x.Mul(cosTheta).Add(y.Mul(sinTheta))
		if lng.Contains(math.Atan2(isect.Y, isect.X)) {
			return true
		}
	}

	if abTheta.Contains(-theta) {
		// Check if the other intersection point is also in the given lng interval.
		isect := x.Mul(cosTheta).Sub(y.Mul(sinTheta))
		if lng.Contains(math.Atan2(isect.Y, isect.X)) {
			return true
		}
	}
	return false
}

// intersectsLngEdge reports whether the edge AB intersects the given edge of constant
// longitude. Requires the points to have unit length.
func intersectsLngEdge(a, b Point, lat r1.Interval, lng s1.Angle) bool {
	// The nice thing about edges of constant longitude is that
	// they are straight lines on the sphere (geodesics).
	return SimpleCrossing(a, b, PointFromLatLng(LatLng{s1.Angle(lat.Lo), lng}),
		PointFromLatLng(LatLng{s1.Angle(lat.Hi), lng}))
}

// IntersectsCell reports whether this rectangle intersects the given cell. This is an
// exact test and may be fairly expensive.
func (r Rect) IntersectsCell(c Cell) bool {
	// First we eliminate the cases where one region completely contains the
	// other. Once these are disposed of, then the regions will intersect
	// if and only if their boundaries intersect.
	if r.IsEmpty() {
		return false
	}
	if r.ContainsPoint(Point{c.id.rawPoint()}) {
		return true
	}
	if c.ContainsPoint(PointFromLatLng(r.Center())) {
		return true
	}

	// Quick rejection test (not required for correctness).
	if !r.Intersects(c.RectBound()) {
		return false
	}

	// Precompute the cell vertices as points and latitude-longitudes. We also
	// check whether the Cell contains any corner of the rectangle, or
	// vice-versa, since the edge-crossing tests only check the edge interiors.
	vertices := [4]Point{}
	latlngs := [4]LatLng{}

	for i := range vertices {
		vertices[i] = c.Vertex(i)
		latlngs[i] = LatLngFromPoint(vertices[i])
		if r.ContainsLatLng(latlngs[i]) {
			return true
		}
		if c.ContainsPoint(PointFromLatLng(r.Vertex(i))) {
			return true
		}
	}

	// Now check whether the boundaries intersect. Unfortunately, a
	// latitude-longitude rectangle does not have straight edges: two edges
	// are curved, and at least one of them is concave.
	for i := range vertices {
		edgeLng := s1.IntervalFromEndpoints(latlngs[i].Lng.Radians(), latlngs[(i+1)&3].Lng.Radians())
		if !r.Lng.Intersects(edgeLng) {
			continue
		}

		a := vertices[i]
		b := vertices[(i+1)&3]
		if edgeLng.Contains(r.Lng.Lo) && intersectsLngEdge(a, b, r.Lat, s1.Angle(r.Lng.Lo)) {
			return true
		}
		if edgeLng.Contains(r.Lng.Hi) && intersectsLngEdge(a, b, r.Lat, s1.Angle(r.Lng.Hi)) {
			return true
		}
		if intersectsLatEdge(a, b, s1.Angle(r.Lat.Lo), r.Lng) {
			return true
		}
		if intersectsLatEdge(a, b, s1.Angle(r.Lat.Hi), r.Lng) {
			return true
		}
	}
	return false
}

// Encode encodes the Rect.
func (r Rect) Encode(w io.Writer) error {
	e := &encoder{w: w}
	r.encode(e)
	return e.err
}

func (r Rect) encode(e *encoder) {
	e.writeInt8(encodingVersion)
	e.writeFloat64(r.Lat.Lo)
	e.writeFloat64(r.Lat.Hi)
	e.writeFloat64(r.Lng.Lo)
	e.writeFloat64(r.Lng.Hi)
}

// Decode decodes a rectangle.
func (r *Rect) Decode(rd io.Reader) error {
	d := &decoder{r: asByteReader(rd)}
	r.decode(d)
	return d.err
}

func (r *Rect) decode(d *decoder) {
	if version := d.readUint8(); int(version) > int(encodingVersion) && d.err == nil {
		d.err = fmt.Errorf("can't decode version %d; my version: %d", version, encodingVersion)
		return
	}
	r.Lat.Lo = d.readFloat64()
	r.Lat.Hi = d.readFloat64()
	r.Lng.Lo = d.readFloat64()
	r.Lng.Hi = d.readFloat64()
	return
}

// BUG: The major differences from the C++ version are:
//   - GetCentroid, Get*Distance, Vertex, InteriorContains(LatLng|Rect|Point)
