// SPDX-License-Identifier: Unlicense OR MIT

package clip

import (
	"gioui.org/f32"
	"gioui.org/op"
)

// RRect represents the clip area of a rectangle with rounded
// corners.
//
// Specify a square with corner radii equal to half the square size to
// construct a circular clip area.
type RRect struct {
	Rect f32.Rectangle
	// The corner radii.
	SE, SW, NW, NE float32
}

// op returns the op for the rectangle.
func (rr RRect) op(ops *op.Ops) Op {
	var p Path
	p.Begin(ops)
	p.Move(rr.Rect.Min)
	roundRect(&p, rr.Rect.Size(), rr.SE, rr.SW, rr.NW, rr.NE)
	return p.End()
}

// Add the rectangle clip.
func (rr RRect) Add(ops *op.Ops) {
	rr.op(ops).Add(ops)
}

// Border represents the clip area of a rectangular border.
type Border struct {
	// Rect is the bounds of the border.
	Rect  f32.Rectangle
	Width float32
	// The corner radii.
	SE, SW, NW, NE float32
}

func (b Border) op(ops *op.Ops) Op {
	var p Path
	p.Begin(ops)
	w := b.Width

	// Outer outline.
	r := b.Rect
	p.Move(r.Min)
	end := roundRect(&p, r.Size(), b.SE, b.SW, b.NW, b.NE)

	// Inner outline
	r = b.Rect
	r.Min.X += w
	r.Min.Y += w
	r.Max.X -= w
	r.Max.Y -= w
	p.Move(r.Min.Sub(end))
	roundRectRev(&p, r.Size(), b.SE-w, b.SW-w, b.NW-w, b.NE-w)

	return p.End()
}

// Add the border clip.
func (rr Border) Add(ops *op.Ops) {
	rr.op(ops).Add(ops)
}

// roundRect adds the outline of a rectangle with rounded corners to a
// path.
func roundRect(p *Path, size f32.Point, se, sw, nw, ne float32) f32.Point {
	// https://pomax.github.io/bezierinfo/#circles_cubic.
	w, h := size.X, size.Y
	const c = 0.55228475 // 4*(sqrt(2)-1)/3
	p.Move(f32.Point{X: w, Y: h - se})
	p.Cube(f32.Point{X: 0, Y: se * c}, f32.Point{X: -se + se*c, Y: se}, f32.Point{X: -se, Y: se}) // SE
	p.Line(f32.Point{X: sw - w + se, Y: 0})
	p.Cube(f32.Point{X: -sw * c, Y: 0}, f32.Point{X: -sw, Y: -sw + sw*c}, f32.Point{X: -sw, Y: -sw}) // SW
	p.Line(f32.Point{X: 0, Y: nw - h + sw})
	p.Cube(f32.Point{X: 0, Y: -nw * c}, f32.Point{X: nw - nw*c, Y: -nw}, f32.Point{X: nw, Y: -nw}) // NW
	p.Line(f32.Point{X: w - ne - nw, Y: 0})
	p.Cube(f32.Point{X: ne * c, Y: 0}, f32.Point{X: ne, Y: ne - ne*c}, f32.Point{X: ne, Y: ne}) // NE
	return p.pen
}

// roundRectRev is like roundRect but counter-clockwise.
func roundRectRev(p *Path, size f32.Point, se, sw, nw, ne float32) {
	w, h := size.X, size.Y
	const c = 0.55228475
	p.Move(f32.Point{X: 0, Y: h - sw})
	p.Cube(f32.Point{X: 0, Y: sw * c}, f32.Point{X: sw - sw*c, Y: sw}, f32.Point{X: sw, Y: sw}) // SW
	p.Line(f32.Point{X: -se + w - sw, Y: 0})
	p.Cube(f32.Point{X: se * c, Y: 0}, f32.Point{X: se, Y: -se + se*c}, f32.Point{X: se, Y: -se}) // SE
	p.Line(f32.Point{X: 0, Y: ne - h + se})
	p.Cube(f32.Point{X: 0, Y: -ne * c}, f32.Point{X: -ne + ne*c, Y: -ne}, f32.Point{X: -ne, Y: -ne}) // NE
	p.Line(f32.Point{X: -w + ne + nw, Y: 0})
	p.Cube(f32.Point{X: -nw * c, Y: 0}, f32.Point{X: -nw, Y: nw - nw*c}, f32.Point{X: -nw, Y: nw}) // NW
}