package clockface

import (
	"fmt"
	"io"
	"math"
	"time"
)

// Point represents a two-dimentional Cartesian coordinate
type Point struct {
	X float64
	Y float64
}

const (
	hourHandLength   = 50
	minuteHandLength = 80
	secondHandLength = 90
	clockCentreX     = 150
	clockCentreY     = 150
)

const (
	secondsInHalfClock = 30
	secondsInClock     = 2 * secondsInHalfClock
	minutesInHalfClock = 30
	minutesInClock     = 2 * minutesInHalfClock
	hoursInHalfClock   = 6
	hoursInClock       = 2 * hoursInHalfClock
)

const svgStart = `<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg"
     width="100%"
     height="100%"
     viewBox="0 0 300 300"
     version="2.0">`

const bezel = `<circle cx="150" cy="150" r="100" style="fill:#fff;stroke:#000;stroke-width:5px;"/>`

const svgEnd = `</svg>`

func SVGWriter(w io.Writer, t time.Time) {
	io.WriteString(w, svgStart)
	io.WriteString(w, bezel)
	secondHand(w, t)
	minuteHand(w, t)
	hourHand(w, t)
	io.WriteString(w, svgEnd)
}

// SecondHand is the unit vector of the second hand of an analogue clock at the time `t` represented as a Point
func secondHand(w io.Writer, t time.Time) {
	p := secondHandPoint(t)
	makeHand(w, secondHandLength, p)
}

// MinuteHand is the unit vector of the minute hand of an analogue clock at the time `t` represented as a Point
func minuteHand(w io.Writer, t time.Time) {
	p := minuteHandPoint(t)
	makeHand(w, minuteHandLength, p)
}

// MinuteHand is the unit vector of the minute hand of an analogue clock at the time `t` represented as a Point
func hourHand(w io.Writer, t time.Time) {
	p := hourHandPoint(t)
	makeHand(w, hourHandLength, p)
}

func makeHand(w io.Writer, length float64, p Point) {
	p = Point{p.X * length, p.Y * length}             // scale
	p = Point{p.X, -p.Y}                              // flip
	p = Point{p.X + clockCentreX, p.Y + clockCentreY} // translate
	fmt.Fprintf(
		w,
		`<line x1="150" y1="150" x2="%f" y2="%f" style="fill:none;stroke:#f00;stroke-width:3px;"/>`,
		p.X,
		p.Y,
	)
}

func hoursInRadians(t time.Time) float64 {
	return (minutesInRadians(t) / hoursInClock) + math.Pi/(hoursInHalfClock/float64(t.Hour()%hoursInClock))
}

func hourHandPoint(t time.Time) Point {
	return angleToPoint(hoursInRadians(t))
}

func minutesInRadians(t time.Time) float64 {
	return (secondsInRadians(t) / minutesInClock) + math.Pi/(minutesInHalfClock/float64(t.Minute()))
}

func minuteHandPoint(t time.Time) Point {
	return angleToPoint(minutesInRadians(t))
}

func secondsInRadians(t time.Time) float64 {
	return math.Pi / (secondsInHalfClock / float64(t.Second()))
}

func secondHandPoint(t time.Time) Point {
	return angleToPoint(secondsInRadians(t))
}

func angleToPoint(angle float64) Point {
	x := math.Sin(angle)
	y := math.Cos(angle)

	return Point{x, y}
}