clockface: refactor magic numbers

.gitignore

@@ -0,0 +1,2 @@
+clock.svg
+gobytest

clockface/clockface.go

@@ -0,0 +1,113 @@
+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}
+}

clockface/clockface_acceptance_test.go

@@ -0,0 +1,123 @@
+package clockface
+
+import (
+	"bytes"
+	"encoding/xml"
+	"testing"
+	"time"
+)
+
+type Svg struct {
+	XMLName xml.Name `xml:"svg"`
+	Xmlns   string   `xml:"xmlns,attr"`
+	Width   string   `xml:"width,attr"`
+	Height  string   `xml:"height,attr"`
+	ViewBox string   `xml:"viewBox,attr"`
+	Version string   `xml:"version,attr"`
+	Circle  Circle   `xml:"circle"`
+	Line    []Line   `xml:"line"`
+}
+
+type Circle struct {
+	Cx float64 `xml:"cx,attr"`
+	Cy float64 `xml:"cy,attr"`
+	R  float64 `xml:"r,attr"`
+}
+
+type Line struct {
+	X1 float64 `xml:"x1,attr"`
+	Y1 float64 `xml:"y1,attr"`
+	X2 float64 `xml:"x2,attr"`
+	Y2 float64 `xml:"y2,attr"`
+}
+
+func TestSVGWriterSecondHand(t *testing.T) {
+	cases := []struct {
+		time time.Time
+		line Line
+	}{
+		{simpleTime(0, 0, 0), Line{150, 150, 150, 60}},
+		{simpleTime(0, 0, 30), Line{150, 150, 150, 240}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			b := bytes.Buffer{}
+			SVGWriter(&b, c.time)
+
+			svg := Svg{}
+			xml.Unmarshal(b.Bytes(), &svg)
+
+			if !containsLine(c.line, svg.Line) {
+				t.Errorf(
+					"Expected to find the second hand line %+v in the SVG lines %v",
+					c.line,
+					svg.Line,
+				)
+			}
+		})
+	}
+}
+
+func TestSVGWriterMinuteHand(t *testing.T) {
+	cases := []struct {
+		time time.Time
+		line Line
+	}{
+		{simpleTime(0, 0, 0), Line{150, 150, 150, 70}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			b := bytes.Buffer{}
+			SVGWriter(&b, c.time)
+
+			svg := Svg{}
+			xml.Unmarshal(b.Bytes(), &svg)
+
+			if !containsLine(c.line, svg.Line) {
+				t.Errorf(
+					"Expected to find the minute hand line %+v in the SVG lines %v",
+					c.line,
+					svg.Line,
+				)
+			}
+		})
+	}
+}
+
+func TestSVGWriterHourHand(t *testing.T) {
+	cases := []struct {
+		time time.Time
+		line Line
+	}{
+		{simpleTime(6, 0, 0), Line{150, 150, 150, 200}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			b := bytes.Buffer{}
+			SVGWriter(&b, c.time)
+
+			svg := Svg{}
+			xml.Unmarshal(b.Bytes(), &svg)
+
+			if !containsLine(c.line, svg.Line) {
+				t.Errorf(
+					"Expected to find the hour hand line %+v in the SVG lines %v",
+					c.line,
+					svg.Line,
+				)
+			}
+		})
+	}
+}
+
+func containsLine(l Line, ls []Line) bool {
+	for _, line := range ls {
+		if line == l {
+			return true
+		}
+	}
+	return false
+}

clockface/clockface_test.go

@@ -0,0 +1,145 @@
+package clockface
+
+import (
+	"math"
+	"testing"
+	"time"
+)
+
+func TestHoursInRadians(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		angle float64
+	}{
+		{simpleTime(6, 0, 0), math.Pi},
+		{simpleTime(0, 0, 0), 0},
+		{simpleTime(21, 0, 0), math.Pi * 1.5},
+		{simpleTime(0, 1, 30), math.Pi / ((6 * 60 * 60) / 90)},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := hoursInRadians(c.time)
+
+			if !roughlyEqualFloat64(c.angle, got) {
+				t.Fatalf("Wanted %v radians, but got %v", c.angle, got)
+			}
+		})
+	}
+}
+
+func TestHourHandPoint(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		point Point
+	}{
+		{simpleTime(6, 0, 0), Point{0, -1}},
+		{simpleTime(9, 0, 0), Point{-1, 0}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := hourHandPoint(c.time)
+			if !roughlyEqualPoint(got, c.point) {
+				t.Fatalf("Wanted %v Point, but got %v", c.point, got)
+			}
+		})
+	}
+}
+
+func TestMinutesInRadians(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		angle float64
+	}{
+		{simpleTime(0, 30, 0), math.Pi},
+		{simpleTime(0, 0, 7), 7 * (math.Pi / (30 * 60))},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := minutesInRadians(c.time)
+
+			if c.angle != got {
+				t.Fatalf("Wanted %v radians, but got %v", c.angle, got)
+			}
+		})
+	}
+}
+
+func TestMinuteHandPoint(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		point Point
+	}{
+		{simpleTime(0, 30, 0), Point{0, -1}},
+		{simpleTime(0, 45, 0), Point{-1, 0}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := minuteHandPoint(c.time)
+			if !roughlyEqualPoint(got, c.point) {
+				t.Fatalf("Wanted %v Point, but got %v", c.point, got)
+			}
+		})
+	}
+}
+
+func TestSecondsInRadians(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		angle float64
+	}{
+		{simpleTime(0, 0, 30), math.Pi},
+		{simpleTime(0, 0, 0), 0},
+		{simpleTime(0, 0, 45), (math.Pi / 2) * 3},
+		{simpleTime(0, 0, 7), (math.Pi / 30) * 7},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := secondsInRadians(c.time)
+
+			if c.angle != got {
+				t.Fatalf("Wanted %v radians, but got %v", c.angle, got)
+			}
+		})
+	}
+}
+
+func TestSecondHandPoint(t *testing.T) {
+	cases := []struct {
+		time  time.Time
+		point Point
+	}{
+		{simpleTime(0, 0, 30), Point{0, -1}},
+		{simpleTime(0, 0, 45), Point{-1, 0}},
+	}
+
+	for _, c := range cases {
+		t.Run(testName(c.time), func(t *testing.T) {
+			got := secondHandPoint(c.time)
+			if !roughlyEqualPoint(got, c.point) {
+				t.Fatalf("Wanted %v Point, but got %v", c.point, got)
+			}
+		})
+	}
+}
+
+func simpleTime(hours, minutes, seconds int) time.Time {
+	return time.Date(321, time.October, 28, hours, minutes, seconds, 0, time.UTC)
+}
+
+func testName(t time.Time) string {
+	return t.Format("15:04:05")
+}
+
+func roughlyEqualFloat64(a, b float64) bool {
+	const equalityThreshold = 1e-7
+	return math.Abs(a-b) < equalityThreshold
+}
+
+func roughlyEqualPoint(a, b Point) bool {
+	return roughlyEqualFloat64(a.X, b.X) && roughlyEqualFloat64(a.Y, b.Y)
+}

main.go

@@ -1,14 +1,20 @@
 package main
 
 import (
-	"gobytest/countdown"
+	"gobytest/clockface"
 	"os"
 	"time"
 )
 
 func main() {
 	// greet.Greet(os.Stdout, "Elodie")
-	sleeper := countdown.NewConfigurableSleeper(1*time.Second, time.Sleep)
+	// sleeper := countdown.NewConfigurableSleeper(1*time.Second, time.Sleep)
 
-	countdown.Countdown(os.Stdout, sleeper)
+	// countdown
+	// countdown.Countdown(os.Stdout, sleeper)
+
+	// clockface
+	t := time.Now()
+
+	clockface.SVGWriter(os.Stdout, t)
 }