server, post: add about images for social media

Signed-off-by: Naman Sood <mail@nsood.in>

server.go

@@ -1,12 +1,22 @@
 package main
 
 import (
+	"bytes"
+	"io"
 	"log"
+	"math"
 	"net/http"
 	"strings"
 	"sync"
 
 	"github.com/aymerick/raymond"
+	"github.com/fogleman/gg"
+)
+
+const (
+	blogTitle   = "Prose"
+	blogURL     = "https://prose.nsood.in"
+	blogSummary = "Where I infodump in Markdown and nobody can stop me."
 )
 
 type server struct {
@@ -15,7 +25,8 @@ type server struct {
 	mu        sync.RWMutex
 	templates map[string]*raymond.Template
 	postList
-	styles map[string]string
+	styles    map[string]string
+	homeImage bytes.Buffer
 }
 
 func newServer() (*server, error) {
@@ -23,6 +34,11 @@ func newServer() (*server, error) {
 		staticHandler: http.FileServer(http.Dir("static/")),
 	}
 
+	err := createImage(blogTitle, blogSummary, blogURL, &s.homeImage)
+	if err != nil {
+		return nil, err
+	}
+
 	posts, err := newPostList()
 	if err != nil {
 		return nil, err
@@ -92,11 +108,18 @@ func (s *server) router(res http.ResponseWriter, req *http.Request) {
 		s.homePage(res, req)
 		return
 	}
+	if slug == "about.png" {
+		s.renderImage(res, req, &s.homeImage)
+		return
+	}
 
 	for _, p := range s.postList {
-		if p.Slug == slug {
+		if slug == p.Slug {
 			s.postPage(p, res, req)
 			return
+		} else if slug == p.Slug+"/about.png" {
+			s.renderImage(res, req, &p.Image)
+			return
 		}
 	}
 
@@ -152,7 +175,7 @@ func (s *server) homePage(res http.ResponseWriter, req *http.Request) {
 		posts = posts + summary
 	}
 
-	page, err := s.createWebPage("Home", "Where I infodump in Markdown and nobody can stop me.", posts)
+	page, err := s.createWebPage("Home", blogSummary, posts)
 
 	if err != nil {
 		s.errorInRequest(res, req, err)
@@ -161,6 +184,14 @@ func (s *server) homePage(res http.ResponseWriter, req *http.Request) {
 	res.Write([]byte(page))
 }
 
+func (s *server) renderImage(res http.ResponseWriter, req *http.Request, img io.Reader) {
+	res.Header().Add("content-type", "image/png")
+	_, err := io.Copy(res, img)
+	if err != nil {
+		s.errorInRequest(res, req, err)
+	}
+}
+
 func (s *server) loadStylesheet(res http.ResponseWriter, req *http.Request, filename string) (ok bool) {
 	contents, ok := s.styles[filename]
 	if !ok {
@@ -170,3 +201,74 @@ func (s *server) loadStylesheet(res http.ResponseWriter, req *http.Request, file
 	res.Write([]byte(contents))
 	return ok
 }
+
+func createImage(title, summary, url string, out io.Writer) error {
+	imgWidth, imgPaddingX, imgPaddingY := 800, 30, 60
+	titleSize, summarySize, urlSize := 42.0, 28.0, 18.0
+	lineHeight := 1.5
+	textWidth := float64(imgWidth - 2*imgPaddingX)
+
+	// temporarily set height = 0 for context only used to generate
+	// wrapped strings
+	draw := gg.NewContext(imgWidth, 0)
+
+	titleFont, err := gg.LoadFontFace("fonts/Nunito-Bold.ttf", titleSize)
+	if err != nil {
+		return err
+	}
+	summaryFont, err := gg.LoadFontFace("fonts/Nunito-LightItalic.ttf", summarySize)
+	if err != nil {
+		return err
+	}
+	urlFont, err := gg.LoadFontFace("fonts/JetBrainsMono-ExtraLight.ttf", urlSize)
+	if err != nil {
+		return err
+	}
+
+	draw.SetFontFace(titleFont)
+	wrappedTitle := draw.WordWrap(title, textWidth)
+	draw.SetFontFace(summaryFont)
+	wrappedSummary := draw.WordWrap(summary, textWidth)
+
+	imgHeight := 2 * imgPaddingY
+	for range wrappedTitle {
+		imgHeight += int(math.Ceil(lineHeight * titleSize))
+	}
+	for range wrappedSummary {
+		imgHeight += int(math.Ceil(lineHeight * summarySize))
+	}
+	imgHeight += int(math.Ceil(lineHeight * urlSize))
+
+	// actual context with actual height
+	draw = gg.NewContext(imgWidth, imgHeight)
+	draw.SetHexColor("#fff")
+	draw.DrawRectangle(0, 0, float64(imgWidth), float64(imgHeight))
+	draw.Fill()
+	draw.SetHexColor("#3498db")
+	accentHeight := 5.0
+	draw.DrawRectangle(0, float64(imgHeight)-accentHeight, float64(imgWidth), accentHeight)
+	draw.Fill()
+
+	offset := float64(imgPaddingY)
+
+	draw.SetFontFace(titleFont)
+	draw.SetHexColor("#333")
+	for _, line := range wrappedTitle {
+		draw.DrawString(line, float64(imgPaddingX), offset)
+		offset += lineHeight * titleSize
+	}
+
+	draw.SetFontFace(summaryFont)
+	draw.SetHexColor("#999")
+	for _, line := range wrappedSummary {
+		draw.DrawString(line, float64(imgPaddingX), offset)
+		offset += lineHeight * summarySize
+	}
+
+	draw.SetHexColor("#333")
+	draw.SetFontFace(urlFont)
+	urlY := float64(imgHeight - imgPaddingY)
+	draw.DrawStringWrapped(url, float64(imgPaddingX), urlY, 0, 0, textWidth, lineHeight, gg.AlignRight)
+
+	return draw.EncodePNG(out)
+}