From d9057f2aaae9bc97e26a2fbb02c79d5c889a230a Mon Sep 17 00:00:00 2001
From: Ian Gulliver <github@flamingcow.io>
Date: Tue, 26 Nov 2024 22:20:10 -0600
Subject: [PATCH] Auto generate short links if empty

---
 go.mod            |  9 +++++++--
 go.sum            |  2 ++
 main.go           | 36 ++++++++++++++++++++++++++++++++++++
 static/index.html | 11 ++++++++---
 4 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/go.mod b/go.mod
index 528ea91..b109a0a 100644
--- a/go.mod
+++ b/go.mod
@@ -1,5 +1,10 @@
 module github.com/gopatchy/shortlinks
 
-go 1.22
+go 1.22.0
 
-require github.com/lib/pq v1.10.9
+toolchain go1.23.3
+
+require (
+	github.com/lib/pq v1.10.9
+	golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f
+)
diff --git a/go.sum b/go.sum
index aeddeae..51eebe0 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,4 @@
 github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
 github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
+golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f h1:XdNn9LlyWAhLVp6P/i8QYBW+hlyhrhei9uErw2B5GJo=
+golang.org/x/exp v0.0.0-20241108190413-2d47ceb2692f/go.mod h1:D5SMRVC3C2/4+F/DB1wZsLRnSNimn2Sp/NPsCrsv8ak=
diff --git a/main.go b/main.go
index 3cc7f33..f85e1fa 100644
--- a/main.go
+++ b/main.go
@@ -7,14 +7,17 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"time"
 
 	_ "github.com/lib/pq"
+	"golang.org/x/exp/rand"
 )
 
 type ShortLinks struct {
 	tmpl *template.Template
 	mux  *http.ServeMux
 	db   *sql.DB
+	r    *rand.Rand
 }
 
 type response struct {
@@ -33,6 +36,7 @@ func NewShortLinks(db *sql.DB) (*ShortLinks, error) {
 		tmpl: tmpl,
 		mux:  http.NewServeMux(),
 		db:   db,
+		r:    rand.New(rand.NewSource(uint64(time.Now().UnixNano()))),
 	}
 
 	sl.mux.HandleFunc("GET /{$}", sl.serveRoot)
@@ -88,6 +92,14 @@ func (sl *ShortLinks) serveSet(w http.ResponseWriter, r *http.Request) {
 
 	short := r.Form.Get("short")
 
+	if short == "" {
+		short, err = sl.genShort()
+		if err != nil {
+			sendError(w, http.StatusInternalServerError, "genShort: %s", err)
+			return
+		}
+	}
+
 	long := r.Form.Get("long")
 	if long == "" {
 		sendError(w, http.StatusBadRequest, "long= param required")
@@ -110,6 +122,30 @@ DO UPDATE SET long = $2;
 	})
 }
 
+func (sl *ShortLinks) genShort() (string, error) {
+	for chars := 3; chars <= 10; chars++ {
+		b := make([]byte, chars)
+
+		for i := range b {
+			b[i] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"[sl.r.Intn(62)]
+		}
+
+		short := string(b)
+
+		exists := false
+		err := sl.db.QueryRow("SELECT EXISTS(SELECT 1 FROM links WHERE short = $1)", short).Scan(&exists)
+		if err != nil {
+			return "", fmt.Errorf("check exists: %w", err)
+		}
+
+		if !exists {
+			return short, nil
+		}
+	}
+
+	return "", fmt.Errorf("no available short link found")
+}
+
 func main() {
 	port := os.Getenv("PORT")
 	if port == "" {
diff --git a/static/index.html b/static/index.html
index ad88ad7..26f6c74 100644
--- a/static/index.html
+++ b/static/index.html
@@ -87,7 +87,10 @@ async function set() {
 
     document.getElementById('short-icon').setAttribute('name', 'check-square-fill');
     document.getElementById('long-icon').setAttribute('name', 'check-square-fill');
-    setShortItem(short, 'check-square-fill');
+
+    if (short != '') {  
+        setShortItem(short, 'check-square-fill');
+    }
 
     const params = new URLSearchParams();
     params.set('short', short);
@@ -98,14 +101,16 @@ async function set() {
     });
 
     if (resp.status !== 200) {
-        error('Failed to set', await resp.text());
+        error('Failed to set', (await resp.json()).message);
         return;
     }
 
+    const newShort = (await resp.json()).short;
+
     if (document.getElementById('short').value == short && document.getElementById('long').value == long) {
         document.getElementById('short-icon').setAttribute('name', 'check-square');
         document.getElementById('long-icon').setAttribute('name', 'check-square');
-        setShortItem(short, 'check-square');
+        setShortItem(newShort, 'check-square');
     }
 }