Truncate too long product names for Twitter

Signed-off-by: Julien Riou <julien@riou.xyz>

twitter.go

@@ -5,6 +5,7 @@ import (
 	"regexp"
 	"strings"
 	"time"
+	"unicode/utf8"
 
 	"github.com/dghubble/go-twitter/twitter"
 	"github.com/dghubble/oauth1"
@@ -12,6 +13,9 @@ import (
 	"gorm.io/gorm"
 )
 
+// maximum number of characters a tweet can support
+const tweetMaxSize = 280
+
 // Tweet to store relationship between a Product and a Twitter notification
 type Tweet struct {
 	gorm.Model
@@ -107,11 +111,8 @@ func formatPrice(value float64, currency string) string {
 // NotifyWhenAvailable create a Twitter status for announcing that a product is available
 // implements the Notifier interface
 func (c *TwitterNotifier) NotifyWhenAvailable(shopName string, productName string, productPrice float64, productCurrency string, productURL string) error {
-	// format message
-	formattedPrice := formatPrice(productPrice, productCurrency)
 	hashtags := c.buildHashtags(productName)
-	message := fmt.Sprintf("%s: %s for %s is available at %s %s", shopName, productName, formattedPrice, productURL, hashtags)
-
+	message := formatAvailableTweet(shopName, productName, productPrice, productCurrency, productURL, hashtags)
 	// create thread
 	tweetID, err := c.createTweet(message)
 	if err != nil {
@@ -129,6 +130,22 @@ func (c *TwitterNotifier) NotifyWhenAvailable(shopName string, productName strin
 	return nil
 }
 
+func formatAvailableTweet(shopName string, productName string, productPrice float64, productCurrency string, productURL string, hashtags string) string {
+	// format message
+	formattedPrice := formatPrice(productPrice, productCurrency)
+	message := fmt.Sprintf("%s: %s for %s is available at %s %s", shopName, productName, formattedPrice, productURL, hashtags)
+
+	// truncate tweet if too big
+	if utf8.RuneCountInString(message) > tweetMaxSize {
+		// maximum tweet size - other characters - additional "…" to say product name has been truncated
+		productNameSize := tweetMaxSize - utf8.RuneCountInString(fmt.Sprintf("%s:  for %s is available at %s %s", shopName, formattedPrice, productURL, hashtags)) - 1
+		format := fmt.Sprintf("%%s: %%.%ds… for %%s is available at %%s %%s", productNameSize)
+		message = fmt.Sprintf(format, shopName, productName, formattedPrice, productURL, hashtags)
+	}
+
+	return message
+}
+
 // NotifyWhenNotAvailable create a Twitter status replying to the NotifyWhenAvailable status to say it's over
 // implements the Notifier interface
 func (c *TwitterNotifier) NotifyWhenNotAvailable(productURL string, duration time.Duration) error {

twitter_test.go

@@ -79,3 +79,46 @@ func TestFormatPrice(t *testing.T) {
 		})
 	}
 }
+
+/*
+func formatAvailableTweet(shopName string, productName string, productPrice float64, productCurrency string, productURL string, hashtags string) string {
+	// format message
+	formattedPrice := formatPrice(productPrice, productCurrency)
+	message := fmt.Sprintf("%s: %s for %s is available at %s %s", shopName, productName, formattedPrice, productURL, hashtags)
+
+	// truncate tweet if too big
+	if utf8.RuneCountInString(message) > tweetMaxSize {
+		// maximum tweet size - other characters - additional "…" to say product name has been truncated
+		productNameSize := tweetMaxSize - utf8.RuneCountInString(fmt.Sprintf("%s:  for %s is available at %s %s", shopName, formattedPrice, productURL, hashtags)) - 1
+		format := fmt.Sprintf("%%s: %%.%ds… for %%s is available at %%s %%s", productNameSize)
+		message = fmt.Sprintf(format, shopName, productName, formattedPrice, productURL, hashtags)
+	}
+
+	return message
+}
+*/
+
+func TestFormatAvailableTweet(t *testing.T) {
+	tests := []struct {
+		shopName        string
+		productName     string
+		productPrice    float64
+		productCurrency string
+		productURL      string
+		hashtags        string
+		expected        string
+	}{
+		{"shop.com", "my awesome product", 999.99, "USD", "https://shop.com/awesome", "#awesome #product", "shop.com: my awesome product for $999.99 is available at https://shop.com/awesome #awesome #product"},
+		{"shop.com", "my awesome product with very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very long name", 999.99, "USD", "https://shop.com/awesome", "#awesome #product", "shop.com: my awesome product with very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very very… for $999.99 is available at https://shop.com/awesome #awesome #product"},
+	}
+	for i, tc := range tests {
+		t.Run(fmt.Sprintf("TestFormatAvailableTweet#%d", i), func(t *testing.T) {
+			got := formatAvailableTweet(tc.shopName, tc.productName, tc.productPrice, tc.productCurrency, tc.productURL, tc.hashtags)
+			if got != tc.expected {
+				t.Errorf("for %s, got '%s', want '%s'", tc.productName, got, tc.expected)
+			} else {
+				t.Logf("for %s, got '%s', want '%s'", tc.productName, got, tc.expected)
+			}
+		})
+	}
+}