add previous button

pages/post.go

@@ -11,6 +11,34 @@ import (
 	"github.com/gofiber/fiber/v2"
 )
 
+func prevInTag(client *api.Client, tagname, sort, page, I string) string {
+	i, err := strconv.Atoi(I)
+	if err != nil || i < 0 {
+		return ""
+	}
+	if i == 0 {
+		// Don't go before the first in tag
+		if page == "1" {
+			return ""
+		}
+		pagen, err := strconv.Atoi(page)
+		if err != nil || pagen < 0 {
+			return ""
+		}
+		pagen--
+		page = strconv.Itoa(pagen)
+	}
+
+	tag, err := client.FetchTag(tagname, sort, page)
+	if err != nil {
+		return ""
+	}
+	if i == 0 {
+		return tag.Posts[len(tag.Posts)-1].Link
+	}
+	return tag.Posts[i-1].Link
+}
+
 // Cursed function
 func nextInTag(client *api.Client, tagname, sort, page, I string) string {
 	i, err := strconv.Atoi(I)
@@ -78,15 +106,17 @@ func HandlePost(c *fiber.Ctx) error {
 	}
 	c.Set("Content-Security-Policy", csp)
 
-	var next string
+	var prev, next string
 	tagParam := strings.Split(c.Query("tag"), ".")
 	if len(tagParam) == 4 {
 		tag, sort, page, index := tagParam[0], tagParam[1], tagParam[2], tagParam[3]
+		prev = prevInTag(ApiClient, tag, sort, page, index)
 		next = nextInTag(ApiClient, tag, sort, page, index)
 	}
 
 	return c.Render("post", fiber.Map{
 		"post":     post,
+		"prev":     prev,
 		"next":     next,
 		"comments": comments,
 		"nonce":    nonce,