implemented pagination for shows

api/v1/shows.go

@@ -26,6 +26,7 @@ package v1
 
 import (
 	"net/http"
+	"sort"
 
 	"github.com/gin-gonic/gin"
 	"gitlab.servus.at/autoradio/tank/store"
@@ -38,10 +39,6 @@ func (api *API) ListShows(c *gin.Context) {
 		return
 	}
 
-	// TODO: implemement pagination, since the list of shows is rather short
-	//       and the result-set is filtered below we should implement this manually and
-	//       not use the database...
-
 	s := getAuthSession(c.Request) // this will panic if there is no session
 	showsMap := make(map[string]store.Show)
 	for _, showName := range s.Shows {
@@ -55,9 +52,33 @@ func (api *API) ListShows(c *gin.Context) {
 			showsMap[show.Name] = show
 		}
 	}
+
+	showNames := []string{}
+	for name, _ := range showsMap {
+		showNames = append(showNames, name)
+	}
+	sort.Strings(showNames)
+
+	offset, limit, ok := getPaginationParameter(c)
+	if !ok {
+		return
+	}
+
 	result := ShowsListing{}
-	for _, show := range showsMap {
-		result.Shows = append(result.Shows, show)
+	if offset > 0 {
+		if offset >= len(showNames) {
+			result.Shows = store.Shows{}
+			c.JSON(http.StatusOK, result)
+			return
+		}
+		showNames = showNames[offset:]
+	}
+	if limit > 0 && limit < len(showNames) {
+		showNames = showNames[:limit]
+	}
+
+	for _, name := range showNames {
+		result.Shows = append(result.Shows, showsMap[name])
 	}
 
 	c.JSON(http.StatusOK, result)

api/v1/utils.go

@@ -98,6 +98,31 @@ func sendError(c *gin.Context, err error) {
 	c.JSON(code, response)
 }
 
+func parsePositiveIntegerParameter(c *gin.Context, name string) (int, bool) {
+	valueStr := c.Query(name)
+	if valueStr == "" {
+		return -1, true
+	}
+	value, err := strconv.Atoi(valueStr)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Error: "query parameter " + name + " is invalid: " + err.Error()})
+		return -1, false
+	}
+	if value < 0 {
+		c.JSON(http.StatusBadRequest, ErrorResponse{Error: "query parameter " + name + " must be >= 0"})
+		return -1, false
+	}
+	return value, true
+}
+
+func getPaginationParameter(c *gin.Context) (offset, limit int, ok bool) {
+	if offset, ok = parsePositiveIntegerParameter(c, "offset"); !ok {
+		return
+	}
+	limit, ok = parsePositiveIntegerParameter(c, "limit")
+	return
+}
+
 func getAuthSession(r *http.Request) *auth.Session {
 	s, ok := auth.SessionFromRequest(r)
 	if !ok || s == nil {