add support for page-based cursortokens (like goext)

scnserver/db/cursortoken/token.go

@@ -4,21 +4,27 @@ import (
 	"encoding/base32"
 	"encoding/json"
 	"errors"
+	"fmt"
+	"strconv"
 	"strings"
 	"time"
+
+	"git.blackforestbytes.com/BlackForestBytes/goext/langext"
 )
 
 type Mode string //@enum:type
 
 const (
-	CTMStart  = "START"
-	CTMNormal = "NORMAL"
-	CTMEnd    = "END"
+	CTMStart     = "START"
+	CTMNormal    = "NORMAL"
+	CTMPaginated = "PAGINATED"
+	CTMEnd       = "END"
 )
 
 type CursorToken struct {
 	Mode       Mode
-	Timestamp  int64
+	Timestamp  *int64
+	Page       *int
 	Id         string
 	Direction  string
 	FilterHash string
@@ -34,7 +40,8 @@ type cursorTokenSerialize struct {
 func Start() CursorToken {
 	return CursorToken{
 		Mode:       CTMStart,
-		Timestamp:  0,
+		Timestamp:  langext.Ptr[int64](0),
+		Page:       nil,
 		Id:         "",
 		Direction:  "",
 		FilterHash: "",
@@ -44,7 +51,8 @@ func Start() CursorToken {
 func End() CursorToken {
 	return CursorToken{
 		Mode:       CTMEnd,
-		Timestamp:  0,
+		Timestamp:  nil,
+		Page:       nil,
 		Id:         "",
 		Direction:  "",
 		FilterHash: "",
@@ -54,13 +62,22 @@ func End() CursorToken {
 func Normal(ts time.Time, id string, dir string, filter string) CursorToken {
 	return CursorToken{
 		Mode:       CTMNormal,
-		Timestamp:  ts.UnixMilli(),
+		Timestamp:  langext.Ptr(ts.UnixMilli()),
+		Page:       nil,
 		Id:         id,
 		Direction:  dir,
 		FilterHash: filter,
 	}
 }
 
+func Paginated(p int) CursorToken {
+	return CursorToken{
+		Mode:      CTMPaginated,
+		Timestamp: nil,
+		Page:      langext.Ptr(p),
+	}
+}
+
 func (c *CursorToken) Token() string {
 	if c.Mode == CTMStart {
 		return "@start"
@@ -69,6 +86,10 @@ func (c *CursorToken) Token() string {
 		return "@end"
 	}
 
+	if c.Page != nil {
+		return fmt.Sprintf("$%d", *c.Page)
+	}
+
 	// We kinda manually implement omitempty for the CursorToken here
 	// because omitempty does not work for time.Time and otherwise we would always
 	// get weird time values when decoding a token that initially didn't have an Timestamp set
@@ -80,8 +101,8 @@ func (c *CursorToken) Token() string {
 		sertok.Id = &c.Id
 	}
 
-	if c.Timestamp != 0 {
-		sertok.Timestamp = &c.Timestamp
+	if c.Timestamp != nil && *c.Timestamp != 0 {
+		sertok.Timestamp = langext.Ptr(*c.Timestamp)
 	}
 
 	if c.Direction != "" {
@@ -111,6 +132,14 @@ func Decode(tok string) (CursorToken, error) {
 		return End(), nil
 	}
 
+	if strings.HasPrefix(tok, "$") {
+		p, err := strconv.ParseInt(tok[1:], 10, 0)
+		if err != nil {
+			return CursorToken{}, errors.New("could not decode paginated token")
+		}
+		return Paginated(int(p)), nil
+	}
+
 	if !strings.HasPrefix(tok, "tok_") {
 		return CursorToken{}, errors.New("could not decode token, missing prefix")
 	}
@@ -129,7 +158,7 @@ func Decode(tok string) (CursorToken, error) {
 	token := CursorToken{Mode: CTMNormal}
 
 	if tokenDeserialize.Timestamp != nil {
-		token.Timestamp = *tokenDeserialize.Timestamp
+		token.Timestamp = langext.Ptr(*tokenDeserialize.Timestamp)
 	}
 	if tokenDeserialize.Id != nil {
 		token.Id = *tokenDeserialize.Id