ListMessages()

server/db/cursortoken/token.go

@@ -0,0 +1,133 @@
+package cursortoken
+
+import (
+	"encoding/base32"
+	"encoding/json"
+	"errors"
+	"strings"
+	"time"
+)
+
+type Mode string
+
+const (
+	CTMStart  = "START"
+	CTMNormal = "NORMAL"
+	CTMEnd    = "END"
+)
+
+type CursorToken struct {
+	Mode      Mode
+	Timestamp int64
+	Id        int64
+	Direction string
+}
+
+type cursorTokenSerialize struct {
+	Timestamp *int64  `json:"ts,omitempty"`
+	Id        *int64  `json:"id,omitempty"`
+	Direction *string `json:"dir,omitempty"`
+}
+
+func Start() CursorToken {
+	return CursorToken{
+		Mode:      CTMStart,
+		Timestamp: 0,
+		Id:        0,
+		Direction: "",
+	}
+}
+
+func End() CursorToken {
+	return CursorToken{
+		Mode:      CTMEnd,
+		Timestamp: 0,
+		Id:        0,
+		Direction: "",
+	}
+}
+
+func Normal(ts time.Time, id int64, dir string) CursorToken {
+	return CursorToken{
+		Mode:      CTMNormal,
+		Timestamp: ts.UnixMilli(),
+		Id:        id,
+		Direction: dir,
+	}
+}
+
+func (c *CursorToken) Token() string {
+	if c.Mode == CTMStart {
+		return "@start"
+	}
+	if c.Mode == CTMEnd {
+		return "@end"
+	}
+
+	// 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
+	// For this usecase we treat Unix=0 as an empty timestamp
+
+	sertok := cursorTokenSerialize{}
+
+	if c.Id != 0 {
+		sertok.Id = &c.Id
+	}
+
+	if c.Timestamp != 0 {
+		sertok.Timestamp = &c.Timestamp
+	}
+
+	if c.Direction != "" {
+		sertok.Direction = &c.Direction
+	}
+
+	body, err := json.Marshal(sertok)
+	if err != nil {
+		panic(err)
+	}
+
+	return "tok_" + base32.StdEncoding.EncodeToString(body)
+}
+
+func Decode(tok string) (CursorToken, error) {
+	if tok == "" {
+		return Start(), nil
+	}
+	if strings.ToLower(tok) == "@start" {
+		return Start(), nil
+	}
+	if strings.ToLower(tok) == "@end" {
+		return End(), nil
+	}
+
+	if !strings.HasPrefix(tok, "tok_") {
+		return CursorToken{}, errors.New("could not decode token, missing prefix")
+	}
+
+	body, err := base32.StdEncoding.DecodeString(tok[len("tok_"):])
+	if err != nil {
+		return CursorToken{}, err
+	}
+
+	var tokenDeserialize cursorTokenSerialize
+	err = json.Unmarshal(body, &tokenDeserialize)
+	if err != nil {
+		return CursorToken{}, err
+	}
+
+	token := CursorToken{Mode: CTMNormal}
+
+	if tokenDeserialize.Timestamp != nil {
+		token.Timestamp = *tokenDeserialize.Timestamp
+	}
+	if tokenDeserialize.Id != nil {
+		token.Id = *tokenDeserialize.Id
+	}
+	if tokenDeserialize.Direction != nil {
+		token.Direction = *tokenDeserialize.Direction
+	}
+
+	return token, nil
+}