package redisstate

import (
	"encoding/json"
	"fmt"
	"time"
)

// StreamOffset stores the persisted progress of one plain-XREAD consumer.
type StreamOffset struct {
	// Stream stores the Redis Stream key the offset belongs to.
	Stream string `json:"stream"`

	// LastProcessedEntryID stores the most recently processed Stream entry id.
	LastProcessedEntryID string `json:"last_processed_entry_id"`

	// UpdatedAt stores when the offset was last persisted.
	UpdatedAt time.Time `json:"updated_at"`
}

// MarshalStreamOffset returns the JSON encoding of the persisted offset.
func MarshalStreamOffset(offset StreamOffset) ([]byte, error) {
	payload, err := json.Marshal(offset)
	if err != nil {
		return nil, fmt.Errorf("marshal stream offset: %w", err)
	}
	return payload, nil
}

// UnmarshalStreamOffset parses one persisted offset payload.
func UnmarshalStreamOffset(payload []byte) (StreamOffset, error) {
	var offset StreamOffset
	if err := json.Unmarshal(payload, &offset); err != nil {
		return StreamOffset{}, fmt.Errorf("unmarshal stream offset: %w", err)
	}
	if offset.UpdatedAt.IsZero() {
		return StreamOffset{}, fmt.Errorf("unmarshal stream offset: updated_at must not be zero")
	}
	return offset, nil
}