// Package telemetry parses and validates raw device telemetry payloads.
package telemetry

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

// Reading is a single validated sensor reading, ready to be stored in
// ClickHouse and published as an event for rule-engine-service.
type Reading struct {
	DeviceID   string
	ZoneID     string
	SensorType string
	Value      float64
	RecordedAt time.Time
	ReceivedAt time.Time
}

// payload mirrors the wire format devices publish to devices/{device_id}/telemetry.
//
// ZoneID travels with the payload (rather than being looked up from
// PostgreSQL) so ingest-service stays decoupled from the device registry,
// matching the ingest→ClickHouse/RabbitMQ-only data flow in the platform
// architecture — the publishing client is responsible for knowing its own zone.
type payload struct {
	DeviceID   string  `json:"device_id"`
	ZoneID     string  `json:"zone_id"`
	SensorType string  `json:"sensor_type"`
	Value      float64 `json:"value"`
	Timestamp  string  `json:"timestamp"`
}

// ParseReading decodes and validates a raw MQTT message body. receivedAt is
// the time the server received the message, stamped independently of
// whatever the device claims, so ingest/processing delay can be measured later.
func ParseReading(raw []byte, receivedAt time.Time) (Reading, error) {
	var p payload
	if err := json.Unmarshal(raw, &p); err != nil {
		return Reading{}, fmt.Errorf("invalid json: %w", err)
	}

	if p.DeviceID == "" {
		return Reading{}, fmt.Errorf("device_id is required")
	}
	if p.ZoneID == "" {
		return Reading{}, fmt.Errorf("zone_id is required")
	}
	if p.SensorType == "" {
		return Reading{}, fmt.Errorf("sensor_type is required")
	}
	if p.Timestamp == "" {
		return Reading{}, fmt.Errorf("timestamp is required")
	}
	recordedAt, err := time.Parse(time.RFC3339, p.Timestamp)
	if err != nil {
		return Reading{}, fmt.Errorf("invalid timestamp %q: %w", p.Timestamp, err)
	}

	return Reading{
		DeviceID:   p.DeviceID,
		ZoneID:     p.ZoneID,
		SensorType: p.SensorType,
		Value:      p.Value,
		RecordedAt: recordedAt,
		ReceivedAt: receivedAt,
	}, nil
}