PKGBUILD/pkg/storage/storage.go

package storage

import (
	"context"
	"fmt"
	"math"
	"net/url"
	"sort"

	"github.com/go-flucky/flucky/pkg/internal/format"
	"github.com/go-flucky/flucky/pkg/storage/db"
	"github.com/go-flucky/flucky/pkg/storage/logfile"
	"github.com/go-flucky/flucky/pkg/types"
)

// Compression the measured values. The system checks whether the measured values
// of the same type correspond to those of the predecessor. If this is the case,
// the current value is discarded and the validity date of the previous value is
// set to that of the current value. This means that no information is lost.
// Only the validity period of the measured value is increased.
func Compression(measuredValues []*types.MeasuredValue) []*types.MeasuredValue {
	compressedMeasuredValues := make([]*types.MeasuredValue, 0)
	lastMeasuredValuesBySensors := make(map[string]map[types.MeasuredValueType]*types.MeasuredValue, 0)

	// Sort all measured values according to the start time of the validity date
	// in order to successfully implement the subsequent compression.
	sort.SliceStable(measuredValues, func(i int, j int) bool {
		return measuredValues[i].FromDate.Before(measuredValues[j].TillDate)
	})

	now := format.FormatedTime()

	for _, measuredValue := range measuredValues {

		// If the sensor id does not exist in the map, a new map is initialized,
		// which can assume measured value types as the key. Behind this key there
		// is a pointer which refers to a measured value in the memory. This new map
		// is added to the map "lastMeasuredValuesBySensors" under the sensor ID.
		// This makes it possible to store one measured value per measured value
		// type per sensor.
		if _, ok := lastMeasuredValuesBySensors[measuredValue.SensorID]; !ok {
			lastMeasuredValuesBySensors[measuredValue.SensorID] = make(map[types.MeasuredValueType]*types.MeasuredValue, 0)
		}

		if _, ok := lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType]; !ok {
			lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType] = measuredValue
			continue
		}

		if lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType].Value == measuredValue.Value {
			lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType].TillDate = measuredValue.TillDate
			lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType].UpdateDate = &now
		} else if lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType].Value != measuredValue.Value {
			compressedMeasuredValues = append(compressedMeasuredValues, lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType])
			delete(lastMeasuredValuesBySensors[measuredValue.SensorID], measuredValue.ValueType)
			lastMeasuredValuesBySensors[measuredValue.SensorID][measuredValue.ValueType] = measuredValue
		}
	}

	// Copy all remaining entries from the map into the cache array
	for _, lastMeasuredValuesBySensor := range lastMeasuredValuesBySensors {
		for _, measuredValueType := range types.MeasuredValueTypes {
			if measuredValue, ok := lastMeasuredValuesBySensor[measuredValueType]; ok {
				compressedMeasuredValues = append(compressedMeasuredValues, measuredValue)
			}
		}
	}

	// Sort all measured values again to include the measured values from the
	// cache.
	sort.SliceStable(compressedMeasuredValues, func(i int, j int) bool {
		return compressedMeasuredValues[i].FromDate.Before(compressedMeasuredValues[j].FromDate)
	})

	return compressedMeasuredValues
}

// Read measured values from the given storage endpoint url. The scheme must be
// matched to a provider, if the scheme is not implemented, the function
// returns an error
func Read(ctx context.Context, storageEndpoint *url.URL) ([]*types.MeasuredValue, error) {
	switch storageEndpoint.Scheme {
	case "file":
		measuredValueLogfile := logfile.New(storageEndpoint.Path)
		return measuredValueLogfile.Read()
	case "postgres":
		database, err := db.New(storageEndpoint)
		if err != nil {
			return nil, err
		}
		defer database.Close()
		return database.SelectMeasuredValues(ctx)
	}
	return nil, fmt.Errorf("No supported scheme")
}

func Round(measuredValues []*types.MeasuredValue, round float64) {
	for _, measuredValue := range measuredValues {
		measuredValue.Value = math.Round(measuredValue.Value/round) * round
	}
}

// Write measured values to the given storage endpoint url. If the storage
// provider defined to a file, the data will be overwritten. If a database
// provider is used, the data is simply added without deleting the existing
// data. The scheme must be matched to a storage provider, if the scheme is not
// implemented, the function returns an error
func Write(ctx context.Context, measuredValues []*types.MeasuredValue, storageEndpoint *url.URL) error {
	writeCreationDate(measuredValues)
	switch storageEndpoint.Scheme {
	case "file":
		measuredValueLogfile := logfile.New(storageEndpoint.Path)
		return measuredValueLogfile.Write(measuredValues)
	case "postgres":
		database, err := db.New(storageEndpoint)
		if err != nil {
			return err
		}
		defer database.Close()
		return database.InsertMeasuredValues(ctx, measuredValues)
	default:
		return fmt.Errorf("No supported scheme")
	}
}

func writeCreationDate(measuredValues []*types.MeasuredValue) {
	now := format.FormatedTime()
	for _, measuredValue := range measuredValues {
		if measuredValue.CreationDate == nil {
			measuredValue.CreationDate = &now
		}
	}
}