spaceapid/util/util.go

package util

import (
	"encoding/json"
	"errors"
	"log"
	"os"
	"path"

	"gitlab.hamburg.ccc.de/ccchh/spaceapid/types"
)

const (
	savedStateJSONPath = "/var/lib/spaceapid/spaceapid-state.json"
)

// MergeOldState merges a given SpaceAPIResponse with the state saved at the time of last program exit and then deletes
// the file containing the old state.
func MergeOldState(response *types.SpaceAPIResponseV14) {
	var (
		err            error
		oldState       []byte
		persistedState types.PersistentStateV14
	)

	log.Println("Merging old state from", savedStateJSONPath, "...")

	// Check if state.json is present
	_, err = os.Stat(savedStateJSONPath)
	if err != nil {
		log.Println("Old state json not accessible at", savedStateJSONPath, ", skipping merge... error:", err)
		if errors.Is(err, os.ErrNotExist) {
			return
		}
		goto removeOld
	}

	// Read file and load persisted state
	oldState, err = os.ReadFile(savedStateJSONPath)
	if err != nil {
		log.Println("Error reading old state from", savedStateJSONPath, ", skipping merge... error:", err)
		goto removeOld
	}
	err = json.Unmarshal(oldState, &persistedState)
	if err != nil {
		log.Println(savedStateJSONPath, "doesn't seem to contain valid data... error:", err)
		goto removeOld
	}

	// Merge state
	response.State = persistedState.State

	// Merge sensors
	for key, environmentSensors := range persistedState.Sensors {
		for _, sensor := range environmentSensors {
			// Order or amount of sensors might have changed, so check sensors already present in response
			// and then look for matching values in persisted state
			for i := range response.Sensors[key] {
				if rs := &response.Sensors[key][i]; rs.Location == sensor.Location && rs.Name == sensor.Name {
					rs.Value = sensor.Value
					rs.LastChange = sensor.LastChange
				}
			}
		}
	}

	// Delete old state json
removeOld:
	err = os.RemoveAll(savedStateJSONPath)
	if err != nil {
		log.Println("Failed to remove", savedStateJSONPath, ", continuing... error:", err)
	}
}

func SaveCurrentState(response types.SpaceAPIResponseV14) {
	// Create state directory if not present
	err := os.MkdirAll(path.Dir(savedStateJSONPath), 0750)
	if err != nil {
		log.Fatalln("Failed creating", savedStateJSONPath, ", aborting... error:", err)
	}

	// Open persistent state file
	file, err := os.OpenFile(savedStateJSONPath, os.O_WRONLY|os.O_CREATE, 0644)
	if err != nil {
		log.Fatalln("Failed opening", savedStateJSONPath, "while trying to save current state... error:", err)
	}
	defer file.Close()

	// Create persistent state
	persistentStateV14 := types.PersistentStateV14{
		State: struct {
			Open       bool  `json:"open"`
			LastChange int64 `json:"lastchange"`
		}{Open: response.State.Open, LastChange: response.State.LastChange},
	}
	// Save sensor state
	persistentStateV14.Sensors = make(map[string][]types.PersistentEnvironmentSensor)
	for key, environmentSensors := range response.Sensors {
		persistentStateV14.Sensors[key] = make([]types.PersistentEnvironmentSensor, len(environmentSensors))
		for i, sensor := range environmentSensors {
			persistentStateV14.Sensors[key][i].Value = sensor.Value
			persistentStateV14.Sensors[key][i].Location = sensor.Location
			persistentStateV14.Sensors[key][i].Name = sensor.Name
			persistentStateV14.Sensors[key][i].LastChange = sensor.LastChange
		}
	}

	// Serialize persistent state
	marshal, err := json.MarshalIndent(persistentStateV14, "", "\t")
	if err != nil {
		log.Fatalln("Failed serializing persistent state... error:", err)
	}

	// Write to file
	_, err = file.Write(marshal)
	if err != nil {
		log.Fatalln("Failed writing persistent state to file", file.Name(), "... error:", err)
	}
}