First working? version with persistent state

util/util.go

@@ -3,13 +3,17 @@ package util
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"log"
 	"os"
+	"path"
 	"slices"
 
 	"gitlab.hamburg.ccc.de/ccchh/spaceapid/types"
 )
 
+const savedStateJSONPath = "/var/lib/spaceapid/spaceapid-state.json"
+
 // ParseTemplate parses the given file and
 func ParseTemplate(file string) (resp types.SpaceAPIResponseV14) {
 
@@ -34,3 +38,77 @@ func ParseTemplate(file string) (resp types.SpaceAPIResponseV14) {
 
 	return
 }
+
+// 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
+	)
+
+	// Create state directory if not present
+	err = os.MkdirAll(path.Dir(savedStateJSONPath), 0750)
+	if err != nil {
+		log.Fatalln("Failed creating", savedStateJSONPath, ", aborting... error:", err)
+	}
+
+	// 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 merge
+	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, response)
+	if err != nil {
+		log.Println(savedStateJSONPath, "doesn't seem to contain valid data... error:", err)
+		goto removeOld
+	}
+
+	// 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) {
+	file, err := os.OpenFile(savedStateJSONPath, os.O_RDWR|os.O_CREATE, 0644)
+	if err != nil {
+		log.Fatalln("Failed opening", savedStateJSONPath, "while trying to save current state... error:", err)
+	}
+	defer func(file *os.File) {
+		_ = file.Close()
+	}(file)
+
+	// Create persistent state
+	persistentStateV14 := types.PersistentStateV14{
+		State: struct {
+			Open       bool  `json:"open"`
+			LastChange int64 `json:"lastchange"`
+		}{Open: response.State.Open, LastChange: response.State.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)
+	}
+}