adding basic data storage

internal/data/FileDatastore.go

@@ -0,0 +1,126 @@
+package data
+
+import (
+    "os"
+    "maps"
+    "errors"
+    "encoding/json"
+)
+
+type FileDatastore struct {
+    /* A very simple datastructure, implementing the IDatastore interface. It
+    * uses a simple text file to the data as json. */
+    path string
+}
+
+
+func NewFileDatastore(path string) (*FileDatastore, error) {
+    /* Creates a new FileDatastore object, creating the storage file in the
+    * process. */
+
+    fds := &FileDatastore{ path: path }
+
+    if _, err := fds.readMapObj(); err != nil {
+        if err := fds.writeMapObj(make(map[string]string)); err != nil { return nil, err }
+    }
+
+    return fds, nil
+}
+
+func (fds *FileDatastore) readMapObj() (map[string]string, error) {
+    /* Read the contents of the storage file and convert to a map object. May
+    * throw an error, if the file does not exit or the file content can not be
+    * converted. */
+    
+    dat, err := os.ReadFile(fds.path)
+    if err != nil { return nil, err }
+
+    var mapobj map[string]string
+    err = json.Unmarshal(dat, &mapobj)
+    if err != nil { return nil, err }
+
+    return mapobj, nil
+}
+
+func (fds *FileDatastore) writeMapObj(m map[string]string) error {
+    /* Write the map object to the storage file. Will overwrite the content of
+    * the file. May throw an error, if the file cannot be created or written
+    * to. */
+
+    file, err := os.Create(fds.path)
+    if err != nil { return err }
+    defer file.Close()
+
+    encoder := json.NewEncoder(file)
+    if err := encoder.Encode(m); err != nil { return err }
+
+    return nil
+}
+
+// --- implement IDatastore interface ---
+
+func (fds *FileDatastore) Set(key string, val string) error {
+    /* Sets the key value pair given, overwriting if the key already exists.
+    * May through an error if the file cannot be opened or the contents cannot
+    * be decoded correctly. */
+    
+    m, err := fds.readMapObj()
+    if err != nil { return err }
+
+    m[key] = val
+
+    err = fds.writeMapObj(m)
+    if err != nil { return err }
+
+    return nil
+}
+
+func (fds *FileDatastore) KeyExists(key string) (bool, error) {
+    /* Check if for the given key a entry does exit. May through an error if
+    * the file cannot be opened or the contents cannot be decoded correctly. */
+
+    m, err := fds.readMapObj()
+    if err != nil { return false, err }
+    
+    _, ok := m[key]
+
+    return ok, nil 
+}
+
+func (fds *FileDatastore) Get(key string) (string, error) {
+    /* Gets the value for the given key. May through an error if the key does
+    * not exit, the file cannot be opened or the contents cannot be decoded
+    * correctly. */
+
+    m, err := fds.readMapObj()
+    if err != nil { return "", err }
+
+    val, ok := m[key]
+    if !ok { return "", errors.New("key not found") }
+
+    return val, nil
+}
+
+func (fds *FileDatastore) GetAll() (map[string]string, error) {
+    /* Gets all the key value pairs from the file and returns them as a map
+    * object. May through an error if the file cannot be opened or the contents
+    * cannot be decoded correctly. */
+
+    return fds.readMapObj()
+}
+
+func (fds *FileDatastore) GetAllKeys() (map[string]bool, error) {
+    /* Gets all the key the file and returns them as a map object. May through
+    * an error if the file cannot be opened or the contents cannot be decoded
+    * correctly. */
+
+    m, err := fds.readMapObj()
+    if err != nil { return nil, err }
+
+    out := make(map[string]bool)
+    for key := range maps.Keys(m) {
+        out[key] = true
+    }
+
+    return out, nil 
+}