adding basic data storage

cmd/crowsnest-frontend/main.go

@@ -4,6 +4,7 @@ import (
     "fmt"
     "net/http"
     "crowsnest-frontend/internal/model"
+    "crowsnest-frontend/internal/data"
 )
 
 func test(w http.ResponseWriter, req *http.Request) {
@@ -14,6 +15,11 @@ func test(w http.ResponseWriter, req *http.Request) {
     }
 }
 
+func PrintAllKeys(ds data.IDatastore) {
+    m, err := ds.GetAllKeys()
+    fmt.Println(m, err)
+}
+
 func main() {
     http.HandleFunc("/test", test)
 
@@ -24,7 +30,10 @@ func main() {
 
     a := &model.Article{}
     
-    fmt.Println(a.Hash())
+    fds, _ := data.NewFileDatastore("data.json")
+    fmt.Println(fds.jetAll())
+    repo := data.NewDefaultRepository[*model.Article](fds, "article")
+    fmt.Println(repo.Create(a))
 
     //http.ListenAndServe(":8090", nil)
 }

data.json

@@ -0,0 +1 @@
+{"article:0":"{\"Identifier\":0,\"SourceUrl\":\"\",\"PublishDate\":\"0001-01-01T00:00:00Z\",\"FetchDate\":\"0001-01-01T00:00:00Z\",\"Title\":\"\",\"Content\":\"\"}"}

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 
+}

internal/data/IDatastore.go

@@ -0,0 +1,9 @@
+package data
+
+type IDatastore interface {
+    Set(key string, val string) error
+    KeyExists(key string)       (bool, error)
+    Get(key string)             (string, error)
+    GetAll()                    (map[string]string, error)
+    GetAllKeys()                (map[string]bool, error)
+}

internal/data/IIdentifiable.go

@@ -0,0 +1,5 @@
+package data
+
+type IIdentifiable interface {
+    Id() uint
+}

internal/data/IRepository.go

@@ -0,0 +1,89 @@
+package data
+
+import (
+    "encoding/json"
+    "errors"
+    "strconv"
+)
+
+
+type IRepository[T IIdentifiable] interface {
+    /* An interface to manage generic structure objects persistently. Should
+    * use an IDatastore as the interface that actually stores and retrieves the
+    * data from an external source. */
+    Create(t T)                         error
+    Update(t T)                         error
+    Delete(t T)                         error
+    GetAll()                            ([]T, error)
+    GetById(id uint)                    (T, error)
+    GetByCriteria(c ISearchCriteria[T]) ([]T, error)
+}
+
+// --- default implementation ---
+
+type DefaultRepository[T IIdentifiable] struct {
+    ds      IDatastore
+    prefix  string
+}
+
+func NewDefaultRepository[T IIdentifiable](ds IDatastore, prefix string) *DefaultRepository[T] {
+    return &DefaultRepository[T]{ ds: ds, prefix: prefix }
+}
+
+func (repo *DefaultRepository[T]) Create(t T) error {
+    /* Creates a new entry in the repository with the given object t. Throws an
+    * error if there already exists an entry with the same id, the json
+    * encoding fails or the connection to the IDatastore fails. */
+
+    key := repo.prefix + ":" + strconv.FormatUint(uint64(t.Id()), 10)
+    exists, err := repo.ds.KeyExists(key)
+    if err != nil { return err }
+    if exists { return errors.New("key already exits") }
+
+    d, err := json.Marshal(t)
+    if err != nil { return err }
+    
+    err = repo.ds.Set(key, string(d))
+    if err != nil { return err }
+
+    return nil
+}
+
+func (repo *DefaultRepository[T]) Update(t T) error {
+    /* Updates the entry with the same id as t in the repository with the
+    * values of t. Trows an error if the json encoding fails or the connection
+    * to the IDatastore fails. */
+
+    key := repo.prefix + ":" + strconv.FormatUint(uint64(t.Id()), 10)
+    exists, err := repo.ds.KeyExists(key)
+    if err != nil { return err }
+    if !exists { return errors.New("key does not exits") }
+
+    d, err := json.Marshal(t)
+    if err != nil { return err }
+    
+    err = repo.ds.Set(key, string(d))
+    if err != nil { return err }
+
+    return nil
+}
+
+func (repo *DefaultRepository[T]) Delete(t T) error {
+    // TODO
+    return nil
+}
+
+func (repo *DefaultRepository[T]) GetAll() ([]T, error) {
+    // TODO
+    return nil, nil
+}
+
+func (repo *DefaultRepository[T]) GetById(id uint) (T, error) {
+    // TODO
+    return *new(T), nil
+}
+
+func (repo *DefaultRepository[T]) GetByCriteria(c ISearchCriteria[T]) ([]T, error) {
+    // TODO
+    return nil, nil
+}

internal/data/ISearchCriteria.go

@@ -0,0 +1,5 @@
+package data
+
+type ISearchCriteria[T any] interface {
+    Matches(t T) bool
+}

internal/data/datastore.go

@@ -1,8 +0,0 @@
-package data
-
-type Datastore interface {
-    Set(key string)         error
-    Get(key string)         string, error
-    GetAll(rowkey string)   map[string]string, error
-    GetAllKeys()            map[string]bool, error
-}

internal/model/article.go

@@ -6,8 +6,8 @@ import (
     "encoding/hex"
 )
 
-
 type Article struct {
+    Identifier  uint
     SourceUrl   string
     PublishDate time.Time
     FetchDate   time.Time
@@ -15,6 +15,7 @@ type Article struct {
     Content     string
 }
 
+
 func (article *Article) Hash() string {
     /* Generates a hash based on the source url of the article. Can be used to
      * identify the article. */
@@ -22,3 +23,10 @@ func (article *Article) Hash() string {
     hash := sha256.Sum256([]byte(article.SourceUrl))
     return hex.EncodeToString(hash[:])
 }
+
+
+// --- implementation of the IIdentifiable interface ---
+
+func (article *Article) Id() uint {
+    return article.Identifier
+}