feat: Add initial caching

References: https://todo.sr.ht/~timharek/yr/1
Signed-off-by: Tim Hårek Andreassen <tim@harek.no>

pkg/cache/cache.go

@@ -0,0 +1,69 @@
+package cache
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+type Cache[T any] struct {
+	Path string
+}
+
+func New[T any](path string) *Cache[T] {
+	if path == "" {
+		path = os.TempDir()
+	}
+	return &Cache[T]{path}
+}
+
+// Add data as JSON-file into cache-dir, returns nil if success
+func (c *Cache[T]) Add(name string, data any) error {
+	j, err := json.MarshalIndent(data, "", " ")
+	if err != nil {
+		return fmt.Errorf("Failed to convert data as JSON.")
+	}
+	err = os.MkdirAll(c.Path, 0646)
+	if err != nil {
+		return fmt.Errorf("Failed to ensure cache-dir is present.")
+	}
+
+	filePath := filepath.Join(c.Path, fmt.Sprintf("%s.json", name))
+	d := []byte(j)
+	err = os.WriteFile(filePath, d, 0646)
+	if err != nil {
+		return fmt.Errorf("Failed write data to cache-file.")
+	}
+
+	return nil
+}
+
+// Get data from JSON-file from cache-dir, returns nil if no result
+func (c *Cache[T]) Get(name string) (*T, error) {
+	filePath := filepath.Join(c.Path, fmt.Sprintf("%s.json", name))
+	if _, err := os.Stat(filePath); errors.Is(err, os.ErrNotExist) {
+		return nil, nil
+	}
+
+	rawFile, err := os.Open(filePath)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to read cache-file.")
+	}
+
+	var result T
+
+	bytes, err := io.ReadAll(rawFile)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to read data from cache-file.")
+	}
+
+	err = json.Unmarshal(bytes, &result)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to parse JSON from cache-file.")
+	}
+
+	return &result, nil
+}

pkg/cache/cache_test.go

@@ -0,0 +1,27 @@
+package cache
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type testType struct {
+	Prop1 string `json:"prop1"`
+	Prop2 string `json:"prop2"`
+}
+
+func TestCache(t *testing.T) {
+	assert := assert.New(t)
+	c := New[testType]("")
+	assert.Equal(os.TempDir(), c.Path)
+
+	err := c.Add("something", &testType{Prop1: "test1", Prop2: "test2"})
+	assert.NoError(err)
+
+	result, err := c.Get("something")
+	assert.NoError(err)
+	assert.Equal("test1", result.Prop1)
+	assert.Equal("test2", result.Prop2)
+}