1 files changed, 104 insertions, 0 deletions
diff --git a/cache.go b/cache.go
new file mode 100644
index 0000000..12c7b74
--- /dev/null
+++ b/cache.go
@@ -0,0 +1,104 @@
+// SPDX-FileCopyrightText: 2025 M. Shulhan <ms@kilabit.info>
+// SPDX-License-Identifier: GPL-3.0-only
+
+package jarink
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"sync"
+
+	"git.sr.ht/~shulhan/jarink/internal"
+)
+
+// ScannedLink store information about the link.
+type ScannedLink struct {
+	Url          string `json:"url"`
+	Size         int64  `json:"size"`
+	ResponseCode int    `json:"response_code"`
+}
+
+// Cache store external links that has been scanned, to minize
+// request to the same URL in the future.
+// The cache is stored as JSON file under user's cache directory, inside
+// "jarink" directory.
+// For example, in Linux it should be "$HOME/.cache/jarink/cache.json".
+// See [os.UserCacheDir] for location specific to operating system.
+type Cache struct {
+	ScannedLinks map[string]*ScannedLink `json:"scanned_links"`
+	file         string
+	mtx          sync.Mutex
+}
+
+// LoadCache from local storage.
+func LoadCache() (cache *Cache, err error) {
+	var logp = `LoadCache`
+
+	cache = &Cache{
+		ScannedLinks: map[string]*ScannedLink{},
+	}
+
+	cache.file, err = internal.CacheFile()
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	var cacheJson []byte
+	cacheJson, err = os.ReadFile(cache.file)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return cache, nil
+		}
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	err = json.Unmarshal(cacheJson, &cache)
+	if err != nil {
+		return nil, fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	return cache, nil
+}
+
+// Get return the scanned link information by url.
+func (cache *Cache) Get(url string) (scannedLink *ScannedLink) {
+	cache.mtx.Lock()
+	scannedLink = cache.ScannedLinks[url]
+	cache.mtx.Unlock()
+	return scannedLink
+}
+
+// Save the cache into local storage.
+func (cache *Cache) Save() (err error) {
+	var logp = `Save`
+	var cacheJson []byte
+	cacheJson, err = json.MarshalIndent(cache, ``, `  `)
+	if err != nil {
+		return fmt.Errorf(`%s: %w`, logp, err)
+	}
+
+	cacheJson = append(cacheJson, '\n')
+
+	err = os.WriteFile(cache.file, cacheJson, 0600)
+	if err != nil {
+		return fmt.Errorf(`%s: %w`, logp, err)
+	}
+	return nil
+}
+
+func (cache *Cache) Set(url string, respCode int, size int64) {
+	cache.mtx.Lock()
+	defer cache.mtx.Unlock()
+
+	var scannedLink = cache.ScannedLinks[url]
+	if scannedLink != nil {
+		return
+	}
+	scannedLink = &ScannedLink{
+		Url:          url,
+		Size:         size,
+		ResponseCode: respCode,
+	}
+	cache.ScannedLinks[url] = scannedLink
+}