Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/integration/linkding/linkding.go

@@ -0,0 +1,84 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package linkding // import "miniflux.app/v2/internal/integration/linkding"
+
+import (
+	"fmt"
+	"net/url"
+	"strings"
+
+	"miniflux.app/v2/internal/http/client"
+)
+
+// Document structure of a Linkding document
+type Document struct {
+	Url      string   `json:"url,omitempty"`
+	Title    string   `json:"title,omitempty"`
+	TagNames []string `json:"tag_names,omitempty"`
+	Unread   bool     `json:"unread,omitempty"`
+}
+
+// Client represents an Linkding client.
+type Client struct {
+	baseURL string
+	apiKey  string
+	tags    string
+	unread  bool
+}
+
+// NewClient returns a new Linkding client.
+func NewClient(baseURL, apiKey, tags string, unread bool) *Client {
+	return &Client{baseURL: baseURL, apiKey: apiKey, tags: tags, unread: unread}
+}
+
+// AddEntry sends an entry to Linkding.
+func (c *Client) AddEntry(title, url string) error {
+	if c.baseURL == "" || c.apiKey == "" {
+		return fmt.Errorf("linkding: missing credentials")
+	}
+
+	tagsSplitFn := func(c rune) bool {
+		return c == ',' || c == ' '
+	}
+
+	doc := &Document{
+		Url:      url,
+		Title:    title,
+		TagNames: strings.FieldsFunc(c.tags, tagsSplitFn),
+		Unread:   c.unread,
+	}
+
+	apiURL, err := getAPIEndpoint(c.baseURL, "/api/bookmarks/")
+	if err != nil {
+		return err
+	}
+
+	clt := client.New(apiURL)
+	clt.WithAuthorization("Token " + c.apiKey)
+	response, err := clt.PostJSON(doc)
+	if err != nil {
+		return fmt.Errorf("linkding: unable to send entry: %v", err)
+	}
+
+	if response.HasServerFailure() {
+		return fmt.Errorf("linkding: unable to send entry, status=%d", response.StatusCode)
+	}
+
+	return nil
+}
+
+func getAPIEndpoint(baseURL, pathURL string) (string, error) {
+	u, err := url.Parse(baseURL)
+	if err != nil {
+		return "", fmt.Errorf("linkding: invalid API endpoint: %v", err)
+	}
+
+	relative, err := url.Parse(pathURL)
+	if err != nil {
+		return "", fmt.Errorf("linkding: invalid API endpoint: %v", err)
+	}
+
+	u = u.ResolveReference(relative)
+	return u.String(), nil
+}