feat(story-2.3): add OPML import/export functionality

internal/opml/opml.go

@@ -0,0 +1,130 @@
+// Package opml provides OPML file parsing for feed import/export.
+package opml
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// OPML represents the root OPML document.
+type OPML struct {
+	XMLName xml.Name `xml:"opml"`
+	Version string   `xml:"version,attr"`
+	Head    Head     `xml:"head"`
+	Body    Body     `xml:"body"`
+}
+
+// Head contains OPML metadata.
+type Head struct {
+	Title       string `xml:"title"`
+	DateCreated string `xml:"dateCreated,omitempty"`
+}
+
+// Body contains the outline elements.
+type Body struct {
+	Outlines []Outline `xml:"outline"`
+}
+
+// Outline represents an OPML outline element (feed or folder).
+type Outline struct {
+	Text        string    `xml:"text,attr"`
+	Title       string    `xml:"title,attr"`
+	Type        string    `xml:"type,attr"`
+	XMLURL      string    `xml:"xmlUrl,attr"`
+	HTMLURL     string    `xml:"htmlUrl,attr"`
+	Description string    `xml:"description,attr"`
+	Category    string    `xml:"category,attr"`
+	Outlines    []Outline `xml:"outline"` // Nested outlines (folders)
+}
+
+// FeedInfo contains extracted feed information.
+type FeedInfo struct {
+	URL         string
+	Title       string
+	SiteURL     string
+	Description string
+	Category    string
+}
+
+// Parse reads an OPML file and extracts feed information.
+func Parse(r io.Reader) ([]FeedInfo, error) {
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, fmt.Errorf("reading OPML: %w", err)
+	}
+
+	var opml OPML
+	if err := xml.Unmarshal(data, &opml); err != nil {
+		return nil, fmt.Errorf("parsing OPML: %w", err)
+	}
+
+	var feeds []FeedInfo
+	extractFeeds(opml.Body.Outlines, "", &feeds)
+
+	return feeds, nil
+}
+
+// extractFeeds recursively extracts feeds from outlines.
+func extractFeeds(outlines []Outline, category string, feeds *[]FeedInfo) {
+	for _, outline := range outlines {
+		// If it has nested outlines, it's a folder
+		if len(outline.Outlines) > 0 {
+			folderName := outline.Text
+			if folderName == "" {
+				folderName = outline.Title
+			}
+			extractFeeds(outline.Outlines, folderName, feeds)
+			continue
+		}
+
+		// If it has an XML URL, it's a feed
+		if outline.XMLURL != "" {
+			title := outline.Title
+			if title == "" {
+				title = outline.Text
+			}
+
+			cat := category
+			if outline.Category != "" {
+				cat = outline.Category
+			}
+
+			*feeds = append(*feeds, FeedInfo{
+				URL:         strings.TrimSpace(outline.XMLURL),
+				Title:       strings.TrimSpace(title),
+				SiteURL:     strings.TrimSpace(outline.HTMLURL),
+				Description: strings.TrimSpace(outline.Description),
+				Category:    strings.TrimSpace(cat),
+			})
+		}
+	}
+}
+
+// Generate creates an OPML document from feeds.
+func Generate(title string, feeds []FeedInfo) ([]byte, error) {
+	opml := OPML{
+		Version: "2.0",
+		Head: Head{
+			Title: title,
+		},
+	}
+
+	for _, feed := range feeds {
+		opml.Body.Outlines = append(opml.Body.Outlines, Outline{
+			Text:    feed.Title,
+			Title:   feed.Title,
+			Type:    "rss",
+			XMLURL:  feed.URL,
+			HTMLURL: feed.SiteURL,
+		})
+	}
+
+	output, err := xml.MarshalIndent(opml, "", "  ")
+	if err != nil {
+		return nil, fmt.Errorf("generating OPML: %w", err)
+	}
+
+	return append([]byte(xml.Header), output...), nil
+}