First attempt at Feed.Update (experimental!)

rss.go

@@ -1,90 +1,133 @@
 package rss
 
 import (
-	"bytes"
-	"fmt"
-	"io/ioutil"
-	"net/http"
-	"strings"
-	"time"
+  "bytes"
+  "errors"
+  "fmt"
+  "io/ioutil"
+  "net/http"
+  "strings"
+  "time"
 )
 
 // Parse RSS or Atom data.
 func Parse(data []byte) (*Feed, error) {
-	if strings.Contains(string(data), "<rss") {
-		return parseRSS2(data, database)
-	} else if strings.Contains(string(data), "xmlns=\"http://purl.org/rss/1.0/\"") {
-		return parseRSS1(data, database)
-	} else {
-		return parseAtom(data, database)
-	}
-
-	panic("Unreachable.")
+  if strings.Contains(string(data), "<rss") {
+    return parseRSS2(data, database)
+  } else if strings.Contains(string(data), "xmlns=\"http://purl.org/rss/1.0/\"") {
+    return parseRSS1(data, database)
+  } else {
+    return parseAtom(data, database)
+  }
+
+  panic("Unreachable.")
 }
 
 // Fetch downloads and parses the RSS feed at the given URL
 func Fetch(url string) (*Feed, error) {
-	resp, err := http.Get(url)
-	if err != nil {
-		return nil, err
-	}
-	defer resp.Body.Close()
-
-	body, err := ioutil.ReadAll(resp.Body)
-	if err != nil {
-		return nil, err
-	}
-
-	return Parse(body)
+  resp, err := http.Get(url)
+  if err != nil {
+    return nil, err
+  }
+  defer resp.Body.Close()
+
+  body, err := ioutil.ReadAll(resp.Body)
+  if err != nil {
+    return nil, err
+  }
+
+  return Parse(body)
 }
 
 // Feed is the top-level structure.
 type Feed struct {
-	Title       string
-	Description string
-	Link        string
-	Image       *Image
-	Items       []*Item
-	Refresh     time.Time
-	Unread      uint32
+  Title       string
+  Description string
+  Link        string
+  Image       *Image
+  Items       []*Item
+  Refresh     time.Time
+  Unread      uint32
+}
+
+// Update fetches any new items and updates f.
+func (f *Feed) Update() error {
+
+  // Check that we don't update too often.
+  if f.Refresh.After(time.Now()) {
+    return nil
+  }
+
+  if f.Link == "" {
+    return errors.New("Error: feed has no URL.")
+  }
+
+  update, err := Fetch(f.Link)
+  if err != nil {
+    return err
+  }
+
+  f.Refresh = update.Refresh
+  f.Title = update.Title
+  f.Description = update.Description
+
+  // Find the offset between items.
+  offset := 0
+  for _, item := range f.Items {
+    if item.ID == update.Items[0].ID {
+      break
+    }
+    offset++
+  }
+
+  for i, item := range update.Items {
+    if i+offset >= len(f.Items) {
+      f.Items = append(f.Items, item)
+      f.Unread++
+    } else if f.Items[i+offset].ID != item.ID {
+      return errors.New("Error: offsets don't match.")
+    }
+  }
+
+  return nil
 }
 
 func (f *Feed) String() string {
-	buf := new(bytes.Buffer)
-	buf.WriteString(fmt.Sprintf("Feed %q\n\t%q\n\t%q\n\t%s\n\tRefresh at %s\n\tUnread: %d\n\tItems:\n",
-		f.Title, f.Description, f.Link, f.Image, f.Refresh.Format("Mon 2 Jan 2006 15:04:05 MST"), f.Unread))
-	for _, item := range f.Items {
-		buf.WriteString(fmt.Sprintf("\t%s\n", item.Format("\t\t")))
-	}
-	return buf.String()
+  buf := new(bytes.Buffer)
+  buf.WriteString(fmt.Sprintf("Feed %q\n\t%q\n\t%q\n\t%s\n\tRefresh at %s\n\tUnread: %d\n\tItems:\n",
+    f.Title, f.Description, f.Link, f.Image, f.Refresh.Format("Mon 2 Jan 2006 15:04:05 MST"), f.Unread))
+  for _, item := range f.Items {
+    buf.WriteString(fmt.Sprintf("\t%s\n", item.Format("\t\t")))
+  }
+  return buf.String()
 }
 
 // Item represents a single story.
 type Item struct {
-	Title   string
-	Content string
-	Link    string
-	Date    time.Time
-	ID      string
-	Read    bool
+  Title   string
+  Content string
+  Link    string
+  Date    time.Time
+  ID      string
+  Read    bool
 }
 
 func (i *Item) String() string {
-	return i.Format("")
+  return i.Format("")
 }
 
 func (i *Item) Format(s string) string {
-	return fmt.Sprintf("Item %q\n\t%s%q\n\t%s%s\n\t%s%q\n\t%sRead: %v\n\t%s%q", i.Title, s, i.Link, s,
-		i.Date.Format("Mon 2 Jan 2006 15:04:05 MST"), s, i.ID, s, i.Read, s, i.Content)
+  return fmt.Sprintf("Item %q\n\t%s%q\n\t%s%s\n\t%s%q\n\t%sRead: %v\n\t%s%q", i.Title, s, i.Link, s,
+    i.Date.Format("Mon 2 Jan 2006 15:04:05 MST"), s, i.ID, s, i.Read, s, i.Content)
 }
 
 type Image struct {
-	Title  string
-	Url    string
-	Height uint32
-	Width  uint32
+  Title  string
+  Url    string
+  Height uint32
+  Width  uint32
 }
 
 func (i *Image) String() string {
-	return fmt.Sprintf("Image %q", i.Title)
+  return fmt.Sprintf("Image %q", i.Title)
 }