1 // Package hn provides a filesystem interface to items on Hacker News.
2 package hn
3 
4 import (
5 	"bytes"
6 	"encoding/json"
7 	"fmt"
8 	"html"
9 	"io"
10 	"io/fs"
11 	"net/http"
12 	"os"
13 	"path"
14 	"strconv"
15 	"strings"
16 	"time"
17 )
18 
19 const APIRoot = "https://hacker-news.firebaseio.com/v0"
20 
21 type Item struct {
22 	ID     int
23 	Type   string
24 	By     string
25 	Time   int
26 	Text   string
27 	Parent int
28 	URL    string
29 	Title  string
30 }
31 
32 func (it *Item) Name() string       { return strconv.Itoa(it.ID) }
33 func (it *Item) Size() int64        { r := toMessage(it); return r.Size() }
34 func (it *Item) Mode() fs.FileMode  { return 0o444 }
35 func (it *Item) ModTime() time.Time { return time.Unix(int64(it.Time), 0) }
36 func (it *Item) IsDir() bool        { return false }
37 func (it *Item) Sys() any           { return nil }
38 
39 type FS struct {
40 	cache fs.FS
41 }
42 
43 func CacheDirFS(name string) *FS {
44 	return &FS{cache: os.DirFS(name)}
45 }
46 
47 func (fsys *FS) Open(name string) (fs.File, error) {
48 	if !fs.ValidPath(name) {
49 		return nil, &fs.PathError{"open", name, fs.ErrInvalid}
50 	}
51 	name = path.Clean(name)
52 	switch name {
53 	case ".":
54 		return nil, fmt.Errorf("TODO")
55 	default:
56 		if _, err := strconv.Atoi(name); err != nil {
57 			return nil, &fs.PathError{"open", name, fs.ErrNotExist}
58 		}
59 	}
60 	if fsys.cache != nil {
61 		if f, err := fsys.cache.Open(name); err == nil {
62 			return f, nil
63 		}
64 	}
65 
66 	u := fmt.Sprintf("%s/item/%s.json", APIRoot, name)
67 	resp, err := http.Get(u)
68 	if err != nil {
69 		return nil, err
70 	}
71 	if resp.StatusCode != http.StatusOK {
72 		return nil, err
73 	}
74 	return &file{rc: resp.Body}, nil
75 }
76 
77 type file struct {
78 	rc   io.ReadCloser
79 	item *Item
80 	msg  *bytes.Reader
81 }
82 
83 func (f *file) Read(p []byte) (int, error) {
84 	var n int
85 	if f.item == nil {
86 		if err := json.NewDecoder(f.rc).Decode(&f.item); err != nil {
87 			return n, fmt.Errorf("decode item: %v", err)
88 		}
89 	}
90 	if f.msg == nil {
91 		f.msg = toMessage(f.item)
92 	}
93 	return f.msg.Read(p)
94 }
95 
96 func (f *file) Stat() (fs.FileInfo, error) { return f.item, nil }
97 
98 func (f *file) Close() error {
99 	f.msg = nil
100 	return f.rc.Close()
101 }
102 
103 func toMessage(item *Item) *bytes.Reader {
104 	buf := &bytes.Buffer{}
105 	fmt.Fprintf(buf, "From: %s\n", item.By)
106 	fmt.Fprintf(buf, "Message-ID: <%d@news.ycombinator.com>\n", item.ID)
107 	fmt.Fprintf(buf, "Date: %s\n", time.Unix(int64(item.Time), 0).Format(time.RFC1123Z))
108 	if item.Parent != 0 {
109 		fmt.Fprintf(buf, "References: <%d@news.ycombinator.com>\n", item.Parent)
110 	}
111 	if item.Title != "" {
112 		fmt.Fprintf(buf, "Subject: %s\n", item.Title)
113 	}
114 	fmt.Fprintln(buf)
115 	if item.URL != "" {
116 		fmt.Fprintln(buf, item.URL)
117 	}
118 	if item.Text != "" {
119 		fmt.Fprintln(buf, strings.ReplaceAll(html.UnescapeString(item.Text), "<p>", "\n\n"))
120 	}
121 	return bytes.NewReader(buf.Bytes())
122 }