aboutsummaryrefslogtreecommitdiff
path: root/internal/feed/cache.go
blob: 411ed478e02c1d32396e18415611da1edb0d4491 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
package feed

import (
	"bufio"
	"crypto/sha256"
	"encoding/gob"
	"errors"
	"fmt"
	"os"
	"time"

	"github.com/Necoro/feed2imap-go/pkg/log"
)

const (
	currentVersion byte   = 1
	startFeedId    uint64 = 1
)

type Cache interface {
	findItem(*Feed) CachedFeed
	Version() byte
	transformToCurrent() (Cache, error)
}

type feedId uint64

type feedDescriptor struct {
	Name string
	Url  string
}

type CachedFeed interface {
	Checked(withFailure bool)
	Failures() uint
}

type cachedFeed struct {
	LastCheck   time.Time
	NumFailures uint // can't be named `Failures` b/c it'll collide with the interface
	Items       []cachedItem
}

func (cf *cachedFeed) Checked(withFailure bool) {
	cf.LastCheck = time.Now()
	if withFailure {
		cf.NumFailures++
	} else {
		cf.NumFailures = 0
	}
}

func (cf *cachedFeed) Failures() uint {
	return cf.NumFailures
}

type itemHash [sha256.Size]byte

type cachedItem struct {
	Uid     string
	Title   string
	Link    string
	Date    time.Time
	Updated time.Time
	Creator string
	Hash    itemHash
}

type v1Cache struct {
	version byte
	Ids     map[feedDescriptor]feedId
	NextId  uint64
	Feeds   map[feedId]*cachedFeed
}

func (cache *v1Cache) Version() byte {
	return cache.version
}

func newCache() Cache {
	cache := v1Cache{
		Ids:    map[feedDescriptor]feedId{},
		Feeds:  map[feedId]*cachedFeed{},
		NextId: startFeedId,
	}
	cache.version = currentVersion
	return &cache
}

func cacheForVersion(version byte) (Cache, error) {
	switch version {
	case 1:
		return newCache(), nil
	default:
		return nil, fmt.Errorf("unknown cache version '%d'", version)
	}
}

func (cache *v1Cache) transformToCurrent() (Cache, error) {
	return cache, nil
}

func (cache *v1Cache) getItem(id feedId) CachedFeed {
	feed, ok := cache.Feeds[id]
	if !ok {
		feed = &cachedFeed{}
		cache.Feeds[id] = feed
	}
	return feed
}

func (cache *v1Cache) findItem(feed *Feed) CachedFeed {
	if feed.cached != nil {
		return feed.cached.(*cachedFeed)
	}

	fDescr := feed.descriptor()
	id, ok := cache.Ids[fDescr]
	if !ok {
		var otherId feedDescriptor
		changed := false
		for otherId, id = range cache.Ids {
			if otherId.Name == fDescr.Name {
				log.Warnf("Feed %s seems to have changed URLs: newCache '%s', old '%s'. Updating.",
					fDescr.Name, fDescr.Url, otherId.Url)
				changed = true
				break
			} else if otherId.Url == fDescr.Url {
				log.Warnf("Feed with URL '%s' seems to have changed its name: newCache '%s', old '%s'. Updating",
					fDescr.Url, fDescr.Name, otherId.Name)
				changed = true
				break
			}
		}
		if changed {
			delete(cache.Ids, otherId)
		} else {
			id = feedId(cache.NextId)
			cache.NextId++
		}

		cache.Ids[fDescr] = id
	}

	item := cache.getItem(id)
	feed.cached = item
	return item
}

func storeCache(cache Cache, fileName string) error {
	if cache == nil {
		return fmt.Errorf("trying to store nil cache")
	}
	if cache.Version() != currentVersion {
		return fmt.Errorf("trying to store cache with unsupported version '%d' (current: '%d')", cache.Version(), currentVersion)
	}

	f, err := os.Create(fileName)
	if err != nil {
		return fmt.Errorf("trying to store cache to '%s': %w", fileName, err)
	}
	defer f.Close()

	writer := bufio.NewWriter(f)
	if err = writer.WriteByte(currentVersion); err != nil {
		return fmt.Errorf("writing to '%s': %w", fileName, err)
	}

	encoder := gob.NewEncoder(writer)
	if err = encoder.Encode(cache); err != nil {
		return fmt.Errorf("encoding cache: %w", err)
	}

	writer.Flush()
	log.Printf("Stored cache to '%s'.", fileName)

	return nil
}

func loadCache(fileName string) (Cache, error) {
	f, err := os.Open(fileName)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			// no cache there yet -- make new
			return newCache(), nil
		}
		return nil, fmt.Errorf("opening cache at '%s': %w", fileName, err)
	}
	defer f.Close()

	log.Printf("Loading cache from '%s'", fileName)

	reader := bufio.NewReader(f)
	version, err := reader.ReadByte()
	if err != nil {
		return nil, fmt.Errorf("reading from '%s': %w", fileName, err)
	}

	cache, err := cacheForVersion(version)
	if err != nil {
		return nil, err
	}

	decoder := gob.NewDecoder(reader)
	if err = decoder.Decode(cache); err != nil {
		return nil, fmt.Errorf("decoding for version '%d' from '%s': %w", version, fileName, err)
	}

	if cache, err = cache.transformToCurrent(); err != nil {
		return nil, fmt.Errorf("cannot transform from version %d to %d: %w", version, currentVersion, err)
	}

	log.Printf("Loaded cache (version %d), transformed to version %d.", version, currentVersion)

	return cache, nil
}