arr-tui/internal/ui/diskcache.go

package ui

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"time"

	"git.stinnesbeck.com/nils/arr-tui/internal/trakt"
)

const (
	posterTTL      = 30 * 24 * time.Hour // a poster on disk is used this long
	posterCacheCap = 200 << 20           // bytes of posters kept on disk
	peopleTTL      = 7 * 24 * time.Hour  // a cast on disk is used this long
	maxPeopleSaved = 2000                // casts kept (in memory and on disk)
)

// cacheDirFunc returns the directory for the disk cache, "" for none. It is a
// variable so tests can turn the cache off.
var cacheDirFunc = func() string {
	dir, err := os.UserCacheDir() // $XDG_CACHE_HOME or ~/.cache, ~/Library/Caches on macOS
	if err != nil {
		return ""
	}
	return filepath.Join(dir, "arr-tui")
}

// diskCache keeps posters and casts between runs. With an empty dir it does
// nothing. Safe for use from any goroutine (each file is written atomically).
type diskCache struct{ dir string }

func newDiskCache() *diskCache { return &diskCache{dir: cacheDirFunc()} }

func (d *diskCache) posterPath(key string, large bool) string {
	size := "small"
	if large {
		size = "large"
	}
	sum := sha256.Sum256([]byte(size + "|" + key))
	return filepath.Join(d.dir, "posters", hex.EncodeToString(sum[:16])+".img")
}

// readPoster returns the stored bytes of a poster, if they are not too old.
func (d *diskCache) readPoster(key string, large bool) ([]byte, bool) {
	if d.dir == "" {
		return nil, false
	}
	p := d.posterPath(key, large)
	info, err := os.Stat(p)
	if err != nil || time.Since(info.ModTime()) > posterTTL {
		return nil, false
	}
	data, err := os.ReadFile(p)
	return data, err == nil
}

// writePoster stores the bytes of a poster as downloaded.
func (d *diskCache) writePoster(key string, large bool, data []byte) {
	if d.dir == "" {
		return
	}
	_ = writeAtomic(d.posterPath(key, large), data)
}

// dropPoster removes a stored poster (it could not be read).
func (d *diskCache) dropPoster(key string, large bool) {
	if d.dir != "" {
		_ = os.Remove(d.posterPath(key, large))
	}
}

// prunePosters deletes posters older than posterTTL, then the oldest ones
// until the rest fit posterCacheCap.
func (d *diskCache) prunePosters() {
	if d.dir == "" {
		return
	}
	type file struct {
		path string
		size int64
		mod  time.Time
	}
	var files []file
	var total int64
	_ = filepath.WalkDir(filepath.Join(d.dir, "posters"), func(p string, e fs.DirEntry, err error) error {
		if err != nil || e.IsDir() {
			return nil
		}
		info, err := e.Info()
		if err != nil {
			return nil
		}
		if time.Since(info.ModTime()) > posterTTL {
			_ = os.Remove(p)
			return nil
		}
		files = append(files, file{p, info.Size(), info.ModTime()})
		total += info.Size()
		return nil
	})
	slices.SortFunc(files, func(a, b file) int { return a.mod.Compare(b.mod) })
	for _, f := range files {
		if total <= posterCacheCap {
			break
		}
		if os.Remove(f.path) == nil {
			total -= f.size
		}
	}
}

// savedPeople is a cast as stored on disk.
type savedPeople struct {
	Saved   time.Time      `json:"saved"`
	Cast    []trakt.Person `json:"cast,omitempty"`
	Leaders []trakt.Person `json:"leaders,omitempty"`
}

func (d *diskCache) peoplePath() string { return filepath.Join(d.dir, "people.json") }

// loadPeople reads the stored casts that are not too old.
func (d *diskCache) loadPeople() map[string]savedPeople {
	out := map[string]savedPeople{}
	if d.dir == "" {
		return out
	}
	data, err := os.ReadFile(d.peoplePath())
	if err != nil {
		return out
	}
	var all map[string]savedPeople
	if json.Unmarshal(data, &all) != nil {
		return out // unreadable: start afresh, it is only a cache
	}
	for k, p := range all {
		if time.Since(p.Saved) <= peopleTTL {
			out[k] = p
		}
	}
	return out
}

// savePeople writes the casts.
func (d *diskCache) savePeople(all map[string]savedPeople) error {
	if d.dir == "" {
		return nil
	}
	data, err := json.Marshal(all)
	if err != nil {
		return err
	}
	return writeAtomic(d.peoplePath(), data)
}

// writeAtomic writes a file through a temporary file and a rename, creating
// the directory (private) if needed.
func writeAtomic(path string, data []byte) error {
	if err := os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return err
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), ".tmp-*")
	if err != nil {
		return err
	}
	defer os.Remove(tmp.Name()) // no-op after the rename
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	return os.Rename(tmp.Name(), path)
}