90 lines
1.8 KiB
Go
90 lines
1.8 KiB
Go
package cafes
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import (
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"errors"
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"fmt"
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"sync"
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"time"
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"github.com/dhconnelly/rtreego"
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)
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// Size (in metres) of the bounding box around a stop
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const stopRectangleSize = 500
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type RefreshmentStop struct {
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Name string
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Url string
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Easting float64
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Northing float64
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}
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func (s *RefreshmentStop) Bounds() *rtreego.Rect {
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p := rtreego.Point{s.Easting, s.Northing}
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return p.ToRect(stopRectangleSize)
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}
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func (s *RefreshmentStop) Contains(p rtreego.Point) bool {
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if len(p) != 2 {
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panic("Expected a 2-dimensional point")
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}
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bounds := s.Bounds()
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for i := 0; i < 2; i++ {
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if p[i] < bounds.PointCoord(i) || p[i] > bounds.PointCoord(i)+bounds.LengthsCoord(i) {
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return false
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}
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}
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return true
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}
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// TTL cache based on "9.7 Example: Concurrent Non-Blocking Cache" from
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// "The Go Programming Language", Alan A. A. Donovan and Brian W. Kernighan
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type result struct {
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value *rtreego.Rtree
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err error
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}
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type entry struct {
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res result
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expires time.Time
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ready chan struct{} // closed when res is ready
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}
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type Cache struct {
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mu sync.Mutex
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entries map[string]*entry
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}
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func New() *Cache {
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return &Cache{entries: make(map[string]*entry)}
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}
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func (c *Cache) Get(k string) (*rtreego.Rtree, error) {
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c.mu.Lock()
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e := c.entries[k]
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if e == nil || e.expires.Before(time.Now()) {
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e = &entry{ready: make(chan struct{}), expires: time.Now().Add(4 * time.Hour)}
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c.entries[k] = e
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c.mu.Unlock()
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e.res.value, e.res.err = FetchStops(k)
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close(e.ready)
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} else {
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c.mu.Unlock()
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<-e.ready
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}
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return e.res.value, e.res.err
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}
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var ErrInvalidStops = errors.New("invalid stops")
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func FetchStops(k string) (*rtreego.Rtree, error) {
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switch k {
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case "ctccambridge":
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return FetchCtcCamIndex()
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case "cyclingmaps":
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return FetchCyclingMapsIndex()
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default:
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return nil, fmt.Errorf("%w: %s", ErrInvalidStops, k)
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}
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}
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