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// Package weather provides functions to retrieve eweather forecast data from yr.no
package weather
import (
"encoding/json"
"fmt"
"log"
"net/http"
"strings"
"time"
"github.com/silvasur/startpage/http_getter"
"github.com/silvasur/startpage/interval"
)
type TimeseriesEntry struct {
Time time.Time `json:"time"`
Data struct {
Instant struct {
Details struct {
AirTemperature float64 `json:"air_temperature"`
} `json:"details"`
} `json:"instant"`
Next1Hours struct {
Summary struct {
SymbolCode string `json:"symbol_code"`
} `json:"summary"`
} `json:"next_1_hours"`
} `json:"data"`
}
func (te TimeseriesEntry) Temperature() float64 {
return te.Data.Instant.Details.AirTemperature
}
func (te TimeseriesEntry) SymbolCode() string {
return te.Data.Next1Hours.Summary.SymbolCode
}
type Timeseries []TimeseriesEntry
func (ts Timeseries) Current(now time.Time) *TimeseriesEntry {
if ts == nil {
return nil
}
found := false
var out TimeseriesEntry
for _, entry := range ts {
if entry.Time.After(now) {
// Is in the future, not interested
continue
}
if !found || now.Sub(out.Time) < now.Sub(entry.Time) {
out = entry
found = true
}
}
if found {
return &out
} else {
return nil
}
}
type ApiResponse struct {
Properties struct {
Timeseries Timeseries `json:"timeseries"`
} `json:"properties"`
}
func truncateCoord(coord string) string {
parts := strings.SplitN(coord, ".", 2)
if len(parts) == 1 {
return parts[0] + ".0"
}
tail := parts[1]
if len(tail) > 4 {
tail = tail[0:4]
}
return parts[0] + "." + tail
}
type WeatherProvider struct {
lat, lon string
intervalRunner *interval.IntervalRunner
timeseries Timeseries
expires time.Time
lastModified time.Time
err error
}
const (
UPDATE_INTERVAL = 30 * time.Minute
RETRY_INTERVAL = 1 * time.Minute
)
func NewWeatherProvider(lat, lon string) *WeatherProvider {
return &WeatherProvider{
lat: lat,
lon: lon,
intervalRunner: interval.NewIntervalRunner(UPDATE_INTERVAL, RETRY_INTERVAL),
}
}
func parseTimeFromHeader(header http.Header, key string) (*time.Time, error) {
raw := header.Get(key)
if raw == "" {
return nil, fmt.Errorf("Could not parse time from header %s: Not set or empty", key)
}
t, err := http.ParseTime(raw)
if err != nil {
return nil, fmt.Errorf("Could not parse time from header %s: %w", key, err)
}
return &t, nil
}
func updateTimeFromHeaderIfOK(header http.Header, key string, time *time.Time) {
newTime, err := parseTimeFromHeader(header, key)
if err != nil {
log.Printf("Will not update time for key=%s: %s", key, err)
return
}
*time = *newTime
}
func (wp *WeatherProvider) update() error {
if time.Now().Before(wp.expires) {
log.Printf("Will not update weather yet, as it's not yet expired (expires=%s)", wp.expires)
return nil
}
url := "https://api.met.no/weatherapi/locationforecast/2.0/compact?lat=" + truncateCoord(wp.lat) + "&lon=" + truncateCoord(wp.lon)
req, err := http_getter.BuildGetRequest(url)
if err != nil {
return err
}
if wp.timeseries != nil {
req.Header.Add("If-Modified-Since", wp.lastModified.Format(http.TimeFormat))
}
resp, err := http_getter.Do(req)
if err != nil {
return err
}
defer resp.Body.Close()
if resp.StatusCode == 304 {
log.Println("Weather was not modified yet (got a 304)")
return nil
} else if resp.StatusCode != 200 {
log.Println("Warning: Got a non-200 response from the weather API: %d", resp.StatusCode)
}
updateTimeFromHeaderIfOK(resp.Header, "Expires", &wp.expires)
updateTimeFromHeaderIfOK(resp.Header, "Last-Modified", &wp.lastModified)
var apiResponse ApiResponse
dec := json.NewDecoder(resp.Body)
if err := dec.Decode(&apiResponse); err != nil {
return fmt.Errorf("Failed decoding weather API response: %w", err)
}
wp.timeseries = apiResponse.Properties.Timeseries
return nil
}
func (wp *WeatherProvider) CurrentWeather() (*TimeseriesEntry, error) {
wp.intervalRunner.Run(func() bool {
wp.err = wp.update()
if wp.err == nil {
log.Printf("Successfully updated weather data")
} else {
log.Printf("Failed updating weather data: %s", wp.err)
}
return wp.err == nil
})
if wp.err != nil {
return nil, wp.err
}
return wp.timeseries.Current(time.Now()), nil
}
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