98 lines
2.4 KiB
Go
98 lines
2.4 KiB
Go
// Access [Meteorologisk institutt's API](https://api.met.no)
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package met
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import (
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"net/http"
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"time"
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)
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type Met struct {
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siteName string
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}
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var (
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ErrorMissingSiteName = errors.New("siteName must be defined")
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ErrorMissingHeaderExpires = errors.New("missing header 'Expires'")
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ErrorMissingHeaderLastModified = errors.New("missing header 'Last-Modified'")
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ErrorParseExpires = errors.New("unable to parse 'Expires'")
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ErrorParseLastModified = errors.New("unable to parse 'Last-Modified'")
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)
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// Returns valid Met client or error if empty siteName is provided
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func New(siteName string) (*Met, error) {
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if siteName == "" {
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return nil, ErrorMissingSiteName
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}
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return &Met{
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siteName: siteName,
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}, nil
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}
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// Get LocationForecast from Met, returns error if Met doesn't answer or response is missing required headers
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// API endpoint: https://api.met.no/weatherapi/locationforecast/2.0/documentation
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func (m *Met) Forecast(lat, lon float64, alt *int) (*LocationForecastResult, error) {
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url := "https://api.met.no/weatherapi/locationforecast/2.0/complete"
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req, err := http.NewRequest("GET", url, nil)
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if err != nil {
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return nil, err
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}
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q := req.URL.Query()
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q.Add("lat", fmt.Sprintf("%.4f", lat))
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q.Add("lon", fmt.Sprintf("%.4f", lon))
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if alt != nil {
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q.Add("altitude", fmt.Sprintf("%d", alt))
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}
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req.URL.RawQuery = q.Encode()
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req.Header.Set("User-Agent", m.siteName)
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resp, err := http.DefaultClient.Do(req)
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if err != nil {
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return nil, err
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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return nil, fmt.Errorf("%s", resp.Status)
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}
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body, err := io.ReadAll(resp.Body)
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if err != nil {
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return nil, err
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}
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expiresRaw, ok := resp.Header["Expires"]
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if !ok {
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return nil, ErrorMissingHeaderExpires
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}
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expires, err := time.Parse(time.RFC1123, expiresRaw[0])
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if err != nil {
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return nil, errors.Join(ErrorParseExpires, err)
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}
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lastModifiedRaw, ok := resp.Header["Last-Modified"]
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if !ok {
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return nil, ErrorMissingHeaderLastModified
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}
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lastModified, err := time.Parse(time.RFC1123, lastModifiedRaw[0])
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if err != nil {
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return nil, errors.Join(ErrorParseLastModified, err)
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}
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forecast := LocationForecast{}
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err = json.Unmarshal(body, &forecast)
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if err != nil {
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return nil, err
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}
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return &LocationForecastResult{
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Expires: expires,
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LastModified: lastModified,
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LocationForecast: forecast,
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}, nil
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}
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