1 files changed, 156 insertions, 0 deletions
diff --git a/internal/imgw/imgw.go b/internal/imgw/imgw.go
new file mode 100644
index 0000000..48ffe19
--- /dev/null
+++ b/internal/imgw/imgw.go
@@ -0,0 +1,156 @@
+// Package imgw fetches official Polish meteorological warnings and resolves a
+// point to the powiat code those warnings are tagged with.
+//
+// Both services are public and need no key.
+package imgw
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strconv"
+	"time"
+)
+
+// Endpoints are variables so tests can serve recorded fixtures locally.
+var (
+	warningsURL = "https://danepubliczne.imgw.pl/api/data/warningsmeteo"
+	gugikURL    = "https://services.gugik.gov.pl/uug/"
+)
+
+// now is the clock, replaceable in tests: whether a warning has expired depends
+// on it.
+var now = time.Now
+
+// Timeout bounds every request.
+var Timeout = 15 * time.Second
+
+// Status is the outcome of resolving a point to a powiat.
+type Status int
+
+const (
+	// StatusOK means the point resolved to a powiat code.
+	StatusOK Status = iota
+	// StatusOutside means GUGiK answered but knows no address there. It covers
+	// Poland only, so the point is abroad.
+	StatusOutside
+	// StatusError means the service could not be asked.
+	//
+	// This must never be conflated with StatusOutside: one means "no warnings
+	// apply here", the other "I do not know whether any apply".
+	StatusError
+)
+
+// Warning is one IMGW warning in force.
+type Warning struct {
+	Event       string `json:"nazwa_zdarzenia"`
+	Level       string `json:"stopien"`
+	Probability string `json:"prawdopodobienstwo"`
+	From        string `json:"obowiazuje_od"`
+	To          string `json:"obowiazuje_do"`
+	Text        string `json:"tresc"`
+	Teryt       []any  `json:"teryt"`
+}
+
+func fetch(rawURL string, params url.Values, into any) error {
+	host := ""
+	if u, err := url.Parse(rawURL); err == nil {
+		host = u.Host
+	}
+	full := rawURL
+	if len(params) > 0 {
+		full += "?" + params.Encode()
+	}
+	req, err := http.NewRequest("GET", full, nil)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("User-Agent", "prognosis/1.0")
+	resp, err := (&http.Client{Timeout: Timeout}).Do(req)
+	if err != nil {
+		return fmt.Errorf("cannot reach %s: %w", host, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("%s returned HTTP %d", host, resp.StatusCode)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(body, into)
+}
+
+type gugikResponse struct {
+	Results map[string]struct {
+		Teryt string `json:"teryt"`
+	} `json:"results"`
+}
+
+// Powiat resolves a point to its 4-digit TERYT powiat code via GUGiK.
+//
+// IMGW tags every warning with the powiat codes it covers, so this is what
+// makes "warnings for my area" mean this area rather than the whole country.
+func Powiat(lat, lon float64) (string, Status, error) {
+	var r gugikResponse
+	err := fetch(gugikURL, url.Values{
+		"request":  {"GetAddressReverse"},
+		"location": {fmt.Sprintf("POINT(%.6f %.6f)", lon, lat)},
+		"srid":     {"4326"},
+		// The default 100 m radius finds nothing in the mountains or deep
+		// countryside, which looks identical to being abroad and would suppress
+		// real warnings. GUGiK clamps this to its own 5 km maximum.
+		"radius": {"10000"},
+	}, &r)
+	if err != nil {
+		return "", StatusError, err
+	}
+	for _, entry := range r.Results {
+		if len(entry.Teryt) >= 4 {
+			return entry.Teryt[:4], StatusOK, nil
+		}
+	}
+	return "", StatusOutside, nil
+}
+
+// Warnings returns the warnings in force for a powiat.
+func Warnings(powiat string) ([]Warning, error) {
+	var all []Warning
+	if err := fetch(warningsURL, nil, &all); err != nil {
+		return nil, err
+	}
+	cut := now()
+	var live []Warning
+	for _, w := range all {
+		if !w.covers(powiat) {
+			continue
+		}
+		// An expired warning is dropped; one whose date will not parse is kept,
+		// because showing a stale warning beats hiding a live one.
+		if to, err := time.ParseInLocation("2006-01-02 15:04:05", w.To, time.Local); err == nil {
+			if to.Before(cut) {
+				continue
+			}
+		}
+		live = append(live, w)
+	}
+	return live, nil
+}
+
+func (w Warning) covers(powiat string) bool {
+	for _, a := range w.Teryt {
+		switch v := a.(type) {
+		case string:
+			if v == powiat {
+				return true
+			}
+		case float64:
+			if strconv.Itoa(int(v)) == powiat {
+				return true
+			}
+		}
+	}
+	return false
+}