Initial commit: prognosis, the Go implementation

An hour-by-hour forecast for the terminal, with official IMGW warnings for
Polish locations. Replaces the Python version, whose cache file format it
keeps so the two can coexist until this reaches parity.

Open-Meteo provides the forecast, geocoding and pollen; GUGiK turns
coordinates into a TERYT powiat code; IMGW supplies the warnings, filtered
to that powiat rather than the whole country. Only the two lookups that
never change are cached. Forecasts never are.

Silence is never allowed to read as all-clear: "no warnings in force" and
"the check failed" are reported as distinct states.

Place names are resolved without guessing. A name matching several places
is refused with a numbered list carrying each candidate's region and
coordinates, and -pick N chooses one and remembers it. A stray positional
beside -l is an error, so an unquoted "Wiry, PL" cannot silently resolve to
somewhere else.

The cache is written one entry per line with sorted keys, and treated as
disposable but not worthless: an entry that will not parse is skipped and
the rest kept, and a file that will not parse at all is moved to
cache.json.bad rather than overwritten.

No third-party dependencies. `make ci` is the gate: gofmt clean, vet, tests.

1 files changed, 57 insertions, 0 deletions

diff --git a/internal/render/scale_test.go b/internal/render/scale_test.go
new file mode 100644
index 0000000..9754bdc
--- /dev/null
+++ b/internal/render/scale_test.go
@@ -0,0 +1,57 @@
+package render
+
+import (
+	"testing"
+
+	"github.com/lukaszkasprzak/prognosis/internal/config"
+)
+
+// IMGW's criteria are in Celsius. Switching the display to Fahrenheit must not
+// move the temperature at which the met office is said to warn.
+func TestThresholdsAreComparedInCelsiusWhateverTheDisplayUnits(t *testing.T) {
+	metric := ctx{cfg: config.Config{Units: "metric"}}
+	imperial := ctx{cfg: config.Config{Units: "imperial"}}
+
+	cases := []struct {
+		celsius    float64
+		fahrenheit float64
+		want       string
+		why        string
+	}{
+		{29, 84.2, Yellow, "below the upal threshold"},
+		{30, 86, Red, "upal stopien 1 is Tmax >= 30C"},
+		{36, 96.8, BrightRed, "the higher heat level is Tmax > 35C"},
+		{-15, 5, BrightBlue, "silny mroz stopien 1 is Tmin <= -15C"},
+		{-14, 6.8, Blue, "just above the frost threshold"},
+	}
+	for _, c := range cases {
+		if got := TempStyle(metric.celsius(c.celsius)); got != c.want {
+			t.Errorf("%.0fC -> %s, want %s (%s)", c.celsius, got, c.want, c.why)
+		}
+		if got := TempStyle(imperial.celsius(c.fahrenheit)); got != c.want {
+			t.Errorf("%.1fF (=%.0fC) -> %s, want %s (%s)",
+				c.fahrenheit, c.celsius, got, c.want, c.why)
+		}
+	}
+}
+
+func TestPollenBandEdges(t *testing.T) {
+	cases := []struct {
+		species string
+		value   float64
+		want    string
+	}{
+		{"grass", 0.5, "none"}, {"grass", 19, "low"}, {"grass", 20, "medium"},
+		{"grass", 49, "medium"}, {"grass", 50, "high"}, {"grass", 64, "high"},
+		{"grass", 65, "very high"}, {"grass", 200, "very high"},
+		{"birch", 79, "low"}, {"birch", 80, "high"},
+		{"mugwort", 69, "low"}, {"mugwort", 70, "high"},
+		{"ragweed", 50, ""}, // no Polish threshold sourced: deliberately unbanded
+		{"alder", 500, ""},
+	}
+	for _, c := range cases {
+		if got := PollenBand(c.species, c.value); got != c.want {
+			t.Errorf("PollenBand(%q, %v) = %q, want %q", c.species, c.value, got, c.want)
+		}
+	}
+}