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, 84 insertions, 0 deletions

diff --git a/internal/render/icons.go b/internal/render/icons.go
new file mode 100644
index 0000000..59ae3d3
--- /dev/null
+++ b/internal/render/icons.go
@@ -0,0 +1,84 @@
+package render
+
+// Weather glyphs per icon set, keyed by WMO code group.
+//
+// The "nerd" codepoints are from the Nerd Fonts Weather range (U+E300-U+E3E3),
+// which JetBrains Mono Nerd Font and MesloLGS NF both carry. They are single
+// cell and monochrome, so they take the terminal's foreground colour and do not
+// break a remapped palette.
+//
+// The "emoji" set is colour and comes from a fallback font. Its glyphs are not
+// all one cell wide -- see width.go -- which is why every pad goes through
+// DisplayWidth.
+var iconSets = map[string]map[string]string{
+	"nerd": {
+		"clear":   "",
+		"partly":  "",
+		"cloudy":  "",
+		"fog":     "",
+		"drizzle": "",
+		"rain":    "",
+		"snow":    "",
+		"storm":   "",
+	},
+	"emoji": {
+		"clear":   "☀",
+		"partly":  "⛅",
+		"cloudy":  "☁",
+		"fog":     "\U0001F32B",
+		"drizzle": "\U0001F326",
+		"rain":    "\U0001F327",
+		"snow":    "\U0001F328",
+		"storm":   "⛈",
+	},
+}
+
+// iconGroup maps a WMO weather code onto a glyph group.
+func iconGroup(code int) string {
+	switch {
+	case code == 0 || code == 1:
+		return "clear"
+	case code == 2:
+		return "partly"
+	case code == 3:
+		return "cloudy"
+	case code == 45 || code == 48:
+		return "fog"
+	case code >= 51 && code <= 57:
+		return "drizzle"
+	case code >= 61 && code <= 67, code >= 80 && code <= 82:
+		return "rain"
+	case code >= 71 && code <= 77, code == 85 || code == 86:
+		return "snow"
+	case code >= 95:
+		return "storm"
+	}
+	return "cloudy"
+}
+
+// Icon returns the glyph for a weather code in the named set. An unknown set,
+// or "none", yields an empty string so the column simply renders blank.
+func Icon(set string, code int) string {
+	glyphs, ok := iconSets[set]
+	if !ok {
+		return ""
+	}
+	return glyphs[iconGroup(code)]
+}
+
+// IconWidth is the display width the icon column should reserve for a set.
+// The emoji set contains wide glyphs, so its column is two cells even for the
+// entries that happen to be one.
+func IconWidth(set string) int {
+	glyphs, ok := iconSets[set]
+	if !ok {
+		return 0
+	}
+	w := 1
+	for _, g := range glyphs {
+		if gw := DisplayWidth(g); gw > w {
+			w = gw
+		}
+	}
+	return w
+}