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, 62 insertions, 0 deletions

diff --git a/internal/render/color.go b/internal/render/color.go
new file mode 100644
index 0000000..cf2af89
--- /dev/null
+++ b/internal/render/color.go
@@ -0,0 +1,62 @@
+package render
+
+import "strings"
+
+// Colour uses ANSI slots 0-15 only -- codes 30-37 and 90-97, plus the
+// attributes 1 (bold), 2 (dim) and 4 (underline). Never 256-colour indices:
+// this runs on terminals whose palette remaps the low slots (the phone's is
+// entirely green), where a hardcoded 38;5;196 would be the one off-palette
+// thing on screen.
+const (
+	Reset     = "0"
+	Bold      = "1"
+	Dim       = "2"
+	Underline = "4"
+
+	Blue        = "34"
+	Cyan        = "36"
+	Green       = "32"
+	Yellow      = "33"
+	Red         = "31"
+	BrightBlue  = "94"
+	BrightRed   = "91"
+	BrightWhite = "97"
+)
+
+// Styler returns a function that wraps text in an ANSI code, or returns it
+// unchanged when colour is off.
+func Styler(colour bool) func(code, text string) string {
+	if !colour {
+		return func(_, text string) string { return text }
+	}
+	return func(code, text string) string {
+		if code == "" {
+			return text
+		}
+		return "\033[" + code + "m" + text + "\033[0m"
+	}
+}
+
+// Cell is one character of chart output with the style it should carry.
+type Cell struct {
+	Style string
+	Text  string
+}
+
+// Paint joins cells, emitting one escape sequence per run of identical style
+// rather than one per character. A per-character version makes the chart around
+// ten times larger for output that looks exactly the same.
+func Paint(cells []Cell, c func(string, string) string) string {
+	var b strings.Builder
+	for i := 0; i < len(cells); {
+		j := i
+		var run strings.Builder
+		for j < len(cells) && cells[j].Style == cells[i].Style {
+			run.WriteString(cells[j].Text)
+			j++
+		}
+		b.WriteString(c(cells[i].Style, run.String()))
+		i = j
+	}
+	return b.String()
+}