1 files changed, 92 insertions, 0 deletions
diff --git a/internal/render/scale.go b/internal/render/scale.go
new file mode 100644
index 0000000..a2eb2dc
--- /dev/null
+++ b/internal/render/scale.go
@@ -0,0 +1,92 @@
+package render
+
+import "math"
+
+// Temperature bands. The two ends are IMGW's own warning criteria, so a red
+// temperature means the met office would issue a warning about it rather than
+// that it looked hot to whoever wrote this:
+//
+//	Tmin <= -15   silny mroz, stopien 1   -> bright blue
+//	Tmax >= 30    upal, stopien 1         -> red
+//	Tmax >  35    the higher heat level   -> bright red
+//
+// The splits between (0, 10, 20) are round numbers, not thresholds from any
+// source; they only subdivide the range nobody warns about.
+var tempBands = []struct {
+	below float64
+	code  string
+}{
+	{0, Blue}, {10, Cyan}, {20, Green}, {30, Yellow},
+}
+
+// Deg rounds to whole degrees. Rounding through int conversion avoids "-0",
+// which is arithmetically fine and visually wrong.
+func Deg(t float64) int {
+	return int(math.Round(t))
+}
+
+// TempStyle is the ANSI code for a temperature in Celsius.
+//
+// The warning edges are written out rather than folded into tempBands so they
+// match IMGW's criteria exactly, inclusive and exclusive included.
+//
+// The value is rounded first, so the colour always matches the number printed
+// beside it: otherwise -14.6 prints as "-15" in a different colour than a true
+// -15 and looks like a rendering bug.
+func TempStyle(celsius float64) string {
+	t := float64(Deg(celsius))
+	switch {
+	case t <= -15:
+		return BrightBlue
+	case t > 35:
+		return BrightRed
+	case t >= 30:
+		return Red
+	}
+	for _, b := range tempBands {
+		if t < b.below {
+			return b.code
+		}
+	}
+	return Yellow
+}
+
+// Pollen bands in grains/m3, from Polish clinical sources. Each entry is an
+// upper bound (exclusive) and a band key; a nil bound means "everything above".
+//
+//	grass   -- alergen.info.pl symptom table: 20 = first nasal symptoms in 25%
+//	           of sufferers, 50 = symptoms in all tested, 65 = intensified in
+//	           over 75%, 120 = dyspnoea after 30 minutes of exposure.
+//	birch   -- mp.pl: 80 provokes symptoms in over 95% of allergics.
+//	mugwort -- mp.pl: over 70 counts as high, intensified symptoms.
+//
+// Birch and mugwort have a single published anchor each, so they get a two-way
+// split rather than four bands: their "low" is weaker evidence than grass's.
+// Alder, olive and ragweed have no Polish threshold that could be sourced and
+// are deliberately left unbanded rather than banded on a guess.
+var pollenBands = map[string][]struct {
+	below float64
+	band  string
+}{
+	"grass":   {{20, "low"}, {50, "medium"}, {65, "high"}, {math.Inf(1), "very high"}},
+	"birch":   {{80, "low"}, {math.Inf(1), "high"}},
+	"mugwort": {{70, "low"}, {math.Inf(1), "high"}},
+}
+
+// PollenBand is the qualitative level for a count, or "" where no threshold
+// exists for that species.
+func PollenBand(species string, value float64) string {
+	if value < 1 {
+		return "none"
+	}
+	bands, ok := pollenBands[species]
+	if !ok {
+		return ""
+	}
+	for _, b := range bands {
+		if value < b.below {
+			return b.band
+		}
+	}
+	return ""
+}