jtricerolph
435b59b3fe
Neither Met Office's Global Spot API nor Open-Meteo return a narrative text summary -- both are purely numeric/coded. New lib/summary.js derives one rule-based from today's already-fetched hourly points (icon + precip_prob), no extra API call, no LLM: - Headline: "Scattered showers today", "Rain likely later", "Heavy rain today", "Dry today", etc. -- compares rain distribution across the whole day vs specifically the hours still ahead of "now". - Note: "Thunderstorms possible", appended when a thunder icon shows up. - Umbrella nudge: shown when there's a real rain chance now or later today. Computed fresh per-request (not cached at fetch time), since "later" means later than whoever's looking at the screen right now, not later than the last hourly refresh. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
68 lines
3 KiB
JavaScript
68 lines
3 KiB
JavaScript
// Plain-language summary of today's forecast ("Scattered showers today",
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// "Rain likely later", "Don't forget your umbrella"...). Neither Met Office's Global
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// Spot API nor Open-Meteo return anything like this — both are purely numeric/coded
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// (temps, weather codes, precip%) — so this is generated from today's already-fetched
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// hourly points (icon + precip_prob), rule-based, no extra API call and no LLM.
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//
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// Computed fresh per-request in routes/forecast.js (not stored/cached at fetch time),
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// since "later" is relative to whoever's looking at the screen right now, not to when
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// the hourly data was last fetched.
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const RAIN_ICONS = new Set(['drizzle', 'rain-light', 'rain-heavy', 'sleet', 'hail'])
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const SNOW_ICONS = new Set(['snow-light', 'snow-heavy'])
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// summarizeToday(points, nowHour) — `points` is today's hourly forecast_points rows
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// (already icon-normalized), `nowHour` is 0-23 in Europe/London. Returns null if
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// there's nothing to summarize (no data yet).
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export function summarizeToday(points, nowHour) {
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if (!points.length) return null
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const isRain = p => RAIN_ICONS.has(p.icon)
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const isSnow = p => SNOW_ICONS.has(p.icon)
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const isThunder = p => p.icon === 'thunder'
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const isHeavyRain = p => p.icon === 'rain-heavy'
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const rainPoints = points.filter(isRain)
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const snowPoints = points.filter(isSnow)
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const thunderPoints = points.filter(isThunder)
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const rainFraction = rainPoints.length / points.length
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const snowFraction = snowPoints.length / points.length
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const laterPoints = points.filter(p => hourOf(p) >= nowHour)
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const earlierPoints = points.filter(p => hourOf(p) < nowHour)
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const laterWetFraction = laterPoints.length
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? laterPoints.filter(p => isRain(p) || isThunder(p)).length / laterPoints.length
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: 0
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const earlierWetCount = earlierPoints.filter(p => isRain(p) || isThunder(p)).length
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let headline
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if (snowFraction > 0.3) {
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headline = 'Snow expected today'
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} else if (rainPoints.length === 0 && thunderPoints.length === 0) {
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headline = 'Dry today'
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} else if (rainPoints.some(isHeavyRain) && rainFraction > 0.5) {
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headline = 'Heavy rain today'
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} else if (rainFraction > 0.6) {
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headline = 'Rain likely for much of the day'
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} else if (laterWetFraction > 0.4 && earlierWetCount === 0) {
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headline = 'Rain likely later'
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} else if (rainFraction > 0) {
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headline = 'Scattered showers today'
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} else {
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headline = 'Thunderstorms possible'
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}
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// Append rather than replace the headline when thunder shows up alongside a
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// rain pattern that already earned its own headline above.
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const note = thunderPoints.length > 0 && headline !== 'Thunderstorms possible'
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? 'Thunderstorms possible'
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: null
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// Umbrella nudge: real rain chance either right now or coming up later today.
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const umbrella = laterWetFraction > 0.25 || rainFraction > 0.25
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return { headline, note, umbrella }
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}
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function hourOf(point) {
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return parseInt(new Date(point.ts).toLocaleString('en-GB', { timeZone: 'Europe/London', hour: '2-digit', hour12: false }))
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}
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