Split cost/estimate across mid-period tariff changes
Rate changes are often scheduled ahead of time or confirmed by finance after the fact and backdated — assign-tariff already supported any effective_from date, but cost-calc previously priced a whole period at a single tariff (whichever was in force on the period-end date), silently mispricing the days on the other side of a change. getTariffSegments() finds every tariff assignment overlapping a date range; getMeterCostForPeriod/getMeterEstimateForPeriod now split consumption pro-rata by day count across segments and price each against its own tariff, summing to the period total. Estimates project the remaining days across a future-scheduled change the same way, rather than assuming today's tariff holds for the rest of the period. Also consolidates internal.js's cost/estimate routes (previously their own duplicate calc) onto the same shared functions reports.js and estimates.js use, so the Directors' report can't drift from the in-app numbers. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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5 changed files with 151 additions and 63 deletions
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@ -108,6 +108,37 @@ export async function getTariffForMeter(meterId, date) {
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return open[0] || null
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}
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function toISODate(d) {
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return new Date(d).toISOString().slice(0, 10)
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}
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// Every tariff assignment whose range overlaps [periodStart, periodEnd], clipped
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// to the period and ordered chronologically. A rate change — scheduled ahead of
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// time or entered late/backdated once finance confirms it — shows up here as two
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// (or more) segments instead of a single tariff covering the whole period, so
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// cost calculations split correctly at the change boundary rather than pricing
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// the whole period at whichever tariff happens to apply on one edge date.
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export async function getTariffSegments(meterId, periodStart, periodEnd) {
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const { rows } = await pool.query(
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`SELECT mt.effective_from AS mt_from, mt.effective_to AS mt_to, t.* FROM meter_tariffs mt
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JOIN tariffs t ON t.id = mt.tariff_id
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WHERE mt.meter_id = $1
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AND mt.effective_from <= $3
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AND (mt.effective_to IS NULL OR mt.effective_to >= $2)
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ORDER BY mt.effective_from ASC`,
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[meterId, periodStart, periodEnd]
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)
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return rows
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.map(r => {
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const from = toISODate(r.mt_from)
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const to = r.mt_to ? toISODate(r.mt_to) : null
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const segStart = from > periodStart ? from : periodStart
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const segEnd = to && to < periodEnd ? to : periodEnd
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return { ...r, seg_start: segStart, seg_end: segEnd }
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})
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.filter(s => s.seg_start <= s.seg_end)
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}
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export async function getRateWindows(tariffId) {
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const { rows } = await pool.query(
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'SELECT * FROM tariff_rate_windows WHERE tariff_id = $1 ORDER BY sort_order, id',
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@ -163,16 +194,92 @@ export function computeCost({ tariff, windows, consumption, daysInPeriod }) {
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}
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}
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// Full cost breakdown for one meter over a period — fetches tariff + windows
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// + consumption and runs computeCost. `asOfDate` picks which historical
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// tariff applies (defaults to periodEnd).
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const ZERO_TOTALS = { usage_cost_pence: 0, standing_cost_pence: 0, ccl_cost_pence: 0, subtotal_pence: 0, vat_pence: 0, total_pence: 0 }
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// Cost a single amount of consumption over [rangeStart, rangeEnd], splitting it
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// pro-rata (by day count) across every tariff segment active in that range. Used
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// both for a closed historical period and for a projected future range — in both
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// cases we only have a total consumption figure (from readings or a trailing
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// average), never a day-by-day breakdown, so a rate change inside the range is
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// apportioned by day count rather than known per-day usage.
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async function splitCostAcrossSegments(meterId, rangeStart, rangeEnd, consumption, asOfDate) {
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const rangeDays = daysInclusive(rangeStart, rangeEnd)
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const segments = await getTariffSegments(meterId, rangeStart, rangeEnd)
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if (!segments.length) {
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const tariff = await getTariffForMeter(meterId, asOfDate || rangeEnd)
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const windows = tariff ? await getRateWindows(tariff.id) : []
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const cost = computeCost({ tariff, windows, consumption, daysInPeriod: rangeDays })
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return { tariff, windows, segments: [], rate_changed_mid_period: false, ...cost }
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}
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const dailyAvg = consumption == null ? null : consumption / rangeDays
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const segmentResults = []
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const agg = { ...ZERO_TOTALS }
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for (const seg of segments) {
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const segDays = daysInclusive(seg.seg_start, seg.seg_end)
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const segConsumption = dailyAvg == null ? null : dailyAvg * segDays
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const windows = await getRateWindows(seg.id)
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const cost = computeCost({ tariff: seg, windows, consumption: segConsumption, daysInPeriod: segDays })
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for (const k of Object.keys(agg)) agg[k] += cost[k]
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segmentResults.push({
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tariff_id: seg.id, tariff_name: seg.name,
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seg_start: seg.seg_start, seg_end: seg.seg_end, days: segDays,
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consumption: segConsumption, ...cost,
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})
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}
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const lastSeg = segments[segments.length - 1]
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const lastWindows = await getRateWindows(lastSeg.id)
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const rateChanged = segments.length > 1
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return {
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tariff: lastSeg, windows: lastWindows, segments: segmentResults,
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...agg, split: rateChanged ? null : segmentResults[0]?.split ?? null,
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rate_changed_mid_period: rateChanged,
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}
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}
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// Full cost breakdown for one meter over a period — fetches consumption from
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// readings, then splits cost across any tariff change (scheduled ahead of time
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// or backdated after the fact) that falls inside the period. `asOfDate` is only
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// used as a fallback when the meter has no tariff-assignment history at all.
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export async function getMeterCostForPeriod(meterId, periodStart, periodEnd, asOfDate) {
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const { consumption, first, last, has_data } = await getPeriodConsumption(meterId, periodStart, periodEnd)
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const tariff = await getTariffForMeter(meterId, asOfDate || periodEnd)
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const windows = tariff ? await getRateWindows(tariff.id) : []
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const daysInPeriod = daysInclusive(periodStart, periodEnd)
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const cost = computeCost({ tariff, windows, consumption, daysInPeriod })
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return { consumption, has_data, first_reading: first, last_reading: last, tariff, windows, days_in_period: daysInPeriod, ...cost }
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const costed = await splitCostAcrossSegments(meterId, periodStart, periodEnd, consumption, asOfDate || periodEnd)
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return { consumption, has_data, first_reading: first, last_reading: last, days_in_period: daysInPeriod, ...costed }
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}
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// Estimate for the remainder of an open period: actual consumption to date +
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// trailing-average projection for the remaining days, cost-split across any
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// tariff segments covering the whole period — including a rate change already
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// scheduled for later in the period, which a same-tariff-for-everything
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// projection would otherwise miss.
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export async function getMeterEstimateForPeriod(meterId, periodStart, periodEnd, windowDays) {
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const today = toISODate(new Date())
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const asOfDate = today < periodEnd ? today : periodEnd
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const daysInPeriod = daysInclusive(periodStart, periodEnd)
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const remainingDays = Math.max(daysBetween(asOfDate, periodEnd), 0)
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const { daily_rate } = await getTrailingDailyRate(meterId, windowDays)
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const { consumption: actualToDate, has_data } = await getPeriodConsumption(meterId, periodStart, asOfDate)
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let projectedConsumption = null
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if (daily_rate != null) {
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projectedConsumption = (has_data ? actualToDate : 0) + daily_rate * remainingDays
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} else if (has_data) {
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projectedConsumption = actualToDate
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}
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const costed = await splitCostAcrossSegments(meterId, periodStart, periodEnd, projectedConsumption, asOfDate)
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return {
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trailing_window_days: windowDays, daily_rate,
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actual_to_date: has_data ? actualToDate : null,
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remaining_days: remainingDays, days_in_period: daysInPeriod,
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projected_consumption: projectedConsumption, ...costed,
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}
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}
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// [periodStart, periodEnd] for a YYYY-MM period string, or the current
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@ -1,44 +1,15 @@
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import { requireAuth, requireCap } from '../auth.js'
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import { pool, getConfig } from '../db.js'
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import {
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getPeriodConsumption, getTrailingDailyRate, getTariffForMeter, getRateWindows,
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computeCost, resolvePeriod, daysInclusive, daysBetween,
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} from '../lib/cost-calc.js'
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import { getMeterEstimateForPeriod, resolvePeriod } from '../lib/cost-calc.js'
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const VALID_WINDOWS = [7, 14, 30]
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async function estimateForMeter(meter, periodStart, periodEnd, windowDays) {
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const today = new Date().toISOString().slice(0, 10)
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const asOfDate = today < periodEnd ? today : periodEnd
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const { daily_rate } = await getTrailingDailyRate(meter.id, windowDays)
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const { consumption: actualToDate, has_data } = await getPeriodConsumption(meter.id, periodStart, asOfDate)
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const daysInPeriod = daysInclusive(periodStart, periodEnd)
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const remainingDays = Math.max(daysBetween(asOfDate, periodEnd), 0)
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let projectedConsumption = null
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if (daily_rate != null) {
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const base = has_data ? actualToDate : 0
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projectedConsumption = base + daily_rate * remainingDays
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} else if (has_data) {
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// No trailing rate available (too few readings) — fall back to actuals only
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projectedConsumption = actualToDate
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}
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const tariff = await getTariffForMeter(meter.id, asOfDate)
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const windows = tariff ? await getRateWindows(tariff.id) : []
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const cost = computeCost({ tariff, windows, consumption: projectedConsumption, daysInPeriod })
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const estimate = await getMeterEstimateForPeriod(meter.id, periodStart, periodEnd, windowDays)
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return {
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meter_id: meter.id, meter_name: meter.name,
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category_id: meter.category_id, category_name: meter.category_name, unit_label: meter.unit_label,
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trailing_window_days: windowDays,
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daily_rate,
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actual_to_date: has_data ? actualToDate : null,
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remaining_days: remainingDays,
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projected_consumption: projectedConsumption,
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...cost,
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...estimate,
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}
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}
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@ -3,8 +3,8 @@
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// internal API pattern (X-API-Key header, static key from env).
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import { pool } from '../db.js'
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import {
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getPeriodConsumption, getTariffForMeter, getRateWindows, computeCost,
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getTrailingDailyRate, resolvePeriod, daysInclusive, daysBetween,
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getPeriodConsumption, getMeterCostForPeriod, getMeterEstimateForPeriod,
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resolvePeriod, daysInclusive,
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} from '../lib/cost-calc.js'
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async function requireApiKey(req, reply) {
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@ -70,11 +70,8 @@ export async function internalRoutes(app) {
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const catTotals = { usage_cost_pence: 0, standing_cost_pence: 0, ccl_cost_pence: 0, vat_pence: 0, total_pence: 0, consumption: 0 }
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for (const m of meters) {
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const { consumption, has_data } = await getPeriodConsumption(m.id, start, end)
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const tariff = await getTariffForMeter(m.id, end)
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const windows = tariff ? await getRateWindows(tariff.id) : []
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const cost = computeCost({ tariff, windows, consumption, daysInPeriod })
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if (has_data) catTotals.consumption += consumption
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const cost = await getMeterCostForPeriod(m.id, start, end)
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if (cost.has_data) catTotals.consumption += cost.consumption
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catTotals.usage_cost_pence += cost.usage_cost_pence
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catTotals.standing_cost_pence += cost.standing_cost_pence
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catTotals.ccl_cost_pence += cost.ccl_cost_pence
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@ -92,10 +89,6 @@ export async function internalRoutes(app) {
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// GET /api/internal/estimate?period=current — projected cost for the open period
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app.get('/api/internal/estimate', async (req) => {
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const { start, end, year, month } = resolvePeriod(req.query.period)
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const today = new Date().toISOString().slice(0, 10)
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const asOfDate = today < end ? today : end
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const daysInPeriod = daysInclusive(start, end)
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const remainingDays = Math.max(daysBetween(asOfDate, end), 0)
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const { rows: config } = await pool.query("SELECT value FROM config WHERE key = 'estimate_trailing_days'")
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const globalDefault = config[0]?.value ?? 30
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@ -103,6 +96,7 @@ export async function internalRoutes(app) {
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const { rows: categories } = await pool.query('SELECT * FROM meter_categories WHERE active = TRUE ORDER BY sort_order')
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const breakdown = []
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const totals = { total_pence: 0, projected_consumption: 0 }
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let remainingDays = 0
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for (const cat of categories) {
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const windowDays = cat.estimate_trailing_days || globalDefault
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@ -111,18 +105,10 @@ export async function internalRoutes(app) {
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let catTotalPence = 0
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for (const m of meters) {
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const { daily_rate } = await getTrailingDailyRate(m.id, windowDays)
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const { consumption: actualToDate, has_data } = await getPeriodConsumption(m.id, start, asOfDate)
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let projected = null
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if (daily_rate != null) projected = (has_data ? actualToDate : 0) + daily_rate * remainingDays
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else if (has_data) projected = actualToDate
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const tariff = await getTariffForMeter(m.id, asOfDate)
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const windows = tariff ? await getRateWindows(tariff.id) : []
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const cost = computeCost({ tariff, windows, consumption: projected, daysInPeriod })
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if (projected != null) catConsumption += projected
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catTotalPence += cost.total_pence
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const estimate = await getMeterEstimateForPeriod(m.id, start, end, windowDays)
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remainingDays = estimate.remaining_days
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if (estimate.projected_consumption != null) catConsumption += estimate.projected_consumption
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catTotalPence += estimate.total_pence
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}
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breakdown.push({ category: cat.key, category_name: cat.name, unit_label: cat.unit_label, projected_consumption: catConsumption, total_pence: catTotalPence })
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