// Cost Forecasting (Custom Date Range, Next 3 Months)
// Forecasts future cost using time series decomposition and forecasting.
// Parameters: startDate, endDate, forecastPeriods (default: 90), interval (default: 1d)
// Author: FinOps Toolkit Team
// Last Tested: 2025-05-17
//
let startDate = startofmonth(ago(365d)); // Default: last 12 months
let endDate = startofmonth(now());
let forecastPeriods = 90;
let interval = 1d;
Costs()
| where ChargePeriodStart >= startDate and ChargePeriodStart < endDate
| summarize EffectiveCost = sum(EffectiveCost) by bin(ChargePeriodStart, interval)
| make-series EffectiveCostSeries = sum(EffectiveCost) on ChargePeriodStart from startDate to endDate step interval
| extend forecast = series_decompose_forecast(EffectiveCostSeries, forecastPeriods)
| project ChargePeriodStart, EffectiveCostSeries, forecast
// | render timechart