import type { CategoryId } from "@transportationer/shared";
import type { GridCell } from "@transportationer/shared";

export interface SigmoidParams {
  thresholdSec: number;
  k: number;
}

/**
 * Sigmoid decay: 1 / (1 + exp(k * (t - threshold)))
 * score = 1.0 when t = 0 (POI at doorstep)
 * score = 0.5 when t = threshold
 * score ≈ 0.02 when t = 2 * threshold
 */
export function sigmoid(travelTimeSec: number, params: SigmoidParams): number {
  return 1 / (1 + Math.exp(params.k * (travelTimeSec - params.thresholdSec)));
}

export function defaultSigmoidParams(thresholdMin: number): SigmoidParams {
  const thresholdSec = thresholdMin * 60;
  return { thresholdSec, k: 4 / thresholdSec };
}

/**
 * Weighted composite score, normalized to [0, 1].
 * Missing categories contribute 0 to the numerator and their weight to the denominator.
 */
export function compositeScore(
  categoryScores: Partial<Record<CategoryId, number>>,
  weights: Record<CategoryId, number>,
): number {
  const totalWeight = Object.values(weights).reduce((a, b) => a + b, 0);
  if (totalWeight === 0) return 0;
  let sum = 0;
  for (const [cat, w] of Object.entries(weights) as [CategoryId, number][]) {
    sum += (w / totalWeight) * (categoryScores[cat] ?? 0);
  }
  return Math.min(1, Math.max(0, sum));
}

/** Re-apply weights to rows already fetched from PostGIS */
export function reweightCells(
  rows: Omit<GridCell, "score">[],
  weights: Record<CategoryId, number>,
): GridCell[] {
  return rows.map((row) => ({
    ...row,
    score: compositeScore(row.categoryScores, weights),
  }));
}