fix(image-pipeline): preserve worker errors and skip aborted histograms

lib/image-pipeline/histogram-plot.ts

@@ -0,0 +1,97 @@
+import type { HistogramData } from "@/lib/image-pipeline/histogram";
+
+type HistogramChannels = Pick<HistogramData, "red" | "green" | "blue" | "rgb">;
+
+type HistogramPlotOptions = {
+  points?: number;
+  width: number;
+  height: number;
+};
+
+export type HistogramPlot = {
+  series: {
+    red: number[];
+    green: number[];
+    blue: number[];
+    rgb: number[];
+    max: number;
+  };
+  polylines: {
+    red: string;
+    green: string;
+    blue: string;
+    rgb: string;
+  };
+};
+
+function compactHistogram(values: readonly number[], points: number): number[] {
+  if (points <= 0) {
+    return [];
+  }
+
+  if (values.length === 0) {
+    return Array.from({ length: points }, () => 0);
+  }
+
+  const bucket = values.length / points;
+  const compacted: number[] = [];
+  for (let pointIndex = 0; pointIndex < points; pointIndex += 1) {
+    let sum = 0;
+    const start = Math.floor(pointIndex * bucket);
+    const end = Math.min(values.length, Math.floor((pointIndex + 1) * bucket) || start + 1);
+    for (let index = start; index < end; index += 1) {
+      sum += values[index] ?? 0;
+    }
+    compacted.push(sum);
+  }
+  return compacted;
+}
+
+function histogramPolyline(
+  values: readonly number[],
+  maxValue: number,
+  width: number,
+  height: number,
+): string {
+  if (values.length === 0) {
+    return "";
+  }
+
+  const divisor = Math.max(1, values.length - 1);
+  return values
+    .map((value, index) => {
+      const x = (index / divisor) * width;
+      const normalized = maxValue > 0 ? value / maxValue : 0;
+      const y = height - normalized * height;
+      return `${x.toFixed(2)},${y.toFixed(2)}`;
+    })
+    .join(" ");
+}
+
+export function buildHistogramPlot(
+  histogram: HistogramChannels,
+  options: HistogramPlotOptions,
+): HistogramPlot {
+  const points = options.points ?? 64;
+  const red = compactHistogram(histogram.red, points);
+  const green = compactHistogram(histogram.green, points);
+  const blue = compactHistogram(histogram.blue, points);
+  const rgb = compactHistogram(histogram.rgb, points);
+  const max = Math.max(1, ...red, ...green, ...blue, ...rgb);
+
+  return {
+    series: {
+      red,
+      green,
+      blue,
+      rgb,
+      max,
+    },
+    polylines: {
+      red: histogramPolyline(red, max, options.width, options.height),
+      green: histogramPolyline(green, max, options.width, options.height),
+      blue: histogramPolyline(blue, max, options.width, options.height),
+      rgb: histogramPolyline(rgb, max, options.width, options.height),
+    },
+  };
+}