feat(compare): trends explorer with England line; gap-honest axis; series regression guard

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB
2026-07-13 23:54:58 +01:00
parent 2573cd2490
commit 519584f34b
6 changed files with 523 additions and 16 deletions
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+/**
+ * Pure series-building for the comparison trend chart, extracted from
+ * ComparisonChart so it is unit-testable without a canvas.
+ *
+ * Chart truthfulness rules (spec §8.1): every academic year between the
+ * first and last data point appears on the axis — cancelled test years
+ * (2019/20, 2020/21) and the unpublished 2021/22 school-level year render
+ * as real gaps, never as compressed time; school lines never bridge gaps.
+ */
+
+import type { ComparisonData } from './types';
+
+/** 201819 → 201920 (academic-year arithmetic on YYYYYY codes). */
+function nextAcademicYear(year: number): number {
+  const start = Math.floor(year / 100);
+  const end = year % 100;
+  return (start + 1) * 100 + (end + 1);
+}
+
+/** Every academic year from min(years) to max(years), inclusive. */
+export function fillAcademicYears(years: number[]): number[] {
+  if (years.length === 0) return [];
+  const ints = [...new Set(years.map((y) => Math.trunc(y)))].sort((a, b) => a - b);
+  const out: number[] = [];
+  let y = ints[0];
+  const last = ints[ints.length - 1];
+  while (y <= last && out.length < 50) {
+    out.push(y);
+    y = nextAcademicYear(y);
+  }
+  return out;
+}
+
+export interface CompareChartSeries {
+  label: string;
+  data: Array<number | null>;
+  /** Index into CHART_COLORS / point styles. */
+  schoolIndex: number;
+  spanGaps: false;
+}
+
+export interface EnglandSeries {
+  label: 'England average';
+  data: Array<number | null>;
+  borderDash: [number, number];
+  spanGaps: false;
+}
+
+export interface CompareChart {
+  years: number[];
+  schoolDatasets: CompareChartSeries[];
+  englandDataset: EnglandSeries | null;
+  /** True when England published a 2021/22 figure but no school has one —
+   * the UI shows: "DfE didn't publish school-level figures for 2021/22". */
+  showUnpublished202122Note: boolean;
+}
+
+export function buildCompareChart(
+  comparisonData: Record<string, ComparisonData>,
+  schools: Array<{ urn: number; school_name: string }>,
+  metric: string,
+  nationalByYear?: Record<number, number | null | undefined>,
+): CompareChart {
+  const rawYears = schools.flatMap(
+    (s) => comparisonData[String(s.urn)]?.yearly_data.map((d) => Math.trunc(d.year)) ?? [],
+  );
+  const years = fillAcademicYears(rawYears);
+
+  const schoolDatasets: CompareChartSeries[] = schools.map((school, schoolIndex) => {
+    const rows = comparisonData[String(school.urn)]?.yearly_data ?? [];
+    const byYear = new Map<number, Record<string, unknown>>();
+    for (const row of rows) byYear.set(Math.trunc(row.year), row as unknown as Record<string, unknown>);
+    return {
+      label: school.school_name,
+      data: years.map((year) => {
+        const v = byYear.get(year)?.[metric];
+        return typeof v === 'number' && !Number.isNaN(v) ? v : null;
+      }),
+      schoolIndex,
+      spanGaps: false,
+    };
+  });
+
+  let englandDataset: EnglandSeries | null = null;
+  if (nationalByYear) {
+    const data = years.map((year) => {
+      const v = nationalByYear[year];
+      return typeof v === 'number' && !Number.isNaN(v) ? v : null;
+    });
+    if (data.some((v) => v != null)) {
+      englandDataset = { label: 'England average', data, borderDash: [5, 4], spanGaps: false };
+    }
+  }
+
+  const idx202122 = years.indexOf(202122);
+  const showUnpublished202122Note =
+    idx202122 >= 0 &&
+    englandDataset?.data[idx202122] != null &&
+    schoolDatasets.every((ds) => ds.data[idx202122] == null);
+
+  return { years, schoolDatasets, englandDataset, showUnpublished202122Note };
+}