Profile per-column cardinality and extent; add data-aware chart warnings (M4, A3/A4)

src/core/profile.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from 'vitest';
-import { profileData } from './profile';
+import { DISTINCT_CAP, profileData } from './profile';
 
 describe('profileData', () => {
   test('profiles a JSON-array dataset fully', () => {
@@ -53,3 +53,47 @@ describe('profileData', () => {
     expect(profile.columnTypes).toEqual([{ name: 'v', type: 'number' }]);
   });
 });
+
+describe('profileData — column stats (cardinality + numeric extent)', () => {
+  test('counts distinct values and reports numeric extent for number columns', () => {
+    const rows = [
+      { region: 'N', sales: 10 },
+      { region: 'S', sales: -4 },
+      { region: 'N', sales: 25 }, // region repeats → 2 distinct, not 3
+    ];
+    const stats = profileData(rows, 0).columnStats;
+    expect(stats).toEqual([
+      { name: 'region', distinct: 2, distinctCapped: false, numericExtent: null },
+      { name: 'sales', distinct: 3, distinctCapped: false, numericExtent: { min: -4, max: 25 } },
+    ]);
+  });
+
+  test('distinct counting is empty-insensitive and case/whitespace literal', () => {
+    const rows = [{ c: 'A' }, { c: ' A ' }, { c: '' }, { c: null }, { c: 'b' }];
+    // '  A  ' trims to 'A' (one key); '' and null are empties (no signal) → 2 distinct.
+    expect(profileData(rows, 0).columnStats[0]).toEqual({
+      name: 'c',
+      distinct: 2,
+      distinctCapped: false,
+      numericExtent: null,
+    });
+  });
+
+  test('caps distinct at DISTINCT_CAP and flags the overflow', () => {
+    const rows = Array.from({ length: DISTINCT_CAP + 25 }, (_, i) => ({ id: `v${i}` }));
+    const stat = profileData(rows, 0).columnStats[0];
+    expect(stat.distinct).toBe(DISTINCT_CAP);
+    expect(stat.distinctCapped).toBe(true);
+  });
+
+  test('numericExtent is null for a non-numeric column even if some cells parse', () => {
+    // A 'string' column (one non-numeric value knocks the type down) carries no extent.
+    const rows = [{ v: '1' }, { v: '2' }, { v: 'oops' }];
+    const stat = profileData(rows, 0).columnStats[0];
+    expect(stat.numericExtent).toBeNull();
+  });
+
+  test('N/A profile carries empty column stats', () => {
+    expect(profileData(null, 9).columnStats).toEqual([]);
+  });
+});