BadNote/test/page_viewport_test.dart

// Unit tests for continuous-single windowing math (P0.5 step 10, automatable
// slice). Pure geometry — no widgets, no pdfrx.

import 'package:flutter_test/flutter_test.dart';

import 'package:badnote/editor/layout/page_viewport.dart';

void main() {
  group('PageStackMetrics geometry', () {
    test('cumulative tops and total extent (uniform pages + gap)', () {
      final m = PageStackMetrics(pageHeights: [100, 100, 100], gap: 10);
      expect(m.pageCount, 3);
      expect(m.offsetOf(0), 0);
      expect(m.offsetOf(1), 110); // 100 + 10 gap
      expect(m.offsetOf(2), 220);
      expect(m.totalExtent, 320); // 220 + last height 100, no trailing gap
    });

    test('variable page heights', () {
      final m = PageStackMetrics(pageHeights: [50, 200, 75]);
      expect(m.offsetOf(0), 0);
      expect(m.offsetOf(1), 50);
      expect(m.offsetOf(2), 250);
      expect(m.totalExtent, 325);
    });

    test('empty document', () {
      final m = PageStackMetrics(pageHeights: []);
      expect(m.pageCount, 0);
      expect(m.totalExtent, 0);
      expect(m.visibleRange(0, 800), PageWindow.empty);
    });
  });

  group('PageStackMetrics.visibleRange', () {
    final m = PageStackMetrics(pageHeights: List.filled(10, 100)); // 0..1000

    test('top of document shows the first pages', () {
      // viewport [0,250) → pages 0,1,2 (page 2 is [200,300), overlaps top 250)
      expect(m.visibleRange(0, 250), const PageWindow(0, 2));
    });

    test('mid scroll shows the intersecting band', () {
      // viewport [420,720) → pages 4 [400,500) .. 7 [700,800)
      expect(m.visibleRange(420, 300), const PageWindow(4, 7));
    });

    test('cacheExtent grows the window on both sides', () {
      // base [420,720) → 4..7; +150 cache → [270,870) → pages 2..8
      expect(
        m.visibleRange(420, 300, cacheExtent: 150),
        const PageWindow(2, 8),
      );
    });

    test('exact page boundary is half-open (no spurious extra page)', () {
      // viewport [0,200): page 0 [0,100), page 1 [100,200). Page 2 starts at
      // 200 which is the exclusive bottom → NOT included.
      expect(m.visibleRange(0, 200), const PageWindow(0, 1));
    });

    test('last page at the bottom', () {
      expect(m.visibleRange(950, 50), const PageWindow(9, 9));
    });

    test('clamps to valid indices at the ends', () {
      // Overscroll below 0 (cache reaches negative) still starts at page 0.
      expect(m.visibleRange(0, 100, cacheExtent: 500).first, 0);
      // Overscroll past the end still ends at the last page.
      expect(m.visibleRange(900, 200, cacheExtent: 500).last, 9);
    });

    test('window entirely above content is empty', () {
      // Scrolled far past the end with no cache reaching back.
      expect(m.visibleRange(5000, 300), PageWindow.empty);
    });

    test('window entirely below content (negative, no overlap) is empty', () {
      // viewport sitting above page 0 with bottom <= 0.
      expect(m.visibleRange(-1000, 500), PageWindow.empty);
    });

    test('PageWindow helpers', () {
      const w = PageWindow(2, 5);
      expect(w.count, 4);
      expect(w.contains(2), isTrue);
      expect(w.contains(5), isTrue);
      expect(w.contains(6), isFalse);
      expect(PageWindow.empty.isEmpty, isTrue);
      expect(PageWindow.empty.count, 0);
    });
  });

  group('navigation math', () {
    final m = PageStackMetrics(pageHeights: List.filled(10, 100)); // 0..1000

    test('maxScrollExtent leaves the last page bottom at the viewport bottom',
        () {
      expect(m.maxScrollExtent(300), 700); // 1000 - 300
    });

    test('maxScrollExtent is 0 when content is shorter than the viewport', () {
      final short = PageStackMetrics(pageHeights: [100]);
      expect(short.maxScrollExtent(800), 0);
    });

    test('clampScroll keeps offset within [0, maxScrollExtent]', () {
      expect(m.clampScroll(-50, 300), 0);
      expect(m.clampScroll(5000, 300), 700);
      expect(m.clampScroll(420, 300), 420);
    });

    test('dominantPageAt picks the page covering most of the viewport', () {
      // viewport [0,100) fully on page 0.
      expect(m.dominantPageAt(0, 100), 0);
      // viewport [180,280): page1 [100,200) covers 20, page2 [200,300) covers
      // 80 → page 2 dominates.
      expect(m.dominantPageAt(180, 100), 2);
      // viewport [150,250): page1 covers [150,200)=50, page2 [200,250)=50 →
      // tie resolves to the first (page1) since overlap must strictly exceed.
      expect(m.dominantPageAt(150, 100), 1);
    });

    test('dominantPageAt clamps past the ends', () {
      expect(m.dominantPageAt(-500, 100), 0);
      expect(m.dominantPageAt(99999, 100), 9);
    });

    test('dominantPageAt is 0 for an empty document', () {
      final empty = PageStackMetrics(pageHeights: []);
      expect(empty.dominantPageAt(0, 800), 0);
    });
  });

  group('visibleRange with gaps', () {
    test('gap bands are not page bands (a scroll inside a gap shows neighbors)',
        () {
      final m = PageStackMetrics(pageHeights: [100, 100, 100], gap: 20);
      // page0 [0,100), gap [100,120), page1 [120,220), gap [220,240), page2 [240,340)
      // viewport [105,115) sits inside the first gap → nearest pages 0 and 1
      // both within a tiny window? window [105,115): page0 bottom 100 < 105 so
      // page0 excluded; page1 top 120 > 115 so excluded → empty band in gap.
      expect(m.visibleRange(105, 10), PageWindow.empty);
      // A slightly taller viewport spanning the gap catches both.
      expect(m.visibleRange(90, 40), const PageWindow(0, 1));
    });
  });
}