import 'package:flutter/rendering.dart';

class SliverGridDelegateWithFixedHeight extends SliverGridDelegate {
  /// Creates a delegate that makes grid layouts with a fixed height.
  const SliverGridDelegateWithFixedHeight({
    required this.maxCrossAxisExtent,
    this.mainAxisSpacing = 0.0,
    this.crossAxisSpacing = 0.0,
    this.height = 56.0,
  })  : assert(mainAxisSpacing >= 0),
        assert(crossAxisSpacing >= 0),
        assert(height > 0);

  /// The maximum extent of tiles in the cross axis.
  ///
  /// This delegate will select a cross-axis extent for the tiles that is as
  /// large as possible subject to the following conditions:
  ///
  ///  - The extent evenly divides the cross-axis extent of the grid.
  ///  - The extent is at most [maxCrossAxisExtent].
  ///
  /// For example, if the grid is vertical, the grid is 500.0 pixels wide, and
  /// [maxCrossAxisExtent] is 150.0, this delegate will create a grid with 4
  /// columns that are 125.0 pixels wide.
  final double maxCrossAxisExtent;

  /// The number of logical pixels between each child along the main axis.
  final double mainAxisSpacing;

  /// The number of logical pixels between each child along the cross axis.
  final double crossAxisSpacing;

  /// The height of the crossAxis.
  final double height;

  bool _debugAssertIsValid() {
    assert(mainAxisSpacing >= 0.0);
    assert(crossAxisSpacing >= 0.0);
    assert(height > 0.0);

    return true;
  }

  @override
  SliverGridLayout getLayout(SliverConstraints constraints) {
    assert(_debugAssertIsValid());
    final crossAxisCount =
        (constraints.crossAxisExtent / (maxCrossAxisExtent + crossAxisSpacing))
            .ceil();
    final usableCrossAxisExtent =
        constraints.crossAxisExtent - crossAxisSpacing * (crossAxisCount - 1);
    final childCrossAxisExtent = usableCrossAxisExtent / crossAxisCount;
    final childMainAxisExtent = height;

    return SliverGridRegularTileLayout(
      crossAxisCount: crossAxisCount,
      mainAxisStride: childMainAxisExtent + mainAxisSpacing,
      crossAxisStride: childCrossAxisExtent + crossAxisSpacing,
      childMainAxisExtent: childMainAxisExtent,
      childCrossAxisExtent: childCrossAxisExtent,
      reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),
    );
  }

  @override
  bool shouldRelayout(SliverGridDelegateWithFixedHeight oldDelegate) {
    return oldDelegate.maxCrossAxisExtent != maxCrossAxisExtent ||
        oldDelegate.mainAxisSpacing != mainAxisSpacing ||
        oldDelegate.crossAxisSpacing != crossAxisSpacing ||
        oldDelegate.height != height;
  }
}