import 'dart:ui';

import 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';

// Copied from bottom_sheet.dart as is a private class
// https://github.com/flutter/flutter/issues/51627

// TODO(guidezpl): Look into making this public. A copy of this class is in
//  scaffold.dart, for now, https://github.com/flutter/flutter/issues/51627

/// A curve that progresses linearly until a specified [startingPoint], at which
/// point [curve] will begin. Unlike [Interval], [curve] will not start at zero,
/// but will use [startingPoint] as the Y position.
///
/// For example, if [startingPoint] is set to `0.5`, and [curve] is set to
/// [Curves.easeOut], then the bottom-left quarter of the curve will be a
/// straight line, and the top-right quarter will contain the entire contents of
/// [Curves.easeOut].
///
/// This is useful in situations where a widget must track the user's finger
/// (which requires a linear animation), and afterwards can be flung using a
/// curve specified with the [curve] argument, after the finger is released. In
/// such a case, the value of [startingPoint] would be the progress of the
/// animation at the time when the finger was released.
///
/// The [startingPoint] and [curve] arguments must not be null.
class BottomSheetSuspendedCurve extends Curve {
  /// Creates a suspended curve.
  const BottomSheetSuspendedCurve(
    this.startingPoint, {
    this.curve = Curves.easeOutCubic,
  });

  /// The progress value at which [curve] should begin.
  ///
  /// This defaults to [Curves.easeOutCubic].
  final double startingPoint;

  /// The curve to use when [startingPoint] is reached.
  final Curve curve;

  @override
  double transform(double t) {
    assert(t >= 0.0 && t <= 1.0);
    assert(startingPoint >= 0.0 && startingPoint <= 1.0);

    if (t < startingPoint) {
      return t;
    }

    if (t == 1.0) {
      return t;
    }

    final curveProgress = (t - startingPoint) / (1 - startingPoint);
    final transformed = curve.transform(curveProgress);
    return lerpDouble(startingPoint, 1, transformed)!;
  }

  @override
  String toString() {
    return '${describeIdentity(this)}($startingPoint, $curve)';
  }
}