feat: create Gradient and GradientImmu

Closes #83

CHANGELOG.md

@@ -9,8 +9,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Gradient interface — [83](https://github.com/dartoos-dev/eo_color/issues/83).
 - doc comments about the purpose of each library.
 
+### Changed
+
+- add a code quality badge to REAME.
+
 ## [1.0.0] - 2021-06-19
 
 ### Changed

lib/eo_color.dart

@@ -5,5 +5,6 @@
 /// - an elegant, object-oriented framework for more specific color packages.
 library eo_color;
 
+export 'gradients.dart';
 export 'palettes.dart';
 export 'swatches.dart';

lib/gradients.dart

@@ -0,0 +1,7 @@
+/// Gradients
+///
+/// Suitable classes for working with Flutter's Gradient Apis.
+library gradients;
+
+export 'src/gradient.dart';
+export 'src/gradient_immu.dart';

lib/palettes.dart

@@ -1,7 +1,7 @@
 /// Palettes.
 ///
 /// `Palette` is a general purpose interface that represents any color palette
-/// from which a single color can be picked at a time.
+/// from which a single color can be selected at a time.
 library palettes;
 
 export 'src/material/amber/amber.dart';

lib/src/gradient.dart

@@ -0,0 +1,18 @@
+import 'dart:ui';
+
+import 'swatch.dart';
+
+/// Represents a color gradient.
+///
+/// A Color Gradient specifies a range of position-dependent colors, usually
+/// used to fill a region.  For example, many window managers allow the screen
+/// background to be specified as a gradient.  The colors produced by a gradient
+/// vary continuously with position, producing smooth color transitions.
+///
+/// See also:
+/// - [color-gradient](https://en.wikipedia.org/wiki/Color_gradient)
+abstract class Gradient implements Swatch {
+  /// A list of position-dependent colors — a color gradient.
+  @override
+  List<Color> get colors;
+}

lib/src/gradient_immu.dart

@@ -0,0 +1,22 @@
+import 'dart:ui';
+
+import 'package:eo_color/src/palette.dart';
+
+import 'gradient.dart';
+import 'swatch_base.dart';
+
+/// Convenience [Gradient].
+///
+/// It retrieves an immutable list of colors.
+abstract class GradientImmu extends SwatchBase implements Gradient {
+  /// [palettes] is the iterable of colors to be turned into an immutable list.
+  const GradientImmu(Iterable<Palette> palettes) : super(palettes);
+
+  /// An **immutable list** of position-dependent colors — a color gradient.
+  @override
+  List<Color> get colors => List.unmodifiable(super.colors);
+
+  /// Forwards to [colors].
+  @override
+  List<Color> call() => colors;
+}

lib/src/palette_rgb.dart

@@ -31,6 +31,7 @@ abstract class PaletteRGB implements Palette {
   /// the color's 32 bits.
   final int _value;
 
+  /// The rgb color.
   @override
   Color get color => Color(_value);
 

lib/src/swatch_base.dart

@@ -13,6 +13,7 @@ abstract class SwatchBase implements Swatch {
   // Source of picked colors.
   final Iterable<Palette> _palettes;
 
+  /// A new lazy [Iterable] of [Color].
   @override
   Iterable<Color> get colors => _palettes.map((palette) => palette.color);
 

test/gradient_immu_test.dart

@@ -0,0 +1,53 @@
+import 'package:eo_color/eo_color.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+const aGrey = [Grey()];
+const manyGreys = [
+  Grey.light(),
+  Grey.bitLighter(),
+  Grey(),
+  Grey.bitDarker(),
+  Grey.dark(),
+];
+
+class GradTest extends GradientImmu {
+  const GradTest.empty() : super(const []);
+  const GradTest.single() : super(aGrey);
+  const GradTest.many() : super(manyGreys);
+}
+
+void main() {
+  group('GradientImmu class', () {
+    test('empty', () {
+      const emptyList = GradTest.empty();
+      expect(emptyList.colors.isEmpty, true);
+    });
+    test('single', () {
+      const singleElem = GradTest.single();
+      expect(singleElem.colors.length, 1);
+      expect(singleElem().first, aGrey.first.color);
+    });
+    test('many', () {
+      const manyElems = GradTest.many();
+      expect(manyElems.colors.length, manyGreys.length);
+      expect(manyElems.colors, manyGreys.map((p) => p.color).toList());
+    });
+    test('immutability', () {
+      final emptyImmuList = const GradTest.empty().colors;
+      expect(
+        () => emptyImmuList.add(const Transparent().color),
+        throwsUnsupportedError,
+      );
+      final singleElemImmuList = const GradTest.single().colors;
+      expect(
+        () => singleElemImmuList.add(const Transparent().color),
+        throwsUnsupportedError,
+      );
+      final manyElemsImmuList = const GradTest.many().colors;
+      expect(
+        () => manyElemsImmuList.add(const Transparent().color),
+        throwsUnsupportedError,
+      );
+    });
+  });
+}