Add presets.js as single source of truth for filter definitions

src/presets.js

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+/**
+ * Single source of truth for filter presets.
+ *
+ * The CSS rules in src/styles/style.scss MUST match this list one-to-one.
+ * Adding a preset = add an entry here + add a matching .has-filter-<slug>
+ * rule in style.scss. Do not duplicate filter values elsewhere.
+ *
+ * @package ImageFilters
+ */
+
+export const PRESETS = [
+    {
+        slug: 'normal',
+        label: 'Normal',
+        color: '#f0f0f0',
+        cssFilter: 'none',
+    },
+    {
+        slug: 'warm',
+        label: 'Warm',
+        color: '#f4a261',
+        cssFilter: 'saturate(1.25) sepia(0.18) brightness(1.05) contrast(1.05)',
+    },
+    {
+        slug: 'cool',
+        label: 'Cool',
+        color: '#a8dadc',
+        cssFilter: 'saturate(0.95) hue-rotate(-10deg) brightness(1.02) contrast(1.05)',
+    },
+    {
+        slug: 'vivid',
+        label: 'Vivid',
+        color: '#e63946',
+        cssFilter: 'saturate(1.6) contrast(1.15) brightness(1.03)',
+    },
+    {
+        slug: 'fade',
+        label: 'Fade',
+        color: '#cdb4db',
+        cssFilter: 'saturate(0.85) contrast(0.9) brightness(1.08) sepia(0.08)',
+    },
+    {
+        slug: 'mono',
+        label: 'Mono',
+        color: '#6c757d',
+        cssFilter: 'grayscale(1) contrast(1.05)',
+    },
+    {
+        slug: 'dramatic',
+        label: 'Dramatic',
+        color: '#1d3557',
+        cssFilter: 'contrast(1.35) saturate(1.15) brightness(0.92)',
+    },
+    {
+        slug: 'sepia',
+        label: 'Sepia',
+        color: '#d4a373',
+        cssFilter: 'sepia(0.85) saturate(1.1) contrast(1.05)',
+    },
+];
+
+export const DEFAULT_PRESET = 'normal';
+
+const VALID_SLUGS = new Set( PRESETS.map( ( p ) => p.slug ) );
+
+/**
+ * Returns true if the given slug is a known preset.
+ *
+ * @param {string} slug
+ * @return {boolean}
+ */
+export function isValidPresetSlug( slug ) {
+    return VALID_SLUGS.has( slug );
+}

tests/jest/presets.test.js

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+import { PRESETS, DEFAULT_PRESET, isValidPresetSlug } from '../../src/presets';
+
+describe( 'presets', () => {
+    test( 'exports 8 presets', () => {
+        expect( PRESETS ).toHaveLength( 8 );
+    } );
+
+    test( 'each preset has the required shape', () => {
+        for ( const preset of PRESETS ) {
+            expect( preset ).toEqual(
+                expect.objectContaining( {
+                    slug: expect.stringMatching( /^[a-z-]+$/ ),
+                    label: expect.any( String ),
+                    color: expect.stringMatching( /^#[0-9a-f]{3,6}$/i ),
+                    cssFilter: expect.any( String ),
+                } )
+            );
+        }
+    } );
+
+    test( 'slugs are unique', () => {
+        const slugs = PRESETS.map( ( p ) => p.slug );
+        expect( new Set( slugs ).size ).toBe( slugs.length );
+    } );
+
+    test( 'normal preset has filter: none', () => {
+        const normal = PRESETS.find( ( p ) => p.slug === 'normal' );
+        expect( normal.cssFilter ).toBe( 'none' );
+    } );
+
+    test( 'DEFAULT_PRESET is "normal" and exists in PRESETS', () => {
+        expect( DEFAULT_PRESET ).toBe( 'normal' );
+        expect( PRESETS.map( ( p ) => p.slug ) ).toContain( DEFAULT_PRESET );
+    } );
+
+    test( 'isValidPresetSlug returns true for known slugs', () => {
+        expect( isValidPresetSlug( 'normal' ) ).toBe( true );
+        expect( isValidPresetSlug( 'dramatic' ) ).toBe( true );
+    } );
+
+    test( 'isValidPresetSlug returns false for unknown slugs', () => {
+        expect( isValidPresetSlug( 'foobar' ) ).toBe( false );
+        expect( isValidPresetSlug( '' ) ).toBe( false );
+    } );
+} );