### Implement Keyboard Shortcut System

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Sets up a global keyboard event listener to handle various actions based on key presses. It includes logic to ignore input fields and maps specific keys to application functions like navigation, toggling UI elements, and exporting data. Dependencies include application state variables and helper functions like `cycle`, `toggleFavorite`, `cssSnippet`, `downloadBlob`, `doExportPNG`, `visibleThumbnails`, and `showToast`.

```typescript
useEffect(() => {
  function handleKeyDown(e: KeyboardEvent) {
    // Ignore if typing in input field
    const target = e.target as HTMLElement;
    if (["INPUT", "TEXTAREA", "SELECT"].includes(target.tagName)) return;

    switch(e.key) {
      case "ArrowLeft":
        cycle(-1); // Previous background
        break;
      case "ArrowRight":
        cycle(1); // Next background
        break;
      case "f":
      case "F":
        toggleFavorite(items[index].id); // Star current
        break;
      case "c":
      case "C":
        setShowB(!showB); // Toggle A/B compare
        break;
      case "y":
      case "Y":
        // Copy CSS to clipboard
        const css = cssSnippet(items[index], fit, repeat, pos, overlay);
        navigator.clipboard.writeText(css);
        showToast("CSS copied to clipboard");
        break;
      case "j":
      case "J":
        // Export JSON state
        const state = { items, index, fit, repeat, pos, overlay, blur };
        const json = JSON.stringify(state, null, 2);
        downloadBlob("mai-background-state.json", json);
        showToast("State exported as JSON");
        break;
      case "p":
      case "P":
        // Export PNG
        doExportPNG();
        showToast("Exporting PNG...");
        break;
      case "m":
      case "M":
        setMeterOpen(!meterOpen); // Toggle contrast meter
        break;
      case "?":
        setHelpOpen(!helpOpen); // Toggle help overlay
        break;
      case "1":
      case "2":
      case "3":
      case "4":
      case "5":
      case "6":
      case "7":
      case "8":
      case "9":
        // Select visible thumbnail by number
        const num = parseInt(e.key) - 1;
        const visible = visibleThumbnails();
        if (num < visible.length) {
          const targetIndex = items.findIndex(x => x.id === visible[num].id);
          setIndex(targetIndex);
        }
        break;
    }
  }

  window.addEventListener("keydown", handleKeyDown);
  return () => window.removeEventListener("keydown", handleKeyDown);
}, [items, index, fit, repeat, pos, overlay, blur, showB, meterOpen, helpOpen]);

// Assume the following are defined elsewhere in the component scope:
// cycle: (direction: number) => void;
// toggleFavorite: (id: string) => void;
// items: any[];
// index: number;
// fit: string;
// repeat: string;
// pos: string;
// overlay: boolean;
// blur: number;
// showB: boolean;
// meterOpen: boolean;
// helpOpen: boolean;
// cssSnippet: (item: any, fit: string, repeat: string, pos: string, overlay: boolean) => string;
// downloadBlob: (filename: string, data: string) => void;
// doExportPNG: () => void;
// visibleThumbnails: () => any[];
// setIndex: (index: number) => void;
// setShowB: (value: boolean) => void;
// setMeterOpen: (value: boolean) => void;
// setHelpOpen: (value: boolean) => void;
// showToast: (message: string) => void;

```

--------------------------------

### Estimate WCAG Contrast From Overlay

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Calculates text-to-background contrast ratios for accessibility compliance using overlay opacity values. Returns ratio values and WCAG AA/AAA compliance status. Takes a single overlay opacity parameter (0-1). Does not account for all real-world viewing conditions.

```typescript
// Check if white text on dark overlay meets WCAG standards
const result = estimateMinContrastFromOverlay(0.4);
console.log(result);
// {
//   ratio: 6.82,
//   passAA: true,    // ≥ 4.5:1 required
//   passAAA: false   // ≥ 7.0:1 required
// }

// Higher overlay = better contrast
const darkResult = estimateMinContrastFromOverlay(0.7);
console.log(darkResult);
// {
//   ratio: 11.23,
//   passAA: true,
//   passAAA: true
// }

// Display in UI
function ContrastIndicator({ overlay }) {
  const { ratio, passAA, passAAA } = estimateMinContrastFromOverlay(overlay);
  return (
    <div>
      <span>Contrast: {ratio.toFixed(2)}:1</span>
      <span className={passAA ? "text-green-500" : "text-red-500"}>
        {passAA ? "✓ WCAG AA" : "✗ WCAG AA"}
      </span>
      <span className={passAAA ? "text-green-500" : "text-red-500"}>
        {passAAA ? "✓ WCAG AAA" : "✗ WCAG AAA"}
      </span>
    </div>
  );
}
```

--------------------------------

### Export Background as PNG using Canvas Rendering (TypeScript)

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

This TypeScript code provides functionality to render a background configuration to a PNG image file using the HTML Canvas API. The `exportBackgroundPNG` function takes various styling options, draws either an image or a CSS gradient, applies an optional overlay, and returns a blob URL for the generated PNG. A helper function `downloadBlob` is assumed to handle the actual file download.

```typescript
// Export current background as PNG
async function handleExport() {
  const currentItem = items[index];

  const blobUrl = await exportBackgroundPNG({
    item: currentItem,
    fit: "cover",
    repeat: false,
    pos: "center center",
    overlay: 0.4,
    blur: 5,
    width: 1920,
    height: 1080
  });

  // blobUrl is a blob:// URL ready for download
  downloadBlob("mai-background.png", blobUrl);
}

// Implementation creates canvas, renders background, and returns blob
async function exportBackgroundPNG(opts) {
  const { item, fit, repeat, pos, overlay, blur, width, height } = opts;

  const canvas = document.createElement("canvas");
  canvas.width = width;
  canvas.height = height;
  const ctx = canvas.getContext("2d");

  // Draw background (image or gradient)
  if (item.type === "image" && item.src) {
    await drawImageBackground(ctx, item.src, fit, pos, repeat, blur, width, height);
  } else if (item.type === "css" && item.css) {
    drawGradientBackground(ctx, item.css, width, height);
  }

  // Apply overlay
  if (overlay > 0) {
    ctx.fillStyle = `rgba(0,0,0,${overlay})`;
    ctx.fillRect(0, 0, width, height);
  }

  // Convert to blob
  return new Promise((resolve) => {
    canvas.toBlob((blob) => {
      const url = URL.createObjectURL(blob);
      resolve(url);
    }, "image/png");
  });
}
```

--------------------------------

### A/B Background Comparison - TypeScript React Implementation

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Implements a side-by-side background comparison system with slot management, toggle functionality, and overlay rendering. Uses React state hooks to manage comparison slots and display mode. Provides user feedback through toast notifications and includes keyboard shortcuts for efficient workflow. The code manages two background slots (A and B) with toggle functionality to switch between them and displays an overlay with opacity for visual comparison.

```typescript
// Store comparison slots
const [slotA, setSlotA] = useState<number | null>(null);
const [slotB, setSlotB] = useState<number | null>(null);
const [showB, setShowB] = useState(false);

// Set comparison slot A to current background
function setCompareSlotA() {
  setSlotA(index);
  showToast("Slot A set");
}

// Set comparison slot B to current background
function setCompareSlotB() {
  setSlotB(index);
  showToast("Slot B set");
}

// Toggle between A and B views
function toggleCompare() {
  if (slotA === null || slotB === null) {
    showToast("Set both slots first");
    return;
  }
  setShowB(!showB);
}

// Render with comparison overlay
const displayIndex = showB && slotB !== null ? slotB : index;
const currentStyle = buildBackgroundStyle(items[displayIndex], { fit, repeat, pos, overlay, blur });

<div className="relative">
  {/* Main background */}
  <div style={currentStyle} className="absolute inset-0" />

  {/* Comparison overlay */}
  {showB && slotB !== null && (
    <div className="absolute inset-0" style={{ opacity: 0.5 }}>
      <div style={buildBackgroundStyle(items[slotB], { fit, repeat, pos, overlay, blur })}
           className="absolute inset-0" />
    </div>
  )}

  {/* UI controls */}
  <button onClick={setCompareSlotA}>Set Slot A</button>
  <button onClick={setCompareSlotB}>Set Slot B</button>
  <button onClick={toggleCompare} disabled={slotA === null || slotB === null}>
    Toggle Compare (C)
  </button>
</div>
```

--------------------------------

### Choose Text Color For Card

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Automatically determines optimal black or white text color for card content based on background, overlay, and card properties. Returns text color, contrast ratio, WCAG compliance status, and card luminance. Requires overlay opacity, card opacity, and card color parameters. Limited to black/white text choices.

```typescript
// Calculate best text color for semi-transparent white card
const result = chooseTextColorForCard(
  0.3,        // overlay opacity
  0.85,       // card opacity
  "#ffffff"   // card color (white)
);

console.log(result);
// {
//   color: "#000000",  // Black text chosen
//   ratio: 8.45,       // Contrast ratio
//   passAA: true,
//   passAAA: true,
//   L_card: 0.92       // Card luminance
// }

// For dark card on light background
const darkCardResult = chooseTextColorForCard(
  0.1,        // light overlay
  0.9,        // opaque card
  "#1a1a1a"   // dark gray card
);

console.log(darkCardResult);
// {
//   color: "#ffffff",  // White text chosen
//   ratio: 12.3,
//   passAA: true,
//   passAAA: true,
//   L_card: 0.05
// }

// Apply in card styling
const { color, passAA } = chooseTextColorForCard(overlay, cardOpacity, cardColor);
const cardStyle = {
  color: color,
  backgroundColor: `rgba(${hexToRgb(cardColor)}, ${cardOpacity})`,
  border: passAA ? "2px solid green" : "2px solid red"
};
```

--------------------------------

### Persist Application State to Local Storage with Debouncing (TypeScript)

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

This code demonstrates how to automatically save the application's state to `localStorage` using React's `useEffect` hook. State changes trigger debounced writes to `localStorage` every 250ms to optimize performance. It also includes logic for loading the state when the component mounts and a manual save function triggered by a keyboard shortcut.

```typescript
// State auto-save with useEffect (runs every 250ms after changes)
useEffect(() => {
  const state: ExportState = {
    items,
    index,
    fit,
    repeat,
    pos,
    overlay,
    blur,
    device,
    rotate,
    cardOpacity,
    darkMode,
    cardColor,
    cardCount,
    generatedCards,
    sidebarCollapsed
  };

  const id = setTimeout(() => {
    localStorage.setItem("mai-bg-chooser-v1", JSON.stringify(state));
    console.log("State saved");
  }, 250);

  return () => clearTimeout(id);
}, [items, index, fit, repeat, pos, overlay, blur, device, rotate,
    cardOpacity, darkMode, cardColor, cardCount, generatedCards, sidebarCollapsed]);

// Load state on mount
useEffect(() => {
  const stored = localStorage.getItem("mai-bg-chooser-v1");
  if (stored) {
    try {
      const state = JSON.parse(stored);
      setItems(state.items || []);
      setIndex(state.index || 0);
      setFit(state.fit || "cover");
      // ... restore all state properties
      console.log("State restored from localStorage");
    } catch (err) {
      console.error("Failed to parse stored state:", err);
    }
  }
}, []);

// Manual save with keyboard shortcut (S key)
function handleKeyDown(e: KeyboardEvent) {
  if (e.key === 's' || e.key === 'S') {
    const state = { /* ... */ };
    localStorage.setItem("mai-bg-chooser-v1", JSON.stringify(state));
    showToast("State saved manually");
  }
}
```

--------------------------------

### Calculate Device Viewport Styles with Rotation Support (TypeScript)

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

The `computeFrameStyle` function calculates CSS styles for device viewports, including support for landscape rotation. It accepts device configuration and a rotation flag, returning an object with 'width' and 'height' in 'px' units. This is useful for implementing responsive previews within a web application.

```typescript
const mobileStyle = computeFrameStyle({
  key: "mobile",
  w: 390,
  h: 844
}, false); // not rotated

console.log(mobileStyle);
// { width: "390px", height: "844px" }

const mobileRotated = computeFrameStyle({
  key: "mobile",
  w: 390,
  h: 844
}, true); // rotated

console.log(mobileRotated);
// { width: "844px", height: "390px" }

const fluidStyle = computeFrameStyle({
  key: "fluid",
  w: "100%",
  h: "100%"
}, false);

console.log(fluidStyle);
// { width: "100%", height: "100%" }

// Apply to preview frame
<div className="device-frame" style={computeFrameStyle(DEVICES[device], rotate)}>
  {/* Background preview content */}
</div>
```

--------------------------------

### Export production-ready CSS snippets

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

The cssSnippet function generates production-ready CSS code including overlay pseudo-element styling for deployment. It supports both image and gradient backgrounds with configurable fit, repeat, position, and overlay properties.

```typescript
// Export CSS for a gradient background with overlay
const item = {
  type: "css",
  css: "linear-gradient(135deg, #5A8DFF, #A0E7E5)"
};

const css = cssSnippet(item, "cover", false, "center center", 0.35);

console.log(css);
// Output:
// .my-background {
//   background-image: linear-gradient(135deg, #5A8DFF, #A0E7E5);
//   background-size: cover;
//   background-repeat: no-repeat;
//   background-position: center center;
//   position: relative;
// }
// .my-background::before {
//   content: "";
//   position: absolute;
//   inset: 0;
//   background: rgba(0,0,0,0.35);
//   pointer-events: none;
// }

// Copy to clipboard in the app
navigator.clipboard.writeText(css).then(() => {
  console.log("CSS copied successfully");
});
```

--------------------------------

### Handle file uploads and convert to data URLs

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

The fileToDataURL and addUploads functions handle image file uploads and convert them to data URLs for in-app storage. The implementation supports multiple file selection and validates file types before processing.

```typescript
// Convert a single file to data URL
const file = document.querySelector('input[type="file"]').files[0];
const dataURL = await fileToDataURL(file);
console.log(dataURL); // "data:image/png;base64,iVBORw0KGgo..."

// Handle multiple file uploads in the component
async function handleUpload(event) {
  const files = event.target.files;
  await addUploads(files);
  // Images are now added to the beginning of the items array
  // Index automatically resets to 0 to show the first uploaded image
}

// Internal implementation of addUploads
async addUploads(files: FileList | null) {
  if (!files || files.length === 0) return;
  const arr: BGItem[] = [];

  for (let i = 0; i < files.length; i++) {
    const f = files[i];
    if (!f.type.startsWith("image/")) continue;
    const dataUrl = await fileToDataURL(f);
    arr.push({
      id: uid(),
      name: f.name,
      type: "image",
      src: dataUrl,
      origin: "upload",
      favorite: false
    });
  }

  setItems([...arr, ...items]);
  setIndex(0);
}
```

--------------------------------

### Generate Random Cards for Testing

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Generates a specified number of demo card objects, each with a unique ID, randomized title, and content. Useful for populating UI components like grids for layout testing and development.

```typescript
function generateRandomCards(count: number) {
  const cards = [];
  for (let i = 0; i < count; i++) {
    cards.push({
      id: `card-${Math.random().toString(36).substr(2, 9)}`,
      title: getRandomTitle(),
      content: getRandomContent()
    });
  }
  return cards;
}

function getRandomTitle() {
  const titles = ["Neural Networks", "Computer Vision", "Machine Learning", "Data Science", "AI Ethics"];
  return titles[Math.floor(Math.random() * titles.length)];
}

function getRandomContent() {
  const contents = [
    "Explore deep learning architectures and training methods...",
    "Image recognition and object detection systems...",
    "Algorithms for learning from data and making predictions...",
    "Analyzing large datasets to extract insights...",
    "Ethical considerations and societal impact of AI..."
  ];
  return contents[Math.floor(Math.random() * contents.length)];
}

// Example usage:
// const cards = generateRandomCards(6);
// console.log(cards);
```

--------------------------------

### Generate background CSS styles with TypeScript

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

The buildBackgroundStyle function generates React CSS properties for background rendering based on configuration options. It supports both image and CSS gradient backgrounds with options for fit, repeat, position, overlay, and blur effects.

```typescript
// Generate background CSS for an image with cover fit and dark overlay
const item = {
  id: "img-001",
  name: "Hero Background",
  type: "image",
  src: "data:image/jpeg;base64,/9j/4AAQSkZJRg...",
  origin: "upload"
};

const style = buildBackgroundStyle(item, {
  fit: "cover",
  repeat: false,
  pos: "center center",
  overlay: 0.4,
  blur: 0
});

// Returns:
// {
//   backgroundImage: 'url("data:image/jpeg;base64,/9j/4AAQSkZJRg...")',
//   backgroundSize: 'cover',
//   backgroundRepeat: 'no-repeat',
//   backgroundPosition: 'center center',
//   filter: 'blur(0px)'
// }

// For CSS gradient backgrounds
const gradientItem = {
  id: "grad-001",
  name: "Auro",
  type: "css",
  css: "linear-gradient(135deg, #FF6B6B, #FFD166)",
  origin: "preset"
};

const gradientStyle = buildBackgroundStyle(gradientItem, {
  fit: "cover",
  repeat: false,
  pos: "center center",
  overlay: 0.3,
  blur: 5
});

// Returns:
// {
//   backgroundImage: 'linear-gradient(135deg, #FF6B6B, #FFD166)',
//   backgroundSize: 'cover',
//   backgroundRepeat: 'no-repeat',
//   backgroundPosition: 'center center',
//   filter: 'blur(5px)'
// }
```

--------------------------------

### Draw Image Background On Canvas

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Renders image backgrounds on HTML canvas with proper scaling, positioning, and blur effects. Supports different fit modes, positions, repeat options, and blur levels. Requires canvas context, image source, dimensions, and rendering parameters. Large images may impact performance.

```typescript
// Draw image background on canvas with cover fit and blur
const canvas = document.createElement('canvas');
canvas.width = 1440;
canvas.height = 900;
const ctx = canvas.getContext('2d');

await drawImageBackground(
  ctx,
  "data:image/jpeg;base64,/9j/4AAQSkZJRg...", // image src
  "cover",                                      // fit mode
  "center center",                              // position
  false,                                        // repeat
  8,                                            // blur pixels
  1440,                                         // canvas width
  900                                           // canvas height
);

// Canvas now contains the rendered background
// Export to PNG
const dataUrl = canvas.toDataURL('image/png');
console.log(dataUrl); // "data:image/png;base64,iVBORw0KGgo..."

// Download as file
const blob = await (await fetch(dataUrl)).blob();
const url = URL.createObjectURL(blob);
const a = document.createElement('a');
a.href = url;
a.download = 'background-preview.png';
a.click();
```

--------------------------------

### Draw Gradient Background On Canvas

Source: https://context7.com/mindprints/backgroundchecker/llms.txt

Renders CSS gradients on HTML canvas by extracting colors and creating gradient fills. Automatically parses linear gradient syntax, extracts colors, calculates angles, and creates evenly-spaced color stops. Requires canvas context, CSS gradient string, and dimensions. Only supports linear gradients.

```typescript
// Render gradient on canvas
const canvas = document.createElement('canvas');
canvas.width = 800;
canvas.height = 600;
const ctx = canvas.getContext('2d');

const gradientCSS = "linear-gradient(135deg, #FF6B6B, #FFD166, #06FFA5)";

drawGradientBackground(ctx, gradientCSS, 800, 600);

// Canvas now shows the gradient
// The function automatically:
// - Extracts colors: ["#FF6B6B", "#FFD166", "#06FFA5"]
// - Calculates 135deg angle
// - Creates evenly-spaced color stops
// - Applies to canvas context

// Export gradient canvas
const imageData = canvas.toDataURL('image/png');

// Use in img element
document.querySelector('#preview').src = imageData;
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.