Implement copy to clipboard functionality

[nullcoder]

Description

Implement secure copy to clipboard functionality for code blocks and share links, ensuring sensitive data is never logged.

Security Requirements

• NEVER log or console.log copied content (could contain decrypted data)
• Copy full URLs including hash fragments (e.g., https://ghostpaste.dev/g/abc123#key=...)
• Ensure clipboard API doesn't leak data to browser extensions
• Clear clipboard data from memory after copy

Core Features

1. Share Link Copying

• Copy button next to share URL after gist creation
• Must include full URL with fragment (contains encryption key)
• Visual feedback: "Copied!" tooltip or button text change
• Button text: "Copy Link" → "Copied!" → "Copy Link" (after 2s)

2. Individual File Copying

• Copy button for each file in multi-file gists
• Appears on hover or always visible on mobile
• Copies only the content of that specific file
• Include filename in toast notification: "Copied file.js"

3. Full Gist Copying

• Optional: Copy all files as concatenated text
• Format: // filename.js\n[content]\n\n// nextfile.js\n[content]
• Use case: Quick paste into single file

Visual Feedback

• Success: Green check icon + "Copied!" message
• Error: Red X icon + "Failed to copy" message
• Use toast notifications or inline feedback
• Animation: Subtle scale or fade effect

Implementation Details

// Secure copy function
async function secureCopy(text: string, label?: string) {
  try {
    await navigator.clipboard.writeText(text);
    // Show success feedback
    showToast({
      title: "Copied\!",
      description: label ? `Copied ${label}` : undefined,
      variant: "success"
    });
  } catch (err) {
    // Fallback for older browsers
    const textArea = document.createElement("textarea");
    textArea.value = text;
    textArea.style.position = "fixed";
    textArea.style.left = "-999999px";
    document.body.appendChild(textArea);
    textArea.select();
    try {
      document.execCommand("copy");
      showToast({ title: "Copied\!", variant: "success" });
    } catch {
      showToast({ title: "Failed to copy", variant: "error" });
    } finally {
      document.body.removeChild(textArea);
    }
  }
  // Clear from memory
  text = "";
}

Acceptance Criteria

• Copy share link includes full URL with hash fragment
• Individual file copy buttons work for each file
• NO console.log or logging of copied content
• Visual feedback shows success/failure
• Fallback works for browsers without clipboard API
• Mobile touch targets are appropriately sized (44x44px min)
• Keyboard shortcut (Cmd/Ctrl+C) works when content selected
• Toast notifications don't block user interaction
• Memory is cleared after copy operation

UI/UX Guidelines

• Copy buttons use consistent icon (e.g., clipboard icon from Lucide)
• Hover state shows tooltip "Copy to clipboard"
• Success state changes icon to checkmark temporarily
• Error state explains why copy failed
• Mobile: Consider long-press to copy as alternative

Technical Notes

• Use navigator.clipboard API as primary method
• Implement textarea fallback for older browsers
• Test Safari iOS clipboard permissions
• Consider rate limiting to prevent spam (max 10 copies per minute)
• Use React hooks for copy state management
• Integrate with existing toast system from feat: add toast notification system #68

Related

• Part of Phase 4 UI Components
• Enhances user experience in viewer (feat: create loading state components #67)
• Works with CodeEditor component (feat: implement PIN authentication with PBKDF2-SHA256 #46)
• Uses toast notifications (feat: add toast notification system #68)