# Agent J: File Sharing UI

## Phase: 4 (Feature Completion)
## Depends on: Agent F (Chat Screen), Agent C (models with FileInfo/ImageInfo)

## Context
File sharing uses chunked encrypted upload/download (AES-256-GCM).
The UI handles image/file picking, thumbnail display, download progress, and file type icons.
Encryption logic is handled by ChatClient (Claude Code) — this agent only handles UI.

## Task
Create file/image picker integration, download UI, file type icons, and thumbnail display.

## Files to Create

### 1. ui/chat/AttachmentSheet.kt
Bottom sheet shown when attachment button is tapped:
- **"Image"** option with gallery icon
  - Opens system image picker (ActivityResultContracts.PickVisualMedia)
  - Shows selected image preview before sending
- **"File"** option with document icon
  - Opens system file picker (ActivityResultContracts.OpenDocument)
  - Shows selected file name + size before sending
- **"Camera"** option with camera icon
  - Opens camera to take photo (ActivityResultContracts.TakePicture)

### 2. ui/chat/ImageThumbnail.kt
Composable for image message display in chat:
- Shows base64 JPEG thumbnail from ImageInfo.thumbnail
- Max width 200dp, maintain aspect ratio
- Rounded corners (8dp)
- Loading shimmer while full image loads
- On tap: navigate to ImageViewer with full image URL
- Download progress overlay (if downloading full resolution)

### 3. ui/chat/FileCard.kt
Composable for file attachment display in chat:
- Horizontal layout:
  - File type icon (40dp, left):
    - PDF: Red document icon
    - Image: Blue image icon
    - Video: Purple play icon
    - Audio: Green music icon
    - Archive: Yellow archive icon
    - Default: Gray document icon
  - Center (weight 1f):
    - Filename (bold, 1 line, ellipsize end)
    - File size (formatted: KB, MB) + mime type
  - Download button/progress (right):
    - Download icon (if not downloaded)
    - CircularProgressIndicator (if downloading)
    - Checkmark (if downloaded)
- Background: Surface1 with 1dp Surface2 border, rounded 8dp
- On tap: download if not downloaded, open if downloaded

### 4. ui/chat/DownloadProgress.kt
Reusable download progress composable:
- Circular progress indicator with percentage text
- Cancel button
- File size downloaded / total

### 5. util/FileUtils.kt
```kotlin
package com.kecalek.chat.util

import android.content.Context
import android.net.Uri
import android.webkit.MimeTypeMap

object FileUtils {
    fun getFileName(context: Context, uri: Uri): String {
        // Query ContentResolver for display name
        val cursor = context.contentResolver.query(uri, null, null, null, null)
        cursor?.use {
            if (it.moveToFirst()) {
                val nameIndex = it.getColumnIndex(android.provider.OpenableColumns.DISPLAY_NAME)
                if (nameIndex >= 0) return it.getString(nameIndex)
            }
        }
        return uri.lastPathSegment ?: "unknown"
    }

    fun getFileSize(context: Context, uri: Uri): Long {
        val cursor = context.contentResolver.query(uri, null, null, null, null)
        cursor?.use {
            if (it.moveToFirst()) {
                val sizeIndex = it.getColumnIndex(android.provider.OpenableColumns.SIZE)
                if (sizeIndex >= 0) return it.getLong(sizeIndex)
            }
        }
        return 0
    }

    fun getMimeType(context: Context, uri: Uri): String {
        return context.contentResolver.getType(uri)
            ?: MimeTypeMap.getSingleton()
                .getMimeTypeFromExtension(uri.toString().substringAfterLast('.'))
            ?: "application/octet-stream"
    }

    fun formatFileSize(bytes: Long): String = when {
        bytes < 1024 -> "$bytes B"
        bytes < 1024 * 1024 -> "${bytes / 1024} KB"
        bytes < 1024 * 1024 * 1024 -> "${"%.1f".format(bytes / (1024.0 * 1024.0))} MB"
        else -> "${"%.1f".format(bytes / (1024.0 * 1024.0 * 1024.0))} GB"
    }

    fun getFileTypeIcon(mimeType: String): FileTypeIcon = when {
        mimeType.startsWith("image/") -> FileTypeIcon.IMAGE
        mimeType.startsWith("video/") -> FileTypeIcon.VIDEO
        mimeType.startsWith("audio/") -> FileTypeIcon.AUDIO
        mimeType == "application/pdf" -> FileTypeIcon.PDF
        mimeType.contains("zip") || mimeType.contains("tar") || mimeType.contains("rar") -> FileTypeIcon.ARCHIVE
        else -> FileTypeIcon.DOCUMENT
    }

    enum class FileTypeIcon { PDF, IMAGE, VIDEO, AUDIO, ARCHIVE, DOCUMENT }
}
```

## Constraints
- Use ActivityResultContracts for file/image picking (no deprecated startActivityForResult)
- Thumbnail display from base64 data (not URL loading)
- Max image display width: 200dp in chat
- File cards: consistent height, ellipsize long filenames
- Download progress: 0-100% with cancel option

## DO NOT
- Implement actual file encryption/decryption
- Implement actual chunked upload/download
- Handle server communication
- Store files on disk (that's ChatClient's job)