Add channel URL lookup and auto-detection

- Accept YouTube URLs in any format (@handle, /c/, /user/, /channel/)
- Auto-extract channel ID from URLs using yt-dlp
- Auto-detect channel name from URL (optional field)
- Support direct channel ID input (backwards compatible)
- Prevent duplicate channels
- Updated UI with better instructions and examples
- Improved user experience - just paste channel URL

app.py

@@ -7,8 +7,10 @@ Provides a web UI for managing YouTube channel downloads
 import os
 import subprocess
 import json
+import re
 from datetime import datetime
 from pathlib import Path
+from urllib.parse import urlparse, parse_qs
 from flask import Flask, render_template, request, jsonify, redirect, url_for, flash
 
 app = Flask(__name__)
@@ -45,6 +47,51 @@ def save_settings(settings):
     with open(SETTINGS_FILE, 'w') as f:
         json.dump(settings, f, indent=2)
 
+def extract_channel_id(url_or_id):
+    """
+    Extract channel ID from various YouTube URL formats or validate direct ID
+    Returns tuple: (channel_id, channel_name_hint or None)
+    """
+    # If it looks like a channel ID already (24 characters starting with UC)
+    if re.match(r'^UC[\w-]{22}$', url_or_id.strip()):
+        return url_or_id.strip(), None
+
+    # Parse as URL
+    try:
+        parsed = urlparse(url_or_id)
+
+        # Format: youtube.com/channel/CHANNEL_ID
+        if '/channel/' in parsed.path:
+            channel_id = parsed.path.split('/channel/')[-1].split('/')[0]
+            if channel_id:
+                return channel_id, None
+
+        # Format: youtube.com/@handle or youtube.com/c/name or youtube.com/user/name
+        # These require fetching the page to get the actual channel ID
+        if parsed.netloc in ['youtube.com', 'www.youtube.com', 'm.youtube.com']:
+            # Use yt-dlp to extract channel ID from URL
+            try:
+                result = subprocess.run(
+                    ['yt-dlp', '--dump-json', '--playlist-items', '0', url_or_id],
+                    capture_output=True,
+                    text=True,
+                    timeout=10
+                )
+
+                if result.returncode == 0 and result.stdout:
+                    data = json.loads(result.stdout.split('\n')[0])
+                    channel_id = data.get('channel_id')
+                    channel_name = data.get('channel')
+
+                    if channel_id:
+                        return channel_id, channel_name
+            except:
+                pass
+    except:
+        pass
+
+    return None, None
+
 def get_channels():
     """Read channels from channels.txt"""
     channels = []
@@ -166,18 +213,38 @@ def channels():
 @app.route('/channels/add', methods=['POST'])
 def add_channel():
     """Add a new channel"""
-    channel_id = request.form.get('channel_id', '').strip()
+    channel_input = request.form.get('channel_id', '').strip()
     channel_name = request.form.get('channel_name', '').strip()
 
-    if not channel_id or not channel_name:
-        flash('Channel ID and Name are required', 'error')
+    if not channel_input:
+        flash('Channel ID or URL is required', 'error')
         return redirect(url_for('channels'))
 
+    # Extract channel ID from URL or validate direct ID
+    channel_id, auto_name = extract_channel_id(channel_input)
+
+    if not channel_id:
+        flash('Invalid channel ID or URL. Please check and try again.', 'error')
+        return redirect(url_for('channels'))
+
+    # Use auto-detected name if no name was provided
+    if not channel_name and auto_name:
+        channel_name = auto_name
+    elif not channel_name:
+        flash('Channel name is required (could not auto-detect from URL)', 'error')
+        return redirect(url_for('channels'))
+
+    # Check for duplicates
     channels = get_channels()
+    for existing in channels:
+        if existing['id'] == channel_id:
+            flash(f'Channel already exists: {existing["name"]}', 'error')
+            return redirect(url_for('channels'))
+
     channels.append({'id': channel_id, 'name': channel_name})
     save_channels(channels)
 
-    flash(f'Added channel: {channel_name}', 'success')
+    flash(f'Added channel: {channel_name} ({channel_id})', 'success')
     return redirect(url_for('channels'))
 
 @app.route('/channels/delete/<int:index>')