#!/usr/bin/env python3
"""
Requirements Version Verifier
This script checks if all packages and versions in a requirements.txt file actually exist on PyPI.
It helps prevent runtime errors from non-existent package versions.
"""

import sys
import requests
import re
from typing import List, Tuple, Dict
import json

def parse_requirements(requirements_text: str) -> List[Tuple[str, str]]:
    """Parse requirements.txt content and extract package names and versions."""
    packages = []
    for line in requirements_text.strip().split('\n'):
        line = line.strip()
        # Skip comments and empty lines
        if not line or line.startswith('#') or line.startswith('=='):
            continue
        
        # Extract package name and version
        if '==' in line:
            parts = line.split('==')
            if len(parts) == 2:
                package_name = parts[0].strip()
                version = parts[1].strip()
                packages.append((package_name, version))
        elif '>=' in line or '<=' in line or '~=' in line:
            # Handle other version specifiers
            match = re.match(r'^([a-zA-Z0-9-_.]+)\s*([><=~]+)\s*([\d.]+.*)', line)
            if match:
                package_name = match.group(1)
                operator = match.group(2)
                version = match.group(3)
                packages.append((package_name, f"{operator}{version}"))
    
    return packages

def check_package_version(package_name: str, version: str) -> Dict[str, any]:
    """Check if a specific package version exists on PyPI."""
    try:
        # Get package info from PyPI
        response = requests.get(f"https://pypi.org/pypi/{package_name}/json", timeout=10)
        
        if response.status_code == 404:
            return {
                "exists": False,
                "error": "Package not found on PyPI",
                "available_versions": []
            }
        
        if response.status_code != 200:
            return {
                "exists": False,
                "error": f"HTTP {response.status_code}: {response.reason}",
                "available_versions": []
            }
        
        data = response.json()
        available_versions = list(data.get("releases", {}).keys())
        
        # Check if the specific version exists
        if version.startswith('=='):
            version_check = version[2:]
        else:
            version_check = version
            
        if version_check in available_versions:
            return {
                "exists": True,
                "available_versions": sorted(available_versions, reverse=True)[:10]  # Show latest 10
            }
        else:
            return {
                "exists": False,
                "error": f"Version {version_check} not found",
                "available_versions": sorted(available_versions, reverse=True)[:10]
            }
            
    except requests.exceptions.RequestException as e:
        return {
            "exists": False,
            "error": f"Network error: {str(e)}",
            "available_versions": []
        }
    except json.JSONDecodeError:
        return {
            "exists": False,
            "error": "Invalid response from PyPI",
            "available_versions": []
        }

def verify_requirements(requirements_text: str) -> Dict[str, any]:
    """Verify all packages in requirements text."""
    packages = parse_requirements(requirements_text)
    results = {
        "total": len(packages),
        "valid": 0,
        "invalid": 0,
        "errors": []
    }
    
    print(f"Checking {len(packages)} packages...")
    print("-" * 70)
    
    for package_name, version in packages:
        result = check_package_version(package_name, version)
        
        if result["exists"]:
            results["valid"] += 1
            print(f"✅ {package_name}=={version}")
        else:
            results["invalid"] += 1
            error_info = {
                "package": package_name,
                "version": version,
                "error": result["error"],
                "available_versions": result["available_versions"][:5]  # Show top 5
            }
            results["errors"].append(error_info)
            
            print(f"❌ {package_name}=={version}")
            print(f"   Error: {result['error']}")
            if result["available_versions"]:
                print(f"   Available versions: {', '.join(result['available_versions'][:5])}")
            print()
    
    return results

def suggest_fixes(errors: List[Dict]) -> None:
    """Suggest fixes for invalid packages."""
    if not errors:
        return
        
    print("\n" + "=" * 70)
    print("SUGGESTED FIXES:")
    print("=" * 70)
    
    for error in errors:
        package = error["package"]
        requested_version = error["version"]
        available = error["available_versions"]
        
        print(f"\n{package}=={requested_version}")
        
        if available:
            # Find the closest available version
            if requested_version.replace('==', '') in [v.split('rc')[0].split('b')[0].split('a')[0] for v in available]:
                # Pre-release version might exist
                print(f"  → Try: {package}=={available[0]}")
            else:
                # Suggest the latest stable version
                stable_versions = [v for v in available if not any(x in v for x in ['rc', 'a', 'b', 'dev'])]
                if stable_versions:
                    print(f"  → Try: {package}=={stable_versions[0]}")
                else:
                    print(f"  → Try: {package}=={available[0]}")
        else:
            print(f"  → Package might not exist. Check the package name.")

def main():
    """Main function to verify requirements file."""
    if len(sys.argv) > 1:
        # Read from file
        filename = sys.argv[1]
        try:
            with open(filename, 'r') as f:
                requirements_text = f.read()
        except FileNotFoundError:
            print(f"Error: File '{filename}' not found")
            sys.exit(1)
    else:
        # Read from stdin or use the example
        print("Paste your requirements.txt content (press Ctrl+D when done):")
        try:
            requirements_text = sys.stdin.read()
        except KeyboardInterrupt:
            print("\nCancelled")
            sys.exit(0)
    
    results = verify_requirements(requirements_text)
    
    print("\n" + "=" * 70)
    print("SUMMARY:")
    print("=" * 70)
    print(f"Total packages: {results['total']}")
    print(f"Valid packages: {results['valid']} ✅")
    print(f"Invalid packages: {results['invalid']} ❌")
    
    if results["errors"]:
        suggest_fixes(results["errors"])
        sys.exit(1)
    else:
        print("\nAll packages and versions are valid! 🎉")
        sys.exit(0)

if __name__ == "__main__":
    main()