class DependencyManager:
    def __init__(self):
        self.dependencies = {}
        self.logger = self._initialize_logger()
        
    def _initialize_logger(self):
        import logging
        logger = logging.getLogger(__name__)
        logger.setLevel(logging.INFO)
        formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')
        handler = logging.StreamHandler()
        handler.setFormatter(formatter)
        logger.addHandler(handler)
        return logger

    def add_dependency(self, package_name, version=None):
        """Add a new dependency to the manager."""
        if package_name in self.dependencies:
            self.logger.error(f"Dependency '{package_name}' already exists.")
            raise ValueError(f"Duplicate dependency: {package_name}")
        try:
            # Simulate adding a package using pip
            self.logger.info(f"Adding dependency: {package_name}=={version or 'latest'}")
            self.dependencies[package_name] = version or "latest"
            return True
        except Exception as e:
            self.logger.error(f"Failed to add dependency '{package_name}': {str(e)}")
            raise

    def resolve_dependencies(self, requirements_file):
        """Resolve and install dependencies from a requirements file."""
        try:
            with open(requirements_file, 'r') as f:
                packages = f.read().splitlines()
            for package in packages:
                name, _, version = package.partition('==')
                if not version:
                    version = "latest"
                self.add_dependency(name.strip(), version.strip())
            self.logger.info("Dependencies resolved successfully.")
            return True
        except FileNotFoundError:
            self.logger.error(f"Requirements file '{requirements_file}' not found.")
            raise FileNotFoundError(f"File '{requirements_file}' does not exist.")
        except Exception as e:
            self.logger.error(f"Failed to resolve dependencies: {str(e)}")
            raise

    def update_dependency(self, package_name):
        """Update an existing dependency to the latest version."""
        if package_name not in self.dependencies:
            self.logger.error(f"Dependency '{package_name}' not found.")
            raise ValueError(f"Dependency '{package_name}' does not exist.")
        try:
            # Simulate updating a package using pip
            current_version = self.dependencies[package_name]
            new_version = "latest"
            if current_version != new_version:
                self.logger.info(f"Updating dependency '{package_name}' to latest version.")
                self.dependencies[package_name] = new_version
            else:
                self.logger.info(f"Dependency '{package_name}' is already up-to-date.")
            return True
        except Exception as e:
            self.logger.error(f"Failed to update dependency '{package_name}': {str(e)}")
            raise

    def remove_dependency(self, package_name):
        """Remove a dependency."""
        if package_name not in self.dependencies:
            self.logger.warning(f"Dependency '{package_name}' not found. Nothing to remove.")
            return False
        try:
            # Simulate removing a package using pip
            self.logger.info(f"Removing dependency '{package_name}'.")
            del self.dependencies[package_name]
            return True
        except Exception as e:
            self.logger.error(f"Failed to remove dependency '{package_name}': {str(e)}")
            raise

    def list_dependencies(self):
        """List all installed dependencies with versions."""
        if not self.dependencies:
            self.logger.info("No dependencies are currently managed.")
            return []
        self.logger.info("Current dependencies:")
        for package, version in self.dependencies.items():
            self.logger.info(f"- {package}=={version}")
        return self.dependencies.copy()