Feature Flag Management System in Python

Feature flags (also known as feature toggles) are a powerful technique for enabling or disabling features in your application without deploying new code. This challenge asks you to implement a basic feature flag management system in Python, allowing you to control feature availability based on a configuration. This is useful for A/B testing, gradual rollouts, and emergency feature disabling.

Problem Description

You need to create a FeatureFlagManager class that handles feature flag configurations and provides a method to check if a feature is enabled for a given user. The configuration will be stored in a dictionary where keys are feature flag names (strings) and values are dictionaries containing the flag's status ("enabled" or "disabled") and optionally, a list of user IDs for whom the feature is specifically enabled.

The check_feature method should return True if the feature is enabled for the given user, and False otherwise. The logic should follow these rules:

1. Default State: If a feature flag is not present in the configuration, it should be considered disabled.
2. Explicit Enable/Disable: If a feature flag exists, its enabled status dictates its state.
3. User-Specific Enable: If a feature flag has a user_ids list, the feature is enabled only for users present in that list. If the user is not in the list, the enabled status in the configuration dictates the state.
4. Case-Insensitive User ID Matching: User ID matching should be case-insensitive.

Examples

Example 1:

Input:
config = {
    "new_feature": {"enabled": True, "user_ids": ["user1", "user2"]},
    "old_feature": {"enabled": False}
}
user_id = "user1"

Output: True
Explanation: "new_feature" is enabled and "user1" is in the user_ids list.

Example 2:

Input:
config = {
    "new_feature": {"enabled": True, "user_ids": ["user1", "user2"]},
    "old_feature": {"enabled": False}
}
user_id = "user3"

Output: False
Explanation: "new_feature" is enabled, but "user3" is not in the user_ids list, so the default enabled status is checked.

Example 3:

Input:
config = {
    "new_feature": {"enabled": True, "user_ids": ["user1", "user2"]},
    "old_feature": {"enabled": False}
}
user_id = "USER1"

Output: True
Explanation: User ID matching is case-insensitive.

Example 4:

Input:
config = {}
user_id = "any_user"

Output: False
Explanation: The feature flag "any_feature" does not exist in the configuration, so it's considered disabled.

Constraints

• The config dictionary will contain strings as keys (feature flag names) and dictionaries as values.
• The inner dictionaries will contain keys "enabled" (boolean) and optionally "user_ids" (list of strings).
• user_ids will be a list of strings, or an empty list.
• enabled will always be a boolean.
• The user_id will be a string.
• The solution should be reasonably efficient for a small number of feature flags (less than 100). Performance is not a primary concern for this challenge.

Notes

• Consider using a class to encapsulate the feature flag management logic.
• Think about how to handle cases where the configuration is missing or invalid. For simplicity, you can assume the configuration is always valid in this challenge.
• Focus on clear and readable code.
• The enabled status in the configuration is a boolean value (True or False).
• User ID matching should be case-insensitive.