PolicyEvaluation

PolicyEvaluation is a small library for parsing logical expressions containing policy names, to evaluate if the expression passes or fails. The policy evaluation itself is provided externally (through a delegate); the main job of this library is to evaluate the policies in the context of a logical expression.

A few sample expressions (where Policy1, Policy2, Policy3 and Policy4 are policy names):

• Policy1 AND Policy2
• Policy1 OR Policy2
• Policy1 AND (Policy2 OR Policy3)
• (Policy1 AND Policy2) OR Policy3
• (Policy1 OR Policy2) AND (Policy3 OR Policy4)

Rules for expressions:

• Policy names should start with a letter, followed by alphanumeric characters and underscores.
• Only AND and OR logical operators are allowed, and they are case-sensitive.
• Nesting is allowed using parentheses. Only one level of nesting is allowed.

Installation

Via Package Manager:

PM> Install-Package Jeevan.PolicyEvaluation

Via dotnet CLI:

dotnet add package Jeevan.PolicyEvaluation

dotnet add <project> package Jeevan.PolicyEvaluation

Usage

// Import the namespace Jeevan.PolicyEvaluation
using Jeevan.PolicyEvaluation;

// Declare a function to evaluate a policy, given its name.
Func<string, IPolicyOutcome> policyEvaluatorLogic = policyName =>
{
    // Perform policy evaluation here.
    // Use methods from PolicyOutcome to generate the result.
};

// Instantiate the PolicyEvaluator class
PolicyEvaluator evaluator = new(policyEvaluatorLogic);

// Call the EvaluateExpression method to evaluate an expression.
const string expression = "Policy1 AND (Policy2 OR Policy3)";
var result = evaluator.EvaluateExpression(expression);

// You can check whether the expression was satisfied.
if (result.IsSatisfied)
    Console.WriteLine("Expression was satisfied.");

// OR you can check whether the expression was not satisfied and get the reason and which policy
// caused the expression to fail.
if (result.IsNotSatisfied(out string? policyName, out string? failureMessage))
    Console.WriteLine($"Policy {policyName} failed with error {failureMessage}.");