import re
import time
import pprint
import json


class HttpVerb:
    GET     = "GET"
    POST    = "POST"
    PUT     = "PUT"
    PATCH   = "PATCH"
    HEAD    = "HEAD"
    DELETE  = "DELETE"
    OPTIONS = "OPTIONS"
    ALL     = "*"


class AuthPolicy(object):
    awsAccountId = ""
    """The AWS account id the policy will be generated for. This is used to create the method ARNs."""
    principalId = ""
    """The principal used for the policy, this should be a unique identifier for the end user."""
    version = "2012-10-17"
    """The policy version used for the evaluation. This should always be '2012-10-17'"""
    pathRegex = "^[/.a-zA-Z0-9-\*]+$"
    """The regular expression used to validate resource paths for the policy"""

    """these are the internal lists of allowed and denied methods. These are lists
    of objects and each object has 2 properties: A resource ARN and a nullable
    conditions statement.
    the build method processes these lists and generates the approriate
    statements for the final policy"""
    allowMethods = []
    denyMethods = []

    restApiId = "*"
    """The API Gateway API id. By default this is set to '*'"""
    region = "*"
    """The region where the API is deployed. By default this is set to '*'"""
    stage = "*"
    """The name of the stage used in the policy. By default this is set to '*'"""

    def __init__(self, principal, awsAccountId):
        self.awsAccountId = awsAccountId
        self.principalId = principal
        self.allowMethods = []
        self.denyMethods = []

    def _addMethod(self, effect, verb, resource, conditions):
        """Adds a method to the internal lists of allowed or denied methods. Each object in
        the internal list contains a resource ARN and a condition statement. The condition
        statement can be null."""
        if verb != "*" and not hasattr(HttpVerb, verb):
            raise NameError("Invalid HTTP verb " + verb + ". Allowed verbs in HttpVerb class")
        resourcePattern = re.compile(self.pathRegex)
        if not resourcePattern.match(resource):
            raise NameError("Invalid resource path: " + resource + ". Path should match " + self.pathRegex)

        if resource[:1] == "/":
            resource = resource[1:]

        resourceArn = ("arn:aws:execute-api:" +
            self.region + ":" +
            self.awsAccountId + ":" +
            self.restApiId + "/" +
            self.stage + "/" +
            verb + "/" +
            resource)

        if effect.lower() == "allow":
            self.allowMethods.append({
                'resourceArn' : resourceArn,
                'conditions' : conditions
            })
        elif effect.lower() == "deny":
            self.denyMethods.append({
                'resourceArn' : resourceArn,
                'conditions' : conditions
            })

    def _getEmptyStatement(self, effect):
        """Returns an empty statement object prepopulated with the correct action and the
        desired effect."""
        statement = {
            'Action': 'execute-api:Invoke',
            'Effect': effect[:1].upper() + effect[1:].lower(),
            'Resource': []
        }

        return statement

    def _getStatementForEffect(self, effect, methods):
        """This function loops over an array of objects containing a resourceArn and
        conditions statement and generates the array of statements for the policy."""
        statements = []

        if len(methods) > 0:
            statement = self._getEmptyStatement(effect)

            for curMethod in methods:
                if curMethod['conditions'] is None or len(curMethod['conditions']) == 0:
                    statement['Resource'].append(curMethod['resourceArn'])
                else:
                    conditionalStatement = self._getEmptyStatement(effect)
                    conditionalStatement['Resource'].append(curMethod['resourceArn'])
                    conditionalStatement['Condition'] = curMethod['conditions']
                    statements.append(conditionalStatement)

            statements.append(statement)

        return statements

    def allowAllMethods(self):
        """Adds a '*' allow to the policy to authorize access to all methods of an API"""
        self._addMethod("Allow", HttpVerb.ALL, "*", [])

    def denyAllMethods(self):
        """Adds a '*' allow to the policy to deny access to all methods of an API"""
        self._addMethod("Deny", HttpVerb.ALL, "*", [])

    def allowMethod(self, verb, resource):
        """Adds an API Gateway method (Http verb + Resource path) to the list of allowed
        methods for the policy"""
        self._addMethod("Allow", verb, resource, [])

    def denyMethod(self, verb, resource):
        """Adds an API Gateway method (Http verb + Resource path) to the list of denied
        methods for the policy"""
        self._addMethod("Deny", verb, resource, [])

    def allowMethodWithConditions(self, verb, resource, conditions):
        """Adds an API Gateway method (Http verb + Resource path) to the list of allowed
        methods and includes a condition for the policy statement. More on AWS policy
        conditions here: http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html#Condition"""
        self._addMethod("Allow", verb, resource, conditions)

    def denyMethodWithConditions(self, verb, resource, conditions):
        """Adds an API Gateway method (Http verb + Resource path) to the list of denied
        methods and includes a condition for the policy statement. More on AWS policy
        conditions here: http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html#Condition"""
        self._addMethod("Deny", verb, resource, conditions)

    def build(self):
        """Generates the policy document based on the internal lists of allowed and denied
        conditions. This will generate a policy with two main statements for the effect:
        one statement for Allow and one statement for Deny.
        Methods that includes conditions will have their own statement in the policy."""
        if ((self.allowMethods is None or len(self.allowMethods) == 0) and
            (self.denyMethods is None or len(self.denyMethods) == 0)):
            raise NameError("No statements defined for the policy")

        policy = {
            'principalId' : self.principalId,
            'policyDocument' : {
                'Version' : self.version,
                'Statement' : []
            }
        }

        policy['policyDocument']['Statement'].extend(self._getStatementForEffect("Allow", self.allowMethods))
        policy['policyDocument']['Statement'].extend(self._getStatementForEffect("Deny", self.denyMethods))

        return policy