import boto3
from botocore.exceptions import ClientError
import datetime

class SSMParameterStore(object):
    """
    Provide a dictionary-like interface to access AWS SSM Parameter Store
    """
    def __init__(self, prefix=None, ssm_client=None, ttl=None):
        self._prefix = (prefix or "").rstrip("/") + "/"
        self._client = ssm_client or boto3.client('ssm')
        self._keys = None
        self._substores = {}
        self._ttl = ttl
    
    def get(self, name, **kwargs):
        assert name, 'Name can not be empty'
        if self._keys is None:
            self.refresh()
        
        abs_key = "%s%s" % (self._prefix, name)
        if name not in self._keys:
            if 'default' in kwargs:
                return kwargs['default']
            
            raise KeyError(name)
        elif self._keys[name]['type'] == 'prefix':
            if abs_key not in self._substores:
                store = self.__class__(prefix=abs_key, ssm_client=self._client, ttl=self._ttl)
                self._substores[abs_key] = store
                
            return self._substores[abs_key]
        else:
            return self._get_value(name, abs_key)
    
    def refresh(self):
        self._keys = {}
        self._substores = {}
        responses = self._client.describe_parameters(
            ParameterFilters=[
                dict(Key="Path", Option="Recursive", Values=[self._prefix])
            ]
        )
        
        for p in responses[u'Parameters']:
            paths = p['Name'][len(self._prefix):].split('/')
            name = paths[0]
            
            # this is a prefix
            if len(paths) > 1:
                self._keys[name] = {'type': 'prefix'}
            else:
                self._keys[name] = {'type': 'parameter', 'expire': None}

    def keys(self):
        if self._keys is None:
            self.refresh()
            
        return self._keys.keys()
        
    def _get_value(self, name, abs_key):
        entry = self._keys[name]

        # simple ttl
        if self._ttl == False or (entry['expire'] and entry['expire'] <= datetime.datetime.now()):
            entry.pop('value', None)
        
        if 'value' not in entry:
            parameter = self._client.get_parameter(Name=abs_key, WithDecryption=True)['Parameter']
            value = parameter['Value']
            if parameter['Type'] == 'StringList':
                value = value.split(",")

            entry['value'] = value
            
            if self._ttl:
                entry['expire'] = datetime.datetime.now() + datetime.timedelta(seconds=self._ttl)
            else:
                entry['expire'] = None

        return entry['value']
        
    def __contains__(self, name):
        try:
            self.get(name)
            return True
        except:
            return False

    def __getitem__(self, name):
        return self.get(name)

    def __setitem__(self, key, value):
        raise NotImplementedError()
    
    def __delitem__(self, name):
        raise NotImplementedError()
        
    def __repr__(self):
        return 'ParameterStore[%s]' % self._prefix