import boto3
import os
from contextlib import closing
from boto3.dynamodb.conditions import Key, Attr

def lambda_handler(event, context):

    postId = event["Records"][0]["Sns"]["Message"]
    
    print "Text to Speech function. Post ID in DynamoDB: " + postId
    
    #Retrieving information about the post from DynamoDB table
    dynamodb = boto3.resource('dynamodb')
    table = dynamodb.Table(os.environ['DB_TABLE_NAME'])
    postItem = table.query(
        KeyConditionExpression=Key('id').eq(postId)
    )
    

    text = postItem["Items"][0]["text"]
    voice = postItem["Items"][0]["voice"] 
    
    rest = text
    
    #Because single invocation of the polly synthesize_speech api can 
    # transform text with about 1,500 characters, we are dividing the 
    # post into blocks of approximately 1,000 characters.
    textBlocks = []
    while (len(rest) > 1100):
        begin = 0
        end = rest.find(".", 1000)

        if (end == -1):
            end = rest.find(" ", 1000)
            
        textBlock = rest[begin:end]
        rest = rest[end:]
        textBlocks.append(textBlock)
    textBlocks.append(rest)            

    #For each block, invoke Polly API, which will transform text into audio
    polly = boto3.client('polly')
    for textBlock in textBlocks: 
        response = polly.synthesize_speech(
            OutputFormat='mp3',
            Text = textBlock,
            VoiceId = voice
        )
        
        #Save the audio stream returned by Amazon Polly on Lambda's temp 
        # directory. If there are multiple text blocks, the audio stream
        # will be combined into a single file.
        if "AudioStream" in response:
            with closing(response["AudioStream"]) as stream:
                output = os.path.join("/tmp/", postId)
                with open(output, "a") as file:
                    file.write(stream.read())



    s3 = boto3.client('s3')
    s3.upload_file('/tmp/' + postId, 
      os.environ['BUCKET_NAME'], 
      postId + ".mp3")
    s3.put_object_acl(ACL='public-read', 
      Bucket=os.environ['BUCKET_NAME'], 
      Key= postId + ".mp3")

    location = s3.get_bucket_location(Bucket=os.environ['BUCKET_NAME'])
    region = location['LocationConstraint']
    
    if region is None:
        url_begining = "https://s3.amazonaws.com/"
    else:
        url_begining = "https://s3-" + str(region) + ".amazonaws.com/" \
    
    url = url_begining \
            + str(os.environ['BUCKET_NAME']) \
            + "/" \
            + str(postId) \
            + ".mp3"

    #Updating the item in DynamoDB
    response = table.update_item(
        Key={'id':postId},
          UpdateExpression=
            "SET #statusAtt = :statusValue, #urlAtt = :urlValue",                   
          ExpressionAttributeValues=
            {':statusValue': 'UPDATED', ':urlValue': url},
        ExpressionAttributeNames=
          {'#statusAtt': 'status', '#urlAtt': 'url'},
    )
        
    return