#!/usr/bin/env python

# Imported from https://github.com/logandk/serverless-wsgi/blob/master/serverless_wsgi.py
# Copyright (c) 2016 Logan Raarup
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
import base64
import os
import sys
from io import BytesIO

from werkzeug.datastructures import Headers, MultiDict, iter_multi_items
from werkzeug.http import HTTP_STATUS_CODES
from werkzeug.urls import url_encode, url_unquote, url_unquote_plus
from werkzeug.wrappers import Response

# List of MIME types that should not be base64 encoded. MIME types within `text/*`
# are included by default.
TEXT_MIME_TYPES = [
    "application/json",
    "application/javascript",
    "application/xml",
    "application/vnd.api+json",
    "image/svg+xml",
]


def all_casings(input_string):
    """
    Permute all casings of a given string.
    A pretty algoritm, via @Amber
    http://stackoverflow.com/questions/6792803/finding-all-possible-case-permutations-in-python
    """
    if not input_string:
        yield ""
    else:
        first = input_string[:1]
        if first.lower() == first.upper():
            for sub_casing in all_casings(input_string[1:]):
                yield first + sub_casing
        else:
            for sub_casing in all_casings(input_string[1:]):
                yield first.lower() + sub_casing
                yield first.upper() + sub_casing


def split_headers(headers):
    """
    If there are multiple occurrences of headers, create case-mutated variations
    in order to pass them through APIGW. This is a hack that's currently
    needed. See: https://github.com/logandk/serverless-wsgi/issues/11
    Source: https://github.com/Miserlou/Zappa/blob/master/zappa/middleware.py
    """
    new_headers = {}

    for key in headers.keys():
        values = headers.get_all(key)
        if len(values) > 1:
            for value, casing in zip(values, all_casings(key)):
                new_headers[casing] = value
        elif len(values) == 1:
            new_headers[key] = values[0]

    return new_headers


def group_headers(headers):
    new_headers = {}

    for key in headers.keys():
        new_headers[key] = headers.get_all(key)

    return new_headers


def is_alb_event(event):
    return event.get("requestContext", {}).get("elb")


def encode_query_string(event):
    params = event.get(u"multiValueQueryStringParameters")
    if not params:
        params = event.get(u"queryStringParameters")
    if not params:
        params = ""
    if is_alb_event(event):
        params = MultiDict((url_unquote_plus(k), url_unquote_plus(v)) for k, v in iter_multi_items(params))
    return url_encode(params)


def get_script_name(headers, request_context):
    strip_stage_path = os.environ.get("STRIP_STAGE_PATH", "").lower().strip() in ["yes", "y", "true", "t", "1"]

    if u"amazonaws.com" in headers.get(u"Host", u"") and not strip_stage_path:
        script_name = "/{}".format(request_context.get(u"stage", ""))
    else:
        script_name = ""
    return script_name


def get_body_bytes(event, body):
    if event.get("isBase64Encoded", False):
        body = base64.b64decode(body)
    if isinstance(body, str):
        body = body.encode(encoding="utf-8", errors="strict")
    return body


def setup_environ_items(environ, headers):
    for key, value in environ.items():
        if isinstance(value, str):
            environ[key] = value.encode("utf-8").decode("latin1", "replace")

    for key, value in headers.items():
        key = "HTTP_" + key.upper().replace("-", "_")
        if key not in ("HTTP_CONTENT_TYPE", "HTTP_CONTENT_LENGTH"):
            environ[key] = value
    return environ


def generate_response(response, event):
    returndict = {u"statusCode": response.status_code}

    if u"multiValueHeaders" in event:
        returndict[u"multiValueHeaders"] = group_headers(response.headers)
    else:
        returndict[u"headers"] = split_headers(response.headers)

    if is_alb_event(event):
        # If the request comes from ALB we need to add a status description
        returndict["statusDescription"] = u"%d %s" % (response.status_code, HTTP_STATUS_CODES[response.status_code])

    if response.data:
        mimetype = response.mimetype or "text/plain"
        if (mimetype.startswith("text/") or mimetype in TEXT_MIME_TYPES) and not response.headers.get(
            "Content-Encoding", ""
        ):
            returndict["body"] = response.get_data(as_text=True)
            returndict["isBase64Encoded"] = False
        else:
            returndict["body"] = base64.b64encode(response.data).decode("utf-8")
            returndict["isBase64Encoded"] = True

    return returndict


def handle_request(app, event, context):
    if event.get("source") in ["aws.events", "serverless-plugin-warmup"]:
        #  Lambda warming event received, skipping handler
        return {}

    if event.get("version") == "2.0":
        return handle_payload_v2(app, event, context)

    return handle_payload_v1(app, event, context)


def handle_payload_v1(app, event, context):
    if u"multiValueHeaders" in event:
        headers = Headers(event[u"multiValueHeaders"])
    else:
        headers = Headers(event[u"headers"])

    script_name = get_script_name(headers, event.get("requestContext", {}))

    # If a user is using a custom domain on API Gateway, they may have a base
    # path in their URL. This allows us to strip it out via an optional
    # environment variable.
    path_info = event[u"path"]
    base_path = os.environ.get("API_GATEWAY_BASE_PATH")
    if base_path:
        script_name = "/" + base_path

        if path_info.startswith(script_name):
            path_info = path_info[len(script_name) :]  # noqa: E203

    body = event[u"body"] or ""
    body = get_body_bytes(event, body)

    environ = {
        "CONTENT_LENGTH": str(len(body)),
        "CONTENT_TYPE": headers.get(u"Content-Type", ""),
        "PATH_INFO": url_unquote(path_info),
        "QUERY_STRING": encode_query_string(event),
        "REMOTE_ADDR": event.get(u"requestContext", {}).get(u"identity", {}).get(u"sourceIp", ""),
        "REMOTE_USER": event.get(u"requestContext", {}).get(u"authorizer", {}).get(u"principalId", ""),
        "REQUEST_METHOD": event.get(u"httpMethod", {}),
        "SCRIPT_NAME": script_name,
        "SERVER_NAME": headers.get(u"Host", "lambda"),
        "SERVER_PORT": headers.get(u"X-Forwarded-Port", "80"),
        "SERVER_PROTOCOL": "HTTP/1.1",
        "wsgi.errors": sys.stderr,
        "wsgi.input": BytesIO(body),
        "wsgi.multiprocess": False,
        "wsgi.multithread": False,
        "wsgi.run_once": False,
        "wsgi.url_scheme": headers.get(u"X-Forwarded-Proto", "http"),
        "wsgi.version": (1, 0),
        "serverless.authorizer": event.get(u"requestContext", {}).get(u"authorizer"),
        "serverless.event": event,
        "serverless.context": context,
        # TODO: Deprecate the following entries, as they do not comply with the WSGI
        # spec. For custom variables, the spec says:
        #
        #  Finally, the environ dictionary may also contain server-defined variables.
        #  These variables should be named using only lower-case letters, numbers, dots,
        #  and underscores, and should be prefixed with a name that is unique to the
        #  defining server or gateway.
        "API_GATEWAY_AUTHORIZER": event.get(u"requestContext", {}).get(u"authorizer"),
        "event": event,
        "context": context,
    }

    environ = setup_environ_items(environ, headers)

    response = Response.from_app(app, environ)
    returndict = generate_response(response, event)

    return returndict


def handle_payload_v2(app, event, context):
    headers = Headers(event[u"headers"])

    script_name = get_script_name(headers, event.get("requestContext", {}))

    path_info = event[u"rawPath"]

    body = event.get("body", "")
    body = get_body_bytes(event, body)

    headers["Cookie"] = "; ".join(event.get("cookies", []))

    environ = {
        "CONTENT_LENGTH": str(len(body)),
        "CONTENT_TYPE": headers.get(u"Content-Type", ""),
        "PATH_INFO": url_unquote(path_info),
        "QUERY_STRING": url_encode(event.get(u"queryStringParameters", {})),
        "REMOTE_ADDR": event.get("requestContext", {}).get(u"http", {}).get(u"sourceIp", ""),
        "REMOTE_USER": event.get("requestContext", {}).get(u"authorizer", {}).get(u"principalId", ""),
        "REQUEST_METHOD": event.get("requestContext", {}).get("http", {}).get("method", ""),
        "SCRIPT_NAME": script_name,
        "SERVER_NAME": headers.get(u"Host", "lambda"),
        "SERVER_PORT": headers.get(u"X-Forwarded-Port", "80"),
        "SERVER_PROTOCOL": "HTTP/1.1",
        "wsgi.errors": sys.stderr,
        "wsgi.input": BytesIO(body),
        "wsgi.multiprocess": False,
        "wsgi.multithread": False,
        "wsgi.run_once": False,
        "wsgi.url_scheme": headers.get(u"X-Forwarded-Proto", "http"),
        "wsgi.version": (1, 0),
        "serverless.authorizer": event.get("requestContext", {}).get(u"authorizer"),
        "serverless.event": event,
        "serverless.context": context,
        # TODO: Deprecate the following entries, as they do not comply with the WSGI
        # spec. For custom variables, the spec says:
        #
        #  Finally, the environ dictionary may also contain server-defined variables.
        #  These variables should be named using only lower-case letters, numbers, dots,
        #  and underscores, and should be prefixed with a name that is unique to the
        #  defining server or gateway.
        "API_GATEWAY_AUTHORIZER": event.get("requestContext", {}).get(u"authorizer"),
        "event": event,
        "context": context,
    }

    environ = setup_environ_items(environ, headers)

    response = Response.from_app(app, environ)

    returndict = generate_response(response, event)

    return returndict