naive_parser.py

# -*- coding: utf-8 -*-

import functools
import operator
from typing import Optional

ANY = object()


class regex:
    """ super stupid regex class for equality checking
    """
    def __init__(self, ptn):
        self.ptn = ptn

    def __repr__(self):
        return f"/{self.ptn}/"

    def __eq__(self, o):
        return self.ptn == o


cases = [
    (
        "nomad.scale",
        {"action": "nomad.scale", "params": {}},
    ),
    (
        "nomad.scale{}",
        {"action": "nomad.scale", "params": {}},
    ),
    (
        "nomad.scale{region=/us-(east|west)-[12]/}",
        {"action": "nomad.scale", "params": {
            "region": regex("us-(east|west)-[12]"),
        }}
    ),
    (
        "nomad.scale{region=*, service=\"usage\"}",
        {"action": "nomad.scale", "params": {
            "region": ANY, "service": "usage",
        }}
    ),
    (
        "nomad.scale {}",
        {"action": "nomad.scale", "params": {}},
    ),
    (
        "nomad.scale { region=* ,   service=*  } ",
        {"action": "nomad.scale", "params": {
            "region": ANY, "service": ANY,
        }}
    ),
    (
        "nomad.scale { region=*",
        Exception,
    ),
    (
        "nomad.scale{regions=[us-east-1,us-west-2], service=\"usage\"}",
        {"action": "nomad.scale", "params": {
            "regions": ["us-east-1", "us-west-2"], "service": "usage",
        }}
    ),
    (
        "nomad.scale { service=\"usage\" , region=* }",
        {"action": "nomad.scale", "params": {
            "service": "usage", "region": ANY,
        }}
    )
]


def parse(spec: str) -> dict:
    """ Parses an action specifier string into dictionary representation
    """

    try:
        params_start = spec.index("{")
    except ValueError:
        # This is just a plain action
        return {"action": spec, "params": {}}

    try:
        params_end = spec.rindex("}")
    except ValueError as err:
        # Missing ending brace
        raise Exception(f"Action spec is missing an ending brace: {spec=}") from err

    action = spec[:params_start].strip()
    params_str = spec[params_start+1:params_end].strip()

    params = {}
    while True:
        if not params_str:
            break

        key, rest = params_str.split("=", 1)
        key = key.strip()
        # Peek ahead to determine the value type
        if rest[0] == "/":
            rest = rest[1:]
            end = find_next_unescaped(rest, "/")
            if end is None:
                raise Exception(f"Unmatched `/` in spec: {spec=}")

            value = rest[:end]
            rest = rest[end+1:]
            value = regex(value)
        elif rest[0] == "[":
            rest = rest[1:]
            end = find_next_unescaped(rest, "]")
            if end is None:
                raise Exception(f"Unmatched `]` in spec: {spec=}")

            value = rest[:end]
            rest = rest[end+1:]
            value = value.split(",")
            value = [item.strip() for item in value]
        elif rest[0] == "\"":
            rest = rest[1:]
            end = find_next_unescaped(rest, "\"")
            if end is None:
                raise Exception(f"Unmatched `\"` in spec: {spec=}")

            value = rest[:end]
            rest = rest[end+1:]
        elif rest[0] == "*":
            rest = rest[1:]
            value = ANY

        if len(rest.strip()) > 1 and rest.strip()[0] == ",":
            rest = rest.strip()[1:].lstrip()

        params[key] = value
        params_str = rest

    return {
        "action": action,
        "params": params,
    }


def find_next_unescaped(haystack: str, needle: str) -> Optional[int]:
    escapes = 0

    for idx, char in enumerate(haystack):
        if char == needle and escapes % 2 == 0:
            return idx
        elif char == "\\":
            escapes += 1
        else:
            escapes = 0

    return None


def assertEq(value, expected):
    ok = "✔️"
    fail = "❌"

    if value == expected:
        print(f" {ok}\t{value=} == {expected=}")
    else:
        print(f" {fail}\t{value=} != {expected=}")


for test, expectation in cases:
    print(f" -> {test}")
    try:
        if issubclass(expectation, Exception):
            try:
                parse(test)
            except Exception as err:
                assertEq(isinstance(err, expectation), True)
        else:
            # wut
            raise "fuck"
    except TypeError:
        received = parse(test)
        assertEq(received, expectation)

test.txt

[sean:...ts/mailgun/director-chatops] λ python director_chatops/util/abac/naive.py                                                                                                                   ( ⇌ master ✱  ) (director-chatops)
 -> nomad.scale
 ✔️      value={'action': 'nomad.scale', 'params': {}} == expected={'action': 'nomad.scale', 'params': {}}
 -> nomad.scale{}
 ✔️      value={'action': 'nomad.scale', 'params': {}} == expected={'action': 'nomad.scale', 'params': {}}
 -> nomad.scale{region=/us-(east|west)-[12]/}
 ✔️      value={'action': 'nomad.scale', 'params': {'region': /us-(east|west)-[12]/}} == expected={'action': 'nomad.scale', 'params': {'region': /us-(east|west)-[12]/}}
 -> nomad.scale{region=*, service="usage"}
 ✔️      value={'action': 'nomad.scale', 'params': {'region': <object object at 0x10324eec0>, 'service': 'usage'}} == expected={'action': 'nomad.scale', 'params': {'region': <object object at 0x10324eec0>, 'service': 'usage'}}
 -> nomad.scale {}
 ✔️      value={'action': 'nomad.scale', 'params': {}} == expected={'action': 'nomad.scale', 'params': {}}
 -> nomad.scale { region=* ,   service=*  } 
 ✔️      value={'action': 'nomad.scale', 'params': {'region': <object object at 0x10324eec0>, 'service': <object object at 0x10324eec0>}} == expected={'action': 'nomad.scale', 'params': {'region': <object object at 0x10324eec0>, 'service': <object object at 0x10324eec0>}}
 -> nomad.scale { region=*
 ✔️      value=True == expected=True
 -> nomad.scale{regions=[us-east-1,us-west-2], service="usage"}
 ✔️      value={'action': 'nomad.scale', 'params': {'regions': ['us-east-1', 'us-west-2'], 'service': 'usage'}} == expected={'action': 'nomad.scale', 'params': {'regions': ['us-east-1', 'us-west-2'], 'service': 'usage'}}
 -> nomad.scale { service="usage" , region=* }
 ✔️      value={'action': 'nomad.scale', 'params': {'service': 'usage', 'region': <object object at 0x10324eec0>}} == expected={'action': 'nomad.scale', 'params': {'service': 'usage', 'region': <object object at 0x10324eec0>}}