"""Dice rolling operations (outside of the lex/yacc roller)."""
import random

import numexpr

rand = random.SystemRandom()


def cypher_roll(difficulty=None, mods=0):
    """Make a Cypher System roll.

    Args:
        difficulty: the original difficulty to beat; if provided, success or failure is indicated in the results
        mods: eases(-) and hindrances(+) to apply to the check, as a string (e.g. '-3+1')
    Returns:
        tuple of:
            - the result on the d20
            - the highest difficulty beaten
            - if the difficulty is known, if the target was beat
            - miscellaneous effects
    """
    roll = rand.randint(1, 20)
    if roll == 1:
        return (roll, None, False if difficulty else None, 'a GM intrusion')

    effect = None
    if roll == 17:
        effect = '+1 damage'
    elif roll == 18:
        effect = '+2 damage'
    elif roll == 19:
        effect = 'a minor effect'
    elif roll == 20:
        effect = 'a MAJOR EFFECT'

    # if we know the difficulty, the mods would adjust the difficulty, but for the case where we don't,
    # and maybe just in general, it's easier to modify the difficulty that the roll beats, so we flip the logic
    # if incoming eases are a negative number, they should add to the difficulty the roll beats
    beats = (roll // 3) - (numexpr.evaluate(mods).item() if mods else 0)
    beats = 0 if beats < 0 else beats
    return (roll, beats, difficulty <= beats if difficulty else None, effect)