"""Validation and unit conversion for command-line resource options."""

from __future__ import annotations

import math
import re
from decimal import Decimal, InvalidOperation

from .errors import ValidationError


_RAM_PATTERN = re.compile(r"\s*(\d+(?:\.\d+)?)\s*([BKMG]i?B?)?\s*", re.IGNORECASE)
_USERNAME_PATTERN = re.compile(r"[a-z_][a-z0-9_-]{0,31}\$?")
_MIB_FACTORS = {
    "b": Decimal(1) / Decimal(1024 * 1024),
    "k": Decimal(1) / Decimal(1024),
    "kb": Decimal(1) / Decimal(1024),
    "ki": Decimal(1) / Decimal(1024),
    "kib": Decimal(1) / Decimal(1024),
    "m": Decimal(1),
    "mb": Decimal(1),
    "mi": Decimal(1),
    "mib": Decimal(1),
    "g": Decimal(1024),
    "gb": Decimal(1024),
    "gi": Decimal(1024),
    "gib": Decimal(1024),
}


def parse_ram(value: str) -> int:
    """Parse a MiB-default RAM value, including B/K/M/G suffixes."""

    match = _RAM_PATTERN.fullmatch(value)
    if not match:
        raise ValidationError(f"invalid RAM value: {value}")

    try:
        amount = Decimal(match.group(1))
    except InvalidOperation as error:
        raise ValidationError(f"invalid RAM value: {value}") from error

    unit = (match.group(2) or "MiB").lower()
    mib = int(amount * _MIB_FACTORS[unit])
    if mib < 128:
        raise ValidationError("RAM must be at least 128 MiB")
    return mib


def parse_cpu(value: str) -> float:
    """Parse a positive finite CPU capacity request."""

    try:
        cpu = float(value)
    except ValueError as error:
        raise ValidationError(f"invalid CPU value: {value}") from error

    if not math.isfinite(cpu) or cpu <= 0:
        raise ValidationError("CPU must be a finite value greater than 0")
    return cpu


def parse_username(value: str) -> str:
    """Validate a conventional Linux account name."""

    if not _USERNAME_PATTERN.fullmatch(value):
        raise ValidationError(
            "username must start with a lowercase letter or underscore and contain "
            "at most 32 lowercase letters, digits, underscores, or hyphens"
        )
    return value


def parse_password(value: str) -> str:
    """Validate a guest password without including it in error messages."""

    if not value:
        raise ValidationError("password must not be empty")
    if len(value) > 128:
        raise ValidationError("password must be at most 128 characters")
    if any(ord(character) < 32 or ord(character) == 127 for character in value):
        raise ValidationError("password must not contain control characters")
    return value