import re
from datetime import date

from pydantic import BaseModel, ConfigDict, Field, field_validator

# Shared email format regex — used by RegisterRequest, ProfileUpdate, and admin.CreateUserRequest
_EMAIL_REGEX = re.compile(r"^[^\s@]+@[^\s@]+\.[^\s@]+$")


def _validate_email_format(v: str | None, *, required: bool = False) -> str | None:
    """Shared email validation. Returns normalised email or None."""
    if v is None:
        if required:
            raise ValueError("Email is required")
        return None
    v = v.strip().lower()
    if not v:
        if required:
            raise ValueError("Email is required")
        return None
    if not _EMAIL_REGEX.match(v):
        raise ValueError("Invalid email format")
    return v


def _validate_name_field(v: str | None) -> str | None:
    """Shared name field validation (strips, rejects control chars)."""
    if v is None:
        return None
    v = v.strip()
    if not v:
        return None
    if re.search(r"[\x00-\x1f]", v):
        raise ValueError("Name must not contain control characters")
    return v


def _validate_password_strength(v: str) -> str:
    """
    Shared password validation (OWASP ASVS v4 Level 1).
    - Minimum 12 chars (OWASP minimum)
    - Maximum 128 chars (prevents DoS via large input to argon2)
    - Must contain at least one letter and one non-letter
    - No complexity rules per NIST SP 800-63B
    """
    if len(v) < 12:
        raise ValueError("Password must be at least 12 characters")
    if len(v) > 128:
        raise ValueError("Password must be 128 characters or fewer")
    if not re.search(r"[A-Za-z]", v):
        raise ValueError("Password must contain at least one letter")
    if not re.search(r"[^A-Za-z]", v):
        raise ValueError("Password must contain at least one non-letter character")
    return v


def _validate_username(v: str) -> str:
    """Shared username validation."""
    v = v.strip().lower()
    if not 3 <= len(v) <= 50:
        raise ValueError("Username must be 3–50 characters")
    if not re.fullmatch(r"[a-z0-9_.\-]+", v):
        raise ValueError("Username may only contain letters, numbers, _ . and -")
    return v


class SetupRequest(BaseModel):
    model_config = ConfigDict(extra="forbid")

    username: str
    password: str

    @field_validator("username")
    @classmethod
    def validate_username(cls, v: str) -> str:
        return _validate_username(v)

    @field_validator("password")
    @classmethod
    def validate_password(cls, v: str) -> str:
        return _validate_password_strength(v)


class RegisterRequest(BaseModel):
    """
    Public registration schema — SEC-01: extra="forbid" prevents role injection.
    An attacker sending {"username": "...", "password": "...", "role": "admin"}
    will get a 422 Validation Error instead of silent acceptance.
    """
    model_config = ConfigDict(extra="forbid")

    username: str
    password: str
    email: str = Field(..., max_length=254)
    date_of_birth: date
    preferred_name: str | None = Field(None, max_length=100)

    @field_validator("username")
    @classmethod
    def validate_username(cls, v: str) -> str:
        return _validate_username(v)

    @field_validator("password")
    @classmethod
    def validate_password(cls, v: str) -> str:
        return _validate_password_strength(v)

    @field_validator("email")
    @classmethod
    def validate_email(cls, v: str) -> str:
        result = _validate_email_format(v, required=True)
        assert result is not None  # required=True guarantees non-None
        return result

    @field_validator("date_of_birth")
    @classmethod
    def validate_date_of_birth(cls, v: date) -> date:
        if v > date.today():
            raise ValueError("Date of birth cannot be in the future")
        if v.year < 1900:
            raise ValueError("Date of birth is not valid")
        return v

    @field_validator("preferred_name")
    @classmethod
    def validate_preferred_name(cls, v: str | None) -> str | None:
        return _validate_name_field(v)


class LoginRequest(BaseModel):
    model_config = ConfigDict(extra="forbid")

    username: str
    password: str

    @field_validator("username")
    @classmethod
    def normalize_username(cls, v: str) -> str:
        """Normalise to lowercase so 'Admin' and 'admin' resolve to the same user."""
        return v.strip().lower()


class ChangePasswordRequest(BaseModel):
    model_config = ConfigDict(extra="forbid")

    old_password: str
    new_password: str

    @field_validator("new_password")
    @classmethod
    def validate_new_password(cls, v: str) -> str:
        return _validate_password_strength(v)


class VerifyPasswordRequest(BaseModel):
    model_config = ConfigDict(extra="forbid")

    password: str

    @field_validator("password")
    @classmethod
    def validate_length(cls, v: str) -> str:
        if len(v) > 128:
            raise ValueError("Password must be 128 characters or fewer")
        return v


class ProfileUpdate(BaseModel):
    model_config = ConfigDict(extra="forbid")

    first_name: str | None = Field(None, max_length=100)
    last_name: str | None = Field(None, max_length=100)
    email: str | None = Field(None, max_length=254)
    date_of_birth: date | None = None
    umbral_name: str | None = Field(None, min_length=3, max_length=50)

    @field_validator("umbral_name")
    @classmethod
    def validate_umbral_name(cls, v: str | None) -> str | None:
        if v is None:
            return v
        import re
        if not re.match(r'^[a-zA-Z0-9_-]{3,50}$', v):
            raise ValueError('Umbral name must be 3-50 alphanumeric characters, hyphens, or underscores')
        return v

    @field_validator("email")
    @classmethod
    def validate_email(cls, v: str | None) -> str | None:
        return _validate_email_format(v)

    @field_validator("date_of_birth")
    @classmethod
    def validate_date_of_birth(cls, v: date | None) -> date | None:
        if v is None:
            return v
        if v > date.today():
            raise ValueError("Date of birth cannot be in the future")
        if v.year < 1900:
            raise ValueError("Date of birth is not valid")
        return v

    @field_validator("first_name", "last_name")
    @classmethod
    def validate_name_fields(cls, v: str | None) -> str | None:
        return _validate_name_field(v)


class ProfileResponse(BaseModel):
    model_config = ConfigDict(from_attributes=True)

    username: str
    umbral_name: str
    email: str | None
    first_name: str | None
    last_name: str | None
    date_of_birth: date | None