"""The typed shapes a Pydantic model lowers to before Rust is emitted.

`TypeShape` is deliberately isomorphic to Mizan's KDL `TypeShape`, so the
two can be converted without a lookup table.
"""

from __future__ import annotations

from dataclasses import dataclass, field
from enum import Enum
from typing import Optional


class Primitive(str, Enum):
    INTEGER = "integer"
    NUMBER = "number"
    BOOLEAN = "boolean"
    STRING = "string"


@dataclass(frozen=True)
class TypeShape:
    """A recursive type shape. Exactly one variant field is set."""

    primitive: Optional[Primitive] = None

    int_width: Optional[int] = None
    """8 / 16 / 32 / 64, or None when unspecified. Only read alongside
    `primitive == INTEGER`, and only by emitters that distinguish widths."""

    int_signed: Optional[bool] = None
    """True for i8..i64, False for u8..u64, None when unspecified."""

    float_width: Optional[int] = None
    """16 / 32 / 64, or None when unspecified. Only meaningful alongside
    `primitive == NUMBER`."""

    ref: Optional[str] = None
    list_inner: Optional["TypeShape"] = None
    optional_inner: Optional["TypeShape"] = None
    enum_variants: Optional[tuple[str, ...]] = None
    union_branches: Optional[tuple["TypeShape", ...]] = None

    map_value: Optional["TypeShape"] = None
    """`dict[K, V]` value shape."""

    map_key: Optional["TypeShape"] = None
    """Set only when the key is a NewType. Wire keys are always strings;
    this keeps the typed identity on the Rust side."""

    array_element: Optional["TypeShape"] = None
    """Fixed-length element: `tuple[T, T, T]` lowers to element T, length 3,
    and emits `[T; 3]`."""

    array_length: Optional[int] = None


@dataclass(frozen=True)
class DefaultValue:
    """A field default captured during introspection. `kind` discriminates
    how the emitter renders `literal`."""

    kind: str  # integer | number | boolean | string | null | empty_seq |
    # empty_map | tuple | enum_variant | compound_model | compound
    literal: object


@dataclass(frozen=True)
class FieldDecl:
    name: str
    shape: TypeShape
    required: bool
    default: Optional[DefaultValue] = None


@dataclass(frozen=True)
class ModelDecl:
    """One Pydantic class, lowered field by field."""

    name: str
    fields: tuple[FieldDecl, ...] = field(default_factory=tuple)
    docstring: Optional[str] = None