"""
Core types for the s-expression language.

Symbol  — unquoted identifier (e.g. div, ~card, map)
Keyword — colon-prefixed key (e.g. :class, :id)
Lambda  — callable closure created by (lambda ...) or (fn ...)
Nil     — singleton null value
"""

from __future__ import annotations

from dataclasses import dataclass, field
from typing import Any


# ---------------------------------------------------------------------------
# Nil
# ---------------------------------------------------------------------------

class _Nil:
    """Singleton nil value — falsy, serialises as 'nil'."""
    _instance: _Nil | None = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

    def __bool__(self):
        return False

    def __repr__(self):
        return "nil"

    def __eq__(self, other):
        return other is None or isinstance(other, _Nil)

    def __hash__(self):
        return hash(None)


NIL = _Nil()


# ---------------------------------------------------------------------------
# Symbol
# ---------------------------------------------------------------------------

@dataclass(frozen=True)
class Symbol:
    """An unquoted symbol/identifier."""
    name: str

    def __repr__(self):
        return f"Symbol({self.name!r})"

    def __eq__(self, other):
        if isinstance(other, Symbol):
            return self.name == other.name
        if isinstance(other, str):
            return self.name == other
        return False

    def __hash__(self):
        return hash(self.name)

    @property
    def is_component(self) -> bool:
        """True if this symbol names a component (~prefix)."""
        return self.name.startswith("~")


# ---------------------------------------------------------------------------
# Keyword
# ---------------------------------------------------------------------------

@dataclass(frozen=True)
class Keyword:
    """A keyword starting with colon (e.g. :class, :id)."""
    name: str

    def __repr__(self):
        return f"Keyword({self.name!r})"

    def __eq__(self, other):
        if isinstance(other, Keyword):
            return self.name == other.name
        return False

    def __hash__(self):
        return hash((":", self.name))


# ---------------------------------------------------------------------------
# Lambda
# ---------------------------------------------------------------------------

@dataclass
class Lambda:
    """A callable closure.

    Created by ``(lambda (x) body)`` or ``(fn (x) body)``.
    Captures the defining environment so free variables resolve correctly.
    """
    params: list[str]
    body: Any
    closure: dict[str, Any] = field(default_factory=dict)
    name: str | None = None  # optional, set by (define name (fn ...))

    def __repr__(self):
        tag = self.name or "lambda"
        return f"<{tag}({', '.join(self.params)})>"

    def __call__(self, *args: Any, evaluator: Any = None, caller_env: dict | None = None) -> Any:
        """Invoke the lambda.  Requires *evaluator* — the evaluate() function."""
        if evaluator is None:
            raise RuntimeError("Lambda requires evaluator to be called")
        if len(args) != len(self.params):
            raise RuntimeError(
                f"{self!r} expects {len(self.params)} args, got {len(args)}"
            )
        local = dict(self.closure)
        if caller_env:
            local.update(caller_env)
        for p, v in zip(self.params, args):
            local[p] = v
        return evaluator(self.body, local)


# ---------------------------------------------------------------------------
# Macro
# ---------------------------------------------------------------------------

@dataclass
class Macro:
    """A macro — an AST-transforming function.

    Created by ``(defmacro name (params... &rest rest) body)``.
    Receives unevaluated arguments, evaluates its body to produce a new
    s-expression, which is then evaluated in the caller's environment.
    """
    params: list[str]
    rest_param: str | None    # &rest parameter name
    body: Any                 # unevaluated — returns an s-expression to eval
    closure: dict[str, Any] = field(default_factory=dict)
    name: str | None = None

    def __repr__(self):
        tag = self.name or "macro"
        return f"<{tag}({', '.join(self.params)})>"


# ---------------------------------------------------------------------------
# Component
# ---------------------------------------------------------------------------

@dataclass
class Component:
    """A reusable UI component defined via ``(defcomp ~name (&key ...) body)``.

    Components are like lambdas but accept keyword arguments and support
    a ``children`` rest parameter.
    """
    name: str
    params: list[str]         # keyword parameter names (without &key prefix)
    has_children: bool        # True if &rest children declared
    body: Any                 # unevaluated s-expression body
    closure: dict[str, Any] = field(default_factory=dict)
    css_classes: set[str] = field(default_factory=set)  # pre-scanned :class values

    def __repr__(self):
        return f"<Component ~{self.name}({', '.join(self.params)})>"


# ---------------------------------------------------------------------------
# HandlerDef
# ---------------------------------------------------------------------------

@dataclass
class HandlerDef:
    """A declarative fragment handler defined in an .sx file.

    Created by ``(defhandler name (&key param...) body)``.
    The body is evaluated in a sandboxed environment with only
    s-expression primitives available.
    """
    name: str
    params: list[str]       # keyword parameter names
    body: Any               # unevaluated s-expression body
    closure: dict[str, Any] = field(default_factory=dict)

    def __repr__(self):
        return f"<handler:{self.name}({', '.join(self.params)})>"


# ---------------------------------------------------------------------------
# RelationDef
# ---------------------------------------------------------------------------

@dataclass(frozen=True)
class RelationDef:
    """A declared relation between two entity types.

    Created by ``(defrelation :name ...)`` s-expressions.
    """
    name: str               # "page->market"
    from_type: str          # "page"
    to_type: str            # "market"
    cardinality: str        # "one-to-one" | "one-to-many" | "many-to-many"
    inverse: str | None     # "market->page"
    nav: str                # "submenu" | "tab" | "badge" | "inline" | "hidden"
    nav_icon: str | None    # "fa fa-shopping-bag"
    nav_label: str | None   # "markets"


# ---------------------------------------------------------------------------
# PageDef
# ---------------------------------------------------------------------------

@dataclass
class PageDef:
    """A declarative GET page defined in an .sx file.

    Created by ``(defpage name :path "/..." :auth :public :content expr)``.
    Slots are stored as unevaluated AST and resolved at request time.
    """
    name: str
    path: str
    auth: str | list            # "public", "login", "admin", or ["rights", ...]
    layout: Any                 # layout name/config (unevaluated)
    cache: dict | None
    data_expr: Any              # unevaluated AST
    content_expr: Any           # unevaluated AST
    filter_expr: Any
    aside_expr: Any
    menu_expr: Any
    closure: dict[str, Any] = field(default_factory=dict)

    def __repr__(self):
        return f"<page:{self.name} path={self.path!r}>"


# ---------------------------------------------------------------------------
# QueryDef / ActionDef
# ---------------------------------------------------------------------------

@dataclass
class QueryDef:
    """A declarative data query defined in an .sx file.

    Created by ``(defquery name (&key param...) "docstring" body)``.
    The body is evaluated with async I/O primitives to produce JSON data.
    """
    name: str
    params: list[str]       # keyword parameter names
    doc: str                # docstring
    body: Any               # unevaluated s-expression body
    closure: dict[str, Any] = field(default_factory=dict)

    def __repr__(self):
        return f"<query:{self.name}({', '.join(self.params)})>"


@dataclass
class ActionDef:
    """A declarative action defined in an .sx file.

    Created by ``(defaction name (&key param...) "docstring" body)``.
    The body is evaluated with async I/O primitives to produce JSON data.
    """
    name: str
    params: list[str]       # keyword parameter names
    doc: str                # docstring
    body: Any               # unevaluated s-expression body
    closure: dict[str, Any] = field(default_factory=dict)

    def __repr__(self):
        return f"<action:{self.name}({', '.join(self.params)})>"


# ---------------------------------------------------------------------------
# StyleValue
# ---------------------------------------------------------------------------

@dataclass(frozen=True)
class StyleValue:
    """A resolved CSS style produced by ``(css :flex :gap-4 :hover:bg-sky-200)``.

    Generated by the style resolver. The renderer emits ``class_name`` as a
    CSS class and registers the CSS rule for on-demand delivery.
    """
    class_name: str           # "sx-a3f2c1"
    declarations: str         # "display:flex;gap:1rem"
    media_rules: tuple = ()   # ((query, decls), ...)
    pseudo_rules: tuple = ()  # ((selector, decls), ...)
    keyframes: tuple = ()     # (("spin", "@keyframes spin{...}"), ...)

    def __repr__(self):
        return f"<StyleValue {self.class_name}>"

    def __str__(self):
        return self.class_name


# ---------------------------------------------------------------------------
# Continuation
# ---------------------------------------------------------------------------

class Continuation:
    """A captured delimited continuation (shift/reset).

    Callable with one argument — provides the value that the shift
    expression "returns" within the delimited context.
    """
    __slots__ = ("fn",)

    def __init__(self, fn):
        self.fn = fn

    def __call__(self, value=NIL):
        return self.fn(value)

    def __repr__(self):
        return "<continuation>"


class _ShiftSignal(BaseException):
    """Raised by shift to unwind to the nearest reset.

    Inherits from BaseException (not Exception) to avoid being caught
    by generic except clauses in user code.
    """
    __slots__ = ("k_name", "body", "env")

    def __init__(self, k_name, body, env):
        self.k_name = k_name
        self.body = body
        self.env = env


# ---------------------------------------------------------------------------
# Type alias
# ---------------------------------------------------------------------------

# An s-expression value after evaluation
SExp = int | float | str | bool | Symbol | Keyword | Lambda | Macro | Component | Continuation | HandlerDef | RelationDef | PageDef | QueryDef | ActionDef | StyleValue | list | dict | _Nil | None