from __future__ import annotations

import src.zelkelc.ast.types as types
from dataclasses import dataclass
from typing import Optional


@dataclass
class SemanticError:
    message: str


@dataclass
class StructSignature:
    name: str
    irname: str
    members: dict[str, MemberSignature]


@dataclass
class ClassSignature:
    name: str
    irname: str
    members: dict[str, MemberSignature]
    methods: dict[str, list[FunctionSignature]]


@dataclass
class FunctionSignature:
    name: str
    irname: str
    static: bool
    typ: types.Value
    args: dict[str, types.Value]


@dataclass
class ValueSignature:
    name: str
    irname: str
    mutable: bool
    typ: type[types.Integer64] | type[types.String] | type[types.Void]


@dataclass
class MemberSignature:
    name: str
    irname: str
    mutable: bool
    typ: type[types.Integer64] | type[types.String] | type[types.Void]
    member_idx: int


@dataclass
class Scope:
    parent: Optional[Scope]
    classes: dict[str, ClassSignature]
    structs: dict[str, StructSignature]
    functions: dict[str, list[FunctionSignature]]
    values: dict[str, ValueSignature]

    @staticmethod
    def root() -> Scope:
        return Scope(
            parent=None,
            classes={},
            structs={},
            functions={},
            values={},
        )

    def child(self) -> Scope:
        return Scope(
            parent=self,
            classes=self.classes,
            structs=self.structs,
            functions=self.functions,
            values={},
        )

    def resolve_variable(self, name: str) -> Optional[ValueSignature]:
        current: Optional[Scope] = self
        while current is not None:
            if name in current.values:
                return current.values[name]
            current = current.parent
        return None

    def resolve_function(
        self, scope_checker: ScopeChecker, name: str, args: list[types.Expression]
    ) -> Optional[FunctionSignature]:
        current: Optional[Scope] = self
        while current is not None:
            overloads = current.functions.get(name)
            if overloads:
                arg_types = current.expr_args_to_arg_types(scope_checker, args)
                if arg_types is None:
                    return None

                return current.resolve_function_by_types(name, arg_types)
            current = current.parent
        return None

    def resolve_function_by_types(
        self, name: str, arg_types: list[types.Value]
    ) -> Optional[FunctionSignature]:
        current: Optional[Scope] = self
        while current is not None:
            overloads = current.functions.get(name)
            if overloads:
                for candidate in overloads:
                    if list(candidate.args.values()) == arg_types:
                        return candidate
            current = current.parent
        return None

    def expr_args_to_arg_types(
        self, scope_checker: ScopeChecker, args: list[types.Expression]
    ) -> Optional[list[types.Value]]:
        arg_types: list[types.Value] = []
        for arg in args:
            typ = scope_checker._infer_expression_type(arg, self)
            if typ is None:
                return None

            arg_types.append(typ)

        return arg_types

    def _ensure_function_overloads(self, name: str) -> list[FunctionSignature]:
        if name not in self.functions:
            self.functions[name] = []
        return self.functions[name]


class ScopeChecker:
    global_scope: Scope
    errors: list[SemanticError]

    def __init__(self):
        self.global_scope = Scope.root()
        self.errors = []

    def check(self, tree: list[types.Node]) -> tuple[Scope, list[SemanticError]]:
        self._collect_globals(tree)

        for top_level in tree:
            match top_level:
                case types.FunctionDeclaration():
                    self._check_function(top_level, self.global_scope)
                case types.ClassDeclaration():
                    for method in top_level.methods:
                        self._check_function(method, self.global_scope)
                case types.StructDeclaration():
                    continue
                case types.InlineIR():
                    for arg in top_level.args:
                        self._infer_expression_type(arg, self.global_scope)
                case types.MacroCall():
                    self._error(f"unexpanded macro call #{top_level.name}")
                case _:
                    self._error(f"Unsupported top-level node: {type(top_level)}")

        return self.global_scope, self.errors

    def _collect_globals(self, tree: list[types.Node]) -> None:
        for top_level in tree:
            match top_level:
                case types.StructDeclaration(name=name, irname=irname, members=members):
                    if name in self.global_scope.structs:
                        self._error(f"Struct '{name}' is already declared")
                        continue

                    member_table: dict[str, MemberSignature] = {}
                    for member in members:
                        if member.name in member_table:
                            self._error(
                                f"Duplicate member '{member.name}' in struct '{name}'"
                            )
                            continue
                        member_table[member.name] = MemberSignature(
                            name=member.name,
                            irname=f"{irname}.m_{member.name}",
                            mutable=member.mutable,
                            typ=member.typ,
                            member_idx=member.real_idx,
                        )

                    self.global_scope.structs[name] = StructSignature(
                        name=name,
                        irname=irname,
                        members=member_table,
                    )

                case types.ClassDeclaration(
                    name=name, irname=irname, members=members, methods=methods
                ):
                    if name in self.global_scope.classes:
                        self._error(f"Class '{name}' is already declared")
                        continue

                    member_table: dict[str, MemberSignature] = {}
                    for idx, member in enumerate(members):
                        if member.name in member_table:
                            self._error(
                                f"Duplicate member '{member.name}' in class '{name}'"
                            )
                            continue
                        member_table[member.name] = MemberSignature(
                            name=member.name,
                            irname=f"{irname}.m_{member.name}",
                            mutable=member.mutable,
                            typ=member.typ,
                            member_idx=idx,
                        )

                    method_table: dict[str, list[FunctionSignature]] = {}
                    for method in methods:
                        signature = FunctionSignature(
                            name=method.name,
                            irname=method.irname,
                            static=False,
                            typ=method.typ,
                            args=method.args,
                        )

                        overloads = method_table.setdefault(method.name, [])
                        has_duplicate_signature = any(
                            list(existing.args.values())
                            == list(signature.args.values())
                            for existing in overloads
                        )
                        if has_duplicate_signature:
                            self._error(
                                f"Duplicate method '{method.name}' in class '{name}' "
                                f"with same argument signature"
                            )
                            continue

                        overloads.append(signature)

                    self.global_scope.classes[name] = ClassSignature(
                        name=name,
                        irname=irname,
                        members=member_table,
                        methods=method_table,
                    )

                case types.FunctionDeclaration(name, typ, args, _, irname):
                    existing = self.global_scope.resolve_function_by_types(
                        name, list(args.values())
                    )
                    if existing is not None:
                        self._error(
                            f"Function '{name}' is already defined with following signature '{existing}'"
                        )
                        continue

                    self.global_scope._ensure_function_overloads(name).append(
                        FunctionSignature(
                            name=name,
                            irname=irname,
                            static=True,
                            typ=typ,
                            args=args,
                        )
                    )

                case types.MacroCall() | types.InlineIR():
                    continue

                case _:
                    self._error(
                        f"Unsupported top-level node while collecting symbols: {type(top_level)}"
                    )

    def _check_function(
        self, fn: types.FunctionDeclaration, enclosing_scope: Scope
    ) -> None:
        function_scope = enclosing_scope.child()

        for arg_name, arg_type in fn.args.items():
            if arg_name in function_scope.values:
                self._error(f"Duplicate argument '{arg_name}' in function '{fn.name}'")
                continue
            function_scope.values[arg_name] = ValueSignature(
                name=arg_name,
                irname=arg_name,
                mutable=False,
                typ=arg_type,
            )

        has_return = False

        for child in fn.body:
            match child:
                case types.ValueDeclaration():
                    if child.name in function_scope.values:
                        self._error(
                            f"Variable '{child.name}' is already defined in function '{fn.name}'"
                        )
                        continue

                    expression_type = self._infer_expression_type(
                        child.expr, function_scope
                    )
                    if expression_type is not None and not self._same_type(
                        expression_type, child.typ
                    ):
                        self._error(
                            f"Type mismatch for '{child.name}' in function '{fn.name}': "
                            f"expected {self._type_name(child.typ)}, got {self._type_name(expression_type)}"
                        )

                    function_scope.values[child.name] = ValueSignature(
                        name=child.name,
                        irname=child.irname,
                        mutable=child.mutable,
                        typ=child.typ,
                    )

                case types.ReturnStatement():
                    has_return = True
                    if child.expr is None:
                        if fn.typ is not types.Void:
                            self._error(
                                f"Function '{fn.name}' must return {self._type_name(fn.typ)}"
                            )
                        continue

                    return_type = self._infer_expression_type(
                        child.expr, function_scope
                    )
                    if return_type is None:
                        continue

                    if fn.typ is types.Void:
                        self._error(
                            f"Function '{fn.name}' returns a value, but return type is void"
                        )
                        continue

                    if not self._same_type(return_type, fn.typ):
                        self._error(
                            f"Return type mismatch in function '{fn.name}': "
                            f"expected {self._type_name(fn.typ)}, got {self._type_name(return_type)}"
                        )

                case types.FunctionDeclaration():
                    existing_nested = function_scope.resolve_function_by_types(
                        child.name, list(child.args.values())
                    )
                    if existing_nested is not None:
                        self._error(
                            f"Nested function '{child.name}' is already defined in '{fn.name}'"
                        )
                    else:
                        function_scope._ensure_function_overloads(child.name).append(
                            FunctionSignature(
                                name=child.name,
                                irname=child.irname,
                                static=True,
                                typ=child.typ,
                                args=child.args,
                            )
                        )
                    self._check_function(child, function_scope)

                case types.InlineIR():
                    for arg in child.args:
                        self._infer_expression_type(arg, function_scope)

                case _:
                    self._error(
                        f"Unsupported node in function '{fn.name}': {type(child)}"
                    )

        if not has_return and fn.typ is not types.Void:
            self._error(f"Function '{fn.name}' has no return statement")

    def _infer_expression_type(
        self, expr: types.Expression, active_scope: Scope
    ) -> Optional[type[types.Integer64] | type[types.String] | type[types.Void]]:
        match expr:
            case types.PrimaryExpression(types.Integer64()):
                return types.Integer64
            case types.PrimaryExpression(types.Float64()):
                return types.Float64
            case types.PrimaryExpression(types.String()):
                return types.String
            case types.PrimaryExpression(types.VariableRef(name)):
                signature = active_scope.resolve_variable(name)
                if signature is None:
                    self._error(f"Unknown variable '{name}'")
                    return None

                expr.value.irname = signature.irname
                expr.value.typ = signature.typ
                return signature.typ
            case types.PrimaryExpression(types.FunctionCall(name, args)):
                arg_types = active_scope.expr_args_to_arg_types(self, args)
                if arg_types is None:
                    self._error("Could not get argument types from function call")
                    return None

                signature = active_scope.resolve_function_by_types(name, arg_types)
                if signature is None:
                    self._error(
                        f"Unknown function '{name}' with given argument signature"
                    )
                    return None

                expr.value.irname = signature.irname
                return signature.typ
            case types.UnaryExpression(inner_expr, sign):
                inner_type = self._infer_expression_type(inner_expr, active_scope)
                if inner_type is None:
                    return None
                if sign in ("+", "-") and inner_type is not types.Integer64:
                    self._error(
                        f"Unary operator '{sign}' expects i64, got {self._type_name(inner_type)}"
                    )
                    return None
                return inner_type
            case types.BinaryExpression(left=left, right=right, op=op):
                left_type = self._infer_expression_type(left, active_scope)
                right_type = self._infer_expression_type(right, active_scope)
                if left_type is None or right_type is None:
                    return None
                if not self._same_type(left_type, right_type):
                    self._error(
                        f"Binary operator '{op}' type mismatch: "
                        f"{self._type_name(left_type)} vs {self._type_name(right_type)}"
                    )
                    return None

                match left_type:
                    case types.Integer64:
                        if op not in ["+", "-", "*"]:
                            self._error(
                                f"Operator '{op}' does not support {self._type_name(left_type)}"
                            )
                        return types.Integer64
                    case types.Float64:
                        if op not in ["+", "-", "*", "/"]:
                            self._error(
                                f"Operator '{op}' does not support {self._type_name(left_type)}"
                            )
                        return types.Float64
                    case _:
                        return None
            case _:
                self._error(f"Unsupported expression type: {type(expr)}")
                return None

    def _same_type(self, left: object, right: object) -> bool:
        return self._type_token(left) == self._type_token(right)

    def _type_token(self, typ: object) -> str:
        if typ is types.Integer64 or isinstance(typ, types.Integer64):
            return "i64"
        if typ is types.Float64 or isinstance(typ, types.Float64):
            return "f64"
        if typ is types.String or isinstance(typ, types.String):
            return "str"
        if typ is types.Void or isinstance(typ, types.Void):
            return "void"
        return str(typ)

    def _type_name(self, typ: object) -> str:
        return self._type_token(typ)

    def _error(self, message: str) -> None:
        self.errors.append(SemanticError(message))