from __future__ import annotations
from typing import Dict, Mapping, List, Set
from enum import Enum
from itertools import chain


class UnificationError(Exception):
    def __init__(self, msg):
        super().__init__(msg)


class Type:
    def find(self):
        return self

    def unify(self, _):
        raise NotImplementedError()

    def subst(self, _):
        raise NotImplementedError()

    def check(self):
        pass


class TVarType(Enum):
    UNDETERMINED = 1
    SEQUENCE = 2
    RECORD = 5
    TUPLE = 6
    LIST = 8

    def __le__(self, other):
        if self.__class__ is other.__class__:
            return (other.value % self.value) == 0
        return NotImplemented

    def unifier(self, other):
        if self.__class__ is not other.__class__:
            raise NotImplementedError()
        if self <= other:
            return other
        elif other <= self:
            return self
        else:
            raise UnificationError(f'cannot unify {self} and {other}')


class TVar(Type):
    next_id = 0

    def __init__(self, vrange=None):
        self.type = TVarType.UNDETERMINED
        self.rank = 0
        self.parent = self

        self.fields = {}
        self.range = vrange
        self.id = TVar.next_id
        TVar.next_id += 1

    def check(self):
        if self.range is not None:
            ty = self.find()
            # maybe we should replace this with explicit eq
            if ty not in self.range:
                raise UnificationError(
                    f'{self.id} cannot be substituted by {ty}')

    def subst(self, mapping: Mapping[int, Type]):
        # user cannot specify fields...
        # so this is safe
        if self.id in mapping:
            return mapping[self.id]
        return self

    def __str__(self):
        s = self.find()
        if isinstance(s, TVar):
            if len(s.fields) > 0:
                fields = '{' + ', '.join([f'{k}: {v}' for k,
                                          v in s.fields.items()]) + '}'
            else:
                fields = ''
            return str(s.id) + fields
        else:
            return str(s)

    def find(self):
        root = self
        parent = self.parent
        while root is not parent and isinstance(parent, TVar):
            _, parent = root, root.parent = parent, parent.parent
        if isinstance(parent, TCall):
            parent = parent.find()
        return parent

    def unify(self, other):
        x = other.find()
        y = self.find()

        if x is y:
            return
        if isinstance(y, TVar) and isinstance(x, TVar):
            # unify field type
            x.type = x.type.unifier(y.type)
            # unify fields
            for k, v in y.fields.items():
                if k in x.fields:
                    x.fields[k].unify(v)
                else:
                    x.fields[k] = v
            # standard union find
            if x.rank < y.rank:
                x, y = y, x
            y.parent = x
            if x.rank == y.rank:
                x.rank += 1
        elif isinstance(y, TVar):
            # check fields
            if isinstance(x, TObj):
                if y.type not in [TVarType.UNDETERMINED, TVarType.RECORD]:
                    raise UnificationError(f'Cannot unify {y} with {x}')
                for k, v in y.fields.items():
                    if k not in x.fields:
                        raise UnificationError(
                            f'Cannot unify {y} with {x}')
                    if isinstance(v, TFunc):
                        v = v.instantiate()
                    u = x.fields[k]
                    if isinstance(u, TFunc):
                        u = u.instantiate()
                    v.unify(u)
            if isinstance(x, TList):
                if y.type not in [TVarType.UNDETERMINED, TVarType.SEQUENCE, TVarType.LIST]:
                    raise UnificationError(f'Cannot unify {y} with {x}')
                for k, v in y.fields.items():
                    assert isinstance(k, int)
                    v.unify(x.param)
            if isinstance(x, TTuple):
                if y.type not in [TVarType.UNDETERMINED, TVarType.SEQUENCE, TVarType.TUPLE]:
                    raise UnificationError(f'Cannot unify {y} with {x}')
                for k, v in y.fields.items():
                    assert isinstance(k, int)
                    if k >= len(x.params):
                        raise UnificationError(f'Cannot unify {y} with {x}')
                    v.unify(x.params[k])
            y.parent = x
        else:
            y.unify(x)


class FuncArg:
    def __init__(self, name, typ, is_optional):
        self.name = name
        self.typ = typ
        self.is_optional = is_optional

    def __str__(self):
        return f'{self.name}: {self.typ}' + ('?' if self.is_optional else '')


class TCall(Type):
    def __init__(self, posargs: List[Type], kwargs: Dict[str, Type], ret: Type):
        self.posargs = posargs
        self.kwargs = kwargs
        self.ret = ret
        self.fun = TVar()

    def check(self):
        for arg in chain(self.posargs, self.kwargs.values()):
            arg.check()

    def find(self):
        if isinstance(self.fun.find(), TVar):
            return self
        return self.fun.find()

    def unify(self, other):
        if not isinstance(self.fun.find(), TVar):
            self.fun.unify(other)
            return

        other = other.find()
        if other is self:
            return

        if isinstance(other, TCall):
            for a, b in zip(self.posargs, other.posargs):
                a.unify(b)
            for k, v in self.kwargs.items():
                if k in other.kwargs:
                    other.kwargs[k].unify(v)
                else:
                    other.kwargs[k] = v
            for k, v in other.kwargs.items():
                if k not in self.kwargs:
                    self.kwargs[k] = v
            self.fun.unify(other.fun)
        elif isinstance(other, TFunc):
            all_args = set(arg.name for arg in other.args)
            required = set(arg.name for arg in other.args if not
                           arg.is_optional)
            other.ret.unify(self.ret)
            for i, v in enumerate(self.posargs):
                arg = other.args[i]
                arg.typ.unify(v)
                if arg.name in required:
                    required.remove(arg.name)
            for k, v in self.kwargs.items():
                arg = next((arg for arg in other.args if arg.name == k), None)
                if arg is None:
                    raise UnificationError(f'Unknown kwarg {k}')
                if k not in all_args:
                    raise UnificationError(f'Duplicated kwarg {k}')
                arg.typ.unify(v)
                if k in required:
                    required.remove(k)
                all_args.remove(k)
            if len(required) > 0:
                raise UnificationError(f'Missing arguments')
            self.fun.unify(other)
        elif isinstance(other, TVar):
            other.unify(self)
        else:
            raise UnificationError(f'Cannot unify a call with {other}')


class TFunc(Type):
    def __init__(self, args: List[FuncArg], ret: Type, vars: Set[TVar]):
        self.args = args
        self.ret = ret
        self.vars = vars
        self.instantiated = False

    def check(self):
        for arg in self.args:
            arg.typ.check()
        self.ret.check()

    def subst(self, mapping: Mapping[int, Type]):
        if len(mapping) == 0:
            return self
        return TFunc(
            [FuncArg(arg.name, arg.typ.subst(mapping), arg.is_optional)
             for arg in self.args],
            self.ret.subst(mapping),
            self.vars)

    def instantiate(self):
        mapping = {v.id: TVar(v.range) if isinstance(v, TVar)
                   else TVar() for v in self.vars}
        result = self.subst(mapping)
        result.instantiated = True
        return result

    def __str__(self):
        return f'({", ".join(str(arg) for arg in self.args)}) -> {self.ret}'

    def unify(self, other):
        other = other.find()
        if other is self:
            return

        if isinstance(other, (TVar, TCall)):
            other.unify(self)
        elif isinstance(other, TFunc):
            if len(self.args) != len(other.args):
                raise UnificationError(
                    f'cannot unify functions with different parameters')
            self.ret.unify(other.ret)
            for a, b in zip(self.args, other.args):
                if a.name != b.name or a.is_optional != b.is_optional:
                    raise UnificationError(
                        f'cannot unify functions with different parameters')
                a.typ.unify(b.typ)
        else:
            raise UnificationError(f'Cannot unify a function with {other}')


class TObj(Type):
    def __init__(self, name: str, fields: Dict[str, Type], params: List[Type]):
        self.name = name
        self.fields = fields
        self.params = params

    def check(self):
        for arg in self.fields.values():
            arg.check()

    def subst(self, mapping: Mapping[int, Type]):
        if len(mapping) == 0:
            return self
        new_params = []
        for v in self.params:
            if isinstance(v, TVar) and v.id in mapping:
                new_params.append(mapping[v.id])
            else:
                new_params.append(v)

        return TObj(self.name, {k: v.subst(mapping) for k, v in
                                self.fields.items()}, new_params)

    def unify(self, other):
        other = other.find()
        if other is self:
            return
        if isinstance(other, TObj):
            if self.name != other.name:
                raise UnificationError(f'Cannot unify {self} with {other}')
            for k in self.fields:
                self.fields[k].unify(other.fields[k])
        elif isinstance(other, TVar):
            other.unify(self)
        else:
            raise UnificationError(f'Cannot unify an object with {other}')

    def __str__(self):
        if len(self.params) > 0:
            p = '[' + ', '.join(str(p) for p in self.params) + ']'
        else:
            p = ''
        return self.name + p


class TList(Type):
    def __init__(self, param: Type):
        self.param = param

    def unify(self, other):
        other = other.find()
        if isinstance(other, TVar):
            other.unify(self)
        elif isinstance(other, TList):
            self.param.unify(other.param)
        else:
            raise UnificationError(f'Cannot unify list with {other}')

    def __str__(self):
        return f'List[{self.param}]'


class TTuple(Type):
    def __init__(self, params: List[Type]):
        self.params = params

    def unify(self, other):
        other = other.find()
        if isinstance(other, TVar):
            other.unify(self)
        elif isinstance(other, TTuple):
            if len(self.params) != len(other.params):
                raise UnificationError(
                    'cannot unify tuples with different length')
            for a, b in zip(self.params, other.params):
                a.unify(b)
        else:
            raise UnificationError(f'Cannot unify {self} with {other}')

    def __str__(self):
        return f'Tuple[{", ".join(str(p) for p in self.params)}]'


TBool = TObj('bool', {}, [])
TInt = TObj('int', {}, [])