from dataclasses import dataclass
from functools import partial, wraps
from operator import not_
from typing import Any, Callable, Concatenate, Generic, Iterable, Iterator, List, ParamSpec, Sequence, Tuple, TypeVar

A = TypeVar('A')
B = TypeVar('B')
C = TypeVar('C')
D = TypeVar('D')
P = ParamSpec('P')
P1 = ParamSpec('P1')
P2 = ParamSpec('P2')


# Compose
def c(f2: Callable[[B], C], f1: Callable[P, B]) -> Callable[P, C]:
	"""
	Compose two functions by passing the output of the second to the input of the first.

	`c(f1, f2)(*args)` is equivalent to `f1(f2(*args))`.

	This can also be thought of as mapping the output of a function using the first
	parameter as a mapper function.

	>>> double = lambda x: x + x
	>>> succ = lambda x: x + 1
	>>> c(double, succ)(1)
	4

	>>> c(succ, double)(1)
	3
	"""
	@wraps(f1)
	def inner(*args: P.args, **kwargs: P.kwargs) -> C:
		return f2(f1(*args, **kwargs))
	return inner

# Flip: (A -> B -> C) -> B -> A -> C
def flip(f: Callable[P1, Callable[P2, C]]) -> Callable[P2, Callable[P1, C]]:
	"""
	Reverse the order of the first two arguments of a curried function.

	This only works with curried functions, so apply `cur2` or `cur3` before applying
	`flip` if the arguments you want to flip are not curried.

	>>> pair = lambda x: lambda y: (x, y)
	>>> pair(1)(2)
	(1, 2)

	>>> flip(pair)(1)(2)
	(2, 1)
	"""
	@wraps(f)
	def inner1(*args2: P2.args, **kwargs2: P2.kwargs) -> Callable[P1, C]:
		@wraps(f)
		def inner2(*args1: P1.args, **kwargs1: P1.kwargs) -> C:
			return f(*args1, **kwargs1)(*args2, **kwargs2)
		return inner2
	return inner1

# Identity function!
def ident(x: A) -> A:
	"""
	The identity function.  Output is identical to input.

	>>> ident(3)
	3

	>>> ident(('hello', 8))
	('hello', 8)
	"""
	return x

def replace(replace_with: A) -> Callable[..., A]:
	"""
	Get a function which always returns a constant value, regardless of input

	The argument `replace_with` is the value the the returned function should always
	return.  The returned function can be used as if having any arity, and will always
	return the same value originally passed to `replace`.

	>>> always_seven = replace(7)
	>>> always_seven(2)
	7

	>>> always_seven('hello', 'world!')
	7

	>>> replace('uwu')('NYA!')
	'uwu'
	"""
	def constant(*args: Any, **kwargs: Any) -> A:
		"Always return a constant value, typically the one passed to `replace`"
		return replace_with
	return constant

# Partial Appliaction shorthand
p = partial
"An alias for partial application"

# Two and three-argument currying
# Defining these pointfree fucks up the types btw
def cur2(f: Callable[Concatenate[A, P], C]) -> Callable[[A], Callable[P, C]]:
	"""
	Perform two-argument currying.

	For example, a function from (A, B) -> C becomes a function A -> B -> C.  This can
	also be though of as simply moving the first argument of a function out front, since
	it preserves any arguments after the first.  That is, a function (A, B, C, kw=D) -> E
	becomes the function A -> (B, C, kw=D) -> E after being curried using this function.

	Can also be used as an annotation.

	>>> @cur2
	... def pair(x, y):
	...     return (x, y)
	...
	>>> pair(1)(2)
	(1, 2)

	>>> alternate_pair = lambda x, y: (x, y)
	>>> cur2(alternate_pair)(1)(2)
	(1, 2)

	>>> threeple = lambda x, y, z: (x, y, z)
	>>> cur2(threeple)(1)(2, 3)
	(1, 2, 3)
	"""
	return p(p, f) #type:ignore
def cur3(f: Callable[Concatenate[A, B, P], D]) -> Callable[[A], Callable[[B], Callable[P, D]]]:
	"""
	Perform three-argument currying.

	See `cur2` for an explaination of how this works.

	>>> threeple = lambda x, y, z: (x, y, z)
	>>> cur3(threeple)(1)(2)(3)
	(1, 2, 3)
	"""
	return p(p, p, f) #type:ignore


# Curried versions of map & filter with stricter types
def p_map(f: Callable[[A], B]) -> Callable[[Sequence[A]], Sequence[B]]:
	"A curried version of the built in `map` function"
	return partial(map, f) #type: ignore

def p_filter(f: Callable[[A], bool]) -> Callable[[Sequence[A]], Sequence[A]]:
	"A curried version of the built in `filter` function"
	return partial(filter,f) #type: ignore

# Normal Accessors
@cur2
def indx(i: int, s: Sequence[A]) -> A:
	"""
	A curried version of the getitem function

	>>> get_second = indx(1)
	>>> get_second(('a', 'b'))
	'b'

	>>> get_second([1, 2, 3, 4])
	2
	"""
	return s[i]

fst = indx(0)
"Get the first element of a tuple/sequence"

snd = indx(1)
"Get the second element of a tuple/sequence"

# Semantic Editor Combinators
class SemEdComb:
	"""
	A tool which approximates semantic editor combinators in python.

	Please read
	https://web.archive.org/web/20221202200001/http://conal.net/blog/posts/semantic-editor-combinators
	for context.

	Since Python has no infix function composition, using this pattern can get pretty
	ugly.  This class abuses python's ability to override the property accessor (.) in
	order to approximate semantic editor combinators.

	>>> my_func = lambda x: ('abc' + x, 'def')
	>>> my_func('hi')
	('abchi', 'def')

	>>> altered_func = result.first.map(str.upper, my_func)
	>>> altered_func('hi')
	('ABCHI', 'def')

	>>> other_altered_func = arg.map(str.upper, my_func)
	>>> other_altered_func('hello')
	('abcHELLO', 'def')

	Unfortunately, due to limitations of Python's type system, this class is largely
	untyped.
	"""
	class Inner():
		"A chain of semantic editor combinators already paired with a map function"
		def __init__(self, f: Callable, name: str):
			self.f = f
			self.name = name
		def and_then(self, other: 'SemEdComb.Inner') -> 'SemEdComb.Inner':
			"Composes this with another `SemEdComb.Inner`"
			return SemEdComb.Inner(c(other.f, self.f), self.name + ' and ' + other.name)
		def __repr__(self) -> str:
			return f"SemEdComb*({self.name})"
		def __call__(self, *args, **kwargs):
			return self.f(*args, **kwargs)

	def __init__(self, f: Callable[[Callable],Callable], name: str):
		self.f = f
		self.name = name

	def _c(self, next_f: Callable[[Callable], Callable], next_fname: str) -> 'SemEdComb':
		return SemEdComb(c(self.f, next_f), self.name + next_fname)

	RESULT = cur2(c)
	"Map the result of a function"

	ARG = flip(RESULT)
	"Map the argument of a function"

	ALL = p_map
	"Map every element of a list"

	@cur3
	@staticmethod
	def INDEX(i, f, arr):
		"Map the ith element of a mutable sequence"
		arr[i] = f(arr[i])
		return arr

	@cur3
	@staticmethod
	def INDEX_TUP(i: int, f: Callable[[Any], Any], tup: Tuple) -> Tuple:
		"Map the ith element of an immutable sequence"
		l = list(tup)
		l[i] = f(l[i])
		return (*l,)

	@cur2
	@staticmethod
	def FIRST(f: Callable[[A], C], tup: Tuple[A, B]) -> Tuple[C, B]:
		"Map the first element of a two-tuple"
		return (f(tup[0]), tup[1])

	@cur2
	@staticmethod
	def SECOND(f: Callable[[B], C], tup: Tuple[A, B]) -> Tuple[A, C]:
		"Map the second element of a two-tuple"
		return (tup[0], f(tup[1]))

	@property
	def result(self) -> 'SemEdComb':
		"""
		Map the result of a function

		>>> my_func = lambda s: s + ' backwards is ' + s[::-1]
		>>> my_func('hello')
		'hello backwards is olleh'

		>>> altered_func =  result.map(str.upper, my_func)
		>>> altered_func('hello')
		'HELLO BACKWARDS IS OLLEH'

		Can be chained in order to work with curried functions as well.  That is, the
		result of a two argument curried function is the result of the result of that
		function.

		>>> curried_pair = lambda x: lambda y: (x, y)
		>>> altered_pair = result.result.second.map(str.upper, curried_pair)
		>>> altered_pair('hello')('world')
		('hello', 'WORLD')
		"""
		return self._c(SemEdComb.RESULT, '.result')

	@property
	def arg(self) -> 'SemEdComb':
		"""
		Map the argument of a function

		>>> my_func = lambda s: s + ' backwards is ' + s[::-1]
		>>> my_func('hello')
		'hello backwards is olleh'

		>>> altered_func = arg.map(str.upper, my_func)
		>>> altered_func('hello')
		'HELLO backwards is OLLEH'

		Can be combined with `.result` to work with curried functions.

		>>> curried_pair = lambda x: lambda y: (x, y)
		>>> altered_pair = result.arg.map(str.upper, curried_pair)
		>>> altered_pair('hello')('world')
		('hello', 'WORLD')
		"""
		return self._c(SemEdComb.ARG, '.arg')

	@property
	def all(self) -> 'SemEdComb':
		"""
		Map every element of a sequence

		To use this as the base of a chain of SECs, write "all_", since "all" by itself
		refers to the builtin python function, which is different.

		Note that this returns an iterator, not a sequence, even if the thing being mapped
		was a sequence or a list.

		>>> list(all_.map(lambda x: x + x, [1, 2, 3]))
		[2, 4, 6]

		>>> my_func = lambda s: [s] * s
		>>> my_func(3)
		[3, 3, 3]

		>>> altered_func = result.all.map(lambda x: x + x, my_func)
		>>> list(altered_func(3))
		[6, 6, 6]
		"""
		return self._c(SemEdComb.ALL, '.all')

	def index(self, i) -> 'SemEdComb':
		"""
		Map the ith element of a mutable sequence

		>>> index(1).map(lambda x: x + x, [1, 2, 3])
		[1, 4, 3]

		>>> my_func = lambda s: [s] * s
		>>> my_func(3)
		[3, 3, 3]

		>>> altered_func = result.index(1).map(lambda x: x + x, my_func)
		>>> list(altered_func(3))
		[3, 6, 3]

		"""
		return self._c(SemEdComb.INDEX(i), f'.index({i})')

	def index_tup(self, i) -> 'SemEdComb':
		"""
		Map the ith element of an immutable sequence.

		>>> index_tup(2).map(lambda x: x + x, (1, 2, 3, 4))
		(1, 2, 6, 4)

		See Also: `index`

		For a more optimized version of this method specialized to two-tuples, see `first`
		and `second`
		"""
		return self._c(SemEdComb.INDEX_TUP(i), f'.index_tup({i})')

	@property
	def first(self) -> 'SemEdComb':
		"""
		Map the first element of a two-tuple

		>>> first.map(lambda x: x+x, (1, 2))
		(2, 2)

		Doesn't work for threeples and fourples.  If this is the behaviour you need, try
		`index_tup`

		>>> first.map(lambda x: x+x, (1, 2, 3))
		(2, 2)
		"""
		return self._c(SemEdComb.FIRST, f'.first')

	@property
	def second(self) -> 'SemEdComb':
		"""
		Map the second element of a two-tuple

		>>> second.map(lambda x: x+x, (1, 2))
		(1, 4)

		As with `first`, this doesn't work with threeples, fourples, and moreples.

		>>> second.map(lambda x: x+x, (1, 2, 3))
		(1, 4)
		"""
		return self._c(SemEdComb.SECOND, f'.second')

	def __repr__(self):
		return f"SemEdComb({self.name})"

	def pmap(self, mapper):
		"""
		Set the mapper function, but don't call it yet

		The name is short for partial map.

		>>> my_func = lambda s1: lambda s2: f"You entered {s1} and the pair {s2}"
		>>> my_func(1)(('hello', 'world'))
		"You entered 1 and the pair ('hello', 'world')"

		>>> mapper = result.arg.first.pmap(str.upper)
		>>> altered_func = mapper(my_func)
		>>> altered_func(1)(('hello', 'world'))
		"You entered 1 and the pair ('HELLO', 'world')"

		See also: `map`
		"""
		return SemEdComb.Inner(self.f(mapper), self.name)

	def map(self, mapper, thing_to_map) -> Callable:
		"Apply the chain of combinators to a mapper and a mappee"
		return self.pmap(mapper)(thing_to_map)

	def __call__(self, *args, **kwargs):
		return self.f(*args, **kwargs)

# Pre-constructed base semantic editor combinators
result = SemEdComb(SemEdComb.RESULT, 'result')
arg = SemEdComb(SemEdComb.ARG, 'arg')
index = lambda i: SemEdComb(SemEdComb.INDEX(i), f'index({i})')
index_tup = lambda i: SemEdComb(SemEdComb.INDEX_TUP(i), f'index_tup({i})')
first = SemEdComb(SemEdComb.FIRST, 'first')
second = SemEdComb(SemEdComb.SECOND, 'second')
all_ = SemEdComb(SemEdComb.ALL, 'all')

# Tail call optimizing recursion
@dataclass
class Recur(Generic[P]):
	"""
	Indicate that the function this is returned from should be called again with new args.

	Exclusively used with `tco_rec()`
	"""
	def __init__(self, *args: P.args, **kwargs: P.kwargs):
		self.args = args
		self.kwargs = kwargs

@dataclass(frozen = True)
class Return(Generic[B]):
	"""
	Indicate that the function this is returned from should return this value

	Exclusively used with `tco_rec()`
	"""
	val: B

def tco_rec(f: Callable[P, Recur[P] | Return[B]]) -> Callable[P, B]:
	"""
	Run a tail-recursive function in a mannor which will not overflow the stack.

	Wraps a function in a loop which transforms its return type.  The function is expected
	to return an instance of `Recur` rather than calling itself to recur.  The arguments
	passed to the returned `Recur` instance become the arguments to the next iteration of
	the function call.  When the function is ready to return for real, it should return an
	instance of `Return`.

	The function will be transformed by `tco_rec` to look as if it is a normal function.

	>>> @tco_rec
	... def factorial(n, coefficient = 1):
	...    if n > 1:
	...       return Recur(n - 1, coefficient * n)
	...    else:
	...       return Return(coefficient)
	>>> factorial(4)
	24
	"""
	@wraps(f)
	def tco_loop(*args: P.args, **kwargs: P.kwargs) -> B:
		while True:
			match f(*args, **kwargs):
				case Recur(args=args, kwargs=kwargs): #type:ignore
					pass
				case Return(val=val)|val:
					return val #type:ignore
	return tco_loop

# Options!
@dataclass(frozen=True)
class Some(Generic[A]):
	"""
	The positive part of an optional datatype

	Component of `Option` and counterpart of `None`
	"""
	val: A
	def __repr__(self) -> str:
		return f'Some({self.val!r})'

Option = Some[A] | None
"An Option datatype, aka Maybe"

def map_opt(f: Callable[[A], B], o: Option[A]) -> Option[B]:
	"""
	Map the contents of an optional data type.  Has no effect on `None`

	>>> map_opt(str.upper, Some('hello'))
	Some('HELLO')

	>>> map_opt(str.upper, None) is None
	True
	"""
	match o:
		case Some(val):
			return Some(f(val))
		case none:
			return none
def bind_opt(f: Callable[[A], Option[B]], o: Option[A]) -> Option[B]:
	"""
	wow!  monads! (aka 'and_then')

	>>> halve = lambda n: Some(n//2) if n % 2 == 0 else None
	>>> [halve(2), halve(3)]
	[Some(1), None]

	>>> bind_opt(halve, Some(4))
	Some(2)

	>>> bind_opt(halve, Some(5)) is None
	True

	>>> bind_opt(halve, None) is None
	True
	"""
	match o:
		case Some(val):
			return f(val)
		case none:
			return none
def note(e: B, o: Option[A]) -> 'Result[A, B]':
	"""
	Convert an `Option` to a `Result` by attaching an error to the `None` variants

	>>> note('woops!', Some(1))
	Ok(1)

	>>> note('woops!', None)
	Err('woops!')
	"""
	match o:
		case Some(val):
			return Ok(val)
		case None:
			return Err(e)

# Results!
@dataclass(frozen=True)
class Ok(Generic[A]):
	"""
	The positive part of a result (either) datatype

	Component of `Result` and counterpart of `Err`
	"""
	val: A
	def __repr__(self) -> str:
		return f'Ok({self.val!r})'
@dataclass(frozen=True)
class Err(Generic[B]):
	"""
	The error part of a result (either) datatype

	Component of `Result` and counterpart of `Ok`
	"""
	err: B
	def __repr__(self) -> str:
		return f'Err({self.err!r})'
	def __bool__(self):
		return False
Result = Ok[A] | Err[B]
"A Result datatype, aka Either"
def map_res(f: Callable[[A], C], r: Result[A, B]) -> Result[C, B]:
	"""
	Map the success value of a result

	>>> map_res(str.upper, Ok('hai!'))
	Ok('HAI!')

	>>> map_res(str.upper, Err('oh noes'))
	Err('oh noes')
	"""
	match r:
		case Ok(val):
			return Ok(f(val))
		case not_okay:
			return not_okay
def bind_res(f: Callable[[A], Result[C, B]], r: Result[A, B]) -> Result[C, B]:
	"""
	Perform an fallible operation for successful results.

	>>> halve = lambda n: Ok(n//2) if n % 2 == 0 else Err(f'{n} is not divisible by 2')
	>>> [halve(2), halve(3)]
	[Ok(1), Err('3 is not divisible by 2')]

	>>> bind_res(halve, Ok(4))
	Ok(2)

	>>> bind_res(halve, Ok(5))
	Err('5 is not divisible by 2')

	>>> bind_res(halve, Err('not okay in the 1st place'))
	Err('not okay in the 1st place')
	"""
	match r:
		case Ok(val):
			return f(val)
		case not_okay:
			return not_okay
def map_err(f: Callable[[B], C], r: Result[A, B]) -> Result[A, C]:
	"""
	Map the error value of a result

	>>> map_err(str.upper, Ok('hai!'))
	Ok('hai!')

	>>> map_err(str.upper, Err('oh noes'))
	Err('OH NOES')
	"""
	match r:
		case Err(e):
			return Err(f(e))
		case oki_doke:
			return oki_doke
def hush(r: Result[A, Any]) -> Option[A]:
	"""
	Convert a `Result` to an `Option` by converting any errors to `None`

	>>> hush(Ok('hai!'))
	Some('hai!')

	>>> hush(Err('oh noes')) is None
	True
	"""
	match r:
		case Ok(val):
			return Some(val)
		case not_okay:
			return None

def try_(handle: Callable[[Exception], B], f: Callable[P, A], *args: P.args, **kwargs: P.kwargs) -> Result[A, B]:
	"""
	Try-catch in a function!  Attempt to perform and operation, and `Err` on failure

	Arguments:
		handle - A function which handles any exceptions which arise.  The return type is
			what will be wrapped into the resulting `Err`.  This is not called if nothing
			goes wrong.
		f - The fallible function to try.  If this succeeds without raising an error, that
			value is returned in an `Ok`.  If this raises an exception, that exception
			will be passed to `handle`.
		args - Will be passed to `f` when it is called.
		kwargs - Will be passed to `f` when it is called.

	>>> try_(ident, int, '3')
	Ok(3)

	>>> try_(ident, int, 'three')
	Err(ValueError("invalid literal for int() with base 10: 'three'"))
	"""
	try:
		return Ok(f(*args, **kwargs))
	except Exception as e:
		return Err(handle(e))

def unwrap_r(r: Result[A, Any]) -> A:
	"""
	Assert that a `Result` is `Ok` and return it's value.

	Throws:
		`AssertionError` - The result was NOT okay.  The `AssertionError` will have two
			arguments:  The first is a string to make it more obvious what happened.  The
			second is the error that was stored in the `Err`.

	>>> unwrap_r(Ok('hai!'))
	'hai!'

	>>> unwrap_r(Err('oh noes')) is None #doctest: +IGNORE_EXCEPTION_DETAIL
	Traceback (most recent call last):
	AssertionError: ('Tried to unwrap an error: ', 'oh noes')
	"""
	match r:
		case Ok(val):
			return val
		case Err(e):
			raise AssertionError(f'Tried to unwrap an error: ', e)
def sequence(s: Sequence[Result[A, B]]) -> Result[Iterator[A], B]:
	"""
	Convert a list of results into a result of a list.

	If the input sequence contains only `Ok` results, then the output is similarly `Ok`,
	and contains a list of all the unwrapped values of the `Ok`s.  If there are any
	errors, proccessing of the sequence is immediately stopped, and the first error
	encountered is returned.

	>>> map_res(list, sequence([Ok(1), Ok(2), Ok(3)]))
	Ok([1, 2, 3])

	>>> sequence([Ok(1), Err('Oops!'), Err('Aw man!')])
	Err('Oops!')
	"""
	if all(s):
		return Ok(map(unwrap_r, s))
	else:
		o = next(filter(not_, s))
		assert isinstance(o, Err)
		return o

if __name__ == '__main__':
	import doctest
	doctest.testmod()