# Copyright 2020 The JAX Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from functools import partial
import itertools as it

from typing import Any, Callable, Dict, Sequence, Union

import jax.numpy as jnp

from jax import core
from jax.core import Trace, Tracer, jaxpr_as_fun
from jax import lax
from jax import custom_derivatives as cd
from jax.interpreters import partial_eval as pe
from jax import linear_util as lu
from jax._src.util import safe_map, wraps, split_list
from jax._src.lax import control_flow as lcf

import inspect
from jax._src.api_util import flatten_fun_nokwargs
from jax.tree_util import tree_flatten, tree_unflatten, tree_structure, tree_map

map = safe_map

### Public

def callback_transform(
    fun: Callable, callback: Callable, strip_calls: bool=False) -> Callable:
  _check_callable(fun)

  @wraps(fun)
  def wrapped_fun(*args):
    args_flat, in_tree  = tree_flatten(args)
    f = lu.wrap_init(fun)
    flat_fun, out_tree = flatten_fun_nokwargs(f, in_tree)
    out_flat = callback_fun(flat_fun, args_flat, callback, strip_calls)
    return tree_unflatten(out_tree(), out_flat)

  return wrapped_fun

### Example Transform

def find_by_value(fun: Callable, queries) -> Callable:
  def find_callback(
          prim: core.Primitive,
          vals: Sequence[core.Tracer],
          params: Dict[str, Any]) -> Union[core.Tracer, Sequence[core.Tracer]]:
    vals = prim.bind(*vals, **params)
    _contains_query(vals, queries)
    return vals
  return callback_transform(fun, find_callback, True)

def rewrite(fun: Callable, rules) -> Callable:
  assert isinstance(rules, dict)
  def rewrite_callback(
          prim: core.Primitive,
          vals: Sequence[core.Tracer],
          params: Dict[str, Any]) -> Union[core.Tracer, Sequence[core.Tracer]]:
    if prim in rules:
      return rules[prim](*vals, **params)
    return prim.bind(*vals, **params)
  return callback_transform(fun, rewrite_callback)

class FoundValue(Exception):
  pass

def _contains_query(vals, query):
  if isinstance(query, tuple):
    return map(partial(_contains_query, vals), query)

  if jnp.isnan(query):
    if jnp.any(jnp.isnan(vals)):
      raise FoundValue('NaN')
  elif jnp.isinf(query):
    if jnp.any(jnp.isinf(vals)):
      raise FoundValue('Found Inf')
  elif jnp.isscalar(query):
    if jnp.any(vals == query):
      raise FoundValue(str(query))
  else:
    raise ValueError(f'Malformed Query: {query}')

### Helper Functions

def callback_fun(fun : lu.WrappedFun, in_vals, callback, strip_calls):
  fun = callback_subtrace(fun)
  fun = _callback_fun(fun, callback, strip_calls)
  return fun.call_wrapped(*in_vals)

@lu.transformation
def callback_subtrace(main, *in_vals, **params):
  trace = main.with_cur_sublevel()
  in_tracers = [CallbackTracer(trace, val) for val in in_vals]
  outs = yield in_tracers, params
  out_tracers = map(trace.full_raise, outs)
  out_vals = [t.val for t in out_tracers]
  yield out_vals

@lu.transformation
def _callback_fun(callback, strip_calls, *in_vals, **params):
  with core.new_main(CallbackTrace, callback=callback,
                     strip_calls=strip_calls) as main:
    out_vals = yield (main,) + in_vals, params
    del main
  yield out_vals

def callback_jaxpr(closed_jaxpr, callback, strip_calls):
  fun = lu.wrap_init(jaxpr_as_fun(closed_jaxpr))
  fun = callback_subtrace(fun)
  fun = _callback_fun(fun, callback, strip_calls)
  avals_in = closed_jaxpr.in_avals
  jaxpr_out, consts = cd._initial_style_jaxpr(fun, avals_in)
  return core.ClosedJaxpr(jaxpr_out, consts)

def _check_callable(fun):
  if not callable(fun):
    raise TypeError(f"Expected a callable value, got {fun}")
  if inspect.isgeneratorfunction(fun):
    raise TypeError(f"Expected a function, got a generator function: {fun}")

### Tracer

class CallbackTracer(Tracer):
  __slots__ = ['val']

  def __init__(self, trace, val):
    self._trace = trace
    self.val = val

  @property
  def aval(self):
    return core.get_aval(self.val)

  def full_lower(self):
    return self

class CallbackTrace(Trace):
  def __init__(self, *args, callback, strip_calls):
    super().__init__(*args)
    self.callback = callback
    self.strip_calls = strip_calls

  def pure(self, val):
    return CallbackTracer(self, val)

  def lift(self, val):
    return CallbackTracer(self, val)

  def sublift(self, val):
    return CallbackTracer(self, val.val)

  def process_primitive(self, primitive, tracers, params):
    if primitive in custom_callback_rules:
      return custom_callback_rules[primitive](self, *tracers, **params)
    vals_in = [t.val for t in tracers]
    vals_out = self.callback(primitive, vals_in, params)  # type: ignore
    if primitive.multiple_results:
      return [CallbackTracer(self, val) for val in vals_out]
    return CallbackTracer(self, vals_out)

  def process_call(self, call_primitive, f: lu.WrappedFun, tracers, params):
    if self.strip_calls: # type: ignore
      return f.call_wrapped(*tracers)
    vals_in = [t.val for t in tracers]
    f = callback_subtrace(f, self.main)
    vals_out = call_primitive.bind(f, *vals_in, **params)
    return [CallbackTracer(self, val) for val in vals_out]

  def process_custom_jvp_call(self, primitive, fun, jvp, tracers):
    vals_in = [t.val for t in tracers]
    fun = callback_subtrace(fun, self.main)
    jvp = callback_subtrace(jvp, self.main)
    out = primitive.bind(fun, jvp, *vals_in)
    return safe_map(self.pure, out)

  def process_custom_vjp_call(self, primitive, fun, fwd, bwd, tracers,
                              out_trees):
    vals_in = [t.val for t in tracers]
    fun = callback_subtrace(fun, self.main)
    fwd = callback_subtrace(fwd, self.main)
    bwd = callback_subtrace(bwd, self.main)
    out = primitive.bind(fun, fwd, bwd, *vals_in, out_trees=out_trees)
    return safe_map(self.pure, out)

custom_callback_rules: Dict[Any, Any] = {}

def _scan_callback_rule(trace, *tracers, reverse, length, num_consts, num_carry,
                        jaxpr, linear, unroll):
  const_tracers, carry_tracers, xs_tracers = split_list(tracers, [num_consts, num_carry])
  carry_avals, xs_avals = tree_map(lambda x: x.aval, (carry_tracers, xs_tracers))
  const_vals, carry_vals, xs_vals = tree_map(lambda x: x.val, (const_tracers, carry_tracers, xs_tracers))

  x_tracers = [t[0] for t in xs_tracers]
  x_avals = [t.aval for t in x_tracers]

  body_fun = jaxpr_as_fun(jaxpr)

  def new_body(*vals):
    out = body_fun(*vals)
    out_carry, y = split_list(out, [num_carry])
    return out_carry, y
  new_body = callback_transform(new_body, trace.callback,
                                strip_calls=trace.strip_calls)  # type: ignore
  in_tree = tree_structure(carry_avals + xs_avals)
  new_jaxpr, new_consts, _ = lcf._initial_style_jaxpr(
      new_body, in_tree, tuple(carry_avals + x_avals))
  vals = tuple(it.chain(new_consts, carry_vals, xs_vals))
  out_vals = lax.scan_p.bind(*vals, reverse=reverse, length=length,
                             num_consts=len(new_consts), num_carry=num_carry,
                             jaxpr=new_jaxpr, linear=linear, unroll=unroll)
  return safe_map(trace.pure, out_vals)

custom_callback_rules[lax.scan_p] = _scan_callback_rule


def _while_callback_rule(trace, *tracers, cond_jaxpr, body_jaxpr,
                         cond_nconsts, body_nconsts):
  cond_const_tracers, body_const_tracers, init_tracers = split_list(
            tracers, [cond_nconsts, body_nconsts])
  init_avals = safe_map(lambda x: x.aval, init_tracers)
  cond_const_vals, body_const_vals, init_vals = tree_map(
      lambda x: x.val, (cond_const_tracers, body_const_tracers, init_tracers))

  body_fun = jaxpr_as_fun(body_jaxpr)
  cond_fun = jaxpr_as_fun(cond_jaxpr)

  def cond(*carry):
    return cond_fun(*it.chain(cond_const_vals, carry))

  def body(*carry):
    return body_fun(*it.chain(body_const_vals, carry))

  new_cond = callback_transform(cond, trace.callback, strip_calls=trace.strip_calls)  # type: ignore
  new_body = callback_transform(body, trace.callback, strip_calls=trace.strip_calls)  # type: ignore
  in_tree = tree_structure(init_avals)

  new_cond_jaxpr, new_cond_consts, _ = lcf._initial_style_jaxpr(new_cond, in_tree, tuple(init_avals))
  new_body_jaxpr, new_body_consts, _ = lcf._initial_style_jaxpr(new_body, in_tree, tuple(init_avals))
  out = lcf.while_p.bind(
      *it.chain(new_cond_consts, new_body_consts, init_vals),
      cond_nconsts=len(new_cond_consts),
      body_nconsts=len(new_body_consts),
      cond_jaxpr=new_cond_jaxpr,
      body_jaxpr=new_body_jaxpr)
  return safe_map(trace.pure, out)

custom_callback_rules[lax.while_p] = _while_callback_rule

def _custom_derivative_call_jaxpr_callback_rule(primitive, trace, *tracers,
                                                fun_jaxpr, num_consts, **params):
  main = trace.main
  vals = [t.val for t in tracers]

  new_closed_jaxpr = callback_jaxpr(fun_jaxpr, trace.callback, strip_calls=trace.strip_calls)
  if primitive == cd.custom_vjp_call_jaxpr_p:
    thunk_name = 'fwd_jaxpr_thunk'
    params['bwd'] = callback_subtrace(params['bwd'], main)
  else:
    raise NotImplementedError(primitive)

  thunk = params.pop(thunk_name)
  @pe._memoize
  def new_thunk():
    thunk_jaxpr = core.ClosedJaxpr(*thunk())
    closed_jaxpr = callback_jaxpr(thunk_jaxpr, trace.callback, trace.strip_calls)
    return closed_jaxpr.jaxpr, closed_jaxpr.literals

  params[thunk_name] = new_thunk
  new_fun_jaxpr, new_consts = new_closed_jaxpr.jaxpr, new_closed_jaxpr.literals
  closed_fun_jaxpr = core.ClosedJaxpr(pe.convert_constvars_jaxpr(new_fun_jaxpr), ())
  new_num_consts = len(new_consts) + num_consts
  out = primitive.bind(*it.chain(new_consts, vals), fun_jaxpr=closed_fun_jaxpr,
                       num_consts=new_num_consts, **params)
  return safe_map(trace.pure, out)

custom_callback_rules[cd.custom_vjp_call_jaxpr_p] = partial(
    _custom_derivative_call_jaxpr_callback_rule, cd.custom_vjp_call_jaxpr_p)
