# This file is part of Hypothesis, which may be found at
# https://github.com/HypothesisWorks/hypothesis/
#
# Copyright the Hypothesis Authors.
# Individual contributors are listed in AUTHORS.rst and the git log.
#
# This Source Code Form is subject to the terms of the Mozilla Public License,
# v. 2.0. If a copy of the MPL was not distributed with this file, You can
# obtain one at https://mozilla.org/MPL/2.0/.

"""
This file tests for our ability to make precise shrinks.

Terminology: A shrink is *precise* if there is a single example (draw call) that
it replaces, without leaving any of the data before or after that draw call changed.
Otherwise, it is sloppy.

Precise shrinks correspond to the changes we can make to drawn data in isolation
of the rest of the test case. e.g. if we draw a list, we want to always be able
to delete an element from it without affecting things outside that list. If we
draw an integer, we always want to be able to subtract from it.

An example of a sloppy shrink is that we can sloppily replace any list with a prefix
of it by changing the boolean that says if we should draw more elements with False.
However leaves all the data corresponding to the rest of the list after that prefix
in the test case, so everything after the drawn list is deleted.

Having a rich vocabulary of precise shrinks we can make allows us to more easily
reason about shrunk data, because we can look at the data and think in terms of
what changes the shrinker would have made to it, and the fact that it hasn't
means we know that it's important. e.g. this numeric value can't be smaller, this
list can't have fewer elements.

Sloppy shrinks in contrast just make the test case smaller. This is still good,
obviously, and we rely on sloppy shrinks for a lot of shrinker performance and
quality - often what we can expect is that we get to a smaller test case faster
through sloppy shrinks, and then precise shrinks guarantee properties of the final
result.
"""


import itertools
from functools import lru_cache
from random import Random
from typing import Callable, TypeVar

import pytest

from hypothesis import find, settings, strategies as st
from hypothesis.control import BuildContext
from hypothesis.errors import StopTest, UnsatisfiedAssumption
from hypothesis.internal.conjecture.data import ConjectureData, ConjectureResult, Status
from hypothesis.internal.conjecture.engine import (
    ConjectureRunner,
    ExitReason,
    RunIsComplete,
)
from hypothesis.internal.conjecture.shrinker import sort_key

T = TypeVar("T")


def safe_draw(data, strategy):
    """Set up just enough of the Hypothesis machinery to use draw on
    a strategy."""
    with BuildContext(data):
        try:
            return data.draw(strategy)
        except UnsatisfiedAssumption:
            data.mark_invalid()


def precisely_shrink(
    strategy,
    is_interesting=lambda x: True,
    initial_condition=lambda x: True,
    end_marker=st.integers(),
    seed=0,
):
    """Generates a random value from the strategy and then precisely shrinks it,
    by shrinking it with some value immediately afterwards that is not allowed to
    be modified during shrinking."""
    random = Random(seed)

    while True:
        data = ConjectureData(random=random)
        try:
            initial_value = safe_draw(data, strategy)
        except StopTest:
            continue
        if is_interesting(initial_value) and initial_condition(initial_value):
            break

    target_check_value = safe_draw(data, end_marker)

    initial_choices = data.choices

    replay = ConjectureData.for_choices(initial_choices)
    assert safe_draw(replay, strategy) == initial_value
    assert safe_draw(replay, end_marker) == target_check_value

    def test_function(data):
        value = safe_draw(data, strategy)
        check_value = safe_draw(data, end_marker)
        if is_interesting(value) and check_value == target_check_value:
            data.mark_interesting()

    runner = ConjectureRunner(test_function, random=random)
    try:
        buf = runner.cached_test_function(initial_choices)
        assert buf.status == Status.INTERESTING
        assert buf.choices == initial_choices
        assert runner.interesting_examples
        runner.shrink_interesting_examples()
    except RunIsComplete:
        assert runner.exit_reason in (ExitReason.finished, ExitReason.max_shrinks)
    (result,) = runner.interesting_examples.values()

    data = ConjectureData.for_choices(result.choices)
    result_value = safe_draw(data, strategy)
    data.freeze()
    return data.as_result(), result_value


common_strategies_with_types = [
    (type(None), st.none()),
    (bool, st.booleans()),
    (bytes, st.binary()),
    (str, st.text()),
    (int, st.integers()),
]

common_strategies = [v for _, v in common_strategies_with_types]


@lru_cache
def minimal_for_strategy(s):
    return precisely_shrink(s, end_marker=st.none())


def minimal_nodes_for_strategy(s):
    return minimal_for_strategy(s)[0].nodes


def test_strategy_list_is_in_sorted_order():
    assert common_strategies == sorted(
        common_strategies, key=lambda s: sort_key(minimal_nodes_for_strategy(s))
    )


@pytest.mark.parametrize("typ,strat", common_strategies_with_types)
@pytest.mark.parametrize("require_truthy", [False, True])
def test_can_precisely_shrink_values(typ, strat, require_truthy):
    if typ is type(None) and require_truthy:
        pytest.skip("None is falsey")
    if require_truthy:
        cond = bool
    else:
        cond = lambda x: True
    result, shrunk = precisely_shrink(strat, is_interesting=cond)
    assert shrunk == find(strat, cond)


alternatives = [
    comb
    for n in (2, 3, 4)
    for comb in itertools.combinations(common_strategies_with_types, n)
]

indexed_alternatives = [
    (i, j, a) for a in alternatives for i, j in itertools.combinations(range(len(a)), 2)
]


@pytest.mark.parametrize("i,j,a", indexed_alternatives)
@pytest.mark.parametrize("seed", [0, 4389048901])
def test_can_precisely_shrink_alternatives(i, j, a, seed):
    types = [u for u, _ in a]
    combined_strategy = st.one_of(*[v for _, v in a])

    result, value = precisely_shrink(
        combined_strategy,
        initial_condition=lambda x: isinstance(x, types[j]),
        is_interesting=lambda x: not any(isinstance(x, types[k]) for k in range(i)),
        seed=seed,
    )
    assert isinstance(value, types[i])


@pytest.mark.parametrize(
    "a", list(itertools.combinations(common_strategies_with_types, 3))
)
@pytest.mark.parametrize("seed", [0, 4389048901])
def test_precise_shrink_with_blocker(a, seed):
    # We're reordering this so that there is a "blocking" unusually large
    # strategy in the middle.
    x, y, z = a
    a = (x, z, y)

    types = [u for u, _ in a]
    combined_strategy = st.one_of(*[v for _, v in a])

    result, value = precisely_shrink(
        combined_strategy,
        initial_condition=lambda x: isinstance(x, types[2]),
        is_interesting=lambda x: True,
        seed=seed,
    )

    assert isinstance(value, types[0])


def find_random(
    s: st.SearchStrategy[T], condition: Callable[[T], bool], seed=None
) -> tuple[ConjectureResult, T]:
    random = Random(seed)
    while True:
        data = ConjectureData(random=random)
        try:
            with BuildContext(data=data):
                value = data.draw(s)
                if condition(value):
                    data.freeze()
                    return (data.as_result(), value)
        except (StopTest, UnsatisfiedAssumption):
            continue


def shrinks(strategy, nodes, *, allow_sloppy=True, seed=0):
    results = {}
    random = Random(seed)
    choices = tuple(n.value for n in nodes)

    if allow_sloppy:

        def test_function(data):
            value = safe_draw(data, strategy)
            results[data.nodes] = value

        runner = ConjectureRunner(test_function, settings=settings(max_examples=10**9))
        initial = runner.cached_test_function(choices)
        assert isinstance(initial, ConjectureResult)
        try:
            runner.shrink(initial, lambda x: x.choices == initial.choices)
        except RunIsComplete:
            assert runner.exit_reason in (ExitReason.finished, ExitReason.max_shrinks)
    else:
        trial = ConjectureData(prefix=choices, random=random)
        with BuildContext(trial):
            trial.draw(strategy)
            assert trial.choices == choices, "choice sequence is already sloppy"
            padding = safe_draw(trial, st.integers())
        initial_choices = trial.choices

        def test_function(data):
            value = safe_draw(data, strategy)
            key = data.nodes
            padding_check = safe_draw(data, st.integers())
            if padding_check == padding:
                results[key] = value

        runner = ConjectureRunner(test_function, settings=settings(max_examples=10**9))
        initial = runner.cached_test_function(initial_choices)
        assert len(results) == 1
        try:
            runner.shrink(initial, lambda x: x.choices == initial_choices)
        except RunIsComplete:
            assert runner.exit_reason in (ExitReason.finished, ExitReason.max_shrinks)

    results.pop(nodes)
    seen = set()
    result_list = []

    for k, v in sorted(results.items(), key=lambda x: sort_key(x[0])):
        t = repr(v)
        if t in seen:
            continue
        seen.add(t)
        result_list.append((k, v))
    return result_list


@pytest.mark.parametrize("a", list(itertools.product(*([common_strategies[1:]] * 2))))
@pytest.mark.parametrize("block_falsey", [False, True])
@pytest.mark.parametrize("allow_sloppy", [False, True])
@pytest.mark.parametrize("seed", [0, 2452, 99085240570])
def test_always_shrinks_to_none(a, seed, block_falsey, allow_sloppy):
    combined_strategy = st.one_of(st.none(), *a)

    result, value = find_random(combined_strategy, lambda x: x is not None)
    shrunk_values = shrinks(
        combined_strategy, result.nodes, allow_sloppy=allow_sloppy, seed=seed
    )
    assert shrunk_values[0][1] is None


@pytest.mark.parametrize(
    "i,alts", [(i, alt) for alt in alternatives for i in range(1, len(alt))]
)
@pytest.mark.parametrize("force_small", [False, True])
@pytest.mark.parametrize("seed", [0, 2452, 99085240570])
def test_can_shrink_to_every_smaller_alternative(i, alts, seed, force_small):
    types = [t for t, _ in alts]
    strats = [s for _, s in alts]
    combined_strategy = st.one_of(*strats)
    if force_small:
        result, value = precisely_shrink(
            combined_strategy, is_interesting=lambda x: type(x) is types[i], seed=seed
        )
    else:
        result, value = find_random(
            combined_strategy, lambda x: type(x) is types[i], seed=seed
        )

    shrunk = shrinks(
        combined_strategy,
        result.nodes,
        allow_sloppy=False,
        # Arbitrary change so we don't use the same seed for each Random.
        seed=seed * 17,
    )
    shrunk_values = [t for _, t in shrunk]

    for j in range(i):
        assert any(isinstance(x, types[j]) for x in shrunk_values)
