import datetime
import hashlib
import logging
import re
from typing import Optional

from dateutil import parser
from dateutil.relativedelta import relativedelta

from posthog import utils
from posthog.types import FlagValue
from posthog.utils import convert_to_datetime_aware, is_valid_regex

__LONG_SCALE__ = float(0xFFFFFFFFFFFFFFF)

log = logging.getLogger("posthog")

NONE_VALUES_ALLOWED_OPERATORS = ["is_not"]


class InconclusiveMatchError(Exception):
    pass


class RequiresServerEvaluation(Exception):
    """
    Raised when feature flag evaluation requires server-side data that is not
    available locally (e.g., static cohorts, experience continuity).

    This error should propagate immediately to trigger API fallback, unlike
    InconclusiveMatchError which allows trying other conditions.
    """

    pass


# This function takes a distinct_id and a feature flag key and returns a float between 0 and 1.
# Given the same distinct_id and key, it'll always return the same float. These floats are
# uniformly distributed between 0 and 1, so if we want to show this feature to 20% of traffic
# we can do _hash(key, distinct_id) < 0.2
def _hash(key: str, distinct_id: str, salt: str = "") -> float:
    hash_key = f"{key}.{distinct_id}{salt}"
    hash_val = int(hashlib.sha1(hash_key.encode("utf-8")).hexdigest()[:15], 16)
    return hash_val / __LONG_SCALE__


def get_matching_variant(flag, distinct_id):
    hash_value = _hash(flag["key"], distinct_id, salt="variant")
    for variant in variant_lookup_table(flag):
        if hash_value >= variant["value_min"] and hash_value < variant["value_max"]:
            return variant["key"]
    return None


def variant_lookup_table(feature_flag):
    lookup_table = []
    value_min = 0
    multivariates = ((feature_flag.get("filters") or {}).get("multivariate") or {}).get(
        "variants"
    ) or []
    for variant in multivariates:
        value_max = value_min + variant["rollout_percentage"] / 100
        lookup_table.append(
            {"value_min": value_min, "value_max": value_max, "key": variant["key"]}
        )
        value_min = value_max
    return lookup_table


def evaluate_flag_dependency(
    property, flags_by_key, evaluation_cache, distinct_id, properties, cohort_properties
):
    """
    Evaluate a flag dependency property according to the dependency chain algorithm.

    Args:
        property: Flag property with type="flag" and dependency_chain
        flags_by_key: Dictionary of all flags by their key
        evaluation_cache: Cache for storing evaluation results
        distinct_id: The distinct ID being evaluated
        properties: Person properties for evaluation
        cohort_properties: Cohort properties for evaluation

    Returns:
        bool: True if all dependencies in the chain evaluate to True, False otherwise
    """
    if flags_by_key is None or evaluation_cache is None:
        # Cannot evaluate flag dependencies without required context
        raise InconclusiveMatchError(
            f"Cannot evaluate flag dependency on '{property.get('key', 'unknown')}' without flags_by_key and evaluation_cache"
        )

    # Check if dependency_chain is present - it should always be provided for flag dependencies
    if "dependency_chain" not in property:
        # Missing dependency_chain indicates malformed server data
        raise InconclusiveMatchError(
            f"Flag dependency property for '{property.get('key', 'unknown')}' is missing required 'dependency_chain' field"
        )

    dependency_chain = property["dependency_chain"]

    # Handle circular dependency (empty chain means circular)
    if len(dependency_chain) == 0:
        log.debug(f"Circular dependency detected for flag: {property.get('key')}")
        raise InconclusiveMatchError(
            f"Circular dependency detected for flag '{property.get('key', 'unknown')}'"
        )

    # Evaluate all dependencies in the chain order
    for dep_flag_key in dependency_chain:
        if dep_flag_key not in evaluation_cache:
            # Need to evaluate this dependency first
            dep_flag = flags_by_key.get(dep_flag_key)
            if not dep_flag:
                # Missing flag dependency - cannot evaluate locally
                evaluation_cache[dep_flag_key] = None
                raise InconclusiveMatchError(
                    f"Cannot evaluate flag dependency '{dep_flag_key}' - flag not found in local flags"
                )
            else:
                # Check if the flag is active (same check as in client._compute_flag_locally)
                if not dep_flag.get("active"):
                    evaluation_cache[dep_flag_key] = False
                else:
                    # Recursively evaluate the dependency
                    try:
                        dep_result = match_feature_flag_properties(
                            dep_flag,
                            distinct_id,
                            properties,
                            cohort_properties,
                            flags_by_key,
                            evaluation_cache,
                        )
                        evaluation_cache[dep_flag_key] = dep_result
                    except InconclusiveMatchError as e:
                        # If we can't evaluate a dependency, store None and propagate the error
                        evaluation_cache[dep_flag_key] = None
                        raise InconclusiveMatchError(
                            f"Cannot evaluate flag dependency '{dep_flag_key}': {e}"
                        ) from e

        # Check the cached result
        cached_result = evaluation_cache[dep_flag_key]
        if cached_result is None:
            # Previously inconclusive - raise error again
            raise InconclusiveMatchError(
                f"Flag dependency '{dep_flag_key}' was previously inconclusive"
            )
        elif not cached_result:
            # Definitive False result - dependency failed
            return False

    # All dependencies in the chain have been evaluated successfully
    # Now check if the final flag value matches the expected value in the property
    flag_key = property.get("key")
    expected_value = property.get("value")
    operator = property.get("operator", "exact")

    if flag_key and expected_value is not None:
        # Get the actual value of the flag we're checking
        actual_value = evaluation_cache.get(flag_key)

        if actual_value is None:
            # Flag wasn't evaluated - this shouldn't happen if dependency chain is correct
            raise InconclusiveMatchError(
                f"Flag '{flag_key}' was not evaluated despite being in dependency chain"
            )

        # For flag dependencies, we need to compare the actual flag result with expected value
        # using the flag_evaluates_to operator logic
        if operator == "flag_evaluates_to":
            return matches_dependency_value(expected_value, actual_value)
        else:
            # This should never happen, but just to be defensive.
            raise InconclusiveMatchError(
                f"Flag dependency property for '{property.get('key', 'unknown')}' has invalid operator '{operator}'"
            )

    # If no value check needed, return True (all dependencies passed)
    return True


def matches_dependency_value(expected_value, actual_value):
    """
    Check if the actual flag value matches the expected dependency value.

    This follows the same logic as the C# MatchesDependencyValue function:
    - String variant case: check for exact match or boolean true
    - Boolean case: must match expected boolean value

    Args:
        expected_value: The expected value from the property
        actual_value: The actual value returned by the flag evaluation

    Returns:
        bool: True if the values match according to flag dependency rules
    """
    # String variant case - check for exact match or boolean true
    if isinstance(actual_value, str) and len(actual_value) > 0:
        if isinstance(expected_value, bool):
            # Any variant matches boolean true
            return expected_value
        elif isinstance(expected_value, str):
            # variants are case-sensitive, hence our comparison is too
            return actual_value == expected_value
        else:
            return False

    # Boolean case - must match expected boolean value
    elif isinstance(actual_value, bool) and isinstance(expected_value, bool):
        return actual_value == expected_value

    # Default case
    return False


def match_feature_flag_properties(
    flag,
    distinct_id,
    properties,
    cohort_properties=None,
    flags_by_key=None,
    evaluation_cache=None,
) -> FlagValue:
    flag_conditions = (flag.get("filters") or {}).get("groups") or []
    is_inconclusive = False
    cohort_properties = cohort_properties or {}
    # Some filters can be explicitly set to null, which require accessing variants like so
    flag_variants = ((flag.get("filters") or {}).get("multivariate") or {}).get(
        "variants"
    ) or []
    valid_variant_keys = [variant["key"] for variant in flag_variants]

    for condition in flag_conditions:
        try:
            # if any one condition resolves to True, we can shortcircuit and return
            # the matching variant
            if is_condition_match(
                flag,
                distinct_id,
                condition,
                properties,
                cohort_properties,
                flags_by_key,
                evaluation_cache,
            ):
                variant_override = condition.get("variant")
                if variant_override and variant_override in valid_variant_keys:
                    variant = variant_override
                else:
                    variant = get_matching_variant(flag, distinct_id)
                return variant or True
        except RequiresServerEvaluation:
            # Static cohort or other missing server-side data - must fallback to API
            raise
        except InconclusiveMatchError:
            # Evaluation error (bad regex, invalid date, missing property, etc.)
            # Track that we had an inconclusive match, but try other conditions
            is_inconclusive = True

    if is_inconclusive:
        raise InconclusiveMatchError(
            "Can't determine if feature flag is enabled or not with given properties"
        )

    # We can only return False when either all conditions are False, or
    # no condition was inconclusive.
    return False


def is_condition_match(
    feature_flag,
    distinct_id,
    condition,
    properties,
    cohort_properties,
    flags_by_key=None,
    evaluation_cache=None,
) -> bool:
    rollout_percentage = condition.get("rollout_percentage")
    if len(condition.get("properties") or []) > 0:
        for prop in condition.get("properties"):
            property_type = prop.get("type")
            if property_type == "cohort":
                matches = match_cohort(
                    prop,
                    properties,
                    cohort_properties,
                    flags_by_key,
                    evaluation_cache,
                    distinct_id,
                )
            elif property_type == "flag":
                matches = evaluate_flag_dependency(
                    prop,
                    flags_by_key,
                    evaluation_cache,
                    distinct_id,
                    properties,
                    cohort_properties,
                )
            else:
                matches = match_property(prop, properties)
            if not matches:
                return False

        if rollout_percentage is None:
            return True

    if rollout_percentage is not None and _hash(feature_flag["key"], distinct_id) > (
        rollout_percentage / 100
    ):
        return False

    return True


def match_property(property, property_values) -> bool:
    # only looks for matches where key exists in override_property_values
    # doesn't support operator is_not_set
    key = property.get("key")
    operator = property.get("operator") or "exact"
    value = property.get("value")

    if key not in property_values:
        raise InconclusiveMatchError(
            "can't match properties without a given property value"
        )

    if operator == "is_not_set":
        raise InconclusiveMatchError("can't match properties with operator is_not_set")

    override_value = property_values[key]

    if (operator not in NONE_VALUES_ALLOWED_OPERATORS) and override_value is None:
        return False

    if operator in ("exact", "is_not"):

        def compute_exact_match(value, override_value):
            if isinstance(value, list):
                return str(override_value).casefold() in [
                    str(val).casefold() for val in value
                ]
            return utils.str_iequals(value, override_value)

        if operator == "exact":
            return compute_exact_match(value, override_value)
        else:
            return not compute_exact_match(value, override_value)

    if operator == "is_set":
        return key in property_values

    if operator == "icontains":
        return utils.str_icontains(override_value, value)

    if operator == "not_icontains":
        return not utils.str_icontains(override_value, value)

    if operator == "regex":
        return (
            is_valid_regex(str(value))
            and re.compile(str(value)).search(str(override_value)) is not None
        )

    if operator == "not_regex":
        return (
            is_valid_regex(str(value))
            and re.compile(str(value)).search(str(override_value)) is None
        )

    if operator in ("gt", "gte", "lt", "lte"):
        # :TRICKY: We adjust comparison based on the override value passed in,
        # to make sure we handle both numeric and string comparisons appropriately.
        def compare(lhs, rhs, operator):
            if operator == "gt":
                return lhs > rhs
            elif operator == "gte":
                return lhs >= rhs
            elif operator == "lt":
                return lhs < rhs
            elif operator == "lte":
                return lhs <= rhs
            else:
                raise ValueError(f"Invalid operator: {operator}")

        parsed_value = None
        try:
            parsed_value = float(value)  # type: ignore
        except Exception:
            pass

        if parsed_value is not None and override_value is not None:
            if isinstance(override_value, str):
                return compare(override_value, str(value), operator)
            else:
                return compare(override_value, parsed_value, operator)
        else:
            return compare(str(override_value), str(value), operator)

    if operator in ["is_date_before", "is_date_after"]:
        try:
            parsed_date = relative_date_parse_for_feature_flag_matching(str(value))

            if not parsed_date:
                parsed_date = parser.parse(str(value))
                parsed_date = convert_to_datetime_aware(parsed_date)
        except Exception as e:
            raise InconclusiveMatchError(
                "The date set on the flag is not a valid format"
            ) from e

        if not parsed_date:
            raise InconclusiveMatchError(
                "The date set on the flag is not a valid format"
            )

        if isinstance(override_value, datetime.datetime):
            override_date = convert_to_datetime_aware(override_value)
            if operator == "is_date_before":
                return override_date < parsed_date
            else:
                return override_date > parsed_date
        elif isinstance(override_value, datetime.date):
            if operator == "is_date_before":
                return override_value < parsed_date.date()
            else:
                return override_value > parsed_date.date()
        elif isinstance(override_value, str):
            try:
                override_date = parser.parse(override_value)
                override_date = convert_to_datetime_aware(override_date)
                if operator == "is_date_before":
                    return override_date < parsed_date
                else:
                    return override_date > parsed_date
            except Exception:
                raise InconclusiveMatchError("The date provided is not a valid format")
        else:
            raise InconclusiveMatchError(
                "The date provided must be a string or date object"
            )

    # if we get here, we don't know how to handle the operator
    raise InconclusiveMatchError(f"Unknown operator {operator}")


def match_cohort(
    property,
    property_values,
    cohort_properties,
    flags_by_key=None,
    evaluation_cache=None,
    distinct_id=None,
) -> bool:
    # Cohort properties are in the form of property groups like this:
    # {
    #     "cohort_id": {
    #         "type": "AND|OR",
    #         "values": [{
    #            "key": "property_name", "value": "property_value"
    #        }]
    #     }
    # }
    cohort_id = str(property.get("value"))
    if cohort_id not in cohort_properties:
        raise RequiresServerEvaluation(
            f"cohort {cohort_id} not found in local cohorts - likely a static cohort that requires server evaluation"
        )

    property_group = cohort_properties[cohort_id]
    return match_property_group(
        property_group,
        property_values,
        cohort_properties,
        flags_by_key,
        evaluation_cache,
        distinct_id,
    )


def match_property_group(
    property_group,
    property_values,
    cohort_properties,
    flags_by_key=None,
    evaluation_cache=None,
    distinct_id=None,
) -> bool:
    if not property_group:
        return True

    property_group_type = property_group.get("type")
    properties = property_group.get("values")

    if not properties or len(properties) == 0:
        # empty groups are no-ops, always match
        return True

    error_matching_locally = False

    if "values" in properties[0]:
        # a nested property group
        for prop in properties:
            try:
                matches = match_property_group(
                    prop,
                    property_values,
                    cohort_properties,
                    flags_by_key,
                    evaluation_cache,
                    distinct_id,
                )
                if property_group_type == "AND":
                    if not matches:
                        return False
                else:
                    # OR group
                    if matches:
                        return True
            except RequiresServerEvaluation:
                # Immediately propagate - this condition requires server-side data
                raise
            except InconclusiveMatchError as e:
                log.debug(f"Failed to compute property {prop} locally: {e}")
                error_matching_locally = True

        if error_matching_locally:
            raise InconclusiveMatchError(
                "Can't match cohort without a given cohort property value"
            )
        # if we get here, all matched in AND case, or none matched in OR case
        return property_group_type == "AND"

    else:
        for prop in properties:
            try:
                if prop.get("type") == "cohort":
                    matches = match_cohort(
                        prop,
                        property_values,
                        cohort_properties,
                        flags_by_key,
                        evaluation_cache,
                        distinct_id,
                    )
                elif prop.get("type") == "flag":
                    matches = evaluate_flag_dependency(
                        prop,
                        flags_by_key,
                        evaluation_cache,
                        distinct_id,
                        property_values,
                        cohort_properties,
                    )
                else:
                    matches = match_property(prop, property_values)

                negation = prop.get("negation", False)

                if property_group_type == "AND":
                    # if negated property, do the inverse
                    if not matches and not negation:
                        return False
                    if matches and negation:
                        return False
                else:
                    # OR group
                    if matches and not negation:
                        return True
                    if not matches and negation:
                        return True
            except RequiresServerEvaluation:
                # Immediately propagate - this condition requires server-side data
                raise
            except InconclusiveMatchError as e:
                log.debug(f"Failed to compute property {prop} locally: {e}")
                error_matching_locally = True

        if error_matching_locally:
            raise InconclusiveMatchError(
                "can't match cohort without a given cohort property value"
            )

        # if we get here, all matched in AND case, or none matched in OR case
        return property_group_type == "AND"


def relative_date_parse_for_feature_flag_matching(
    value: str,
) -> Optional[datetime.datetime]:
    regex = r"^-?(?P<number>[0-9]+)(?P<interval>[a-z])$"
    match = re.search(regex, value)
    parsed_dt = datetime.datetime.now(datetime.timezone.utc)
    if match:
        number = int(match.group("number"))

        if number >= 10_000:
            # Guard against overflow, disallow numbers greater than 10_000
            return None

        interval = match.group("interval")
        if interval == "h":
            parsed_dt = parsed_dt - relativedelta(hours=number)
        elif interval == "d":
            parsed_dt = parsed_dt - relativedelta(days=number)
        elif interval == "w":
            parsed_dt = parsed_dt - relativedelta(weeks=number)
        elif interval == "m":
            parsed_dt = parsed_dt - relativedelta(months=number)
        elif interval == "y":
            parsed_dt = parsed_dt - relativedelta(years=number)
        else:
            return None

        return parsed_dt
    else:
        return None