DataOps-platform/app/core/data_rules/expressions.py

"""Closed, typed rule expressions for governed DataOps rules.

The module deliberately owns both parsing and validation.  It produces JSON
only; expressions are never delegated to Python, SQL, JavaScript, or a model
runtime.  Compilers consume the resulting AST in a later release.
"""

from __future__ import annotations

from dataclasses import dataclass
from datetime import date as Date
from datetime import datetime
from decimal import Decimal, InvalidOperation, ROUND_HALF_UP
import re
from typing import Any
from zoneinfo import ZoneInfo


MAX_SOURCE_LENGTH = 20_000
MAX_AST_DEPTH = 40
MAX_AST_NODES = 500
MAX_REGEX_LENGTH = 500
ALLOWED_FUNCTIONS = frozenset(
    {
        "matches",
        "lower",
        "upper",
        "trim",
        "length",
        "coalesce",
        "date",
        "timestamp",
        "abs",
        "round",
    }
)
SUPPORTED_BACKENDS = frozenset({"postgresql", "mysql", "polars"})
_FUNCTION_BACKENDS = {
    "matches": SUPPORTED_BACKENDS,
    # The reference oracle verifies Python/Polars Unicode case folding. SQL
    # engines require a deployment-pinned collation before they may opt in.
    "lower": frozenset({"polars"}),
    "upper": frozenset({"polars"}),
    "trim": SUPPORTED_BACKENDS,
    "length": SUPPORTED_BACKENDS,
    "coalesce": SUPPORTED_BACKENDS,
    "date": SUPPORTED_BACKENDS,
    # MySQL timezone conversion depends on server timezone tables; do not
    # advertise it before a deployment can prove that dependency.
    "timestamp": frozenset({"postgresql", "polars"}),
    "abs": SUPPORTED_BACKENDS,
    # Polars rounding mode cannot be assumed to match the V1 decimal policy.
    "round": frozenset({"postgresql", "mysql"}),
}

_IDENTIFIER = re.compile(r"^[A-Za-z_][A-Za-z0-9_]{0,127}$")
_FIELD_TYPE_ALIASES = {
    "bigint": "integer",
    "bool": "boolean",
    "character varying": "string",
    "datetime": "timestamp",
    "int": "integer",
    "numeric": "decimal",
    "text": "string",
    "varchar": "string",
}
_FIELD_TYPES = {
    "binary",
    "boolean",
    "date",
    "decimal",
    "double",
    "float",
    "integer",
    "json",
    "string",
    "timestamp",
    "timestamptz",
}
_NUMERIC_TYPES = {"integer", "decimal", "float", "double"}
_LITERAL_TYPES = {"boolean", "decimal", "integer", "null", "string"}
_DECIMAL_LEXEME = re.compile(r"^[0-9]+\.[0-9]+$")
_BINARY_OPERATORS = {
    "||",
    "&&",
    "==",
    "!=",
    "<",
    "<=",
    ">",
    ">=",
    "+",
    "-",
    "*",
    "/",
    "%",
}
_PRECEDENCE = {
    "||": 10,
    "&&": 20,
    "==": 30,
    "!=": 30,
    "<": 30,
    "<=": 30,
    ">": 30,
    ">=": 30,
    "+": 40,
    "-": 40,
    "*": 50,
    "/": 50,
    "%": 50,
}


@dataclass(frozen=True)
class _Token:
    kind: str
    value: Any
    position: int


def _error(position: int, message: str) -> ValueError:
    return ValueError(f"expression {message} at position {position}")


class _Lexer:
    def __init__(self, source: str):
        self.source = source
        self.length = len(source)
        self.position = 0

    def tokens(self) -> list[_Token]:
        result: list[_Token] = []
        while self.position < self.length:
            char = self.source[self.position]
            if char.isspace():
                self.position += 1
            elif char in "'\"":
                result.append(self._string())
            elif char.isdigit():
                result.append(self._number())
            elif char.isascii() and (char.isalpha() or char == "_"):
                result.append(self._identifier())
            elif char in "(),":
                result.append(_Token(char, char, self.position))
                self.position += 1
            else:
                result.append(self._operator())
        result.append(_Token("EOF", None, self.position))
        return result

    def _string(self) -> _Token:
        start = self.position
        quote = self.source[self.position]
        self.position += 1
        pieces: list[str] = []
        escapes = {"n": "\n", "r": "\r", "t": "\t", "b": "\b", "f": "\f"}
        while self.position < self.length:
            char = self.source[self.position]
            self.position += 1
            if char == quote:
                value = "".join(pieces)
                if len(value) > 4_000:
                    raise _error(start, "string literal exceeds 4000 characters")
                return _Token("LITERAL", ("string", value), start)
            if char != "\\":
                pieces.append(char)
                continue
            if self.position >= self.length:
                raise _error(start, "contains an unfinished string escape")
            escaped = self.source[self.position]
            self.position += 1
            if escaped in escapes:
                pieces.append(escapes[escaped])
            elif escaped in {"\\", "'", '\"'}:
                pieces.append(escaped)
            elif escaped == "u":
                encoded = self.source[self.position : self.position + 4]
                if len(encoded) != 4 or not re.fullmatch(r"[0-9a-fA-F]{4}", encoded):
                    raise _error(start, "contains an invalid unicode escape")
                pieces.append(chr(int(encoded, 16)))
                self.position += 4
            else:
                raise _error(start, "contains an unsupported string escape")
        raise _error(start, "contains an unterminated string")

    def _number(self) -> _Token:
        start = self.position
        while self.position < self.length and self.source[self.position].isdigit():
            self.position += 1
        kind = "integer"
        if self.position < self.length and self.source[self.position] == ".":
            kind = "decimal"
            self.position += 1
            decimal_start = self.position
            while self.position < self.length and self.source[self.position].isdigit():
                self.position += 1
            if self.position == decimal_start:
                raise _error(start, "contains an invalid numeric literal")
        raw = self.source[start : self.position]
        # Decimal tokens keep their lexeme in the JSON AST.  A float here
        # would destroy source precision before a compiler receives it.
        value: int | str = int(raw) if kind == "integer" else raw
        return _Token("LITERAL", (kind, value), start)

    def _identifier(self) -> _Token:
        start = self.position
        self.position += 1
        while self.position < self.length:
            char = self.source[self.position]
            if not (char.isascii() and (char.isalnum() or char == "_")):
                break
            self.position += 1
        value = self.source[start : self.position]
        if len(value) > 128:
            raise _error(start, "identifier exceeds 128 characters")
        lowered = value.lower()
        if lowered == "true":
            return _Token("LITERAL", ("boolean", True), start)
        if lowered == "false":
            return _Token("LITERAL", ("boolean", False), start)
        if lowered == "null":
            return _Token("LITERAL", ("null", None), start)
        return _Token("IDENT", value, start)

    def _operator(self) -> _Token:
        start = self.position
        for operator in ("&&", "||", "==", "!=", "<=", ">="):
            if self.source.startswith(operator, start):
                self.position += len(operator)
                return _Token("OP", operator, start)
        char = self.source[self.position]
        if char in "!<>+-*/%":
            self.position += 1
            return _Token("OP", char, start)
        raise _error(start, f"contains unexpected character {char!r}")


class _Parser:
    def __init__(self, source: str):
        self.tokens = _Lexer(source).tokens()
        self.index = 0

    @property
    def current(self) -> _Token:
        return self.tokens[self.index]

    def consume(self, kind: str, value: str | None = None) -> _Token:
        token = self.current
        if token.kind != kind or (value is not None and token.value != value):
            expected = value if value is not None else kind
            raise _error(token.position, f"expected {expected!r}")
        self.index += 1
        return token

    def parse(self) -> dict[str, Any]:
        expression = self._expression(0)
        if self.current.kind != "EOF":
            raise _error(self.current.position, "contains unexpected trailing input")
        return expression

    def _expression(self, minimum_precedence: int) -> dict[str, Any]:
        token = self.current
        self.index += 1
        if token.kind == "LITERAL":
            literal_type, value = token.value
            left = {"kind": "literal", "type": literal_type, "value": value}
        elif token.kind == "IDENT":
            if self.current.kind == "(":
                if token.value not in ALLOWED_FUNCTIONS:
                    raise _error(
                        token.position,
                        f"uses unsupported expression function {token.value!r}",
                    )
                self.index += 1
                arguments: list[dict[str, Any]] = []
                if self.current.kind != ")":
                    while True:
                        arguments.append(self._expression(0))
                        if self.current.kind != ",":
                            break
                        self.index += 1
                self.consume(")")
                left = {
                    "kind": "call",
                    "function": token.value,
                    "arguments": arguments,
                }
            else:
                left = {"kind": "identifier", "name": token.value}
        elif token.kind == "OP" and token.value in {"!", "-"}:
            left = {
                "kind": "unary",
                "operator": token.value,
                "operand": self._expression(60),
            }
        elif token.kind == "(":
            left = self._expression(0)
            self.consume(")")
        else:
            raise _error(token.position, "contains an unexpected token")

        while self.current.kind == "OP":
            operator = self.current.value
            precedence = _PRECEDENCE.get(operator)
            if precedence is None or precedence < minimum_precedence:
                break
            self.index += 1
            left = {
                "kind": "binary",
                "operator": operator,
                "left": left,
                "right": self._expression(precedence + 1),
            }
        return left


def parse_expression(source: str) -> dict:
    """Parse a V1 expression into the closed, JSON-serializable AST."""

    if not isinstance(source, str) or not source.strip():
        raise ValueError("expression source is required")
    if len(source) > MAX_SOURCE_LENGTH:
        raise ValueError(f"expression source exceeds {MAX_SOURCE_LENGTH} characters")
    ast = _Parser(source).parse()
    _validate_ast(ast)
    return ast


def _validate_ast(ast: Any) -> None:
    count = 0

    def walk(node: Any, depth: int) -> None:
        nonlocal count
        if depth > MAX_AST_DEPTH:
            raise ValueError(f"expression AST depth exceeds {MAX_AST_DEPTH}")
        count += 1
        if count > MAX_AST_NODES:
            raise ValueError(f"expression AST node count exceeds {MAX_AST_NODES}")
        if not isinstance(node, dict):
            raise ValueError("expression AST node must be an object")
        kind = node.get("kind")
        if kind == "literal":
            if set(node) != {"kind", "type", "value"}:
                raise ValueError("literal AST node must have a closed shape")
            literal_type = node.get("type")
            value = node.get("value")
            if literal_type not in _LITERAL_TYPES:
                raise ValueError("literal AST node has an unsupported type")
            if literal_type == "null" and value is not None:
                raise ValueError("null literal must have a null value")
            if literal_type == "boolean" and not isinstance(value, bool):
                raise ValueError("boolean literal must have a boolean value")
            if literal_type == "string" and (
                not isinstance(value, str) or len(value) > 4_000
            ):
                raise ValueError("string literal is invalid")
            if literal_type == "integer" and (
                isinstance(value, bool) or not isinstance(value, int)
            ):
                raise ValueError("integer literal is invalid")
            if literal_type == "decimal" and (
                not isinstance(value, str)
                or _DECIMAL_LEXEME.fullmatch(value) is None
            ):
                raise ValueError("decimal literal is invalid")
            return
        if kind == "identifier":
            if set(node) != {"kind", "name"} or not isinstance(node.get("name"), str):
                raise ValueError("identifier AST node must have a closed shape")
            if _IDENTIFIER.fullmatch(node["name"]) is None:
                raise ValueError("identifier AST node has an invalid name")
            return
        if kind == "unary":
            if set(node) != {"kind", "operator", "operand"}:
                raise ValueError("unary AST node must have a closed shape")
            if node.get("operator") not in {"!", "-"}:
                raise ValueError("unary AST node has an unsupported operator")
            walk(node.get("operand"), depth + 1)
            return
        if kind == "binary":
            if set(node) != {"kind", "operator", "left", "right"}:
                raise ValueError("binary AST node must have a closed shape")
            if node.get("operator") not in _BINARY_OPERATORS:
                raise ValueError("binary AST node has an unsupported operator")
            walk(node.get("left"), depth + 1)
            walk(node.get("right"), depth + 1)
            return
        if kind == "call":
            if set(node) != {"kind", "function", "arguments"}:
                raise ValueError("call AST node must have a closed shape")
            function = node.get("function")
            arguments = node.get("arguments")
            if not isinstance(function, str) or _IDENTIFIER.fullmatch(function) is None:
                raise ValueError("call AST node has an invalid function")
            if function not in ALLOWED_FUNCTIONS:
                raise ValueError(f"unsupported expression function: {function}")
            if not isinstance(arguments, list) or len(arguments) > 100:
                raise ValueError("call AST arguments must be a bounded array")
            for argument in arguments:
                walk(argument, depth + 1)
            # This resource bound is independent of schema typing, so RuleSpec
            # normalization can reject an unsafe regex before compilation.
            if (
                function == "matches"
                and len(arguments) >= 2
                and arguments[1].get("kind") == "literal"
                and arguments[1].get("type") == "string"
            ):
                if len(arguments[1]["value"]) > MAX_REGEX_LENGTH:
                    raise ValueError(
                        f"regex pattern exceeds {MAX_REGEX_LENGTH} characters"
                    )
            return
        raise ValueError("expression AST node kind is unsupported")

    walk(ast, 1)


def _normalized_fields(fields: Any) -> dict[str, str]:
    if not isinstance(fields, dict) or len(fields) > 1_000:
        raise ValueError("expression fields must be a bounded object")
    normalized: dict[str, str] = {}
    for name, field_type in fields.items():
        if not isinstance(name, str) or _IDENTIFIER.fullmatch(name) is None:
            raise ValueError("expression field names must be identifiers")
        if not isinstance(field_type, str):
            raise ValueError(f"expression field {name} type is invalid")
        result_type = _FIELD_TYPE_ALIASES.get(
            field_type.strip().lower(), field_type.strip().lower()
        )
        if result_type not in _FIELD_TYPES:
            raise ValueError(f"expression field {name} has an unsupported type")
        normalized[name] = result_type
    return normalized


def _is_numeric(value_type: str) -> bool:
    return value_type in _NUMERIC_TYPES


def _promote_numeric(left: str, right: str) -> str:
    order = {"integer": 0, "decimal": 1, "float": 2, "double": 3}
    return max((left, right), key=lambda value: order[value])


def _compatible(left: str, right: str) -> bool:
    return left == "null" or right == "null" or left == right or (
        _is_numeric(left) and _is_numeric(right)
    )


def _require_arguments(function: str, arguments: list[dict], expected: int | tuple[int, int]) -> None:
    if isinstance(expected, int):
        valid = len(arguments) == expected
    else:
        valid = expected[0] <= len(arguments) <= expected[1]
    if not valid:
        raise ValueError(f"function {function} received an unsupported argument count")


def type_check_expression(ast: dict, fields: dict[str, str]) -> str:
    """Validate schema-bound identifiers and return the expression result type."""

    _validate_ast(ast)
    normalized_fields = _normalized_fields(fields)

    def check(node: dict) -> str:
        kind = node["kind"]
        if kind == "literal":
            return node["type"]
        if kind == "identifier":
            name = node["name"]
            if name not in normalized_fields:
                raise ValueError(f"unknown expression field: {name}")
            return normalized_fields[name]
        if kind == "unary":
            operand_type = check(node["operand"])
            operator = node["operator"]
            if operator == "!":
                if operand_type != "boolean":
                    raise ValueError("logical not requires a boolean operand")
                return "boolean"
            if not _is_numeric(operand_type):
                raise ValueError("numeric negation requires a numeric operand")
            return operand_type
        if kind == "binary":
            left_type = check(node["left"])
            right_type = check(node["right"])
            operator = node["operator"]
            if operator in {"&&", "||"}:
                if left_type != "boolean" or right_type != "boolean":
                    raise ValueError("logical operators require boolean operands")
                return "boolean"
            if operator in {"+", "-", "*", "/", "%"}:
                if not _is_numeric(left_type) or not _is_numeric(right_type):
                    raise ValueError("arithmetic operators require numeric operands")
                return _promote_numeric(left_type, right_type)
            if not _compatible(left_type, right_type):
                raise ValueError(
                    "comparison operands must have compatible types; use an explicit cast"
                )
            return "boolean"
        function = node["function"]
        arguments = node["arguments"]
        if function not in ALLOWED_FUNCTIONS:
            raise ValueError(f"unsupported expression function: {function}")
        argument_types = [check(argument) for argument in arguments]
        if function == "matches":
            _require_arguments(function, arguments, 2)
            if argument_types != ["string", "string"]:
                raise ValueError("matches requires string arguments")
            pattern = arguments[1]
            if pattern["kind"] != "literal" or pattern["type"] != "string":
                raise ValueError("matches pattern must be a string literal")
            if len(pattern["value"]) > MAX_REGEX_LENGTH:
                raise ValueError(f"regex pattern exceeds {MAX_REGEX_LENGTH} characters")
            try:
                re.compile(pattern["value"])
            except re.error as exc:
                raise ValueError("regex pattern is invalid") from exc
            return "boolean"
        if function in {"lower", "upper", "trim"}:
            _require_arguments(function, arguments, 1)
            if argument_types != ["string"]:
                raise ValueError(f"{function} requires a string argument")
            return "string"
        if function == "length":
            _require_arguments(function, arguments, 1)
            if argument_types != ["string"]:
                raise ValueError("length requires a string argument")
            return "integer"
        if function == "coalesce":
            _require_arguments(function, arguments, (2, 100))
            concrete = [value for value in argument_types if value != "null"]
            if not concrete:
                return "null"
            if not all(_compatible(concrete[0], value) for value in concrete[1:]):
                raise ValueError("coalesce arguments must have compatible types")
            if all(_is_numeric(value) for value in concrete):
                return max(concrete, key=lambda value: {"integer": 0, "decimal": 1, "float": 2, "double": 3}[value])
            return concrete[0]
        if function == "date":
            _require_arguments(function, arguments, 1)
            if argument_types[0] not in {"string", "date", "timestamp", "timestamptz"}:
                raise ValueError("date requires a string or temporal argument")
            return "date"
        if function == "timestamp":
            _require_arguments(function, arguments, 1)
            if argument_types[0] not in {"string", "date", "timestamp", "timestamptz"}:
                raise ValueError("timestamp requires a string or temporal argument")
            return "timestamp"
        if function == "abs":
            _require_arguments(function, arguments, 1)
            if not _is_numeric(argument_types[0]):
                raise ValueError("abs requires a numeric argument")
            return argument_types[0]
        _require_arguments(function, arguments, (1, 2))
        if not _is_numeric(argument_types[0]):
            raise ValueError("round requires a numeric value")
        if len(argument_types) == 2 and argument_types[1] != "integer":
            raise ValueError("round precision requires an integer")
        return argument_types[0]

    return check(ast)


def validate_rule_expressions(
    rule_spec: dict[str, Any], fields: dict[str, str]
) -> frozenset[str]:
    """Type-check every canonical expression in a schema-bound RuleSpec.

    Callers must supply fields from a server-owned schema snapshot, never an
    authoring request.  The return value is immutable-plan metadata rather
    than executable code and lets release reject unsupported backends early.
    """

    if not isinstance(rule_spec, dict) or not isinstance(
        rule_spec.get("steps"), list
    ):
        raise ValueError("rule spec steps are required for expression validation")
    supported_for_rule = SUPPORTED_BACKENDS
    for step in rule_spec["steps"]:
        if not isinstance(step, dict):
            raise ValueError("rule step must be an object")
        operation = step.get("op")
        ast = step.get("expression_ast")
        if operation in {"assert", "filter"} and ast is None:
            raise ValueError(f"{operation} expression is required")
        if ast is None:
            continue
        expression_type = type_check_expression(ast, fields)
        if operation in {"assert", "filter"} and expression_type != "boolean":
            raise ValueError(f"{operation} expression must return boolean")
        supported = backend_support(ast)
        if not supported:
            raise ValueError("expression has no supported execution backend")
        supported_for_rule = supported_for_rule & supported
    return frozenset(supported_for_rule)


def _portable_regex(pattern: str) -> bool:
    """Keep only the portable regular-expression subset advertised by V1."""

    if len(pattern) > MAX_REGEX_LENGTH:
        return False
    if re.search(r"\(\?|\\[1-9]|\\[pP]", pattern):
        return False
    try:
        re.compile(pattern)
    except re.error:
        return False
    return True


def backend_support(ast: dict) -> frozenset[str]:
    """Return backends that can preserve this grammar's V1 semantics.

    The result is intentionally a capability analysis, not a compiler.  It
    validates the closed AST again so hand-authored JSON cannot bypass the
    function allowlist before a compiler sees it.
    """

    _validate_ast(ast)

    def support(node: dict) -> frozenset[str]:
        kind = node["kind"]
        if kind in {"literal", "identifier"}:
            return SUPPORTED_BACKENDS
        if kind == "unary":
            return support(node["operand"])
        if kind == "binary":
            return support(node["left"]) & support(node["right"])
        function = node["function"]
        supported = _FUNCTION_BACKENDS[function]
        for argument in node["arguments"]:
            supported = supported & support(argument)
        if function == "matches":
            arguments = node["arguments"]
            if (
                len(arguments) != 2
                or arguments[1]["kind"] != "literal"
                or arguments[1]["type"] != "string"
                or not _portable_regex(arguments[1]["value"])
            ):
                return frozenset()
        return frozenset(supported)

    return support(ast)


def _decimal(value: Any) -> Decimal:
    if isinstance(value, Decimal):
        return value
    if isinstance(value, bool):
        raise ValueError("reference evaluator expected a numeric value")
    try:
        if isinstance(value, float):
            return Decimal(str(value))
        return Decimal(value)
    except (InvalidOperation, TypeError, ValueError) as exc:
        raise ValueError("reference evaluator expected a numeric value") from exc


def _timestamp(value: Any, timezone: ZoneInfo) -> datetime:
    if isinstance(value, datetime):
        result = value
    elif isinstance(value, Date):
        result = datetime.combine(value, datetime.min.time())
    elif isinstance(value, str):
        try:
            result = datetime.fromisoformat(value.replace("Z", "+00:00"))
        except ValueError as exc:
            raise ValueError("reference evaluator received an invalid timestamp") from exc
    else:
        raise ValueError("reference evaluator expected a temporal value")
    if result.tzinfo is None:
        result = result.replace(tzinfo=timezone)
    return result


def _sql_and(left: Any, right: Any) -> bool | None:
    if left is False or right is False:
        return False
    if left is None or right is None:
        return None
    return bool(left and right)


def _sql_or(left: Any, right: Any) -> bool | None:
    if left is True or right is True:
        return True
    if left is None or right is None:
        return None
    return bool(left or right)


def evaluate_expression(
    ast: dict, row: dict[str, Any], *, timezone: str = "UTC"
) -> Any:
    """Execute only the closed AST as a deterministic semantic test oracle.

    This is intentionally not a production runner.  It has no access to a
    filesystem, network, Python callables, SQL, or model-generated code.
    """

    _validate_ast(ast)
    if not isinstance(row, dict):
        raise ValueError("reference evaluator row must be an object")
    try:
        timezone_info = ZoneInfo(timezone)
    except Exception as exc:
        raise ValueError("reference evaluator timezone is invalid") from exc

    def evaluate(node: dict) -> Any:
        kind = node["kind"]
        if kind == "literal":
            if node["type"] == "decimal":
                return Decimal(node["value"])
            return node["value"]
        if kind == "identifier":
            if node["name"] not in row:
                raise ValueError(f"reference evaluator missing field: {node['name']}")
            return row[node["name"]]
        if kind == "unary":
            value = evaluate(node["operand"])
            if value is None:
                return None
            return (not value) if node["operator"] == "!" else -_decimal(value)
        if kind == "binary":
            left = evaluate(node["left"])
            right = evaluate(node["right"])
            operator = node["operator"]
            if operator == "&&":
                return _sql_and(left, right)
            if operator == "||":
                return _sql_or(left, right)
            if left is None or right is None:
                return None
            if operator in {"+", "-", "*", "/", "%"}:
                left_decimal = _decimal(left)
                right_decimal = _decimal(right)
                return {
                    "+": left_decimal + right_decimal,
                    "-": left_decimal - right_decimal,
                    "*": left_decimal * right_decimal,
                    "/": left_decimal / right_decimal,
                    "%": left_decimal % right_decimal,
                }[operator]
            if operator == "==":
                return left == right
            if operator == "!=":
                return left != right
            if operator == "<":
                return left < right
            if operator == "<=":
                return left <= right
            if operator == ">":
                return left > right
            return left >= right
        function = node["function"]
        arguments = [evaluate(argument) for argument in node["arguments"]]
        if function == "coalesce":
            return next((value for value in arguments if value is not None), None)
        if any(value is None for value in arguments):
            return None
        if function == "matches":
            return re.search(arguments[1], arguments[0]) is not None
        if function == "lower":
            return arguments[0].lower()
        if function == "upper":
            return arguments[0].upper()
        if function == "trim":
            return arguments[0].strip()
        if function == "length":
            return len(arguments[0])
        if function == "date":
            return _timestamp(arguments[0], timezone_info).astimezone(timezone_info).date()
        if function == "timestamp":
            return _timestamp(arguments[0], timezone_info)
        if function == "abs":
            return abs(_decimal(arguments[0]))
        precision = int(arguments[1]) if len(arguments) == 2 else 0
        return _decimal(arguments[0]).quantize(
            Decimal(1).scaleb(-precision), rounding=ROUND_HALF_UP
        )

    return evaluate(ast)