tessellate-core 0.3.0

use chrono::NaiveDate;
use num_bigint::BigInt;
use rust_decimal::Decimal;
use serde::{Deserialize, Serialize};
use serde_json::Value as JsonValue;
use std::collections::BTreeSet;
use std::error::Error;
use std::fmt;

/// A runtime value produced by a Tess expression.
///
/// Variant order is part of the stable ordering used in diagnostics and JSON
/// output. Decimal values are normalized whenever they enter through the
/// constructors in this module, so numerically equal values also render alike.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[serde(tag = "type", content = "value", rename_all = "snake_case")]
pub enum Value {
    Bool(bool),
    Int(i64),
    Decimal(#[serde(with = "exact_decimal_serde")] Decimal),
    String(String),
    Date(NaiveDate),
    /// An exact, signed number of seconds.
    Duration(i64),
    Enum {
        type_name: String,
        variant: String,
    },
    EntityRef {
        type_name: String,
        id: String,
    },
}

impl Value {
    #[must_use]
    pub fn decimal(value: Decimal) -> Self {
        Self::Decimal(value.normalize())
    }

    #[must_use]
    pub const fn kind_name(&self) -> &'static str {
        match self {
            Self::Bool(_) => "Bool",
            Self::Int(_) => "Int",
            Self::Decimal(_) => "Decimal",
            Self::String(_) => "String",
            Self::Date(_) => "Date",
            Self::Duration(_) => "Duration",
            Self::Enum { .. } => "Enum",
            Self::EntityRef { .. } => "Entity",
        }
    }

    #[must_use]
    pub const fn as_bool(&self) -> Option<bool> {
        if let Self::Bool(value) = self {
            Some(*value)
        } else {
            None
        }
    }

    #[must_use]
    pub const fn as_int(&self) -> Option<i64> {
        if let Self::Int(value) = self {
            Some(*value)
        } else {
            None
        }
    }

    #[must_use]
    pub const fn as_decimal(&self) -> Option<Decimal> {
        if let Self::Decimal(value) = self {
            Some(*value)
        } else {
            None
        }
    }

    #[must_use]
    pub const fn as_date(&self) -> Option<NaiveDate> {
        if let Self::Date(value) = self {
            Some(*value)
        } else {
            None
        }
    }

    #[must_use]
    pub const fn as_duration_seconds(&self) -> Option<i64> {
        if let Self::Duration(value) = self {
            Some(*value)
        } else {
            None
        }
    }

    /// Lossless, self-describing JSON representation.
    ///
    /// # Errors
    ///
    /// Returns a serialization error if the configured JSON serializer cannot
    /// represent a value.
    pub fn to_json(&self) -> Result<JsonValue, serde_json::Error> {
        serde_json::to_value(self)
    }

    /// Decodes the lossless, self-describing representation from [`to_json`](Self::to_json).
    ///
    /// # Errors
    ///
    /// Returns [`ValueConversionError::InvalidTaggedValue`] for malformed or
    /// unsupported tagged values.
    pub fn from_json(value: JsonValue) -> Result<Self, ValueConversionError> {
        serde_json::from_value(value)
            .map(Self::normalized)
            .map_err(|error| ValueConversionError::InvalidTaggedValue(error.to_string()))
    }

    /// JSON representation used when a surrounding schema already supplies the type.
    #[must_use]
    pub fn to_plain_json(&self) -> JsonValue {
        match self {
            Self::Bool(value) => JsonValue::Bool(*value),
            Self::Int(value) | Self::Duration(value) => JsonValue::Number((*value).into()),
            // A string keeps the exact schema independent of downstream JSON number parsers.
            Self::Decimal(value) => JsonValue::String(value.normalize().to_string()),
            Self::String(value) | Self::EntityRef { id: value, .. } => {
                JsonValue::String(value.clone())
            }
            Self::Date(value) => JsonValue::String(value.format("%Y-%m-%d").to_string()),
            Self::Enum { variant, .. } => JsonValue::String(variant.clone()),
        }
    }

    /// Decodes conventional JSON using an expected Tess value kind.
    ///
    /// # Errors
    ///
    /// Returns a type or literal conversion error when `value` does not match
    /// `expected`.
    pub fn from_plain_json(
        value: &JsonValue,
        expected: &ValueKind,
    ) -> Result<Self, ValueConversionError> {
        match expected {
            ValueKind::Bool => value
                .as_bool()
                .map(Self::Bool)
                .ok_or_else(|| type_mismatch(expected, value)),
            ValueKind::Int => value
                .as_i64()
                .map(Self::Int)
                .ok_or_else(|| type_mismatch(expected, value)),
            ValueKind::Decimal => {
                let text = match value {
                    JsonValue::Number(number) => number.to_string(),
                    JsonValue::String(text) => text.clone(),
                    _ => return Err(type_mismatch(expected, value)),
                };
                parse_decimal(&text)
                    .map(Self::Decimal)
                    .map_err(|error| ValueConversionError::InvalidDecimal(error.to_string()))
            }
            ValueKind::String => value
                .as_str()
                .map(|value| Self::String(value.to_owned()))
                .ok_or_else(|| type_mismatch(expected, value)),
            ValueKind::Date => {
                let text = value
                    .as_str()
                    .ok_or_else(|| type_mismatch(expected, value))?;
                NaiveDate::parse_from_str(text, "%Y-%m-%d")
                    .map(Self::Date)
                    .map_err(|_| ValueConversionError::InvalidDate(text.to_owned()))
            }
            ValueKind::Duration => value
                .as_i64()
                .map(Self::Duration)
                .ok_or_else(|| type_mismatch(expected, value)),
            ValueKind::Enum(type_name) => value
                .as_str()
                .map(|variant| Self::Enum {
                    type_name: type_name.clone(),
                    variant: variant.to_owned(),
                })
                .ok_or_else(|| type_mismatch(expected, value)),
            ValueKind::EntityRef(type_name) => value
                .as_str()
                .map(|id| Self::EntityRef {
                    type_name: type_name.clone(),
                    id: id.to_owned(),
                })
                .ok_or_else(|| type_mismatch(expected, value)),
        }
    }

    fn normalized(self) -> Self {
        match self {
            Self::Decimal(value) => Self::Decimal(value.normalize()),
            other => other,
        }
    }
}

impl fmt::Display for Value {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Bool(value) => value.fmt(formatter),
            Self::Int(value) => formatter.write_str(&group_integer_digits(&value.to_string())),
            Self::Decimal(value) => {
                let normalized = value.normalize().to_string();
                let (integer, fraction) = normalized.split_once('.').unwrap_or((&normalized, ""));
                formatter.write_str(&group_integer_digits(integer))?;
                if !fraction.is_empty() {
                    write!(formatter, ".{fraction}")?;
                }
                Ok(())
            }
            Self::String(value) => write!(formatter, "{value:?}"),
            Self::Date(value) => write!(formatter, "{}", value.format("%Y-%m-%d")),
            Self::Duration(seconds) => {
                write!(formatter, "{}s", group_integer_digits(&seconds.to_string()))
            }
            Self::Enum { type_name, variant } => write!(formatter, "{type_name}::{variant}"),
            Self::EntityRef { type_name, id } => write!(formatter, "{type_name}#{id}"),
        }
    }
}

pub(crate) fn group_integer_digits(value: &str) -> String {
    let (sign, digits) = value
        .strip_prefix('-')
        .map_or(("", value), |digits| ("-", digits));
    let separator_count = digits.len().saturating_sub(1) / 3;
    let mut grouped = String::with_capacity(value.len() + separator_count);
    grouped.push_str(sign);
    for (index, digit) in digits.chars().enumerate() {
        if index != 0 && (digits.len() - index) % 3 == 0 {
            grouped.push('_');
        }
        grouped.push(digit);
    }
    grouped
}

/// Type information needed to decode untagged, schema-directed JSON values.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[serde(tag = "kind", content = "name", rename_all = "snake_case")]
pub enum ValueKind {
    Bool,
    Int,
    Decimal,
    String,
    Date,
    Duration,
    Enum(String),
    EntityRef(String),
}

impl fmt::Display for ValueKind {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Bool => formatter.write_str("Bool"),
            Self::Int => formatter.write_str("Int"),
            Self::Decimal => formatter.write_str("Decimal"),
            Self::String => formatter.write_str("String"),
            Self::Date => formatter.write_str("Date"),
            Self::Duration => formatter.write_str("Duration"),
            Self::Enum(name) | Self::EntityRef(name) => formatter.write_str(name),
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum ValueConversionError {
    TypeMismatch {
        expected: ValueKind,
        found: &'static str,
    },
    InvalidDecimal(String),
    InvalidDate(String),
    InvalidTaggedValue(String),
}

impl fmt::Display for ValueConversionError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::TypeMismatch { expected, found } => {
                write!(formatter, "expected {expected}, found JSON {found}")
            }
            Self::InvalidDecimal(message) => write!(formatter, "invalid Decimal: {message}"),
            Self::InvalidDate(value) => {
                write!(formatter, "invalid Date `{value}`; expected YYYY-MM-DD")
            }
            Self::InvalidTaggedValue(message) => {
                write!(formatter, "invalid tagged Tess value: {message}")
            }
        }
    }
}

impl Error for ValueConversionError {}

fn type_mismatch(expected: &ValueKind, value: &JsonValue) -> ValueConversionError {
    let found = match value {
        JsonValue::Null => "null",
        JsonValue::Bool(_) => "boolean",
        JsonValue::Number(_) => "number",
        JsonValue::String(_) => "string",
        JsonValue::Array(_) => "array",
        JsonValue::Object(_) => "object",
    };
    ValueConversionError::TypeMismatch {
        expected: expected.clone(),
        found,
    }
}

/// Four-valued truth used by Tess's open-world, paraconsistent logic.
#[derive(
    Clone, Copy, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize,
)]
#[serde(rename_all = "lowercase")]
pub enum TruthValue {
    True,
    False,
    #[default]
    Unknown,
    Conflict,
}

impl TruthValue {
    #[must_use]
    pub const fn not(self) -> Self {
        match self {
            Self::True => Self::False,
            Self::False => Self::True,
            Self::Unknown => Self::Unknown,
            Self::Conflict => Self::Conflict,
        }
    }

    /// Conflict-preserving conjunction.
    ///
    /// Dominance order: `false > conflict > unknown > true`.
    #[must_use]
    pub const fn and(self, other: Self) -> Self {
        if matches!(self, Self::False) || matches!(other, Self::False) {
            Self::False
        } else if matches!(self, Self::Conflict) || matches!(other, Self::Conflict) {
            Self::Conflict
        } else if matches!(self, Self::Unknown) || matches!(other, Self::Unknown) {
            Self::Unknown
        } else {
            Self::True
        }
    }

    /// Conflict-preserving disjunction.
    ///
    /// Dominance order: `true > conflict > unknown > false`.
    #[must_use]
    pub const fn or(self, other: Self) -> Self {
        if matches!(self, Self::True) || matches!(other, Self::True) {
            Self::True
        } else if matches!(self, Self::Conflict) || matches!(other, Self::Conflict) {
            Self::Conflict
        } else if matches!(self, Self::Unknown) || matches!(other, Self::Unknown) {
            Self::Unknown
        } else {
            Self::False
        }
    }

    #[must_use]
    pub const fn is_true(self) -> bool {
        matches!(self, Self::True)
    }

    #[must_use]
    pub const fn is_false(self) -> bool {
        matches!(self, Self::False)
    }

    #[must_use]
    pub const fn is_known(self) -> bool {
        matches!(self, Self::True | Self::False)
    }
}

impl From<bool> for TruthValue {
    fn from(value: bool) -> Self {
        if value { Self::True } else { Self::False }
    }
}

impl std::ops::Not for TruthValue {
    type Output = Self;

    fn not(self) -> Self::Output {
        self.not()
    }
}

impl std::ops::BitAnd for TruthValue {
    type Output = Self;

    fn bitand(self, rhs: Self) -> Self::Output {
        self.and(rhs)
    }
}

impl std::ops::BitOr for TruthValue {
    type Output = Self;

    fn bitor(self, rhs: Self) -> Self::Output {
        self.or(rhs)
    }
}

impl fmt::Display for TruthValue {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str(match self {
            Self::True => "true",
            Self::False => "false",
            Self::Unknown => "unknown",
            Self::Conflict => "conflict",
        })
    }
}

/// A value together with open-world evaluation state.
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
#[serde(tag = "status", content = "value", rename_all = "snake_case")]
pub enum EvalValue {
    Known(Value),
    Unknown {
        #[serde(default, skip_serializing_if = "BTreeSet::is_empty")]
        missing: BTreeSet<String>,
    },
    Conflict {
        reasons: Vec<String>,
    },
}

impl EvalValue {
    #[must_use]
    pub const fn known(value: Value) -> Self {
        Self::Known(value)
    }

    #[must_use]
    pub fn unknown(missing: impl IntoIterator<Item = String>) -> Self {
        Self::Unknown {
            missing: missing.into_iter().collect(),
        }
    }

    #[must_use]
    pub fn missing(name: impl Into<String>) -> Self {
        Self::Unknown {
            missing: BTreeSet::from([name.into()]),
        }
    }

    #[must_use]
    pub fn conflict(reasons: impl IntoIterator<Item = String>) -> Self {
        let mut reasons = reasons.into_iter().collect::<Vec<_>>();
        reasons.sort();
        reasons.dedup();
        Self::Conflict { reasons }
    }

    #[must_use]
    pub const fn as_known(&self) -> Option<&Value> {
        if let Self::Known(value) = self {
            Some(value)
        } else {
            None
        }
    }

    #[must_use]
    pub fn into_known(self) -> Option<Value> {
        if let Self::Known(value) = self {
            Some(value)
        } else {
            None
        }
    }

    #[must_use]
    pub fn truth_value(&self) -> Option<TruthValue> {
        match self {
            Self::Known(Value::Bool(value)) => Some((*value).into()),
            Self::Unknown { .. } => Some(TruthValue::Unknown),
            Self::Conflict { .. } => Some(TruthValue::Conflict),
            Self::Known(_) => None,
        }
    }

    #[must_use]
    pub fn map(self, map: impl FnOnce(Value) -> Value) -> Self {
        match self {
            Self::Known(value) => Self::known(map(value)),
            Self::Unknown { missing } => Self::Unknown { missing },
            Self::Conflict { reasons } => Self::Conflict { reasons },
        }
    }
}

impl From<Value> for EvalValue {
    fn from(value: Value) -> Self {
        Self::known(value)
    }
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum DecimalError {
    Invalid(String),
    Overflow { operation: &'static str },
    DivisionByZero,
    Inexact { operation: &'static str },
}

impl fmt::Display for DecimalError {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Invalid(value) => write!(formatter, "invalid decimal literal `{value}`"),
            Self::Overflow { operation } => {
                write!(formatter, "decimal overflow during {operation}")
            }
            Self::DivisionByZero => formatter.write_str("decimal division by zero"),
            Self::Inexact { operation } => write!(
                formatter,
                "decimal {operation} is not exactly representable; explicit rounding is required"
            ),
        }
    }
}

impl Error for DecimalError {}

mod exact_decimal_serde {
    use super::{Decimal, parse_decimal};
    use serde::{Deserialize, Deserializer, Serializer};

    pub fn serialize<S>(value: &Decimal, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&value.to_string())
    }

    pub fn deserialize<'de, D>(deserializer: D) -> Result<Decimal, D::Error>
    where
        D: Deserializer<'de>,
    {
        let text = String::deserialize(deserializer)?;
        parse_decimal(&text).map_err(serde::de::Error::custom)
    }
}

/// Parses and normalizes an exact base-10 decimal literal.
///
/// # Errors
///
/// Returns [`DecimalError::Invalid`] if `text` is not representable as a
/// `rust_decimal::Decimal`.
pub fn parse_decimal(text: &str) -> Result<Decimal, DecimalError> {
    let expanded = if text.contains(['e', 'E']) {
        expand_scientific_decimal(text).ok_or_else(|| DecimalError::Invalid(text.to_owned()))?
    } else {
        text.to_owned()
    };
    Decimal::from_str_exact(&expanded)
        .map(|value| value.normalize())
        .map_err(|_| DecimalError::Invalid(text.to_owned()))
}

fn expand_scientific_decimal(text: &str) -> Option<String> {
    let (negative, unsigned) = if let Some(value) = text.strip_prefix('-') {
        (true, value)
    } else if let Some(value) = text.strip_prefix('+') {
        (false, value)
    } else {
        (false, text)
    };
    let mut parts = unsigned.split(['e', 'E']);
    let significand = parts.next()?;
    let exponent = parts.next()?.parse::<i32>().ok()?;
    if parts.next().is_some() {
        return None;
    }

    let mut digits = String::new();
    let mut decimal_index = None;
    for character in significand.chars() {
        match character {
            '0'..='9' => digits.push(character),
            '_' => {}
            '.' if decimal_index.is_none() => decimal_index = Some(digits.len()),
            _ => return None,
        }
    }
    if digits.is_empty() {
        return None;
    }
    let decimal_index = decimal_index.unwrap_or(digits.len());
    let shifted = i64::try_from(decimal_index).ok()? + i64::from(exponent);
    let digit_count = i64::try_from(digits.len()).ok()?;
    let padding = if shifted < 0 {
        shifted.unsigned_abs()
    } else if shifted > digit_count {
        (shifted - digit_count).unsigned_abs()
    } else {
        0
    };
    if padding > 128 {
        return None;
    }

    let mut expanded = String::new();
    if negative {
        expanded.push('-');
    }
    if shifted <= 0 {
        expanded.push_str("0.");
        expanded.extend(std::iter::repeat_n('0', usize::try_from(-shifted).ok()?));
        expanded.push_str(&digits);
    } else if shifted >= digit_count {
        expanded.push_str(&digits);
        expanded.extend(std::iter::repeat_n(
            '0',
            usize::try_from(shifted - digit_count).ok()?,
        ));
    } else {
        let split = usize::try_from(shifted).ok()?;
        expanded.push_str(&digits[..split]);
        expanded.push('.');
        expanded.push_str(&digits[split..]);
    }
    Some(expanded)
}

fn aligned_decimal_mantissa(value: Decimal, scale: u32) -> BigInt {
    let factor = BigInt::from(10_u8).pow(scale - value.scale());
    BigInt::from(value.mantissa()) * factor
}

fn decimal_sum_is_exact(result: Decimal, left: Decimal, right: Decimal, subtract: bool) -> bool {
    let scale = result.scale().max(left.scale()).max(right.scale());
    let expected = if subtract {
        aligned_decimal_mantissa(left, scale) - aligned_decimal_mantissa(right, scale)
    } else {
        aligned_decimal_mantissa(left, scale) + aligned_decimal_mantissa(right, scale)
    };
    aligned_decimal_mantissa(result, scale) == expected
}

fn decimal_product_is_exact(result: Decimal, left: Decimal, right: Decimal) -> bool {
    let left_side =
        BigInt::from(result.mantissa()) * BigInt::from(10_u8).pow(left.scale() + right.scale());
    let right_side = BigInt::from(left.mantissa())
        * BigInt::from(right.mantissa())
        * BigInt::from(10_u8).pow(result.scale());
    left_side == right_side
}

fn decimal_quotient_is_exact(result: Decimal, left: Decimal, right: Decimal) -> bool {
    let left_side = BigInt::from(result.mantissa())
        * BigInt::from(right.mantissa())
        * BigInt::from(10_u8).pow(left.scale());
    let right_side =
        BigInt::from(left.mantissa()) * BigInt::from(10_u8).pow(right.scale() + result.scale());
    left_side == right_side
}

/// Adds two decimals without overflow.
///
/// # Errors
///
/// Returns [`DecimalError::Overflow`] when the exact result is out of range.
pub fn checked_decimal_add(left: Decimal, right: Decimal) -> Result<Decimal, DecimalError> {
    let result = left
        .checked_add(right)
        .ok_or(DecimalError::Overflow {
            operation: "addition",
        })?
        .normalize();
    if decimal_sum_is_exact(result, left, right, false) {
        Ok(result)
    } else {
        Err(DecimalError::Inexact {
            operation: "addition",
        })
    }
}

/// Subtracts two decimals without overflow.
///
/// # Errors
///
/// Returns [`DecimalError::Overflow`] when the exact result is out of range.
pub fn checked_decimal_sub(left: Decimal, right: Decimal) -> Result<Decimal, DecimalError> {
    let result = left
        .checked_sub(right)
        .ok_or(DecimalError::Overflow {
            operation: "subtraction",
        })?
        .normalize();
    if decimal_sum_is_exact(result, left, right, true) {
        Ok(result)
    } else {
        Err(DecimalError::Inexact {
            operation: "subtraction",
        })
    }
}

/// Multiplies two decimals without overflow.
///
/// # Errors
///
/// Returns [`DecimalError::Overflow`] when the exact result is out of range.
pub fn checked_decimal_mul(left: Decimal, right: Decimal) -> Result<Decimal, DecimalError> {
    let result = left
        .checked_mul(right)
        .ok_or(DecimalError::Overflow {
            operation: "multiplication",
        })?
        .normalize();
    if decimal_product_is_exact(result, left, right) {
        Ok(result)
    } else {
        Err(DecimalError::Inexact {
            operation: "multiplication",
        })
    }
}

/// Divides without silently accepting a rounded `rust_decimal` result.
///
/// # Errors
///
/// Returns an error for division by zero, overflow, or a quotient that cannot
/// be represented exactly.
pub fn checked_decimal_div(left: Decimal, right: Decimal) -> Result<Decimal, DecimalError> {
    if right.is_zero() {
        return Err(DecimalError::DivisionByZero);
    }
    let quotient = left
        .checked_div(right)
        .ok_or(DecimalError::Overflow {
            operation: "division",
        })?
        .normalize();
    if decimal_quotient_is_exact(quotient, left, right) {
        Ok(quotient)
    } else {
        Err(DecimalError::Inexact {
            operation: "division",
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn truth_negation_preserves_unknown_and_conflict() {
        assert_eq!(TruthValue::Unknown.not(), TruthValue::Unknown);
        assert_eq!(TruthValue::Conflict.not(), TruthValue::Conflict);
        assert_eq!(TruthValue::True.not(), TruthValue::False);
    }

    #[test]
    fn truth_operators_preserve_conflict_over_unknown() {
        assert_eq!(
            TruthValue::False.and(TruthValue::Unknown),
            TruthValue::False
        );
        assert_eq!(TruthValue::True.or(TruthValue::Unknown), TruthValue::True);
        assert_eq!(
            TruthValue::Conflict.and(TruthValue::True),
            TruthValue::Conflict
        );
        assert_eq!(
            TruthValue::Conflict.and(TruthValue::Unknown),
            TruthValue::Conflict
        );
        assert_eq!(
            TruthValue::Conflict.or(TruthValue::Unknown),
            TruthValue::Conflict
        );
    }

    #[test]
    fn decimal_rendering_is_normalized() {
        let value = Value::decimal(parse_decimal("1.2300").unwrap());
        assert_eq!(value.to_string(), "1.23");
    }

    #[test]
    fn decimal_parsing_rejects_values_that_require_rounding() {
        assert_eq!(
            parse_decimal("0.0000000000000000000000000001").unwrap(),
            Decimal::new(1, 28)
        );
        assert_eq!(parse_decimal("1e-28").unwrap(), Decimal::new(1, 28));
        assert!(parse_decimal("0.00000000000000000000000000001").is_err());
        assert!(parse_decimal("1e-29").is_err());
    }

    #[test]
    fn tagged_decimal_json_rejects_values_that_require_rounding() {
        let value = json!({
            "type": "decimal",
            "value": "0.00000000000000000000000000001",
        });
        assert!(matches!(
            Value::from_json(value),
            Err(ValueConversionError::InvalidTaggedValue(_))
        ));
    }

    #[test]
    fn typed_json_preserves_full_decimal_number_precision() {
        let json: JsonValue = serde_json::from_str("0.1234567890123456789012345679").unwrap();
        assert_eq!(
            Value::from_plain_json(&json, &ValueKind::Decimal).unwrap(),
            Value::decimal(parse_decimal("0.1234567890123456789012345679").unwrap())
        );
    }

    #[test]
    fn human_readable_numbers_use_digit_separators() {
        assert_eq!(Value::Int(1_234_567).to_string(), "1_234_567");
        assert_eq!(Value::Int(-1_234_567).to_string(), "-1_234_567");
        assert_eq!(
            Value::decimal(parse_decimal("1234567.8900").unwrap()).to_string(),
            "1_234_567.89"
        );
        assert_eq!(Value::Duration(86_400).to_string(), "86_400s");

        assert_eq!(Value::Int(1_234_567).to_plain_json(), json!(1_234_567));
        assert_eq!(
            Value::decimal(parse_decimal("1234567.8900").unwrap()).to_plain_json(),
            json!("1234567.89")
        );
    }

    #[test]
    fn decimal_division_rejects_rounded_result() {
        assert_eq!(
            checked_decimal_div(parse_decimal("1").unwrap(), parse_decimal("3").unwrap()),
            Err(DecimalError::Inexact {
                operation: "division"
            })
        );
    }

    #[test]
    fn decimal_multiplication_rejects_underflow_rounding() {
        assert_eq!(
            checked_decimal_mul(
                parse_decimal("0.0000000000000000000000000001").unwrap(),
                parse_decimal("0.1").unwrap()
            ),
            Err(DecimalError::Inexact {
                operation: "multiplication"
            })
        );
    }

    #[test]
    fn decimal_addition_and_subtraction_reject_precision_rounding() {
        let tenth = Decimal::new(1, 1);
        assert_eq!(
            checked_decimal_add(Decimal::MAX, tenth),
            Err(DecimalError::Inexact {
                operation: "addition"
            })
        );
        assert_eq!(
            checked_decimal_sub(Decimal::MAX, tenth),
            Err(DecimalError::Inexact {
                operation: "subtraction"
            })
        );
    }

    #[test]
    fn decimal_division_accepts_exact_result() {
        assert_eq!(
            checked_decimal_div(parse_decimal("1").unwrap(), parse_decimal("4").unwrap()).unwrap(),
            parse_decimal("0.25").unwrap()
        );
    }

    #[test]
    fn tagged_json_round_trips_enum() {
        let value = Value::Enum {
            type_name: "등급".to_owned(),
            variant: "A".to_owned(),
        };
        assert_eq!(Value::from_json(value.to_json().unwrap()).unwrap(), value);
    }

    #[test]
    fn typed_json_parses_date_and_duration() {
        assert_eq!(
            Value::from_plain_json(&json!("2026-07-11"), &ValueKind::Date).unwrap(),
            Value::Date(NaiveDate::from_ymd_opt(2026, 7, 11).unwrap())
        );
        assert_eq!(
            Value::from_plain_json(&json!(3_600), &ValueKind::Duration).unwrap(),
            Value::Duration(3_600)
        );
    }

    #[test]
    fn conflict_reasons_are_stable() {
        assert_eq!(
            EvalValue::conflict(["z".to_owned(), "a".to_owned(), "a".to_owned()]),
            EvalValue::Conflict {
                reasons: vec!["a".to_owned(), "z".to_owned()]
            }
        );
    }
}