lemma/planning/

semantics.rs

//! Resolved semantic types for Lemma
//!
//! This module contains all types that represent resolved semantics after planning.
//! These types are created during the planning phase and used by evaluation, inversion, etc.

// Re-exported parsing types: downstream modules (evaluation, inversion, computation,
// serialization) import these from `planning::semantics`, never from `parsing` directly.
pub use crate::parsing::ast::{
    ArithmeticComputation, ComparisonComputation, MathematicalComputation, NegationType, Span,
    VetoExpression,
};
pub use crate::parsing::source::Source;

/// Logical computation operators (defined in semantics, not used by the parser).
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize)]
#[serde(rename_all = "snake_case")]
pub enum LogicalComputation {
    And,
    Or,
    Not,
}

// Internal-only parsing imports (used only within this module for value/type resolution).
use crate::parsing::ast::{
    BooleanValue, CommandArg, ConversionTarget, DateTimeValue, DurationUnit, TimeValue,
};
use crate::parsing::literals::{parse_date_string, parse_duration_from_string, parse_time_string};
use crate::LemmaError;
use rust_decimal::Decimal;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::sync::{Arc, OnceLock};

// -----------------------------------------------------------------------------
// Type specification and units (resolved type shape; apply constraints is planning)
// -----------------------------------------------------------------------------

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct ScaleUnit {
    pub name: String,
    pub value: Decimal,
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(transparent)]
pub struct ScaleUnits(pub Vec<ScaleUnit>);

impl ScaleUnits {
    pub fn new() -> Self {
        ScaleUnits(Vec::new())
    }
    pub fn get(&self, name: &str) -> Result<&ScaleUnit, String> {
        self.0.iter().find(|u| u.name == name).ok_or_else(|| {
            let valid: Vec<&str> = self.0.iter().map(|u| u.name.as_str()).collect();
            format!(
                "Unknown unit '{}' for this scale type. Valid units: {}",
                name,
                valid.join(", ")
            )
        })
    }
    pub fn iter(&self) -> std::slice::Iter<'_, ScaleUnit> {
        self.0.iter()
    }
    pub fn push(&mut self, u: ScaleUnit) {
        self.0.push(u);
    }
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
    pub fn len(&self) -> usize {
        self.0.len()
    }
}

impl Default for ScaleUnits {
    fn default() -> Self {
        ScaleUnits::new()
    }
}

impl From<Vec<ScaleUnit>> for ScaleUnits {
    fn from(v: Vec<ScaleUnit>) -> Self {
        ScaleUnits(v)
    }
}

impl<'a> IntoIterator for &'a ScaleUnits {
    type Item = &'a ScaleUnit;
    type IntoIter = std::slice::Iter<'a, ScaleUnit>;
    fn into_iter(self) -> Self::IntoIter {
        self.0.iter()
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct RatioUnit {
    pub name: String,
    pub value: Decimal,
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(transparent)]
pub struct RatioUnits(pub Vec<RatioUnit>);

impl RatioUnits {
    pub fn new() -> Self {
        RatioUnits(Vec::new())
    }
    pub fn get(&self, name: &str) -> Result<&RatioUnit, String> {
        self.0.iter().find(|u| u.name == name).ok_or_else(|| {
            let valid: Vec<&str> = self.0.iter().map(|u| u.name.as_str()).collect();
            format!(
                "Unknown unit '{}' for this ratio type. Valid units: {}",
                name,
                valid.join(", ")
            )
        })
    }
    pub fn iter(&self) -> std::slice::Iter<'_, RatioUnit> {
        self.0.iter()
    }
    pub fn push(&mut self, u: RatioUnit) {
        self.0.push(u);
    }
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
    pub fn len(&self) -> usize {
        self.0.len()
    }
}

impl Default for RatioUnits {
    fn default() -> Self {
        RatioUnits::new()
    }
}

impl From<Vec<RatioUnit>> for RatioUnits {
    fn from(v: Vec<RatioUnit>) -> Self {
        RatioUnits(v)
    }
}

impl<'a> IntoIterator for &'a RatioUnits {
    type Item = &'a RatioUnit;
    type IntoIter = std::slice::Iter<'a, RatioUnit>;
    fn into_iter(self) -> Self::IntoIter {
        self.0.iter()
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum TypeSpecification {
    Boolean {
        help: String,
        default: Option<bool>,
    },
    Scale {
        minimum: Option<Decimal>,
        maximum: Option<Decimal>,
        decimals: Option<u8>,
        precision: Option<Decimal>,
        units: ScaleUnits,
        help: String,
        default: Option<(Decimal, String)>,
    },
    Number {
        minimum: Option<Decimal>,
        maximum: Option<Decimal>,
        decimals: Option<u8>,
        precision: Option<Decimal>,
        help: String,
        default: Option<Decimal>,
    },
    Ratio {
        minimum: Option<Decimal>,
        maximum: Option<Decimal>,
        decimals: Option<u8>,
        units: RatioUnits,
        help: String,
        default: Option<Decimal>,
    },
    Text {
        minimum: Option<usize>,
        maximum: Option<usize>,
        length: Option<usize>,
        options: Vec<String>,
        help: String,
        default: Option<String>,
    },
    Date {
        minimum: Option<DateTimeValue>,
        maximum: Option<DateTimeValue>,
        help: String,
        default: Option<DateTimeValue>,
    },
    Time {
        minimum: Option<TimeValue>,
        maximum: Option<TimeValue>,
        help: String,
        default: Option<TimeValue>,
    },
    Duration {
        help: String,
        default: Option<(Decimal, DurationUnit)>,
    },
    Veto {
        message: Option<String>,
    },
    /// Sentinel type used during type inference to represent "type could not be determined."
    /// This propagates through expressions without generating cascading errors.
    /// It must never appear in a successfully validated graph or execution plan.
    Error,
}

impl TypeSpecification {
    pub fn boolean() -> Self {
        TypeSpecification::Boolean {
            help: "Values: true, false".to_string(),
            default: None,
        }
    }
    pub fn scale() -> Self {
        TypeSpecification::Scale {
            minimum: None,
            maximum: None,
            decimals: None,
            precision: None,
            units: ScaleUnits::new(),
            help: "Format: value+unit (e.g. 100+unit)".to_string(),
            default: None,
        }
    }
    pub fn number() -> Self {
        TypeSpecification::Number {
            minimum: None,
            maximum: None,
            decimals: None,
            precision: None,
            help: "Numeric value".to_string(),
            default: None,
        }
    }
    pub fn ratio() -> Self {
        TypeSpecification::Ratio {
            minimum: None,
            maximum: None,
            decimals: None,
            units: RatioUnits(vec![
                RatioUnit {
                    name: "percent".to_string(),
                    value: Decimal::from(100),
                },
                RatioUnit {
                    name: "permille".to_string(),
                    value: Decimal::from(1000),
                },
            ]),
            help: "Format: value+unit (e.g. 21+percent)".to_string(),
            default: None,
        }
    }
    pub fn text() -> Self {
        TypeSpecification::Text {
            minimum: None,
            maximum: None,
            length: None,
            options: vec![],
            help: "Text value".to_string(),
            default: None,
        }
    }
    pub fn date() -> Self {
        TypeSpecification::Date {
            minimum: None,
            maximum: None,
            help: "Format: YYYY-MM-DD (e.g. 2024-01-15)".to_string(),
            default: None,
        }
    }
    pub fn time() -> Self {
        TypeSpecification::Time {
            minimum: None,
            maximum: None,
            help: "Format: HH:MM:SS (e.g. 14:30:00)".to_string(),
            default: None,
        }
    }
    pub fn duration() -> Self {
        TypeSpecification::Duration {
            help: "Format: value+unit (e.g. 40+hours). Units: years, months, weeks, days, hours, minutes, seconds".to_string(),
            default: None,
        }
    }
    pub fn veto() -> Self {
        TypeSpecification::Veto { message: None }
    }

    pub fn apply_constraint(mut self, command: &str, args: &[CommandArg]) -> Result<Self, String> {
        match &mut self {
            TypeSpecification::Boolean { help, default } => match command {
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    match arg {
                        CommandArg::Boolean(s) | CommandArg::Label(s) => {
                            let d = s
                                .parse::<BooleanValue>()
                                .map_err(|_| format!("invalid default value: {:?}", s))?;
                            *default = Some(d.into());
                        }
                        other => {
                            return Err(format!(
                                "default for boolean type requires a boolean literal (true/false/yes/no/accept/reject), got {:?}",
                                other.value()
                            ));
                        }
                    }
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for boolean type. Valid commands: help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Scale {
                decimals,
                minimum,
                maximum,
                precision,
                units,
                help,
                default,
            } => match command {
                "decimals" => {
                    let d = args
                        .first()
                        .ok_or_else(|| "decimals requires an argument".to_string())?
                        .value()
                        .parse::<u8>()
                        .map_err(|_| {
                            format!(
                                "invalid decimals value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *decimals = Some(d);
                }
                "unit" if args.len() >= 2 => {
                    let unit_name = args[0].value().to_string();
                    if units.iter().any(|u| u.name == unit_name) {
                        return Err(format!(
                            "Unit '{}' is already defined in this scale type.",
                            unit_name
                        ));
                    }
                    let value = args[1]
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| format!("invalid unit value: {}", args[1].value()))?;
                    units.0.push(ScaleUnit {
                        name: unit_name,
                        value,
                    });
                }
                "minimum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid minimum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *minimum = Some(m);
                }
                "maximum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid maximum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *maximum = Some(m);
                }
                "precision" => {
                    let p = args
                        .first()
                        .ok_or_else(|| "precision requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid precision value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *precision = Some(p);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    if args.len() < 2 {
                        return Err(
                            "default requires a value and unit (e.g., 'default 1 kilogram')"
                                .to_string(),
                        );
                    }
                    match &args[0] {
                        CommandArg::Number(s) => {
                            let value = s
                                .parse::<Decimal>()
                                .map_err(|_| format!("invalid default value: {:?}", s))?;
                            let unit_name = args[1].value().to_string();
                            *default = Some((value, unit_name));
                        }
                        other => {
                            return Err(format!(
                                "default for scale type requires a number literal as value, got {:?}",
                                other.value()
                            ));
                        }
                    }
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for scale type. Valid commands: unit, minimum, maximum, decimals, precision, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Number {
                decimals,
                minimum,
                maximum,
                precision,
                help,
                default,
            } => match command {
                "decimals" => {
                    let d = args
                        .first()
                        .ok_or_else(|| "decimals requires an argument".to_string())?
                        .value()
                        .parse::<u8>()
                        .map_err(|_| {
                            format!(
                                "invalid decimals value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *decimals = Some(d);
                }
                "unit" => {
                    return Err(
                        "Invalid command 'unit' for number type. Number types are dimensionless and cannot have units. Use 'scale' type instead.".to_string()
                    );
                }
                "minimum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid minimum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *minimum = Some(m);
                }
                "maximum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid maximum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *maximum = Some(m);
                }
                "precision" => {
                    let p = args
                        .first()
                        .ok_or_else(|| "precision requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid precision value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *precision = Some(p);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    match arg {
                        CommandArg::Number(s) => {
                            let d = s
                                .parse::<Decimal>()
                                .map_err(|_| format!("invalid default value: {:?}", s))?;
                            *default = Some(d);
                        }
                        other => {
                            return Err(format!(
                                "default for number type requires a number literal, got {:?}",
                                other.value()
                            ));
                        }
                    }
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for number type. Valid commands: minimum, maximum, decimals, precision, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Ratio {
                decimals,
                minimum,
                maximum,
                units,
                help,
                default,
            } => match command {
                "decimals" => {
                    let d = args
                        .first()
                        .ok_or_else(|| "decimals requires an argument".to_string())?
                        .value()
                        .parse::<u8>()
                        .map_err(|_| {
                            format!(
                                "invalid decimals value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *decimals = Some(d);
                }
                "unit" if args.len() >= 2 => {
                    let unit_name = args[0].value().to_string();
                    if units.iter().any(|u| u.name == unit_name) {
                        return Err(format!(
                            "Unit '{}' is already defined in this ratio type.",
                            unit_name
                        ));
                    }
                    let value = args[1]
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| format!("invalid unit value: {}", args[1].value()))?;
                    units.0.push(RatioUnit {
                        name: unit_name,
                        value,
                    });
                }
                "minimum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid minimum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *minimum = Some(m);
                }
                "maximum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| {
                            format!(
                                "invalid maximum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *maximum = Some(m);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    match arg {
                        CommandArg::Number(s) => {
                            let d = s
                                .parse::<Decimal>()
                                .map_err(|_| format!("invalid default value: {:?}", s))?;
                            *default = Some(d);
                        }
                        other => {
                            return Err(format!(
                                "default for ratio type requires a number literal, got {:?}",
                                other.value()
                            ));
                        }
                    }
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for ratio type. Valid commands: unit, minimum, maximum, decimals, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Text {
                minimum,
                maximum,
                length,
                options,
                help,
                default,
            } => match command {
                "option" if args.len() == 1 => {
                    options.push(args[0].value().to_string());
                }
                "options" => {
                    *options = args.iter().map(|a| a.value().to_string()).collect();
                }
                "minimum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?
                        .value()
                        .parse::<usize>()
                        .map_err(|_| {
                            format!(
                                "invalid minimum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *minimum = Some(m);
                }
                "maximum" => {
                    let m = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?
                        .value()
                        .parse::<usize>()
                        .map_err(|_| {
                            format!(
                                "invalid maximum value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *maximum = Some(m);
                }
                "length" => {
                    let l = args
                        .first()
                        .ok_or_else(|| "length requires an argument".to_string())?
                        .value()
                        .parse::<usize>()
                        .map_err(|_| {
                            format!(
                                "invalid length value: {:?}",
                                args.first().map(|a| a.value())
                            )
                        })?;
                    *length = Some(l);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    match arg {
                        CommandArg::Text(s) => {
                            *default = Some(s.clone());
                        }
                        other => {
                            return Err(format!(
                                "default for text type requires a text literal (quoted string), got {:?}",
                                other.value()
                            ));
                        }
                    }
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for text type. Valid commands: options, minimum, maximum, length, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Date {
                minimum,
                maximum,
                help,
                default,
            } => match command {
                "minimum" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?;
                    *minimum = Some(parse_date_string(arg.value())?);
                }
                "maximum" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?;
                    *maximum = Some(parse_date_string(arg.value())?);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    *default = Some(parse_date_string(arg.value())?);
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for date type. Valid commands: minimum, maximum, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Time {
                minimum,
                maximum,
                help,
                default,
            } => match command {
                "minimum" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "minimum requires an argument".to_string())?;
                    *minimum = Some(parse_time_string(arg.value())?);
                }
                "maximum" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "maximum requires an argument".to_string())?;
                    *maximum = Some(parse_time_string(arg.value())?);
                }
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" => {
                    let arg = args
                        .first()
                        .ok_or_else(|| "default requires an argument".to_string())?;
                    *default = Some(parse_time_string(arg.value())?);
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for time type. Valid commands: minimum, maximum, help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Duration { help, default } => match command {
                "help" => {
                    *help = args
                        .first()
                        .map(|a| a.value().to_string())
                        .unwrap_or_default();
                }
                "default" if args.len() >= 2 => {
                    let value = args[0]
                        .value()
                        .parse::<Decimal>()
                        .map_err(|_| format!("invalid duration value: {}", args[0].value()))?;
                    let unit = args[1]
                        .value()
                        .parse::<DurationUnit>()
                        .map_err(|_| format!("invalid duration unit: {}", args[1].value()))?;
                    *default = Some((value, unit));
                }
                _ => {
                    return Err(format!(
                        "Invalid command '{}' for duration type. Valid commands: help, default",
                        command
                    ));
                }
            },
            TypeSpecification::Veto { .. } => {
                return Err(format!(
                    "Invalid command '{}' for veto type. Veto is not a user-declarable type and cannot have constraints",
                    command
                ));
            }
            TypeSpecification::Error => {
                return Err(format!(
                    "Invalid command '{}' for error sentinel type. Error is an internal type used during type inference and cannot have constraints",
                    command
                ));
            }
        }
        Ok(self)
    }
}

/// Parse a "number unit" string into a Scale or Ratio value according to the type.
/// Caller must have obtained the TypeSpecification via unit_index from the unit in the string.
pub fn parse_number_unit(
    value_str: &str,
    type_spec: &TypeSpecification,
) -> Result<crate::parsing::ast::Value, String> {
    use crate::parsing::ast::Value;
    use crate::parsing::literals::parse_number_unit_string;
    use std::str::FromStr;

    let trimmed = value_str.trim();
    match type_spec {
        TypeSpecification::Scale { units, .. } => {
            if units.is_empty() {
                unreachable!(
                    "BUG: Scale type has no units; should have been validated during planning"
                );
            }
            match parse_number_unit_string(trimmed) {
                Ok((n, unit_name)) => {
                    let unit = units.get(&unit_name).map_err(|e| e.to_string())?;
                    Ok(Value::Scale(n, unit.name.clone()))
                }
                Err(e) => {
                    if trimmed.split_whitespace().count() == 1 && !trimmed.is_empty() {
                        let valid: Vec<&str> = units.iter().map(|u| u.name.as_str()).collect();
                        let example_unit = units.iter().next().unwrap().name.as_str();
                        Err(format!(
                            "Scale value must include a unit, for example: '{} {}'. Valid units: {}.",
                            trimmed,
                            example_unit,
                            valid.join(", ")
                        ))
                    } else {
                        Err(e)
                    }
                }
            }
        }
        TypeSpecification::Ratio { units, .. } => {
            if units.is_empty() {
                unreachable!(
                    "BUG: Ratio type has no units; should have been validated during planning"
                );
            }
            match parse_number_unit_string(trimmed) {
                Ok((n, unit_name)) => {
                    let unit = units.get(&unit_name).map_err(|e| e.to_string())?;
                    Ok(Value::Ratio(n / unit.value, Some(unit.name.clone())))
                }
                Err(_) => {
                    if trimmed.split_whitespace().count() == 1 && !trimmed.is_empty() {
                        let clean = trimmed.replace(['_', ','], "");
                        let n = Decimal::from_str(&clean)
                            .map_err(|_| format!("Invalid ratio: '{}'", trimmed))?;
                        Ok(Value::Ratio(n, None))
                    } else {
                        Err("Ratio value must be a number, optionally followed by a unit (e.g. '0.5' or '50 percent').".to_string())
                    }
                }
            }
        }
        _ => Err("parse_number_unit only accepts Scale or Ratio type".to_string()),
    }
}

/// Parse a string value according to a TypeSpecification.
/// Used to parse runtime user input into typed values.
pub fn parse_value_from_string(
    value_str: &str,
    type_spec: &TypeSpecification,
    source: &Source,
) -> Result<crate::parsing::ast::Value, LemmaError> {
    use crate::parsing::ast::{BooleanValue, Value};
    use std::str::FromStr;

    let to_err = |msg: String| LemmaError::engine(msg, Some(source.clone()), None::<String>);

    match type_spec {
        TypeSpecification::Text { .. } => Ok(Value::Text(value_str.to_string())),
        TypeSpecification::Number { .. } => {
            let clean = value_str.replace(['_', ','], "");
            let n = Decimal::from_str(&clean).map_err(|_| to_err(format!("Invalid number: '{}'", value_str)))?;
            Ok(Value::Number(n))
        }
        TypeSpecification::Scale { .. } => {
            parse_number_unit(value_str, type_spec).map_err(to_err)
        }
        TypeSpecification::Boolean { .. } => {
            let bv = match value_str.to_lowercase().as_str() {
                "true" => BooleanValue::True,
                "false" => BooleanValue::False,
                "yes" => BooleanValue::Yes,
                "no" => BooleanValue::No,
                "accept" => BooleanValue::Accept,
                "reject" => BooleanValue::Reject,
                _ => return Err(to_err(format!("Invalid boolean: '{}'", value_str))),
            };
            Ok(Value::Boolean(bv))
        }
        TypeSpecification::Date { .. } => {
            let date = parse_date_string(value_str).map_err(to_err)?;
            Ok(Value::Date(date))
        }
        TypeSpecification::Time { .. } => {
            let time = parse_time_string(value_str).map_err(to_err)?;
            Ok(Value::Time(time))
        }
        TypeSpecification::Duration { .. } => {
            parse_duration_from_string(value_str, source)
        }
        TypeSpecification::Ratio { .. } => {
            parse_number_unit(value_str, type_spec).map_err(to_err)
        }
        TypeSpecification::Veto { .. } => Err(to_err(
            "Veto type cannot be parsed from string".to_string(),
        )),
        TypeSpecification::Error => unreachable!(
            "BUG: parse_value_from_string called with Error sentinel type; this type exists only during type inference"
        ),
    }
}

// -----------------------------------------------------------------------------
// Semantic value types (no parser dependency - used by evaluation, inversion, etc.)
// -----------------------------------------------------------------------------

/// Duration unit for semantic values (duplicated from parser to avoid parser dependency)
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SemanticDurationUnit {
    Year,
    Month,
    Week,
    Day,
    Hour,
    Minute,
    Second,
    Millisecond,
    Microsecond,
}

impl fmt::Display for SemanticDurationUnit {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let s = match self {
            SemanticDurationUnit::Year => "years",
            SemanticDurationUnit::Month => "months",
            SemanticDurationUnit::Week => "weeks",
            SemanticDurationUnit::Day => "days",
            SemanticDurationUnit::Hour => "hours",
            SemanticDurationUnit::Minute => "minutes",
            SemanticDurationUnit::Second => "seconds",
            SemanticDurationUnit::Millisecond => "milliseconds",
            SemanticDurationUnit::Microsecond => "microseconds",
        };
        write!(f, "{}", s)
    }
}

/// Target unit for conversion (semantic; used by evaluation/computation).
/// Planning converts AST ConversionTarget into this so computation does not depend on parsing.
/// Ratio vs scale is determined by looking up the unit in the type registry's unit index.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SemanticConversionTarget {
    Duration(SemanticDurationUnit),
    ScaleUnit(String),
    RatioUnit(String),
}

impl fmt::Display for SemanticConversionTarget {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            SemanticConversionTarget::Duration(u) => write!(f, "{}", u),
            SemanticConversionTarget::ScaleUnit(s) => write!(f, "{}", s),
            SemanticConversionTarget::RatioUnit(s) => write!(f, "{}", s),
        }
    }
}

/// Timezone for semantic date/time values
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
pub struct SemanticTimezone {
    pub offset_hours: i8,
    pub offset_minutes: u8,
}

impl fmt::Display for SemanticTimezone {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.offset_hours == 0 && self.offset_minutes == 0 {
            write!(f, "Z")
        } else {
            let sign = if self.offset_hours >= 0 { "+" } else { "-" };
            let hours = self.offset_hours.abs();
            write!(f, "{}{:02}:{:02}", sign, hours, self.offset_minutes)
        }
    }
}

/// Time-of-day for semantic values
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
pub struct SemanticTime {
    pub hour: u32,
    pub minute: u32,
    pub second: u32,
    pub timezone: Option<SemanticTimezone>,
}

impl fmt::Display for SemanticTime {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:02}:{:02}:{:02}", self.hour, self.minute, self.second)
    }
}

/// Date-time for semantic values
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
pub struct SemanticDateTime {
    pub year: i32,
    pub month: u32,
    pub day: u32,
    pub hour: u32,
    pub minute: u32,
    pub second: u32,
    pub timezone: Option<SemanticTimezone>,
}

impl fmt::Display for SemanticDateTime {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let is_date_only =
            self.hour == 0 && self.minute == 0 && self.second == 0 && self.timezone.is_none();
        if is_date_only {
            write!(f, "{:04}-{:02}-{:02}", self.year, self.month, self.day)
        } else {
            write!(
                f,
                "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}",
                self.year, self.month, self.day, self.hour, self.minute, self.second
            )?;
            if let Some(tz) = &self.timezone {
                write!(f, "{}", tz)?;
            }
            Ok(())
        }
    }
}

/// Value payload (shape of a literal). No type attached.
/// Scale unit is required; Ratio unit is optional (see plan ratio-units-optional.md).
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ValueKind {
    Number(Decimal),
    /// Scale: value + unit (unit required)
    Scale(Decimal, String),
    Text(String),
    Date(SemanticDateTime),
    Time(SemanticTime),
    Boolean(bool),
    /// Duration: value + unit
    Duration(Decimal, SemanticDurationUnit),
    /// Ratio: value + optional unit
    Ratio(Decimal, Option<String>),
}

impl fmt::Display for ValueKind {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use crate::parsing::ast::Value;
        match self {
            ValueKind::Number(n) => {
                let norm = n.normalize();
                let s = if norm.fract().is_zero() {
                    norm.trunc().to_string()
                } else {
                    norm.to_string()
                };
                write!(f, "{}", s)
            }
            ValueKind::Scale(n, u) => write!(f, "{}", Value::Scale(*n, u.clone())),
            ValueKind::Text(s) => write!(f, "{}", Value::Text(s.clone())),
            ValueKind::Ratio(r, u) => write!(f, "{}", Value::Ratio(*r, u.clone())),
            ValueKind::Date(dt) => write!(f, "{}", dt),
            ValueKind::Time(t) => write!(
                f,
                "{}",
                Value::Time(crate::parsing::ast::TimeValue {
                    hour: t.hour as u8,
                    minute: t.minute as u8,
                    second: t.second as u8,
                    timezone: t
                        .timezone
                        .as_ref()
                        .map(|tz| crate::parsing::ast::TimezoneValue {
                            offset_hours: tz.offset_hours,
                            offset_minutes: tz.offset_minutes,
                        }),
                })
            ),
            ValueKind::Boolean(b) => write!(f, "{}", b),
            ValueKind::Duration(v, u) => write!(f, "{} {}", v, u),
        }
    }
}

// -----------------------------------------------------------------------------
// Resolved path types (moved from parsing::ast)
// -----------------------------------------------------------------------------

/// A single segment in a resolved path traversal
///
/// Used in both FactPath and RulePath to represent document traversal.
/// Each segment contains a fact name that points to a document.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct PathSegment {
    /// The fact name in this segment
    pub fact: String,
    /// The document this fact references (resolved during planning)
    pub doc: String,
}

/// Resolved path to a fact (created during planning from AST FactReference)
///
/// Represents a fully resolved path through documents to reach a fact.
/// All document references are resolved during planning.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct FactPath {
    /// Path segments (each is a document traversal)
    pub segments: Vec<PathSegment>,
    /// Final fact name
    pub fact: String,
}

impl FactPath {
    /// Create a fact path from segments and fact name (matches AST FactReference shape)
    pub fn new(segments: Vec<PathSegment>, fact: String) -> Self {
        Self { segments, fact }
    }

    /// Create a local fact path (no document traversal)
    pub fn local(fact: String) -> Self {
        Self {
            segments: vec![],
            fact,
        }
    }
}

/// Resolved path to a rule (created during planning from RuleReference)
///
/// Represents a fully resolved path through documents to reach a rule.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct RulePath {
    /// Path segments (each is a document traversal)
    pub segments: Vec<PathSegment>,
    /// Final rule name
    pub rule: String,
}

impl RulePath {
    /// Create a rule path from segments and rule name (matches AST RuleReference shape)
    pub fn new(segments: Vec<PathSegment>, rule: String) -> Self {
        Self { segments, rule }
    }
}

// -----------------------------------------------------------------------------
// Resolved expression types (created during planning)
// -----------------------------------------------------------------------------

/// Resolved expression (all references resolved to paths, all literals typed)
///
/// Created during planning from AST Expression. All unresolved references
/// are converted to FactPath/RulePath, and all literals are typed.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct Expression {
    pub kind: ExpressionKind,
    pub source_location: Option<Source>,
}

impl Expression {
    pub fn new(kind: ExpressionKind, source_location: Source) -> Self {
        Self {
            kind,
            source_location: Some(source_location),
        }
    }

    /// Create an expression with an optional source location
    pub fn with_source(kind: ExpressionKind, source_location: Option<Source>) -> Self {
        Self {
            kind,
            source_location,
        }
    }

    /// Get source text for this expression if available
    pub fn get_source_text(&self, sources: &HashMap<String, String>) -> Option<String> {
        let source = self.source_location.as_ref()?;
        let file_source = sources.get(&source.attribute)?;
        let span = &source.span;
        Some(file_source.get(span.start..span.end)?.to_string())
    }

    /// Collect all FactPath references from this resolved expression tree
    pub fn collect_fact_paths(&self, facts: &mut std::collections::HashSet<FactPath>) {
        self.kind.collect_fact_paths(facts);
    }

    /// Compute semantic hash - hashes the expression structure, ignoring source location
    pub fn semantic_hash<H: Hasher>(&self, state: &mut H) {
        self.kind.semantic_hash(state);
    }
}

/// Resolved expression kind (only resolved variants, no unresolved references)
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum ExpressionKind {
    /// Resolved literal with type (boxed to keep enum small)
    Literal(Box<LiteralValue>),
    /// Resolved fact path
    FactPath(FactPath),
    /// Resolved rule path
    RulePath(RulePath),
    LogicalAnd(Arc<Expression>, Arc<Expression>),
    LogicalOr(Arc<Expression>, Arc<Expression>),
    Arithmetic(Arc<Expression>, ArithmeticComputation, Arc<Expression>),
    Comparison(Arc<Expression>, ComparisonComputation, Arc<Expression>),
    UnitConversion(Arc<Expression>, SemanticConversionTarget),
    LogicalNegation(Arc<Expression>, NegationType),
    MathematicalComputation(MathematicalComputation, Arc<Expression>),
    Veto(VetoExpression),
}

impl ExpressionKind {
    /// Collect all FactPath references from this expression kind
    fn collect_fact_paths(&self, facts: &mut std::collections::HashSet<FactPath>) {
        match self {
            ExpressionKind::FactPath(fp) => {
                facts.insert(fp.clone());
            }
            ExpressionKind::LogicalAnd(left, right)
            | ExpressionKind::LogicalOr(left, right)
            | ExpressionKind::Arithmetic(left, _, right)
            | ExpressionKind::Comparison(left, _, right) => {
                left.collect_fact_paths(facts);
                right.collect_fact_paths(facts);
            }
            ExpressionKind::UnitConversion(inner, _)
            | ExpressionKind::LogicalNegation(inner, _)
            | ExpressionKind::MathematicalComputation(_, inner) => {
                inner.collect_fact_paths(facts);
            }
            ExpressionKind::Literal(_) | ExpressionKind::RulePath(_) | ExpressionKind::Veto(_) => {}
        }
    }

    /// Compute semantic hash for resolved expression kinds
    pub fn semantic_hash<H: Hasher>(&self, state: &mut H) {
        // Hash discriminant first
        std::mem::discriminant(self).hash(state);

        match self {
            ExpressionKind::Literal(lit) => lit.hash(state),
            ExpressionKind::FactPath(fp) => fp.hash(state),
            ExpressionKind::RulePath(rp) => rp.hash(state),
            ExpressionKind::LogicalAnd(left, right) | ExpressionKind::LogicalOr(left, right) => {
                left.semantic_hash(state);
                right.semantic_hash(state);
            }
            ExpressionKind::Arithmetic(left, op, right) => {
                left.semantic_hash(state);
                op.hash(state);
                right.semantic_hash(state);
            }
            ExpressionKind::Comparison(left, op, right) => {
                left.semantic_hash(state);
                op.hash(state);
                right.semantic_hash(state);
            }
            ExpressionKind::UnitConversion(expr, target) => {
                expr.semantic_hash(state);
                target.hash(state);
            }
            ExpressionKind::LogicalNegation(expr, neg_type) => {
                expr.semantic_hash(state);
                neg_type.hash(state);
            }
            ExpressionKind::MathematicalComputation(op, expr) => {
                op.hash(state);
                expr.semantic_hash(state);
            }
            ExpressionKind::Veto(v) => v.message.hash(state),
        }
    }
}

// -----------------------------------------------------------------------------
// Resolved types and values
// -----------------------------------------------------------------------------

/// What this type extends (primitive built-in or custom type by name).
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum TypeExtends {
    /// Extends a primitive built-in type (number, boolean, text, etc.)
    Primitive,
    /// Extends a custom type: parent is the immediate parent type name; family is the root of the extension chain (topmost custom type name).
    Custom { parent: String, family: String },
}

impl TypeExtends {
    /// Returns the parent type name if this type extends a custom type.
    #[must_use]
    pub fn parent_name(&self) -> Option<&str> {
        match self {
            TypeExtends::Primitive => None,
            TypeExtends::Custom { parent, .. } => Some(parent.as_str()),
        }
    }
}

/// Resolved type after planning
///
/// Contains a type specification and optional name. Created during planning
/// from TypeSpecification and TypeDef in the AST.
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct LemmaType {
    /// Optional type name (e.g., "age", "temperature")
    pub name: Option<String>,
    /// The type specification (Boolean, Number, Scale, etc.)
    pub specifications: TypeSpecification,
    /// What this type extends (primitive or custom from a document)
    pub extends: TypeExtends,
}

impl LemmaType {
    /// Create a new type with a name
    pub fn new(name: String, specifications: TypeSpecification, extends: TypeExtends) -> Self {
        Self {
            name: Some(name),
            specifications,
            extends,
        }
    }

    /// Create a type without a name (anonymous/inline type)
    pub fn without_name(specifications: TypeSpecification, extends: TypeExtends) -> Self {
        Self {
            name: None,
            specifications,
            extends,
        }
    }

    /// Create a primitive type (no name, extends Primitive)
    pub fn primitive(specifications: TypeSpecification) -> Self {
        Self {
            name: None,
            specifications,
            extends: TypeExtends::Primitive,
        }
    }

    /// Get the type name, or a default based on the type specification
    pub fn name(&self) -> String {
        self.name.clone().unwrap_or_else(|| {
            match &self.specifications {
                TypeSpecification::Boolean { .. } => "boolean",
                TypeSpecification::Scale { .. } => "scale",
                TypeSpecification::Number { .. } => "number",
                TypeSpecification::Text { .. } => "text",
                TypeSpecification::Date { .. } => "date",
                TypeSpecification::Time { .. } => "time",
                TypeSpecification::Duration { .. } => "duration",
                TypeSpecification::Ratio { .. } => "ratio",
                TypeSpecification::Veto { .. } => "veto",
                TypeSpecification::Error => "error",
            }
            .to_string()
        })
    }

    /// Check if this type is boolean
    pub fn is_boolean(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Boolean { .. })
    }

    /// Check if this type is scale
    pub fn is_scale(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Scale { .. })
    }

    /// Check if this type is number (dimensionless)
    pub fn is_number(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Number { .. })
    }

    /// Check if this type is numeric (either scale or number)
    pub fn is_numeric(&self) -> bool {
        matches!(
            &self.specifications,
            TypeSpecification::Scale { .. } | TypeSpecification::Number { .. }
        )
    }

    /// Check if this type is text
    pub fn is_text(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Text { .. })
    }

    /// Check if this type is date
    pub fn is_date(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Date { .. })
    }

    /// Check if this type is time
    pub fn is_time(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Time { .. })
    }

    /// Check if this type is duration
    pub fn is_duration(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Duration { .. })
    }

    /// Check if this type is ratio
    pub fn is_ratio(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Ratio { .. })
    }

    /// Check if this type is veto
    pub fn is_veto(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Veto { .. })
    }

    /// Check if this type is the error sentinel (type could not be determined during inference)
    pub fn is_error(&self) -> bool {
        matches!(&self.specifications, TypeSpecification::Error)
    }

    /// Check if two types have the same base type specification (ignoring constraints)
    pub fn has_same_base_type(&self, other: &LemmaType) -> bool {
        use TypeSpecification::*;
        matches!(
            (&self.specifications, &other.specifications),
            (Boolean { .. }, Boolean { .. })
                | (Number { .. }, Number { .. })
                | (Scale { .. }, Scale { .. })
                | (Text { .. }, Text { .. })
                | (Date { .. }, Date { .. })
                | (Time { .. }, Time { .. })
                | (Duration { .. }, Duration { .. })
                | (Ratio { .. }, Ratio { .. })
                | (Veto { .. }, Veto { .. })
                | (Error, Error)
        )
    }

    /// For scale types, returns the family name (root of the extension chain). For Custom extends, returns the family field; for Primitive, returns the type's own name (the type is the root). For non-scale types, returns None.
    #[must_use]
    pub fn scale_family_name(&self) -> Option<&str> {
        if !self.is_scale() {
            return None;
        }
        match &self.extends {
            TypeExtends::Custom { family, .. } => Some(family.as_str()),
            TypeExtends::Primitive => self.name.as_deref(),
        }
    }

    /// Returns true if both types are scale and belong to the same scale family (same family name).
    /// Two anonymous primitive scales (no name, no family) are considered compatible.
    #[must_use]
    pub fn same_scale_family(&self, other: &LemmaType) -> bool {
        if !self.is_scale() || !other.is_scale() {
            return false;
        }
        match (self.scale_family_name(), other.scale_family_name()) {
            (Some(self_family), Some(other_family)) => self_family == other_family,
            // Two anonymous primitive scales are compatible with each other.
            (None, None) => true,
            _ => false,
        }
    }

    /// Create a default value from this type's default constraint (if any)
    pub fn create_default_value(&self) -> Option<LiteralValue> {
        let value = match &self.specifications {
            TypeSpecification::Text { default, .. } => default.clone().map(ValueKind::Text),
            TypeSpecification::Number { default, .. } => (*default).map(ValueKind::Number),
            TypeSpecification::Scale { default, .. } => {
                default.clone().map(|(d, u)| ValueKind::Scale(d, u))
            }
            TypeSpecification::Boolean { default, .. } => (*default).map(ValueKind::Boolean),
            TypeSpecification::Date { default, .. } => default
                .clone()
                .map(|dt| ValueKind::Date(date_time_to_semantic(&dt))),
            TypeSpecification::Time { default, .. } => default
                .clone()
                .map(|t| ValueKind::Time(time_to_semantic(&t))),
            TypeSpecification::Duration { default, .. } => default
                .clone()
                .map(|(v, u)| ValueKind::Duration(v, duration_unit_to_semantic(&u))),
            TypeSpecification::Ratio { .. } => None, // Ratio default requires (value, unit); type spec has only Decimal
            TypeSpecification::Veto { .. } => None,
            TypeSpecification::Error => None,
        };

        value.map(|v| LiteralValue {
            value: v,
            lemma_type: self.clone(),
        })
    }

    /// Create a Veto LemmaType (internal use only - not user-declarable)
    pub fn veto_type() -> Self {
        Self::primitive(TypeSpecification::veto())
    }

    /// Create an Error sentinel LemmaType (used during type inference when a type cannot be determined).
    /// This type propagates through expressions and is never present in a validated graph.
    pub fn error_type() -> Self {
        Self::primitive(TypeSpecification::Error)
    }

    /// Decimal places for display (Number, Scale, and Ratio). Used by formatters.
    /// Ratio: optional, no default; when None display is normalized (no trailing zeros).
    pub fn decimal_places(&self) -> Option<u8> {
        match &self.specifications {
            TypeSpecification::Number { decimals, .. } => *decimals,
            TypeSpecification::Scale { decimals, .. } => *decimals,
            TypeSpecification::Ratio { decimals, .. } => *decimals,
            _ => None,
        }
    }

    /// Get an example value string for this type, suitable for UI help text
    pub fn example_value(&self) -> &'static str {
        match &self.specifications {
            TypeSpecification::Text { .. } => "\"hello world\"",
            TypeSpecification::Scale { .. } => "12.50 eur",
            TypeSpecification::Number { .. } => "3.14",
            TypeSpecification::Boolean { .. } => "true",
            TypeSpecification::Date { .. } => "2023-12-25T14:30:00Z",
            TypeSpecification::Veto { .. } => "veto",
            TypeSpecification::Time { .. } => "14:30:00",
            TypeSpecification::Duration { .. } => "90 minutes",
            TypeSpecification::Ratio { .. } => "50%",
            TypeSpecification::Error => unreachable!(
                "BUG: example_value called on Error sentinel type; this type must never reach user-facing code"
            ),
        }
    }

    /// Factor for a unit of this scale type (for unit conversion during evaluation only).
    /// Planning must validate conversions first and return LemmaError for invalid units.
    /// If called with a non-scale type or unknown unit name, panics (invariant violation).
    #[must_use]
    pub fn scale_unit_factor(&self, unit_name: &str) -> Decimal {
        let units = match &self.specifications {
            TypeSpecification::Scale { units, .. } => units,
            _ => unreachable!(
                "BUG: scale_unit_factor called with non-scale type {}; only call during evaluation after planning validated scale conversion",
                self.name()
            ),
        };
        match units
            .iter()
            .find(|u| u.name.eq_ignore_ascii_case(unit_name))
        {
            Some(ScaleUnit { value, .. }) => *value,
            None => {
                let valid: Vec<&str> = units.iter().map(|u| u.name.as_str()).collect();
                unreachable!(
                    "BUG: unknown unit '{}' for scale type {} (valid: {}); planning must reject invalid conversions with LemmaError",
                    unit_name,
                    self.name(),
                    valid.join(", ")
                );
            }
        }
    }
}

/// Literal value with type. The single value type in semantics.
#[derive(Clone, Debug, PartialEq, Eq, Hash, Deserialize)]
pub struct LiteralValue {
    pub value: ValueKind,
    pub lemma_type: LemmaType,
}

impl Serialize for LiteralValue {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        use serde::ser::SerializeStruct;
        let mut state = serializer.serialize_struct("LiteralValue", 3)?;
        state.serialize_field("value", &self.value)?;
        state.serialize_field("lemma_type", &self.lemma_type)?;
        state.serialize_field("display_value", &self.display_value())?;
        state.end()
    }
}

impl LiteralValue {
    pub fn text(s: String) -> Self {
        Self {
            value: ValueKind::Text(s),
            lemma_type: primitive_text().clone(),
        }
    }

    pub fn text_with_type(s: String, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Text(s),
            lemma_type,
        }
    }

    pub fn number(n: Decimal) -> Self {
        Self {
            value: ValueKind::Number(n),
            lemma_type: primitive_number().clone(),
        }
    }

    pub fn number_with_type(n: Decimal, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Number(n),
            lemma_type,
        }
    }

    pub fn scale_with_type(n: Decimal, unit: String, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Scale(n, unit),
            lemma_type,
        }
    }

    /// Number interpreted as a scale value in the given unit (e.g. "3 in usd" where 3 is a number).
    /// Creates an anonymous one-unit scale type so computation does not depend on parsing types.
    pub fn number_interpreted_as_scale(value: Decimal, unit_name: String) -> Self {
        let lemma_type = LemmaType {
            name: None,
            specifications: TypeSpecification::Scale {
                minimum: None,
                maximum: None,
                decimals: None,
                precision: None,
                units: ScaleUnits::from(vec![ScaleUnit {
                    name: unit_name.clone(),
                    value: Decimal::from(1),
                }]),
                help: "Format: value+unit (e.g. 100+unit)".to_string(),
                default: None,
            },
            extends: TypeExtends::Primitive,
        };
        Self {
            value: ValueKind::Scale(value, unit_name),
            lemma_type,
        }
    }

    pub fn from_bool(b: bool) -> Self {
        Self {
            value: ValueKind::Boolean(b),
            lemma_type: primitive_boolean().clone(),
        }
    }

    pub fn date(dt: SemanticDateTime) -> Self {
        Self {
            value: ValueKind::Date(dt),
            lemma_type: primitive_date().clone(),
        }
    }

    pub fn date_with_type(dt: SemanticDateTime, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Date(dt),
            lemma_type,
        }
    }

    pub fn time(t: SemanticTime) -> Self {
        Self {
            value: ValueKind::Time(t),
            lemma_type: primitive_time().clone(),
        }
    }

    pub fn time_with_type(t: SemanticTime, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Time(t),
            lemma_type,
        }
    }

    pub fn duration(value: Decimal, unit: SemanticDurationUnit) -> Self {
        Self {
            value: ValueKind::Duration(value, unit),
            lemma_type: primitive_duration().clone(),
        }
    }

    pub fn duration_with_type(
        value: Decimal,
        unit: SemanticDurationUnit,
        lemma_type: LemmaType,
    ) -> Self {
        Self {
            value: ValueKind::Duration(value, unit),
            lemma_type,
        }
    }

    pub fn ratio(r: Decimal, unit: Option<String>) -> Self {
        Self {
            value: ValueKind::Ratio(r, unit),
            lemma_type: primitive_ratio().clone(),
        }
    }

    pub fn ratio_with_type(r: Decimal, unit: Option<String>, lemma_type: LemmaType) -> Self {
        Self {
            value: ValueKind::Ratio(r, unit),
            lemma_type,
        }
    }

    /// Get a display string for this value (for UI/output)
    pub fn display_value(&self) -> String {
        format!("{}", self)
    }

    /// Approximate byte size for resource limit checks (string representation length)
    pub fn byte_size(&self) -> usize {
        format!("{}", self).len()
    }

    /// Get the resolved type of this literal
    pub fn get_type(&self) -> &LemmaType {
        &self.lemma_type
    }
}

/// Fact value: literal, type declaration (resolved type only), or document reference.
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum FactValue {
    Literal(LiteralValue),
    TypeDeclaration { resolved_type: LemmaType },
    DocumentReference(String),
}

/// Fact: path, value, and source location.
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub struct Fact {
    pub path: FactPath,
    pub value: FactValue,
    pub source: Option<Source>,
}

/// Resolved fact value for the execution plan: aligned with [`FactValue`] but with source per variant.
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum FactData {
    /// Value-holding fact: current value (literal or default); type is on the value.
    Value { value: LiteralValue, source: Source },
    /// Type-only fact: schema known, value to be supplied (e.g. via with_values).
    TypeDeclaration {
        resolved_type: LemmaType,
        source: Source,
    },
    /// Document reference fact: points to another document.
    DocumentRef { doc_name: String, source: Source },
}

impl FactData {
    /// Returns the schema type for value and type-declaration facts; `None` for document references.
    pub fn schema_type(&self) -> Option<&LemmaType> {
        match self {
            FactData::Value { value, .. } => Some(&value.lemma_type),
            FactData::TypeDeclaration { resolved_type, .. } => Some(resolved_type),
            FactData::DocumentRef { .. } => None,
        }
    }

    /// Returns the literal value for value facts; `None` for type-declaration and document references.
    pub fn value(&self) -> Option<&LiteralValue> {
        match self {
            FactData::Value { value, .. } => Some(value),
            FactData::TypeDeclaration { .. } | FactData::DocumentRef { .. } => None,
        }
    }

    /// Returns the source location for this fact.
    pub fn source(&self) -> &Source {
        match self {
            FactData::Value { source, .. } => source,
            FactData::TypeDeclaration { source, .. } => source,
            FactData::DocumentRef { source, .. } => source,
        }
    }

    /// Returns the referenced document name for document reference facts; `None` otherwise.
    pub fn doc_ref(&self) -> Option<&str> {
        match self {
            FactData::Value { .. } | FactData::TypeDeclaration { .. } => None,
            FactData::DocumentRef { doc_name, .. } => Some(doc_name),
        }
    }
}

/// Convert parser Value to ValueKind. Fails if Scale/Ratio have no unit (strict).
pub fn value_to_semantic(value: &crate::parsing::ast::Value) -> Result<ValueKind, String> {
    use crate::parsing::ast::Value;
    Ok(match value {
        Value::Number(n) => ValueKind::Number(*n),
        Value::Text(s) => ValueKind::Text(s.clone()),
        Value::Boolean(b) => ValueKind::Boolean(bool::from(b.clone())),
        Value::Date(dt) => ValueKind::Date(date_time_to_semantic(dt)),
        Value::Time(t) => ValueKind::Time(time_to_semantic(t)),
        Value::Duration(n, u) => ValueKind::Duration(*n, duration_unit_to_semantic(u)),
        Value::Scale(n, unit) => ValueKind::Scale(*n, unit.clone()),
        Value::Ratio(n, unit) => ValueKind::Ratio(*n, unit.clone()),
    })
}

/// Convert AST date-time to semantic (for tests and planning).
pub(crate) fn date_time_to_semantic(dt: &crate::parsing::ast::DateTimeValue) -> SemanticDateTime {
    SemanticDateTime {
        year: dt.year,
        month: dt.month,
        day: dt.day,
        hour: dt.hour,
        minute: dt.minute,
        second: dt.second,
        timezone: dt.timezone.as_ref().map(|tz| SemanticTimezone {
            offset_hours: tz.offset_hours,
            offset_minutes: tz.offset_minutes,
        }),
    }
}

/// Convert AST time to semantic (for tests and planning).
pub(crate) fn time_to_semantic(t: &crate::parsing::ast::TimeValue) -> SemanticTime {
    SemanticTime {
        hour: t.hour.into(),
        minute: t.minute.into(),
        second: t.second.into(),
        timezone: t.timezone.as_ref().map(|tz| SemanticTimezone {
            offset_hours: tz.offset_hours,
            offset_minutes: tz.offset_minutes,
        }),
    }
}

/// Convert AST duration unit to semantic (for tests and planning).
pub(crate) fn duration_unit_to_semantic(
    u: &crate::parsing::ast::DurationUnit,
) -> SemanticDurationUnit {
    use crate::parsing::ast::DurationUnit as DU;
    match u {
        DU::Year => SemanticDurationUnit::Year,
        DU::Month => SemanticDurationUnit::Month,
        DU::Week => SemanticDurationUnit::Week,
        DU::Day => SemanticDurationUnit::Day,
        DU::Hour => SemanticDurationUnit::Hour,
        DU::Minute => SemanticDurationUnit::Minute,
        DU::Second => SemanticDurationUnit::Second,
        DU::Millisecond => SemanticDurationUnit::Millisecond,
        DU::Microsecond => SemanticDurationUnit::Microsecond,
    }
}

/// Convert AST conversion target to semantic (planning boundary; evaluation/computation use only semantic).
///
/// The AST uses `ConversionTarget::Unit(name)` for non-duration units; this function looks up `name`
/// in the document's unit index and returns `RatioUnit` or `ScaleUnit` based on the type that defines
/// the unit. The unit must be defined by a scale or ratio type in the document (e.g. primitive ratio for
/// "percent", "permille").
pub fn conversion_target_to_semantic(
    ct: &ConversionTarget,
    unit_index: Option<&HashMap<String, LemmaType>>,
) -> Result<SemanticConversionTarget, String> {
    match ct {
        ConversionTarget::Duration(u) => Ok(SemanticConversionTarget::Duration(
            duration_unit_to_semantic(u),
        )),
        ConversionTarget::Unit(name) => {
            let index = unit_index.ok_or_else(|| {
                "Unit conversion requires type resolution; unit index not available.".to_string()
            })?;
            let lemma_type = index.get(name).ok_or_else(|| {
                format!(
                    "Unknown unit '{}'. Unit must be defined by a scale or ratio type.",
                    name
                )
            })?;
            if lemma_type.is_ratio() {
                Ok(SemanticConversionTarget::RatioUnit(name.clone()))
            } else if lemma_type.is_scale() {
                Ok(SemanticConversionTarget::ScaleUnit(name.clone()))
            } else {
                Err(format!(
                    "Unit '{}' is not a ratio or scale type; cannot use it in conversion.",
                    name
                ))
            }
        }
    }
}

// -----------------------------------------------------------------------------
// Primitive type constructors (moved from parsing::ast)
// -----------------------------------------------------------------------------

// Private statics for lazy initialization
static PRIMITIVE_BOOLEAN: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_SCALE: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_NUMBER: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_TEXT: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_DATE: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_TIME: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_DURATION: OnceLock<LemmaType> = OnceLock::new();
static PRIMITIVE_RATIO: OnceLock<LemmaType> = OnceLock::new();

/// Primitive types use the default TypeSpecification from the parser (single source of truth).
#[must_use]
pub fn primitive_boolean() -> &'static LemmaType {
    PRIMITIVE_BOOLEAN.get_or_init(|| LemmaType::primitive(TypeSpecification::boolean()))
}

#[must_use]
pub fn primitive_scale() -> &'static LemmaType {
    PRIMITIVE_SCALE.get_or_init(|| LemmaType::primitive(TypeSpecification::scale()))
}

#[must_use]
pub fn primitive_number() -> &'static LemmaType {
    PRIMITIVE_NUMBER.get_or_init(|| LemmaType::primitive(TypeSpecification::number()))
}

#[must_use]
pub fn primitive_text() -> &'static LemmaType {
    PRIMITIVE_TEXT.get_or_init(|| LemmaType::primitive(TypeSpecification::text()))
}

#[must_use]
pub fn primitive_date() -> &'static LemmaType {
    PRIMITIVE_DATE.get_or_init(|| LemmaType::primitive(TypeSpecification::date()))
}

#[must_use]
pub fn primitive_time() -> &'static LemmaType {
    PRIMITIVE_TIME.get_or_init(|| LemmaType::primitive(TypeSpecification::time()))
}

#[must_use]
pub fn primitive_duration() -> &'static LemmaType {
    PRIMITIVE_DURATION.get_or_init(|| LemmaType::primitive(TypeSpecification::duration()))
}

#[must_use]
pub fn primitive_ratio() -> &'static LemmaType {
    PRIMITIVE_RATIO.get_or_init(|| LemmaType::primitive(TypeSpecification::ratio()))
}

// -----------------------------------------------------------------------------
// Display implementations
// -----------------------------------------------------------------------------

impl fmt::Display for FactPath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        for segment in &self.segments {
            write!(f, "{}.", segment.fact)?;
        }
        write!(f, "{}", self.fact)
    }
}

impl fmt::Display for RulePath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        for segment in &self.segments {
            write!(f, "{}.", segment.fact)?;
        }
        write!(f, "{}?", self.rule)
    }
}

impl fmt::Display for LemmaType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.name())
    }
}

impl fmt::Display for LiteralValue {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.value {
            ValueKind::Ratio(r, Some(unit_name)) => {
                if let TypeSpecification::Ratio { units, .. } = &self.lemma_type.specifications {
                    if let Ok(unit) = units.get(unit_name) {
                        let display_value = (*r * unit.value).normalize();
                        let s = if display_value.fract().is_zero() {
                            display_value.trunc().to_string()
                        } else {
                            display_value.to_string()
                        };
                        // Use shorthand symbols for percent (%) and permille (%%)
                        return match unit_name.as_str() {
                            "percent" => write!(f, "{}%", s),
                            "permille" => write!(f, "{}%%", s),
                            _ => write!(f, "{} {}", s, unit_name),
                        };
                    }
                }
                write!(f, "{}", self.value)
            }
            _ => write!(f, "{}", self.value),
        }
    }
}

// -----------------------------------------------------------------------------
// Eq and Hash implementations for Expression (for use in HashMaps)
// -----------------------------------------------------------------------------

impl Eq for Expression {}

impl Hash for Expression {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.semantic_hash(state);
    }
}

impl Eq for ExpressionKind {}

impl Hash for ExpressionKind {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.semantic_hash(state);
    }
}

// -----------------------------------------------------------------------------
// Tests
// -----------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;
    use crate::parsing::ast::{BooleanValue, DateTimeValue, DurationUnit, TimeValue};
    use rust_decimal::Decimal;
    use std::str::FromStr;

    #[test]
    fn test_literal_value_to_primitive_type() {
        let one = Decimal::from_str("1").unwrap();

        assert_eq!(LiteralValue::text("".to_string()).lemma_type.name(), "text");
        assert_eq!(LiteralValue::number(one).lemma_type.name(), "number");
        assert_eq!(
            LiteralValue::from_bool(bool::from(BooleanValue::True))
                .lemma_type
                .name(),
            "boolean"
        );

        let dt = DateTimeValue {
            year: 2024,
            month: 1,
            day: 1,
            hour: 0,
            minute: 0,
            second: 0,
            timezone: None,
        };
        assert_eq!(
            LiteralValue::date(date_time_to_semantic(&dt))
                .lemma_type
                .name(),
            "date"
        );
        assert_eq!(
            LiteralValue::ratio(one / Decimal::from(100), Some("percent".to_string()))
                .lemma_type
                .name(),
            "ratio"
        );
        assert_eq!(
            LiteralValue::duration(one, duration_unit_to_semantic(&DurationUnit::Second))
                .lemma_type
                .name(),
            "duration"
        );
    }

    #[test]
    fn test_doc_type_display() {
        assert_eq!(format!("{}", primitive_text()), "text");
        assert_eq!(format!("{}", primitive_number()), "number");
        assert_eq!(format!("{}", primitive_date()), "date");
        assert_eq!(format!("{}", primitive_boolean()), "boolean");
        assert_eq!(format!("{}", primitive_duration()), "duration");
    }

    #[test]
    fn test_type_constructor() {
        let specs = TypeSpecification::number();
        let lemma_type = LemmaType::new("dice".to_string(), specs, TypeExtends::Primitive);
        assert_eq!(lemma_type.name(), "dice");
    }

    #[test]
    fn test_type_display() {
        let specs = TypeSpecification::text();
        let lemma_type = LemmaType::new("name".to_string(), specs, TypeExtends::Primitive);
        assert_eq!(format!("{}", lemma_type), "name");
    }

    #[test]
    fn test_type_equality() {
        let specs1 = TypeSpecification::number();
        let specs2 = TypeSpecification::number();
        let lemma_type1 = LemmaType::new("dice".to_string(), specs1, TypeExtends::Primitive);
        let lemma_type2 = LemmaType::new("dice".to_string(), specs2, TypeExtends::Primitive);
        assert_eq!(lemma_type1, lemma_type2);
    }

    #[test]
    fn test_type_serialization() {
        let specs = TypeSpecification::number();
        let lemma_type = LemmaType::new("dice".to_string(), specs, TypeExtends::Primitive);
        let serialized = serde_json::to_string(&lemma_type).unwrap();
        let deserialized: LemmaType = serde_json::from_str(&serialized).unwrap();
        assert_eq!(lemma_type, deserialized);
    }

    #[test]
    fn test_literal_value_display_value() {
        let ten = Decimal::from_str("10").unwrap();

        assert_eq!(
            LiteralValue::text("hello".to_string()).display_value(),
            "hello"
        );
        assert_eq!(LiteralValue::number(ten).display_value(), "10");
        assert_eq!(LiteralValue::from_bool(true).display_value(), "true");
        assert_eq!(LiteralValue::from_bool(false).display_value(), "false");

        // 0.10 ratio with "percent" unit displays as 10% (unit conversion applied)
        let ten_percent_ratio = LiteralValue::ratio(
            Decimal::from_str("0.10").unwrap(),
            Some("percent".to_string()),
        );
        assert_eq!(ten_percent_ratio.display_value(), "10%");

        let time = TimeValue {
            hour: 14,
            minute: 30,
            second: 0,
            timezone: None,
        };
        let time_display = LiteralValue::time(time_to_semantic(&time)).display_value();
        assert!(time_display.contains("14"));
        assert!(time_display.contains("30"));
    }

    #[test]
    fn test_literal_value_time_type() {
        let time = TimeValue {
            hour: 14,
            minute: 30,
            second: 0,
            timezone: None,
        };
        let lit = LiteralValue::time(time_to_semantic(&time));
        assert_eq!(lit.lemma_type.name(), "time");
    }

    #[test]
    fn test_scale_family_name_primitive_root() {
        let scale_spec = TypeSpecification::scale();
        let money_primitive = LemmaType::new(
            "money".to_string(),
            scale_spec.clone(),
            TypeExtends::Primitive,
        );
        assert_eq!(money_primitive.scale_family_name(), Some("money"));
    }

    #[test]
    fn test_scale_family_name_custom() {
        let scale_spec = TypeSpecification::scale();
        let money_custom = LemmaType::new(
            "money".to_string(),
            scale_spec,
            TypeExtends::Custom {
                parent: "money".to_string(),
                family: "money".to_string(),
            },
        );
        assert_eq!(money_custom.scale_family_name(), Some("money"));
    }

    #[test]
    fn test_same_scale_family_same_name_different_extends() {
        let scale_spec = TypeSpecification::scale();
        let money_primitive = LemmaType::new(
            "money".to_string(),
            scale_spec.clone(),
            TypeExtends::Primitive,
        );
        let money_custom = LemmaType::new(
            "money".to_string(),
            scale_spec,
            TypeExtends::Custom {
                parent: "money".to_string(),
                family: "money".to_string(),
            },
        );
        assert!(money_primitive.same_scale_family(&money_custom));
        assert!(money_custom.same_scale_family(&money_primitive));
    }

    #[test]
    fn test_same_scale_family_parent_and_child() {
        let scale_spec = TypeSpecification::scale();
        let type_x = LemmaType::new("x".to_string(), scale_spec.clone(), TypeExtends::Primitive);
        let type_x2 = LemmaType::new(
            "x2".to_string(),
            scale_spec,
            TypeExtends::Custom {
                parent: "x".to_string(),
                family: "x".to_string(),
            },
        );
        assert_eq!(type_x.scale_family_name(), Some("x"));
        assert_eq!(type_x2.scale_family_name(), Some("x"));
        assert!(type_x.same_scale_family(&type_x2));
        assert!(type_x2.same_scale_family(&type_x));
    }

    #[test]
    fn test_same_scale_family_siblings() {
        let scale_spec = TypeSpecification::scale();
        let type_x2_a = LemmaType::new(
            "x2a".to_string(),
            scale_spec.clone(),
            TypeExtends::Custom {
                parent: "x".to_string(),
                family: "x".to_string(),
            },
        );
        let type_x2_b = LemmaType::new(
            "x2b".to_string(),
            scale_spec,
            TypeExtends::Custom {
                parent: "x".to_string(),
                family: "x".to_string(),
            },
        );
        assert!(type_x2_a.same_scale_family(&type_x2_b));
    }

    #[test]
    fn test_same_scale_family_different_families() {
        let scale_spec = TypeSpecification::scale();
        let money = LemmaType::new(
            "money".to_string(),
            scale_spec.clone(),
            TypeExtends::Primitive,
        );
        let temperature = LemmaType::new(
            "temperature".to_string(),
            scale_spec,
            TypeExtends::Primitive,
        );
        assert!(!money.same_scale_family(&temperature));
        assert!(!temperature.same_scale_family(&money));
    }

    #[test]
    fn test_same_scale_family_scale_vs_non_scale() {
        let scale_spec = TypeSpecification::scale();
        let number_spec = TypeSpecification::number();
        let scale_type = LemmaType::new("money".to_string(), scale_spec, TypeExtends::Primitive);
        let number_type = LemmaType::new("amount".to_string(), number_spec, TypeExtends::Primitive);
        assert!(!scale_type.same_scale_family(&number_type));
        assert!(!number_type.same_scale_family(&scale_type));
    }

    #[test]
    fn test_scale_family_name_non_scale_returns_none() {
        let number_spec = TypeSpecification::number();
        let number_type = LemmaType::new("amount".to_string(), number_spec, TypeExtends::Primitive);
        assert_eq!(number_type.scale_family_name(), None);
    }
}