use std::collections::HashSet;

use std::fmt::{self, Display, Formatter};

use std::hash::Hash;

use thiserror::Error;

use crate::ast::{Expression, Name, SymbolTable};

use crate::metadata::Metadata;

use crate::model::Model;

#[derive(Debug, Error)]

pub enum ApplicationError {

    #[error("Rule is not applicable")]

    RuleNotApplicable,

    #[error("Could not calculate the expression domain")]

    DomainError,

}

/// Represents the result of applying a rule to an expression within a model.

///

/// A `Reduction` encapsulates the changes made to a model during a rule application.

/// It includes a new expression to replace the original one, an optional top-level constraint

/// to be added to the model, and any updates to the model's symbol table.

///

/// This struct allows for representing side-effects of rule applications, ensuring that

/// all modifications, including symbol table expansions and additional constraints, are

/// accounted for and can be applied to the model consistently.

///

/// # Fields

/// - `new_expression`: The updated [`Expression`] that replaces the original one after applying the rule.

/// - `new_top`: An additional top-level [`Expression`] constraint that should be added to the model. If no top-level

///   constraint is needed, this field can be set to `Expression::Nothing`.

/// - `symbols`: A [`SymbolTable`] containing any new symbol definitions or modifications to be added to the model's

///   symbol table. If no symbols are modified, this field can be set to an empty symbol table.

///

/// # Usage

/// A `Reduction` can be created using one of the provided constructors:

/// - [`Reduction::new`]: Creates a reduction with a new expression, top-level constraint, and symbol modifications.

/// - [`Reduction::pure`]: Creates a reduction with only a new expression and no side-effects on the symbol table or constraints.

/// - [`Reduction::with_symbols`]: Creates a reduction with a new expression and symbol table modifications, but no top-level constraint.

/// - [`Reduction::with_top`]: Creates a reduction with a new expression and a top-level constraint, but no symbol table modifications.

///

/// The `apply` method allows for applying the changes represented by the `Reduction` to a [`Model`].

///

/// # Example

/// ```

/// # See Also

/// - [`ApplicationResult`]: Represents the result of applying a rule, which may either be a `Reduction` or an `ApplicationError`.

/// - [`Model`]: The structure to which the `Reduction` changes are applied.

#[non_exhaustive]

#[derive(Clone, Debug)]

pub struct Reduction {

    pub new_expression: Expression,

    pub new_top: Expression,

    pub symbols: SymbolTable,

}

/// The result of applying a rule to an expression.

/// Contains either a set of reduction instructions or an error.

pub type ApplicationResult = Result<Reduction, ApplicationError>;

impl Reduction {

    /// Represents a reduction with no side effects on the model.

    /// Represents a reduction that also modifies the symbol table.

    /// Represents a reduction that also adds a top-level constraint to the model.

    // Apply side-effects (e.g. symbol table updates

        // TODO: (yb33) Remove it when we change constraints to a vector

            }

        };

}

/**

 * A rule with a name, application function, and rule sets.

 *

 * # Fields

 * - `name` The name of the rule.

 * - `application` The function to apply the rule.

 * - `rule_sets` A list of rule set names and priorities that this rule is a part of. This is used to populate rulesets at runtime.

 */

#[derive(Clone, Debug)]

pub struct Rule<'a> {

    pub name: &'a str,

    pub application: fn(&Expression, &Model) -> ApplicationResult,

    pub rule_sets: &'a [(&'a str, u16)], // (name, priority). At runtime, we add the rule to rulesets

}

impl<'a> Rule<'a> {

}

impl Display for Rule<'_> {

}

impl PartialEq for Rule<'_> {

}

impl Eq for Rule<'_> {}

impl Hash for Rule<'_> {

}