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use num::Float;

/// Operators can be custom-defined by the library-user in terms of this struct.
///
/// # Examples
///
/// ```
/// use exmex::{BinOp, Operator};
/// let ops = vec![
///     Operator {
///         repr: "-",
///         bin_op: Some(BinOp {
///             op: |a, b| a - b,
///             prio: 0,
///         }),
///         unary_op: Some(|a: f32| (-a)),
///     },
///     Operator {
///         repr: "sin",
///         bin_op: None,
///         unary_op: Some(|a: f32| a.sin()),
///     }
/// ];
/// ```
///
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
pub struct Operator<'a, T> {
    /// Representation of the operator in the string to be parsed, e.g., `-` or `sin`.
    pub repr: &'a str,
    /// Binary operator that contains a priority besides a function pointer, if available.
    pub bin_op: Option<BinOp<T>>,
    /// Unary operator that does not have an explicit priority. Unary operators have
    /// higher priority than binary opertors, e.g., `-1^2 == 1`.
    pub unary_op: Option<fn(T) -> T>,
}

/// A binary operator that consists of a function pointer and a priority.
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
pub struct BinOp<T> {
    /// Implementation of the binary operation, e.g., `|a, b| a * b` for multiplication.
    pub op: fn(T, T) -> T,
    /// Priority of the binary operation. A binary operation with a
    /// higher number will be executed first. For instance, in a sane world `*`
    /// has a higher priority than `+`. However, in Exmex land you could also define
    /// this differently.
    pub prio: i16,
}

/// Returns the default operators.
pub fn make_default_operators<'a, T: Float>() -> Vec<Operator<'a, T>> {
    vec![
        Operator {
            repr: "^",
            bin_op: Some(BinOp {
                op: |a: T, b| a.powf(b),
                prio: 2,
            }),
            unary_op: None,
        },
        Operator {
            repr: "*",
            bin_op: Some(BinOp {
                op: |a, b| a * b,
                prio: 1,
            }),
            unary_op: None,
        },
        Operator {
            repr: "/",
            bin_op: Some(BinOp {
                op: |a, b| a / b,
                prio: 1,
            }),
            unary_op: None,
        },
        Operator {
            repr: "+",
            bin_op: Some(BinOp {
                op: |a, b| a + b,
                prio: 0,
            }),
            unary_op: Some(|a: T| a),
        },
        Operator {
            repr: "-",
            bin_op: Some(BinOp {
                op: |a, b| a - b,
                prio: 0,
            }),
            unary_op: Some(|a: T| (-a)),
        },
        Operator {
            repr: "sin",
            bin_op: None,
            unary_op: Some(|a: T| a.sin()),
        },
        Operator {
            repr: "cos",
            bin_op: None,
            unary_op: Some(|a: T| a.cos()),
        },
        Operator {
            repr: "tan",
            bin_op: None,
            unary_op: Some(|a: T| a.tan()),
        },
        Operator {
            repr: "exp",
            bin_op: None,
            unary_op: Some(|a: T| a.exp()),
        },
        Operator {
            repr: "log",
            bin_op: None,
            unary_op: Some(|a: T| a.ln()),
        },
        Operator {
            repr: "log2",
            bin_op: None,
            unary_op: Some(|a: T| a.log2()),
        },
    ]
}