//! Defines the public-facing data structures for Nix values.
//!
//! These types are used to represent the final result of an evaluation and are
//! designed to be user-friendly and serializable. They are distinct from the
//! internal `Value` types used during evaluation in `nixjit_eval`.

use core::fmt::{Debug, Display, Formatter, Result as FmtResult};
use core::hash::Hash;
use core::ops::Deref;

use std::borrow::Cow;
use std::collections::BTreeMap;
use std::sync::LazyLock;

use derive_more::{Constructor, IsVariant, Unwrap};
use regex::Regex;

/// Represents a constant, primitive value in Nix.
#[derive(Debug, Clone, Copy, PartialEq, IsVariant, Unwrap)]
pub enum Const {
    /// A boolean value (`true` or `false`).
    Bool(bool),
    /// A 64-bit signed integer.
    Int(i64),
    /// A 64-bit floating-point number.
    Float(f64),
    /// The `null` value.
    Null,
}

impl Display for Const {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        use Const::*;
        match self {
            Int(x) => write!(f, "{x}"),
            Float(x) => write!(f, "{x}"),
            Bool(x) => write!(f, "{x}"),
            Null => write!(f, "null"),
        }
    }
}

impl From<bool> for Const {
    fn from(value: bool) -> Self {
        Const::Bool(value)
    }
}

impl From<i64> for Const {
    fn from(value: i64) -> Self {
        Const::Int(value)
    }
}

impl From<f64> for Const {
    fn from(value: f64) -> Self {
        Const::Float(value)
    }
}

/// Represents a Nix symbol, which is used as a key in attribute sets.
#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Constructor)]
pub struct Symbol(String);

impl<T: Into<String>> From<T> for Symbol {
    fn from(value: T) -> Self {
        Symbol(value.into())
    }
}

/// Formats a string slice as a Nix symbol, quoting it if necessary.
pub fn format_symbol<'a>(sym: impl Into<Cow<'a, str>>) -> Cow<'a, str> {
    let sym = sym.into();
    if REGEX.is_match(&sym) {
        sym
    } else {
        Cow::Owned(format!(r#""{sym}""#))
    }
}

impl Display for Symbol {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        if self.normal() {
            write!(f, "{}", self.0)
        } else {
            write!(f, r#""{}""#, self.0)
        }
    }
}

static REGEX: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"^[a-zA-Z_][a-zA-Z0-9_'-]*$").unwrap());
impl Symbol {
    /// Checks if the symbol is a "normal" identifier that doesn't require quotes.
    fn normal(&self) -> bool {
        REGEX.is_match(self)
    }
}

impl Deref for Symbol {
    type Target = str;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl Symbol {
    /// Consumes the `Symbol`, returning its inner `String`.
    pub fn into_inner(self) -> String {
        self.0
    }

    /// Returns a reference to the inner `String`.
    pub fn as_inner(&self) -> &String {
        &self.0
    }
}

/// Represents a Nix attribute set, which is a map from symbols to values.
#[derive(Constructor, Clone, PartialEq)]
pub struct AttrSet {
    data: BTreeMap<Symbol, Value>,
}

impl Debug for AttrSet {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        use Value::*;
        write!(f, "{{")?;
        for (k, v) in self.data.iter() {
            write!(f, " {k:?} = ")?;
            match v {
                List(_) => write!(f, "[ ... ];")?,
                AttrSet(_) => write!(f, "{{ ... }};")?,
                v => write!(f, "{v:?};")?,
            }
        }
        write!(f, " }}")
    }
}

impl Display for AttrSet {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        use Value::*;
        write!(f, "{{ ")?;
        let mut first = true;
        for (k, v) in self.data.iter() {
            if !first {
                write!(f, "; ")?;
            }
            write!(f, "{k} = ")?;
            match v {
                AttrSet(_) => write!(f, "{{ ... }}"),
                List(_) => write!(f, "[ ... ]"),
                v => write!(f, "{v}"),
            }?;
            first = false;
        }
        write!(f, " }}")
    }
}

/// Represents a Nix list, which is a vector of values.
#[derive(Constructor, Clone, Debug, PartialEq)]
pub struct List {
    data: Vec<Value>,
}

impl Display for List {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        write!(f, "[ ")?;
        for v in self.data.iter() {
            write!(f, "{v} ")?;
        }
        write!(f, "]")
    }
}

/// Represents any possible Nix value that can be returned from an evaluation.
#[derive(IsVariant, Unwrap, Clone, Debug, PartialEq)]
pub enum Value {
    /// A constant value (int, float, bool, null).
    Const(Const),
    /// A string value.
    String(String),
    /// An attribute set.
    AttrSet(AttrSet),
    /// A list.
    List(List),
    /// A thunk, representing a delayed computation.
    Thunk,
    /// A function (lambda).
    Func,
    /// A primitive (built-in) operation.
    PrimOp,
    /// A partially applied primitive operation.
    PrimOpApp,
    /// A marker for a value that has been seen before during serialization, to break cycles.
    /// This is used to prevent infinite recursion when printing or serializing cyclic data structures.
    Repeated,
}

impl Display for Value {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        use Value::*;
        match self {
            Const(x) => write!(f, "{x}"),
            String(x) => write!(f, r#""{x}""#),
            AttrSet(x) => write!(f, "{x}"),
            List(x) => write!(f, "{x}"),
            Thunk => write!(f, "<CODE>"),
            Func => write!(f, "<LAMBDA>"),
            PrimOp => write!(f, "<PRIMOP>"),
            PrimOpApp => write!(f, "<PRIMOP-APP>"),
            Repeated => write!(f, "<REPEATED>"),
        }
    }
}