//! Namespace reference type.
#![cfg(not(feature = "no_module"))]

use crate::ast::Ident;
use crate::tokenizer::Token;
use crate::{Position, StaticVec};
#[cfg(feature = "no_std")]
use std::prelude::v1::*;
use std::{
    fmt,
    num::NonZeroUsize,
    ops::{Deref, DerefMut},
};

/// _(internals)_ A chain of [module][crate::Module] names to namespace-qualify a variable or function call.
/// Exported under the `internals` feature only.
///
/// Not available under `no_module`.
///
/// A [`u64`] offset to the current stack of imported [modules][crate::Module] in the
/// [global runtime state][crate::GlobalRuntimeState] is cached for quick search purposes.
///
/// A [`StaticVec`] is used because the vast majority of namespace-qualified access contains only
/// one level, and it is wasteful to always allocate a [`Vec`] with one element.
#[derive(Clone, Eq, PartialEq, Default, Hash)]
pub struct Namespace {
    path: StaticVec<Ident>,
    index: Option<NonZeroUsize>,
}

impl fmt::Debug for Namespace {
    #[cold]
    #[inline(never)]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.is_empty() {
            return f.write_str("NONE");
        }

        if let Some(index) = self.index {
            write!(f, "{index} -> ")?;
        }

        f.write_str(
            &self
                .path
                .iter()
                .map(Ident::as_str)
                .collect::<StaticVec<_>>()
                .join(Token::DoubleColon.literal_syntax()),
        )
    }
}

impl fmt::Display for Namespace {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.is_empty() {
            return Ok(());
        }

        f.write_str(
            &self
                .path
                .iter()
                .map(Ident::as_str)
                .collect::<StaticVec<_>>()
                .join(Token::DoubleColon.literal_syntax()),
        )
    }
}

impl Deref for Namespace {
    type Target = StaticVec<Ident>;

    #[inline(always)]
    fn deref(&self) -> &Self::Target {
        &self.path
    }
}

impl DerefMut for Namespace {
    #[inline(always)]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.path
    }
}

impl From<Vec<Ident>> for Namespace {
    #[inline]
    fn from(mut path: Vec<Ident>) -> Self {
        path.shrink_to_fit();
        Self {
            index: None,
            path: path.into(),
        }
    }
}

impl From<StaticVec<Ident>> for Namespace {
    #[inline]
    fn from(mut path: StaticVec<Ident>) -> Self {
        path.shrink_to_fit();
        Self { index: None, path }
    }
}

impl Namespace {
    /// Constant for no namespace.
    pub const NONE: Self = Self {
        index: None,
        path: StaticVec::new_const(),
    };

    /// Create a new [`Namespace`].
    #[inline(always)]
    #[must_use]
    pub fn new(root: impl Into<Ident>) -> Self {
        let mut path = StaticVec::new_const();
        path.push(root.into());

        Self { index: None, path }
    }
    /// Get the [`Scope`][crate::Scope] index offset.
    #[inline(always)]
    #[must_use]
    pub(crate) const fn index(&self) -> Option<NonZeroUsize> {
        self.index
    }
    /// Set the [`Scope`][crate::Scope] index offset.
    #[inline(always)]
    pub(crate) fn set_index(&mut self, index: Option<NonZeroUsize>) {
        self.index = index;
    }
    /// Get the [position][Position] of this [`Namespace`].
    ///
    /// # Panics
    ///
    /// Panics if the path is empty.
    #[inline(always)]
    #[must_use]
    pub fn position(&self) -> Position {
        self.path[0].pos
    }
    /// Get the first path segment of this [`Namespace`].
    ///
    /// # Panics
    ///
    /// Panics if the path is empty.
    #[inline(always)]
    #[must_use]
    pub fn root(&self) -> &str {
        &self.path[0].name
    }
}