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

use crate::wrapper::{DisplayWithSep, PrintableWrapper};

/// Wraps iterators into [`PrintableWrapper`].
///
/// # Warning
///
/// Avoid creating [`PrintableWrapper`] from resource-owning iterators such as
/// [`std::vec::IntoIter`], since they would clone the owned data or perform
/// other heavy operations every time [`Display::fmt`] is called.
///
/// To statically ensure that you don't use resource-owning iterators in such a
/// context, enable the `unstable-assert-no-drop` feature. However, this
/// approach has serious drawbacks. See the description of this feature in the
/// documentation.
///
/// # Examples
///
/// ```rust
/// use printable::prelude::PrintableIter;
///
/// let v = vec![1, 2, 3];
/// assert_eq!(format!("{}", v.iter().printable()), "[1, 2, 3]");
///
/// let v: Vec<usize> = vec![1];
/// assert_eq!(format!("{}", v.iter().printable()), "[1]");
///
/// let v: Vec<usize> = vec![];
/// assert_eq!(format!("{}", v.iter().printable()), "[]");
/// ```
pub trait PrintableIter: Iterator + Clone
where
    Self::Item: Display,
{
    /// Compile-time assertion that `Self` doesn't own any resource.
    ///
    /// # Warning
    ///
    /// May violate backward compatibility and lead to compilation failure
    /// even if the major semver versions of the underlying crates aren't
    /// updated.
    ///
    /// This may happen due to the following factors:
    /// - The [`std::mem::needs_drop`] documentation does not guarantee its
    ///   stability.
    /// - The fact that the `Self` type, which can be declared in a third-party
    ///   crate, started owning a resource doesn't require increasing the major
    ///   version of this crate.
    #[cfg(feature = "unstable-assert-no-drop")]
    const NO_DROP_CHECK: () = { assert!(!std::mem::needs_drop::<Self>()) };

    /// Wraps custom iterator into [`PrintableWrapper`].
    #[inline]
    fn printable(
        self,
    ) -> PrintableWrapper<&'static str, &'static str, &'static str, IterHandler<Self>> {
        #[cfg(feature = "unstable-assert-no-drop")]
        let () = Self::NO_DROP_CHECK;
        PrintableWrapper {
            inner: IterHandler(self),
            sep: ", ",
            left_bound: "[",
            right_bound: "]",
        }
    }
}

impl<T> PrintableIter for T
where
    T: Iterator + Clone,
    T::Item: Display,
{
}

impl<T> From<T>
    for PrintableWrapper<&'static str, &'static str, &'static str, IterHandler<T::IntoIter>>
where
    T: IntoIterator,
    T::Item: Display,
    T::IntoIter: Clone,
{
    #[inline]
    fn from(value: T) -> Self {
        value.into_iter().printable()
    }
}

/// Handler for iterators used inside the [`PrintableWrapper`].
#[derive(Debug, Clone)]
#[repr(transparent)]
pub struct IterHandler<T>(T);

impl<T> DisplayWithSep for IterHandler<T>
where
    T: Iterator + Clone,
    T::Item: Display,
{
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>, sep: &impl Display) -> std::fmt::Result {
        let mut iter = self.0.clone();
        if let Some(v) = iter.next() {
            v.fmt(f)?;
            for v in iter {
                sep.fmt(f)?;
                v.fmt(f)?;
            }
        };
        Ok(())
    }
}