use std::{error::Error, io};

use super::Id;

pub fn format<W, E>(out: &mut W, error: E) -> Result<(), io::Error>
where
    W: io::Write,
    E: Error,
{
    writeln!(out, "{error}")?;
    format_sources(out, error)?;

    Ok(())
}

pub fn format_with_id<W, E>(out: &mut W, id: &Id, error: E) -> Result<(), io::Error>
where
    W: io::Write,
    E: Error,
{
    writeln!(out, "[{id}] {error}")?;
    format_sources(out, error)?;

    Ok(())
}

fn format_sources<W, E>(out: &mut W, error: E) -> Result<(), io::Error>
where
    W: io::Write,
    E: Error,
{
    let mut sources = Sources::from(&error);
    if let Some(source) = sources.next() {
        writeln!(out)?;
        writeln!(out, "Caused by:")?;
        writeln!(out, "  {source}")?;
        for source in sources {
            writeln!(out, "  {source}")?;
        }
        writeln!(out)?;
    }
    Ok(())
}

struct Sources<'e> {
    next: Option<&'e dyn Error>,
}

impl<'e, E> From<&'e E> for Sources<'e>
where
    E: Error,
{
    fn from(error: &'e E) -> Self {
        Self {
            next: error.source(),
        }
    }
}

// See also: <https://doc.rust-lang.org/std/error/trait.Error.html#method.sources> However, we only
// want to iterate the sources, and not the error itself. Personally, I find the `skip(1)`
// suggestion untidy, since the error itself is non-optional while the sources are optional.
impl<'a> Iterator for Sources<'a> {
    type Item = &'a dyn Error;

    fn next(&mut self) -> Option<Self::Item> {
        let source = self.next;
        self.next = self.next.and_then(|err| err.source());

        source
    }
}