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

/// Path to the current value in the input, like `dependencies.serde.typo1`.

#[derive(Copy, Clone)]

pub enum Path<'a> {

    Root,

    Seq { parent: &'a Path<'a>, index: usize },

    Map { parent: &'a Path<'a>, key: &'a str },

    Alias { parent: &'a Path<'a> },

    Unknown { parent: &'a Path<'a> },

}

impl<'a> Display for Path<'a> {

    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {

        struct Parent<'a>(&'a Path<'a>);

        impl<'a> Display for Parent<'a> {

            fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {

                match self.0 {

                    Path::Root => Ok(()),

                    path => write!(formatter, "{}.", path),

                }

            }

        }

        match self {

            Path::Root => formatter.write_str("."),

            Path::Seq { parent, index } => write!(formatter, "{}[{}]", parent, index),

            Path::Map { parent, key } => write!(formatter, "{}{}", Parent(parent), key),

            Path::Alias { parent } => write!(formatter, "{}", parent),

            Path::Unknown { parent } => write!(formatter, "{}?", Parent(parent)),

        }

    }

}