use std::ops::Deref;

use syn::{Meta, Path};

use crate::ast::NestedMeta;
use crate::{Error, FromMeta, Result};

use super::path_to_string;

/// A list of `syn::Path` instances. This type is used to extract a list of paths from an
/// attribute.
///
/// # Usage
/// An `PathList` field on a struct implementing `FromMeta` will turn `#[builder(derive(serde::Debug, Clone))]` into:
///
/// ```rust,ignore
/// StructOptions {
///     derive: PathList(vec![syn::Path::new("serde::Debug"), syn::Path::new("Clone")])
/// }
/// ```
#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct PathList(Vec<Path>);

impl PathList {
    /// Create a new list.
    pub fn new<T: Into<Path>>(vals: Vec<T>) -> Self {
        PathList(vals.into_iter().map(T::into).collect())
    }

    /// Create a new `Vec` containing the string representation of each path.
    pub fn to_strings(&self) -> Vec<String> {
        self.0.iter().map(path_to_string).collect()
    }

    /// Visits the values representing the intersection, i.e., the values that are both in `self` and `other`.
    ///
    /// Values will be returned in the order they appear in `self`.
    ///
    /// Values that are present multiple times in `self` and present at least once in `other` will be returned multiple times.
    ///
    /// # Performance
    /// This function runs in `O(n * m)` time.
    /// It is believed that path lists are usually short enough that this is better than allocating a set containing the values
    /// of `other` or adding a conditional solution.
    pub fn intersection<'a>(&'a self, other: &'a PathList) -> impl Iterator<Item = &'a Path> {
        self.0.iter().filter(|path| other.0.contains(path))
    }
}

impl Deref for PathList {
    type Target = Vec<Path>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl From<Vec<Path>> for PathList {
    fn from(v: Vec<Path>) -> Self {
        PathList(v)
    }
}

impl FromMeta for PathList {
    fn from_list(v: &[NestedMeta]) -> Result<Self> {
        let mut paths = Vec::with_capacity(v.len());
        for nmi in v {
            if let NestedMeta::Meta(Meta::Path(ref path)) = *nmi {
                paths.push(path.clone());
            } else {
                return Err(Error::unexpected_type("non-word").with_span(nmi));
            }
        }

        Ok(PathList(paths))
    }
}

#[cfg(test)]
mod tests {
    use super::PathList;
    use crate::FromMeta;
    use proc_macro2::TokenStream;
    use quote::quote;
    use syn::{parse_quote, Attribute, Meta};

    /// parse a string as a syn::Meta instance.
    fn pm(tokens: TokenStream) -> ::std::result::Result<Meta, String> {
        let attribute: Attribute = parse_quote!(#[#tokens]);
        Ok(attribute.meta)
    }

    fn fm<T: FromMeta>(tokens: TokenStream) -> T {
        FromMeta::from_meta(&pm(tokens).expect("Tests should pass well-formed input"))
            .expect("Tests should pass valid input")
    }

    #[test]
    fn succeeds() {
        let paths = fm::<PathList>(quote!(ignore(Debug, Clone, Eq)));
        assert_eq!(
            paths.to_strings(),
            vec![
                String::from("Debug"),
                String::from("Clone"),
                String::from("Eq")
            ]
        );
    }

    /// Check that the parser rejects non-word members of the list, and that the error
    /// has an associated span.
    #[test]
    fn fails_non_word() {
        let input = PathList::from_meta(&pm(quote!(ignore(Debug, Clone = false))).unwrap());
        let err = input.unwrap_err();
        assert!(err.has_span());
    }

    #[test]
    fn intersection() {
        let left = fm::<PathList>(quote!(ignore(Debug, Clone, Eq)));
        let right = fm::<PathList>(quote!(ignore(Clone, Eq, Clone)));
        assert_eq!(
            left.intersection(&right).cloned().collect::<Vec<_>>(),
            vec![parse_quote!(Clone), parse_quote!(Eq)],
        );
    }
}
