use crate::{IdentFragment, ToTokens, TokenStreamExt};
use std::fmt;
use std::iter;
use std::ops::BitOr;

pub use proc_macro2::*;

pub struct HasIterator; // True
pub struct ThereIsNoIteratorInRepetition; // False

impl BitOr<ThereIsNoIteratorInRepetition> for ThereIsNoIteratorInRepetition {
    type Output = ThereIsNoIteratorInRepetition;
    fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> ThereIsNoIteratorInRepetition {
        ThereIsNoIteratorInRepetition
    }
}

impl BitOr<ThereIsNoIteratorInRepetition> for HasIterator {
    type Output = HasIterator;
    fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> HasIterator {
        HasIterator
    }
}

impl BitOr<HasIterator> for ThereIsNoIteratorInRepetition {
    type Output = HasIterator;
    fn bitor(self, _rhs: HasIterator) -> HasIterator {
        HasIterator
    }
}

impl BitOr<HasIterator> for HasIterator {
    type Output = HasIterator;
    fn bitor(self, _rhs: HasIterator) -> HasIterator {
        HasIterator
    }
}

/// Extension traits used by the implementation of `quote!`. These are defined
/// in separate traits, rather than as a single trait due to ambiguity issues.
///
/// These traits expose a `quote_into_iter` method which should allow calling
/// whichever impl happens to be applicable. Calling that method repeatedly on
/// the returned value should be idempotent.
pub mod ext {
    use super::RepInterp;
    use super::{HasIterator as HasIter, ThereIsNoIteratorInRepetition as DoesNotHaveIter};
    use crate::ToTokens;
    use std::collections::btree_set::{self, BTreeSet};
    use std::slice;

    /// Extension trait providing the `quote_into_iter` method on iterators.
    pub trait RepIteratorExt: Iterator + Sized {
        fn quote_into_iter(self) -> (Self, HasIter) {
            (self, HasIter)
        }
    }

    impl<T: Iterator> RepIteratorExt for T {}

    /// Extension trait providing the `quote_into_iter` method for
    /// non-iterable types. These types interpolate the same value in each
    /// iteration of the repetition.
    pub trait RepToTokensExt {
        /// Pretend to be an iterator for the purposes of `quote_into_iter`.
        /// This allows repeated calls to `quote_into_iter` to continue
        /// correctly returning DoesNotHaveIter.
        fn next(&self) -> Option<&Self> {
            Some(self)
        }

        fn quote_into_iter(&self) -> (&Self, DoesNotHaveIter) {
            (self, DoesNotHaveIter)
        }
    }

    impl<T: ToTokens + ?Sized> RepToTokensExt for T {}

    /// Extension trait providing the `quote_into_iter` method for types that
    /// can be referenced as an iterator.
    pub trait RepAsIteratorExt<'q> {
        type Iter: Iterator;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter);
    }

    impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a T {
        type Iter = T::Iter;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            <T as RepAsIteratorExt>::quote_into_iter(*self)
        }
    }

    impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a mut T {
        type Iter = T::Iter;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            <T as RepAsIteratorExt>::quote_into_iter(*self)
        }
    }

    impl<'q, T: 'q> RepAsIteratorExt<'q> for [T] {
        type Iter = slice::Iter<'q, T>;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            (self.iter(), HasIter)
        }
    }

    impl<'q, T: 'q> RepAsIteratorExt<'q> for Vec<T> {
        type Iter = slice::Iter<'q, T>;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            (self.iter(), HasIter)
        }
    }

    impl<'q, T: 'q> RepAsIteratorExt<'q> for BTreeSet<T> {
        type Iter = btree_set::Iter<'q, T>;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            (self.iter(), HasIter)
        }
    }

    impl<'q, T: RepAsIteratorExt<'q>> RepAsIteratorExt<'q> for RepInterp<T> {
        type Iter = T::Iter;

        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
            self.0.quote_into_iter()
        }
    }
}

// Helper type used within interpolations to allow for repeated binding names.
// Implements the relevant traits, and exports a dummy `next()` method.
#[derive(Copy, Clone)]
pub struct RepInterp<T>(pub T);

impl<T> RepInterp<T> {
    // This method is intended to look like `Iterator::next`, and is called when
    // a name is bound multiple times, as the previous binding will shadow the
    // original `Iterator` object. This allows us to avoid advancing the
    // iterator multiple times per iteration.
    pub fn next(self) -> Option<T> {
        Some(self.0)
    }
}

impl<T: Iterator> Iterator for RepInterp<T> {
    type Item = T::Item;

    fn next(&mut self) -> Option<Self::Item> {
        self.0.next()
    }
}

impl<T: ToTokens> ToTokens for RepInterp<T> {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.0.to_tokens(tokens);
    }
}

pub fn push_group(tokens: &mut TokenStream, delimiter: Delimiter, inner: TokenStream) {
    tokens.append(Group::new(delimiter, inner));
}

pub fn push_group_spanned(
    tokens: &mut TokenStream,
    span: Span,
    delimiter: Delimiter,
    inner: TokenStream,
) {
    let mut g = Group::new(delimiter, inner);
    g.set_span(span);
    tokens.append(g);
}

pub fn parse(tokens: &mut TokenStream, s: &str) {
    let s: TokenStream = s.parse().expect("invalid token stream");
    tokens.extend(iter::once(s));
}

pub fn parse_spanned(tokens: &mut TokenStream, span: Span, s: &str) {
    let s: TokenStream = s.parse().expect("invalid token stream");
    tokens.extend(s.into_iter().map(|t| respan_token_tree(t, span)));
}

// Token tree with every span replaced by the given one.
fn respan_token_tree(mut token: TokenTree, span: Span) -> TokenTree {
    match &mut token {
        TokenTree::Group(g) => {
            let stream = g
                .stream()
                .into_iter()
                .map(|token| respan_token_tree(token, span))
                .collect();
            *g = Group::new(g.delimiter(), stream);
            g.set_span(span);
        }
        other => other.set_span(span),
    }
    token
}

pub fn push_ident(tokens: &mut TokenStream, s: &str) {
    // Optimization over `mk_ident`, as `s` is guaranteed to be a valid ident.
    //
    // FIXME: When `Ident::new_raw` becomes stable, this method should be
    // updated to call it when available.
    if s.starts_with("r#") {
        parse(tokens, s);
    } else {
        tokens.append(Ident::new(s, Span::call_site()));
    }
}

pub fn push_ident_spanned(tokens: &mut TokenStream, span: Span, s: &str) {
    // Optimization over `mk_ident`, as `s` is guaranteed to be a valid ident.
    //
    // FIXME: When `Ident::new_raw` becomes stable, this method should be
    // updated to call it when available.
    if s.starts_with("r#") {
        parse_spanned(tokens, span, s);
    } else {
        tokens.append(Ident::new(s, span));
    }
}

pub fn push_lifetime(tokens: &mut TokenStream, lifetime: &str) {
    struct Lifetime<'a> {
        name: &'a str,
        state: u8,
    }

    impl<'a> Iterator for Lifetime<'a> {
        type Item = TokenTree;

        fn next(&mut self) -> Option<Self::Item> {
            match self.state {
                0 => {
                    self.state = 1;
                    Some(TokenTree::Punct(Punct::new('\'', Spacing::Joint)))
                }
                1 => {
                    self.state = 2;
                    Some(TokenTree::Ident(Ident::new(self.name, Span::call_site())))
                }
                _ => None,
            }
        }
    }

    tokens.extend(Lifetime {
        name: &lifetime[1..],
        state: 0,
    });
}

pub fn push_lifetime_spanned(tokens: &mut TokenStream, span: Span, lifetime: &str) {
    struct Lifetime<'a> {
        name: &'a str,
        span: Span,
        state: u8,
    }

    impl<'a> Iterator for Lifetime<'a> {
        type Item = TokenTree;

        fn next(&mut self) -> Option<Self::Item> {
            match self.state {
                0 => {
                    self.state = 1;
                    let mut apostrophe = Punct::new('\'', Spacing::Joint);
                    apostrophe.set_span(self.span);
                    Some(TokenTree::Punct(apostrophe))
                }
                1 => {
                    self.state = 2;
                    Some(TokenTree::Ident(Ident::new(self.name, self.span)))
                }
                _ => None,
            }
        }
    }

    tokens.extend(Lifetime {
        name: &lifetime[1..],
        span,
        state: 0,
    });
}

macro_rules! push_punct {
    ($name:ident $spanned:ident $char1:tt) => {
        pub fn $name(tokens: &mut TokenStream) {
            tokens.append(Punct::new($char1, Spacing::Alone));
        }
        pub fn $spanned(tokens: &mut TokenStream, span: Span) {
            let mut punct = Punct::new($char1, Spacing::Alone);
            punct.set_span(span);
            tokens.append(punct);
        }
    };
    ($name:ident $spanned:ident $char1:tt $char2:tt) => {
        pub fn $name(tokens: &mut TokenStream) {
            tokens.append(Punct::new($char1, Spacing::Joint));
            tokens.append(Punct::new($char2, Spacing::Alone));
        }
        pub fn $spanned(tokens: &mut TokenStream, span: Span) {
            let mut punct = Punct::new($char1, Spacing::Joint);
            punct.set_span(span);
            tokens.append(punct);
            let mut punct = Punct::new($char2, Spacing::Alone);
            punct.set_span(span);
            tokens.append(punct);
        }
    };
    ($name:ident $spanned:ident $char1:tt $char2:tt $char3:tt) => {
        pub fn $name(tokens: &mut TokenStream) {
            tokens.append(Punct::new($char1, Spacing::Joint));
            tokens.append(Punct::new($char2, Spacing::Joint));
            tokens.append(Punct::new($char3, Spacing::Alone));
        }
        pub fn $spanned(tokens: &mut TokenStream, span: Span) {
            let mut punct = Punct::new($char1, Spacing::Joint);
            punct.set_span(span);
            tokens.append(punct);
            let mut punct = Punct::new($char2, Spacing::Joint);
            punct.set_span(span);
            tokens.append(punct);
            let mut punct = Punct::new($char3, Spacing::Alone);
            punct.set_span(span);
            tokens.append(punct);
        }
    };
}

push_punct!(push_add push_add_spanned '+');
push_punct!(push_add_eq push_add_eq_spanned '+' '=');
push_punct!(push_and push_and_spanned '&');
push_punct!(push_and_and push_and_and_spanned '&' '&');
push_punct!(push_and_eq push_and_eq_spanned '&' '=');
push_punct!(push_at push_at_spanned '@');
push_punct!(push_bang push_bang_spanned '!');
push_punct!(push_caret push_caret_spanned '^');
push_punct!(push_caret_eq push_caret_eq_spanned '^' '=');
push_punct!(push_colon push_colon_spanned ':');
push_punct!(push_colon2 push_colon2_spanned ':' ':');
push_punct!(push_comma push_comma_spanned ',');
push_punct!(push_div push_div_spanned '/');
push_punct!(push_div_eq push_div_eq_spanned '/' '=');
push_punct!(push_dot push_dot_spanned '.');
push_punct!(push_dot2 push_dot2_spanned '.' '.');
push_punct!(push_dot3 push_dot3_spanned '.' '.' '.');
push_punct!(push_dot_dot_eq push_dot_dot_eq_spanned '.' '.' '=');
push_punct!(push_eq push_eq_spanned '=');
push_punct!(push_eq_eq push_eq_eq_spanned '=' '=');
push_punct!(push_ge push_ge_spanned '>' '=');
push_punct!(push_gt push_gt_spanned '>');
push_punct!(push_le push_le_spanned '<' '=');
push_punct!(push_lt push_lt_spanned '<');
push_punct!(push_mul_eq push_mul_eq_spanned '*' '=');
push_punct!(push_ne push_ne_spanned '!' '=');
push_punct!(push_or push_or_spanned '|');
push_punct!(push_or_eq push_or_eq_spanned '|' '=');
push_punct!(push_or_or push_or_or_spanned '|' '|');
push_punct!(push_pound push_pound_spanned '#');
push_punct!(push_question push_question_spanned '?');
push_punct!(push_rarrow push_rarrow_spanned '-' '>');
push_punct!(push_larrow push_larrow_spanned '<' '-');
push_punct!(push_rem push_rem_spanned '%');
push_punct!(push_rem_eq push_rem_eq_spanned '%' '=');
push_punct!(push_fat_arrow push_fat_arrow_spanned '=' '>');
push_punct!(push_semi push_semi_spanned ';');
push_punct!(push_shl push_shl_spanned '<' '<');
push_punct!(push_shl_eq push_shl_eq_spanned '<' '<' '=');
push_punct!(push_shr push_shr_spanned '>' '>');
push_punct!(push_shr_eq push_shr_eq_spanned '>' '>' '=');
push_punct!(push_star push_star_spanned '*');
push_punct!(push_sub push_sub_spanned '-');
push_punct!(push_sub_eq push_sub_eq_spanned '-' '=');

pub fn push_underscore(tokens: &mut TokenStream) {
    push_underscore_spanned(tokens, Span::call_site());
}

pub fn push_underscore_spanned(tokens: &mut TokenStream, span: Span) {
    tokens.append(Ident::new("_", span));
}

// Helper method for constructing identifiers from the `format_ident!` macro,
// handling `r#` prefixes.
//
// Directly parsing the input string may produce a valid identifier,
// although the input string was invalid, due to ignored characters such as
// whitespace and comments. Instead, we always create a non-raw identifier
// to validate that the string is OK, and only parse again if needed.
pub fn mk_ident(id: &str, span: Option<Span>) -> Ident {
    let span = span.unwrap_or_else(Span::call_site);

    let is_raw = id.starts_with("r#");
    let unraw = Ident::new(if is_raw { &id[2..] } else { id }, span);
    if !is_raw {
        return unraw;
    }

    // At this point, the identifier is raw, and the unraw-ed version of it was
    // successfully converted into an identifier. Try to produce a valid raw
    // identifier by running the `TokenStream` parser, and unwrapping the first
    // token as an `Ident`.
    //
    // FIXME: When `Ident::new_raw` becomes stable, this method should be
    // updated to call it when available.
    if let Ok(ts) = id.parse::<TokenStream>() {
        let mut iter = ts.into_iter();
        if let (Some(TokenTree::Ident(mut id)), None) = (iter.next(), iter.next()) {
            id.set_span(span);
            return id;
        }
    }

    panic!("not allowed as a raw identifier: `{}`", id);
}

// Adapts from `IdentFragment` to `fmt::Display` for use by the `format_ident!`
// macro, and exposes span information from these fragments.
//
// This struct also has forwarding implementations of the formatting traits
// `Octal`, `LowerHex`, `UpperHex`, and `Binary` to allow for their use within
// `format_ident!`.
#[derive(Copy, Clone)]
pub struct IdentFragmentAdapter<T: IdentFragment>(pub T);

impl<T: IdentFragment> IdentFragmentAdapter<T> {
    pub fn span(&self) -> Option<Span> {
        self.0.span()
    }
}

impl<T: IdentFragment> fmt::Display for IdentFragmentAdapter<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        IdentFragment::fmt(&self.0, f)
    }
}

impl<T: IdentFragment + fmt::Octal> fmt::Octal for IdentFragmentAdapter<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Octal::fmt(&self.0, f)
    }
}

impl<T: IdentFragment + fmt::LowerHex> fmt::LowerHex for IdentFragmentAdapter<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::LowerHex::fmt(&self.0, f)
    }
}

impl<T: IdentFragment + fmt::UpperHex> fmt::UpperHex for IdentFragmentAdapter<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::UpperHex::fmt(&self.0, f)
    }
}

impl<T: IdentFragment + fmt::Binary> fmt::Binary for IdentFragmentAdapter<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Binary::fmt(&self.0, f)
    }
}