//! A higher level attributes based on TokenTree, with also some shortcuts.
use std::{fmt, ops};

use base_db::CrateId;
use cfg::CfgExpr;
use either::Either;
use intern::Interned;
use mbe::{syntax_node_to_token_tree, DelimiterKind, Punct};
use smallvec::{smallvec, SmallVec};
use span::Span;
use syntax::{ast, match_ast, AstNode, AstToken, SmolStr, SyntaxNode};
use triomphe::Arc;

use crate::{
    db::ExpandDatabase,
    mod_path::ModPath,
    span_map::SpanMapRef,
    tt::{self, Subtree},
    InFile,
};

/// Syntactical attributes, without filtering of `cfg_attr`s.
#[derive(Default, Debug, Clone, PartialEq, Eq)]
pub struct RawAttrs {
    // FIXME: Make this a ThinArc
    entries: Option<Arc<[Attr]>>,
}

impl ops::Deref for RawAttrs {
    type Target = [Attr];

    fn deref(&self) -> &[Attr] {
        match &self.entries {
            Some(it) => it,
            None => &[],
        }
    }
}

impl RawAttrs {
    pub const EMPTY: Self = Self { entries: None };

    pub fn new(
        db: &dyn ExpandDatabase,
        owner: &dyn ast::HasAttrs,
        span_map: SpanMapRef<'_>,
    ) -> Self {
        let entries = collect_attrs(owner).filter_map(|(id, attr)| match attr {
            Either::Left(attr) => {
                attr.meta().and_then(|meta| Attr::from_src(db, meta, span_map, id))
            }
            Either::Right(comment) => comment.doc_comment().map(|doc| Attr {
                id,
                input: Some(Interned::new(AttrInput::Literal(SmolStr::new(doc)))),
                path: Interned::new(ModPath::from(crate::name!(doc))),
                span: span_map.span_for_range(comment.syntax().text_range()),
            }),
        });
        let entries: Arc<[Attr]> = Arc::from_iter(entries);

        Self { entries: if entries.is_empty() { None } else { Some(entries) } }
    }

    pub fn from_attrs_owner(
        db: &dyn ExpandDatabase,
        owner: InFile<&dyn ast::HasAttrs>,
        span_map: SpanMapRef<'_>,
    ) -> Self {
        Self::new(db, owner.value, span_map)
    }

    pub fn merge(&self, other: Self) -> Self {
        match (&self.entries, other.entries) {
            (None, None) => Self::EMPTY,
            (None, entries @ Some(_)) => Self { entries },
            (Some(entries), None) => Self { entries: Some(entries.clone()) },
            (Some(a), Some(b)) => {
                let last_ast_index = a.last().map_or(0, |it| it.id.ast_index() + 1) as u32;
                Self {
                    entries: Some(Arc::from_iter(a.iter().cloned().chain(b.iter().map(|it| {
                        let mut it = it.clone();
                        it.id.id = (it.id.ast_index() as u32 + last_ast_index)
                            | (it.id.cfg_attr_index().unwrap_or(0) as u32)
                                << AttrId::AST_INDEX_BITS;
                        it
                    })))),
                }
            }
        }
    }

    /// Processes `cfg_attr`s, returning the resulting semantic `Attrs`.
    // FIXME: This should return a different type, signaling it was filtered?
    pub fn filter(self, db: &dyn ExpandDatabase, krate: CrateId) -> RawAttrs {
        let has_cfg_attrs = self
            .iter()
            .any(|attr| attr.path.as_ident().map_or(false, |name| *name == crate::name![cfg_attr]));
        if !has_cfg_attrs {
            return self;
        }

        let crate_graph = db.crate_graph();
        let new_attrs = Arc::from_iter(self.iter().flat_map(|attr| -> SmallVec<[_; 1]> {
            let is_cfg_attr =
                attr.path.as_ident().map_or(false, |name| *name == crate::name![cfg_attr]);
            if !is_cfg_attr {
                return smallvec![attr.clone()];
            }

            let subtree = match attr.token_tree_value() {
                Some(it) => it,
                _ => return smallvec![attr.clone()],
            };

            let (cfg, parts) = match parse_cfg_attr_input(subtree) {
                Some(it) => it,
                None => return smallvec![attr.clone()],
            };
            let index = attr.id;
            let attrs = parts
                .enumerate()
                .take(1 << AttrId::CFG_ATTR_BITS)
                .filter_map(|(idx, attr)| Attr::from_tt(db, attr, index.with_cfg_attr(idx)));

            let cfg_options = &crate_graph[krate].cfg_options;
            let cfg = Subtree { delimiter: subtree.delimiter, token_trees: Box::from(cfg) };
            let cfg = CfgExpr::parse(&cfg);
            if cfg_options.check(&cfg) == Some(false) {
                smallvec![]
            } else {
                cov_mark::hit!(cfg_attr_active);

                attrs.collect()
            }
        }));

        RawAttrs { entries: Some(new_attrs) }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct AttrId {
    id: u32,
}

// FIXME: This only handles a single level of cfg_attr nesting
// that is `#[cfg_attr(all(), cfg_attr(all(), cfg(any())))]` breaks again
impl AttrId {
    const CFG_ATTR_BITS: usize = 7;
    const AST_INDEX_MASK: usize = 0x00FF_FFFF;
    const AST_INDEX_BITS: usize = Self::AST_INDEX_MASK.count_ones() as usize;
    const CFG_ATTR_SET_BITS: u32 = 1 << 31;

    pub fn ast_index(&self) -> usize {
        self.id as usize & Self::AST_INDEX_MASK
    }

    pub fn cfg_attr_index(&self) -> Option<usize> {
        if self.id & Self::CFG_ATTR_SET_BITS == 0 {
            None
        } else {
            Some(self.id as usize >> Self::AST_INDEX_BITS)
        }
    }

    pub fn with_cfg_attr(self, idx: usize) -> AttrId {
        AttrId { id: self.id | (idx as u32) << Self::AST_INDEX_BITS | Self::CFG_ATTR_SET_BITS }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Attr {
    pub id: AttrId,
    pub path: Interned<ModPath>,
    pub input: Option<Interned<AttrInput>>,
    pub span: Span,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum AttrInput {
    /// `#[attr = "string"]`
    // FIXME: This is losing span
    Literal(SmolStr),
    /// `#[attr(subtree)]`
    TokenTree(Box<tt::Subtree>),
}

impl fmt::Display for AttrInput {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            AttrInput::Literal(lit) => write!(f, " = \"{}\"", lit.escape_debug()),
            AttrInput::TokenTree(tt) => tt.fmt(f),
        }
    }
}

impl Attr {
    fn from_src(
        db: &dyn ExpandDatabase,
        ast: ast::Meta,
        span_map: SpanMapRef<'_>,
        id: AttrId,
    ) -> Option<Attr> {
        let path = Interned::new(ModPath::from_src(db, ast.path()?, &mut |range| {
            span_map.span_for_range(range).ctx
        })?);
        let span = span_map.span_for_range(ast.syntax().text_range());
        let input = if let Some(ast::Expr::Literal(lit)) = ast.expr() {
            let value = match lit.kind() {
                ast::LiteralKind::String(string) => string.value()?.into(),
                _ => lit.syntax().first_token()?.text().trim_matches('"').into(),
            };
            Some(Interned::new(AttrInput::Literal(value)))
        } else if let Some(tt) = ast.token_tree() {
            let tree = syntax_node_to_token_tree(tt.syntax(), span_map, span);
            Some(Interned::new(AttrInput::TokenTree(Box::new(tree))))
        } else {
            None
        };
        Some(Attr { id, path, input, span })
    }

    fn from_tt(db: &dyn ExpandDatabase, tt: &[tt::TokenTree], id: AttrId) -> Option<Attr> {
        let span = tt.first()?.first_span();
        let path_end = tt
            .iter()
            .position(|tt| {
                !matches!(
                    tt,
                    tt::TokenTree::Leaf(
                        tt::Leaf::Punct(tt::Punct { char: ':' | '$', .. }) | tt::Leaf::Ident(_),
                    )
                )
            })
            .unwrap_or(tt.len());

        let (path, input) = tt.split_at(path_end);
        let path = Interned::new(ModPath::from_tt(db, path)?);

        let input = match input.first() {
            Some(tt::TokenTree::Subtree(tree)) => {
                Some(Interned::new(AttrInput::TokenTree(Box::new(tree.clone()))))
            }
            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: '=', .. }))) => {
                let input = match input.get(1) {
                    Some(tt::TokenTree::Leaf(tt::Leaf::Literal(tt::Literal { text, .. }))) => {
                        //FIXME the trimming here isn't quite right, raw strings are not handled
                        Some(Interned::new(AttrInput::Literal(text.trim_matches('"').into())))
                    }
                    _ => None,
                };
                input
            }
            _ => None,
        };
        Some(Attr { id, path, input, span })
    }

    pub fn path(&self) -> &ModPath {
        &self.path
    }
}

impl Attr {
    /// #[path = "string"]
    pub fn string_value(&self) -> Option<&SmolStr> {
        match self.input.as_deref()? {
            AttrInput::Literal(it) => Some(it),
            _ => None,
        }
    }

    /// #[path(ident)]
    pub fn single_ident_value(&self) -> Option<&tt::Ident> {
        match self.input.as_deref()? {
            AttrInput::TokenTree(tt) => match &*tt.token_trees {
                [tt::TokenTree::Leaf(tt::Leaf::Ident(ident))] => Some(ident),
                _ => None,
            },
            _ => None,
        }
    }

    /// #[path TokenTree]
    pub fn token_tree_value(&self) -> Option<&Subtree> {
        match self.input.as_deref()? {
            AttrInput::TokenTree(tt) => Some(tt),
            _ => None,
        }
    }

    /// Parses this attribute as a token tree consisting of comma separated paths.
    pub fn parse_path_comma_token_tree<'a>(
        &'a self,
        db: &'a dyn ExpandDatabase,
    ) -> Option<impl Iterator<Item = (ModPath, Span)> + 'a> {
        let args = self.token_tree_value()?;

        if args.delimiter.kind != DelimiterKind::Parenthesis {
            return None;
        }
        let paths = args
            .token_trees
            .split(|tt| matches!(tt, tt::TokenTree::Leaf(tt::Leaf::Punct(Punct { char: ',', .. }))))
            .filter_map(move |tts| {
                let span = tts.first()?.first_span();
                Some((ModPath::from_tt(db, tts)?, span))
            });

        Some(paths)
    }

    pub fn cfg(&self) -> Option<CfgExpr> {
        if *self.path.as_ident()? == crate::name![cfg] {
            self.token_tree_value().map(CfgExpr::parse)
        } else {
            None
        }
    }
}

pub fn collect_attrs(
    owner: &dyn ast::HasAttrs,
) -> impl Iterator<Item = (AttrId, Either<ast::Attr, ast::Comment>)> {
    let inner_attrs = inner_attributes(owner.syntax()).into_iter().flatten();
    let outer_attrs =
        ast::AttrDocCommentIter::from_syntax_node(owner.syntax()).filter(|el| match el {
            Either::Left(attr) => attr.kind().is_outer(),
            Either::Right(comment) => comment.is_outer(),
        });
    outer_attrs.chain(inner_attrs).enumerate().map(|(id, attr)| (AttrId { id: id as u32 }, attr))
}

fn inner_attributes(
    syntax: &SyntaxNode,
) -> Option<impl Iterator<Item = Either<ast::Attr, ast::Comment>>> {
    let node = match_ast! {
        match syntax {
            ast::SourceFile(_) => syntax.clone(),
            ast::ExternBlock(it) => it.extern_item_list()?.syntax().clone(),
            ast::Fn(it) => it.body()?.stmt_list()?.syntax().clone(),
            ast::Impl(it) => it.assoc_item_list()?.syntax().clone(),
            ast::Module(it) => it.item_list()?.syntax().clone(),
            ast::BlockExpr(it) => {
                if !it.may_carry_attributes() {
                    return None
                }
                syntax.clone()
            },
            _ => return None,
        }
    };

    let attrs = ast::AttrDocCommentIter::from_syntax_node(&node).filter(|el| match el {
        Either::Left(attr) => attr.kind().is_inner(),
        Either::Right(comment) => comment.is_inner(),
    });
    Some(attrs)
}

// Input subtree is: `(cfg, $(attr),+)`
// Split it up into a `cfg` subtree and the `attr` subtrees.
pub fn parse_cfg_attr_input(
    subtree: &Subtree,
) -> Option<(&[tt::TokenTree], impl Iterator<Item = &[tt::TokenTree]>)> {
    let mut parts = subtree
        .token_trees
        .split(|tt| matches!(tt, tt::TokenTree::Leaf(tt::Leaf::Punct(Punct { char: ',', .. }))));
    let cfg = parts.next()?;
    Some((cfg, parts.filter(|it| !it.is_empty())))
}