use crate::clean::auto_trait::AutoTraitFinder;
use crate::clean::blanket_impl::BlanketImplFinder;
use crate::clean::render_macro_matchers::render_macro_matcher;
use crate::clean::{
    clean_doc_module, clean_middle_const, clean_middle_region, clean_middle_ty, inline, Crate,
    ExternalCrate, Generic, GenericArg, GenericArgs, ImportSource, Item, ItemKind, Lifetime, Path,
    PathSegment, Primitive, PrimitiveType, Term, Type, TypeBinding, TypeBindingKind,
};
use crate::core::DocContext;
use crate::html::format::visibility_to_src_with_space;

use rustc_ast as ast;
use rustc_ast::tokenstream::TokenTree;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_middle::mir;
use rustc_middle::mir::interpret::ConstValue;
use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
use rustc_middle::ty::{self, DefIdTree, TyCtxt};
use rustc_span::symbol::{kw, sym, Symbol};
use std::fmt::Write as _;
use std::mem;
use thin_vec::{thin_vec, ThinVec};

#[cfg(test)]
mod tests;

pub(crate) fn krate(cx: &mut DocContext<'_>) -> Crate {
    let module = crate::visit_ast::RustdocVisitor::new(cx).visit();

    // Clean the crate, translating the entire librustc_ast AST to one that is
    // understood by rustdoc.
    let mut module = clean_doc_module(&module, cx);

    match *module.kind {
        ItemKind::ModuleItem(ref module) => {
            for it in &module.items {
                // `compiler_builtins` should be masked too, but we can't apply
                // `#[doc(masked)]` to the injected `extern crate` because it's unstable.
                if it.is_extern_crate()
                    && (it.attrs.has_doc_flag(sym::masked)
                        || cx.tcx.is_compiler_builtins(it.item_id.krate()))
                {
                    cx.cache.masked_crates.insert(it.item_id.krate());
                }
            }
        }
        _ => unreachable!(),
    }

    let local_crate = ExternalCrate { crate_num: LOCAL_CRATE };
    let primitives = local_crate.primitives(cx.tcx);
    let keywords = local_crate.keywords(cx.tcx);
    {
        let ItemKind::ModuleItem(ref mut m) = *module.kind
        else { unreachable!() };
        m.items.extend(primitives.iter().map(|&(def_id, prim)| {
            Item::from_def_id_and_parts(
                def_id,
                Some(prim.as_sym()),
                ItemKind::PrimitiveItem(prim),
                cx,
            )
        }));
        m.items.extend(keywords.into_iter().map(|(def_id, kw)| {
            Item::from_def_id_and_parts(def_id, Some(kw), ItemKind::KeywordItem, cx)
        }));
    }

    Crate { module, external_traits: cx.external_traits.clone() }
}

pub(crate) fn substs_to_args<'tcx>(
    cx: &mut DocContext<'tcx>,
    substs: ty::Binder<'tcx, &[ty::subst::GenericArg<'tcx>]>,
    mut skip_first: bool,
) -> Vec<GenericArg> {
    let mut ret_val =
        Vec::with_capacity(substs.skip_binder().len().saturating_sub(if skip_first {
            1
        } else {
            0
        }));
    ret_val.extend(substs.iter().filter_map(|kind| match kind.skip_binder().unpack() {
        GenericArgKind::Lifetime(lt) => {
            Some(GenericArg::Lifetime(clean_middle_region(lt).unwrap_or(Lifetime::elided())))
        }
        GenericArgKind::Type(_) if skip_first => {
            skip_first = false;
            None
        }
        GenericArgKind::Type(ty) => {
            Some(GenericArg::Type(clean_middle_ty(kind.rebind(ty), cx, None)))
        }
        GenericArgKind::Const(ct) => {
            Some(GenericArg::Const(Box::new(clean_middle_const(kind.rebind(ct), cx))))
        }
    }));
    ret_val
}

fn external_generic_args<'tcx>(
    cx: &mut DocContext<'tcx>,
    did: DefId,
    has_self: bool,
    bindings: ThinVec<TypeBinding>,
    substs: ty::Binder<'tcx, SubstsRef<'tcx>>,
) -> GenericArgs {
    let args = substs_to_args(cx, substs.map_bound(|substs| &substs[..]), has_self);

    if cx.tcx.fn_trait_kind_from_def_id(did).is_some() {
        let ty = substs
            .iter()
            .nth(if has_self { 1 } else { 0 })
            .unwrap()
            .map_bound(|arg| arg.expect_ty());
        let inputs =
            // The trait's first substitution is the one after self, if there is one.
            match ty.skip_binder().kind() {
                ty::Tuple(tys) => tys.iter().map(|t| clean_middle_ty(ty.rebind(t), cx, None)).collect::<Vec<_>>().into(),
                _ => return GenericArgs::AngleBracketed { args: args.into(), bindings },
            };
        let output = bindings.into_iter().next().and_then(|binding| match binding.kind {
            TypeBindingKind::Equality { term: Term::Type(ty) } if ty != Type::Tuple(Vec::new()) => {
                Some(Box::new(ty))
            }
            _ => None,
        });
        GenericArgs::Parenthesized { inputs, output }
    } else {
        GenericArgs::AngleBracketed { args: args.into(), bindings }
    }
}

pub(super) fn external_path<'tcx>(
    cx: &mut DocContext<'tcx>,
    did: DefId,
    has_self: bool,
    bindings: ThinVec<TypeBinding>,
    substs: ty::Binder<'tcx, SubstsRef<'tcx>>,
) -> Path {
    let def_kind = cx.tcx.def_kind(did);
    let name = cx.tcx.item_name(did);
    Path {
        res: Res::Def(def_kind, did),
        segments: thin_vec![PathSegment {
            name,
            args: external_generic_args(cx, did, has_self, bindings, substs),
        }],
    }
}

/// Remove the generic arguments from a path.
pub(crate) fn strip_path_generics(mut path: Path) -> Path {
    for ps in path.segments.iter_mut() {
        ps.args = GenericArgs::AngleBracketed { args: Default::default(), bindings: ThinVec::new() }
    }

    path
}

pub(crate) fn qpath_to_string(p: &hir::QPath<'_>) -> String {
    let segments = match *p {
        hir::QPath::Resolved(_, path) => &path.segments,
        hir::QPath::TypeRelative(_, segment) => return segment.ident.to_string(),
        hir::QPath::LangItem(lang_item, ..) => return lang_item.name().to_string(),
    };

    let mut s = String::new();
    for (i, seg) in segments.iter().enumerate() {
        if i > 0 {
            s.push_str("::");
        }
        if seg.ident.name != kw::PathRoot {
            s.push_str(seg.ident.as_str());
        }
    }
    s
}

pub(crate) fn build_deref_target_impls(
    cx: &mut DocContext<'_>,
    items: &[Item],
    ret: &mut Vec<Item>,
) {
    let tcx = cx.tcx;

    for item in items {
        let target = match *item.kind {
            ItemKind::AssocTypeItem(ref t, _) => &t.type_,
            _ => continue,
        };

        if let Some(prim) = target.primitive_type() {
            let _prof_timer = cx.tcx.sess.prof.generic_activity("build_primitive_inherent_impls");
            for did in prim.impls(tcx).filter(|did| !did.is_local()) {
                inline::build_impl(cx, None, did, None, ret);
            }
        } else if let Type::Path { path } = target {
            let did = path.def_id();
            if !did.is_local() {
                inline::build_impls(cx, None, did, None, ret);
            }
        }
    }
}

pub(crate) fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
    use rustc_hir::*;
    debug!("trying to get a name from pattern: {:?}", p);

    Symbol::intern(&match p.kind {
        PatKind::Wild | PatKind::Struct(..) => return kw::Underscore,
        PatKind::Binding(_, _, ident, _) => return ident.name,
        PatKind::TupleStruct(ref p, ..) | PatKind::Path(ref p) => qpath_to_string(p),
        PatKind::Or(pats) => {
            pats.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(" | ")
        }
        PatKind::Tuple(elts, _) => format!(
            "({})",
            elts.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(", ")
        ),
        PatKind::Box(p) => return name_from_pat(&*p),
        PatKind::Ref(p, _) => return name_from_pat(&*p),
        PatKind::Lit(..) => {
            warn!(
                "tried to get argument name from PatKind::Lit, which is silly in function arguments"
            );
            return Symbol::intern("()");
        }
        PatKind::Range(..) => return kw::Underscore,
        PatKind::Slice(begin, ref mid, end) => {
            let begin = begin.iter().map(|p| name_from_pat(p).to_string());
            let mid = mid.as_ref().map(|p| format!("..{}", name_from_pat(&**p))).into_iter();
            let end = end.iter().map(|p| name_from_pat(p).to_string());
            format!("[{}]", begin.chain(mid).chain(end).collect::<Vec<_>>().join(", "))
        }
    })
}

pub(crate) fn print_const(cx: &DocContext<'_>, n: ty::Const<'_>) -> String {
    match n.kind() {
        ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, substs: _ }) => {
            let s = if let Some(def) = def.as_local() {
                print_const_expr(cx.tcx, cx.tcx.hir().body_owned_by(def.did))
            } else {
                inline::print_inlined_const(cx.tcx, def.did)
            };

            s
        }
        // array lengths are obviously usize
        ty::ConstKind::Value(ty::ValTree::Leaf(scalar))
            if *n.ty().kind() == ty::Uint(ty::UintTy::Usize) =>
        {
            scalar.to_string()
        }
        _ => n.to_string(),
    }
}

pub(crate) fn print_evaluated_const(
    tcx: TyCtxt<'_>,
    def_id: DefId,
    underscores_and_type: bool,
) -> Option<String> {
    tcx.const_eval_poly(def_id).ok().and_then(|val| {
        let ty = tcx.type_of(def_id).subst_identity();
        match (val, ty.kind()) {
            (_, &ty::Ref(..)) => None,
            (ConstValue::Scalar(_), &ty::Adt(_, _)) => None,
            (ConstValue::Scalar(_), _) => {
                let const_ = mir::ConstantKind::from_value(val, ty);
                Some(print_const_with_custom_print_scalar(tcx, const_, underscores_and_type))
            }
            _ => None,
        }
    })
}

fn format_integer_with_underscore_sep(num: &str) -> String {
    let num_chars: Vec<_> = num.chars().collect();
    let mut num_start_index = if num_chars.get(0) == Some(&'-') { 1 } else { 0 };
    let chunk_size = match num[num_start_index..].as_bytes() {
        [b'0', b'b' | b'x', ..] => {
            num_start_index += 2;
            4
        }
        [b'0', b'o', ..] => {
            num_start_index += 2;
            let remaining_chars = num_chars.len() - num_start_index;
            if remaining_chars <= 6 {
                // don't add underscores to Unix permissions like 0755 or 100755
                return num.to_string();
            }
            3
        }
        _ => 3,
    };

    num_chars[..num_start_index]
        .iter()
        .chain(num_chars[num_start_index..].rchunks(chunk_size).rev().intersperse(&['_']).flatten())
        .collect()
}

fn print_const_with_custom_print_scalar<'tcx>(
    tcx: TyCtxt<'tcx>,
    ct: mir::ConstantKind<'tcx>,
    underscores_and_type: bool,
) -> String {
    // Use a slightly different format for integer types which always shows the actual value.
    // For all other types, fallback to the original `pretty_print_const`.
    match (ct, ct.ty().kind()) {
        (mir::ConstantKind::Val(ConstValue::Scalar(int), _), ty::Uint(ui)) => {
            if underscores_and_type {
                format!("{}{}", format_integer_with_underscore_sep(&int.to_string()), ui.name_str())
            } else {
                int.to_string()
            }
        }
        (mir::ConstantKind::Val(ConstValue::Scalar(int), _), ty::Int(i)) => {
            let ty = ct.ty();
            let size = tcx.layout_of(ty::ParamEnv::empty().and(ty)).unwrap().size;
            let data = int.assert_bits(size);
            let sign_extended_data = size.sign_extend(data) as i128;
            if underscores_and_type {
                format!(
                    "{}{}",
                    format_integer_with_underscore_sep(&sign_extended_data.to_string()),
                    i.name_str()
                )
            } else {
                sign_extended_data.to_string()
            }
        }
        _ => ct.to_string(),
    }
}

pub(crate) fn is_literal_expr(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
    if let hir::Node::Expr(expr) = tcx.hir().get(hir_id) {
        if let hir::ExprKind::Lit(_) = &expr.kind {
            return true;
        }

        if let hir::ExprKind::Unary(hir::UnOp::Neg, expr) = &expr.kind &&
            let hir::ExprKind::Lit(_) = &expr.kind
        {
            return true;
        }
    }

    false
}

/// Build a textual representation of an unevaluated constant expression.
///
/// If the const expression is too complex, an underscore `_` is returned.
/// For const arguments, it's `{ _ }` to be precise.
/// This means that the output is not necessarily valid Rust code.
///
/// Currently, only
///
/// * literals (optionally with a leading `-`)
/// * unit `()`
/// * blocks (`{ … }`) around simple expressions and
/// * paths without arguments
///
/// are considered simple enough. Simple blocks are included since they are
/// necessary to disambiguate unit from the unit type.
/// This list might get extended in the future.
///
/// Without this censoring, in a lot of cases the output would get too large
/// and verbose. Consider `match` expressions, blocks and deeply nested ADTs.
/// Further, private and `doc(hidden)` fields of structs would get leaked
/// since HIR datatypes like the `body` parameter do not contain enough
/// semantic information for this function to be able to hide them –
/// at least not without significant performance overhead.
///
/// Whenever possible, prefer to evaluate the constant first and try to
/// use a different method for pretty-printing. Ideally this function
/// should only ever be used as a fallback.
pub(crate) fn print_const_expr(tcx: TyCtxt<'_>, body: hir::BodyId) -> String {
    let hir = tcx.hir();
    let value = &hir.body(body).value;

    #[derive(PartialEq, Eq)]
    enum Classification {
        Literal,
        Simple,
        Complex,
    }

    use Classification::*;

    fn classify(expr: &hir::Expr<'_>) -> Classification {
        match &expr.kind {
            hir::ExprKind::Unary(hir::UnOp::Neg, expr) => {
                if matches!(expr.kind, hir::ExprKind::Lit(_)) { Literal } else { Complex }
            }
            hir::ExprKind::Lit(_) => Literal,
            hir::ExprKind::Tup([]) => Simple,
            hir::ExprKind::Block(hir::Block { stmts: [], expr: Some(expr), .. }, _) => {
                if classify(expr) == Complex { Complex } else { Simple }
            }
            // Paths with a self-type or arguments are too “complex” following our measure since
            // they may leak private fields of structs (with feature `adt_const_params`).
            // Consider: `<Self as Trait<{ Struct { private: () } }>>::CONSTANT`.
            // Paths without arguments are definitely harmless though.
            hir::ExprKind::Path(hir::QPath::Resolved(_, hir::Path { segments, .. })) => {
                if segments.iter().all(|segment| segment.args.is_none()) { Simple } else { Complex }
            }
            // FIXME: Claiming that those kinds of QPaths are simple is probably not true if the Ty
            //        contains const arguments. Is there a *concise* way to check for this?
            hir::ExprKind::Path(hir::QPath::TypeRelative(..)) => Simple,
            // FIXME: Can they contain const arguments and thus leak private struct fields?
            hir::ExprKind::Path(hir::QPath::LangItem(..)) => Simple,
            _ => Complex,
        }
    }

    let classification = classify(value);

    if classification == Literal
    && !value.span.from_expansion()
    && let Ok(snippet) = tcx.sess.source_map().span_to_snippet(value.span) {
        // For literals, we avoid invoking the pretty-printer and use the source snippet instead to
        // preserve certain stylistic choices the user likely made for the sake legibility like
        //
        // * hexadecimal notation
        // * underscores
        // * character escapes
        //
        // FIXME: This passes through `-/*spacer*/0` verbatim.
        snippet
    } else if classification == Simple {
        // Otherwise we prefer pretty-printing to get rid of extraneous whitespace, comments and
        // other formatting artifacts.
        rustc_hir_pretty::id_to_string(&hir, body.hir_id)
    } else if tcx.def_kind(hir.body_owner_def_id(body).to_def_id()) == DefKind::AnonConst {
        // FIXME: Omit the curly braces if the enclosing expression is an array literal
        //        with a repeated element (an `ExprKind::Repeat`) as in such case it
        //        would not actually need any disambiguation.
        "{ _ }".to_owned()
    } else {
        "_".to_owned()
    }
}

/// Given a type Path, resolve it to a Type using the TyCtxt
pub(crate) fn resolve_type(cx: &mut DocContext<'_>, path: Path) -> Type {
    debug!("resolve_type({:?})", path);

    match path.res {
        Res::PrimTy(p) => Primitive(PrimitiveType::from(p)),
        Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } if path.segments.len() == 1 => {
            Generic(kw::SelfUpper)
        }
        Res::Def(DefKind::TyParam, _) if path.segments.len() == 1 => Generic(path.segments[0].name),
        _ => {
            let _ = register_res(cx, path.res);
            Type::Path { path }
        }
    }
}

pub(crate) fn get_auto_trait_and_blanket_impls(
    cx: &mut DocContext<'_>,
    item_def_id: DefId,
) -> impl Iterator<Item = Item> {
    // FIXME: To be removed once `parallel_compiler` bugs are fixed!
    // More information in <https://github.com/rust-lang/rust/pull/106930>.
    if cfg!(parallel_compiler) {
        return vec![].into_iter().chain(vec![].into_iter());
    }

    let auto_impls = cx
        .sess()
        .prof
        .generic_activity("get_auto_trait_impls")
        .run(|| AutoTraitFinder::new(cx).get_auto_trait_impls(item_def_id));
    let blanket_impls = cx
        .sess()
        .prof
        .generic_activity("get_blanket_impls")
        .run(|| BlanketImplFinder { cx }.get_blanket_impls(item_def_id));
    auto_impls.into_iter().chain(blanket_impls)
}

/// If `res` has a documentation page associated, store it in the cache.
///
/// This is later used by [`href()`] to determine the HTML link for the item.
///
/// [`href()`]: crate::html::format::href
pub(crate) fn register_res(cx: &mut DocContext<'_>, res: Res) -> DefId {
    use DefKind::*;
    debug!("register_res({:?})", res);

    let (kind, did) = match res {
        Res::Def(
            kind @ (AssocTy | AssocFn | AssocConst | Variant | Fn | TyAlias | Enum | Trait | Struct
            | Union | Mod | ForeignTy | Const | Static(_) | Macro(..) | TraitAlias),
            did,
        ) => (kind.into(), did),

        _ => panic!("register_res: unexpected {:?}", res),
    };
    if did.is_local() {
        return did;
    }
    inline::record_extern_fqn(cx, did, kind);
    did
}

pub(crate) fn resolve_use_source(cx: &mut DocContext<'_>, path: Path) -> ImportSource {
    ImportSource {
        did: if path.res.opt_def_id().is_none() { None } else { Some(register_res(cx, path.res)) },
        path,
    }
}

pub(crate) fn enter_impl_trait<'tcx, F, R>(cx: &mut DocContext<'tcx>, f: F) -> R
where
    F: FnOnce(&mut DocContext<'tcx>) -> R,
{
    let old_bounds = mem::take(&mut cx.impl_trait_bounds);
    let r = f(cx);
    assert!(cx.impl_trait_bounds.is_empty());
    cx.impl_trait_bounds = old_bounds;
    r
}

/// Find the nearest parent module of a [`DefId`].
pub(crate) fn find_nearest_parent_module(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
    if def_id.is_top_level_module() {
        // The crate root has no parent. Use it as the root instead.
        Some(def_id)
    } else {
        let mut current = def_id;
        // The immediate parent might not always be a module.
        // Find the first parent which is.
        while let Some(parent) = tcx.opt_parent(current) {
            if tcx.def_kind(parent) == DefKind::Mod {
                return Some(parent);
            }
            current = parent;
        }
        None
    }
}

/// Checks for the existence of `hidden` in the attribute below if `flag` is `sym::hidden`:
///
/// ```
/// #[doc(hidden)]
/// pub fn foo() {}
/// ```
///
/// This function exists because it runs on `hir::Attributes` whereas the other is a
/// `clean::Attributes` method.
pub(crate) fn has_doc_flag(tcx: TyCtxt<'_>, did: DefId, flag: Symbol) -> bool {
    tcx.get_attrs(did, sym::doc).any(|attr| {
        attr.meta_item_list().map_or(false, |l| rustc_attr::list_contains_name(&l, flag))
    })
}

/// A link to `doc.rust-lang.org` that includes the channel name. Use this instead of manual links
/// so that the channel is consistent.
///
/// Set by `bootstrap::Builder::doc_rust_lang_org_channel` in order to keep tests passing on beta/stable.
pub(crate) const DOC_RUST_LANG_ORG_CHANNEL: &str = env!("DOC_RUST_LANG_ORG_CHANNEL");

/// Render a sequence of macro arms in a format suitable for displaying to the user
/// as part of an item declaration.
pub(super) fn render_macro_arms<'a>(
    tcx: TyCtxt<'_>,
    matchers: impl Iterator<Item = &'a TokenTree>,
    arm_delim: &str,
) -> String {
    let mut out = String::new();
    for matcher in matchers {
        writeln!(out, "    {} => {{ ... }}{}", render_macro_matcher(tcx, matcher), arm_delim)
            .unwrap();
    }
    out
}

pub(super) fn display_macro_source(
    cx: &mut DocContext<'_>,
    name: Symbol,
    def: &ast::MacroDef,
    def_id: DefId,
    vis: ty::Visibility<DefId>,
) -> String {
    let tts: Vec<_> = def.body.tokens.clone().into_trees().collect();
    // Extract the spans of all matchers. They represent the "interface" of the macro.
    let matchers = tts.chunks(4).map(|arm| &arm[0]);

    if def.macro_rules {
        format!("macro_rules! {} {{\n{}}}", name, render_macro_arms(cx.tcx, matchers, ";"))
    } else {
        if matchers.len() <= 1 {
            format!(
                "{}macro {}{} {{\n    ...\n}}",
                visibility_to_src_with_space(Some(vis), cx.tcx, def_id),
                name,
                matchers.map(|matcher| render_macro_matcher(cx.tcx, matcher)).collect::<String>(),
            )
        } else {
            format!(
                "{}macro {} {{\n{}}}",
                visibility_to_src_with_space(Some(vis), cx.tcx, def_id),
                name,
                render_macro_arms(cx.tcx, matchers, ","),
            )
        }
    }
}