use std::any::Any;
use std::cell::{RefCell, RefMut};
use std::sync::Arc;

use rustc_ast as ast;
use rustc_codegen_ssa::traits::CodegenBackend;
use rustc_codegen_ssa::CodegenResults;
use rustc_data_structures::steal::Steal;
use rustc_data_structures::svh::Svh;
use rustc_data_structures::sync::{OnceLock, WorkerLocal};
use rustc_hir::def_id::LOCAL_CRATE;
use rustc_middle::arena::Arena;
use rustc_middle::dep_graph::DepGraph;
use rustc_middle::ty::{GlobalCtxt, TyCtxt};
use rustc_serialize::opaque::FileEncodeResult;
use rustc_session::config::{self, OutputFilenames, OutputType};
use rustc_session::Session;

use crate::errors::FailedWritingFile;
use crate::interface::{Compiler, Result};
use crate::{errors, passes};

/// Represent the result of a query.
///
/// This result can be stolen once with the [`steal`] method and generated with the [`compute`] method.
///
/// [`steal`]: Steal::steal
/// [`compute`]: Self::compute
pub struct Query<T> {
    /// `None` means no value has been computed yet.
    result: RefCell<Option<Result<Steal<T>>>>,
}

impl<T> Query<T> {
    fn compute<F: FnOnce() -> Result<T>>(&self, f: F) -> Result<QueryResult<'_, T>> {
        RefMut::filter_map(
            self.result.borrow_mut(),
            |r: &mut Option<Result<Steal<T>>>| -> Option<&mut Steal<T>> {
                r.get_or_insert_with(|| f().map(Steal::new)).as_mut().ok()
            },
        )
        .map_err(|r| *r.as_ref().unwrap().as_ref().map(|_| ()).unwrap_err())
        .map(QueryResult)
    }
}

pub struct QueryResult<'a, T>(RefMut<'a, Steal<T>>);

impl<'a, T> std::ops::Deref for QueryResult<'a, T> {
    type Target = RefMut<'a, Steal<T>>;

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

impl<'a, T> std::ops::DerefMut for QueryResult<'a, T> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<'a, 'tcx> QueryResult<'a, &'tcx GlobalCtxt<'tcx>> {
    pub fn enter<T>(&mut self, f: impl FnOnce(TyCtxt<'tcx>) -> T) -> T {
        (*self.0).get_mut().enter(f)
    }
}

pub struct Queries<'tcx> {
    compiler: &'tcx Compiler,
    gcx_cell: OnceLock<GlobalCtxt<'tcx>>,

    arena: WorkerLocal<Arena<'tcx>>,
    hir_arena: WorkerLocal<rustc_hir::Arena<'tcx>>,

    parse: Query<ast::Crate>,
    // This just points to what's in `gcx_cell`.
    gcx: Query<&'tcx GlobalCtxt<'tcx>>,
}

impl<'tcx> Queries<'tcx> {
    pub fn new(compiler: &'tcx Compiler) -> Queries<'tcx> {
        Queries {
            compiler,
            gcx_cell: OnceLock::new(),
            arena: WorkerLocal::new(|_| Arena::default()),
            hir_arena: WorkerLocal::new(|_| rustc_hir::Arena::default()),
            parse: Query { result: RefCell::new(None) },
            gcx: Query { result: RefCell::new(None) },
        }
    }

    pub fn finish(&self) -> FileEncodeResult {
        if let Some(gcx) = self.gcx_cell.get() { gcx.finish() } else { Ok(0) }
    }

    pub fn parse(&self) -> Result<QueryResult<'_, ast::Crate>> {
        self.parse.compute(|| passes::parse(&self.compiler.sess))
    }

    pub fn global_ctxt(&'tcx self) -> Result<QueryResult<'tcx, &'tcx GlobalCtxt<'tcx>>> {
        self.gcx.compute(|| {
            let krate = self.parse()?.steal();

            passes::create_global_ctxt(
                self.compiler,
                krate,
                &self.gcx_cell,
                &self.arena,
                &self.hir_arena,
            )
        })
    }
}

pub struct Linker {
    dep_graph: DepGraph,
    output_filenames: Arc<OutputFilenames>,
    // Only present when incr. comp. is enabled.
    crate_hash: Option<Svh>,
    ongoing_codegen: Box<dyn Any>,
}

impl Linker {
    pub fn codegen_and_build_linker(
        tcx: TyCtxt<'_>,
        codegen_backend: &dyn CodegenBackend,
    ) -> Result<Linker> {
        let ongoing_codegen = passes::start_codegen(codegen_backend, tcx)?;

        // This must run after monomorphization so that all generic types
        // have been instantiated.
        if tcx.sess.opts.unstable_opts.print_type_sizes {
            tcx.sess.code_stats.print_type_sizes();
        }

        if tcx.sess.opts.unstable_opts.print_vtable_sizes {
            let crate_name = tcx.crate_name(LOCAL_CRATE);

            tcx.sess.code_stats.print_vtable_sizes(crate_name);
        }

        Ok(Linker {
            dep_graph: tcx.dep_graph.clone(),
            output_filenames: tcx.output_filenames(()).clone(),
            crate_hash: if tcx.needs_crate_hash() {
                Some(tcx.crate_hash(LOCAL_CRATE))
            } else {
                None
            },
            ongoing_codegen,
        })
    }

    pub fn link(self, sess: &Session, codegen_backend: &dyn CodegenBackend) -> Result<()> {
        let (codegen_results, work_products) =
            codegen_backend.join_codegen(self.ongoing_codegen, sess, &self.output_filenames);

        if let Some(guar) = sess.dcx().has_errors() {
            return Err(guar);
        }

        sess.time("serialize_work_products", || {
            rustc_incremental::save_work_product_index(sess, &self.dep_graph, work_products)
        });

        let prof = sess.prof.clone();
        prof.generic_activity("drop_dep_graph").run(move || drop(self.dep_graph));

        // Now that we won't touch anything in the incremental compilation directory
        // any more, we can finalize it (which involves renaming it)
        rustc_incremental::finalize_session_directory(sess, self.crate_hash);

        if !sess
            .opts
            .output_types
            .keys()
            .any(|&i| i == OutputType::Exe || i == OutputType::Metadata)
        {
            return Ok(());
        }

        if sess.opts.unstable_opts.no_link {
            let rlink_file = self.output_filenames.with_extension(config::RLINK_EXT);
            CodegenResults::serialize_rlink(
                sess,
                &rlink_file,
                &codegen_results,
                &*self.output_filenames,
            )
            .map_err(|error| {
                sess.dcx().emit_fatal(FailedWritingFile { path: &rlink_file, error })
            })?;
            return Ok(());
        }

        let _timer = sess.prof.verbose_generic_activity("link_crate");
        codegen_backend.link(sess, codegen_results, &self.output_filenames)
    }
}

impl Compiler {
    pub fn enter<F, T>(&self, f: F) -> T
    where
        F: for<'tcx> FnOnce(&'tcx Queries<'tcx>) -> T,
    {
        // Must declare `_timer` first so that it is dropped after `queries`.
        let _timer;
        let queries = Queries::new(self);
        let ret = f(&queries);

        // NOTE: intentionally does not compute the global context if it hasn't been built yet,
        // since that likely means there was a parse error.
        if let Some(Ok(gcx)) = &mut *queries.gcx.result.borrow_mut() {
            let gcx = gcx.get_mut();
            // We assume that no queries are run past here. If there are new queries
            // after this point, they'll show up as "<unknown>" in self-profiling data.
            {
                let _prof_timer =
                    queries.compiler.sess.prof.generic_activity("self_profile_alloc_query_strings");
                gcx.enter(rustc_query_impl::alloc_self_profile_query_strings);
            }

            self.sess.time("serialize_dep_graph", || gcx.enter(rustc_incremental::save_dep_graph));

            gcx.enter(rustc_query_impl::query_key_hash_verify_all);
        }

        // The timer's lifetime spans the dropping of `queries`, which contains
        // the global context.
        _timer = self.sess.timer("free_global_ctxt");
        if let Err((path, error)) = queries.finish() {
            self.sess.dcx().emit_fatal(errors::FailedWritingFile { path: &path, error });
        }

        ret
    }
}
