//! Refinement type checking

#![feature(
    associated_type_defaults,
    box_patterns,
    extract_if,
    if_let_guard,
    let_chains,
    min_specialization,
    never_type,
    rustc_private,
    unwrap_infallible
)]

extern crate rustc_data_structures;
extern crate rustc_errors;
extern crate rustc_hash;
extern crate rustc_hir;
extern crate rustc_index;
extern crate rustc_infer;
extern crate rustc_middle;
extern crate rustc_mir_dataflow;
extern crate rustc_span;
extern crate rustc_target;
extern crate rustc_type_ir;

mod checker;
mod ghost_statements;
pub mod invariants;
mod primops;
mod queue;
mod type_env;

pub use checker::CheckerConfig;
use checker::{trait_impl_subtyping, Checker};
use flux_common::{cache::QueryCache, dbg, result::ResultExt as _};
use flux_config as config;
use flux_infer::{
    fixpoint_encoding::{FixpointCtxt, KVarGen},
    infer::{ConstrReason, SubtypeReason, Tag},
    refine_tree::RefineTree,
};
use flux_macros::fluent_messages;
use flux_middle::{
    global_env::GlobalEnv,
    queries::QueryResult,
    rty::{self, ESpan},
    MaybeExternId,
};
use itertools::Itertools;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def_id::LocalDefId;
use rustc_span::Span;

use crate::{checker::errors::ResultExt as _, ghost_statements::compute_ghost_statements};

fluent_messages! { "../locales/en-US.ftl" }

fn report_fixpoint_errors(
    genv: GlobalEnv,
    local_id: LocalDefId,
    errors: Vec<Tag>,
) -> Result<(), ErrorGuaranteed> {
    #[expect(clippy::collapsible_else_if, reason = "it looks better")]
    if genv.should_fail(local_id) {
        if errors.is_empty() {
            report_expected_neg(genv, local_id)
        } else {
            Ok(())
        }
    } else {
        if errors.is_empty() {
            Ok(())
        } else {
            report_errors(genv, errors)
        }
    }
}

fn invoke_fixpoint(
    genv: GlobalEnv,
    cache: &mut QueryCache,
    local_id: LocalDefId,
    mut refine_tree: RefineTree,
    kvars: KVarGen,
    config: CheckerConfig,
    ext: &str,
) -> Result<Vec<Tag>, ErrorGuaranteed> {
    if config::dump_constraint() {
        dbg::dump_item_info(genv.tcx(), local_id, ext, &refine_tree).unwrap();
    }
    refine_tree.simplify();
    let simp_ext = format!("simp.{}", ext);
    if config::dump_constraint() {
        dbg::dump_item_info(genv.tcx(), local_id, simp_ext, &refine_tree).unwrap();
    }

    let mut fcx = FixpointCtxt::new(genv, local_id, kvars);
    let cstr = refine_tree.into_fixpoint(&mut fcx).emit(&genv)?;
    fcx.check(cache, cstr, config.scrape_quals).emit(&genv)
}

pub fn check_fn(
    genv: GlobalEnv,
    cache: &mut QueryCache,
    def_id: MaybeExternId,
    mut config: CheckerConfig,
) -> Result<(), ErrorGuaranteed> {
    let span = genv.tcx().def_span(def_id);

    // HACK(nilehmann) this will ignore any code generated by a macro. This is a temporary
    // workaround to deal with a `#[derive(..)]` that generates code that flux cannot handle.
    // Note that this is required because code generated by a `#[derive(..)]` cannot be
    // manually trusted or ignored.
    if !genv.tcx().def_span(def_id).ctxt().is_root() {
        return Ok(());
    }

    // Make sure we run conversion and report errors even if we skip the function for any of
    // the reasons below
    force_conv(genv, def_id).emit(&genv)?;

    // If this is a function wrapping an extern spec its body is irrelevant
    let Some(local_id) = def_id.as_local() else { return Ok(()) };

    // Skip trait methods without body
    if genv.tcx().hir_node_by_def_id(local_id).body_id().is_none() {
        return Ok(());
    }

    // Skip trusted functions
    if genv.trusted(local_id) {
        return Ok(());
    }

    // Since we still want the global check overflow, just override it here if it's set
    if let Some(check_overflow) = genv.check_overflow(local_id) {
        if check_overflow {
            config.check_overflow = true;
        } else if config.check_overflow {
            // In this case, an item was explicitly marked as check_overflow(no)
            // but the cfg attribute is set so we need to override it
            config.check_overflow = false;
        }
    }

    dbg::check_fn_span!(genv.tcx(), local_id).in_scope(|| {
        let ghost_stmts = compute_ghost_statements(genv, local_id)
            .with_span(span)
            .map_err(|err| err.emit_err(&genv, def_id))?;

        // PHASE 1: infer shape of `TypeEnv` at the entry of join points
        let shape_result = Checker::run_in_shape_mode(genv, local_id, &ghost_stmts, config)
            // Augment the possible CheckError with the functions span so we can report
            // helpful error messages for opaque struct field accesses
            .map_err(|err| err.emit_err(&genv, def_id))?;
        tracing::info!("check_fn::shape");

        // PHASE 2: generate refinement tree constraint
        let (refine_tree, kvars) =
            Checker::run_in_refine_mode(genv, local_id, &ghost_stmts, shape_result, config)
                .map_err(|err| err.emit_err(&genv, def_id))?;
        tracing::info!("check_fn::refine");

        // PHASE 3: invoke fixpoint on the constraint
        let errors = invoke_fixpoint(genv, cache, local_id, refine_tree, kvars, config, "fluxc")?;
        tracing::info!("check_fn::fixpoint");
        report_fixpoint_errors(genv, local_id, errors)?;

        // PHASE 4: subtyping check for trait-method implementations
        if let Some((refine_tree, kvars)) =
            trait_impl_subtyping(genv, local_id, config.check_overflow, span)
                .map_err(|err| err.emit_err(&genv, def_id))?
        {
            tracing::info!("check_fn::refine-subtyping");
            let errors =
                invoke_fixpoint(genv, cache, local_id, refine_tree, kvars, config, "sub.fluxc")?;
            tracing::info!("check_fn::fixpoint-subtyping");
            report_fixpoint_errors(genv, local_id, errors)?;
        }
        Ok(())
    })?;

    dbg::check_fn_span!(genv.tcx(), local_id).in_scope(|| Ok(()))
}

fn force_conv(genv: GlobalEnv, def_id: MaybeExternId) -> QueryResult {
    genv.generics_of(def_id)?;
    genv.refinement_generics_of(def_id)?;
    genv.predicates_of(def_id)?;
    genv.fn_sig(def_id)?;
    Ok(())
}

fn call_error(genv: GlobalEnv, span: Span, dst_span: Option<ESpan>) -> ErrorGuaranteed {
    genv.sess()
        .emit_err(errors::RefineError::call(span, dst_span))
}

fn ret_error(genv: GlobalEnv, span: Span, dst_span: Option<ESpan>) -> ErrorGuaranteed {
    genv.sess()
        .emit_err(errors::RefineError::ret(span, dst_span))
}

fn report_errors(genv: GlobalEnv, errors: Vec<Tag>) -> Result<(), ErrorGuaranteed> {
    let mut e = None;
    for err in errors {
        let span = err.src_span;
        e = Some(match err.reason {
            ConstrReason::Call
            | ConstrReason::Subtype(SubtypeReason::Input)
            | ConstrReason::Subtype(SubtypeReason::Requires) => {
                call_error(genv, span, err.dst_span)
            }
            ConstrReason::Assign => genv.sess().emit_err(errors::AssignError { span }),
            ConstrReason::Ret
            | ConstrReason::Subtype(SubtypeReason::Output)
            | ConstrReason::Subtype(SubtypeReason::Ensures) => ret_error(genv, span, err.dst_span),
            ConstrReason::Div => genv.sess().emit_err(errors::DivError { span }),
            ConstrReason::Rem => genv.sess().emit_err(errors::RemError { span }),
            ConstrReason::Goto(_) => genv.sess().emit_err(errors::GotoError { span }),
            ConstrReason::Assert(msg) => genv.sess().emit_err(errors::AssertError { span, msg }),
            ConstrReason::Fold | ConstrReason::FoldLocal => {
                genv.sess().emit_err(errors::FoldError { span })
            }
            ConstrReason::Overflow => genv.sess().emit_err(errors::OverflowError { span }),
            ConstrReason::Other => genv.sess().emit_err(errors::UnknownError { span }),
        });
    }

    if let Some(e) = e {
        Err(e)
    } else {
        Ok(())
    }
}

fn report_expected_neg(genv: GlobalEnv, def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
    Err(genv.sess().emit_err(errors::ExpectedNeg {
        span: genv.tcx().def_span(def_id),
        def_descr: genv.tcx().def_descr(def_id.to_def_id()),
    }))
}

mod errors {
    use flux_errors::E0999;
    use flux_macros::{Diagnostic, Subdiagnostic};
    use flux_middle::rty::ESpan;
    use rustc_span::Span;

    #[derive(Diagnostic)]
    #[diag(refineck_goto_error, code = E0999)]
    pub struct GotoError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_assign_error, code = E0999)]
    pub struct AssignError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Subdiagnostic)]
    #[note(refineck_condition_span_note)]
    pub(crate) struct ConditionSpanNote {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Subdiagnostic)]
    #[note(refineck_call_span_note)]
    pub(crate) struct CallSpanNote {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_refine_error, code = E0999)]
    pub struct RefineError {
        #[primary_span]
        #[label]
        pub span: Span,
        cond: &'static str,
        #[subdiagnostic]
        span_note: Option<ConditionSpanNote>,
        #[subdiagnostic]
        call_span_note: Option<CallSpanNote>,
    }

    impl RefineError {
        pub fn call(span: Span, espan: Option<ESpan>) -> Self {
            RefineError::new("precondition", span, espan)
        }

        pub fn ret(span: Span, espan: Option<ESpan>) -> Self {
            RefineError::new("postcondition", span, espan)
        }

        fn new(cond: &'static str, span: Span, espan: Option<ESpan>) -> RefineError {
            match espan {
                Some(dst_span) => {
                    let span_note = Some(ConditionSpanNote { span: dst_span.span });
                    let call_span_note = dst_span.base.map(|span| CallSpanNote { span });
                    RefineError { span, cond, span_note, call_span_note }
                }
                None => RefineError { span, cond, span_note: None, call_span_note: None },
            }
        }
    }

    #[derive(Diagnostic)]
    #[diag(refineck_div_error, code = E0999)]
    pub struct DivError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_rem_error, code = E0999)]
    pub struct RemError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_assert_error, code = E0999)]
    pub struct AssertError {
        #[primary_span]
        pub span: Span,
        pub msg: &'static str,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_fold_error, code = E0999)]
    pub struct FoldError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_overflow_error, code = E0999)]
    pub struct OverflowError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_unknown_error, code = E0999)]
    pub struct UnknownError {
        #[primary_span]
        pub span: Span,
    }

    #[derive(Diagnostic)]
    #[diag(refineck_expected_neg, code = E0999)]
    pub struct ExpectedNeg {
        #[primary_span]
        pub span: Span,
        pub def_descr: &'static str,
    }
}