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use crate::build::expr::as_place::PlaceBuilder;
use crate::build::matches::MatchPair;
use crate::build::Builder;
use rustc_middle::mir::*;
use rustc_middle::thir::*;
use rustc_middle::ty;
use smallvec::SmallVec;
use std::convert::TryInto;

impl<'a, 'tcx> Builder<'a, 'tcx> {
    pub(crate) fn field_match_pairs<'pat>(
        &mut self,
        place: PlaceBuilder<'tcx>,
        subpatterns: &'pat [FieldPat<'tcx>],
    ) -> Vec<MatchPair<'pat, 'tcx>> {
        subpatterns
            .iter()
            .map(|fieldpat| {
                let place = place.clone().field(fieldpat.field, fieldpat.pattern.ty);
                MatchPair::new(place, &fieldpat.pattern)
            })
            .collect()
    }

    pub(crate) fn prefix_slice_suffix<'pat>(
        &mut self,
        match_pairs: &mut SmallVec<[MatchPair<'pat, 'tcx>; 1]>,
        place: &PlaceBuilder<'tcx>,
        prefix: &'pat [Box<Pat<'tcx>>],
        opt_slice: &'pat Option<Box<Pat<'tcx>>>,
        suffix: &'pat [Box<Pat<'tcx>>],
    ) {
        let tcx = self.tcx;
        let (min_length, exact_size) = if let Ok(place_resolved) =
            place.clone().try_upvars_resolved(tcx, &self.upvars)
        {
            match place_resolved.into_place(tcx, &self.upvars).ty(&self.local_decls, tcx).ty.kind()
            {
                ty::Array(_, length) => (length.eval_usize(tcx, self.param_env), true),
                _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
            }
        } else {
            ((prefix.len() + suffix.len()).try_into().unwrap(), false)
        };

        match_pairs.extend(prefix.iter().enumerate().map(|(idx, subpattern)| {
            let elem =
                ProjectionElem::ConstantIndex { offset: idx as u64, min_length, from_end: false };
            let place = place.clone().project(elem);
            MatchPair::new(place, subpattern)
        }));

        if let Some(subslice_pat) = opt_slice {
            let suffix_len = suffix.len() as u64;
            let subslice = place.clone().project(ProjectionElem::Subslice {
                from: prefix.len() as u64,
                to: if exact_size { min_length - suffix_len } else { suffix_len },
                from_end: !exact_size,
            });
            match_pairs.push(MatchPair::new(subslice, subslice_pat));
        }

        match_pairs.extend(suffix.iter().rev().enumerate().map(|(idx, subpattern)| {
            let end_offset = (idx + 1) as u64;
            let elem = ProjectionElem::ConstantIndex {
                offset: if exact_size { min_length - end_offset } else { end_offset },
                min_length,
                from_end: !exact_size,
            };
            let place = place.clone().project(elem);
            MatchPair::new(place, subpattern)
        }));
    }

    /// Creates a false edge to `imaginary_target` and a real edge to
    /// real_target. If `imaginary_target` is none, or is the same as the real
    /// target, a Goto is generated instead to simplify the generated MIR.
    pub(crate) fn false_edges(
        &mut self,
        from_block: BasicBlock,
        real_target: BasicBlock,
        imaginary_target: Option<BasicBlock>,
        source_info: SourceInfo,
    ) {
        match imaginary_target {
            Some(target) if target != real_target => {
                self.cfg.terminate(
                    from_block,
                    source_info,
                    TerminatorKind::FalseEdge { real_target, imaginary_target: target },
                );
            }
            _ => self.cfg.goto(from_block, source_info, real_target),
        }
    }
}

impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
    pub(crate) fn new(
        place: PlaceBuilder<'tcx>,
        pattern: &'pat Pat<'tcx>,
    ) -> MatchPair<'pat, 'tcx> {
        MatchPair { place, pattern }
    }
}