use crate::*;
use helpers::check_arg_count;
use rustc_middle::ty::{self, TypeAndMut};
use rustc_ast::ast::Mutability;
use rustc_span::BytePos;
use rustc_target::abi::Size;
use std::convert::TryInto as _;
use crate::rustc_target::abi::LayoutOf as _;

impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {

    fn handle_miri_get_backtrace(
        &mut self,
        args: &[OpTy<'tcx, Tag>],
        dest: PlaceTy<'tcx, Tag>
    ) -> InterpResult<'tcx> {
        let this = self.eval_context_mut();
        let tcx = this.tcx;
        let &[flags] = check_arg_count(args)?;

        let flags = this.read_scalar(flags)?.to_u64()?;
        if flags != 0 {
            throw_unsup_format!("unknown `miri_get_backtrace` flags {}", flags);
        }

        let mut data = Vec::new();
        for frame in this.active_thread_stack().iter().rev() {
            data.push((frame.instance, frame.current_span().lo()));
        }

        let ptrs: Vec<_> = data.into_iter().map(|(instance, pos)| {
            // We represent a frame pointer by using the `span.lo` value
            // as an offset into the function's allocation. This gives us an
            // opaque pointer that we can return to user code, and allows us
            // to reconstruct the needed frame information in `handle_miri_resolve_frame`.
            // Note that we never actually read or write anything from/to this pointer -
            // all of the data is represented by the pointer value itself.
            let mut fn_ptr = this.memory.create_fn_alloc(FnVal::Instance(instance));
            fn_ptr.offset = Size::from_bytes(pos.0);
            Scalar::Ptr(fn_ptr)
        }).collect();

        let len = ptrs.len();

        let ptr_ty = tcx.mk_ptr(TypeAndMut {
            ty: tcx.types.unit,
            mutbl: Mutability::Mut
        });

        let array_ty = tcx.mk_array(ptr_ty, ptrs.len().try_into().unwrap());

        // Write pointers into array
        let alloc = this.allocate(this.layout_of(array_ty).unwrap(), MiriMemoryKind::Rust.into());
        for (i, ptr) in ptrs.into_iter().enumerate() {
            let place = this.mplace_index(alloc, i as u64)?;
            this.write_immediate_to_mplace(ptr.into(), place)?;
        }

        this.write_immediate(Immediate::new_slice(alloc.ptr.into(), len.try_into().unwrap(), this), dest)?;
        Ok(())
    }

    fn handle_miri_resolve_frame(
        &mut self,
        args: &[OpTy<'tcx, Tag>],
        dest: PlaceTy<'tcx, Tag>
    ) -> InterpResult<'tcx> {
        let this = self.eval_context_mut();
        let tcx = this.tcx;
        let &[ptr, flags] = check_arg_count(args)?;

        let flags = this.read_scalar(flags)?.to_u64()?;
        if flags != 0 {
            throw_unsup_format!("unknown `miri_resolve_frame` flags {}", flags);
        }

        let ptr = match this.read_scalar(ptr)?.check_init()? {
            Scalar::Ptr(ptr) => ptr,
            Scalar::Raw { .. } => throw_ub_format!("expected a pointer in `rust_miri_resolve_frame`, found {:?}", ptr)
        };

        let fn_instance = if let Some(GlobalAlloc::Function(instance)) = this.tcx.get_global_alloc(ptr.alloc_id) {
            instance
        } else {
            throw_ub_format!("expected function pointer, found {:?}", ptr);
        };

        if dest.layout.layout.fields.count() != 4 {
            throw_ub_format!("bad declaration of miri_resolve_frame - should return a struct with 4 fields");
        }

        let pos = BytePos(ptr.offset.bytes().try_into().unwrap());
        let name = fn_instance.to_string();

        let lo = tcx.sess.source_map().lookup_char_pos(pos);

        let filename = lo.file.name.to_string();
        let lineno: u32 = lo.line as u32;
        // `lo.col` is 0-based - add 1 to make it 1-based for the caller.
        let colno: u32 = lo.col.0 as u32 + 1;

        let name_alloc = this.allocate_str(&name, MiriMemoryKind::Rust.into());
        let filename_alloc = this.allocate_str(&filename, MiriMemoryKind::Rust.into());
        let lineno_alloc = Scalar::from_u32(lineno);
        let colno_alloc = Scalar::from_u32(colno);

        let dest = this.force_allocation(dest)?;
        if let ty::Adt(adt, _) = dest.layout.ty.kind() {
            if !adt.repr.c() {
                throw_ub_format!("miri_resolve_frame must be declared with a `#[repr(C)]` return type");
            }
        }

        this.write_immediate(name_alloc.to_ref(), this.mplace_field(dest, 0)?.into())?;
        this.write_immediate(filename_alloc.to_ref(), this.mplace_field(dest, 1)?.into())?;
        this.write_scalar(lineno_alloc, this.mplace_field(dest, 2)?.into())?;
        this.write_scalar(colno_alloc, this.mplace_field(dest, 3)?.into())?;
        Ok(())
    }
}