use rustc_codegen_ssa::debuginfo::{FunctionDebugContext, FunctionDebugContextData, MirDebugScope};
use super::metadata::file_metadata;
use super::utils::{DIB, span_start};

use crate::llvm;
use crate::llvm::debuginfo::{DIScope, DISubprogram};
use crate::common::CodegenCx;
use rustc::mir::{Mir, SourceScope};

use libc::c_uint;

use syntax_pos::Pos;

use rustc_data_structures::bit_set::BitSet;
use rustc_data_structures::indexed_vec::{Idx, IndexVec};

use syntax_pos::BytePos;

/// Produces DIScope DIEs for each MIR Scope which has variables defined in it.
/// If debuginfo is disabled, the returned vector is empty.
pub fn create_mir_scopes(
    cx: &CodegenCx<'ll, '_>,
    mir: &Mir<'_>,
    debug_context: &FunctionDebugContext<&'ll DISubprogram>,
) -> IndexVec<SourceScope, MirDebugScope<&'ll DIScope>> {
    let null_scope = MirDebugScope {
        scope_metadata: None,
        file_start_pos: BytePos(0),
        file_end_pos: BytePos(0)
    };
    let mut scopes = IndexVec::from_elem(null_scope, &mir.source_scopes);

    let debug_context = match *debug_context {
        FunctionDebugContext::RegularContext(ref data) => data,
        FunctionDebugContext::DebugInfoDisabled |
        FunctionDebugContext::FunctionWithoutDebugInfo => {
            return scopes;
        }
    };

    // Find all the scopes with variables defined in them.
    let mut has_variables = BitSet::new_empty(mir.source_scopes.len());
    for var in mir.vars_iter() {
        let decl = &mir.local_decls[var];
        has_variables.insert(decl.visibility_scope);
    }

    // Instantiate all scopes.
    for idx in 0..mir.source_scopes.len() {
        let scope = SourceScope::new(idx);
        make_mir_scope(cx, &mir, &has_variables, debug_context, scope, &mut scopes);
    }

    scopes
}

fn make_mir_scope(cx: &CodegenCx<'ll, '_>,
                  mir: &Mir<'_>,
                  has_variables: &BitSet<SourceScope>,
                  debug_context: &FunctionDebugContextData<&'ll DISubprogram>,
                  scope: SourceScope,
                  scopes: &mut IndexVec<SourceScope, MirDebugScope<&'ll DIScope>>) {
    if scopes[scope].is_valid() {
        return;
    }

    let scope_data = &mir.source_scopes[scope];
    let parent_scope = if let Some(parent) = scope_data.parent_scope {
        make_mir_scope(cx, mir, has_variables, debug_context, parent, scopes);
        scopes[parent]
    } else {
        // The root is the function itself.
        let loc = span_start(cx, mir.span);
        scopes[scope] = MirDebugScope {
            scope_metadata: Some(debug_context.fn_metadata),
            file_start_pos: loc.file.start_pos,
            file_end_pos: loc.file.end_pos,
        };
        return;
    };

    if !has_variables.contains(scope) {
        // Do not create a DIScope if there are no variables
        // defined in this MIR Scope, to avoid debuginfo bloat.

        // However, we don't skip creating a nested scope if
        // our parent is the root, because we might want to
        // put arguments in the root and not have shadowing.
        if parent_scope.scope_metadata.unwrap() != debug_context.fn_metadata {
            scopes[scope] = parent_scope;
            return;
        }
    }

    let loc = span_start(cx, scope_data.span);
    let file_metadata = file_metadata(cx,
                                      &loc.file.name,
                                      debug_context.defining_crate);

    let scope_metadata = unsafe {
        Some(llvm::LLVMRustDIBuilderCreateLexicalBlock(
            DIB(cx),
            parent_scope.scope_metadata.unwrap(),
            file_metadata,
            loc.line as c_uint,
            loc.col.to_usize() as c_uint))
    };
    scopes[scope] = MirDebugScope {
        scope_metadata,
        file_start_pos: loc.file.start_pos,
        file_end_pos: loc.file.end_pos,
    };
}