// checkSelection checks that all uses and selections that resolve to
// the specified object would continue to do so after the renaming.
func (r *Unexporter) checkSelections(objsToUpdate map[types.Object]string, from types.Object, to string) {
	for pkg, info := range r.packages {
		if id := someUse(info, from); id != nil {
			if !r.checkExport(id, pkg, from, to) {
				return
			}
		}

		for syntax, sel := range info.Selections {
			// There may be extant selections of only the old
			// name or only the new name, so we must check both.
			// (If neither, the renaming is sound.)
			//
			// In both cases, we wish to compare the lengths
			// of the implicit field path (Selection.Index)
			// to see if the renaming would change it.
			//
			// If a selection that resolves to 'from', when renamed,
			// would yield a path of the same or shorter length,
			// this indicates ambiguity or a changed referent,
			// analogous to same- or sub-block lexical conflict.
			//
			// If a selection using the name 'to' would
			// yield a path of the same or shorter length,
			// this indicates ambiguity or shadowing,
			// analogous to same- or super-block lexical conflict.

			// TODO(adonovan): fix: derive from Types[syntax.X].Mode
			// TODO(adonovan): test with pointer, value, addressable value.
			isAddressable := true

			if sel.Obj() == from {
				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), to); obj != nil {
					// Renaming this existing selection of
					// 'from' may block access to an existing
					// type member named 'to'.
					delta := len(indices) - len(sel.Index())
					if delta > 0 {
						continue // no ambiguity
					}
					r.selectionConflict(objsToUpdate, from, to, delta, syntax, obj)
					return
				}

			} else if sel.Obj().Name() == to {
				if obj, indices, _ := types.LookupFieldOrMethod(sel.Recv(), isAddressable, from.Pkg(), from.Name()); obj == from {
					// Renaming 'from' may cause this existing
					// selection of the name 'to' to change
					// its meaning.
					delta := len(indices) - len(sel.Index())
					if delta > 0 {
						continue //  no ambiguity
					}
					r.selectionConflict(objsToUpdate, from, to, -delta, syntax, sel.Obj())
					return
				}
			}
		}
	}
}

func isStringer(obj types.Object) bool {
	switch obj := obj.(type) {
	case *types.Func:
		if obj.Name() != "String" {
			return false
		}
		sig, ok := obj.Type().(*types.Signature)
		if !ok {
			return false
		}
		if sig.Recv() == nil {
			return false
		}
		if sig.Params().Len() != 0 {
			return false
		}
		res := sig.Results()
		if res.Len() != 1 {
			return false
		}
		ret := res.At(0).Type()
		if ret != types.Universe.Lookup("string").Type() {
			return false
		}
		return true
	default:
		return false
	}

	return false
}

// lookup returns the address of the named variable identified by obj
// that is local to function f or one of its enclosing functions.
// If escaping, the reference comes from a potentially escaping pointer
// expression and the referent must be heap-allocated.
//
func (f *Function) lookup(obj types.Object, escaping bool) Value {
	if v, ok := f.objects[obj]; ok {
		if alloc, ok := v.(*Alloc); ok && escaping {
			alloc.Heap = true
		}
		return v // function-local var (address)
	}

	// Definition must be in an enclosing function;
	// plumb it through intervening closures.
	if f.parent == nil {
		panic("no Value for type.Object " + obj.Name())
	}
	outer := f.parent.lookup(obj, true) // escaping
	v := &FreeVar{
		name:   obj.Name(),
		typ:    outer.Type(),
		pos:    outer.Pos(),
		outer:  outer,
		parent: f,
	}
	f.objects[obj] = v
	f.FreeVars = append(f.FreeVars, v)
	return v
}

func (r *Unexporter) selectionConflict(objsToUpdate map[types.Object]string, from types.Object, to string, delta int, syntax *ast.SelectorExpr, obj types.Object) {
	rename := r.errorf(from.Pos(), "renaming this %s %q to %q",
		objectKind(from), from.Name(), to)

	switch {
	case delta < 0:
		// analogous to sub-block conflict
		r.warn(from, rename,
			r.errorf(syntax.Sel.Pos(),
				"\twould change the referent of this selection"),
			r.errorf(obj.Pos(), "\tof this %s", objectKind(obj)))
	case delta == 0:
		// analogous to same-block conflict
		r.warn(from, rename,
			r.errorf(syntax.Sel.Pos(),
				"\twould make this reference ambiguous"),
			r.errorf(obj.Pos(), "\twith this %s", objectKind(obj)))
	case delta > 0:
		// analogous to super-block conflict
		r.warn(from, rename,
			r.errorf(syntax.Sel.Pos(),
				"\twould shadow this selection"),
			r.errorf(obj.Pos(), "\tof the %s declared here",
				objectKind(obj)))
	}
}

// checkInPackageBlock performs safety checks for renames of
// func/var/const/type objects in the package block.
func (e *Export) checkInPackageBlock(from types.Object, to string) {
	info := e.u.pkgInfo
	lexinfo := lexical.Structure(e.u.prog.Fset, from.Pkg(), &info.Info, info.Files)

	// We don't rename anything in the package block to init, as that might
	// conflict or otherwise break stuff
	if to == "init" {
		e.Conflicting = true
		return
	}

	// Check for conflicts between package block and all file blocks.
	for _, f := range info.Files {
		if _, b := lexinfo.Blocks[f].Lookup(to); b == lexinfo.Blocks[f] {
			e.Conflicting = true
			return
		}
	}

	if f, ok := from.(*types.Func); ok && recv(f) == nil {
		e.checkFunction(f, to)
		if e.Conflicting {
			return
		}
	}

	// Check for conflicts in lexical scope.
	// Do not need to check all imported packages:
	// Since it's unnecessarily exported, no one else is going to be sad if I unexport it!
	e.checkInLexicalScope(from, to)
}

// isLocal reports whether obj is local to some function.
// Precondition: not a struct field or interface method.
func isLocal(obj types.Object) bool {
	// [... 5=stmt 4=func 3=file 2=pkg 1=universe]
	var depth int
	for scope := obj.Parent(); scope != nil; scope = scope.Parent() {
		depth++
	}
	return depth >= 4
}

func simpleObjInfo(obj types.Object) string {
	pkg := obj.Pkg()
	s := simpleType(obj.String())
	if pkg != nil && pkg.Name() == "main" {
		return strings.Replace(s, simpleType(pkg.Path())+".", "", -1)
	}
	return s
}

func (v *visitor) decl(obj types.Object) {
	key := getKey(obj)
	if _, ok := v.uses[key]; !ok {
		v.uses[key] = 0
	}
	if _, ok := v.positions[key]; !ok {
		v.positions[key] = v.prog.Fset.Position(obj.Pos())
	}
}

// same reports whether x and y are identical, or both are PkgNames
// that import the same Package.
//
func sameObj(x, y types.Object) bool {
	if x == y {
		return true
	}
	if x, ok := x.(*types.PkgName); ok {
		if y, ok := y.(*types.PkgName); ok {
			return x.Imported() == y.Imported()
		}
	}
	return false
}

func (r *resolver) defineObject(b *Block, name string, obj types.Object) {
	if obj.Name() == "_" {
		return
	}
	i := len(b.bindings)
	b.bindings = append(b.bindings, obj)
	b.index[name] = i
	if trace {
		logf("def %s = %s in %s\n", name, types.ObjectString(obj, r.qualifier), b)
	}
	r.result.Defs[obj] = b
}

func (e *Export) checkInLexicalScope(from types.Object, to string) {
	info := e.u.pkgInfo
	lexinfo := lexical.Structure(e.u.prog.Fset, info.Pkg, &info.Info, info.Files)

	b := lexinfo.Defs[from] // the block defining the 'from' object
	if b != nil {
		to, toBlock := b.Lookup(to)
		if toBlock == b {
			e.Conflicting = true
			return // same-block conflict
		} else if toBlock != nil {
			for _, ref := range lexinfo.Refs[to] {
				if obj, _ := ref.Env.Lookup(from.Name()); obj == from {
					e.Conflicting = true
					return // super-block conflict
				}
			}
		}
	}

	// Check for sub-block conflict.
	// Is there an intervening definition of r.to between
	// the block defining 'from' and some reference to it?
	for _, ref := range lexinfo.Refs[from] {
		_, fromBlock := ref.Env.Lookup(from.Name())
		fromDepth := fromBlock.Depth()

		to, toBlock := ref.Env.Lookup(to)
		if to != nil {
			// sub-block conflict
			if toBlock.Depth() > fromDepth {
				e.Conflicting = true
				return
			}
		}
	}

	// Renaming a type that is used as an embedded field
	// requires renaming the field too. e.g.
	// 	type T int // if we rename this to U..
	// 	var s struct {T}
	// 	print(s.T) // ...this must change too
	if _, ok := from.(*types.TypeName); ok {
		for id, obj := range info.Uses {
			if obj == from {
				if field := info.Defs[id]; field != nil {
					e.check(field, to)
				}
			}
		}
	}
}

func printObject(u *unexporter.Unexporter, o types.Object) {
	var objName string
	if simpleNamesFlag {
		objName = o.Name()
	} else {
		objName = o.String()
	}
	if showFilename {
		pos := u.PositionForObject(o)
		fmt.Printf("%s:%d:%d: %s\n", pos.Filename, pos.Line, pos.Column, objName)
	} else {
		fmt.Println(objName)
	}
}

func (r *Unexporter) checkInLocalScope(objsToUpdate map[types.Object]string, from types.Object, to string) {
	info := r.packages[from.Pkg()]

	// Is this object an implicit local var for a type switch?
	// Each case has its own var, whose position is the decl of y,
	// but Ident in that decl does not appear in the Uses map.
	//
	//   switch y := x.(type) {	 // Defs[Ident(y)] is undefined
	//   case int:    print(y)       // Implicits[CaseClause(int)]    = Var(y_int)
	//   case string: print(y)       // Implicits[CaseClause(string)] = Var(y_string)
	//   }
	//
	var isCaseVar bool
	for syntax, obj := range info.Implicits {
		if _, ok := syntax.(*ast.CaseClause); ok && obj.Pos() == from.Pos() {
			isCaseVar = true
			r.check(objsToUpdate, obj, to)
		}
	}

	r.checkInLexicalScope(objsToUpdate, from, to, info)

	// Finally, if this was a type switch, change the variable y.
	if isCaseVar {
		_, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
		path[0].(*ast.Ident).Name = to // path is [Ident AssignStmt TypeSwitchStmt...]
	}
}

func getKey(obj types.Object) object {
	if obj == nil {
		return object{}
	}

	pkg := obj.Pkg()
	pkgPath := ""
	if pkg != nil {
		pkgPath = pkg.Path()
	}

	return object{
		pkgPath: pkgPath,
		name:    obj.Name(),
	}
}

func objectKind(obj types.Object) string {
	switch obj := obj.(type) {
	case *types.PkgName:
		return "imported package name"
	case *types.TypeName:
		return "type"
	case *types.Var:
		if obj.IsField() {
			return "field"
		}
	case *types.Func:
		if obj.Type().(*types.Signature).Recv() != nil {
			return "method"
		}
	}
	// label, func, var, const
	return strings.ToLower(strings.TrimPrefix(reflect.TypeOf(obj).String(), "*types."))
}

// getDoc returns the doc string associated with types.Object
func (p *Package) getDoc(o types.Object) string {
	n := o.Name()
	switch o.(type) {
	case *types.Const:
		for _, c := range p.doc.Consts {
			for _, cn := range c.Names {
				if n == cn {
					return c.Doc
				}
			}
		}

	case *types.Var:
		for _, v := range p.doc.Vars {
			for _, vn := range v.Names {
				if n == vn {
					return v.Doc
				}
			}
		}

	case *types.Func:
		for _, f := range p.doc.Funcs {
			if n == f.Name {
				return f.Doc
			}
		}

	case *types.TypeName:
		for _, t := range p.doc.Types {
			if n == t.Name {
				return t.Doc
			}
		}

	default:
		// TODO(sbinet)
		panic(fmt.Errorf("not yet supported: %v (%T)", o, o))
	}

	return ""
}

func (c *funcContext) objectName(o types.Object) string {
	if isPkgLevel(o) {
		c.p.dependencies[o] = true

		if o.Pkg() != c.p.Pkg || (isVarOrConst(o) && o.Exported()) {
			return c.pkgVar(o.Pkg()) + "." + o.Name()
		}
	}

	name, ok := c.p.objectNames[o]
	if !ok {
		name = c.newVariableWithLevel(o.Name(), isPkgLevel(o))
		c.p.objectNames[o] = name
	}

	if v, ok := o.(*types.Var); ok && c.p.escapingVars[v] {
		return name + "[0]"
	}
	return name
}

// ssaValueForIdent returns the ssa.Value for the ast.Ident whose path
// to the root of the AST is path.  isAddr reports whether the
// ssa.Value is the address denoted by the ast.Ident, not its value.
//
func ssaValueForIdent(prog *ssa.Program, qinfo *loader.PackageInfo, obj types.Object, path []ast.Node) (value ssa.Value, isAddr bool, err error) {
	switch obj := obj.(type) {
	case *types.Var:
		pkg := prog.Package(qinfo.Pkg)
		pkg.Build()
		if v, addr := prog.VarValue(obj, pkg, path); v != nil {
			return v, addr, nil
		}
		return nil, false, fmt.Errorf("can't locate SSA Value for var %s", obj.Name())

	case *types.Func:
		fn := prog.FuncValue(obj)
		if fn == nil {
			return nil, false, fmt.Errorf("%s is an interface method", obj)
		}
		// TODO(adonovan): there's no point running PTA on a *Func ident.
		// Eliminate this feature.
		return fn, false, nil
	}
	panic(obj)
}

func (r *renamer) selectionConflict(from types.Object, delta int, syntax *ast.SelectorExpr, obj types.Object) {
	r.errorf(from.Pos(), "renaming this %s %q to %q",
		objectKind(from), from.Name(), r.to)

	switch {
	case delta < 0:
		// analogous to sub-block conflict
		r.errorf(syntax.Sel.Pos(),
			"\twould change the referent of this selection")
		r.errorf(obj.Pos(), "\tto this %s", objectKind(obj))
	case delta == 0:
		// analogous to same-block conflict
		r.errorf(syntax.Sel.Pos(),
			"\twould make this reference ambiguous")
		r.errorf(obj.Pos(), "\twith this %s", objectKind(obj))
	case delta > 0:
		// analogous to super-block conflict
		r.errorf(syntax.Sel.Pos(),
			"\twould shadow this selection")
		r.errorf(obj.Pos(), "\tto the %s declared here",
			objectKind(obj))
	}
}

func (f *Function) addParamObj(obj types.Object) *Parameter {
	name := obj.Name()
	if name == "" {
		name = fmt.Sprintf("arg%d", len(f.Params))
	}
	param := f.addParam(name, obj.Type(), obj.Pos())
	param.object = obj
	return param
}