// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package source

import (
	"context"
	"fmt"
	"go/ast"
	"go/types"

	"golang.org/x/tools/internal/span"
)

// ReferenceInfo holds information about reference to an identifier in Go source.
type ReferenceInfo struct {
	Name          string
	Range         span.Range
	ident         *ast.Ident
	obj           types.Object
	isDeclaration bool
}

// References returns a list of references for a given identifier within a package.
func (i *IdentifierInfo) References(ctx context.Context) ([]*ReferenceInfo, error) {
	var references []*ReferenceInfo
	if i.pkg == nil || i.pkg.IsIllTyped() {
		return nil, fmt.Errorf("package for %s is ill typed", i.File.URI())
	}
	info := i.pkg.GetTypesInfo()
	if info == nil {
		return nil, fmt.Errorf("package %s has no types info", i.pkg.PkgPath())
	}
	// If the object declaration is nil, assume it is an import spec and do not look for references.
	if i.decl.obj == nil {
		return nil, fmt.Errorf("no references for an import spec")
	}
	if i.decl.wasImplicit {
		// The definition is implicit, so we must add it separately.
		// This occurs when the variable is declared in a type switch statement
		// or is an implicit package name.
		references = append(references, &ReferenceInfo{
			Name:          i.decl.obj.Name(),
			Range:         i.decl.rng,
			obj:           i.decl.obj,
			isDeclaration: true,
		})
	}
	for ident, obj := range info.Defs {
		if obj == nil || obj.Pos() != i.decl.obj.Pos() {
			continue
		}
		references = append(references, &ReferenceInfo{
			Name:          ident.Name,
			Range:         span.NewRange(i.File.FileSet(), ident.Pos(), ident.End()),
			ident:         ident,
			obj:           obj,
			isDeclaration: true,
		})
	}
	for ident, obj := range info.Uses {
		if obj == nil || obj.Pos() != i.decl.obj.Pos() {
			continue
		}
		references = append(references, &ReferenceInfo{
			Name:  ident.Name,
			Range: span.NewRange(i.File.FileSet(), ident.Pos(), ident.End()),
			ident: ident,
			obj:   obj,
		})
	}
	return references, nil
}