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// Copyright 2009 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.

// This file implements scopes and the objects they contain.

package ast

import (
        "bytes"
        "fmt"
        "go/token"
)

// A Scope maintains the set of named language entities declared
// in the scope and a link to the immediately surrounding (outer)
// scope.
//
type Scope struct {
        Outer   *Scope
        Objects map[string]*Object
}

// NewScope creates a new scope nested in the outer scope.
func NewScope(outer *Scope) *Scope {
        const n = 4 // initial scope capacity
        return &Scope{outer, make(map[string]*Object, n)}
}

// Lookup returns the object with the given name if it is
// found in scope s, otherwise it returns nil. Outer scopes
// are ignored.
//
func (s *Scope) Lookup(name string) *Object {
        return s.Objects[name]
}

// Insert attempts to insert a named object obj into the scope s.
// If the scope already contains an object alt with the same name,
// Insert leaves the scope unchanged and returns alt. Otherwise
// it inserts obj and returns nil."
//
func (s *Scope) Insert(obj *Object) (alt *Object) {
        if alt = s.Objects[obj.Name]; alt == nil {
                s.Objects[obj.Name] = obj
        }
        return
}

// Debugging support
func (s *Scope) String() string {
        var buf bytes.Buffer
        fmt.Fprintf(&buf, "scope %p {", s)
        if s != nil && len(s.Objects) > 0 {
                fmt.Fprintln(&buf)
                for _, obj := range s.Objects {
                        fmt.Fprintf(&buf, "\t%s %s\n", obj.Kind, obj.Name)
                }
        }
        fmt.Fprintf(&buf, "}\n")
        return buf.String()
}

// ----------------------------------------------------------------------------
// Objects

// TODO(gri) Consider replacing the Object struct with an interface
//           and a corresponding set of object implementations.

// An Object describes a named language entity such as a package,
// constant, type, variable, function (incl. methods), or label.
//
// The Data fields contains object-specific data:
//
//      Kind    Data type    Data value
//      Pkg     *Scope       package scope
//      Con     int          iota for the respective declaration
//      Con     != nil       constant value
//
type Object struct {
        Kind ObjKind
        Name string      // declared name
        Decl interface{} // corresponding Field, XxxSpec, FuncDecl, LabeledStmt, AssignStmt, Scope; or nil
        Data interface{} // object-specific data; or nil
        Type interface{} // place holder for type information; may be nil
}

// NewObj creates a new object of a given kind and name.
func NewObj(kind ObjKind, name string) *Object {
        return &Object{Kind: kind, Name: name}
}

// Pos computes the source position of the declaration of an object name.
// The result may be an invalid position if it cannot be computed
// (obj.Decl may be nil or not correct).
func (obj *Object) Pos() token.Pos {
        name := obj.Name
        switch d := obj.Decl.(type) {
        case *Field:
                for _, n := range d.Names {
                        if n.Name == name {
                                return n.Pos()
                        }
                }
        case *ImportSpec:
                if d.Name != nil && d.Name.Name == name {
                        return d.Name.Pos()
                }
                return d.Path.Pos()
        case *ValueSpec:
                for _, n := range d.Names {
                        if n.Name == name {
                                return n.Pos()
                        }
                }
        case *TypeSpec:
                if d.Name.Name == name {
                        return d.Name.Pos()
                }
        case *FuncDecl:
                if d.Name.Name == name {
                        return d.Name.Pos()
                }
        case *LabeledStmt:
                if d.Label.Name == name {
                        return d.Label.Pos()
                }
        case *AssignStmt:
                for _, x := range d.Lhs {
                        if ident, isIdent := x.(*Ident); isIdent && ident.Name == name {
                                return ident.Pos()
                        }
                }
        case *Scope:
                // predeclared object - nothing to do for now
        }
        return token.NoPos
}

// ObKind describes what an object represents.
type ObjKind int

// The list of possible Object kinds.
const (
        Bad ObjKind = iota // for error handling
        Pkg                // package
        Con                // constant
        Typ                // type
        Var                // variable
        Fun                // function or method
        Lbl                // label
)

var objKindStrings = [...]string{
        Bad: "bad",
        Pkg: "package",
        Con: "const",
        Typ: "type",
        Var: "var",
        Fun: "func",
        Lbl: "label",
}

func (kind ObjKind) String() string { return objKindStrings[kind] }