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// Copyright 2011 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 NewPackage.

package ast

import (
        "fmt"
        "go/scanner"
        "go/token"
        "strconv"
)

type pkgBuilder struct {
        scanner.ErrorVector
        fset *token.FileSet
}

func (p *pkgBuilder) error(pos token.Pos, msg string) {
        p.Error(p.fset.Position(pos), msg)
}

func (p *pkgBuilder) errorf(pos token.Pos, format string, args ...interface{}) {
        p.error(pos, fmt.Sprintf(format, args...))
}

func (p *pkgBuilder) declare(scope, altScope *Scope, obj *Object) {
        alt := scope.Insert(obj)
        if alt == nil && altScope != nil {
                // see if there is a conflicting declaration in altScope
                alt = altScope.Lookup(obj.Name)
        }
        if alt != nil {
                prevDecl := ""
                if pos := alt.Pos(); pos.IsValid() {
                        prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.fset.Position(pos))
                }
                p.error(obj.Pos(), fmt.Sprintf("%s redeclared in this block%s", obj.Name, prevDecl))
        }
}

func resolve(scope *Scope, ident *Ident) bool {
        for ; scope != nil; scope = scope.Outer {
                if obj := scope.Lookup(ident.Name); obj != nil {
                        ident.Obj = obj
                        return true
                }
        }
        return false
}

// An Importer resolves import paths to package Objects.
// The imports map records the packages already imported,
// indexed by package id (canonical import path).
// An Importer must determine the canonical import path and
// check the map to see if it is already present in the imports map.
// If so, the Importer can return the map entry.  Otherwise, the
// Importer should load the package data for the given path into 
// a new *Object (pkg), record pkg in the imports map, and then
// return pkg.
type Importer func(imports map[string]*Object, path string) (pkg *Object, err error)

// NewPackage creates a new Package node from a set of File nodes. It resolves
// unresolved identifiers across files and updates each file's Unresolved list
// accordingly. If a non-nil importer and universe scope are provided, they are
// used to resolve identifiers not declared in any of the package files. Any
// remaining unresolved identifiers are reported as undeclared. If the files
// belong to different packages, one package name is selected and files with
// different package names are reported and then ignored.
// The result is a package node and a scanner.ErrorList if there were errors.
//
func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, universe *Scope) (*Package, error) {
        var p pkgBuilder
        p.fset = fset

        // complete package scope
        pkgName := ""
        pkgScope := NewScope(universe)
        for _, file := range files {
                // package names must match
                switch name := file.Name.Name; {
                case pkgName == "":
                        pkgName = name
                case name != pkgName:
                        p.errorf(file.Package, "package %s; expected %s", name, pkgName)
                        continue // ignore this file
                }

                // collect top-level file objects in package scope
                for _, obj := range file.Scope.Objects {
                        p.declare(pkgScope, nil, obj)
                }
        }

        // package global mapping of imported package ids to package objects
        imports := make(map[string]*Object)

        // complete file scopes with imports and resolve identifiers
        for _, file := range files {
                // ignore file if it belongs to a different package
                // (error has already been reported)
                if file.Name.Name != pkgName {
                        continue
                }

                // build file scope by processing all imports
                importErrors := false
                fileScope := NewScope(pkgScope)
                for _, spec := range file.Imports {
                        if importer == nil {
                                importErrors = true
                                continue
                        }
                        path, _ := strconv.Unquote(spec.Path.Value)
                        pkg, err := importer(imports, path)
                        if err != nil {
                                p.errorf(spec.Path.Pos(), "could not import %s (%s)", path, err)
                                importErrors = true
                                continue
                        }
                        // TODO(gri) If a local package name != "." is provided,
                        // global identifier resolution could proceed even if the
                        // import failed. Consider adjusting the logic here a bit.

                        // local name overrides imported package name
                        name := pkg.Name
                        if spec.Name != nil {
                                name = spec.Name.Name
                        }

                        // add import to file scope
                        if name == "." {
                                // merge imported scope with file scope
                                for _, obj := range pkg.Data.(*Scope).Objects {
                                        p.declare(fileScope, pkgScope, obj)
                                }
                        } else {
                                // declare imported package object in file scope
                                // (do not re-use pkg in the file scope but create
                                // a new object instead; the Decl field is different
                                // for different files)
                                obj := NewObj(Pkg, name)
                                obj.Decl = spec
                                obj.Data = pkg.Data
                                p.declare(fileScope, pkgScope, obj)
                        }
                }

                // resolve identifiers
                if importErrors {
                        // don't use the universe scope without correct imports
                        // (objects in the universe may be shadowed by imports;
                        // with missing imports, identifiers might get resolved
                        // incorrectly to universe objects)
                        pkgScope.Outer = nil
                }
                i := 0
                for _, ident := range file.Unresolved {
                        if !resolve(fileScope, ident) {
                                p.errorf(ident.Pos(), "undeclared name: %s", ident.Name)
                                file.Unresolved[i] = ident
                                i++
                        }

                }
                file.Unresolved = file.Unresolved[0:i]
                pkgScope.Outer = universe // reset universe scope
        }

        return &Package{pkgName, pkgScope, imports, files}, p.GetError(scanner.Sorted)
}