/*
Copyright 2018 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Forked from go's go/internal/srcimporter

// Copyright 2017 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 srcimporter implements importing directly
// from source files rather than installed packages.
package srcimporter

import (
	"fmt"
	"go/ast"
	"go/build"
	"go/parser"
	"go/token"
	"path/filepath"
	"sync"

	"k8s.io/kubernetes/third_party/forked/golang/go/types"
)

// An Importer provides the context for importing packages from source code.
type Importer struct {
	ctxt     *build.Context
	fset     *token.FileSet
	sizes    types.Sizes
	packages map[string]*types.Package
}

// New returns a new Importer for the given context, file set, and map
// of packages. The context is used to resolve import paths to package paths,
// and identifying the files belonging to the package. If the context provides
// non-nil file system functions, they are used instead of the regular package
// os functions. The file set is used to track position information of package
// files; and imported packages are added to the packages map.
func New(ctxt *build.Context, fset *token.FileSet, packages map[string]*types.Package) *Importer {
	return &Importer{
		ctxt:     ctxt,
		fset:     fset,
		sizes:    types.SizesFor(ctxt.Compiler, ctxt.GOARCH), // uses go/types default if GOARCH not found
		packages: packages,
	}
}

// Importing is a sentinel taking the place in Importer.packages
// for a package that is in the process of being imported.
var importing types.Package

// Import (path) is a shortcut for ImportFrom(path, "", 0).
func (p *Importer) Import(path string) (*types.Package, error) {
	return p.ImportFrom(path, "", 0)
}

// ImportFrom imports the package with the given import path resolved from the given srcDir,
// adds the new package to the set of packages maintained by the importer, and returns the
// package. Package path resolution and file system operations are controlled by the context
// maintained with the importer. The import mode must be zero but is otherwise ignored.
// Packages that are not comprised entirely of pure Go files may fail to import because the
// type checker may not be able to determine all exported entities (e.g. due to cgo dependencies).
func (p *Importer) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
	if mode != 0 {
		panic("non-zero import mode")
	}

	// determine package path (do vendor resolution)
	var bp *build.Package
	var err error
	switch {
	default:
		if abs, err := p.absPath(srcDir); err == nil { // see issue #14282
			srcDir = abs
		}
		bp, err = p.ctxt.Import(path, srcDir, build.FindOnly)

	case build.IsLocalImport(path):
		// "./x" -> "srcDir/x"
		bp, err = p.ctxt.ImportDir(filepath.Join(srcDir, path), build.FindOnly)

	case p.isAbsPath(path):
		return nil, fmt.Errorf("invalid absolute import path %q", path)
	}
	if err != nil {
		return nil, err // err may be *build.NoGoError - return as is
	}

	// package unsafe is known to the type checker
	if bp.ImportPath == "unsafe" {
		return types.Unsafe, nil
	}

	// no need to re-import if the package was imported completely before
	pkg := p.packages[bp.ImportPath]
	if pkg != nil {
		if pkg == &importing {
			return nil, fmt.Errorf("import cycle through package %q", bp.ImportPath)
		}
		if !pkg.Complete() {
			// Package exists but is not complete - we cannot handle this
			// at the moment since the source importer replaces the package
			// wholesale rather than augmenting it (see #19337 for details).
			// Return incomplete package with error (see #16088).
			return pkg, fmt.Errorf("reimported partially imported package %q", bp.ImportPath)
		}
		return pkg, nil
	}

	p.packages[bp.ImportPath] = &importing
	defer func() {
		// clean up in case of error
		// TODO(gri) Eventually we may want to leave a (possibly empty)
		// package in the map in all cases (and use that package to
		// identify cycles). See also issue 16088.
		if p.packages[bp.ImportPath] == &importing {
			p.packages[bp.ImportPath] = nil
		}
	}()

	// collect package files
	bp, err = p.ctxt.ImportDir(bp.Dir, 0)
	if err != nil {
		return nil, err // err may be *build.NoGoError - return as is
	}
	var filenames []string
	filenames = append(filenames, bp.GoFiles...)
	filenames = append(filenames, bp.CgoFiles...)

	files, err := p.parseFiles(bp.Dir, filenames)
	if err != nil {
		return nil, err
	}

	// type-check package files
	var firstHardErr error
	conf := types.Config{
		IgnoreFuncBodies: true,
		FakeImportC:      true,
		// continue type-checking after the first error
		Error: func(err error) {
			if firstHardErr == nil && !err.(types.Error).Soft {
				firstHardErr = err
			}
		},
		Importer: p,
		Sizes:    p.sizes,
	}
	pkg, err = conf.Check(bp.ImportPath, p.fset, files, nil)
	if err != nil {
		// If there was a hard error it is possibly unsafe
		// to use the package as it may not be fully populated.
		// Do not return it (see also #20837, #20855).
		if firstHardErr != nil {
			pkg = nil
			err = firstHardErr // give preference to first hard error over any soft error
		}
		return pkg, fmt.Errorf("type-checking package %q failed (%v)", bp.ImportPath, err)
	}
	if firstHardErr != nil {
		// this can only happen if we have a bug in go/types
		panic("package is not safe yet no error was returned")
	}

	p.packages[bp.ImportPath] = pkg
	return pkg, nil
}

func (p *Importer) parseFiles(dir string, filenames []string) ([]*ast.File, error) {
	open := p.ctxt.OpenFile // possibly nil

	files := make([]*ast.File, len(filenames))
	errors := make([]error, len(filenames))

	var wg sync.WaitGroup
	wg.Add(len(filenames))
	for i, filename := range filenames {
		go func(i int, filepath string) {
			defer wg.Done()
			if open != nil {
				src, err := open(filepath)
				if err != nil {
					errors[i] = fmt.Errorf("opening package file %s failed (%v)", filepath, err)
					return
				}
				files[i], errors[i] = parser.ParseFile(p.fset, filepath, src, 0)
				src.Close() // ignore Close error - parsing may have succeeded which is all we need
			} else {
				// Special-case when ctxt doesn't provide a custom OpenFile and use the
				// parser's file reading mechanism directly. This appears to be quite a
				// bit faster than opening the file and providing an io.ReaderCloser in
				// both cases.
				// TODO(gri) investigate performance difference (issue #19281)
				files[i], errors[i] = parser.ParseFile(p.fset, filepath, nil, 0)
			}
		}(i, p.joinPath(dir, filename))
	}
	wg.Wait()

	// if there are errors, return the first one for deterministic results
	for _, err := range errors {
		if err != nil {
			return nil, err
		}
	}

	return files, nil
}

// context-controlled file system operations

func (p *Importer) absPath(path string) (string, error) {
	// TODO(gri) This should be using p.ctxt.AbsPath which doesn't
	// exist but probably should. See also issue #14282.
	return filepath.Abs(path)
}

func (p *Importer) isAbsPath(path string) bool {
	if f := p.ctxt.IsAbsPath; f != nil {
		return f(path)
	}
	return filepath.IsAbs(path)
}

func (p *Importer) joinPath(elem ...string) string {
	if f := p.ctxt.JoinPath; f != nil {
		return f(elem...)
	}
	return filepath.Join(elem...)
}