package remotecontext

import (
	"encoding/hex"
	"io"
	"os"
	"path/filepath"

	"github.com/docker/docker/builder"
	"github.com/docker/docker/pkg/pools"
	"github.com/docker/docker/pkg/symlink"
	"github.com/pkg/errors"
)

// NewLazyContext creates a new LazyContext. LazyContext defines a hashed build
// context based on a root directory. Individual files are hashed first time
// they are asked. It is not safe to call methods of LazyContext concurrently.
func NewLazyContext(root string) (builder.Context, error) {
	return &lazyContext{
		root: root,
		sums: make(map[string]string),
	}, nil
}

type lazyContext struct {
	root string
	sums map[string]string
}

func (c *lazyContext) Close() error {
	return nil
}

func (c *lazyContext) Open(path string) (io.ReadCloser, error) {
	cleanPath, fullPath, err := c.normalize(path)
	if err != nil {
		return nil, err
	}

	r, err := os.Open(fullPath)
	if err != nil {
		return nil, errors.WithStack(convertPathError(err, cleanPath))
	}
	return r, nil
}

func (c *lazyContext) Stat(path string) (string, builder.FileInfo, error) {
	// TODO: although stat returns builder.FileInfo it builder.Context actually requires Hashed
	cleanPath, fullPath, err := c.normalize(path)
	if err != nil {
		return "", nil, err
	}

	st, err := os.Lstat(fullPath)
	if err != nil {
		return "", nil, errors.WithStack(convertPathError(err, cleanPath))
	}

	relPath, err := filepath.Rel(c.root, fullPath)
	if err != nil {
		return "", nil, errors.WithStack(convertPathError(err, cleanPath))
	}

	sum, ok := c.sums[relPath]
	if !ok {
		sum, err = c.prepareHash(relPath, st)
		if err != nil {
			return "", nil, err
		}
	}

	fi := &builder.HashedFileInfo{
		builder.PathFileInfo{st, fullPath, filepath.Base(cleanPath)},
		sum,
	}
	return relPath, fi, nil
}

func (c *lazyContext) Walk(root string, walkFn builder.WalkFunc) error {
	_, fullPath, err := c.normalize(root)
	if err != nil {
		return err
	}
	return filepath.Walk(fullPath, func(fullPath string, fi os.FileInfo, err error) error {
		relPath, err := filepath.Rel(c.root, fullPath)
		if err != nil {
			return errors.WithStack(err)
		}
		if relPath == "." {
			return nil
		}

		sum, ok := c.sums[relPath]
		if !ok {
			sum, err = c.prepareHash(relPath, fi)
			if err != nil {
				return err
			}
		}

		hfi := &builder.HashedFileInfo{
			builder.PathFileInfo{FileInfo: fi, FilePath: fullPath},
			sum,
		}
		if err := walkFn(relPath, hfi, nil); err != nil {
			return err
		}
		return nil
	})
}

func (c *lazyContext) prepareHash(relPath string, fi os.FileInfo) (string, error) {
	p := filepath.Join(c.root, relPath)
	h, err := NewFileHash(p, relPath, fi)
	if err != nil {
		return "", errors.Wrapf(err, "failed to create hash for %s", relPath)
	}
	if fi.Mode().IsRegular() && fi.Size() > 0 {
		f, err := os.Open(p)
		if err != nil {
			return "", errors.Wrapf(err, "failed to open %s", relPath)
		}
		defer f.Close()
		if _, err := pools.Copy(h, f); err != nil {
			return "", errors.Wrapf(err, "failed to copy file data for %s", relPath)
		}
	}
	sum := hex.EncodeToString(h.Sum(nil))
	c.sums[relPath] = sum
	return sum, nil
}

func (c *lazyContext) normalize(path string) (cleanPath, fullPath string, err error) {
	// todo: combine these helpers with tarsum after they are moved to same package
	cleanPath = filepath.Clean(string(os.PathSeparator) + path)[1:]
	fullPath, err = symlink.FollowSymlinkInScope(filepath.Join(c.root, path), c.root)
	if err != nil {
		return "", "", errors.Wrapf(err, "forbidden path outside the build context: %s (%s)", path, fullPath)
	}
	return
}

func convertPathError(err error, cleanpath string) error {
	if err, ok := err.(*os.PathError); ok {
		err.Path = cleanpath
		return err
	}
	return err
}