package dockerfile

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/docker/docker/pkg/system"
)

// normaliseWorkdir normalises a user requested working directory in a
// platform sematically consistent way.
func normaliseWorkdir(current string, requested string) (string, error) {
	if requested == "" {
		return "", fmt.Errorf("cannot normalise nothing")
	}

	current = filepath.FromSlash(current)
	requested = filepath.FromSlash(requested)

	// Target semantics is C:\somefolder, specifically in the format:
	// UPPERCASEDriveLetter-Colon-Backslash-FolderName. We are already
	// guaranteed that `current`, if set, is consistent. This allows us to
	// cope correctly with any of the following in a Dockerfile:
	//	WORKDIR a                       --> C:\a
	//	WORKDIR c:\\foo                 --> C:\foo
	//	WORKDIR \\foo                   --> C:\foo
	//	WORKDIR /foo                    --> C:\foo
	//	WORKDIR c:\\foo \ WORKDIR bar   --> C:\foo --> C:\foo\bar
	//	WORKDIR C:/foo \ WORKDIR bar    --> C:\foo --> C:\foo\bar
	//	WORKDIR C:/foo \ WORKDIR \\bar  --> C:\foo --> C:\bar
	//	WORKDIR /foo \ WORKDIR c:/bar   --> C:\foo --> C:\bar
	if len(current) == 0 || system.IsAbs(requested) {
		if (requested[0] == os.PathSeparator) ||
			(len(requested) > 1 && string(requested[1]) != ":") ||
			(len(requested) == 1) {
			requested = filepath.Join(`C:\`, requested)
		}
	} else {
		requested = filepath.Join(current, requested)
	}
	// Upper-case drive letter
	return (strings.ToUpper(string(requested[0])) + requested[1:]), nil
}