package basic

import (
	"crypto/sha1"
	"encoding/base64"
	"encoding/csv"
	"errors"
	"os"
	"regexp"
	"strings"
	
	"golang.org/x/crypto/bcrypt"
)

// AuthenticationFailureErr - a generic error message for authentication failure to be presented to agent.
var AuthenticationFailureErr = errors.New("Bad username or password")

// HTPasswd - holds a path to a system .htpasswd file and the machinery to parse it.
type HTPasswd struct {
	path   string
	reader *csv.Reader
}

// AuthType represents a particular hash function used in the htpasswd file.
type AuthType int 
const (
	PlainText 	AuthType 	= iota
	SHA1
	ApacheMD5
	BCrypt
	Crypt
)

// String returns a text representation of the AuthType
func (at AuthType) String() string {
	switch(at) {
		case PlainText: return "plaintext"
		case SHA1: return "sha1"
		case ApacheMD5: return "md5"
		case BCrypt: return "bcrypt"
		case Crypt: return "system crypt"
	}
	return "unknown"
}


// NewHTPasswd - Create a new HTPasswd with the given path to .htpasswd file.
func NewHTPasswd(htpath string) *HTPasswd {
	return &HTPasswd{path: htpath}
}

var bcryptPrefixRegexp *regexp.Regexp = regexp.MustCompile(`^\$2[ab]?y\$`)

// GetAuthCredentialType - Inspect an htpasswd file credential and guess the encryption algorithm used.
func GetAuthCredentialType(cred string) AuthType {
	if strings.HasPrefix(cred, "{SHA}") {
		return SHA1
	}
	if strings.HasPrefix(cred, "$apr1$") {
		return ApacheMD5
	}
	if bcryptPrefixRegexp.MatchString(cred) {
		return BCrypt
	}
	// There's just not a great way to distinguish between these next two...
	if len(cred) == 13 {
		return Crypt
	}
	return PlainText
}

// AuthenticateUser - Check a given user:password credential against the receiving HTPasswd's file.
func (htpasswd *HTPasswd) AuthenticateUser(user string, pwd string) (bool, error) {


	// Open the file.
	in, err := os.Open(htpasswd.path)
	if err != nil {
		return false, err
	}

	// Parse the contents of the standard .htpasswd until we hit the end or find a match.
	reader := csv.NewReader(in)
	reader.Comma = ':'
	reader.Comment = '#'
	reader.TrimLeadingSpace = true
	for entry, readerr := reader.Read(); entry != nil || readerr != nil; entry, readerr = reader.Read() {
		if readerr != nil {
			return false, readerr
		}
		if len(entry) == 0 {
			continue
		}
		if entry[0] == user {
			credential := entry[1]
			credType := GetAuthCredentialType(credential)
			switch(credType) {
				case SHA1: {
					sha := sha1.New()
					sha.Write([]byte(pwd))
					hash := base64.StdEncoding.EncodeToString(sha.Sum(nil))
					return entry[1][5:] == hash, nil
				}
				case ApacheMD5: {
					return false, errors.New(ApacheMD5.String()+" htpasswd hash function not yet supported")
				}
				case BCrypt: {
					err := bcrypt.CompareHashAndPassword([]byte(credential),[]byte(pwd))
					if err != nil {
						return false, err
					}
					return true, nil
				}
				case Crypt: {
					return false, errors.New(Crypt.String()+" htpasswd hash function not yet supported")
				}
				case PlainText: {
					if pwd == credential {
						return true, nil
					} 
					return false, AuthenticationFailureErr
				}
			}
		}
	}
	return false, AuthenticationFailureErr
}