package base

import (
	"crypto/md5"
	"crypto/tls"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"os/user"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/pgio"
	"github.com/jackc/pgx/pgproto3"
)

const batchBufferSize = 4096

// PgError represents an error reported by the PostgreSQL server. See
// http://www.postgresql.org/docs/9.3/static/protocol-error-fields.html for
// detailed field description.
type PgError struct {
	Severity         string
	Code             string
	Message          string
	Detail           string
	Hint             string
	Position         int32
	InternalPosition int32
	InternalQuery    string
	Where            string
	SchemaName       string
	TableName        string
	ColumnName       string
	DataTypeName     string
	ConstraintName   string
	File             string
	Line             int32
	Routine          string
}

func (pe PgError) Error() string {
	return pe.Severity + ": " + pe.Message + " (SQLSTATE " + pe.Code + ")"
}

// DialFunc is a function that can be used to connect to a PostgreSQL server
type DialFunc func(network, addr string) (net.Conn, error)

// ErrTLSRefused occurs when the connection attempt requires TLS and the
// PostgreSQL server refuses to use TLS
var ErrTLSRefused = errors.New("server refused TLS connection")

type ConnConfig struct {
	Host          string // host (e.g. localhost) or path to unix domain socket directory (e.g. /private/tmp)
	Port          uint16 // default: 5432
	Database      string
	User          string // default: OS user name
	Password      string
	TLSConfig     *tls.Config // config for TLS connection -- nil disables TLS
	Dial          DialFunc
	RuntimeParams map[string]string // Run-time parameters to set on connection as session default values (e.g. search_path or application_name)
}

func (cc *ConnConfig) NetworkAddress() (network, address string) {
	// If host is a valid path, then address is unix socket
	if _, err := os.Stat(cc.Host); err == nil {
		network = "unix"
		address = cc.Host
		if !strings.Contains(address, "/.s.PGSQL.") {
			address = filepath.Join(address, ".s.PGSQL.") + strconv.FormatInt(int64(cc.Port), 10)
		}
	} else {
		network = "tcp"
		address = fmt.Sprintf("%s:%d", cc.Host, cc.Port)
	}

	return network, address
}

func (cc *ConnConfig) assignDefaults() error {
	if cc.User == "" {
		user, err := user.Current()
		if err != nil {
			return err
		}
		cc.User = user.Username
	}

	if cc.Port == 0 {
		cc.Port = 5432
	}

	if cc.Dial == nil {
		defaultDialer := &net.Dialer{KeepAlive: 5 * time.Minute}
		cc.Dial = defaultDialer.Dial
	}

	return nil
}

// PgConn is a low-level PostgreSQL connection handle. It is not safe for concurrent usage.
type PgConn struct {
	NetConn           net.Conn          // the underlying TCP or unix domain socket connection
	PID               uint32            // backend pid
	SecretKey         uint32            // key to use to send a cancel query message to the server
	parameterStatuses map[string]string // parameters that have been reported by the server
	TxStatus          byte
	Frontend          *pgproto3.Frontend

	Config ConnConfig

	batchBuf   []byte
	batchCount int32

	pendingReadyForQueryCount int32

	closed bool
}

func Connect(cc ConnConfig) (*PgConn, error) {
	err := cc.assignDefaults()
	if err != nil {
		return nil, err
	}

	pgConn := new(PgConn)
	pgConn.Config = cc

	pgConn.NetConn, err = cc.Dial(cc.NetworkAddress())
	if err != nil {
		return nil, err
	}

	pgConn.parameterStatuses = make(map[string]string)

	if cc.TLSConfig != nil {
		if err := pgConn.startTLS(cc.TLSConfig); err != nil {
			return nil, err
		}
	}

	pgConn.Frontend, err = pgproto3.NewFrontend(pgConn.NetConn, pgConn.NetConn)
	if err != nil {
		return nil, err
	}

	startupMsg := pgproto3.StartupMessage{
		ProtocolVersion: pgproto3.ProtocolVersionNumber,
		Parameters:      make(map[string]string),
	}

	// Copy default run-time params
	for k, v := range cc.RuntimeParams {
		startupMsg.Parameters[k] = v
	}

	startupMsg.Parameters["user"] = cc.User
	if cc.Database != "" {
		startupMsg.Parameters["database"] = cc.Database
	}

	if _, err := pgConn.NetConn.Write(startupMsg.Encode(nil)); err != nil {
		return nil, err
	}

	for {
		msg, err := pgConn.ReceiveMessage()
		if err != nil {
			return nil, err
		}

		switch msg := msg.(type) {
		case *pgproto3.BackendKeyData:
			pgConn.PID = msg.ProcessID
			pgConn.SecretKey = msg.SecretKey
		case *pgproto3.Authentication:
			if err = pgConn.rxAuthenticationX(msg); err != nil {
				return nil, err
			}
		case *pgproto3.ReadyForQuery:
			return pgConn, nil
		case *pgproto3.ParameterStatus:
			// handled by ReceiveMessage
		case *pgproto3.ErrorResponse:
			return nil, PgError{
				Severity:         msg.Severity,
				Code:             msg.Code,
				Message:          msg.Message,
				Detail:           msg.Detail,
				Hint:             msg.Hint,
				Position:         msg.Position,
				InternalPosition: msg.InternalPosition,
				InternalQuery:    msg.InternalQuery,
				Where:            msg.Where,
				SchemaName:       msg.SchemaName,
				TableName:        msg.TableName,
				ColumnName:       msg.ColumnName,
				DataTypeName:     msg.DataTypeName,
				ConstraintName:   msg.ConstraintName,
				File:             msg.File,
				Line:             msg.Line,
				Routine:          msg.Routine,
			}
		default:
			return nil, errors.New("unexpected message")
		}
	}
}

func (pgConn *PgConn) startTLS(tlsConfig *tls.Config) (err error) {
	err = binary.Write(pgConn.NetConn, binary.BigEndian, []int32{8, 80877103})
	if err != nil {
		return
	}

	response := make([]byte, 1)
	if _, err = io.ReadFull(pgConn.NetConn, response); err != nil {
		return
	}

	if response[0] != 'S' {
		return ErrTLSRefused
	}

	pgConn.NetConn = tls.Client(pgConn.NetConn, tlsConfig)

	return nil
}

func (c *PgConn) rxAuthenticationX(msg *pgproto3.Authentication) (err error) {
	switch msg.Type {
	case pgproto3.AuthTypeOk:
	case pgproto3.AuthTypeCleartextPassword:
		err = c.txPasswordMessage(c.Config.Password)
	case pgproto3.AuthTypeMD5Password:
		digestedPassword := "md5" + hexMD5(hexMD5(c.Config.Password+c.Config.User)+string(msg.Salt[:]))
		err = c.txPasswordMessage(digestedPassword)
	default:
		err = errors.New("Received unknown authentication message")
	}

	return
}

func (pgConn *PgConn) txPasswordMessage(password string) (err error) {
	msg := &pgproto3.PasswordMessage{Password: password}
	_, err = pgConn.NetConn.Write(msg.Encode(nil))
	return err
}

func hexMD5(s string) string {
	hash := md5.New()
	io.WriteString(hash, s)
	return hex.EncodeToString(hash.Sum(nil))
}

func (pgConn *PgConn) ReceiveMessage() (pgproto3.BackendMessage, error) {
	msg, err := pgConn.Frontend.Receive()
	if err != nil {
		return nil, err
	}

	switch msg := msg.(type) {
	case *pgproto3.ReadyForQuery:
		// Under normal circumstances pendingReadyForQueryCount will be > 0 when a
		// ReadyForQuery is received. However, this is not the case on initial
		// connection.
		if pgConn.pendingReadyForQueryCount > 0 {
			pgConn.pendingReadyForQueryCount -= 1
		}
		pgConn.TxStatus = msg.TxStatus
	case *pgproto3.ParameterStatus:
		pgConn.parameterStatuses[msg.Name] = msg.Value
	case *pgproto3.ErrorResponse:
		if msg.Severity == "FATAL" {
			// TODO - close pgConn
			return nil, errorResponseToPgError(msg)
		}
	}

	return msg, nil
}

// Close closes a connection. It is safe to call Close on a already closed
// connection.
func (pgConn *PgConn) Close() error {
	if pgConn.closed {
		return nil
	}
	pgConn.closed = true

	_, err := pgConn.NetConn.Write([]byte{'X', 0, 0, 0, 4})
	if err != nil {
		pgConn.NetConn.Close()
		return err
	}

	_, err = pgConn.NetConn.Read(make([]byte, 1))
	if err != io.EOF {
		pgConn.NetConn.Close()
		return err
	}

	return pgConn.NetConn.Close()
}

// ParameterStatus returns the value of a parameter reported by the server (e.g.
// server_version). Returns an empty string for unknown parameters.
func (pgConn *PgConn) ParameterStatus(key string) string {
	return pgConn.parameterStatuses[key]
}

// CommandTag is the result of an Exec function
type CommandTag string

// RowsAffected returns the number of rows affected. If the CommandTag was not
// for a row affecting command (e.g. "CREATE TABLE") then it returns 0.
func (ct CommandTag) RowsAffected() int64 {
	s := string(ct)
	index := strings.LastIndex(s, " ")
	if index == -1 {
		return 0
	}
	n, _ := strconv.ParseInt(s[index+1:], 10, 64)
	return n
}

// SendExec enqueues the execution of sql via the PostgreSQL simple query
// protocol. sql may contain multipe queries. Multiple queries will be processed
// within a single transation. It is only sent to the PostgreSQL server when
// Flush is called.
func (pgConn *PgConn) SendExec(sql string) {
	pgConn.batchBuf = appendQuery(pgConn.batchBuf, sql)
	pgConn.batchCount += 1
}

// appendQuery appends a PostgreSQL wire protocol query message to buf and returns it.
func appendQuery(buf []byte, query string) []byte {
	buf = append(buf, 'Q')
	buf = pgio.AppendInt32(buf, int32(len(query)+5))
	buf = append(buf, query...)
	buf = append(buf, 0)
	return buf
}

type PgResultReader struct {
	pgConn            *PgConn
	fieldDescriptions []pgproto3.FieldDescription
	rowValues         [][]byte
	commandTag        CommandTag
	err               error
	complete          bool
}

// GetResult returns a PgResultReader for the next result. If all results are
// consumed it returns nil. If an error occurs it will be reported on the
// returned PgResultReader.
func (pgConn *PgConn) GetResult() *PgResultReader {
	if pgConn.pendingReadyForQueryCount == 0 {
		return nil
	}

	return &PgResultReader{pgConn: pgConn}
}

func (rr *PgResultReader) NextRow() (present bool) {
	if rr.complete {
		return false
	}

	for {
		msg, err := rr.pgConn.ReceiveMessage()
		if err != nil {
			return false
		}

		switch msg := msg.(type) {
		case *pgproto3.RowDescription:
			rr.fieldDescriptions = msg.Fields
		case *pgproto3.DataRow:
			rr.rowValues = msg.Values
			return true
		case *pgproto3.CommandComplete:
			rr.commandTag = CommandTag(msg.CommandTag)
			rr.complete = true
			return false
		case *pgproto3.ErrorResponse:
			rr.err = errorResponseToPgError(msg)
			rr.complete = true
			return false
		}
	}
}

func (rr *PgResultReader) Value(c int) []byte {
	return rr.rowValues[c]
}

// Close consumes any remaining result data and returns the command tag or
// error.
func (rr *PgResultReader) Close() (CommandTag, error) {
	if rr.complete {
		return rr.commandTag, rr.err
	}

	for {
		msg, err := rr.pgConn.ReceiveMessage()
		if err != nil {
			rr.err = err
			rr.complete = true
			return rr.commandTag, rr.err
		}

		switch msg := msg.(type) {
		case *pgproto3.CommandComplete:
			rr.commandTag = CommandTag(msg.CommandTag)
			rr.complete = true
			return rr.commandTag, rr.err
		case *pgproto3.ErrorResponse:
			rr.err = errorResponseToPgError(msg)
			rr.complete = true
			return rr.commandTag, rr.err
		}
	}
}

// Flush sends the enqueued execs to the server.
func (pgConn *PgConn) Flush() error {
	defer pgConn.resetBatch()

	n, err := pgConn.NetConn.Write(pgConn.batchBuf)
	if err != nil {
		if n > 0 {
			// TODO - kill connection - we sent a partial message
		}
		return err
	}

	pgConn.pendingReadyForQueryCount += pgConn.batchCount
	return nil
}

func (pgConn *PgConn) resetBatch() {
	pgConn.batchCount = 0
	if len(pgConn.batchBuf) > batchBufferSize {
		pgConn.batchBuf = make([]byte, 0, batchBufferSize)
	} else {
		pgConn.batchBuf = pgConn.batchBuf[0:0]
	}
}

func errorResponseToPgError(msg *pgproto3.ErrorResponse) PgError {
	return PgError{
		Severity:         msg.Severity,
		Code:             msg.Code,
		Message:          msg.Message,
		Detail:           msg.Detail,
		Hint:             msg.Hint,
		Position:         msg.Position,
		InternalPosition: msg.InternalPosition,
		InternalQuery:    msg.InternalQuery,
		Where:            msg.Where,
		SchemaName:       msg.SchemaName,
		TableName:        msg.TableName,
		ColumnName:       msg.ColumnName,
		DataTypeName:     msg.DataTypeName,
		ConstraintName:   msg.ConstraintName,
		File:             msg.File,
		Line:             msg.Line,
		Routine:          msg.Routine,
	}
}