/*
 * Copyright (c) 2006-2017 Hypertriton, Inc. <http://www.hypertriton.com/>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>

#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <stdarg.h>
#include <errno.h>
#include <unistd.h>
#include <pwd.h>
#include <grp.h>
#include <ctype.h>
#include <netdb.h>

#include "mailprocd.h"

int smtpMasterPipe = -1;		/* Pipe to master process */
int smtpMsgsTot;			/* Total messages processed */

static int looping = 0;			/* Loop detected during DATA */
static int outofmem = 0;		/* Out of memory during DATA */
static int inHeader = 1;		/* Currently reading header */
static int inData = 0;			/* DATA phase */
static MPD_Message *msg = NULL;
static enum {
	ST_HELO,
	ST_MAIL_FROM,
	ST_RCPT_TO,
	ST_DATA,
	ST_DATA_IN,
	ST_QUIT
} state = ST_HELO;

static __inline__ void
WriteClient(const char *code, const char *ext, const char *s)
{
	fputs(code, stdout);
	fputc(' ', stdout);
	if (ext != NULL) {
		fputs(ext, stdout);
		fputc(' ', stdout);
	}
	fputs(s, stdout);
	fputc('\n', stdout);

	fflush(stdout);
}

/*
 * Remove whitespace/brackets from an address and convert to lowercase.
 * Destination must be able to hold ADDRESS_MAX characters.
 */
static int
GetAddress(char *dest, char *buf)
{
	char *c, *cStart;

	for (c = &buf[0]; *c == ' ' || *c == '<'; c++)
		;;
	cStart = c;

	for (; *c != '>' && *c != '\0'; c++)
		;;
	if (*c == '>')
		*c = '\0';

	if (Strlcpy(dest, cStart, ADDRESS_MAX) >= ADDRESS_MAX) {
		return (-1);
	}
	for (c = &dest[0]; *c != '\0'; c++) {
		*c = tolower((int)*c);
	}
	return (0);
}

static void
GoodBye(void)
{
	WriteClient("221", "2.0.0", "Bye");
	shutdown(fileno(stdin), SHUT_RDWR);
	shutdown(fileno(stdout), SHUT_RDWR);
}

/* Respond to a bad command or one issued out of sequence. */
static void
InvalidCmd(const char *expected, const char *cmd)
{
	if (expected != NULL && cmd != NULL) {
		syslog(LOG_ERR, "SMTP Error: Expected %s, got `%s'",
		    expected, cmd);
	}
	WriteClient("503", "5.5.1", "Invalid command");
	fflush(stdout);
}

static __inline__ void
ResetState(void)
{
	if (msg != NULL) {
		MPD_MessageFree(msg);
		msg = NULL;
	}
	looping = 0;
	outofmem = 0;
}

static void
ProcessMailLoop(MPD_Message *msg)
{
	MPD_Recipient *rcpt;

	ResetState();
	WriteClient("550", "5.4.6", "User mail-to-command loop detected!");
	/* XXX */
	TAILQ_FOREACH(rcpt, &msg->rcpts, rcpts) {
		syslog(LOG_ERR, "Mail loop with <%s>?", rcpt->addr);
		Debug("Mail loop detected under <%s>?", rcpt->addr);
	}
}

/* Process an incoming SMTP/LMTP session initiated by the MTA. */
int
SMTP_Main(enum smtp_prot prot)
{
	char *buf, *lbuf = NULL, *pbuf, *p;
	size_t len;
	
	setvbuf(stdout, NULL, _IOFBF, 0);

	WriteClient("220", NULL, (prot == ESMTP_PROTOCOL) ?
	    "localhost ESMTP" :
	    "localhost LMTP");

	while ((buf = Fgetln(stdin, &len)) != NULL) {
		if (buf[len-1] == '\n') {
			if (len > 1 && buf[len-2] == '\r') {
				len--;
			}
			buf[len-1] = '\0';
		} else {
			if ((lbuf = malloc(len+1)) == NULL) {
				MPD_SetErrorS("malloc line");
				goto fail;
			}
			memcpy(lbuf, buf, len);
			lbuf[len] = '\0';
			buf = lbuf;
		}

		if (!inData) {
			/*
			 * Commands allowed in any context other than DATA.
			 */
			if (strcasecmp(buf, "quit") == 0) {
				GoodBye();
				goto out;
			}
			if (strncasecmp(buf, "rset", 4) == 0) {
				ResetState();
				WriteClient("250", "2.0.0", "Ok");
				state = ST_MAIL_FROM;
				goto next_line;
			}
			if (strncasecmp(buf, "noop", 4) == 0) {
				WriteClient("250", "2.0.0", "Ok");
				goto next_line;
			}
			if (state != ST_HELO &&
			    (strncasecmp(buf, "helo", 4) == 0 ||
			     strncasecmp(buf, "ehlo", 4) == 0 ||
			     strncasecmp(buf, "lhlo", 4) == 0)) {
				/*
				 * Per RFC2821, we reset the state as
				 * if RSET had been issued.
				 */
				state = ST_HELO;
			}
		}
reprocess:
		switch (state) {
		case ST_HELO:
			if (strncasecmp(buf, "helo", 4) == 0) {
				WriteClient("221", NULL, "localhost");
				state = ST_MAIL_FROM;
			} else if (strncasecmp(buf, "ehlo", 4) == 0 ||
			           strncasecmp(buf, "lhlo", 4) == 0) {
				fputs("250-localhost\n"
				      "250-PIPELINING\n"
				      "250-8BITMIME\n"
			              "250-SIZE 104857600\n"
			              "250 ENHANCEDSTATUSCODES\n", stdout);
				fflush(stdout);
				state = ST_MAIL_FROM;
			} else if (strncasecmp(buf, "mail from", 9) == 0) {
				state = ST_MAIL_FROM;
				goto reprocess;
			} else {
				InvalidCmd("HELO/EHLO", buf);
			}
			break;
		case ST_MAIL_FROM:
			if (strncasecmp(buf, "mail from:", 10) == 0) {
				ResetState();
				if ((msg = MPD_MessageNew()) == NULL) {
					WriteClient("452", "4.3.2", "Out of memory");
					goto fail;
				}
				if ((msg->text = malloc(1)) == NULL) {
					WriteClient("452", "4.3.2", "Out of memory");
					MPD_SetErrorS("Out of memory");
					goto fail;
				}
				msg->text[0] = '\0';
				msg->text_len = 0;
				if (GetAddress(msg->mail_from, &buf[10]) == -1){
					WriteClient("503", "5.1.7", "Bad sender address");
					ResetState();
					state = ST_HELO;
					break;
				}
				WriteClient("250", "2.1.0", "Ok");
				state = ST_RCPT_TO;
			} else {
				InvalidCmd("MAIL FROM", buf);
			}
			break;
		case ST_RCPT_TO:
			if (strncasecmp(buf, "rcpt to:", 8) == 0) {
				MPD_Recipient *rcpt;

				if (msg == NULL) {
					InvalidCmd("FROM", buf);
					break;
				}
				if ((rcpt = MPD_MessageAddRecipient(msg, NULL))
				    == NULL) {
					WriteClient("452", "4.3.2", "Out of memory");
					MPD_SetErrorS("Out of memory");
					goto fail;
				}
				if (GetAddress(rcpt->addr, &buf[8]) == -1 ||
				    MPD_ParseRecipientParts(rcpt) == -1) {
					WriteClient("503", "5.1.3",
					            "Bad recipient address");
					ResetState();
					state = ST_HELO;
					break;
				}
				WriteClient("250", "2.1.5", "Ok");
				state = ST_DATA;
			} else {
				InvalidCmd("RCPT TO", buf);
			}
			break;
		case ST_DATA:
			if (msg == NULL) {
				WriteClient("503", "5.5.1",
				            "DATA without RCPT/TO");
				break;
			}
			if (strncasecmp(buf, "data", 4) == 0) {
				WriteClient("354", NULL, "End data with "
					                 "<CR><LF>.<CR><LF>");
				state = ST_DATA_IN;
				inData = 1;
				inHeader = 1;
			} else if (strncasecmp(buf, "mail from:", 10) == 0) {
				state = ST_MAIL_FROM;
				goto reprocess;
			} else if (strncasecmp(buf, "rcpt to:", 8) == 0) {
				state = ST_RCPT_TO;
				goto reprocess;
			} else {
				InvalidCmd("DATA/RCPT TO", buf);
			}
			break;
		case ST_DATA_IN:
			if (msg == NULL) {
				WriteClient("503", "5.5.1",
			                           "DATA without RCPT/TO");
				break;
			}
			if (buf[0] == '.' && buf[1] == '\0') {
				MPD_Recipient *rcpt;
				int nsuccess = 0;

				inHeader = 0;
				inData = 0;
				if (outofmem) {
					WriteClient("452", "4.3.2", "Out of memory");
					MPD_SetErrorS("Out of memory");
					goto fail;
				}
				if (looping) {
					ProcessMailLoop(msg);
					state = ST_QUIT;
					break;
				}
				msg->text[msg->text_len] = '\0';

				TAILQ_FOREACH(rcpt, &msg->rcpts, rcpts) {
					if (QMGR_Queue(msg, rcpt,
					    smtpMasterPipe) == 0) {
						nsuccess++;
					} else {
						syslog(LOG_ERR,
						    "QMGR Error: %s",
						    MPD_GetError());
					}
				}
				if (nsuccess > 0) {
					WriteClient("250", "2.0.0", "Ok");
				} else {
					WriteClient("452", "4.3.1",
					            "Mail system full");
				}
				ResetState();
				state = ST_QUIT;
				break;
			}
			if (outofmem || looping) {
				break;
			}
			if (buf[0] == '\0') {
				inHeader = 0;
			} else if (inHeader && buf[0] == 'X' &&
			    strncmp(buf, "X-Csoft-Pipe: ", 14) == 0) {
				MPD_Recipient *xRcpt;

				TAILQ_FOREACH(xRcpt, &msg->rcpts, rcpts) {
					if (strcasecmp(&buf[14], xRcpt->addr)
					    == 0) {
						looping = 1;
						break;
					}
				}
			} else if (inHeader && msg->ip[0] == '\0' &&
			    buf[0] == 'R' && !strncmp(buf, "Received:",9)) {
				if ((p = strchr(buf, '[')) != NULL &&
				    p[1] != '\0') {
					int nIP = 0;
					for (p++;
					    *p != ']' && *p != '\0' &&
					    nIP < IP_ADDRESS_MAX;
					    p++) {
						msg->ip[nIP++] = *p;
					}
					msg->ip[nIP] = '\0';
				}
			}
			pbuf = realloc(msg->text, msg->text_len+len+1);
			if (pbuf == NULL) {
				outofmem = 1;
				break;
			}
			msg->text = pbuf;
			buf[len-1] = '\n';
			memcpy(&msg->text[msg->text_len], buf, len);
			msg->text_len += len;
			break;
		case ST_QUIT:
			if (strncasecmp(buf, "quit", 4) == 0) {
				GoodBye();
				goto out;
			} else if (strncasecmp(buf, "mail from:", 10) == 0) {
				state = ST_MAIL_FROM;
				goto reprocess;
			} else if (strncasecmp(buf, "rcpt to:", 8) == 0) {
				state = ST_RCPT_TO;
				goto reprocess;
			} else {
				InvalidCmd(NULL, NULL);
				break;
			}
			break;
		default:
			Debug("SMTP invalid command: %s\n", buf);
			InvalidCmd(NULL, NULL);
			break;
		}
next_line:
		Free(lbuf);
		lbuf = NULL;
	}
	if (ferror(stdin)) {
		MPD_SetErrorS("Read error");
		goto fail;
	}
out:
	Free(lbuf);
	if (msg != NULL) { MPD_MessageFree(msg); }
	return (0);
fail:
	Free(lbuf);
	if (msg != NULL) { MPD_MessageFree(msg); }
	return (-1);
}