/*
 * mal - simple command line mail client
 * 
 * Copyright (c) 2024 Jeremy Baxter.  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.
 * 3. Neither the name of the copyright holder nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * 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 REGENTS 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.
 */

module mal;

static import std.file;

import core.runtime : Runtime;

import std.conv     : to;
import std.getopt   : getopt, GetOptException;
import std.path     : baseName;
import std.stdio    : stderr, writeln;
import std.string   : fromStringz;
import std.typecons : No;

import std.net.curl    : CurlCode, SMTP, ThrowOnError;
import std.net.isemail : isEmail, EmailStatus;

import etc.c.curl : CurlError;

string   fromAddr;     /* [1] */
string   serverAddr;   /* -a */
string   fqdn;         /* -F */
string[] mailHeaders;  /* -H */
bool     useSmtps;     /* -k/-s */
string   messageFile;  /* -M */
string   message;      /* -m */
string   realName;     /* -n */
string   passPhrase;   /* -P */
string   serverPort;   /* -p */
string   subject;      /* -S */
string[] toAddrs;      /* -t */
string   authUser;     /* -u */
bool     showVersion;  /* -V */

int
main(string[] args)
{
	SMTP mail;
	EmailStatus fromStatus;
	string messageBuf, protocol;
	CurlCode err;

	fqdn = hostName() ~ ".local";
	mailHeaders = toAddrs = [];
	useSmtps = true;
	authUser = message = messageFile = passPhrase =
		realName = serverAddr = serverPort = subject = null;

	try {
		import std.getopt : config;

		void
		securityHandler(string opt) @safe
		{
			if (opt == "k") {
				useSmtps = false;
			} else {
				assert(opt == "s");
				useSmtps = true;
			}
		}

		getopt(args,
			config.bundling,
			config.caseSensitive,
			"a", &serverAddr,
			"F", &fqdn,
			"H", &mailHeaders,
			"k", &securityHandler,
			"M", &messageFile,
			"m", &message,
			"n", &realName,
			"P", &passPhrase,
			"p", &serverPort,
			"S", &subject,
			"s", &securityHandler,
			"t", &toAddrs,
			"u", &authUser,
			"V", &showVersion
		);
	} catch (GetOptException e) {
		import std.algorithm : startsWith;

		enforceDie(!e.msg.startsWith("Unrecognized option"),
			"unknown option " ~ extractOpt(e));
		enforceDie(!e.msg.startsWith("Missing value for argument"),
			"missing argument for option " ~ extractOpt(e));

		die(e.msg); /* catch-all */
	}

	if (showVersion) {
		writeln("mal version 1.0");
		return 0;
	}

	if (args.length != 2) {
		stderr.writeln(
`usage: mal [-ksV] [-a server] [-F fqdn] [-H header] [-n name]
           [-P passphrase] [-p port] [-S subject] [-t toaddress]
           [-u user] {-M file | -m message} fromaddress`);
		return 1;
	}

	enforceDie(message || messageFile,
		"a message has to be provided with -M or -m");
	enforceDie(!(message && messageFile),
		"flags -M and -m cannot both be supplied in one invocation");

	fromAddr = args[1];
	fromStatus = isEmail(fromAddr);
	enforceDie(fromStatus.valid, "invalid email address: %s", fromAddr);

	if (toAddrs.length == 0) {
		warn("warning: -t not supplied, sending to " ~ fromAddr);
		toAddrs = [fromAddr];
	}

	foreach (ref string addr; toAddrs) {
		enforceDie(isEmail(addr).valid,
			"invalid email address: %s", addr);

		addr = "<" ~ addr ~ ">";
	}

	/* https://todo.sr.ht/~jeremy/mal/2 */
	authUser = authUser ? authUser : fromAddr;
	protocol = useSmtps ? "smtps" : "smtp";
	serverAddr = serverAddr ? serverAddr : fromStatus.domainPart;
	serverPort = serverPort ? serverPort : useSmtps ? "465" : "587";

	if (!passPhrase) {
		warn("warning: -P not supplied, using empty passphrase");
		passPhrase = "";
	}
	if (!subject) {
		warn("warning: -S not supplied, using empty subject line");
		subject = "";
	}

	try {
		messageBuf =
			messageFile ? std.file.read(messageFile).to!string()
			: message;
	} catch (std.file.FileException e) {
		die(e.msg);
	}

	mail = SMTP(protocol ~ "://" ~
		serverAddr ~
		":" ~ serverPort ~
		"/" ~ fqdn);
	mail.mailFrom = "<" ~ fromAddr ~ ">";
	mail.mailTo = toAddrs.to!(const(char)[][]);
	mail.message = formHeaders() ~ messageBuf;
	mail.setAuthentication(authUser, passPhrase);
	err = mail.perform(No.throwOnError);
	
	if (err != CurlError.ok) {
		import etc.c.curl : curl_easy_strerror;

		/* known common errors */
		switch (err) {
		case CurlError.send_error:
			warn("Failed sending data to " ~ serverAddr);
			writeln("If the server uses STARTTLS, please try to connect");
			writeln("using regular SSL (-s) or using plain insecure SMTP");
			writeln("(-k). If none of those work, check the SMTP/SMTPS");
			writeln("port for your server and provide it with -p.");
			return 1;
		default:
			die(curl_easy_strerror(err).fromStringz().idup());
			break;
		}
	}

	return 0;
}

private string
formHeaders() @safe
{
	string headerBuf;

	headerBuf ~= "Content-Type: text/plain;charset=UTF-8\n";
	headerBuf ~= "Subject: " ~ subject ~ "\n";
	headerBuf ~= "From: " ~
		(realName ? `"` ~ realName ~ `" <` : "<") ~
		fromAddr ~ ">\n";

	headerBuf ~= "To: ";
	foreach (string addr; toAddrs) {
		headerBuf ~= addr ~ ", ";
	}
	headerBuf.length -= 2;
	headerBuf ~= "\n";

	foreach (string hdr; mailHeaders) {
		headerBuf ~= hdr ~ "\n";
	}
	
	return headerBuf ~ "\n";
}

private string
hostName()
{
	import core.stdc.stdlib : free, malloc;
	import core.sys.posix.unistd : gethostname;

	/* according to POSIX */
	enum HOST_NAME_MAX = 256;

	char *hp;
	string name;

	hp = cast(char *)malloc(HOST_NAME_MAX * char.sizeof);
	gethostname(hp, HOST_NAME_MAX);
	name = hp.fromStringz().idup();
	free(hp);

	return name;
}

private void
warn(string mesg)
{
	stderr.writeln(baseName(Runtime.args[0]) ~ ": " ~ mesg);
}

private void
die(string mesg)
{
	import core.stdc.stdlib : exit;

	warn(mesg);
	Runtime.terminate();
	exit(1);
}

private void
enforceDie(A...)(bool cond, string fmt, A a)
{
	import std.format : format;

	if (!cond)
		die(format(fmt, a));
}

private string
extractOpt(in GetOptException e) @safe
{
	import std.regex : matchFirst;

	return e.msg.matchFirst("-.")[0];
}