/* Copyright (C) 2020  C. McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <err.h>
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sysexits.h>
#include <time.h>
#include <unistd.h>

#include "archive.h"
#include "imap.h"

#define ENV_PASSWORD "BUBGER_IMAP_PASSWORD"

static const char *uidPath(uint32_t uid, const char *type) {
	static char buf[PATH_MAX];
	snprintf(buf, sizeof(buf), "UID/%" PRIu32 ".%s", uid, type);
	return buf;
}

static void flatten(struct List *flat, struct List nested) {
	for (size_t i = 0; i < nested.len; ++i) {
		if (nested.ptr[i].type == List) {
			flatten(flat, nested.ptr[i].list);
		} else {
			listPush(flat, nested.ptr[i]);
		}
	}
}

static enum Atom fetchNew(FILE *imap, struct List threads) {
	struct List uids = {0};
	flatten(&uids, threads);
	for (size_t i = uids.len - 1; i < uids.len; --i) {
		if (uids.ptr[i].type != Number) {
			errx(EX_PROTOCOL, "invalid thread UID");
		}
		uint32_t uid = uids.ptr[i].number;
		int error = 0;
		if (!error) error = access(uidPath(uid, "atom"), F_OK);
		if (!error) error = access(uidPath(uid, "html"), F_OK);
		if (!error) error = access(uidPath(uid, "mbox"), F_OK);
		if (!error) {
			uids.ptr[i] = uids.ptr[--uids.len];
		}
	}
	enum Atom tag = 0;
	if (!uids.len) goto done;

	int error = mkdir("UID", 0775);
	if (error && errno != EEXIST) err(EX_CANTCREAT, "UID");

	tag = atom("fetchNew");
	fprintf(imap, "%s UID FETCH ", Atoms[tag]);
	for (size_t i = 0; i < uids.len; ++i) {
		fprintf(imap, "%s%" PRIu32, (i ? "," : ""), uids.ptr[i].number);
	}
	fprintf(
		imap,
		" ("
		"UID ENVELOPE "
		"BODY[HEADER.FIELDS (" MBOX_HEADERS ")] BODY[TEXT]"
		")\r\n"
	);

done:
	listFree(uids);
	return tag;
}

static struct Address parseAddress(struct List list) {
	if (list.len < 4) {
		errx(EX_PROTOCOL, "missing address structure fields");
	}
	struct Address addr = {0};
	if (list.ptr[0].type == String) {
		// TODO: Decode UTF-8 in name.
		addr.name = strdup(list.ptr[0].string);
		if (!addr.name) err(EX_OSERR, "strdup");
	}
	if (list.ptr[2].type == String) addr.mailbox = list.ptr[2].string;
	if (list.ptr[3].type == String) addr.host = list.ptr[3].string;
	return addr;
}

static struct AddressList parseAddressList(struct List list) {
	struct Address *addrs = calloc(list.len, sizeof(*addrs));
	if (!addrs) err(EX_OSERR, "calloc");
	for (size_t i = 0; i < list.len; ++i) {
		if (list.ptr[i].type != List) {
			errx(EX_PROTOCOL, "invalid address field");
		}
		addrs[i] = parseAddress(list.ptr[i].list);
	}
	return (struct AddressList) { list.len, addrs };
}

static char *parseID(char *id) {
	size_t len = strlen(id);
	if (id[0] != '<' || !len || id[len - 1] != '>') {
		errx(EX_PROTOCOL, "invalid message ID");
	}
	id[len - 1] = '\0';
	return &id[1];
}

static struct Envelope parseEnvelope(struct List list) {
	enum {
		Date, Subject, From, Sender, ReplyTo,
		To, Cc, Bcc, InReplyTo, MessageID,
		EnvelopeLen,
	};
	if (list.len < EnvelopeLen) {
		errx(EX_PROTOCOL, "missing envelope structure fields");
	}
	struct Envelope envelope = {0};

	if (list.ptr[Date].type != String) {
		errx(EX_PROTOCOL, "invalid envelope date field");
	}
	const char *date = list.ptr[Date].string;
	date = strptime(date, "%a, %e %b %Y %H:%M:%S %z", &envelope.date);
	if (!date) errx(EX_PROTOCOL, "invalid envelope date format");

	if (list.ptr[Subject].type != String) {
		errx(EX_PROTOCOL, "invalid envelope subject field");
	}
	// TODO: Decode UTF-8 in subject.
	envelope.subject = strdup(list.ptr[Subject].string);
	if (!envelope.subject) err(EX_OSERR, "strdup");

	for (size_t i = From; i <= Bcc; ++i) {
		if (list.ptr[i].type == List) continue;
		if (list.ptr[i].type == Atom && list.ptr[i].atom == AtomNil) {
			list.ptr[i].type = List;
			list.ptr[i].list = (struct List) {0};
			continue;
		}
		errx(EX_PROTOCOL, "invalid envelope address field");
	}
	for (size_t i = From; i <= ReplyTo; ++i) {
		if (!list.ptr[i].list.len || list.ptr[i].list.ptr[0].type != List) {
			errx(EX_PROTOCOL, "invalid envelope address field");
		}
	}
	envelope.from = parseAddress(list.ptr[From].list.ptr[0].list);
	envelope.sender = parseAddress(list.ptr[Sender].list.ptr[0].list);
	envelope.replyTo = parseAddress(list.ptr[ReplyTo].list.ptr[0].list);
	envelope.to = parseAddressList(list.ptr[To].list);
	envelope.cc = parseAddressList(list.ptr[Cc].list);
	envelope.bcc = parseAddressList(list.ptr[Bcc].list);

	if (list.ptr[InReplyTo].type == String) {
		envelope.inReplyTo = parseID(list.ptr[InReplyTo].string);
	}
	if (list.ptr[MessageID].type != String) {
		errx(EX_PROTOCOL, "invalid envelope message-id field");
	}
	envelope.messageID = parseID(list.ptr[MessageID].string);

	return envelope;
}

static void exportMessage(struct List items) {
	static enum Atom AtomUID, AtomEnvelope, AtomBody;
	static enum Atom AtomHeaderFields, AtomText;
	if (!AtomUID) AtomUID = atom("UID");
	if (!AtomEnvelope) AtomEnvelope = atom("ENVELOPE");
	if (!AtomBody) AtomBody = atom("BODY");
	if (!AtomHeaderFields) AtomHeaderFields = atom("HEADER.FIELDS");
	if (!AtomText) AtomText = atom("TEXT");

	uint32_t uid = 0;
	struct Envelope envelope = {0};
	char *header = NULL;
	char *body = NULL;

	for (size_t i = 0; i + 1 < items.len; i += 2) {
		enum Atom name;
		if (items.ptr[i].type == Atom) {
			name = items.ptr[i].atom;
		} else if (
			items.ptr[i].type == List &&
			items.ptr[i].list.len &&
			items.ptr[i].list.ptr[0].type == Atom
		) {
			name = items.ptr[i].list.ptr[0].atom;
		} else {
			errx(EX_PROTOCOL, "invalid data item name");
		}

		if (name == AtomBody) {
			i--;
			continue;
		} else if (name == AtomUID) {
			if (items.ptr[i + 1].type != Number) {
				errx(EX_PROTOCOL, "invalid UID data item value");
			}
			uid = items.ptr[i + 1].number;
		} else if (name == AtomEnvelope) {
			if (items.ptr[i + 1].type != List) {
				errx(EX_PROTOCOL, "invalid ENVELOPE data item value");
			}
			envelope = parseEnvelope(items.ptr[i + 1].list);
		} else if (name == AtomHeaderFields) {
			if (items.ptr[i + 1].type != String) {
				errx(EX_PROTOCOL, "invalid BODY[HEADER.FIELDS] data item value");
			}
			header = items.ptr[i + 1].string;
		} else if (name == AtomText) {
			if (items.ptr[i + 1].type != String) {
				errx(EX_PROTOCOL, "invalid BODY[TEXT] data item value");
			}
			body = items.ptr[i + 1].string;
		}
	}

	if (!uid) errx(EX_PROTOCOL, "missing UID data item");
	if (!envelope.subject) errx(EX_PROTOCOL, "missing ENVELOPE data item");
	if (!header) errx(EX_PROTOCOL, "missing BODY[HEADER.FIELDS] data item");
	if (!body) errx(EX_PROTOCOL, "missing BODY[TEXT] data item");

	const char *path;
	FILE *file;
	int error;

	path = uidPath(uid, "mbox");
	file = fopen(path, "w");
	if (!file) err(EX_CANTCREAT, "%s", path);
	error = mboxFrom(file)
		|| mboxHeader(file, header)
		|| mboxBody(file, body)
		|| fclose(file);
	if (error) err(EX_IOERR, "%s", path);

	path = uidPath(uid, "html");
	file = fopen(path, "w");
	if (!file) err(EX_CANTCREAT, "%s", path);
	error = htmlEnvelope(file, &envelope)
		|| fclose(file);
	if (error) err(EX_IOERR, "%s", path);

	envelopeFree(envelope);
}

static void checkValidity(uint32_t validity) {
	FILE *file = fopen("UIDVALIDITY", "r");
	if (file) {
		uint32_t previous;
		int n = fscanf(file, "%" SCNu32, &previous);
		if (n < 1) errx(EX_DATAERR, "invalid UIDVALIDITY file");

		if (validity != previous) {
			errx(EX_TEMPFAIL, "UIDVALIDITY changed; fresh export required");
		}

	} else {
		FILE *file = fopen("UIDVALIDITY", "w");
		if (!file) err(EX_CANTCREAT, "UIDVALIDITY");

		int n = fprintf(file, "%" PRIu32 "\n", validity);
		if (n < 0) err(EX_IOERR, "UIDVALIDITY");

		int error = fclose(file);
		if (error) err(EX_IOERR, "UIDVALIDITY");
	}
}

int main(int argc, char *argv[]) {
	const char *host = NULL;
	const char *port = "imaps";
	const char *user = NULL;
	const char *passPath = NULL;

	const char *mailbox = "Archive";
	const char *algo = "REFERENCES";
	const char *search = "ALL";

	const char *title = NULL;
	const char *headPath = NULL;

	for (int opt; 0 < (opt = getopt(argc, argv, "C:a:h:p:s:t:vw:"));) {
		switch (opt) {
			break; case 'C': {
				int error = chdir(optarg);
				if (error) err(EX_NOINPUT, "%s", optarg);
			}
			break; case 'a': algo = optarg;
			break; case 'h': headPath = optarg;
			break; case 'p': port = optarg;
			break; case 's': search = optarg;
			break; case 't': title = optarg;
			break; case 'v': imapVerbose = true;
			break; case 'w': passPath = optarg;
		}
	}
	if (optind < argc) host = argv[optind++];
	if (optind < argc) user = argv[optind++];
	if (optind < argc) mailbox = argv[optind++];

	if (!host) errx(EX_USAGE, "host required");
	if (!user) errx(EX_USAGE, "user required");
	if (!title) title = mailbox;

	char *pass = NULL;
	if (passPath) {
		FILE *file = fopen(passPath, "r");
		if (!file) err(EX_NOINPUT, "%s", passPath);

		size_t cap = 0;
		ssize_t len = getline(&pass, &cap, file);
		if (len < 0) err(EX_IOERR, "%s", passPath);
		if (len && pass[len - 1] == '\n') pass[len - 1] = '\0';
		fclose(file);
	} else {
		pass = getenv(ENV_PASSWORD);
		if (!pass) errx(EX_CONFIG, ENV_PASSWORD " unset");
	}

	enum Atom login = 0;
	enum Atom examine = atom("EXAMINE");
	enum Atom thread = atom("THREAD");
	enum Atom export = 0;

	FILE *imap = imapOpen(host, port);
	for (struct Resp resp; resp = imapResp(imap), resp.resp != AtomBye;) {
		if (resp.resp == AtomNo || resp.resp == AtomBad) {
			errx(EX_CONFIG, "%s %s", Atoms[resp.resp], resp.text);
		}

		if (!login) {
			login = atom("login");
			fprintf(
				imap, "%s LOGIN \"%s\" \"%s\"\r\n",
				Atoms[login], user, pass
			);
		}

		if (resp.tag == login) {
			fprintf(imap, "%s EXAMINE \"%s\"\r\n", Atoms[examine], mailbox);
		}

		if (
			resp.resp == AtomOk &&
			resp.code.len > 1 &&
			resp.code.ptr[0].type == Atom &&
			resp.code.ptr[0].atom == AtomUIDValidity
		) {
			if (resp.code.ptr[1].type != Number) {
				errx(EX_PROTOCOL, "invalid UIDVALIDITY");
			}
			checkValidity(resp.code.ptr[1].number);
		}

		if (resp.tag == examine) {
			fprintf(
				imap, "%s UID THREAD %s UTF-8 %s\r\n",
				Atoms[thread], algo, search
			);
		}

		if (resp.resp == thread) {
			if (!resp.data.len) {
				errx(EX_TEMPFAIL, "no messages matching %s", search);
			}
			export = fetchNew(imap, resp.data);
		}

		if (export && resp.resp == AtomFetch) {
			if (!resp.data.len || resp.data.ptr[0].type != List) {
				errx(EX_PROTOCOL, "invalid FETCH data");
			}
			exportMessage(resp.data.ptr[0].list);
		}

		respFree(resp);
	}
	fclose(imap);
}