/* message.c - Utility functions for parsing an email message for notmuch.
 *
 * Copyright © 2009 Carl Worth
 *
 * 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 http://www.gnu.org/licenses/ .
 *
 * Author: Carl Worth <cworth@cworth.org>
 */

#include <stdarg.h>

#include "notmuch-private.h"

#include <gmime/gmime.h>

#include <glib.h> /* GHashTable */

struct _notmuch_message_file {
    /* File object */
    FILE *file;
    char *filename;

    /* Header storage */
    int restrict_headers;
    GHashTable *headers;

    GMimeStream *stream;
    GMimeParser *parser;
    GMimeMessage *message;
    notmuch_bool_t parsed;
};

static int
strcase_equal (const void *a, const void *b)
{
    return strcasecmp (a, b) == 0;
}

static unsigned int
strcase_hash (const void *ptr)
{
    const char *s = ptr;

    /* This is the djb2 hash. */
    unsigned int hash = 5381;
    while (s && *s) {
	hash = ((hash << 5) + hash) + tolower (*s);
	s++;
    }

    return hash;
}

static int
_notmuch_message_file_destructor (notmuch_message_file_t *message)
{
    if (message->headers)
	g_hash_table_destroy (message->headers);

    if (message->message)
	g_object_unref (message->message);

    if (message->parser)
	g_object_unref (message->parser);

    if (message->stream)
	g_object_unref (message->stream);
    else if (message->file) /* GMimeStream takes over the FILE* */
	fclose (message->file);

    return 0;
}

/* Create a new notmuch_message_file_t for 'filename' with 'ctx' as
 * the talloc owner. */
notmuch_message_file_t *
_notmuch_message_file_open_ctx (void *ctx, const char *filename)
{
    notmuch_message_file_t *message;

    message = talloc_zero (ctx, notmuch_message_file_t);
    if (unlikely (message == NULL))
	return NULL;

    /* only needed for error messages during parsing */
    message->filename = talloc_strdup (message, filename);
    if (message->filename == NULL)
	goto FAIL;

    talloc_set_destructor (message, _notmuch_message_file_destructor);

    message->file = fopen (filename, "r");
    if (message->file == NULL)
	goto FAIL;

    message->headers = g_hash_table_new_full (strcase_hash, strcase_equal,
					      free, g_free);
    if (message->headers == NULL)
	goto FAIL;

    return message;

  FAIL:
    fprintf (stderr, "Error opening %s: %s\n", filename, strerror (errno));
    notmuch_message_file_close (message);

    return NULL;
}

notmuch_message_file_t *
notmuch_message_file_open (const char *filename)
{
    return _notmuch_message_file_open_ctx (NULL, filename);
}

void
notmuch_message_file_close (notmuch_message_file_t *message)
{
    talloc_free (message);
}

void
notmuch_message_file_restrict_headersv (notmuch_message_file_t *message,
					va_list va_headers)
{
    char *header;

    if (message->parsed)
	INTERNAL_ERROR ("notmuch_message_file_restrict_headers called after parsing has started");

    while (1) {
	header = va_arg (va_headers, char*);
	if (header == NULL)
	    break;
	g_hash_table_insert (message->headers,
			     xstrdup (header), NULL);
    }

    message->restrict_headers = 1;
}

void
notmuch_message_file_restrict_headers (notmuch_message_file_t *message, ...)
{
    va_list va_headers;

    va_start (va_headers, message);

    notmuch_message_file_restrict_headersv (message, va_headers);
}

/*
 * gmime does not provide access to all headers, so we need to use the
 * parser header callback to gather them into a hash table.
 */
static void header_cb (unused(GMimeParser *parser), const char *header,
		       const char *value, unused(gint64 offset),
		       gpointer user_data)
{
    notmuch_message_file_t *message = (notmuch_message_file_t *) user_data;
    char *existing = NULL;
    notmuch_bool_t found;

    found = g_hash_table_lookup_extended (message->headers, header,
					  NULL, (gpointer *) &existing);
    if (! found && message->restrict_headers)
	return;

    if (existing == NULL) {
	/* No value, add one */
	char *decoded = g_mime_utils_header_decode_text (value);
	g_hash_table_insert (message->headers, xstrdup (header), decoded);
    } else if (strcasecmp (header, "received") == 0) {
	/* Concat all of the Received: headers we encounter. */
	char *combined, *decoded;
	size_t combined_size;

	decoded = g_mime_utils_header_decode_text (value);

	combined_size = strlen(existing) + strlen(decoded) + 2;
	combined = g_malloc (combined_size);
	snprintf (combined, combined_size, "%s %s", existing, decoded);
	g_free (decoded);
	g_hash_table_insert (message->headers, xstrdup (header), combined);
    }
}

notmuch_status_t
notmuch_message_file_parse (notmuch_message_file_t *message)
{
    static int initialized = 0;
    char from_buf[5];
    notmuch_bool_t is_mbox = FALSE;
    static notmuch_bool_t mbox_warning = FALSE;

    if (! initialized) {
	g_mime_init (GMIME_ENABLE_RFC2047_WORKAROUNDS);
	initialized = 1;
    }

    /* Is this mbox? */
    if (fread (from_buf, sizeof (from_buf), 1, message->file) == 1 &&
	strncmp (from_buf, "From ", 5) == 0)
	is_mbox = TRUE;
    rewind (message->file);

    message->stream = g_mime_stream_file_new (message->file);
    message->parser = g_mime_parser_new_with_stream (message->stream);
    g_mime_parser_set_scan_from (message->parser, is_mbox);
    g_mime_parser_set_header_regex (message->parser, ".*", header_cb,
				    (gpointer) message);

    message->message = g_mime_parser_construct_message (message->parser);
    if (! message->message)
	return NOTMUCH_STATUS_FILE_NOT_EMAIL;

    if (is_mbox) {
	if (!g_mime_parser_eos (message->parser)) {
	    /* This is a multi-message mbox. */
	    return NOTMUCH_STATUS_FILE_NOT_EMAIL;
	}
	/* For historical reasons, we support single-message mboxes,
	 * but this behavior is likely to change in the future, so
	 * warn. */
	if (!mbox_warning) {
	    mbox_warning = TRUE;
	    fprintf (stderr, "\
Warning: %s is an mbox containing a single message,\n\
likely caused by misconfigured mail delivery.  Support for single-message\n\
mboxes is deprecated and may be removed in the future.\n", message->filename);
	}
    }

    message->parsed = TRUE;

    return NOTMUCH_STATUS_SUCCESS;
}

/* return NULL on errors, empty string for non-existing headers */
const char *
notmuch_message_file_get_header (notmuch_message_file_t *message,
				 const char *header)
{
    const char *value = NULL;
    notmuch_bool_t found;

    /* the caller shouldn't ask for headers before parsing */
    if (! message->parsed)
	return NULL;

    found = g_hash_table_lookup_extended (message->headers, header,
					  NULL, (gpointer *) &value);

    /* the caller shouldn't ask for non-restricted headers */
    if (! found && message->restrict_headers)
	return NULL;

    return value ? value : "";
}