/* notmuch - Not much of an email program, (just index and search)
 *
 * Copyright © 2009 Carl Worth
 * Copyright © 2009 Keith Packard
 *
 * 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/ .
 *
 * Authors: Carl Worth <cworth@cworth.org>
 *          Keith Packard <keithp@keithp.com>
 *          Austin Clements <aclements@csail.mit.edu>
 */

#include "notmuch-client.h"

/* Context that gets inherited from the root node. */
typedef struct mime_node_context {
    /* Per-message resources.  These are allocated internally and must
     * be destroyed. */
    FILE *file;
    GMimeStream *stream;
    GMimeParser *parser;
    GMimeMessage *mime_message;

    /* Context provided by the caller. */
    _notmuch_crypto_t *crypto;
} mime_node_context_t;

static int
_mime_node_context_free (mime_node_context_t *res)
{
    if (res->mime_message)
	g_object_unref (res->mime_message);

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

    if (res->stream)
	g_object_unref (res->stream);

    if (res->file)
	fclose (res->file);

    return 0;
}

notmuch_status_t
mime_node_open (const void *ctx, notmuch_message_t *message,
		_notmuch_crypto_t *crypto, mime_node_t **root_out)
{
    const char *filename = notmuch_message_get_filename (message);
    mime_node_context_t *mctx;
    mime_node_t *root;
    notmuch_status_t status;

    root = talloc_zero (ctx, mime_node_t);
    if (root == NULL) {
	fprintf (stderr, "Out of memory.\n");
	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
	goto DONE;
    }

    /* Create the tree-wide context */
    mctx = talloc_zero (root, mime_node_context_t);
    if (mctx == NULL) {
	fprintf (stderr, "Out of memory.\n");
	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
	goto DONE;
    }
    talloc_set_destructor (mctx, _mime_node_context_free);

    /* Fast path */
    mctx->file = fopen (filename, "r");
    if (! mctx->file) {
	/* Slow path - for some reason the first file in the list is
	 * not available anymore. This is clearly a problem in the
	 * database, but we are not going to let this problem be a
	 * show stopper */
	notmuch_filenames_t *filenames;
	for (filenames = notmuch_message_get_filenames (message);
	     notmuch_filenames_valid (filenames);
	     notmuch_filenames_move_to_next (filenames))
	{
	    filename = notmuch_filenames_get (filenames);
	    mctx->file = fopen (filename, "r");
	    if (mctx->file)
		break;
	}

	talloc_free (filenames);
	if (! mctx->file) {
	    /* Give up */
	    fprintf (stderr, "Error opening %s: %s\n", filename, strerror (errno));
		status = NOTMUCH_STATUS_FILE_ERROR;
		goto DONE;
	    }
	}

    mctx->stream = g_mime_stream_file_new (mctx->file);
    if (!mctx->stream) {
	fprintf (stderr, "Out of memory.\n");
	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
	goto DONE;
    }
    g_mime_stream_file_set_owner (GMIME_STREAM_FILE (mctx->stream), false);

    mctx->parser = g_mime_parser_new_with_stream (mctx->stream);
    if (!mctx->parser) {
	fprintf (stderr, "Out of memory.\n");
	status = NOTMUCH_STATUS_OUT_OF_MEMORY;
	goto DONE;
    }

    mctx->mime_message = g_mime_parser_construct_message (mctx->parser);
    if (!mctx->mime_message) {
	fprintf (stderr, "Failed to parse %s\n", filename);
	status = NOTMUCH_STATUS_FILE_ERROR;
	goto DONE;
    }

    mctx->crypto = crypto;

    /* Create the root node */
    root->part = GMIME_OBJECT (mctx->mime_message);
    root->envelope_file = message;
    root->nchildren = 1;
    root->ctx = mctx;

    root->parent = NULL;
    root->part_num = 0;
    root->next_child = 0;
    root->next_part_num = 1;

    *root_out = root;
    return NOTMUCH_STATUS_SUCCESS;

DONE:
    talloc_free (root);
    return status;
}

/* Signature list destructor (GMime 2.6) */
static int
_signature_list_free (GMimeSignatureList **proxy)
{
    g_object_unref (*proxy);
    return 0;
}

/* Set up signature list destructor (GMime 2.6) */
static void
set_signature_list_destructor (mime_node_t *node)
{
    GMimeSignatureList **proxy = talloc (node, GMimeSignatureList *);
    if (proxy) {
	*proxy = node->sig_list;
	talloc_set_destructor (proxy, _signature_list_free);
    }
}

/* Verify a signed mime node (GMime 2.6) */
static void
node_verify (mime_node_t *node, GMimeObject *part,
	     g_mime_3_unused(GMimeCryptoContext *cryptoctx))
{
    GError *err = NULL;

    node->verify_attempted = true;
    node->sig_list = g_mime_multipart_signed_verify
	(GMIME_MULTIPART_SIGNED (part), cryptoctx, &err);

    if (node->sig_list)
	set_signature_list_destructor (node);
    else
	fprintf (stderr, "Failed to verify signed part: %s\n",
		 err ? err->message : "no error explanation given");

    if (err)
	g_error_free (err);
}

/* Decrypt and optionally verify an encrypted mime node (GMime 2.6) */
static void
node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
			 g_mime_3_unused(GMimeCryptoContext *cryptoctx))
{
    GError *err = NULL;
    GMimeDecryptResult *decrypt_result = NULL;
    notmuch_message_t *message = NULL;

    if (GMIME_IS_PART (part) || /* must be inline */
	(GMIME_IS_MULTIPART_ENCRYPTED (part) && ! node->decrypted_child)) {
	for (mime_node_t *parent = node; parent; parent = parent->parent)
	    if (parent->envelope_file) {
		message = parent->envelope_file;
		break;
	    }

	node->decrypted_child = _notmuch_crypto_decrypt (&node->decrypt_attempted,
							 node->ctx->crypto->decrypt,
							 message,
							 cryptoctx, part, &decrypt_result, &err);
    }
    if (! node->decrypted_child) {
	fprintf (stderr, "Failed to decrypt part: %s\n",
		 err ? err->message : "no error explanation given");
	goto DONE;
    }


    if (decrypt_result) {
	node->decrypt_success = true;
	if (GMIME_IS_MULTIPART_ENCRYPTED (part)) {
	    /* Only check signatures on PGP/MIME messages, not inline
	       messages. To understand why, see
	       https://dkg.fifthhorseman.net/notes/inline-pgp-harmful/ */
	    node->verify_attempted = true;
	    node->sig_list = g_mime_decrypt_result_get_signatures (decrypt_result);
	    if (node->sig_list) {
		g_object_ref (node->sig_list);
		set_signature_list_destructor (node);
	    }
	}

#if HAVE_GMIME_SESSION_KEYS
	if (node->ctx->crypto->decrypt == NOTMUCH_DECRYPT_TRUE && message) {
	    notmuch_database_t *db = notmuch_message_get_database (message);
	    const char *sk = g_mime_decrypt_result_get_session_key (decrypt_result);
	    if (db && sk) {
		notmuch_status_t status;
		status = notmuch_message_add_property (message, "session-key", sk);
		if (status)
		    fprintf (stderr, "Failed to stash session key in the database (%d) %s\n",
			     status, notmuch_status_to_string (status));
	    }
	}
#endif
	g_object_unref (decrypt_result);
    }

 DONE:
    if (err)
	g_error_free (err);
}

static mime_node_t *
_mime_node_create (mime_node_t *parent, GMimeObject *part)
{
    mime_node_t *node = talloc_zero (parent, mime_node_t);
    GMimeCryptoContext *cryptoctx = NULL;

    /* Set basic node properties */
    node->part = part;
    node->ctx = parent->ctx;
    if (!talloc_reference (node, node->ctx)) {
	fprintf (stderr, "Out of memory.\n");
	talloc_free (node);
	return NULL;
    }
    node->parent = parent;
    node->part_num = node->next_part_num = -1;
    node->next_child = 0;

    /* Deal with the different types of parts */
    if (GMIME_IS_PART (part)) {
	node->nchildren = 0;
    } else if (GMIME_IS_MULTIPART (part)) {
	node->nchildren = g_mime_multipart_get_count (GMIME_MULTIPART (part));
    } else if (GMIME_IS_MESSAGE_PART (part)) {
	/* Promote part to an envelope and open it */
	GMimeMessagePart *message_part = GMIME_MESSAGE_PART (part);
	GMimeMessage *message = g_mime_message_part_get_message (message_part);
	node->envelope_part = message_part;
	node->part = GMIME_OBJECT (message);
	node->nchildren = 1;
    } else {
	fprintf (stderr, "Warning: Unknown mime part type: %s.\n",
		 g_type_name (G_OBJECT_TYPE (part)));
	talloc_free (node);
	return NULL;
    }

#if (GMIME_MAJOR_VERSION < 3)
    if ((GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt != NOTMUCH_DECRYPT_FALSE))
	|| (GMIME_IS_MULTIPART_SIGNED (part) && node->ctx->crypto->verify)) {
	GMimeContentType *content_type = g_mime_object_get_content_type (part);
	const char *protocol = g_mime_content_type_get_parameter (content_type, "protocol");
	notmuch_status_t status;
	status = _notmuch_crypto_get_gmime_ctx_for_protocol (node->ctx->crypto,
							     protocol, &cryptoctx);
	if (status) /* this is a warning, not an error */
	    fprintf (stderr, "Warning: %s (%s).\n", notmuch_status_to_string (status),
		     protocol ? protocol : "NULL");
	if (!cryptoctx)
	    return node;
    }
#endif

    /* Handle PGP/MIME parts */
    if (GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt != NOTMUCH_DECRYPT_FALSE)) {
	if (node->nchildren != 2) {
	    /* this violates RFC 3156 section 4, so we won't bother with it. */
	    fprintf (stderr, "Error: %d part(s) for a multipart/encrypted "
		     "message (must be exactly 2)\n",
		     node->nchildren);
	} else {
	    node_decrypt_and_verify (node, part, cryptoctx);
	}
    } else if (GMIME_IS_MULTIPART_SIGNED (part) && node->ctx->crypto->verify) {
	if (node->nchildren != 2) {
	    /* this violates RFC 3156 section 5, so we won't bother with it. */
	    fprintf (stderr, "Error: %d part(s) for a multipart/signed message "
		     "(must be exactly 2)\n",
		     node->nchildren);
	} else {
	    node_verify (node, part, cryptoctx);
	}
    }

    return node;
}

mime_node_t *
mime_node_child (mime_node_t *parent, int child)
{
    GMimeObject *sub;
    mime_node_t *node;

    if (!parent || !parent->part || child < 0 || child >= parent->nchildren)
	return NULL;

    if (GMIME_IS_MULTIPART (parent->part)) {
	if (child == 1 && parent->decrypted_child)
	    sub = parent->decrypted_child;
	else
	    sub = g_mime_multipart_get_part
		(GMIME_MULTIPART (parent->part), child);
    } else if (GMIME_IS_MESSAGE (parent->part)) {
	sub = g_mime_message_get_mime_part (GMIME_MESSAGE (parent->part));
    } else {
	/* This should have been caught by message_part_create */
	INTERNAL_ERROR ("Unexpected GMimeObject type: %s",
			g_type_name (G_OBJECT_TYPE (parent->part)));
    }
    node = _mime_node_create (parent, sub);

    if (child == parent->next_child && parent->next_part_num != -1) {
	/* We're traversing in depth-first order.  Record the child's
	 * depth-first numbering. */
	node->part_num = parent->next_part_num;
	node->next_part_num = node->part_num + 1;

	/* Prepare the parent for its next depth-first child. */
	parent->next_child++;
	parent->next_part_num = -1;

	if (node->nchildren == 0) {
	    /* We've reached a leaf, so find the parent that has more
	     * children and set it up to number its next child. */
	    mime_node_t *iter = node->parent;
	    while (iter && iter->next_child == iter->nchildren)
		iter = iter->parent;
	    if (iter)
		iter->next_part_num = node->part_num + 1;
	}
    }

    return node;
}

static mime_node_t *
_mime_node_seek_dfs_walk (mime_node_t *node, int *n)
{
    int i;

    if (*n == 0)
	return node;

    *n -= 1;
    for (i = 0; i < node->nchildren; i++) {
	mime_node_t *child = mime_node_child (node, i);
	mime_node_t *ret = _mime_node_seek_dfs_walk (child, n);
	if (ret)
	    return ret;

	talloc_free (child);
    }
    return NULL;
}

mime_node_t *
mime_node_seek_dfs (mime_node_t *node, int n)
{
    if (n < 0)
	return NULL;
    return _mime_node_seek_dfs_walk (node, &n);
}