[PATCH v4 1/3] mime node: Record depth-first part numbers

[Austin Clements]

This makes the part numbers readily accessible to formatters.
Hierarchical part numbering would be a more natural and efficient fit
for MIME and may be the way to go in the future, but depth-first
numbering maintains compatibility with what we currently do.
---
 mime-node.c      |   37 ++++++++++++++++++++++++++++++++++---
 notmuch-client.h |   14 +++++++++++++-
 2 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/mime-node.c b/mime-node.c
index 27077f7..025c537 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -112,6 +112,10 @@ mime_node_open (const void *ctx, notmuch_message_t *message,
     root->nchildren = 1;
     root->ctx = mctx;
 
+    root->part_num = 0;
+    root->next_child = 0;
+    root->next_part_num = 1;
+
     *root_out = root;
     return NOTMUCH_STATUS_SUCCESS;
 
@@ -137,7 +141,7 @@ _signature_validity_free (GMimeSignatureValidity **proxy)
 #endif
 
 static mime_node_t *
-_mime_node_create (const mime_node_t *parent, GMimeObject *part)
+_mime_node_create (mime_node_t *parent, GMimeObject *part)
 {
     mime_node_t *node = talloc_zero (parent, mime_node_t);
     GError *err = NULL;
@@ -150,6 +154,8 @@ _mime_node_create (const mime_node_t *parent, GMimeObject *part)
 	talloc_free (node);
 	return NULL;
     }
+    node->parent = parent;
+    node->part_num = node->next_part_num = -1;
 
     /* Deal with the different types of parts */
     if (GMIME_IS_PART (part)) {
@@ -267,9 +273,10 @@ _mime_node_create (const mime_node_t *parent, GMimeObject *part)
 }
 
 mime_node_t *
-mime_node_child (const mime_node_t *parent, int child)
+mime_node_child (mime_node_t *parent, int child)
 {
     GMimeObject *sub;
+    mime_node_t *node;
 
     if (!parent || child < 0 || child >= parent->nchildren)
 	return NULL;
@@ -287,7 +294,31 @@ mime_node_child (const mime_node_t *parent, int child)
 	INTERNAL_ERROR ("Unexpected GMimeObject type: %s",
 			g_type_name (G_OBJECT_TYPE (parent->part)));
     }
-    return _mime_node_create (parent, sub);
+    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;
+
+	/* Drop the const qualifier because these are internal fields
+	 * whose mutability doesn't affect the interface. */
+	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 *it = node;
+	    while (it && it->next_child == it->nchildren)
+		it = it->parent;
+	    if (it)
+		it->next_part_num = node->part_num + 1;
+	}
+    }
+
+    return node;
 }
 
 static mime_node_t *
diff --git a/notmuch-client.h b/notmuch-client.h
index 9c1d383..abfe5d3 100644
--- a/notmuch-client.h
+++ b/notmuch-client.h
@@ -297,6 +297,13 @@ typedef struct mime_node {
     /* The number of children of this part. */
     int nchildren;
 
+    /* The parent of this node or NULL if this is the root node. */
+    struct mime_node *parent;
+
+    /* The depth-first part number of this child if the MIME tree is
+     * being traversed in depth-first order, or -1 otherwise. */
+    int part_num;
+
     /* True if decryption of this part was attempted. */
     notmuch_bool_t decrypt_attempted;
     /* True if decryption of this part's child succeeded.  In this
@@ -324,6 +331,11 @@ typedef struct mime_node {
     /* Internal: For successfully decrypted multipart parts, the
      * decrypted part to substitute for the second child. */
     GMimeObject *decrypted_child;
+
+    /* Internal: The next child for depth-first traversal and the part
+     * number to assign it (or -1 if unknown). */
+    int next_child;
+    int next_part_num;
 } mime_node_t;
 
 /* Construct a new MIME node pointing to the root message part of
@@ -356,7 +368,7 @@ mime_node_open (const void *ctx, notmuch_message_t *message,
  * an error message on stderr).
  */
 mime_node_t *
-mime_node_child (const mime_node_t *parent, int child);
+mime_node_child (mime_node_t *parent, int child);
 
 /* Return the nth child of node in a depth-first traversal.  If n is
  * 0, returns node itself.  Returns NULL if there is no such part. */
-- 
1.7.7.3