feat(tree): add tree iterator

include/vieter_tree.h

@@ -9,7 +9,8 @@ typedef struct vieter_tree vieter_tree;
 typedef enum vieter_tree_error {
   vieter_tree_ok = 0,
   vieter_tree_already_present = 1,
-  vieter_tree_not_present = 2
+  vieter_tree_not_present = 2,
+  vieter_tree_iterator_done = 3
 } vieter_tree_error;
 
 /*
@@ -45,4 +46,25 @@ vieter_tree_error vieter_tree_remove(void **out, vieter_tree *tree,
  */
 uint64_t vieter_tree_size(vieter_tree *tree);
 
+/*
+ * An iterator that can be used to traverse a tree in-order.
+ */
+typedef struct vieter_tree_iterator vieter_tree_iterator;
+
+/*
+ * Allocate and initialize a new iterator from the given tree.
+ */
+vieter_tree_iterator *vieter_tree_iterator_from(vieter_tree *tree);
+
+/*
+ * Free an iterator.
+ */
+void vieter_tree_iterator_free(vieter_tree_iterator **ptp);
+
+/*
+ * Return the iterator's next element.
+ */
+vieter_tree_error vieter_tree_iterator_next(void **out,
+                                            vieter_tree_iterator *iter);
+
 #endif

src/tree/vieter_tree.c

@@ -1,11 +1,5 @@
-#include "vieter_tree_internal.h"
-#include "vieter_tree_node.h"
 #include "vieter_tree_balancing.h"
-
-struct vieter_tree {
-  uint64_t size;
-  vieter_tree_node *root;
-};
+#include "vieter_tree_internal.h"
 
 vieter_tree *vieter_tree_init() { return calloc(1, sizeof(vieter_tree)); }
 

src/tree/vieter_tree_internal.h

@@ -1,10 +1,22 @@
 #include "vieter_tree.h"
+#include "vieter_tree_node.h"
 
 #include <stdbool.h>
 
+struct vieter_tree {
+  uint64_t size;
+  vieter_tree_node *root;
+};
+
 /*
  * Inspect whether the tree is still a valid red-black-tree.
  *
  * @return true if valid, false otherwise.
  */
 bool vieter_tree_validate(vieter_tree *tree);
+
+struct vieter_tree_iterator {
+    vieter_tree_node *current_node;
+    bool started;
+    bool done;
+};

src/tree/vieter_tree_iterator.c

@@ -0,0 +1,49 @@
+#include "vieter_tree.h"
+#include "vieter_tree_internal.h"
+
+vieter_tree_iterator *vieter_tree_iterator_from(vieter_tree *tree) {
+  vieter_tree_iterator *iter = calloc(1, sizeof(vieter_tree_iterator));
+
+  // An empty tree's iterator will be done immediately
+  if (tree->size == 0) {
+    iter->started = true;
+    iter->done = true;
+
+    return iter;
+  }
+
+  iter->current_node = tree->root;
+
+  return iter;
+}
+
+vieter_tree_error vieter_tree_iterator_next(void **out,
+                                            vieter_tree_iterator *iter) {
+  if (iter->done) {
+    return vieter_tree_iterator_done;
+  }
+
+  if (!iter->started) {
+    while (iter->current_node->children[0] != NULL) {
+      iter->current_node = iter->current_node->children[0];
+    }
+
+    iter->started = true;
+  }
+
+  *out = iter->current_node->data;
+
+  iter->current_node = vieter_tree_node_next(iter->current_node);
+
+  if (iter->current_node == NULL) {
+    iter->done = true;
+  }
+
+  return vieter_tree_ok;
+}
+
+void vieter_tree_iterator_free(vieter_tree_iterator **ptp) {
+  free(*ptp);
+
+  *ptp = NULL;
+}

src/tree/vieter_tree_node.c

@@ -150,3 +150,22 @@ void vieter_tree_node_set(vieter_tree_node *node, vieter_tree_node_flag flag,
 bool vieter_tree_node_get(vieter_tree_node *node, vieter_tree_node_flag flag) {
   return (node->flags & flag) != 0;
 }
+
+vieter_tree_node *vieter_tree_node_next(vieter_tree_node *node) {
+  if (node->children[1] != NULL) {
+    node = node->children[1];
+
+    while (node->children[0] != NULL) {
+      node = node->children[0];
+    }
+
+    return node;
+  }
+
+  while (node->parent != NULL &&
+         vieter_tree_node_get(node, vieter_tree_node_right)) {
+    node = node->parent;
+  }
+
+  return node->parent;
+}

src/tree/vieter_tree_node.h

@@ -77,4 +77,10 @@ void vieter_tree_node_set_children(vieter_tree_node *parent, vieter_tree_node **
  */
 void vieter_tree_node_set_child(vieter_tree_node *parent, vieter_tree_node *child, bool right);
 
+/*
+ * Return the in-order successor of the given node, or NULL if it's the last
+ * node in the tree.
+ */
+vieter_tree_node *vieter_tree_node_next(vieter_tree_node *node);
+
 #endif

test/tree/test_tree.c

@@ -16,19 +16,30 @@ void test_insert() {
     vieter_tree *tree = vieter_tree_init();
 
     for (uint64_t i = 0; i < 250; i++) {
-        TEST_CHECK(vieter_tree_insert(tree, i, NULL) == vieter_tree_ok);
+        TEST_CHECK(vieter_tree_insert(tree, i, (void *)i) == vieter_tree_ok);
         TEST_SIZE(tree, i + 1);
         TEST_CHECK(vieter_tree_validate(tree));
     }
 
-    void *out;
+    vieter_tree_iterator *iter = vieter_tree_iterator_from(tree);
+
+    void *out = NULL;
 
     for (uint64_t i = 0; i < 250; i++) {
         TEST_CHECK(vieter_tree_search(&out, tree, i) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)i);
         TEST_CHECK(vieter_tree_insert(tree, i, NULL) == vieter_tree_already_present);
         TEST_CHECK(vieter_tree_search(&out, tree, i) == vieter_tree_ok);
+
+        out = NULL;
+
+        TEST_CHECK(vieter_tree_iterator_next(&out, iter) == vieter_tree_ok);
+        TEST_CHECK(out == (void *)i);
     }
 
+    TEST_CHECK(vieter_tree_iterator_next(&out, iter) == vieter_tree_iterator_done);
+
+    vieter_tree_iterator_free(&iter);
     vieter_tree_free(tree);
 }