1 files changed, 165 insertions, 0 deletions

diff --git a/source/btree_impl.h b/source/btree_impl.h
new file mode 100644
index 0000000..8eb0723
--- /dev/null
+++ b/source/btree_impl.h
@@ -0,0 +1,165 @@
+/* single header b-tree implementation by Abdellah El Morabit */
+#ifndef B_TREE_H
+#define B_TREE_H
+
+// maximum height of the tree the lower the lower the lower amount
+// of disk reads which translates into faster?
+#if 0
+global_variable read_only s16 B_TREE_ORDER = 4;
+#endif
+#define B_TREE_ORDER  4
+
+//- NOTE(nasr): defining a key to improve sorting
+//  i think saying that a key is a combination of the column + row is a good way of appraoching this
+typedef struct key key;
+struct key
+{
+    string8 header;
+    s32     row;
+};
+
+typedef struct b_tree_node b_tree_node;
+struct b_tree_node
+{
+    // store the key values of the sub nodes? if they are leaves?
+    key keys[B_TREE_ORDER - 1];
+    // TODO(nasr): replace with something more generic?
+    // NOTE(nasr): cons of void * -> no type safety
+    // is there a way to still have some sort of that?
+    // size not variable
+    void *payload_per_key[B_TREE_ORDER - 1];
+    b_tree_node *parent;
+    // handle to store children faster than linked list
+    // because now we can iterate over the nodes instead of having cache misses
+    // when jumping through linked nodes
+    b_tree_node *children[B_TREE_ORDER];
+    // this shouldn't change things but could be a performance improvement on a bigger scale??
+    s32 *max_children;
+    // NOTE(nasr): reference count ::: check how many leaves are using this node
+    // also not needed for now because we don't free individual node because of arena allocator
+    // s32 *refc;
+    s32 key_count;
+    b32 leaf;
+
+
+    // NOTE(nasr): do we hold the reference to the arena? or do we pass is it as a reference? 
+    // this could solve memory location issues?
+};
+
+typedef struct b_tree b_tree;
+struct b_tree
+{
+    // NOTE(nasr): make sure this always stays in memory
+    // so that initial fetch never requires a disk read
+    b_tree_node *root;
+};
+
+#ifdef B_TREE_IMPLEMENTATION
+///////////////////////////////////////////////////////////////////////////////
+//- b_tree.c
+
+// TODO(nasr): 1. splitting the tree when getting too big? (horizontally) 2. joining trees?
+
+internal b_tree_node *
+btree_node_alloc(mem_arena *arena)
+{
+    b_tree_node *node = PushStructZero(arena, b_tree_node);
+    node->leaf = 1;
+    return node;
+}
+
+// NOTE(nasr): @return the index of the found element
+internal s32
+btree_node_find_pos(string8 value, b_tree_node *node)
+{
+    unused(value);
+    unused(node);
+
+#if 0
+    s32 i = 0;
+    for (; i < node->key_count && string8_cmp(node->keys[i], value) < 0; ++i);
+    return i;
+#endif
+
+    return 0;
+
+}
+
+internal void
+b_tree_create(mem_arena *arena, b_tree *tree)
+{
+    tree->root = btree_node_alloc(arena);
+    tree->root->leaf = 1;
+    tree->root->key_count = 0;
+}
+
+
+// NOTE(nasr): nodes that get passed as parameters should've already been loaded into memory
+internal void *
+b_tree_search(b_tree_node *node, string8 key)
+{
+    unused(node);
+    unused(key);
+
+#if 0
+    s32 i = btree_node_find_pos(key, node);
+
+    if (i < node->key_count && string8_cmp(node->keys[i], key) == 0)
+    {
+        return node->payload_per_key[i];
+    }
+    if (node->leaf)
+    {
+        return NULL;
+    }
+    return b_tree_search(node->children[i], key);
+#endif
+
+    return NULL;
+}
+
+
+// TODO(nasr): split node when key_count == B_TREE_ORDER - 1 (node is full)
+internal void
+b_tree_insert(b_tree *tree, string8 key, void *payload)
+{
+    unused(tree);
+    unused(key);
+    unused(payload);
+#if 0
+    b_tree_node *current_node = tree->root;
+
+    if (current_node->leaf)
+    {
+        // find the insertion position and shift keys right to make room
+        s32 i = btree_node_find_pos(key, current_node);
+        for (s32 j = current_node->key_count; j > i; --j)
+        {
+            current_node->keys[j]            = current_node->keys[j - 1];
+            current_node->payload_per_key[j] = current_node->payload_per_key[j - 1];
+        }
+        current_node->keys[i]            = key;
+        current_node->payload_per_key[i] = payload;
+
+        if(current_node->key_count < (B_TREE_ORDER - 1))
+        {
+            current_node->key_count         += 1;
+        }
+        else {
+            // TODO(nasr): creating a new branch / tree?
+            // make a seperate function for this
+        }
+    }
+    // TODO(nasr): internal node case walk down then split on the way back up
+#endif
+}
+
+internal void
+b_tree_write(b_tree *bt)
+{
+    // TODO(nasr): write the b_tree to disk
+    unused(bt);
+}
+
+#endif /* B_TREE_IMPLEMENTATION */
+#endif /* B_TREE_H */