refactor(main): refactor directory structuremain

1 files changed, 209 insertions, 0 deletions

diff --git a/source/tb_db/btree_impl.h b/source/tb_db/btree_impl.h
new file mode 100644
index 0000000..b7015bd
--- /dev/null
+++ b/source/tb_db/btree_impl.h
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+/**
+ * >> api notes
+ * >> by Abdellah El Morabit
+ *
+ * - creation of a btree happens when doing an insertion on an
+ *  empty btree where the root is null or nil
+ *
+ **/
+
+/* single header b-tree implementation by Abdellah El Morabit */
+#ifndef BTREE_H
+#define BTREE_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 btree_ORDER = 4;
+#endif
+#define BTREE_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
+{
+    s32     header_index; //- col number
+    s32     row_index;
+};
+
+typedef struct btree_node btree_node;
+struct btree_node
+{
+    // store the key values of the sub nodes? if they are leaves?
+    key keys[BTREE_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[BTREE_ORDER - 1];
+    btree_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
+    btree_node *children[BTREE_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 btree btree;
+struct btree
+{
+    // NOTE(nasr): make sure this always stays in memory
+    // so that initial fetch never requires a disk read
+    btree_node *root;
+};
+
+
+
+#ifdef BTREE_IMPLEMENTATION
+///////////////////////////////////////////////////////////////////////////////
+//- btree.c
+
+
+internal b32
+is_nil_btree_node(btree_node *node)
+{
+    // NOTE(nasr): looks like a useless function but could be usefull when we implement a nil_btree_node 
+    return (node == NULL);
+}
+
+// TODO(nasr): 1. splitting the tree when getting too big? (horizontally) 2. joining trees?
+
+internal b8 
+key_compare(key destination_key, key source_key)
+{
+    s32 source_index      = source_key.header_index      + source_key.row_index;
+    s32 destination_index = destination_key.header_index + destination_key.row_index;
+
+    if(destination_index > source_index) return 1;
+    else if(destination_index < source_index) return -1;
+    else return 0;
+}
+
+// NOTE(nasr): @return the index of the found element
+//- @param: start node could be the root node for all we care. but this enables optimizations in the future if we need them
+internal s32
+btree_find_ipos(key k, btree_node *start_node)
+{
+    s32 index = 0;
+    // scan right while the node's key at [index] is strictly less than k
+    while (index < start_node->key_count && key_compare(start_node->keys[index], k) < 0)
+    {
+        ++index;
+    }
+    return index;
+}
+
+// NOTE(nasr): nodes that get passed as parameters should've already been loaded into memory
+internal void *
+btree_search(btree_node *node, key key)
+{
+    s32 index = btree_find_ipos(key, node);
+
+    if (index < node->key_count && key_compare(node->keys[index], key) == 0)
+    {
+        return node->payload_per_key[index];
+    }
+    if (node->leaf)
+    {
+        return NULL;
+    }
+    return btree_search(node->children[index], key);
+}
+
+// TODO(nasr): split node when key_count == btree_ORDER - 1 (node is full)
+// -- each node has max btree_ORDER - 1 keys
+//
+internal void
+btree_insert(mem_arena *arena, btree *tree, key key, void *payload)
+{
+    if(is_nil_btree_node(tree->root)) 
+    {
+        tree->root = PushStructZero(arena, btree_node);
+        tree->root->leaf = 1;
+        tree->root->key_count = 0;
+    }
+
+    btree_node *current_node = tree->root;
+
+    if (current_node->leaf)
+    {
+        // find the insertion position and shift keys right to make room
+        //- after: but what is this. we are expecting a new key.but we are looking for 
+        //- its position in the tree is useless because it's non existent
+
+        s32 i = btree_find_ipos(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 < (BTREE_ORDER - 1))
+        {
+            current_node->key_count += 1;
+        }
+        else {
+            // TODO(nasr): creating a new branch / tree?
+            // make a seperate function for this
+            // NOTE(nasr): only split through the parent when one actually exists;
+            // root splits need to be handled separately (promote mid key, create two children)
+            if(current_node->parent != NULL)
+            {
+                s32 split_pos = current_node->parent->key_count / 2 - 1;
+                s32 updated_keycount_p = 0;
+                for(s32 index = 0; index <= split_pos; ++index)
+                {
+                    ++updated_keycount_p;
+                }
+                current_node->parent->key_count = updated_keycount_p;
+            }
+        }
+    }
+    // TODO(nasr): internal node case walk down then split on the way back up
+}
+
+
+internal void
+btree_write(btree *bt)
+{
+    unused(bt);
+#if 0
+    temp_arena *temp_arena = temp_arena_begin(arena);
+    btree_node *root = bt->root;
+
+    for(btree_node *bt = PushStruct(arena); root->next; next = root;)
+    {
+        
+    }
+
+    temp_arena_end(temp);
+#endif
+}
+
+// - load the entire db into memory.
+#if 0
+internal void
+btree_load(mem_arena *arena)
+{
+
+
+}
+#endif
+
+#endif /* BTREE_IMPLEMENTATION */
+#endif /* BTREE_H */