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#include "VM.h"
#include "Types.h"
namespace nt {
VM::VM(CursorManager& cursors) : cursors_(cursors) {
}
std::vector<std::string> VM::ResolveArgs(const std::vector<PathArg>& tmpl, Tuple* from) {
std::vector<std::string> resolved;
resolved.reserve(tmpl.size());
for (const auto& arg : tmpl) {
if (arg.kind == PathArg::Kind::Const) {
resolved.push_back(arg.name);
continue;
}
std::string val;
for (const auto& attr : from->attrs())
if (attr.name == arg.name) {
val = attr.value;
break;
}
resolved.push_back(std::move(val));
}
return resolved;
}
void VM::ResetInner(CursorManager::cursor* c, std::vector<std::string> args) {
c->args = std::move(args);
c->page.clear();
c->page_position = 0;
c->fetch_offset = 0;
c->exhausted = false;
}
void VM::Rewind(PlanNode* node, Tuple* outer) {
if (node == nullptr)
return;
switch (node->op) {
case Operation::FOL_OPERATION_SCAN:
ResetInner(node->scan_cursor, ResolveArgs(node->scan_args, outer));
break;
case Operation::FOL_OPERATION_PROJECT:
Rewind(node->left, outer);
break;
case Operation::FOL_OPERATION_TAKE:
node->take_count = 0;
Rewind(node->left, outer);
break;
case Operation::FOL_OPERATION_JOIN:
node->join_left = nullptr;
Rewind(node->left, outer);
Rewind(node->right, outer);
break;
case Operation::FOL_OPERATION_MATERIALIZE:
// Rewind the replay cursor only, and don't pass `outer` to the child.
// The point of this node is to reuse the cached tuples for every
// outer tuple, so it must not re-run or rebind what it cached.
node->mat_pos = 0;
break;
case Operation::FOL_OPERATION_RENAME:
Rewind(node->upstream, outer);
break;
case Operation::FOL_OPERATION_UNION:
node->current_node = node->nodes.begin();
for (auto& node : node->nodes)
Rewind(node, outer);
break;
}
}
Tuple* VM::MergeInto(PlanNode* node, Tuple* left, Tuple* right) {
std::vector<Attribute> merged;
for (const auto& a : left->attrs())
merged.push_back(a);
for (const auto& a : right->attrs())
merged.push_back(a);
node->join_buffer.emplace(std::move(merged));
return &*node->join_buffer;
}
Tuple* VM::Next(PlanNode* node) {
if (node == nullptr)
return nullptr;
switch (node->op) {
case Operation::FOL_OPERATION_SCAN:
return cursors_.Next(node->scan_cursor);
case Operation::FOL_OPERATION_PROJECT: {
Tuple* next = Next(node->left);
if (next == nullptr)
return nullptr;
std::vector<Attribute> projected;
for (const auto& attr : next->attrs()) {
if (node->project_attrs.find(attr.name) != node->project_attrs.end())
projected.push_back(attr);
}
node->project_buffer.emplace(std::move(projected));
return &*node->project_buffer;
}
case Operation::FOL_OPERATION_JOIN: {
while (true) {
again:
if (node->join_left == nullptr) {
node->join_left = Next(node->left);
if (node->join_left == nullptr) return nullptr;
Rewind(node->right, node->join_left);
}
Tuple* right = Next(node->right);
if (right != nullptr) {
for (auto &attr : node->join_attrs)
if ((*node->join_left)[attr] != (*right)[attr])
goto again;
return MergeInto(node, node->join_left, right);
}
node->join_left = nullptr;
}
}
case Operation::FOL_OPERATION_TAKE: {
if (node->take_count >= node->take_limit)
return nullptr;
Tuple* t = Next(node->left);
if (t)
++node->take_count;
return t;
}
case Operation::FOL_OPERATION_MATERIALIZE: {
if (!node->mat_done) {
// First scan: pull a tuple and keep our own copy. We rebuild it
// from attrs() rather than copying the Tuple, because a Tuple
// holds an iterator into its own map and a plain copy would leave
// that iterator dangling. The child also overwrites its output
// buffer on the next pull, so we cannot just keep its pointer.
Tuple* t = Next(node->left);
if (t != nullptr) {
std::vector<Attribute> attrs;
for (const auto& a : t->attrs())
attrs.push_back(a);
node->mat_buffer.emplace_back(std::move(attrs));
return &node->mat_buffer.back();
}
node->mat_done = true;
return nullptr; // child exhausted; do not fall into replay
}
// Later scans: hand back cached tuples until the cache runs out.
if (node->mat_pos < node->mat_buffer.size())
return &node->mat_buffer[node->mat_pos++];
return nullptr;
}
case Operation::FOL_OPERATION_RENAME: {
Tuple* t = Next(node->upstream);
if (!t)
return nullptr;
std::vector<Attribute> attrs;
for (const auto& a : t->attrs()) {
std::string name = a.name;
if (node->attrs.contains(name))
name = node->attrs[name];
Attribute new_attr { name, a.value };
attrs.push_back(new_attr);
}
delete t;
return new Tuple(attrs);
}
case Operation::FOL_OPERATION_UNION: {
if (node->current_node == node->nodes.end())
return nullptr;
Tuple* t = Next(*node->current_node);
if (!t) {
node->current_node++;
return Next(node);
}
return t;
}
}
return nullptr;
}
} // namespace nt
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