From 05a6616803af1af8b2e1ebe111dca479c201e25a Mon Sep 17 00:00:00 2001
From: jussisaurio <jussi.saurio@gmail.com>
Date: Sat, 17 Aug 2024 14:12:57 +0300
Subject: [PATCH] BytecodeGenerator struct

---
 core/translate/emitter.rs | 144 +++++++++++++++++++++++++-------------
 1 file changed, 94 insertions(+), 50 deletions(-)

diff --git a/core/translate/emitter.rs b/core/translate/emitter.rs
index a772165a6..e263a4ee0 100644
--- a/core/translate/emitter.rs
+++ b/core/translate/emitter.rs
@@ -807,64 +807,108 @@ impl Emitter for Operator {
     }
 }
 
-pub fn emit_program(
+pub struct BytecodeGenerator {
+    program: ProgramBuilder,
     database_header: Rc<RefCell<DatabaseHeader>>,
-    mut select_plan: Plan,
-) -> Result<Program> {
-    let mut program = ProgramBuilder::new();
-    let init_label = program.allocate_label();
-    let halt_label = program.allocate_label();
-    program.emit_insn_with_label_dependency(
-        Insn::Init {
-            target_pc: init_label,
-        },
-        init_label,
-    );
-    let start_offset = program.offset();
+    metadata: Metadata,
+    plan: Plan,
+}
 
-    let mut metadata = Metadata {
-        termination_labels: vec![halt_label],
-        next_row_labels: HashMap::new(),
-        rewind_labels: Vec::new(),
-        aggregation_start_registers: HashMap::new(),
-        sorts: HashMap::new(),
-        left_joins: HashMap::new(),
-    };
-
-    loop {
-        match select_plan.root_operator.step(
-            &mut program,
-            &mut metadata,
-            &select_plan.referenced_tables,
-        )? {
-            OpStepResult::Continue => {}
-            OpStepResult::ReadyToEmit => {
-                select_plan.root_operator.result_row(
-                    &mut program,
-                    &select_plan.referenced_tables,
-                    &mut metadata,
-                    None,
-                )?;
-            }
-            OpStepResult::Done => {
-                break;
-            }
+impl BytecodeGenerator {
+    pub fn new(plan: Plan, database_header: Rc<RefCell<DatabaseHeader>>) -> Self {
+        Self {
+            program: ProgramBuilder::new(),
+            database_header,
+            metadata: Metadata {
+                termination_labels: Vec::new(),
+                next_row_labels: HashMap::new(),
+                rewind_labels: Vec::new(),
+                aggregation_start_registers: HashMap::new(),
+                sorts: HashMap::new(),
+                left_joins: HashMap::new(),
+            },
+            plan,
         }
     }
 
-    program.resolve_label(halt_label, program.offset());
-    program.emit_insn(Insn::Halt);
+    fn prologue(&mut self) -> Result<(BranchOffset, BranchOffset, BranchOffset)> {
+        let init_label = self.program.allocate_label();
+        let halt_label = self.program.allocate_label();
+        self.metadata.termination_labels.push(halt_label);
 
-    program.resolve_label(init_label, program.offset());
-    program.emit_insn(Insn::Transaction);
+        self.program.emit_insn_with_label_dependency(
+            Insn::Init {
+                target_pc: init_label,
+            },
+            init_label,
+        );
 
-    program.emit_constant_insns();
-    program.emit_insn(Insn::Goto {
-        target_pc: start_offset,
-    });
+        let start_offset = self.program.offset();
 
-    program.resolve_deferred_labels();
-    Ok(program.build(database_header))
+        Ok((init_label, halt_label, start_offset))
+    }
+
+    fn epilogue(
+        &mut self,
+        init_label: BranchOffset,
+        halt_label: BranchOffset,
+        start_offset: BranchOffset,
+    ) -> Result<()> {
+        self.program
+            .resolve_label(halt_label, self.program.offset());
+        self.program.emit_insn(Insn::Halt);
+
+        self.program
+            .resolve_label(init_label, self.program.offset());
+        self.program.emit_insn(Insn::Transaction);
+
+        self.program.emit_constant_insns();
+        self.program.emit_insn(Insn::Goto {
+            target_pc: start_offset,
+        });
+
+        self.program.resolve_deferred_labels();
+
+        Ok(())
+    }
+
+    fn build(self) -> Result<Program> {
+        Ok(self.program.build(self.database_header))
+    }
+
+    pub fn generate(mut self) -> Result<Program> {
+        let (init_label, halt_label, start_offset) = self.prologue()?;
+
+        loop {
+            match self.plan.root_operator.step(
+                &mut self.program,
+                &mut self.metadata,
+                &self.plan.referenced_tables,
+            )? {
+                OpStepResult::Continue => {}
+                OpStepResult::ReadyToEmit => {
+                    self.plan.root_operator.result_row(
+                        &mut self.program,
+                        &self.plan.referenced_tables,
+                        &mut self.metadata,
+                        None,
+                    )?;
+                }
+                OpStepResult::Done => {
+                    break;
+                }
+            }
+        }
+
+        self.epilogue(init_label, halt_label, start_offset)?;
+
+        self.build()
+    }
+}
+
+pub fn emit_program(database_header: Rc<RefCell<DatabaseHeader>>, plan: Plan) -> Result<Program> {
+    let generator = BytecodeGenerator::new(plan, database_header);
+    generator.generate()
 }
 
 fn table_columns(