refactor(codemode): split runtime into focused interpreter modules (#36540)

packages/codemode/src/interpreter/scope.ts

@@ -0,0 +1,84 @@
+import { type AstNode, type Binding, InterpreterRuntimeError } from "./model.js"
+
+export class ScopeStack {
+  private readonly scopes: Array<Map<string, Binding>>
+
+  constructor(scopes: Array<Map<string, Binding>>) {
+    this.scopes = scopes
+  }
+
+  declare(name: string, value: unknown, mutable: boolean, node: AstNode): void {
+    const scope = this.current()
+
+    const existing = scope.get(name)
+    if (existing && existing.initialized !== false) {
+      throw new InterpreterRuntimeError(`Identifier '${name}' has already been declared.`, node)
+    }
+
+    scope.set(name, { mutable, value, initialized: true })
+  }
+
+  get(name: string, node: AstNode): unknown {
+    const binding = this.resolve(name)
+
+    if (!binding) {
+      throw new InterpreterRuntimeError(`Unknown identifier '${name}'.`, node).as("ReferenceError")
+    }
+
+    if (binding.initialized === false) {
+      throw new InterpreterRuntimeError(`Cannot access '${name}' before initialization.`, node).as("ReferenceError")
+    }
+
+    return binding.value
+  }
+
+  set(name: string, value: unknown, node: AstNode): unknown {
+    const binding = this.resolve(name)
+
+    if (!binding) {
+      throw new InterpreterRuntimeError(`Unknown identifier '${name}'.`, node).as("ReferenceError")
+    }
+
+    if (!binding.mutable) {
+      throw new InterpreterRuntimeError(`Cannot assign to constant '${name}'.`, node).as("TypeError")
+    }
+
+    binding.value = value
+    return value
+  }
+
+  resolve(name: string): Binding | undefined {
+    for (let index = this.scopes.length - 1; index >= 0; index -= 1) {
+      const scope = this.scopes[index]
+      const binding = scope?.get(name)
+
+      if (binding) {
+        return binding
+      }
+    }
+
+    return undefined
+  }
+
+  current(): Map<string, Binding> {
+    const scope = this.scopes[this.scopes.length - 1]
+
+    if (!scope) {
+      throw new InterpreterRuntimeError("Interpreter scope stack is empty.")
+    }
+
+    return scope
+  }
+
+  push(scope: Map<string, Binding> = new Map()): void {
+    this.scopes.push(scope)
+  }
+
+  pop(): void {
+    this.scopes.pop()
+  }
+
+  capture(): Array<Map<string, Binding>> {
+    return this.scopes.slice()
+  }
+}