import { test, expect } from "bun:test"
import { VM, toBytecode } from "#reef"

test("REPL mode - demonstrates PC reset problem", async () => {
  // Track how many times each line executes
  let line1Count = 0
  let line2Count = 0

  // Line 1: Set x = 5, track execution
  const line1 = toBytecode([
    ["LOAD", "trackLine1"],
    ["PUSH", 0],
    ["PUSH", 0],
    ["CALL"],
    ["POP"],
    ["PUSH", 5],
    ["STORE", "x"]
  ])

  const vm = new VM(line1, {
    trackLine1: () => { line1Count++; return null },
    trackLine2: () => { line2Count++; return null }
  })

  await vm.run()
  expect(vm.scope.get("x")).toEqual({ type: "number", value: 5 })
  expect(line1Count).toBe(1)
  expect(line2Count).toBe(0)

  // Line 2: Track execution, load x
  const line2 = toBytecode([
    ["LOAD", "trackLine2"],
    ["PUSH", 0],
    ["PUSH", 0],
    ["CALL"],
    ["POP"],
    ["LOAD", "x"]
  ])

  // Append line2 bytecode to VM (what a REPL would do)
  vm.instructions.push(...line2.instructions)
  for (const constant of line2.constants) {
    if (!vm.constants.includes(constant)) {
      vm.constants.push(constant)
    }
  }

  // Current behavior: run() resets PC to 0, re-executing everything
  await vm.run()

  // PROBLEM: Line 1 ran AGAIN (count is now 2, not 1)
  // This is the issue for REPL - side effects run multiple times
  expect(line1Count).toBe(2) // Ran twice! Should still be 1
  expect(line2Count).toBe(1) // This is correct

  // What we WANT for REPL:
  // - Only execute the NEW bytecode (line 2)
  // - line1Count should stay at 1
  // - line2Count should be 1
})

test("REPL mode - continue() executes only new bytecode", async () => {
  // Track how many times each line executes
  let line1Count = 0
  let line2Count = 0

  // Line 1: Set x = 5, track execution
  const line1 = toBytecode([
    ["LOAD", "trackLine1"],
    ["PUSH", 0],
    ["PUSH", 0],
    ["CALL"],
    ["POP"],
    ["PUSH", 5],
    ["STORE", "x"]
  ])

  const vm = new VM(line1, {
    trackLine1: () => { line1Count++; return null },
    trackLine2: () => { line2Count++; return null }
  })

  await vm.run()
  expect(vm.scope.get("x")).toEqual({ type: "number", value: 5 })
  expect(line1Count).toBe(1)
  expect(line2Count).toBe(0)

  // Line 2: Track execution, load x and add 10
  const line2 = toBytecode([
    ["LOAD", "trackLine2"],
    ["PUSH", 0],
    ["PUSH", 0],
    ["CALL"],
    ["POP"],
    ["LOAD", "x"],
    ["PUSH", 10],
    ["ADD"]
  ])

  // Append line2 bytecode to VM using the helper method
  vm.appendBytecode(line2)

  // SOLUTION: Use continue() instead of run() to resume from current PC
  await vm.continue()

  const result = vm.stack[vm.stack.length - 1]

  // SUCCESS: Line 1 only ran once, line 2 ran once
  expect(line1Count).toBe(1) // Still 1! Side effect didn't re-run
  expect(line2Count).toBe(1) // Ran once as expected
  expect(result).toEqual({ type: "number", value: 15 }) // 5 + 10
})