#!/usr/bin/env python3
"""
MCP Debugger Demo Script
========================
This script demonstrates how an LLM would use mcp-debugger to find and fix
a bug in the swap_vars.py example.
This is designed to be recorded as a GIF/video for the README.
"""
import time
import sys
from pathlib import Path
# ANSI color codes for pretty output
class Colors:
BLUE = '\033[94m'
GREEN = '\033[92m'
YELLOW = '\033[93m'
RED = '\033[91m'
MAGENTA = '\033[95m'
CYAN = '\033[96m'
BOLD = '\033[1m'
UNDERLINE = '\033[4m'
END = '\033[0m'
def print_llm(message: str):
"""Print a message as if from the LLM"""
print(f"\n{Colors.BLUE}{Colors.BOLD}🤖 LLM:{Colors.END} {message}")
time.sleep(0.5)
def print_debugger(message: str):
"""Print a message as if from the debugger"""
print(f"{Colors.GREEN}🐛 Debugger:{Colors.END} {message}")
time.sleep(0.3)
def print_code(code: str, highlight_line: int = None):
"""Print code with optional line highlighting"""
lines = code.strip().split('\n')
print(f"\n{Colors.CYAN}📄 swap_vars.py:{Colors.END}")
for i, line in enumerate(lines, 1):
if i == highlight_line:
print(f"{Colors.YELLOW}{Colors.BOLD}{i:2d} →{Colors.END} {line}")
else:
print(f"{Colors.CYAN}{i:2d} |{Colors.END} {line}")
print()
def print_variables(vars_dict: dict):
"""Print variable values"""
print(f"{Colors.MAGENTA}📊 Variables:{Colors.END}")
for name, value in vars_dict.items():
print(f" {name} = {value}")
print()
def demo_title():
"""Print demo title"""
print("\n" + "="*60)
print(f"{Colors.BOLD}MCP Debugger Demo - Finding and Fixing a Python Bug{Colors.END}")
print("="*60)
time.sleep(1)
def main():
# The buggy code
buggy_code = """def swap_variables(a, b):
print(f"Initial values: a = {a}, b = {b}")
# Intentionally buggy swap logic
a = b # Bug: 'a' loses its original value here
b = a # Bug: 'b' gets the new value of 'a'
print(f"Swapped values: a = {a}, b = {b}")
return a, b
x = 10
y = 20
swapped_x, swapped_y = swap_variables(x, y)"""
demo_title()
# Step 1: LLM identifies the task
print_llm("I need to debug swap_vars.py to find why the swap function doesn't work correctly.")
time.sleep(1)
# Step 2: Create debug session
print_llm("Let me create a debug session for Python...")
print_debugger("✓ Debug session created: session-123")
time.sleep(1)
# Step 3: Show the code
print_llm("First, let me examine the code:")
print_code(buggy_code)
time.sleep(2)
# Step 4: Set breakpoint
print_llm("I'll set a breakpoint at line 4 where the swap happens:")
print_debugger("✓ Breakpoint set at line 4")
print_code(buggy_code, highlight_line=4)
time.sleep(1)
# Step 5: Run the script
print_llm("Now let's run the script and see what happens:")
print_debugger("⏸️ Paused at breakpoint (line 4)")
time.sleep(1)
# Step 6: Inspect variables before the bug
print_llm("Let me check the variable values at this point:")
print_variables({"a": 10, "b": 20})
time.sleep(1)
# Step 7: Step over
print_llm("I'll step over to the next line:")
print_debugger("⏩ Stepped to line 5")
print_code(buggy_code, highlight_line=5)
# Step 8: Inspect variables after first assignment
print_llm("Now let's check the variables again:")
print_variables({"a": 20, "b": 20})
# Step 9: Identify the bug
print_llm(f"{Colors.RED}{Colors.BOLD}Found the bug!{Colors.END} The value of 'a' was overwritten before being saved.")
print_llm("When we do 'a = b', we lose the original value of 'a'.")
print_llm("Then 'b = a' just copies the new value of 'a' (which is 20) back to 'b'.")
time.sleep(2)
# Step 10: Suggest fix
print(f"\n{Colors.GREEN}{Colors.BOLD}💡 Solution:{Colors.END}")
fixed_code = """def swap_variables(a, b):
print(f"Initial values: a = {a}, b = {b}")
# Correct swap using tuple unpacking
a, b = b, a
print(f"Swapped values: a = {a}, b = {b}")
return a, b"""
print_code(fixed_code)
print_llm("The fix is to use Python's tuple unpacking: 'a, b = b, a'")
print_llm("This swaps the values in a single atomic operation without losing data!")
# Step 11: Verify fix
print(f"\n{Colors.GREEN}{Colors.BOLD}✅ Verification:{Colors.END}")
print("Initial: x=10, y=20")
print("After swap: x=20, y=10")
print(f"{Colors.GREEN}Swap successful!{Colors.END}")
print("\n" + "="*60)
print(f"{Colors.BOLD}Demo Complete - Bug Fixed!{Colors.END}")
print("="*60 + "\n")
if __name__ == "__main__":
try:
main()
except KeyboardInterrupt:
print("\n\nDemo interrupted.")
sys.exit(0)
