"""
Expression Evaluator -- Learn DAGs & State Machines
====================================================
CLI entry point and interactive REPL.

Usage:
  python main.py "3 + 4 * 2"                          # evaluate
  python main.py                                        # REPL mode
  python main.py --show-tokens --show-ast --trace "expr" # show internals
  python main.py --dot "3 + 4 * 2" | dot -Tpng -o ast.png
  python main.py --dot-fsm | dot -Tpng -o fsm.png
"""

import argparse
import sys

from tokenizer import tokenize, TokenError
from parser import Parser, ParseError
from evaluator import evaluate, evaluate_traced, EvalError
from visualize import ast_to_dot, fsm_to_dot, ast_to_text


def process_expression(expr, args):
    """Tokenize, parse, and evaluate a single expression."""
    try:
        tokens = tokenize(expr)
    except TokenError as e:
        _print_error(expr, e)
        return

    if args.show_tokens:
        print("\nTokens:")
        for tok in tokens:
            print(f"  {tok}")

    try:
        ast = Parser(tokens).parse()
    except ParseError as e:
        _print_error(expr, e)
        return

    if args.show_ast:
        print("\nAST (text tree):")
        print(ast_to_text(ast))

    if args.dot:
        print(ast_to_dot(ast))
        return  # dot output goes to stdout, skip numeric result

    if args.trace:
        try:
            result, steps = evaluate_traced(ast)
        except EvalError as e:
            print(f"Eval error: {e}")
            return
        print("\nEvaluation trace (topological order):")
        for step in steps:
            print(step)
        print(f"\nResult: {_format_result(result)}")
    else:
        try:
            result = evaluate(ast)
        except EvalError as e:
            print(f"Eval error: {e}")
            return
        print(_format_result(result))


def repl(args):
    """Interactive read-eval-print loop."""
    print("Expression Evaluator REPL")
    print("Type an expression, or 'quit' to exit.")
    flags = []
    if args.show_tokens:
        flags.append("--show-tokens")
    if args.show_ast:
        flags.append("--show-ast")
    if args.trace:
        flags.append("--trace")
    if flags:
        print(f"Active flags: {' '.join(flags)}")
    print()

    while True:
        try:
            line = input(">>> ").strip()
        except (EOFError, KeyboardInterrupt):
            print()
            break
        if line.lower() in ("quit", "exit", "q"):
            break
        if not line:
            continue
        process_expression(line, args)
        print()


def _print_error(expr, error):
    """Print an error with a caret pointing to the position."""
    print(f"Error: {error}")
    if hasattr(error, 'position') and error.position is not None:
        print(f"  {expr}")
        print(f"  {' ' * error.position}^")


def _format_result(v):
    """Format a numeric result: show as int when possible."""
    if isinstance(v, float) and v == int(v) and abs(v) < 1e15:
        return str(int(v))
    return str(v)


def main():
    arg_parser = argparse.ArgumentParser(
        description="Expression Evaluator -- learn DAGs and state machines",
        epilog="Examples:\n"
               "  python main.py '3 + 4 * 2'\n"
               "  python main.py --show-tokens --trace '-(3 + 4) ^ 2'\n"
               "  python main.py --dot '(2+3)*4' | dot -Tpng -o ast.png\n"
               "  python main.py --dot-fsm | dot -Tpng -o fsm.png",
        formatter_class=argparse.RawDescriptionHelpFormatter,
    )
    arg_parser.add_argument(
        "expression", nargs="?",
        help="Expression to evaluate (omit for REPL mode)",
    )
    arg_parser.add_argument(
        "--show-tokens", action="store_true",
        help="Display tokenizer output",
    )
    arg_parser.add_argument(
        "--show-ast", action="store_true",
        help="Display AST as indented text tree",
    )
    arg_parser.add_argument(
        "--trace", action="store_true",
        help="Show step-by-step evaluation trace",
    )
    arg_parser.add_argument(
        "--dot", action="store_true",
        help="Output AST as graphviz dot (pipe to: dot -Tpng -o ast.png)",
    )
    arg_parser.add_argument(
        "--dot-fsm", action="store_true",
        help="Output tokenizer FSM as graphviz dot",
    )

    args = arg_parser.parse_args()

    # Special mode: just print the FSM diagram and exit
    if args.dot_fsm:
        print(fsm_to_dot())
        return

    # REPL mode if no expression given
    if args.expression is None:
        repl(args)
    else:
        process_expression(args.expression, args)


if __name__ == "__main__":
    main()