from tokens import *
from std import STD


def peek(inp):
    if len(inp) == 0:
        return None
    return inp[0]

def evaluate_expression(expr):
    if not expr.symbol.name in STD:
        raise Exception(f"no such symbol: {expr.symbol.name}")
    this_func = STD[expr.symbol.name]

    # try to match the signature
    in_sig = expr.in_sig()
    if in_sig in this_func:
        ret = this_func[expr.in_sig()].impl(*(expr.args))
        return ret

    # evaluate inner expressions, if possible/necessary
    for idx, arg in enumerate(expr.args):
        if arg.type_ == NebType.EXPR:
            expr.args[idx] = evaluate_expression(arg)
            return evaluate_expression(expr)

    raise Exception(f"'{expr.symbol.name}' called with unknown signature: '{expr.in_sig()}'")

def evaluate(items, pop):
    nxt = peek(items)
    if nxt is None:
        return pop
    elif isinstance(nxt, NebLiteral):
        return evaluate(items[1:], nxt)
    elif isinstance(nxt, NebSymbol):
        if not nxt.name in STD:
            raise Exception(f"no such symbol: '{nxt.name}'")
        this_func = STD[nxt.name]
        return evaluate(items[1:], this_func[list(this_func.keys())[0]].impl) # TODO show all
    elif isinstance(nxt, NebExpression):
        return evaluate(items[1:], evaluate_expression(nxt))
    else:
        raise Exception("expected a literal or an expression")