"""
Ethereum Virtual Machine (EVM) Control Flow Instructions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. contents:: Table of Contents
    :backlinks: none
    :local:

Introduction
------------

Implementations of the EVM control flow instructions.
"""

from ethereum.base_types import U256, Uint

from ...vm.gas import GAS_BASE, GAS_HIGH, GAS_JUMPDEST, GAS_MID, charge_gas
from .. import Evm
from ..exceptions import InvalidJumpDestError
from ..stack import pop, push


def stop(evm: Evm) -> None:
    """
    Stop further execution of EVM code.

    Parameters
    ----------
    evm :
        The current EVM frame.
    """
    # STACK
    pass

    # GAS
    pass

    # OPERATION
    evm.running = False

    # PROGRAM COUNTER
    evm.pc += 1


def jump(evm: Evm) -> None:
    """
    Alter the program counter to the location specified by the top of the
    stack.

    Parameters
    ----------
    evm :
        The current EVM frame.

    """
    # STACK
    jump_dest = Uint(pop(evm.stack))

    # GAS
    charge_gas(evm, GAS_MID)

    # OPERATION
    if jump_dest not in evm.valid_jump_destinations:
        raise InvalidJumpDestError

    # PROGRAM COUNTER
    evm.pc = Uint(jump_dest)


def jumpi(evm: Evm) -> None:
    """
    Alter the program counter to the specified location if and only if a
    condition is true. If the condition is not true, then the program counter
    would increase only by 1.

    Parameters
    ----------
    evm :
        The current EVM frame.

    """
    # STACK
    jump_dest = Uint(pop(evm.stack))
    conditional_value = pop(evm.stack)

    # GAS
    charge_gas(evm, GAS_HIGH)

    # OPERATION
    if conditional_value == 0:
        destination = evm.pc + 1
    elif jump_dest not in evm.valid_jump_destinations:
        raise InvalidJumpDestError
    else:
        destination = jump_dest

    # PROGRAM COUNTER
    evm.pc = Uint(destination)


def pc(evm: Evm) -> None:
    """
    Push onto the stack the value of the program counter after reaching the
    current instruction and without increasing it for the next instruction.

    Parameters
    ----------
    evm :
        The current EVM frame.

    """
    # STACK
    pass

    # GAS
    charge_gas(evm, GAS_BASE)

    # OPERATION
    push(evm.stack, U256(evm.pc))

    # PROGRAM COUNTER
    evm.pc += 1


def gas_left(evm: Evm) -> None:
    """
    Push the amount of available gas (including the corresponding reduction
    for the cost of this instruction) onto the stack.

    Parameters
    ----------
    evm :
        The current EVM frame.

    """
    # STACK
    pass

    # GAS
    charge_gas(evm, GAS_BASE)

    # OPERATION
    push(evm.stack, U256(evm.gas_left))

    # PROGRAM COUNTER
    evm.pc += 1


def jumpdest(evm: Evm) -> None:
    """
    Mark a valid destination for jumps. This is a noop, present only
    to be used by `JUMP` and `JUMPI` opcodes to verify that their jump is
    valid.

    Parameters
    ----------
    evm :
        The current EVM frame.

    """
    # STACK
    pass

    # GAS
    charge_gas(evm, GAS_JUMPDEST)

    # OPERATION
    pass

    # PROGRAM COUNTER
    evm.pc += 1
