"""
Finite State Machine
====================

API:
on_enter_<state>()
on_exit_<state>()

Machine.is_<state>()
Machine.to_<state>()
"""

from transitions import Machine


class Material(Machine):

    states = ['solid', 'liquid', 'gas', 'plasma']

    transitions = [
        ['melt', 'solid', 'liquid'],
        ['evaporate', 'liquid', 'gas'],
        ['sublimate', 'solid', 'gas'],
        ['ionize', 'gas', 'plasma']
    ]

    def __init__(self):
        Machine.__init__(
            self,
            states=Material.states,
            transitions=Material.transitions,
            initial='liquid'
        )

    def on_enter_gas(self):
        print('entering gas state')

    def on_exit_gas(self):
        print('exiting gas state')


if __name__ == '__main__':
    lump = Material()
    print('current state:', lump.state)
    lump.evaporate()
    print('current state:', lump.state)
    lump.ionize()
    print('current state:', lump.state)

    print('change state back to solid')
    lump.to_solid()
    print('is it in solid state?:', lump.is_solid())