# first import everything we will need for the scheduling
import astropy.units as u
from astropy.time import Time
from astroplan import (Observer, FixedTarget, ObservingBlock, Transitioner, PriorityScheduler,
                       Schedule)
from astroplan.constraints import AtNightConstraint, AirmassConstraint, TimeConstraint
from astroplan.plots import plot_schedule_airmass
import matplotlib.pyplot as plt

# Now we define the targets, observer, start time, and end time of the schedule.
deneb = FixedTarget.from_name('Deneb')
m13 = FixedTarget.from_name('M13')

noon_before = Time('2016-07-06 19:00')
noon_after = Time('2016-07-07 19:00')
apo = Observer.at_site('apo')

# Then define the constraints (global and specific) and make a list of the
# observing blocks that you want scheduled
global_constraints = [AirmassConstraint(max = 3, boolean_constraint = False),
                      AtNightConstraint.twilight_civil()]
# defining the read-out time, exposure duration and number of exposures
read_out = 20 * u.second
deneb_exp = 60*u.second
m13_exp = 100*u.second
n = 16
blocks = []
first_half_night = TimeConstraint(Time('2016-07-07 02:00'), Time('2016-07-07 08:00'))
for priority, bandpass in enumerate(['B', 'G', 'R']):
    # We want each filter to have separate priority (so that target
    # and reference are both scheduled)
    b = ObservingBlock.from_exposures(deneb, priority, deneb_exp, n, read_out,
                                        configuration = {'filter': bandpass},
                                        constraints = [first_half_night])
    blocks.append(b)
    b = ObservingBlock.from_exposures(m13, priority, m13_exp, n, read_out,
                                        configuration = {'filter': bandpass},
                                        constraints = [first_half_night])
    blocks.append(b)
# add the new target's block
alpha_cen = FixedTarget.from_name('Alpha Centauri A')
blocks.append(ObservingBlock(alpha_cen, 20*u.minute, -1))

# Define how the telescope transitions between the configurations defined in the
# observing blocks (target, filter, instrument, etc.).
transitioner = Transitioner(.8*u.deg/u.second,
                            {'filter':{('B','G'): 10*u.second,
                                       ('G','R'): 10*u.second,
                                       'default': 30*u.second}})

# Initialize the scheduler
prior_scheduler = PriorityScheduler(constraints = global_constraints,
                                    observer = apo, transitioner = transitioner)
# Create a schedule for the scheduler to insert the blocks into, and run the scheduler
priority_schedule = Schedule(noon_before, noon_after)
prior_scheduler(blocks, priority_schedule)

# To get a plot of the airmass vs where the blocks were scheduled
plt.figure(figsize = (14,6))
plot_schedule_airmass(priority_schedule)
plt.tight_layout()
plt.legend(loc="upper right")
plt.show()