# SPDX-FileCopyrightText: : 2017-2020 The PyPSA-Eur Authors
#
# SPDX-License-Identifier: MIT

"""
Solves linear optimal power flow for a network iteratively while updating reactances.

Relevant Settings
-----------------

.. code:: yaml

    solving:
        tmpdir:
        options:
            formulation:
            clip_p_max_pu:
            load_shedding:
            noisy_costs:
            nhours:
            min_iterations:
            max_iterations:
            skip_iterations:
            track_iterations:
        solver:
            name:

.. seealso::
    Documentation of the configuration file ``config.yaml`` at
    :ref:`electricity_cf`, :ref:`solving_cf`, :ref:`plotting_cf`

Inputs
------

- ``networks/elec_s{simpl}_{clusters}_ec_l{ll}_{opts}.nc``: confer :ref:`prepare`

Outputs
-------

- ``results/networks/elec_s{simpl}_{clusters}_ec_l{ll}_{opts}.nc``: Solved PyPSA network including optimisation results

    .. image:: ../img/results.png
        :scale: 40 %

Description
-----------

Total annual system costs are minimised with PyPSA. The full formulation of the
linear optimal power flow (plus investment planning
is provided in the
`documentation of PyPSA <https://pypsa.readthedocs.io/en/latest/optimal_power_flow.html#linear-optimal-power-flow>`_.
The optimization is based on the ``pyomo=False`` setting in the :func:`network.lopf` and  :func:`pypsa.linopf.ilopf` function.
Additionally, some extra constraints specified in :mod:`prepare_network` are added.

Solving the network in multiple iterations is motivated through the dependence of transmission line capacities and impedances.
As lines are expanded their electrical parameters change, which renders the optimisation bilinear even if the power flow
equations are linearized.
To retain the computational advantage of continuous linear programming, a sequential linear programming technique
is used, where in between iterations the line impedances are updated.
Details (and errors made through this heuristic) are discussed in the paper

- Fabian Neumann and Tom Brown. `Heuristics for Transmission Expansion Planning in Low-Carbon Energy System Models <https://arxiv.org/abs/1907.10548>`_), *16th International Conference on the European Energy Market*, 2019. `arXiv:1907.10548 <https://arxiv.org/abs/1907.10548>`_.

.. warning::
    Capital costs of existing network components are not included in the objective function,
    since for the optimisation problem they are just a constant term (no influence on optimal result).

    Therefore, these capital costs are not included in ``network.objective``!

    If you want to calculate the full total annual system costs add these to the objective value.

.. tip::
    The rule :mod:`solve_all_networks` runs
    for all ``scenario`` s in the configuration file
    the rule :mod:`solve_network`.

"""

import logging
from _helpers import configure_logging

import numpy as np
import pandas as pd
import re

import pypsa
from pypsa.linopf import (get_var, define_constraints, define_variables,
                          linexpr, join_exprs, network_lopf, ilopf)
from pypsa.descriptors import get_switchable_as_dense as get_as_dense

from pathlib import Path
from vresutils.benchmark import memory_logger

logger = logging.getLogger(__name__)


def prepare_network(n, solve_opts):

    if 'clip_p_max_pu' in solve_opts:
        for df in (n.generators_t.p_max_pu, n.storage_units_t.inflow):
            df.where(df>solve_opts['clip_p_max_pu'], other=0., inplace=True)

    load_shedding = solve_opts.get('load_shedding')
    if load_shedding:
        n.add("Carrier", "Load")
        buses_i = n.buses.query("carrier == 'AC'").index
        if not np.isscalar(load_shedding): load_shedding = 1e2
        # intersect between macroeconomic and surveybased
        # willingness to pay
        # http://journal.frontiersin.org/article/10.3389/fenrg.2015.00055/full)
        n.madd("Generator", buses_i, " load",
               bus=buses_i,
               carrier='load',
               sign=1e-3, # Adjust sign to measure p and p_nom in kW instead of MW
               marginal_cost=load_shedding, 
               p_nom=1e9 # kW
               )

    if solve_opts.get('noisy_costs'):
        for t in n.iterate_components(n.one_port_components):
            #if 'capital_cost' in t.df:
            #    t.df['capital_cost'] += 1e1 + 2.*(np.random.random(len(t.df)) - 0.5)
            if 'marginal_cost' in t.df:
                t.df['marginal_cost'] += (1e-2 + 2e-3 *
                                          (np.random.random(len(t.df)) - 0.5))

        for t in n.iterate_components(['Line', 'Link']):
            t.df['capital_cost'] += (1e-1 +
                2e-2*(np.random.random(len(t.df)) - 0.5)) * t.df['length']

    if solve_opts.get('nhours'):
        nhours = solve_opts['nhours']
        n.set_snapshots(n.snapshots[:nhours])
        n.snapshot_weightings[:] = 8760. / nhours

    return n


def add_CCL_constraints(n, config):
    agg_p_nom_limits = config['electricity'].get('agg_p_nom_limits')

    try:
        agg_p_nom_minmax = pd.read_csv(agg_p_nom_limits,
                                       index_col=list(range(2)))
    except IOError:
        logger.exception("Need to specify the path to a .csv file containing "
                          "aggregate capacity limits per country in "
                          "config['electricity']['agg_p_nom_limit'].")
    logger.info("Adding per carrier generation capacity constraints for "
                "individual countries")

    gen_country = n.generators.bus.map(n.buses.country)
    # cc means country and carrier
    p_nom_per_cc = (pd.DataFrame(
                    {'p_nom': linexpr((1, get_var(n, 'Generator', 'p_nom'))),
                    'country': gen_country, 'carrier': n.generators.carrier})
                    .dropna(subset=['p_nom'])
                    .groupby(['country', 'carrier']).p_nom
                    .apply(join_exprs))
    minimum = agg_p_nom_minmax['min'].dropna()
    if not minimum.empty:
        minconstraint = define_constraints(n, p_nom_per_cc[minimum.index],
                                           '>=', minimum, 'agg_p_nom', 'min')
    maximum = agg_p_nom_minmax['max'].dropna()
    if not maximum.empty:
        maxconstraint = define_constraints(n, p_nom_per_cc[maximum.index],
                                           '<=', maximum, 'agg_p_nom', 'max')


def add_EQ_constraints(n, o, scaling=1e-1):
    float_regex = "[0-9]*\.?[0-9]+"
    level = float(re.findall(float_regex, o)[0])
    if o[-1] == 'c':
        ggrouper = n.generators.bus.map(n.buses.country)
        lgrouper = n.loads.bus.map(n.buses.country)
        sgrouper = n.storage_units.bus.map(n.buses.country)
    else:
        ggrouper = n.generators.bus
        lgrouper = n.loads.bus
        sgrouper = n.storage_units.bus
    load = n.snapshot_weightings.generators @ \
           n.loads_t.p_set.groupby(lgrouper, axis=1).sum()
    inflow = n.snapshot_weightings.stores @ \
             n.storage_units_t.inflow.groupby(sgrouper, axis=1).sum()
    inflow = inflow.reindex(load.index).fillna(0.)
    rhs = scaling * ( level * load - inflow )
    lhs_gen = linexpr((n.snapshot_weightings.generators * scaling,
                       get_var(n, "Generator", "p").T)
              ).T.groupby(ggrouper, axis=1).apply(join_exprs)
    lhs_spill = linexpr((-n.snapshot_weightings.stores * scaling,
                         get_var(n, "StorageUnit", "spill").T)
                ).T.groupby(sgrouper, axis=1).apply(join_exprs)
    lhs_spill = lhs_spill.reindex(lhs_gen.index).fillna("")
    lhs = lhs_gen + lhs_spill
    define_constraints(n, lhs, ">=", rhs, "equity", "min")


def add_BAU_constraints(n, config):
    mincaps = pd.Series(config['electricity']['BAU_mincapacities'])
    lhs = (linexpr((1, get_var(n, 'Generator', 'p_nom')))
           .groupby(n.generators.carrier).apply(join_exprs))
    define_constraints(n, lhs, '>=', mincaps[lhs.index], 'Carrier', 'bau_mincaps')


def add_SAFE_constraints(n, config):
    peakdemand = (1. + config['electricity']['SAFE_reservemargin']) *\
                  n.loads_t.p_set.sum(axis=1).max()
    conv_techs = config['plotting']['conv_techs']
    exist_conv_caps = n.generators.query('~p_nom_extendable & carrier in @conv_techs')\
                       .p_nom.sum()
    ext_gens_i = n.generators.query('carrier in @conv_techs & p_nom_extendable').index
    lhs = linexpr((1, get_var(n, 'Generator', 'p_nom')[ext_gens_i])).sum()
    rhs = peakdemand - exist_conv_caps
    define_constraints(n, lhs, '>=', rhs, 'Safe', 'mintotalcap')


def add_operational_reserve_margin_constraint(n, config):
    
    reserve_config = config["electricity"]["operational_reserve"]
    EPSILON_LOAD = reserve_config["epsilon_load"]
    EPSILON_VRES = reserve_config["epsilon_vres"]
    CONTINGENCY = reserve_config["contingency"]

    # Reserve Variables 
    reserve = get_var(n, 'Generator', 'r')
    lhs = linexpr((1, reserve)).sum(1)

    # Share of extendable renewable capacities
    ext_i = n.generators.query('p_nom_extendable').index
    vres_i = n.generators_t.p_max_pu.columns
    if not ext_i.empty and not vres_i.empty:
        capacity_factor = n.generators_t.p_max_pu[vres_i.intersection(ext_i)]
        renewable_capacity_variables = get_var(n, 'Generator', 'p_nom')[vres_i.intersection(ext_i)]
        lhs += linexpr((-EPSILON_VRES * capacity_factor, renewable_capacity_variables)).sum(1)

    # Total demand at t
    demand =  n.loads_t.p.sum(1)
    
    # VRES potential of non extendable generators
    capacity_factor = n.generators_t.p_max_pu[vres_i.difference(ext_i)]
    renewable_capacity = n.generators.p_nom[vres_i.difference(ext_i)]
    potential = (capacity_factor * renewable_capacity).sum(1)
    
    # Right-hand-side
    rhs = EPSILON_LOAD * demand + EPSILON_VRES * potential + CONTINGENCY
        
    define_constraints(n, lhs, '>=', rhs, "Reserve margin")


def update_capacity_constraint(n):
    gen_i = n.generators.index
    ext_i = n.generators.query('p_nom_extendable').index
    fix_i = n.generators.query('not p_nom_extendable').index

    dispatch = get_var(n, 'Generator', 'p')
    reserve = get_var(n, 'Generator', 'r')
        
    capacity_fixed = n.generators.p_nom[fix_i]
    
    p_max_pu = get_as_dense(n, 'Generator', 'p_max_pu')
    
    lhs = linexpr((1, dispatch), (1, reserve))
    
    if not ext_i.empty:
        capacity_variable = get_var(n, 'Generator', 'p_nom')
        lhs += linexpr((-p_max_pu[ext_i], capacity_variable)).reindex(columns=gen_i, fill_value='')
    
    rhs = (p_max_pu[fix_i] * capacity_fixed).reindex(columns=gen_i, fill_value=0)
    
    define_constraints(n, lhs, '<=', rhs, 'Generators', 'updated_capacity_constraint')


def add_operational_reserve_margin(n, sns, config):

    define_variables(n, 0, np.inf, 'Generator', 'r', axes=[sns, n.generators.index])

    add_operational_reserve_margin_constraint(n, config)
    
    update_capacity_constraint(n)


def add_battery_constraints(n):
    nodes = n.buses.index[n.buses.carrier == "battery"]
    if nodes.empty or ('Link', 'p_nom') not in n.variables.index:
        return
    link_p_nom = get_var(n, "Link", "p_nom")
    lhs = linexpr((1,link_p_nom[nodes + " charger"]),
                  (-n.links.loc[nodes + " discharger", "efficiency"].values,
                   link_p_nom[nodes + " discharger"].values))
    define_constraints(n, lhs, "=", 0, 'Link', 'charger_ratio')


def extra_functionality(n, snapshots):
    """
    Collects supplementary constraints which will be passed to ``pypsa.linopf.network_lopf``.
    If you want to enforce additional custom constraints, this is a good location to add them.
    The arguments ``opts`` and ``snakemake.config`` are expected to be attached to the network.
    """
    opts = n.opts
    config = n.config
    if 'BAU' in opts and n.generators.p_nom_extendable.any():
        add_BAU_constraints(n, config)
    if 'SAFE' in opts and n.generators.p_nom_extendable.any():
        add_SAFE_constraints(n, config)
    if 'CCL' in opts and n.generators.p_nom_extendable.any():
        add_CCL_constraints(n, config)
    reserve = config["electricity"].get("operational_reserve", {})
    if reserve.get("activate"):
        add_operational_reserve_margin(n, snapshots, config)
    for o in opts:
        if "EQ" in o:
            add_EQ_constraints(n, o)
    add_battery_constraints(n)


def solve_network(n, config, opts='', **kwargs):
    solver_options = config['solving']['solver'].copy()
    solver_name = solver_options.pop('name')
    cf_solving = config['solving']['options']
    track_iterations = cf_solving.get('track_iterations', False)
    min_iterations = cf_solving.get('min_iterations', 4)
    max_iterations = cf_solving.get('max_iterations', 6)

    # add to network for extra_functionality
    n.config = config
    n.opts = opts

    skip_iterations = cf_solving.get('skip_iterations', False)
    if not n.lines.s_nom_extendable.any():
        skip_iterations = True
        logger.info("No expandable lines found. Skipping iterative solving.")

    if skip_iterations:
        network_lopf(n, solver_name=solver_name, solver_options=solver_options,
                     extra_functionality=extra_functionality, **kwargs)
    else:
        ilopf(n, solver_name=solver_name, solver_options=solver_options,
              track_iterations=track_iterations,
              min_iterations=min_iterations,
              max_iterations=max_iterations,
              extra_functionality=extra_functionality, **kwargs)
    return n


if __name__ == "__main__":
    if 'snakemake' not in globals():
        from _helpers import mock_snakemake
        snakemake = mock_snakemake('solve_network', network='elec', simpl='',
                                  clusters='5', ll='copt', opts='Co2L-BAU-CCL-24H')
    configure_logging(snakemake)

    tmpdir = snakemake.config['solving'].get('tmpdir')
    if tmpdir is not None:
        Path(tmpdir).mkdir(parents=True, exist_ok=True)
    opts = snakemake.wildcards.opts.split('-')
    solve_opts = snakemake.config['solving']['options']

    fn = getattr(snakemake.log, 'memory', None)
    with memory_logger(filename=fn, interval=30.) as mem:
        n = pypsa.Network(snakemake.input[0])
        n = prepare_network(n, solve_opts)
        n = solve_network(n, snakemake.config, opts, solver_dir=tmpdir,
                          solver_logfile=snakemake.log.solver)
        n.export_to_netcdf(snakemake.output[0])

    logger.info("Maximum memory usage: {}".format(mem.mem_usage))
