"""
    SESANS reader (based on ASCII reader)

    Reader for .ses or .sesans file format

    Jurrian Bakker
"""
import numpy as np
import os
from sas.sascalc.dataloader.data_info import Data1D

# Check whether we have a converter available
has_converter = True
try:
    from sas.sascalc.data_util.nxsunit import Converter
except:
    has_converter = False
_ZERO = 1e-16


class Reader:
    """
    Class to load sesans files (6 columns).
    """
    # File type
    type_name = "SESANS"

    # Wildcards
    type = ["SESANS files (*.ses)|*.ses",
            "SESANS files (*..sesans)|*.sesans"]
    # List of allowed extensions
    ext = ['.ses', '.SES', '.sesans', '.SESANS']

    # Flag to bypass extension check
    allow_all = True

    def read(self, path):
        """
        Load data file

        :param path: file path

        :return: SESANSData1D object, or None

        :raise RuntimeError: when the file can't be opened
        :raise ValueError: when the length of the data vectors are inconsistent
        """
        if os.path.isfile(path):
            basename = os.path.basename(path)
            _, extension = os.path.splitext(basename)
            if not (self.allow_all or extension.lower() in self.ext):
                raise RuntimeError("{} has an unrecognized file extension".format(path))
        else:
            raise RunetimeError("{} is not a file".format(path))
        with open(path, 'r') as input_f:
            # Read in binary mode since GRASP frequently has no-ascii
            # characters that brakes the open operation
            line = input_f.readline()
            params = {}
            while line.strip() != "":
                terms = line.strip().split("\t")
                params[terms[0].strip()] = " ".join(terms[1:]).strip()
                line = input_f.readline()
            headers_temp = input_f.readline().strip().split("\t")
            headers = {}
            for h in headers_temp:
                temp = h.strip().split()
                headers[h[:-1].strip()] = temp[-1][1:-1]
            data = np.loadtxt(input_f)
            if data.size < 1:
                raise RuntimeError("{} is empty".format(path))
            x = data[:, 0]
            dx = data[:, 3]
            lam = data[:, 4]
            dlam = data[:, 5]
            y = data[:, 1]
            dy = data[:, 2]

            lam_unit = self._header_fetch(headers, "wavelength")
            if lam_unit == "AA":
                lam_unit = "A"

            x, x_unit = self._unit_conversion(
                x, lam_unit,
                self._fetch_unit(headers, "spin echo length"))
            dx, dx_unit = self._unit_conversion(
                dx, lam_unit,
                self._fetch_unit(headers, "error SEL"))
            dlam, dlam_unit = self._unit_conversion(
                dlam, lam_unit,
                self._fetch_unit(headers, "error wavelength"))
            y_unit = r'\AA^{-2} cm^{-1}'

            output = Data1D(x=x, y=y, lam=lam, dy=dy, dx=dx, dlam=dlam,
                            isSesans=True)
            self.filename = output.filename = basename
            output.xaxis(r"\rm{z}", x_unit)
            # Adjust label to ln P/(lam^2 t), remove lam column refs
            output.yaxis(r"\rm{ln(P)/(t \lambda^2)}", y_unit)
            # Store loading process information
            output.meta_data['loader'] = self.type_name
            output.sample.name = params["Sample"]
            output.sample.ID = params["DataFileTitle"]

            output.sample.zacceptance = (
                float(self._header_fetch(params, "Q_zmax")),
                self._fetch_unit(params, "Q_zmax"))

            output.sample.yacceptance = (
                float(self._header_fetch(params, "Q_ymax")),
                self._fetch_unit(params, "Q_ymax"))
            return output

    @staticmethod
    def _unit_conversion(value, value_unit, default_unit):
        """
        Performs unit conversion on a measurement.

        :param value: The magnitude of the measurement
        :param value_unit: a string containing the final desired unit
        :param default_unit: a string containing the units of the original measurement
        :return: The magnitude of the measurement in the new units
        """
        # (float, string, string) -> float
        if has_converter and value_unit != default_unit:
            data_conv_q = Converter(value_unit)
            value = data_conv_q(value, units=default_unit)
            new_unit = default_unit
        else:
            new_unit = value_unit
        return value, new_unit

    @staticmethod
    def _header_fetch(headers, key):
        """
        Pull the value of a unit defined header from a dict. Example::

         d = {"Length [m]": 17}
         self._header_fetch(d, "Length") == 17

        :param header: A dictionary of values
        :param key: A string which is a prefix for one of the keys in the dict
        :return: The value of the dictionary for the specified key
        """
        # (dict<string, x>, string) -> x
        index = [k for k in headers.keys()
                 if k.startswith(key)][0]
        return headers[index]

    @staticmethod
    def _fetch_unit(params, key):
        """
        Pull the unit off of a dictionary header. Example::

         d = {"Length [m]": 17}
         self._fetch_unit(d, "Length") == "m"

        :param header: A dictionary of values, where the keys are strings
        with the units for the values appended onto the string within square
        brackets (See the example above)
        :param key: A string with the prefix of the dictionary key whose unit
        is being fetched
        :return: A string containing the unit specifed in the header
        """
        # (dict<string, _>, string) -> string
        index = [k for k in params.keys()
                 if k.startswith(key)][0]
        unit = index.strip().split()[-1][1:-1]
        if unit.startswith(r"\A"):
            unit = "1/A"
        return unit