#!/usr/bin/env python3

# This program is a direct translation of the sample program
# "write_bands.c" bundled with the EPR-API distribution.
#
# Source code of the C program is available at:
# https://github.com/bcdev/epr-api/blob/master/src/examples/write_bands.c

import os
import sys
import epr


def write_raw_image(output_dir, product, band_name):
    """Generate the ENVI binary pattern image file for an actual DS.

    The first parameter is the output directory path.
    """
    # Build ENVI file path, DS name specifically
    image_file_path = os.path.join(output_dir, band_name + ".raw")

    band = product.get_band(band_name)
    source_w = product.get_scene_width()
    source_h = product.get_scene_height()
    source_step_x = 1
    source_step_y = 1

    raster = band.create_compatible_raster(source_w, source_h,
                                           source_step_x, source_step_y)

    print(f"Reading band {band_name!r}...")
    raster = band.read_raster(0, 0, raster)

    with open(image_file_path, "wb") as out_stream:
        for line in raster.data:
            out_stream.write(line.tostring())
        # or better: raster.data.tofile(out_stream)

    print(f"Raw image data successfully written to {image_file_path!r}.")
    print("C data type is %r, element size %u byte(s), "
          "raster size is %u x %u pixels." % (
          epr.data_type_id_to_str(raster.data_type),
          raster.get_elem_size(),
          raster.get_width(),
          raster.get_height()))


def main(*argv):
    """A program for converting producing ENVI raster information from
    dataset.

    It generates as many raster as there are dataset entrance parameters.

    Call::

        $ python3 write_bands.py <envisat-product>
                                 <output directory for the raster file>
                                 <dataset name 1>
                                 [<dataset name 2> ... <dataset name N>]

    Example::

        $ python3 write_bands.py \
        MER_RR__1PNPDK20020415_103725_000002702005_00094_00649_1059.N1 \
        . latitude

    """
    if not argv:
        argv = sys.argv

    if len(argv) <= 3:
        print("Usage: write_bands.py <envisat-product> <output-dir> "
              "<dataset-name-1>")
        print("                      [<dataset-name-2> ... <dataset-name-N>]")
        print("  where envisat-product is the input filename")
        print("  and output-dir is the output directory")
        print("  and dataset-name-1 is the name of the first band to be "
              "extracted (mandatory)")
        print("  and dataset-name-2 ... dataset-name-N are the names of "
              "further bands to be extracted (optional)")
        print("Example:")
        print("  write_bands MER_RR__2P_TEST.N1 . latitude")
        print()
        sys.exit(1)

    product_file_path = argv[1]
    output_dir_path = argv[2]

    # Open the product; the argument is the path to product the data file
    with epr.open(product_file_path) as product:
        for band_name in argv[3:]:
            write_raw_image(output_dir_path, product, band_name)


if __name__ == "__main__":
    main()