"""polyline_to_points.py
Extract interpolated points along transects in a shapefile.

D. Howe
d.howe@wrl.unsw.edu.au
2020-02-19
"""
import sys
import argparse
import numpy as np
import pandas as pd
import geopandas as gpd
from shapely.geometry import LineString


def extract(shp_path, spacing=1, field=None):

    rows = []
    shp = gpd.read_file(shp_path)

    if field is None:
        # Assume profile name is second field in shapefile
        field = shp.columns[1]

    for i, line in shp.iterrows():
        g = line.geometry
        chainages = np.arange(0, g.length, step=spacing)
        for chainage in chainages:
            easting, northing = g.interpolate(chainage).xy

            row = {
                'ProfileNum': line[field],
                'Easting': easting[0],
                'Northing': northing[0],
                'Chainage': chainage,
            }
            rows.append(row)

    # Create output dataframe
    df = pd.DataFrame(rows)

    # Re-order columns
    df = df[['ProfileNum', 'Easting', 'Northing', 'Chainage']]

    # Export to csv
    csv_path = shp_path.replace('.shp', '.csv')
    df.to_csv(csv_path, index=False)


def main():
    example_text = """examples:
    # Extract points at default spacing (1m)
    $ python polyline_to_points.py path/to/shp

    # Extract points at 5m increments
    $ python polyline_to_points.py -s 5 path/to/shp

    # Extract points from field "ProfileID"
    $ python polyline_to_points.py -f ProfileID path/to/shp
    """
    # Set up command line arguments
    parser = argparse.ArgumentParser(
        epilog=example_text,
        formatter_class=argparse.RawDescriptionHelpFormatter)
    parser.add_argument('shp_path',
                        metavar='SHAPEFILE',
                        help='path to input shapefile')
    parser.add_argument('-s',
                        '--spacing',
                        metavar='SPACING',
                        default=1,
                        type=int,
                        help='space between points (default=1)')
    parser.add_argument('-f',
                        '--field',
                        metavar='FIELDNAME',
                        help='profile field name in attribute table')

    # Print usage if no arguments are provided
    if len(sys.argv) == 1:
        parser.print_help(sys.stderr)
        sys.exit(1)

    # Parse arguments
    args = parser.parse_args()

    # Combine images
    extract(**vars(args))


if __name__ == '__main__':
    main()