import logging
import re
from math import floor

from pyproj import Transformer

TRANSFORMER_OS_GRID_TO_WGS84 = Transformer.from_crs("EPSG:27700", "EPSG:4326")
TRANSFORMER_IRISH_GRID_TO_WGS84 = Transformer.from_crs("EPSG:29903", "EPSG:4326")
TRANSFORMER_CI_UTM_GRID_TO_WGS84 = Transformer.from_crs("+proj=utm +zone=30 +ellps=WGS84", "EPSG:4326")


# Convert a Worked All Britain or Worked All Ireland reference to a lat/lon point.
def wab_wai_square_to_lat_lon(ref):
    # First check we have a valid grid square, and based on what it looks like, use either the Ordnance Survey, Irish,
    # or UTM grid systems to perform the conversion.
    if re.match(r"^[HNOST][ABCDEFGHJKLMNOPQRSTUVWXYZ][0-9]{2}$", ref):
        return os_grid_square_to_lat_lon(ref)
    elif re.match(r"^[ABCDEFGHJKLMNOPQRSTUVWXYZ][0-9]{2}$", ref):
        return irish_grid_square_to_lat_lon(ref)
    elif re.match(r"^W[AV][0-9]{2}$", ref):
        return utm_grid_square_to_lat_lon(ref)
    else:
        logging.warn("Invalid WAB/WAI square: " + ref)
        return None


# Get a lat/lon point for the centre of an Ordnance Survey grid square
def os_grid_square_to_lat_lon(ref):
    # Convert the letters into multipliers for the 500km squares and 100km squares
    offset_500km_multiplier = ord(ref[0]) - 65
    offset_100km_multiplier = ord(ref[1]) - 65

    # The letter "I" is not used in the grid, so any offset of 8 or more needs to be reduced by 1.
    if offset_500km_multiplier >= 8:
        offset_500km_multiplier = offset_500km_multiplier - 1
    if offset_100km_multiplier >= 8:
        offset_100km_multiplier = offset_100km_multiplier - 1

    # Convert the offsets into increments of 100km from the false origin (grid square SV):
    easting_100km = ((offset_500km_multiplier - 2) % 5) * 5 + (offset_100km_multiplier % 5)
    northing_100km = (19 - floor(offset_500km_multiplier / 5) * 5) - floor(offset_100km_multiplier / 5)

    # Take the numeric parts of the grid square and multiply by 10000 to get metres, then combine with the 100km
    # box offsets
    easting = int(ref[2]) * 10000 + easting_100km * 100000
    northing = int(ref[3]) * 10000 + northing_100km * 100000

    # Add 5000m to each value to get the middle of the box rather than the south-west corner
    easting = easting + 5000
    northing = northing + 5000

    # Reproject to WGS84 lat/lon
    lat, lon = TRANSFORMER_OS_GRID_TO_WGS84.transform(easting, northing)
    return lat, lon


# Get a lat/lon point for the centre of an Irish Grid square.
def irish_grid_square_to_lat_lon(ref):
    # Convert the letters into multipliers for the 100km squares
    offset_100km_multiplier = ord(ref[0]) - 65

    # The letter "I" is not used in the grid, so any offset of 8 or more needs to be reduced by 1.
    if offset_100km_multiplier >= 8:
        offset_100km_multiplier = offset_100km_multiplier - 1

    # Convert the offsets into increments of 100km from the false origin:
    easting_100km = offset_100km_multiplier % 5
    northing_100km = 4 - floor(offset_100km_multiplier / 5)

    # Take the numeric parts of the grid square and multiply by 10000 to get metres, then combine with the 100km
    # box offsets
    easting = int(ref[1]) * 10000 + easting_100km * 100000
    northing = int(ref[2]) * 10000 + northing_100km * 100000

    # Add 5000m to each value to get the middle of the box rather than the south-west corner
    easting = easting + 5000
    northing = northing + 5000

    # Reproject to WGS84 lat/lon
    lat, lon = TRANSFORMER_IRISH_GRID_TO_WGS84.transform(easting, northing)
    return lat, lon


# Get a lat/lon point for the centre of a UTM grid square (supports only squares WA & WV for the Channel Islands, nothing else implemented)
def utm_grid_square_to_lat_lon(ref):
    # Take the numeric parts of the grid square and multiply by 10000 to get metres from the corner of the letter-based grid square
    easting = int(ref[2]) * 10000
    northing = int(ref[3]) * 10000

    # Apply the appropriate offset based on whether the square is WA or WV
    easting = easting + 500000
    if ref[1] == "A":
        northing = northing + 5500000
    else:
        northing = northing + 5400000

    # Add 5000m to each value to get the middle of the box rather than the south-west corner
    easting = easting + 5000
    northing = northing + 5000

    # Reproject to WGS84 lat/lon
    lat, lon = TRANSFORMER_CI_UTM_GRID_TO_WGS84.transform(easting, northing)
    return lat, lon