import json
import sys

def usage():
    print("python swap_layers.py <source layout JSON file> <destination layout JSON file> <first layer index> <second layer index>")
    sys.exit(1)

if len(sys.argv) != 5:
    usage()

try:
     first = int(sys.argv[3])
     second = int(sys.argv[4])
except ValueError:
    usage()

if first < 0 or first > 9 or second < 0 or second > 9:
    print("Layers must be between 0 and 9")
    usage()

if first == second:
    print("Layers must be unique")
    usage()

layout = json.load(open(sys.argv[1]))
maps = layout['keymaps']
first_layer = maps[first]
maps[first] = maps[second]
maps[second] = first_layer

for m in maps:
    for k in m:
        if 'layer' in k.get('categories', []):
            target = k['target']
            if target == first:
                shift = second - first
                k['target'] = second
            elif target == second:
                shift = first - second
                k['target']  = first
            else:
                continue
            # One shot and pure layer shift keys offset by the layer index into their base,
            # so we shift by the difference directly for them
            # dualuse keys multiply by 256 to get the offset, so make that adjustment for it:
            # https://github.com/keyboardio/Chrysalis/blob/master/src/api/keymap/db/base/dualuse.js#L34
            if 'dualuse' in k['categories']:
                shift *= 256
            k['code'] += shift
json.dump(layout, open(sys.argv[2], 'w'), sort_keys=True, indent=4)