Read and test command line arguments.

First try at reading command line arguments. Still needs testing the
command `--sort`.

2 files changed, 84 insertions, 0 deletions

diff --git a/ledger.py b/ledger.py
new file mode 100755
index 0000000..61eb6a5
--- /dev/null
+++ b/ledger.py
@@ -0,0 +1,12 @@
+#!/usr/bin/env python3
+from utils.args import get_arguments, test_args
+
+def main():
+    args = get_arguments()
+    test_args(args)
+
+    print(args)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/utils/args.py b/utils/args.py
new file mode 100644
index 0000000..e39d2fe
--- /dev/null
+++ b/utils/args.py
@@ -0,0 +1,72 @@
+import argparse
+import sys
+from os.path import isfile, exists
+
+
+def get_arguments():
+    parser = argparse.ArgumentParser(
+        prog=sys.argv[0],
+        description='A simple implementation of ledger-cli. Supports only the \
+            following commands and flags: `balance`, `register`, `print`, \
+            `--sort`, `--price-db` and `--file`.',
+        epilog='This implementation is inspired in \
+            [ledger-cli](https://ledger-cli.org/).')
+    parser.add_argument('-v', '--version',
+                        action='version', version='%(prog)s 0.1')
+
+    parser.add_argument('verb', metavar='Action', action='store',
+                        help='Specify an action between balance, report and \
+                            print.')
+    parser.add_argument('-S', '--sort', metavar='value-expression',
+                        action='store', dest='sort',
+                        help='Sort postings by evaluating the given \
+                            value-expression.')
+    parser.add_argument('--price-db', metavar='FILE',
+                        action='store', dest='price_db',
+                        help='Set the FILE that is used for recording \
+                            downloaded commodity prices')
+    parser.add_argument('-f', '--file', metavar='FILE',
+                        action='append', dest='files',
+                        help='Read journal data from FILE.')
+
+    my_args = parser.parse_args()
+    return my_args
+
+
+def test_args(my_args):
+    # Test if verb is valid.
+    valid_verbs = [
+        'balance', 'bal', 'b',
+        'register', 'reg', 'r',
+        'print'
+    ]
+    if my_args.verb not in valid_verbs:
+        raise Exception(f'{my_args.verb} is NOT a valid verb! Valid verbs are: {", ".join(valid_verbs)}.')
+
+    # Test if expression for sorting is valid.
+    # TODO: How can we validate an expression???
+
+    # Test if price_db file exists and is a file.
+    if my_args.price_db and not exists(my_args.price_db):
+        raise Exception(f'Command: `--price-db {my_args.price_db}`. File {my_args.price_db} does NOT exist.')
+    elif my_args.price_db and not isfile(my_args.price_db):
+        raise Exception(f'Command: `--price-db {my_args.price_db}`. {my_args.price_db} is NOT a file.')
+
+    # Test files.
+    if my_args.files:
+        if len(my_args.files) == 1 and my_args.files[0] == '-':
+            # Check if there's data in stdin.
+            #
+            # https://stackoverflow.com/questions/53541223/read-python-stdin-from-pipe-without-blocking-on-empty-input
+            if sys.stdin.isatty():
+                raise Exception(f'Command: --file -. No info from STDIN.')
+
+        else:
+            for file in my_args.files:
+                if not exists(file):
+                    raise Exception(f'Command: `--file {file}`. File {file} does NOT exist.')
+                elif not isfile(file):
+                    raise Exception(f'Command: `--file {file}`. {file} is NOT a file.')
+    else:
+        if sys.stdin.isatty():
+            raise Exception(f'No info from STDIN. Please specify a file with `--file FILE`.')