FEAT: --update/overwrite option TODOed by #20,

- CLI options described in the 2nd case explained in #211,
  due to simplicity.
- The precedence for deciding update/overwrite:
  env-var, --update/overwrite, --source exist?
- Function defaults are false, as suggested in
  [#20](#20 (comment)).
- Both index & demo updated.
- Env-var now checks its value one of (update|overwrite).
- All update/overwrite decision logic moved to __main_.

src/promnesia/__main__.py

@@ -2,6 +2,7 @@
 import os
 import logging
 import inspect
+import os
 import sys
 from typing import List, Tuple, Optional, Dict, Sequence, Iterable, Iterator
 from pathlib import Path
@@ -66,7 +67,7 @@ def iter_all_visits(sources_subset: Iterable[str]=()) -> Iterator[Res[DbVisit]]:
                     yield e
 
 
-def _do_index(dry: bool=False, sources_subset: Iterable[str]=()) -> Iterable[Exception]:
+def _do_index(dry: bool=False, sources_subset: Iterable[str]=(), overwrite_db=False) -> Iterable[Exception]:
     # also keep & return errors for further display
     errors: List[Exception] = []
     def it() -> Iterable[Res[DbVisit]]:
@@ -81,17 +82,23 @@ def it() -> Iterable[Res[DbVisit]]:
         for v in res:
             print(v)
     else:
-        dump_errors = visits_to_sqlite(it())
+        dump_errors = visits_to_sqlite(it(), overwrite_db)
         for e in dump_errors:
             logger.exception(e)
             errors.append(e)
     return errors
 
 
-def do_index(config_file: Path, dry: bool=False, sources_subset: Iterable[str]=()) -> None:
+def do_index(
+        config_file: Path,
+        dry: bool=False,
+        sources_subset: Iterable[str]=(),
+        overwrite: bool=None,
+        overwrite_db=False,
+    ) -> None:
     config.load_from(config_file) # meh.. should be cleaner
     try:
-        errors = list(_do_index(dry=dry, sources_subset=sources_subset))
+        errors = list(_do_index(dry=dry, sources_subset=sources_subset, overwrite_db=overwrite_db))
     finally:
         config.reset()
     if len(errors) > 0:
@@ -131,6 +138,7 @@ def do_demo(*
         config_file: Optional[Path],
         name: str='demo',
         sources_subset: Iterable[str]=(),
+        overwrite_db: bool=False,
     ) -> None:
     from pprint import pprint
     with TemporaryDirectory() as tdir:
@@ -147,7 +155,7 @@ def do_demo(*
             )
             config.instance = cfg
 
-        errors = list(_do_index(sources_subset=sources_subset))
+        errors = list(_do_index(sources_subset=sources_subset, overwrite_db=overwrite_db))
         if len(errors) > 0:
             logger.error('%d errors during indexing (see logs above for backtraces)', len(errors))
         for e in errors:
@@ -293,6 +301,22 @@ def main() -> None:
     ep.add_argument('--intermediate', required=False, help="Used for development, you don't need it")
     ep.add_argument('--sources', required=False, action="extend", nargs="+", type=_parse_ordinal_or_name,
                     help="Subset of source(s) to run (name or 0-indexed position);  use `promnisia --dry` to view sources")
+    overwrite = ep.add_mutually_exclusive_group()
+    overwrite.add_argument(
+        '--update',
+        required=False,
+        action="store_const",
+        const=True,
+        dest="overwrite_db",
+        help=
+            "Keep existing visits in db and merge new ones collected."
+            "  If neither is given, --update assumed when --sources given (the default)"
+            ", unless PROMNESIA_INDEX_POLICY=(update|overwrite) env-var defined"
+            ", which takes precendance."
+            "  Conflicts with --update.%(default)0.0s"
+    )
+    overwrite.add_argument('--overwrite', required=False, action="store_const", const=False, dest="overwrite_db",
+                    help="The opposite of --update:  recreate db with newly indexed visits%(default)0.0s")
 
     sp = subp.add_parser('serve', help='Serve a link database', formatter_class=F) # type: ignore
     server.setup_parser(sp)
@@ -348,13 +372,33 @@ def main() -> None:
         p.print_help(sys.stderr)
         sys.exit(1)
 
+    overwrite_policy_var = os.environ.get("PROMNESIA_INDEX_POLICY")
+    if overwrite_policy_var:
+        overwrite_policy_var = overwrite_policy_var.lower()
+        if overwrite_policy_var not in ("update", "overwrite"):
+            print(
+                f"Invalid value for PROMNESIA_INDEX_POLICY env-var: {overwrite_policy_var}"
+                "\n  Must be one of (update | overwrite).",
+                file=sys.stderr)
+            sys.exit(2)
+        args.overwrite_db = overwrite_policy_var == "overwrite"
+    if args.overwrite_db is None:
+        args.overwrite_db = not bool(args.sources)
+
+    logger.info("CLI args: %s", args)
+
     # TODO maybe, it's better for server to compute intermediate represetnation?
     # the only downside is storage. dunno.
     # worst case -- could use database?
 
     with get_tmpdir() as tdir: # TODO??
         if args.mode == 'index':
-             do_index(config_file=args.config, dry=args.dry, sources_subset=args.sources)
+            do_index(
+                config_file=args.config,
+                dry=args.dry,
+                sources_subset=args.sources,
+                overwrite_db=args.overwrite_db,
+            )
         elif args.mode == 'serve':
             server.run(args)
         elif args.mode == 'demo':
@@ -367,6 +411,7 @@ def main() -> None:
                 config_file=args.config,
                 name=args.name,
                 sources_subset=args.sources,
+                overwrite_db=args.overwrite_db,
                 )
         elif args.mode == 'install-server': # todo rename to 'autostart' or something?
             install_server.install(args)

src/promnesia/dump.py

@@ -1,4 +1,3 @@
-import os
 from pathlib import Path
 import shutil
 from typing import Dict, List, Tuple, Set, Iterable
@@ -14,14 +13,6 @@
 from . import config
 
 
-def update_policy_active() -> bool:
-    # NOTE: experimental.. need to make it a proper cmdline argument later
-    INDEX_POLICY = os.environ.get('PROMNESIA_INDEX_POLICY', 'overwrite_all')
-    # if 'update' is passed, will run against the existing db and only tough the sources present in the current index run
-    # not sue if a good name for this..
-    return INDEX_POLICY == 'update'
-
-
 # NOTE: I guess the main performance benefit from this is not creating too many tmp lists and avoiding overhead
 # since as far as sql is concerned it should all be in the same transaction. only a guess
 # not sure it's the proper way to handle it
@@ -30,7 +21,7 @@ def update_policy_active() -> bool:
 
 
 # returns critical warnings
-def visits_to_sqlite(vit: Iterable[Res[DbVisit]]) -> List[Exception]:
+def visits_to_sqlite(vit: Iterable[Res[DbVisit]], overwrite_db: bool) -> List[Exception]:
     logger = get_logger()
     db_path = config.get().db
 
@@ -58,8 +49,7 @@ def vit_ok() -> Iterable[DbVisit]:
                 yield ev
 
     tpath = Path(get_tmpdir().name) / 'promnesia.tmp.sqlite'
-    policy_update = update_policy_active()
-    if not policy_update:
+    if overwrite_db:
         engine = create_engine(f'sqlite:///{tpath}')
     else:
         engine = create_engine(f'sqlite:///{db_path}')
@@ -82,12 +72,12 @@ def vit_ok() -> Iterable[DbVisit]:
             # pylint: disable=no-value-for-parameter
             conn.execute(table.insert().values(bound))
 
-    if not policy_update:
+    if overwrite_db:
         shutil.move(str(tpath), str(db_path))
 
     errs = '' if errors == 0 else f', {errors} ERRORS'
     total = ok + errors
-    what = 'updated' if policy_update else 'overwritten'
+    what = 'overwritten' if overwrite_db else 'updated'
     logger.info('%s database "%s". %d total (%d OK%s)', what, db_path, total, ok, errs)
     res: List[Exception] = []
     if total == 0: