"""One-time settings migrations (phase 173).

``migrate_legacy_docs_creds`` splits a legacy ``://user:pass@``
``docs_repo`` value into ``docs_repo`` (clean) + ``docs_user`` +
``docs_token`` — DB rows that SHADOW the env (the settings model's
standing rule: the database wins over the environment). ``.env`` is
never read for writing or rewritten. Idempotent: it runs only while
no ``docs_token`` override exists, so owner-set values are never
clobbered. One INFO line when it acts (AGENTS rule 10).

The read side rides the overlay (``load_overrides`` /
``resolve_settings`` — the same fail-soft engine); the write side is
the PUT route's own write (an ``app_settings`` upsert through the app
session — the overlay exposes no write path). A malformed
``://user:pass@`` segment (an empty user OR pass) is NOT the legacy
shape: the value stays as-is (the pre-phase behavior — nothing breaks,
nothing half-migrates), no rows, no log.

Called ONCE from ``create_app()`` (the composition root, task 04
step 2), after the DB is available; a failure there logs a WARNING
and never blocks startup — the app boots with the pre-phase behavior
(the migration is a convenience, not a dependency).
"""
from __future__ import annotations

import logging
import re

from sqlalchemy import func
from sqlalchemy.dialects.postgresql import insert as pg_insert
from sqlalchemy.orm import Session

from app.core.settings_overlay import load_overrides, resolve_settings
from app.db import SessionLocal
from app.models import AppSetting

logger = logging.getLogger("app.settings")

#: ``://<user>:<pass>@`` — the legacy credentials-bearing docs-push
#: remote (the phase-173 leak class). BOTH groups must be non-empty:
#: ``://:@…`` / ``://u:@…`` are malformed, not the legacy shape. The
#: same regex the PUT guard uses (``admin_settings._EMBEDDED_CREDS``)
#: plus the capture groups; a ``://user:pass@`` subdomain cannot match
#: (the character classes exclude ``/`` and the trailing ``@``
#: requirement does the job).
_EMBEDDED_CREDS = re.compile(r"://([^/@:]+):([^@/]+)@")


def _write_rows(rows: dict[str, str]) -> None:
    """Write one row per (key, value) into ``app_settings`` — the PUT
    route's own write (INSERT … ON CONFLICT (key) DO UPDATE, the row's
    ``updated_at`` moves), one session, one commit. The overlay
    exposes no write path, so the direct upsert IS the write path.
    ``.env`` is never touched (LOCKED A1 — the DB rows shadow the env;
    the env file stays the base)."""
    db: Session = SessionLocal()
    try:
        for key, value in rows.items():
            stmt = pg_insert(AppSetting).values(key=key, value=value)
            stmt = stmt.on_conflict_do_update(
                index_elements=["key"],
                set_={"value": stmt.excluded.value, "updated_at": func.now()},
            )
            db.execute(stmt)
        db.commit()
    finally:
        db.close()


def migrate_legacy_docs_creds() -> bool:
    """The phase-173 C3 migration — split a legacy
    ``://user:pass@`` ``docs_repo`` into three ``app_settings`` rows.

    (1) read the ``app_settings`` overrides (the overlay's state);
    (2) the target is the EFFECTIVE ``docs_repo`` (an override if
    present, else the env value — what ``resolve_settings()``
    resolves to); (3) match ``://<user>:<pass>@`` with BOTH groups
    non-empty — otherwise no-op (a malformed segment stays as-is, the
    pre-phase value: nothing breaks, nothing half-migrates); (4) a
    ``docs_token`` override already present → no-op (idempotent —
    owner-set values are never clobbered, and a previous run of this
    migration counts as one); (5) otherwise write the three rows
    (clean repo / user / token — the PUT route's own write) and log
    ONE INFO line. Returns ``True`` when it acted, ``False`` for
    every no-op shape. ``.env`` is never read for writing or
    rewritten: the DB rows shadow the env (the settings model's
    standing rule).
    """
    effective = resolve_settings().docs_repo
    match = _EMBEDDED_CREDS.search(effective)
    if match is None:
        # (3) clean value OR malformed ``user:pass@`` (empty user or
        # pass) — the pre-phase value stays as-is; no rows, no log.
        return False
    if "docs_token" in load_overrides():
        # (4) idempotent: a token override (owner-set, or this
        # migration's own previous run) is never clobbered.
        return False
    user, token = match.group(1), match.group(2)
    # (5) the ``user:pass@`` segment removed, the ``://`` separator
    # KEPT — ``https://u:pass@host/r.git`` → ``https://host/r.git``.
    clean = effective.replace(match.group(0), "://", 1)
    _write_rows(
        {
            "docs_repo": clean,
            "docs_user": user,
            "docs_token": token,
        }
    )
    # ONE INFO line when it acts (AGENTS rule 10 — the value is never
    # in the line, A4's log discipline).
    logger.info(
        "settings: migrated embedded docs-push credentials out of "
        "docs_repo into docs_user/docs_token"
    )
    return True