"""Move audit records from a SQLite store into PostgreSQL (AUDIT-WP-0005-T04).

As of 2026-08-10 there are no pre-production records to move: audit-core was
never deployed, so the only SQLite stores that ever existed were test
fixtures. See the workplan for that finding.

The tool exists anyway because the SQLite path is still reachable — the
entrypoint falls back to it when ``AUDIT_CORE_DATABASE_URL`` is unset. If that
fallback is ever used in anger, the records it accumulates are audit records
and cannot simply be dropped.

Fidelity is the whole point. Records are transferred with their original
``event_id``, ``payload_hash``, and ``accepted_at`` intact; a migration that
rewrote acceptance times would destroy the evidence it was meant to preserve.
That is why this bypasses ``accept()``, which stamps ``accepted_at`` with the
current time.
"""

from __future__ import annotations

import json
import sqlite3
from dataclasses import dataclass, field

from audit_core.interface import BackendUnavailableError


@dataclass
class MigrationReport:
    """What happened, in enough detail to be evidence."""

    events_read: int = 0
    events_written: int = 0
    events_already_present: int = 0
    dead_letters_written: int = 0
    findings_written: int = 0
    conflicts: list[str] = field(default_factory=list)
    verified: bool = False

    @property
    def ok(self) -> bool:
        return not self.conflicts and self.verified

    def summary(self) -> str:
        lines = [
            f"events read:            {self.events_read}",
            f"events written:         {self.events_written}",
            f"already present:        {self.events_already_present}",
            f"dead letters written:   {self.dead_letters_written}",
            f"secret findings written:{self.findings_written}",
            f"verified:               {self.verified}",
        ]
        if self.conflicts:
            lines.append(f"CONFLICTS ({len(self.conflicts)}):")
            lines += [f"  - {c}" for c in self.conflicts]
        return "\n".join(lines)


def migrate(sqlite_path: str, backend, *, verify: bool = True) -> MigrationReport:
    """Copy every record from ``sqlite_path`` into ``backend``.

    Idempotent: re-running skips events already present with a matching payload
    hash. An event present with a *different* hash is reported as a conflict
    and never overwritten — the destination record wins, and a human decides.
    """
    report = MigrationReport()
    source = sqlite3.connect(f"file:{sqlite_path}?mode=ro", uri=True)
    try:
        rows = source.execute(
            "SELECT event_id, payload_hash, accepted_at, correlation_id, tenant, record "
            "FROM events ORDER BY accepted_at, event_id"
        ).fetchall()
        report.events_read = len(rows)

        for event_id, payload_hash, accepted_at, correlation_id, tenant, record in rows:
            outcome = _import_event(
                backend, event_id, payload_hash, accepted_at, correlation_id,
                tenant, json.loads(record),
            )
            if outcome == "written":
                report.events_written += 1
            elif outcome == "present":
                report.events_already_present += 1
            else:
                report.conflicts.append(outcome)

        report.dead_letters_written = _copy_dead_letters(source, backend)
        report.findings_written = _copy_findings(source, backend)

        if verify:
            report.verified = _verify(source, backend, report)
    finally:
        source.close()
    return report


def _import_event(
    backend, event_id, payload_hash, accepted_at, correlation_id, tenant, record
) -> str:
    existing = backend._query(
        f"SELECT payload_hash FROM {backend._events} WHERE event_id = %s", (event_id,)
    )
    if existing:
        if existing[0][0] != payload_hash:
            return (
                f"{event_id}: destination holds a different payload "
                f"(source {payload_hash[:12]}…, destination {existing[0][0][:12]}…) "
                "— left untouched"
            )
        return "present"

    backend._execute(
        f"INSERT INTO {backend._events} "
        "(event_id, payload_hash, accepted_at, observed_at, tenant, correlation_id, "
        " source, action, record) "
        "VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s) "
        "ON CONFLICT (event_id) DO NOTHING",
        (
            event_id, payload_hash, accepted_at, record.get("observed_at"),
            tenant, correlation_id, record.get("source", ""), record.get("action", ""),
            json.dumps(record, sort_keys=True),
        ),
    )
    return "written"


def _copy_dead_letters(source: sqlite3.Connection, backend) -> int:
    try:
        rows = source.execute(
            "SELECT event_id, received_at, sender, reason, payload_hash, payload, "
            "payload_withheld FROM dead_letters ORDER BY id"
        ).fetchall()
    except sqlite3.Error:
        return 0
    for event_id, received_at, sender, reason, payload_hash, payload, withheld in rows:
        backend._execute(
            f'INSERT INTO "{backend.schema}".dead_letters '
            "(event_id, received_at, sender, reason, payload_hash, payload, payload_withheld) "
            "VALUES (%s, %s, %s, %s, %s, %s, %s)",
            (event_id, received_at, sender, reason, payload_hash, payload, bool(withheld)),
        )
    return len(rows)


def _copy_findings(source: sqlite3.Connection, backend) -> int:
    try:
        rows = source.execute(
            "SELECT sender, source, action, field_path, outcome, persisted, "
            "occurrences, first_seen, last_seen FROM secret_findings"
        ).fetchall()
    except sqlite3.Error:
        return 0
    for r in rows:
        backend._execute(
            f'INSERT INTO "{backend.schema}".secret_findings '
            "(sender, source, action, field_path, outcome, persisted, occurrences, "
            " first_seen, last_seen) VALUES (%s,%s,%s,%s,%s,%s,%s,%s,%s) "
            "ON CONFLICT (sender, source, action, field_path, outcome) DO UPDATE "
            "SET occurrences = secret_findings.occurrences + excluded.occurrences",
            (r[0], r[1], r[2], r[3], r[4], bool(r[5]), r[6], r[7], r[8]),
        )
    return len(rows)


def _verify(source: sqlite3.Connection, backend, report: MigrationReport) -> bool:
    """Confirm every source event is present with its hash and time intact.

    Verification reads back rather than trusting the write path: a migration
    that reports success without checking is the same as no migration at all.
    """
    rows = source.execute("SELECT event_id, payload_hash, accepted_at FROM events").fetchall()
    for event_id, payload_hash, accepted_at in rows:
        found = backend._query(
            f"SELECT payload_hash, accepted_at FROM {backend._events} WHERE event_id = %s",
            (event_id,),
        )
        if not found:
            report.conflicts.append(f"{event_id}: missing from destination after migration")
            return False
        if found[0][0] != payload_hash:
            report.conflicts.append(f"{event_id}: payload hash differs after migration")
            return False
        if not _same_instant(found[0][1], accepted_at):
            report.conflicts.append(
                f"{event_id}: accepted_at not preserved "
                f"(source {accepted_at}, destination {found[0][1]})"
            )
            return False
    return True


def _same_instant(destination, source_iso: str) -> bool:
    from datetime import datetime

    try:
        want = datetime.fromisoformat(str(source_iso).replace("Z", "+00:00"))
    except ValueError:
        return False
    if not hasattr(destination, "timestamp"):
        return False
    if want.tzinfo is None or destination.tzinfo is None:
        return False
    return abs(destination.timestamp() - want.timestamp()) < 1.0