"""Access database compact & repair.

Uses the DAO ``DBEngine.CompactDatabase`` method (via pywin32 COM) to compact
and repair one or more ``.accdb`` / ``.mdb`` files. The compact process:

1. Creates a temporary copy in the same directory (compact requires exclusive
   access, so we compact the copy, not the live file).
2. Compacts the copy to a second temp file.
3. Atomically replaces the original with the compacted file (delete original,
   rename compacted → original).
4. Cleans up temp files.

Failures at any step leave the original file unchanged. This is intentionally
separate from the sync loop — compact should only be requested explicitly
(during a maintenance window or when an Access file is bloated).
"""
from __future__ import annotations

import logging
import os
import shutil
import tempfile
import time
from dataclasses import dataclass, field

from .config import SyncConfig
from .logging_setup import setup_compact_log

log = logging.getLogger(__name__)

# ACE DAO ProgID. "DAO.DBEngine.120" ships with Access 2007+ / ACE runtime;
# it supports both .mdb (Jet) and .accdb (ACE) formats.
_DAO_PROGID = "DAO.DBEngine.120"

# Guard: only set up the compact file handler once per process.
_compact_log_ready = False


# ------------------------------------------------------------------ result types

@dataclass
class CompactFileResult:
    """Outcome of compacting one Access file."""

    file: str            # config FileMapping.file name
    source_path: str     # resolved full path
    ok: bool
    before_bytes: int = 0
    after_bytes: int = 0
    duration_s: float = 0.0
    error: str | None = None


@dataclass
class CompactSummary:
    """Aggregate summary across files."""

    results: list[CompactFileResult] = field(default_factory=list)

    @property
    def total_files(self) -> int:
        return len(self.results)

    @property
    def ok(self) -> int:
        return sum(1 for r in self.results if r.ok)

    @property
    def failed(self) -> int:
        return sum(1 for r in self.results if not r.ok)

    @property
    def before_bytes_total(self) -> int:
        return sum(r.before_bytes for r in self.results)

    @property
    def after_bytes_total(self) -> int:
        return sum(r.after_bytes for r in self.results)

    @property
    def saved_bytes(self) -> int:
        return max(0, self.before_bytes_total - self.after_bytes_total)

    @property
    def all_ok(self) -> bool:
        return self.failed == 0


# --------------------------------------------------------------------- compact

def compact_file(db_path: str) -> CompactFileResult:
    """Compact and repair one Access file in-place.

    Two strategies depending on the path type:

    **Local path** (``D:\\...`` or mapped drive):
        ``rename original → .bak``, ``CompactDatabase(bak → original)``,
        delete ``.bak``. Zero extra copies — the file never leaves its drive.

    **UNC path** (``\\\\server\\share\\...``):
        Copy to a local temp file, compact locally, copy back to the network
        share. The local temp staging avoids a C-level segfault in DAO when
        the destination already exists on a network share.

    *db_path* must be an absolute Windows path (local or UNC).
    """
    if _is_unc(db_path):
        return _compact_unc(db_path)
    return _compact_local(db_path)


def _compact_local(db_path: str) -> CompactFileResult:
    """In-place compact for local paths: rename → compact → cleanup."""
    file_name = os.path.basename(db_path)
    result = CompactFileResult(file=file_name, source_path=db_path, ok=False)
    t0 = time.monotonic()

    try:
        before = os.path.getsize(db_path)
        result.before_bytes = before
    except OSError as e:
        result.error = f"cannot stat source: {e}"
        result.duration_s = time.monotonic() - t0
        return result

    bak = db_path + ".compact_bak"
    try:
        # 1. Rename original → bak so DAO can compact bak → original in-place.
        if os.path.exists(bak):
            os.remove(bak)
        os.rename(db_path, bak)

        # 2. Compact bak → original (the original path is now free).
        _dao_compact(bak, db_path)

        # 3. Success — delete bak.
        os.remove(bak)

        result.ok = True
        result.after_bytes = os.path.getsize(db_path)
        result.duration_s = time.monotonic() - t0
        log.info("compact OK (local): %s (%s → %s, %.1fs)",
                 file_name, _human(result.before_bytes),
                 _human(result.after_bytes), result.duration_s)

    except Exception as e:
        # Rollback: restore original from bak.
        if os.path.exists(bak):
            if os.path.exists(db_path):
                _rm_f(db_path)
            os.rename(bak, db_path)
        result.ok = False
        result.error = str(e)
        result.duration_s = time.monotonic() - t0
        log.warning("compact FAIL (local): %s — %s", file_name, e)

    finally:
        # Best-effort bak cleanup (normally already deleted on success).
        _rm_f(bak)

    return result


def _compact_unc(db_path: str) -> CompactFileResult:
    """Compact a UNC-path file via local-temp staging."""
    file_name = os.path.basename(db_path)
    result = CompactFileResult(file=file_name, source_path=db_path, ok=False)
    t0 = time.monotonic()

    try:
        before = os.path.getsize(db_path)
        result.before_bytes = before
    except OSError as e:
        result.error = f"cannot stat source: {e}"
        result.duration_s = time.monotonic() - t0
        return result

    stem, ext = os.path.splitext(file_name)
    tmp_dir = tempfile.gettempdir()
    tmp_src = None   # local copy of original
    tmp_dst = None   # compacted output (local)

    try:
        # 1. Copy original → local temp.
        fd, tmp_src = tempfile.mkstemp(suffix=ext, prefix=f"{stem}_cpysrc_", dir=tmp_dir)
        os.close(fd)
        _rm_f(tmp_src)
        shutil.copy2(db_path, tmp_src)

        # 2. Get a guaranteed-non-existent destination, then compact.
        fd2, tmp_dst = tempfile.mkstemp(suffix=ext, prefix=f"{stem}_cpydst_", dir=tmp_dir)
        os.close(fd2)
        _rm_f(tmp_dst)
        if os.path.exists(tmp_dst):
            raise OSError(f"cannot remove stale temp file: {tmp_dst}")

        _dao_compact(tmp_src, tmp_dst)

        # 3. Replace original with compacted file.
        bak = db_path + ".compact_bak"
        try:
            os.rename(db_path, bak)
        except OSError:
            os.remove(db_path)
            bak = None

        try:
            shutil.copy2(tmp_dst, db_path)
        except Exception:
            if bak and os.path.exists(bak):
                if os.path.exists(db_path):
                    os.remove(db_path)
                os.rename(bak, db_path)
            raise

        if bak and os.path.exists(bak):
            try:
                os.remove(bak)
            except OSError:
                pass

        result.ok = True
        result.after_bytes = os.path.getsize(db_path)
        result.duration_s = time.monotonic() - t0
        log.info("compact OK (UNC): %s (%s → %s, %.1fs)",
                 file_name, _human(result.before_bytes),
                 _human(result.after_bytes), result.duration_s)

    except Exception as e:
        result.ok = False
        result.error = str(e)
        result.duration_s = time.monotonic() - t0
        log.warning("compact FAIL (UNC): %s — %s", file_name, e)

    finally:
        for p in (tmp_src, tmp_dst):
            if p:
                _rm_f(p)

    return result


def _filter_files(cfg: SyncConfig,
                  db_filter: str | None,
                  file_list: list[str] | None) -> list:
    """Return the configured FileMappings after applying optional filters."""
    files = cfg.files
    if db_filter:
        files = [f for f in files if f.file == db_filter]
        if not files:
            log.warning("compact: no file matches --db %r", db_filter)
    elif file_list:
        name_set = set(file_list)
        files = [f for f in files if f.file in name_set]
    return files


def compact_files(cfg: SyncConfig,
                  db_filter: str | None = None,
                  file_list: list[str] | None = None,
                  dry_run: bool = False) -> CompactSummary:
    """Compact every configured Access file (optionally filtered).

    *db_filter* restricts to a single file (CLI ``--db``). *file_list*
    restricts to a named subset (API ``files`` body field). Both can be
    given — *db_filter* wins when both are set.

    When *dry_run* is True, only checks file accessibility and lock status
    without modifying anything. Each file is compacted independently; one
    failure does not abort the run.

    Logs are written to a dedicated ``logs/compact.log`` file (separate from
    ``sync.log``) with the same rotation and daily-archive semantics.
    """
    global _compact_log_ready
    if not _compact_log_ready:
        setup_compact_log(cfg.logging)
        _compact_log_ready = True

    if dry_run:
        return compact_dry_run(cfg, db_filter=db_filter, file_list=file_list)

    files = _filter_files(cfg, db_filter, file_list)

    summary = CompactSummary()
    for fm in files:
        path = fm.source_path(cfg)
        if not os.path.exists(path):
            r = CompactFileResult(
                file=fm.file, source_path=path, ok=False,
                error=f"file not found: {path}",
            )
            summary.results.append(r)
            continue
        summary.results.append(compact_file(path))

    ok, fail = summary.ok, summary.failed
    log.info("compact summary: %d OK, %d FAIL, saved %s across %d files",
             ok, fail, _human(summary.saved_bytes), summary.total_files)
    return summary


# -------------------------------------------------------------------- internal

def _dao_compact(src: str, dst: str) -> None:
    """Compact *src* → *dst* via DAO DBEngine.CompactDatabase.

    Raises on failure; the caller owns temp-file cleanup and rollback.
    """
    import pythoncom
    import win32com.client

    # Per-call COM init so the thread is safe regardless of caller's COM state.
    pythoncom.CoInitialize()
    try:
        dao = win32com.client.Dispatch(_DAO_PROGID)
        # dbVersion120 = 128 → .accdb (ACE); works for .mdb too when ACE is
        # installed because ACE can compact Jet formats.
        dao.CompactDatabase(src, dst, 128)
    finally:
        pythoncom.CoUninitialize()


def _human(n: int) -> str:
    """Format a byte count for log messages."""
    if n < 1024:
        return f"{n}B"
    for unit in ("KB", "MB", "GB"):
        n /= 1024.0
        if n < 1024:
            return f"{n:.1f}{unit}"
    return f"{n:.1f}TB"


def _is_unc(path: str) -> bool:
    """True if *path* is a UNC path (``\\\\server\\share\\...``)."""
    return path.startswith(("\\\\", "//"))


def _check_lock(db_path: str) -> str | None:
    """Check whether *db_path* can be opened for exclusive write.

    Returns ``None`` if the file is accessible (not locked). Returns an error
    message string describing why the file cannot be compacted right now.
    """
    if not os.path.exists(db_path):
        return "file not found"
    # Access creates a .laccdb / .ldb lock file alongside the database when
    # it is open (even from another machine over the share). Its presence is
    # a strong signal; its absence does NOT guarantee the file is free, so
    # we also try an exclusive open.
    laccdb = os.path.splitext(db_path)[0] + ".laccdb"
    ldb = os.path.splitext(db_path)[0] + ".ldb"
    if os.path.exists(laccdb) or os.path.exists(ldb):
        return "locked (Access lock file present)"
    try:
        fd = os.open(db_path, os.O_RDWR)
        os.close(fd)
    except OSError as e:
        return f"locked ({e})"
    return None


def compact_dry_run(cfg: SyncConfig,
                    db_filter: str | None = None,
                    file_list: list[str] | None = None) -> CompactSummary:
    """Check which files are ready for compaction without modifying anything.

    Same filtering as ``compact_files``, but only stats each file and checks
    for locks. Returns a ``CompactSummary`` where ``ok=True`` means the file
    is ready to compact, and ``error`` contains the lock reason when not ready.
    """
    files = _filter_files(cfg, db_filter, file_list)
    summary = CompactSummary()
    for fm in files:
        path = fm.source_path(cfg)
        lock_err = _check_lock(path)
        if lock_err:
            size = 0
            try:
                size = os.path.getsize(path) if os.path.exists(path) else 0
            except OSError:
                pass
            summary.results.append(CompactFileResult(
                file=fm.file, source_path=path, ok=False,
                before_bytes=size, error=lock_err,
            ))
        else:
            size = os.path.getsize(path)
            summary.results.append(CompactFileResult(
                file=fm.file, source_path=path, ok=True,
                before_bytes=size,
            ))
    log.info("dry-run: %d ready, %d locked/missing across %d files",
             summary.ok, summary.failed, summary.total_files)
    return summary


def _rm_f(path: str) -> None:
    """Remove *path* if it exists, suppressing any error (best-effort)."""
    try:
        if os.path.exists(path):
            os.remove(path)
    except OSError:
        pass