"""Single-file import pipeline.

The Importer is the synchronous core of FC-2a's import path. A Celery task
(tasks/import_file.py) instantiates one per job and calls import_one().

The service is intentionally not async — Celery tasks are run in a
synchronous worker process, and the DB session is a sync session passed in
by the task. The Quart side uses an async session via the same models.
"""

import hashlib
import json
import logging
import shutil
from dataclasses import dataclass
from enum import StrEnum
from pathlib import Path

from PIL import Image
from sqlalchemy import select
from sqlalchemy.orm import Session

from ..models import (
    Artist,
    ImageProvenance,
    ImageRecord,
    ImportSettings,
    Post,
    Source,
)
from ..utils.paths import derive_subdir, derive_top_level_artist, hash_suffixed_name
from ..utils.phash import compute_phash, find_similar
from ..utils.sidecar import find_sidecar, parse_sidecar
from ..utils.slug import slugify
from .thumbnailer import Thumbnailer

log = logging.getLogger(__name__)


class SkipReason(StrEnum):
    too_small = "too_small"
    too_transparent = "too_transparent"
    single_color = "single_color"
    duplicate_hash = "duplicate_hash"
    duplicate_phash = "duplicate_phash"
    invalid_image = "invalid_image"


@dataclass(frozen=True)
class ImportResult:
    status: str  # 'imported' | 'skipped' | 'failed' | 'superseded'
    image_id: int | None = None
    skip_reason: SkipReason | None = None
    error: str | None = None


IMAGE_EXTS = {".png", ".jpg", ".jpeg", ".gif", ".webp", ".bmp", ".tif", ".tiff"}
VIDEO_EXTS = {".mp4", ".mov", ".avi", ".mkv", ".webm", ".m4v", ".wmv", ".flv"}
ALL_EXTS = IMAGE_EXTS | VIDEO_EXTS


def is_supported(path: Path) -> bool:
    return path.suffix.lower() in ALL_EXTS


def is_video(path: Path) -> bool:
    return path.suffix.lower() in VIDEO_EXTS


def _mime_for(path: Path) -> str:
    suffix = path.suffix.lower()
    image_mimes = {
        ".png": "image/png",
        ".jpg": "image/jpeg",
        ".jpeg": "image/jpeg",
        ".gif": "image/gif",
        ".webp": "image/webp",
        ".bmp": "image/bmp",
        ".tif": "image/tiff",
        ".tiff": "image/tiff",
    }
    video_mimes = {
        ".mp4": "video/mp4",
        ".mov": "video/quicktime",
        ".avi": "video/x-msvideo",
        ".mkv": "video/x-matroska",
        ".webm": "video/webm",
        ".m4v": "video/x-m4v",
        ".wmv": "video/x-ms-wmv",
        ".flv": "video/x-flv",
    }
    return image_mimes.get(suffix) or video_mimes.get(suffix) or "application/octet-stream"


def _sha256_of(path: Path, chunk_size: int = 1 << 20) -> str:
    h = hashlib.sha256()
    with path.open("rb") as fp:
        while True:
            block = fp.read(chunk_size)
            if not block:
                break
            h.update(block)
    return h.hexdigest()


class Importer:
    """Imports one file at a time. Constructed per-task by the Celery task."""

    def __init__(
        self,
        session: Session,
        images_root: Path,
        import_root: Path,
        thumbnailer: Thumbnailer,
        settings: ImportSettings,
    ):
        self.session = session
        self.images_root = images_root
        self.import_root = import_root
        self.thumbnailer = thumbnailer
        self.settings = settings

    def import_one(self, source: Path) -> ImportResult:
        """The full pipeline for a single file.

        Returns an ImportResult; callers (the Celery task) are responsible for
        translating that into ImportTask.status and ImageRecord linkage.
        """
        if not is_supported(source):
            return ImportResult(
                status="skipped", skip_reason=SkipReason.invalid_image,
                error=f"unsupported extension {source.suffix}",
            )

        # Compute file dimensions (images only) and apply filters.
        width = height = None
        has_alpha = False
        if not is_video(source):
            try:
                with Image.open(source) as im:
                    im.verify()
                with Image.open(source) as im:
                    width, height = im.size
                    has_alpha = im.mode in ("RGBA", "LA") or (
                        im.mode == "P" and "transparency" in im.info
                    )
            except Exception as exc:
                return ImportResult(
                    status="skipped", skip_reason=SkipReason.invalid_image, error=str(exc),
                )

            if (self.settings.min_width and width < self.settings.min_width) or (
                self.settings.min_height and height < self.settings.min_height
            ):
                return ImportResult(
                    status="skipped", skip_reason=SkipReason.too_small,
                    error=f"{width}x{height} below min {self.settings.min_width}x{self.settings.min_height}",
                )

            if self.settings.skip_transparent and has_alpha:
                pct = self._transparency_pct(source)
                if pct >= self.settings.transparency_threshold:
                    return ImportResult(
                        status="skipped", skip_reason=SkipReason.too_transparent,
                        error=f"{pct:.2%} transparent",
                    )

        # Hash dedup (exact).
        sha = _sha256_of(source)
        existing_stmt = select(ImageRecord).where(ImageRecord.sha256 == sha)
        existing = self.session.execute(existing_stmt).scalar_one_or_none()
        if existing:
            return ImportResult(
                status="skipped", skip_reason=SkipReason.duplicate_hash,
                image_id=existing.id, error="sha256 already present",
            )

        # Perceptual near-dup (images only; videos keep phash NULL).
        phash = None
        if not is_video(source):
            with Image.open(source) as im:
                phash = compute_phash(im)
            if phash is not None:
                cand_rows = self.session.execute(
                    select(
                        ImageRecord.phash,
                        ImageRecord.width,
                        ImageRecord.height,
                        ImageRecord.id,
                    ).where(ImageRecord.phash.is_not(None))
                ).all()
                candidates = [
                    (c.phash, c.width or 0, c.height or 0, c.id)
                    for c in cand_rows
                ]
                rel, match_id = find_similar(
                    phash, width or 0, height or 0,
                    candidates, self.settings.phash_threshold,
                )
                if rel == "larger_exists":
                    return ImportResult(
                        status="skipped",
                        skip_reason=SkipReason.duplicate_phash,
                        image_id=match_id,
                        error="perceptual near-duplicate of larger existing image",
                    )
                if rel == "smaller_exists":
                    target = self.session.get(ImageRecord, match_id)
                    self._supersede(target, source, sha, phash, width, height)
                    return ImportResult(
                        status="superseded", image_id=match_id
                    )

        # Destination path.
        subdir = derive_subdir(source, self.import_root)
        dest_dir = self.images_root / subdir if subdir else self.images_root
        dest_dir.mkdir(parents=True, exist_ok=True)
        dest_name = hash_suffixed_name(source.stem, sha, source.suffix)
        dest = dest_dir / dest_name

        # Atomic copy: write to .partial, rename. Avoids half-imported files on crash.
        partial = dest.with_suffix(dest.suffix + ".partial")
        shutil.copy2(source, partial)
        partial.rename(dest)

        record = ImageRecord(
            path=str(dest),
            sha256=sha,
            phash=phash,
            size_bytes=dest.stat().st_size,
            mime=_mime_for(source),
            width=width,
            height=height,
            origin="imported_filesystem",
            integrity_status="unknown",
        )
        self.session.add(record)
        self.session.flush()

        # Folder→artist auto-tag.
        artist = None
        artist_name = derive_top_level_artist(source, self.import_root)
        if artist_name:
            artist = self._attach_artist(record, artist_name)

        # Sidecar provenance (best-effort; never fails the import).
        self._apply_sidecar(record, source, artist)

        # Thumbnail is queued separately by the calling task; the importer
        # does not generate thumbnails inline so the import queue stays moving.

        self.session.commit()
        return ImportResult(status="imported", image_id=record.id)

    def _upsert_artist(self, name: str) -> Artist:
        slug = slugify(name)
        artist = self.session.execute(
            select(Artist).where(Artist.slug == slug)
        ).scalar_one_or_none()
        if artist is None:
            artist = Artist(name=name, slug=slug, is_subscription=False)
            self.session.add(artist)
            self.session.flush()
        return artist

    def _attach_artist(self, record: ImageRecord, artist_name: str) -> Artist:
        """Upsert the Artist and set it as the image's canonical artist.
        Artist-kind tags were retired in FC-2d-vii-c — the Artist row is
        the single source of truth. Returns the Artist (sidecar
        provenance attaches its Source to it)."""
        artist = self._upsert_artist(artist_name)
        if record.artist_id is None:
            record.artist_id = artist.id
            self.session.flush()
        return artist

    @staticmethod
    def _sidecar_artist_name(data: dict) -> str | None:
        for k in ("artist", "author_name"):
            v = data.get(k)
            if isinstance(v, str) and v.strip():
                return v.strip()
        for k in ("user", "creator"):
            v = data.get(k)
            if isinstance(v, str) and v.strip():
                return v.strip()
            if isinstance(v, dict):
                for sub in ("name", "full_name", "vanity", "account"):
                    sv = v.get(sub)
                    if isinstance(sv, str) and sv.strip():
                        return sv.strip()
        return None

    def _apply_sidecar(
        self, record: ImageRecord, source: Path, artist: Artist | None
    ) -> None:
        sc = find_sidecar(source)
        if sc is None:
            return
        try:
            data = json.loads(sc.read_text("utf-8"))
            if not isinstance(data, dict):
                raise ValueError("sidecar JSON is not an object")
        except Exception as exc:
            log.warning("sidecar parse failed for %s: %s", sc, exc)
            return

        sd = parse_sidecar(data)

        if artist is None:
            name = self._sidecar_artist_name(data)
            if name:
                artist = self._upsert_artist(name)
        if artist is None:
            log.warning(
                "sidecar present for %s but no artist; skipping provenance",
                source,
            )
            return

        if record.artist_id is None:
            record.artist_id = artist.id

        platform = sd.platform or "unknown"
        url = sd.post_url or f"sidecar:{platform}"
        src = self.session.execute(
            select(Source).where(
                Source.artist_id == artist.id,
                Source.platform == platform,
                Source.url == url,
            )
        ).scalar_one_or_none()
        if src is None:
            src = Source(artist_id=artist.id, platform=platform, url=url)
            self.session.add(src)
            self.session.flush()

        epid = sd.external_post_id or sc.stem
        post = self.session.execute(
            select(Post).where(
                Post.source_id == src.id,
                Post.external_post_id == epid,
            )
        ).scalar_one_or_none()
        if post is None:
            post = Post(source_id=src.id, external_post_id=epid)
            self.session.add(post)
            self.session.flush()
        if sd.post_url is not None:
            post.post_url = sd.post_url
        if sd.post_title is not None:
            post.post_title = sd.post_title
        if sd.post_date is not None:
            post.post_date = sd.post_date
        if sd.description is not None:
            post.description = sd.description
        if sd.attachment_count is not None:
            post.attachment_count = sd.attachment_count
        post.raw_metadata = sd.raw

        exists = self.session.execute(
            select(ImageProvenance.id).where(
                ImageProvenance.image_record_id == record.id,
                ImageProvenance.post_id == post.id,
            )
        ).scalar_one_or_none()
        if exists is None:
            self.session.add(
                ImageProvenance(
                    image_record_id=record.id,
                    post_id=post.id,
                    source_id=src.id,
                    captured_metadata=sd.raw,
                )
            )
        if record.primary_post_id is None:
            record.primary_post_id = post.id
        self.session.flush()

    def _supersede(
        self, existing: ImageRecord, source: Path, sha: str,
        phash: str, width: int | None, height: int | None,
    ) -> None:
        """Replace `existing`'s file with the larger `source`, keeping the
        row id (so tags/series/curation stay attached). ML is cleared so
        the import task re-derives it on the new pixels."""
        subdir = derive_subdir(source, self.import_root)
        dest_dir = self.images_root / subdir if subdir else self.images_root
        dest_dir.mkdir(parents=True, exist_ok=True)
        dest = dest_dir / hash_suffixed_name(source.stem, sha, source.suffix)
        partial = dest.with_suffix(dest.suffix + ".partial")
        shutil.copy2(source, partial)
        partial.rename(dest)

        old_path = existing.path
        old_thumb = existing.thumbnail_path

        existing.path = str(dest)
        existing.sha256 = sha
        existing.phash = phash
        existing.size_bytes = dest.stat().st_size
        existing.mime = _mime_for(source)
        existing.width = width
        existing.height = height
        existing.thumbnail_path = None
        existing.integrity_status = "unknown"
        existing.tagger_predictions = None
        existing.tagger_model_version = None
        existing.siglip_embedding = None
        existing.siglip_model_version = None
        existing.centroid_scores = None
        # created_at intentionally preserved; updated_at auto-bumps.
        self.session.flush()
        self.session.commit()

        for stale in (old_path, old_thumb):
            if not stale:
                continue
            try:
                p = Path(stale)
                if p.exists():
                    p.unlink()
            except Exception:
                # Benign orphan; the DB swap already committed. Don't undo it.
                pass

    def _transparency_pct(self, source: Path) -> float:
        """Fraction of fully-transparent pixels in the image. 0.0 if no alpha."""
        with Image.open(source) as im:
            if im.mode not in ("RGBA", "LA") and not (
                im.mode == "P" and "transparency" in im.info
            ):
                return 0.0
            if im.mode != "RGBA":
                im = im.convert("RGBA")
            alpha = im.getchannel("A")
            histogram = alpha.histogram()
            transparent = histogram[0]
            total = sum(histogram)
            return transparent / total if total else 0.0