from __future__ import annotations

import secrets
from datetime import datetime, timedelta
from pathlib import Path

from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app import config
from app.models import Item
from app.schemas import ItemCreate, TTLOption

TTL_DELTAS: dict[TTLOption, timedelta | None] = {
    "1h": timedelta(hours=1),
    "24h": timedelta(days=1),
    "7d": timedelta(days=7),
    "never": None,
}


def _slug() -> str:
    return secrets.token_urlsafe(8)


def _expires_at(ttl: TTLOption, now: datetime | None = None) -> datetime | None:
    delta = TTL_DELTAS[ttl]
    if delta is None:
        return None
    return (now or datetime.utcnow()) + delta


def _title_from_body(body: str) -> str:
    first = body.split("\n", 1)[0].strip()
    return first[:255]


def _is_unavailable(item: Item, now: datetime | None = None) -> bool:
    if item.burned:
        return True
    now = now or datetime.utcnow()
    if item.expires_at is not None and item.expires_at <= now:
        return True
    return False


def item_to_dict(item: Item, *, include_body: bool = True) -> dict:
    data = {
        "slug": item.slug,
        "kind": item.kind,
        "title": item.title,
        "file_name": item.file_name,
        "mime": item.mime,
        "size_bytes": item.size_bytes,
        "is_public": item.is_public,
        "burn_after_read": item.burn_after_read,
        "expires_at": item.expires_at,
        "created_at": item.created_at,
        "view_count": item.view_count,
    }
    if include_body:
        data["body"] = item.body
    return data


def create_text_item(db: Session, payload: ItemCreate, created_ip: str) -> Item:
    now = datetime.utcnow()
    title = payload.title if payload.title is not None else _title_from_body(payload.body)
    item = Item(
        slug=_slug(),
        kind="text",
        title=title[:255],
        body=payload.body,
        is_public=payload.is_public,
        burn_after_read=payload.burn_after_read,
        expires_at=_expires_at(payload.ttl, now),
        created_ip=created_ip,
        created_at=now,
    )
    db.add(item)
    db.commit()
    db.refresh(item)
    return item


def create_file_item(
    db: Session,
    *,
    file_name: str,
    file_path: str,
    mime: str,
    size_bytes: int,
    is_public: bool,
    burn_after_read: bool,
    ttl: TTLOption,
    created_ip: str,
    title: str | None = None,
) -> Item:
    now = datetime.utcnow()
    item = Item(
        slug=_slug(),
        kind="file",
        title=(title or file_name)[:255],
        body=None,
        file_name=file_name,
        file_path=file_path,
        mime=mime,
        size_bytes=size_bytes,
        is_public=is_public,
        burn_after_read=burn_after_read,
        expires_at=_expires_at(ttl, now),
        created_ip=created_ip,
        created_at=now,
    )
    db.add(item)
    db.commit()
    db.refresh(item)
    return item


def resolve_file_path(item: Item) -> Path | None:
    if not item.file_path:
        return None
    path = Path(item.file_path)
    if not path.is_absolute():
        path = config.settings.data_dir / path
    return path


def get_file_item(db: Session, slug: str) -> Item | None:
    item = db.scalar(select(Item).where(Item.slug == slug))
    if item is None or item.kind != "file" or _is_unavailable(item):
        return None
    return item


def claim_burn(db: Session, item: Item) -> None:
    """Mark burn consumed in DB before streaming bytes."""
    item.burned = True
    db.commit()


def delete_item_file(item: Item) -> None:
    """Remove file bytes from disk (safe after response has finished streaming)."""
    path = resolve_file_path(item)
    if path is not None:
        try:
            path.unlink(missing_ok=True)
        except OSError:
            pass


def burn_file_item(db: Session, item: Item) -> None:
    """Mark a file item burned and remove its bytes from disk."""
    claim_burn(db, item)
    delete_item_file(item)


def get_item(db: Session, slug: str) -> Item | None:
    item = db.scalar(select(Item).where(Item.slug == slug))
    if item is None or _is_unavailable(item):
        return None

    item.view_count += 1
    # File items burn on download, not metadata fetch.
    if item.burn_after_read and item.kind != "file":
        item.burned = True
    db.commit()
    db.refresh(item)
    return item


def list_wall(
    db: Session,
    *,
    page: int = 1,
    page_size: int = 20,
) -> tuple[list[Item], int]:
    page = max(page, 1)
    page_size = min(max(page_size, 1), 100)
    now = datetime.utcnow()

    filters = [
        Item.is_public.is_(True),
        Item.burned.is_(False),
        (Item.expires_at.is_(None) | (Item.expires_at > now)),
    ]
    total = db.scalar(select(func.count()).select_from(Item).where(*filters)) or 0
    items = list(
        db.scalars(
            select(Item)
            .where(*filters)
            .order_by(Item.created_at.desc())
            .offset((page - 1) * page_size)
            .limit(page_size)
        ).all()
    )
    return items, total