"""Backup routes: upload, download, history, and delete E2E-encrypted backups.

Blobs are stored in S3 via BlobStore. Backup metadata is persisted in the
PostgreSQL ``backup_metadata`` table.

IMPORTANT: GET /history must be declared BEFORE GET / to avoid FastAPI
treating "history" as a ``{backup_id}`` path parameter.
"""

from __future__ import annotations

import uuid
from email.utils import parsedate_to_datetime

from fastapi import APIRouter, Depends, Header, HTTPException, Request, Response, status
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

from app.api.deps import get_current_user
from app.billing.tier_manager import tier_manager
from app.db import get_session
from app.models import BackupMetadata as BackupMetadataModel
from app.schemas import BackupMetadata, UserProfile
from app.storage.blob_store import BlobStore
from app.storage.encryption import reject_if_tampered

router = APIRouter(prefix="/backup", tags=["backup"])

_blob_store = BlobStore()


async def _current_backup_bytes(user_id: str, db: AsyncSession) -> int:
    """Return total backup bytes stored by *user_id*."""
    result = await db.execute(
        select(func.coalesce(func.sum(BackupMetadataModel.size_bytes), 0)).where(
            BackupMetadataModel.user_id == user_id
        )
    )
    return int(result.scalar_one())


async def _check_backup_quota(
    user: UserProfile, size_bytes: int, db: AsyncSession
) -> None:
    """Raise HTTP 402 if the upload would exceed the tier's backup limit."""
    current = await _current_backup_bytes(user.id, db)
    tier_manager.enforce_backup_quota(
        user.tier, current_bytes=current, additional_bytes=size_bytes
    )


@router.put("")
async def upload_backup(
    request: Request,
    x_backup_version: int = Header(..., alias="X-Backup-Version"),
    x_backup_timestamp: int = Header(..., alias="X-Backup-Timestamp"),
    x_backup_checksum: str = Header(..., alias="X-Backup-Checksum"),
    current_user: UserProfile = Depends(get_current_user),
    db: AsyncSession = Depends(get_session),
) -> dict[str, bool]:
    """Upload an E2E-encrypted backup blob.

    Metadata is passed via custom headers; the raw body is the encrypted blob.
    """
    blob = await request.body()
    reject_if_tampered(blob, x_backup_checksum)
    await _check_backup_quota(current_user, len(blob), db)

    s3_key = await _blob_store.upload(
        current_user.id, "backup", str(x_backup_timestamp), blob, x_backup_checksum
    )

    row = BackupMetadataModel(
        id=str(uuid.uuid4()),
        user_id=current_user.id,
        s3_key=s3_key,
        version=x_backup_version,
        timestamp=x_backup_timestamp,
        checksum=x_backup_checksum,
        size_bytes=len(blob),
    )
    db.add(row)
    await db.commit()

    return {"ok": True}


@router.get("/history", response_model=list[BackupMetadata])
async def backup_history(
    current_user: UserProfile = Depends(get_current_user),
    db: AsyncSession = Depends(get_session),
) -> list[BackupMetadata]:
    """Return backup metadata records for the authenticated user (no blob bytes)."""
    result = await db.execute(
        select(BackupMetadataModel)
        .where(BackupMetadataModel.user_id == current_user.id)
        .order_by(BackupMetadataModel.timestamp.desc())
    )
    rows = result.scalars().all()
    return [
        BackupMetadata(
            version=r.version,
            timestamp=r.timestamp,
            checksum=r.checksum,
            chunk_count=1,
        )
        for r in rows
    ]


@router.get("")
async def download_backup(
    request: Request,
    current_user: UserProfile = Depends(get_current_user),
    db: AsyncSession = Depends(get_session),
) -> Response:
    """Download the latest backup blob. Supports ``If-Modified-Since``."""
    result = await db.execute(
        select(BackupMetadataModel)
        .where(BackupMetadataModel.user_id == current_user.id)
        .order_by(BackupMetadataModel.timestamp.desc())
        .limit(1)
    )
    latest = result.scalar_one_or_none()
    if latest is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="No backup found")

    ims_header = request.headers.get("If-Modified-Since")
    if ims_header:
        try:
            ims_dt = parsedate_to_datetime(ims_header)
            ims_ms = int(ims_dt.timestamp() * 1000)
            if latest.timestamp <= ims_ms:
                return Response(status_code=status.HTTP_304_NOT_MODIFIED)
        except Exception:
            pass  # malformed header — ignore and serve the blob

    blob = await _blob_store.download(current_user.id, latest.s3_key)
    return Response(
        content=blob,
        media_type="application/octet-stream",
        headers={
            "X-Backup-Version": str(latest.version),
            "X-Backup-Timestamp": str(latest.timestamp),
            "X-Checksum": latest.checksum,
        },
    )


@router.delete("/{backup_id}", response_model=dict)
async def delete_backup(
    backup_id: str,
    current_user: UserProfile = Depends(get_current_user),
    db: AsyncSession = Depends(get_session),
) -> dict[str, bool]:
    """Delete a specific backup by ID."""
    result = await db.execute(
        select(BackupMetadataModel).where(
            BackupMetadataModel.id == backup_id,
            BackupMetadataModel.user_id == current_user.id,
        )
    )
    target = result.scalar_one_or_none()
    if target is None:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Backup not found")

    await _blob_store.delete(current_user.id, target.s3_key)
    await db.delete(target)
    await db.commit()

    return {"ok": True}