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

Blobs are stored in S3 via BlobStore. Backup metadata is kept in an
in-memory dict until Step 12 migrates it to 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 time
from email.utils import parsedate_to_datetime
from typing import Any

from fastapi import APIRouter, Depends, Header, HTTPException, Request, Response, status

from app.api.deps import get_current_user
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()

# In-memory backup metadata — replaced by PostgreSQL backup_metadata table in Step 12
_backups: dict[str, list[dict[str, Any]]] = {}  # user_id → list of backup records

# TODO(Step11/12): replace with TierManager.check_quota(user_id)
_TIER_BACKUP_LIMITS_GB: dict[str, int] = {
    "free": 0,
    "pro": 5,
    "power": 25,
    "team": -1,  # unlimited
}


def _check_backup_quota(user_id: str, tier: str, size_bytes: int) -> None:
    """Raise HTTP 402 if the upload would exceed the tier's backup limit."""
    limit_gb = _TIER_BACKUP_LIMITS_GB.get(tier, 0)
    if limit_gb == 0:
        raise HTTPException(
            status_code=status.HTTP_402_PAYMENT_REQUIRED,
            detail="Backup is not available on the free tier",
        )
    if limit_gb == -1:
        return  # unlimited
    limit_bytes = limit_gb * 1024**3
    used = sum(b["size_bytes"] for b in _backups.get(user_id, []))
    if used + size_bytes > limit_bytes:
        raise HTTPException(
            status_code=status.HTTP_402_PAYMENT_REQUIRED,
            detail=f"Backup quota exceeded for tier '{tier}'",
        )


@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),
) -> 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)
    _check_backup_quota(current_user.id, current_user.tier, len(blob))

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

    backup_record: dict[str, Any] = {
        "id": str(x_backup_timestamp),
        "s3_key": s3_key,
        "version": x_backup_version,
        "timestamp": x_backup_timestamp,
        "checksum": x_backup_checksum,
        "size_bytes": len(blob),
    }

    user_backups = _backups.setdefault(current_user.id, [])
    user_backups.append(backup_record)
    user_backups.sort(key=lambda b: b["timestamp"], reverse=True)

    return {"ok": True}


@router.get("/history", response_model=list[BackupMetadata])
async def backup_history(
    current_user: UserProfile = Depends(get_current_user),
) -> list[BackupMetadata]:
    """Return backup metadata records for the authenticated user (no blob bytes)."""
    return [
        BackupMetadata(
            version=b["version"],
            timestamp=b["timestamp"],
            checksum=b["checksum"],
            chunk_count=1,  # single-chunk uploads for now — TODO(Step12): track real count
        )
        for b in _backups.get(current_user.id, [])
    ]


@router.get("")
async def download_backup(
    request: Request,
    current_user: UserProfile = Depends(get_current_user),
) -> Response:
    """Download the latest backup blob. Supports ``If-Modified-Since``."""
    user_backups = _backups.get(current_user.id, [])
    if not user_backups:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="No backup found")

    latest = user_backups[0]

    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),
) -> dict[str, bool]:
    """Delete a specific backup by ID."""
    user_backups = _backups.get(current_user.id, [])
    target = next((b for b in user_backups if b["id"] == backup_id), 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"])
    _backups[current_user.id] = [b for b in user_backups if b["id"] != backup_id]

    return {"ok": True}