import os
from typing import Optional

from fastapi import APIRouter, Depends, HTTPException, Query, status
from pydantic import BaseModel

from core.config import LOG_FILE
from core.dependencies import require_admin

router = APIRouter(prefix="/api/admin/logs", tags=["admin-logs"])

_LEVEL_ORDER = {"DEBUG": 0, "INFO": 1, "WARNING": 2, "ERROR": 3, "CRITICAL": 4}


class LogsResponse(BaseModel):
    lines: list[str]
    log_file: Optional[str]
    total_returned: int


def _read_tail(path: str, n: int) -> list[str]:
    """Return the last *n* lines from *path* using a memory-efficient seek."""
    size = os.path.getsize(path)
    if size == 0:
        return []
    # Read in chunks from the end
    chunk = 1 << 14  # 16 KB
    lines: list[bytes] = []
    with open(path, "rb") as fh:
        pos = size
        while len(lines) <= n and pos > 0:
            pos = max(pos - chunk, 0)
            fh.seek(pos)
            data = fh.read(min(chunk, size - pos))
            lines = data.split(b"\n") + lines
            # If we have more lines than needed, trim from the front
            if len(lines) > n + 1:
                lines = lines[-(n + 1):]
    # Drop empty last element caused by trailing newline
    result = [ln.decode("utf-8", errors="replace") for ln in lines if ln]
    return result[-n:] if len(result) > n else result


@router.get("", response_model=LogsResponse)
async def get_logs(
    _: dict = Depends(require_admin),
    lines: int = Query(200, ge=1, le=2000, description="Number of lines to return (tail)"),
    level: Optional[str] = Query(None, description="Minimum log level: DEBUG, INFO, WARNING, ERROR, CRITICAL"),
):
    if not LOG_FILE:
        raise HTTPException(
            status_code=status.HTTP_404_NOT_FOUND,
            detail="Log file not configured (LOG_FILE env variable is not set).",
        )
    if not os.path.isfile(LOG_FILE):
        return LogsResponse(lines=[], log_file=LOG_FILE, total_returned=0)

    raw = _read_tail(LOG_FILE, lines)

    if level:
        level_upper = level.upper()
        if level_upper not in _LEVEL_ORDER:
            raise HTTPException(
                status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
                detail=f"Invalid level '{level}'. Must be one of: {', '.join(_LEVEL_ORDER)}.",
            )
        min_order = _LEVEL_ORDER[level_upper]
        filtered: list[str] = []
        for line in raw:
            for lvl, order in _LEVEL_ORDER.items():
                if lvl in line and order >= min_order:
                    filtered.append(line)
                    break
            else:
                # Lines that don't match any known level keyword are included
                # only when filtering at DEBUG (include everything)
                if min_order == 0:
                    filtered.append(line)
        raw = filtered

    return LogsResponse(lines=raw, log_file=LOG_FILE, total_returned=len(raw))