import base64
import random
import time

from app.services.auth import create_access_token
from app.utils.redis import get_redis

# In-memory fallback when Redis is not available
_captcha_store: dict[str, tuple[int, float]] = {}


async def generate_slider_captcha() -> dict:
    """Generate a slider captcha challenge."""
    captcha_id = "".join(random.choices("abcdefghijklmnopqrstuvwxyz0123456789", k=16))

    redis = get_redis()
    if redis:
        await redis.setex(f"captcha:{captcha_id}", 300, "1")
    else:
        _captcha_store[captcha_id] = (True, time.time() + 300)

    bg_data = _create_placeholder_image(300, 150, "#e2e8f0", "拖动滑块到最右侧完成验证")
    slider_data = _create_placeholder_image(50, 50, "#6366f1", "")

    return {
        "captcha_id": captcha_id,
        "background_image": bg_data,
        "slider_image": slider_data,
        "slider_width": 50,
    }


async def verify_slider_captcha(captcha_id: str, x_offset: int) -> str | None:
    """Verify slider captcha. Return a captcha_token on success."""
    redis = get_redis()
    valid = False

    if redis:
        stored = await redis.get(f"captcha:{captcha_id}")
        if stored:
            valid = True
        await redis.delete(f"captcha:{captcha_id}")
    else:
        entry = _captcha_store.pop(captcha_id, None)
        if entry:
            _, expires = entry
            if time.time() < expires:
                valid = True

    if not valid:
        return None

    # User must drag at least 70% of the way (x_offset >= 182 out of 260)
    if x_offset >= 180:
        return create_access_token(f"captcha:{captcha_id}")
    return None


def _create_placeholder_image(width: int, height: int, color: str, text: str) -> str:
    svg = (
        f'<svg xmlns="http://www.w3.org/2000/svg" width="{width}" height="{height}">'
        f'<rect width="100%" height="100%" fill="{color}" rx="8"/>'
        f'<text x="50%" y="50%" dominant-baseline="middle" text-anchor="middle" '
        f'font-family="sans-serif" font-size="14" fill="#64748b">{text}</text>'
        f'</svg>'
    )
    return f"data:image/svg+xml;base64,{base64.b64encode(svg.encode()).decode()}"