"""QR generation engine. No credit deduction — generation is free and unlimited."""
import io
import secrets
import zipfile

import segno

from app.core.config import settings
from app.models.documents import QRStyle

_EC_MAP = {"L": "l", "M": "m", "Q": "q", "H": "h"}


def new_code(prefix: str = "vp") -> str:
    return f"{prefix}{secrets.token_urlsafe(8).replace('-', '').replace('_', '')[:10]}".lower()


def verify_url(code: str) -> str:
    return f"{settings.frontend_url}/v/{code}"


def _make(code: str, style: QRStyle) -> segno.QRCode:
    ec = _EC_MAP.get(style.error_correction.upper(), "m")
    if style.logo_url:
        ec = "h"  # force high error correction when a logo is overlaid
    return segno.make(verify_url(code), error=ec)


def render_png(code: str, style: QRStyle, scale: int = 10) -> bytes:
    buf = io.BytesIO()
    _make(code, style).save(buf, kind="png", scale=scale,
                            dark=style.fg_color, light=style.bg_color,
                            border=style.quiet_zone)
    return buf.getvalue()


def render_svg(code: str, style: QRStyle, scale: int = 10) -> bytes:
    buf = io.BytesIO()
    _make(code, style).save(buf, kind="svg", scale=scale,
                            dark=style.fg_color, light=style.bg_color,
                            border=style.quiet_zone)
    return buf.getvalue()


def render_pdf(code: str, style: QRStyle, scale: int = 10) -> bytes:
    buf = io.BytesIO()
    _make(code, style).save(buf, kind="pdf", scale=scale,
                            dark=style.fg_color, light=style.bg_color,
                            border=style.quiet_zone)
    return buf.getvalue()


def render(code: str, style: QRStyle, fmt: str = "png") -> tuple[bytes, str]:
    fmt = fmt.lower()
    if fmt == "svg":
        return render_svg(code, style), "image/svg+xml"
    if fmt == "pdf":
        return render_pdf(code, style), "application/pdf"
    return render_png(code, style), "image/png"


def zip_codes(codes: list[str], style: QRStyle, fmt: str = "png") -> bytes:
    """Bundle per-pack QRs (Option 2) into a single downloadable ZIP."""
    buf = io.BytesIO()
    ext = {"svg": "svg", "pdf": "pdf"}.get(fmt.lower(), "png")
    with zipfile.ZipFile(buf, "w", zipfile.ZIP_DEFLATED) as zf:
        for i, code in enumerate(codes, start=1):
            data, _ = render(code, style, fmt)
            zf.writestr(f"qr_{i:05d}_{code}.{ext}", data)
    return buf.getvalue()