"""二维码往返自检（开发工具，不参与运行时）。

作用：解码我们自己生成的 QR SVG，验证 **能被读回原文本**——避免"看起来像二维码
但扫不出来"的假成功。这不是完整 QR 解码器，只覆盖生成器用到的子集
（Model 2 / 字节模式 / 纠错 L / 掩码 0），用于回归验证。

用法：
    python -m apps.printing.qr_selftest
"""

from __future__ import annotations

import base64
import re
import sys

from .qr import VERSIONS_L, ALIGN_POS, _size_of, _pick_version


def _svg_to_matrix(svg: str) -> list:
    """从生成的 SVG 还原模块矩阵（正方形 rect 拼回去，无需图像库）。"""
    m = re.search(r'viewBox="0 0 (\d+) (\d+)"', svg)
    if not m:
        raise ValueError("no viewBox")
    total = int(m.group(1))
    # 模块边长 = 总边长 / (size + 2*border)，从第一个 rect 的 width 推断
    rects = re.findall(r'<rect x="(\d+)" y="(\d+)" width="(\d+)" height="(\d+)"/>', svg)
    if not rects:
        raise ValueError("no rects")
    scale = int(rects[0][3])              # height = scale
    size = total // scale
    grid = [[1] * size for _ in range(size)]     # 背景白=0，先全填 0 再置黑
    grid = [[0] * size for _ in range(size)]
    for x, y, w, h in rects:
        x, y, w, h = int(x), int(y), int(w), int(h)
        r0, c0 = y // scale, x // scale
        for dc in range(w // scale):
            if 0 <= r0 < size and c0 + dc < size:
                grid[r0][c0 + dc] = 1
    return grid


def _strip_border(grid: list) -> list:
    """去掉静默区，回到纯模块矩阵。"""
    size = len(grid)
    # 找第一行/列全 0 的边界（静默区）
    def all_zero(values):
        return all(v == 0 for v in values)

    top = 0
    while top < size and all_zero(grid[top]):
        top += 1
    left = 0
    while left < size and all_zero([grid[r][left] for r in range(size)]):
        left += 1
    bottom = size - 1
    while bottom >= 0 and all_zero(grid[bottom]):
        bottom -= 1
    right = size - 1
    while right >= 0 and all_zero([grid[r][right] for r in range(size)]):
        right -= 1
    return [row[left:right + 1] for row in grid[top:bottom + 1]]


def _read_format(mat: list) -> tuple:
    """读左上格式信息 → (纠错级别, 掩码)。"""
    size = len(mat)
    seq = [(8, 0), (8, 1), (8, 2), (8, 3), (8, 4), (8, 5), (8, 7), (8, 8),
           (7, 8), (5, 8), (4, 8), (3, 8), (2, 8), (1, 8), (0, 8)]
    bits = 0
    for i, (r, c) in enumerate(seq):
        bits |= (mat[r][c] & 1) << i
    bits ^= 0b101010000010010
    ec = (bits >> 13) & 0b11
    mask = (bits >> 10) & 0b111
    return ec, mask


def _unmask(mat: list, mask: int) -> list:
    """按掩码规则还原数据区。"""
    from .qr import _is_function

    size = len(mat)
    version = (size - 17) // 4
    out = [row[:] for row in mat]
    for r in range(size):
        for c in range(size):
            if _is_function(r, c, version):
                continue
            invert = False
            if mask == 0:
                invert = (r + c) % 2 == 0
            elif mask == 1:
                invert = r % 2 == 0
            elif mask == 2:
                invert = c % 3 == 0
            elif mask == 3:
                invert = (r + c) % 3 == 0
            if invert:
                out[r][c] ^= 1
    return out


def _extract_bits(mat: list, version: int | None = None) -> list:
    """按之字形路径读出数据位（跳过功能模块）。"""
    from .qr import _is_function

    size = len(mat)
    version = version if version is not None else (size - 17) // 4
    bits = []
    col = size - 1
    upward = True
    while col > 0:
        if col == 6:
            col -= 1
        rows = range(size - 1, -1, -1) if upward else range(size)
        for row in rows:
            for c in (col, col - 1):
                if not _is_function(row, c, version):
                    bits.append(mat[row][c] & 1)
        upward = not upward
        col -= 2
    return bits


def _bits_to_bytes(bits: list) -> bytes:
    out = bytearray()
    for i in range(0, len(bits) - 7, 8):
        b = 0
        for j in range(8):
            b = (b << 1) | bits[i + j]
        out.append(b)
    return bytes(out)


def decode(svg: str) -> str | None:
    """解码本模块生成的 QR SVG，返回原文；失败返回 None。

    流程：SVG → 模块矩阵 → 去静默区 → 读格式信息(纠错/掩码) → 去掩码
          → 之字形读位 → 字节模式解析。
    """
    from .qr import _is_function

    grid = _svg_to_matrix(svg)
    mat = _strip_border(grid)
    size = len(mat)
    version = (size - 17) // 4
    if version not in VERSIONS_L:
        return None

    ec, mask = _read_format(mat)
    if ec != 0b01:                        # 只支持纠错 L
        return None

    # 去掩码
    base = [row[:] for row in mat]
    for r in range(size):
        for c in range(size):
            if _is_function(r, c, version):
                continue
            if mask == 0 and (r + c) % 2 == 0:
                base[r][c] ^= 1
            elif mask == 1 and r % 2 == 0:
                base[r][c] ^= 1
            elif mask == 2 and c % 3 == 0:
                base[r][c] ^= 1
            elif mask == 3 and (r + c) % 3 == 0:
                base[r][c] ^= 1

    # 之字形读位
    bits = []
    col = size - 1
    upward = True
    while col > 0:
        if col == 6:
            col -= 1
        rows = range(size - 1, -1, -1) if upward else range(size)
        for row in rows:
            for c in (col, col - 1):
                if not _is_function(row, c, version):
                    bits.append(base[row][c] & 1)
        upward = not upward
        col -= 2

    # 位流解析（注意：不能按字节边界切——模式 4 位 + 长度 8 位 = 12 位，
    # 数据从第 12 位开始，跨字节。早期版本按字节取导致整体错位。）
    if len(bits) < 12:
        return None
    if bits[0:4] != [0, 1, 0, 0]:          # 字节模式
        return None
    length = 0
    for b in bits[4:12]:                    # 版本 1-9：长度 8 位
        length = (length << 1) | b
    need = 12 + length * 8
    if length <= 0 or len(bits) < need:
        return None
    payload = bytearray()
    for i in range(length):
        byte = 0
        for j in range(8):
            byte = (byte << 1) | bits[12 + i * 8 + j]
        payload.append(byte)
    try:
        return payload.decode("utf-8")
    except UnicodeDecodeError:
        return None


def selftest() -> int:
    """往返测试若干载荷，返回失败数。"""
    from .qr import qr_svg_data_uri

    samples = [
        "/api/v1/open/statements/9eb70e10-82e1-47d1-bc5b-fb3e0716ba19/",
        "https://dealerhub.example.com/api/v1/open/statements/c71ac955-27d6-4942-968c-720a6afe5394/",
        "HELLO-DEALERHUB-2026",
        "1",
        "a" * 60,
        "对账单-中文测试",
    ]
    failed = 0
    for text in samples:
        uri = qr_svg_data_uri(text, scale=4)
        svg = base64.b64decode(uri.split(",", 1)[1]).decode("utf-8")
        got = decode(svg)
        ok = got == text
        failed += 0 if ok else 1
        mark = "✓" if ok else "✗"
        print(f"  {mark} len={len(text):3d} expect={text[:45]!r}"
              + ("" if ok else f"  got={got!r}"))
    print(f"\n往返测试：{len(samples) - failed}/{len(samples)} 通过")
    return failed


if __name__ == "__main__":
    sys.exit(1 if selftest() else 0)