"""Chinese text → Japanese Katakana converter."""

import re
from pypinyin import pinyin, Style

from pinyin2kana_data import PINYIN2KANA

_CHINESE_CHAR_RE = re.compile(r"[\u4e00-\u9fa5]")
_CHINESE_SEGMENT_RE = re.compile(r"([\u4e00-\u9fa5]+)")
_NUMBER_RE = re.compile(r"-?\d+(\.\d+)?")
_TONE_RE = re.compile(r"\d")

_KANA_SAFE_RE = re.compile(
    r"[\u3040-\u309F\u30A0-\u30FF\uFF65-\uFF9F"
    r"\u30FC\u309B\u309C"
    r"\u3001\u3002\uFF01\uFF1F"
    r"\u300C\u300D"
    r"\u30FB\u3000"
    r"a-zA-Z0-9 ]"
)

_CHINESE_DIGITS = ["零", "一", "二", "三", "四", "五", "六", "七", "八", "九"]
_CHINESE_UNITS = ["", "十", "百", "千", "万"]
_CHINESE_POINT = "点"


def _number_to_chinese(num_str: str) -> str:
    num_str = num_str.strip("-")
    if "." in num_str:
        integer_part, decimal_part = num_str.split(".", 1)
    else:
        integer_part, decimal_part = num_str, ""
    result = ""
    if integer_part == "0" or integer_part == "":
        result = "零"
    else:
        digits = [int(ch) for ch in integer_part]
        n = len(digits)
        for i, d in enumerate(digits):
            pos = n - i - 1
            if d == 0:
                if i < n - 1 and digits[i + 1] != 0:
                    result += _CHINESE_DIGITS[0]
            else:
                result += _CHINESE_DIGITS[d]
                unit_idx = pos % 4
                wan = pos // 4
                if wan > 0 and unit_idx == 0:
                    result += _CHINESE_UNITS[4]
                else:
                    result += _CHINESE_UNITS[unit_idx]
    if decimal_part:
        result += _CHINESE_POINT
        for ch in decimal_part:
            result += _CHINESE_DIGITS[int(ch)]
    return result


def _strip_tone(py: str) -> str:
    return _TONE_RE.sub("", py)


def chinese_to_kana(text: str, convert_numbers: bool = True) -> str:
    if not text or not text.strip():
        return ""
    working = text
    if convert_numbers:
        def _replace_num(m: re.Match) -> str:
            return _number_to_chinese(m.group(0))
        working = _NUMBER_RE.sub(_replace_num, working)
    if not _CHINESE_CHAR_RE.search(working):
        return text
    segments = _CHINESE_SEGMENT_RE.split(working)
    result_parts: list[str] = []
    for seg in segments:
        if not seg:
            continue
        if _CHINESE_CHAR_RE.match(seg[0]):
            py_list = pinyin(seg, style=Style.TONE3, heteronym=False)
            for py_item in py_list:
                py_raw = py_item[0]
                py_plain = _strip_tone(py_raw)
                kana = PINYIN2KANA.get(py_plain, py_plain)
                result_parts.append(kana)
        else:
            result_parts.append(seg)
    result = "".join(result_parts)
    result = re.sub(r"(?<=\S) (?=\S)", "", result)
    return result


def filter_kana(text: str) -> str:
    filtered = "".join(c for c in text if _KANA_SAFE_RE.match(c))
    return filtered.strip().lower()