watermarks-remover/service/scripts/text_unicode.py

"""Layer A: invisible Unicode / homoglyph space detection and cleaning."""

from __future__ import annotations

import unicodedata
from collections import Counter
from dataclasses import dataclass, field
from difflib import SequenceMatcher

# Format / invisible controls commonly used for steganography or broken pastes.
STRIP_CODEPOINTS: frozenset[int] = frozenset(
    {
        0x00AD,  # soft hyphen
        0x034F,  # combining grapheme joiner
        0x061C,  # Arabic letter mark
        0x115F,  # Hangul choseong filler
        0x1160,  # Hangul jungseong filler
        0x17B4,  # Khmer vowel inherent AQ
        0x17B5,  # Khmer vowel inherent AA
        0x180B,  # Mongolian free variation selector-1
        0x180C,
        0x180D,
        0x180E,  # Mongolian vowel separator
        0x180F,  # Mongolian free variation selector-4 (Unicode 14)
        0x200B,  # zero width space
        0x200C,  # zero width non-joiner
        0x200D,  # zero width joiner
        0x200E,  # LRM
        0x200F,  # RLM
        0x202A,  # LRE
        0x202B,  # RLE
        0x202C,  # PDF
        0x202D,  # LRO
        0x202E,  # RLO
        0x2060,  # word joiner
        0x2061,  # function application
        0x2062,  # invisible times
        0x2063,  # invisible separator
        0x2064,  # invisible plus
        0x2066,  # LRI
        0x2067,  # RLI
        0x2068,  # FSI
        0x2069,  # PDI
        0x206A,  # inhibit symmetric swapping
        0x206B,
        0x206C,
        0x206D,
        0x206E,
        0x206F,
        0xFEFF,  # BOM / ZWNBSP
        0xFE00,  # variation selectors
        0xFE01,
        0xFE02,
        0xFE03,
        0xFE04,
        0xFE05,
        0xFE06,
        0xFE07,
        0xFE08,
        0xFE09,
        0xFE0A,
        0xFE0B,
        0xFE0C,
        0xFE0D,
        0xFE0E,
        0xFE0F,
        0x3164,  # Hangul filler (blank compatibility jamo)
        0xFFA0,  # halfwidth Hangul filler
        0xFFF9,  # interlinear annotation
        0xFFFA,
        0xFFFB,
    }
)

# Spaces that look like (or substitute for) U+0020.
SPACE_HOMOGLYPHS: dict[int, str] = {
    0x00A0: " ",  # no-break space
    0x1680: " ",  # Ogham space mark
    0x2000: " ",  # en quad
    0x2001: " ",  # em quad
    0x2002: " ",  # en space
    0x2003: " ",  # em space
    0x2004: " ",  # three-per-em space
    0x2005: " ",  # four-per-em space
    0x2006: " ",  # six-per-em space
    0x2007: " ",  # figure space
    0x2008: " ",  # punctuation space
    0x2009: " ",  # thin space
    0x200A: " ",  # hair space
    0x202F: " ",  # narrow no-break space
    0x205F: " ",  # medium mathematical space
    0x3000: " ",  # ideographic space
}

# Optional confusable Latin lookalikes (aggressive mode only).
LATIN_CONFUSABLES: dict[int, str] = {
    0x0410: "A",  # Cyrillic
    0x0412: "B",
    0x0415: "E",
    0x041A: "K",
    0x041C: "M",
    0x041D: "H",
    0x041E: "O",
    0x0420: "P",
    0x0421: "C",
    0x0422: "T",
    0x0425: "X",
    0x0430: "a",
    0x0435: "e",
    0x043E: "o",
    0x0440: "p",
    0x0441: "c",
    0x0443: "y",
    0x0445: "x",
    0x0456: "i",
    0xFF21: "A",  # fullwidth
    0xFF22: "B",
    0xFF23: "C",
    0xFF24: "D",
    0xFF25: "E",
    0xFF26: "F",
    0xFF27: "G",
    0xFF28: "H",
    0xFF29: "I",
    0xFF2A: "J",
    0xFF2B: "K",
    0xFF2C: "L",
    0xFF2D: "M",
    0xFF2E: "N",
    0xFF2F: "O",
    0xFF30: "P",
    0xFF31: "Q",
    0xFF32: "R",
    0xFF33: "S",
    0xFF34: "T",
    0xFF35: "U",
    0xFF36: "V",
    0xFF37: "W",
    0xFF38: "X",
    0xFF39: "Y",
    0xFF3A: "Z",
    0xFF41: "a",
    0xFF42: "b",
    0xFF43: "c",
    0xFF44: "d",
    0xFF45: "e",
    0xFF46: "f",
    0xFF47: "g",
    0xFF48: "h",
    0xFF49: "i",
    0xFF4A: "j",
    0xFF4B: "k",
    0xFF4C: "l",
    0xFF4D: "m",
    0xFF4E: "n",
    0xFF4F: "o",
    0xFF50: "p",
    0xFF51: "q",
    0xFF52: "r",
    0xFF53: "s",
    0xFF54: "t",
    0xFF55: "u",
    0xFF56: "v",
    0xFF57: "w",
    0xFF58: "x",
    0xFF59: "y",
    0xFF5A: "z",
}

# Variation selectors beyond FE0x (VS17-VS256 in Supplementary Special-purpose)
_VS_SUPPLEMENT = range(0xE0100, 0xE01F0)

# Unassigned code points with Other_Default_Ignorable_Code_Point=Yes: reserved
# for future default-ignorable characters, so conformant renderers display them
# invisibly today and normalisation preserves them. They have no legitimate use
# in interchange text (conformance clause C7), which makes them ideal covert
# carriers. Kept as explicit ranges, never a category-Cn rule: unicodedata is
# pinned per Python build, so a Cn rule would destroy freshly assigned real
# characters. Re-check these ranges on Unicode version bumps: assignment turns
# a strip entry into a potential preserve-in-context case, exactly as happened
# when U+180F became Mongolian FVS4 in Unicode 14.
_RESERVED_IGNORABLE_CPS: frozenset[int] = frozenset({0x2065, 0xE0000})
_RESERVED_IGNORABLE_RANGES: tuple[range, ...] = (
    range(0xFFF0, 0xFFF9),
    range(0xE0080, 0xE0100),
    range(0xE01F0, 0xE1000),
)


def _is_reserved_ignorable(cp: int) -> bool:
    if cp in _RESERVED_IGNORABLE_CPS:
        return True
    return any(cp in r for r in _RESERVED_IGNORABLE_RANGES)


# The 66 Unicode noncharacters: U+FDD0..U+FDEF plus U+nFFFE/U+nFFFF at the
# end of every plane. Permanently reserved for internal use and prohibited in
# interchange text (TUS 23.7), so any occurrence in interchange is contraband.
# Rendered as nothing or tofu, preserved by normalisation, and permanently
# unassignable, so stripping them carries no future-Unicode risk.
def _is_noncharacter(cp: int) -> bool:
    return 0xFDD0 <= cp <= 0xFDEF or (cp & 0xFFFE) == 0xFFFE


# Bidi / directional format controls (subset of strip set, finer inspect labels)
_BIDI_CPS: frozenset[int] = frozenset(
    {
        0x061C,
        0x200E,
        0x200F,
        0x202A,
        0x202B,
        0x202C,
        0x202D,
        0x202E,
        0x2066,
        0x2067,
        0x2068,
        0x2069,
    }
)

# Directional marks and isolates are legitimate in mixed RTL/LTR prose. Inspect
# them, but preserve them during the default clean. Paired LRE/RLE embeddings
# (see _valid_bidi_embedding_indices) are preserved too; overrides and
# unpaired embeddings remain destructive by default because they can reorder
# unrelated spans.
_PRESERVABLE_BIDI_CPS: frozenset[int] = frozenset(
    {
        0x061C,
        0x200E,
        0x200F,
        0x2066,
        0x2067,
        0x2068,
        0x2069,
    }
)

# Visible-layout format controls: Egyptian hieroglyph quadrat controls,
# Duployan shorthand overlap/step controls, and musical beam/tie/slur/phrase
# controls are Cf but visibly govern how their script renders. Next to their
# own script they are document body, not carriers; floating between unrelated
# text they stay strip-class. Context ranges include each script's own block
# (and the controls themselves) so control sequences survive intact.
_LAYOUT_CF_CONTROLS: tuple[tuple[range, range], ...] = (
    (range(0x13430, 0x13440), range(0x13000, 0x14400)),  # Egyptian hieroglyphs
    (range(0x1BCA0, 0x1BCA4), range(0x1BC00, 0x1BCA4)),  # Duployan shorthand
    (range(0x1D173, 0x1D17B), range(0x1D100, 0x1D200)),  # musical symbols
)


def _layout_cf_script(cp: int) -> range | None:
    for controls, script in _LAYOUT_CF_CONTROLS:
        if cp in controls:
            return script
    return None


# Zero-width family (common edit-based carriers)
_ZW_FAMILY: frozenset[int] = frozenset({0x200B, 0x200C, 0x200D, 0x2060, 0xFEFF, 0x180E})


def _is_private_use(cp: int) -> bool:
    """BMP and supplementary private-use planes (Co: no portable meaning)."""
    return 0xE000 <= cp <= 0xF8FF or 0xF0000 <= cp <= 0xFFFFD or 0x100000 <= cp <= 0x10FFFD


def _is_strip_cp(cp: int) -> bool:
    if cp in STRIP_CODEPOINTS:
        return True
    if cp in _VS_SUPPLEMENT:
        return True
    # Tag characters used in some stego schemes (U+E0001-U+E007F)
    if 0xE0001 <= cp <= 0xE007F:
        return True
    if _is_noncharacter(cp):
        return True
    if _is_reserved_ignorable(cp):
        return True
    return bool(_is_private_use(cp))


def _strip_kind(cp: int) -> str:
    """Finer-grained inspect kind for strip-class codepoints."""
    if 0xE0001 <= cp <= 0xE007F:
        return "tag_chars"
    if _is_noncharacter(cp):
        return "noncharacter"
    if _is_reserved_ignorable(cp):
        return "reserved_ignorable"
    if cp in _VS_SUPPLEMENT or 0xFE00 <= cp <= 0xFE0F or cp in _MONGOLIAN_FVS:
        return "variation_selector"
    if cp in _BIDI_CPS:
        return "bidi"
    if cp in _ZW_FAMILY:
        return "zwj_family"
    if _is_private_use(cp):
        return "private_use"
    return "strip"


# Emoji presentation glue: zero-width joiner and text/emoji variation
# selectors. These are invisible carriers when free-floating, but after an
# emoji base they are part of the visible sequence (⚖️, 👨‍👩‍👧, ❤️‍🔥) and
# stripping them visibly alters the text.
EMOJI_GLUE_CODEPOINTS: frozenset[int] = frozenset({0x200D, 0xFE0E, 0xFE0F})


def _is_emoji_glue(cp: int) -> bool:
    return cp in EMOJI_GLUE_CODEPOINTS


def _is_emoji_base(cp: int) -> bool:
    """Return True for characters that can start or continue an emoji sequence."""
    if 0x1F000 <= cp <= 0x1FAFF:
        return True
    if 0x2190 <= cp <= 0x25FF:  # arrows, technical symbols, enclosed symbols
        return True
    if 0x2600 <= cp <= 0x27BF:  # misc symbols / dingbats / arrows
        return True
    if 0x2B00 <= cp <= 0x2BFF:  # misc symbols and arrows
        return True
    if cp in (0x00A9, 0x00AE, 0x2122, 0x3030, 0x303D, 0x3297, 0x3299):
        return True
    # keycap bases
    return cp in (0x0023, 0x002A) or 0x0030 <= cp <= 0x0039


# ZWNJ/ZWJ are orthographic inside complex scripts (Persian می‌روم, Devanagari
# क्‍ष); flag emoji are an emoji base followed by tag chars (🏴󠁧󠁢󠁳󠁣󠁴󠁿); and a
# handful of Cf codepoints are normal Arabic/Syriac orthography, not carriers.
# So are Mongolian free variation selectors (choose a glyph of the preceding
# letter), Khmer inherent vowels (invisible but phonemic), and Hangul fillers
# (hold a jamo slot in a partial syllable). Each is only meaningful directly
# after a base from its own script; isolated instances are contraband.
_SCRIPT_JOINERS: frozenset[int] = frozenset({0x200C, 0x200D})
_TAG_RANGE = range(0xE0020, 0xE0080)
_ORTHOGRAPHIC_CF: frozenset[int] = frozenset(
    {0x0600, 0x0601, 0x0602, 0x0603, 0x0604, 0x0605, 0x06DD, 0x070F, 0x08E2, 0x110BD, 0x110CD}
)
_MONGOLIAN_FVS: frozenset[int] = frozenset({0x180B, 0x180C, 0x180D, 0x180F})
_KHMER_VOWELS: frozenset[int] = frozenset({0x17B4, 0x17B5})
_HANGUL_FILLERS: frozenset[int] = frozenset({0x115F, 0x1160, 0x3164, 0xFFA0})
_SCRIPT_GLUE: frozenset[int] = _MONGOLIAN_FVS | _KHMER_VOWELS | _HANGUL_FILLERS


def _joining_script(cp: int) -> str | None:
    """Return a broad script group where ZWJ/ZWNJ can be orthographic."""
    for start, end, name in (
        (0x0600, 0x08FF, "arabic"),
        (0x0900, 0x0DFF, "indic"),
        (0x0F00, 0x109F, "south-asian"),
        (0x1780, 0x17FF, "khmer"),
        (0x1800, 0x18AF, "mongolian"),
    ):
        if start <= cp <= end and unicodedata.category(chr(cp))[0] in ("L", "M"):
            return name
    return None


def _is_cjk_ideograph(cp: int) -> bool:
    return (
        0x3400 <= cp <= 0x4DBF
        or 0x4E00 <= cp <= 0x9FFF
        or 0xF900 <= cp <= 0xFAFF
        or 0x20000 <= cp <= 0x323AF
    )


def _is_mongolian_base(cp: int) -> bool:
    return 0x1800 <= cp <= 0x18AF


def _is_variation_selector(cp: int) -> bool:
    return cp in _VS_SUPPLEMENT or 0xFE00 <= cp <= 0xFE0F or cp in _MONGOLIAN_FVS


def _valid_flag_tag_indices(text: str) -> set[int]:
    """Indices in complete subdivision-flag tag sequences."""
    valid: set[int] = set()
    i = 0
    while i < len(text):
        if ord(text[i]) != 0x1F3F4:  # waving black flag
            i += 1
            continue
        j = i + 1
        while j < len(text) and 0xE0020 <= ord(text[j]) <= 0xE007E:
            j += 1
        if j > i + 1 and j < len(text) and ord(text[j]) == 0xE007F:
            valid.update(range(i + 1, j + 1))
            i = j + 1
        else:
            i += 1
    return valid


def _valid_bidi_embedding_indices(text: str) -> set[int]:
    """Indices belonging to complete LRE/RLE ... PDF pairs, excluding overrides."""
    valid: set[int] = set()
    stack: list[tuple[int, int]] = []
    for index, char in enumerate(text):
        cp = ord(char)
        if cp in (0x202A, 0x202B, 0x202D, 0x202E):
            stack.append((cp, index))
        elif cp == 0x202C:
            if not stack:
                continue
            opener, opener_index = stack.pop()
            if opener in (0x202A, 0x202B):
                valid.update((opener_index, index))
    return valid


def _is_mongolian_letter(cp: int) -> bool:
    return 0x1800 <= cp <= 0x18AF and unicodedata.category(chr(cp))[0] == "L"


def _is_khmer_letter(cp: int) -> bool:
    return 0x1780 <= cp <= 0x17FF and unicodedata.category(chr(cp))[0] == "L"


def _is_hangul_jamo(cp: int) -> bool:
    # Conjoining jamo plus the compatibility and halfwidth presentation forms,
    # so each filler can follow letters of its own form (U+115F/U+1160 after
    # conjoining jamo, U+3164 after compatibility jamo, U+FFA0 after halfwidth).
    return (
        0x1100 <= cp <= 0x11FF
        or 0xA960 <= cp <= 0xA97C  # Hangul Jamo Extended-A
        or 0xD7B0 <= cp <= 0xD7C6  # Hangul Jamo Extended-B
        or 0x3131 <= cp <= 0x318E  # Hangul Compatibility Jamo (incl. U+3164)
        or 0xFFA1 <= cp <= 0xFFDC  # halfwidth Hangul jamo letters
    )


def _is_glue(cp: int) -> bool:
    """Load-bearing invisible char: emoji glue, script joiner, flag tag char,
    or same-script filler/selector (Mongolian FVS, Khmer vowel, Hangul filler)."""
    return (
        _is_emoji_glue(cp)
        or _is_variation_selector(cp)
        or cp in _SCRIPT_JOINERS
        or cp in _TAG_RANGE
        or cp in _SCRIPT_GLUE
    )


def _decide(
    ch: str,
    prev_kept: str | None,
    prev_input: str | None,
    next_input: str | None,
    *,
    valid_flag_tag: bool,
    valid_bidi_embedding: bool,
    normalize_spaces: bool,
    treat_confusables: bool,
    strip_emoji_glue: bool,
    strip_bidi: bool,
) -> tuple[str, str, str | None]:
    """Classify one input char for both inspect and clean.

    Returns ``(action, out_char, kind)`` where action is ``keep``, ``strip``
    or ``replace``; out_char is the surviving character for keep/replace; and
    kind is the inspect classification (None when not suspicious).
    """
    cp = ord(ch)
    if valid_bidi_embedding and not strip_bidi:
        return ("keep", ch, None)
    if cp in _PRESERVABLE_BIDI_CPS and not strip_bidi:
        return ("keep", ch, None)
    if prev_input is not None and not strip_emoji_glue:
        prev_cp = ord(prev_input)
        if cp in _VS_SUPPLEMENT and _is_cjk_ideograph(prev_cp):
            return ("keep", ch, None)
        if cp in _MONGOLIAN_FVS and _is_mongolian_base(prev_cp):
            return ("keep", ch, None)
        if 0xFE00 <= cp <= 0xFE0D and _is_cjk_ideograph(prev_cp):
            return ("keep", ch, None)
    if _is_emoji_glue(cp) and not strip_emoji_glue:
        if cp in (0xFE0E, 0xFE0F) and prev_input is not None and _is_emoji_base(ord(prev_input)):
            return ("keep", ch, None)
        if (
            cp == 0x200D
            and prev_kept is not None
            and next_input is not None
            and _is_emoji_base(ord(prev_kept))
            and _is_emoji_base(ord(next_input))
        ):
            return ("keep", ch, None)
    if not strip_emoji_glue:
        if cp in _SCRIPT_JOINERS and prev_input is not None and next_input is not None:
            prev_script = _joining_script(ord(prev_input))
            next_script = _joining_script(ord(next_input))
            if prev_script is not None and prev_script == next_script:
                return ("keep", ch, None)
        if cp in _TAG_RANGE and valid_flag_tag:
            return ("keep", ch, None)
        if cp in _MONGOLIAN_FVS and prev_kept is not None and _is_mongolian_letter(ord(prev_kept)):
            return ("keep", ch, None)
        if cp in _KHMER_VOWELS and prev_kept is not None and _is_khmer_letter(ord(prev_kept)):
            return ("keep", ch, None)
        if cp in _HANGUL_FILLERS and prev_kept is not None and _is_hangul_jamo(ord(prev_kept)):
            return ("keep", ch, None)
        if cp in _ORTHOGRAPHIC_CF:
            return ("keep", ch, None)
        script = _layout_cf_script(cp)
        if script is not None and (
            (prev_input is not None and ord(prev_input) in script)
            or (next_input is not None and ord(next_input) in script)
        ):
            return ("keep", ch, None)
    if _is_strip_cp(cp):
        return ("strip", "", _strip_kind(cp))
    if normalize_spaces and cp in SPACE_HOMOGLYPHS:
        return ("replace", SPACE_HOMOGLYPHS[cp], "space")
    if treat_confusables and cp in LATIN_CONFUSABLES:
        return ("replace", LATIN_CONFUSABLES[cp], "confusable")
    if unicodedata.category(ch) == "Cf" and cp not in SPACE_HOMOGLYPHS:
        return ("strip", "", "other_cf")
    return ("keep", ch, None)


def _char_label(ch: str) -> str:
    cp = ord(ch)
    name = unicodedata.name(ch, "UNKNOWN")
    cat = unicodedata.category(ch)
    return f"U+{cp:04X} {name} ({cat})"


def _hit_confidence(kind: str) -> str:
    """Layer A hits are edit-based carriers; space homoglyphs are weaker context."""
    return "informational" if kind == "space" else "probable"


@dataclass
class CharHit:
    codepoint: int
    char: str
    label: str
    count: int
    kind: str  # strip | bidi | tag_chars | variation_selector | zwj_family | private_use | noncharacter | reserved_ignorable | space | confusable | other_cf
    samples: list[int] = field(default_factory=list)  # character offsets


@dataclass
class TextInspectReport:
    length: int
    suspicious_total: int
    hits: list[CharHit]
    notes: list[str] = field(default_factory=list)

    def to_dict(self) -> dict:
        return {
            "length": self.length,
            "suspicious_total": self.suspicious_total,
            "hits": [
                {
                    "codepoint": f"U+{h.codepoint:04X}",
                    "label": h.label,
                    "count": h.count,
                    "kind": h.kind,
                    "confidence": _hit_confidence(h.kind),
                    "sample_offsets": h.samples[:10],
                }
                for h in self.hits
            ],
            "notes": self.notes,
        }


def inspect_text(
    text: str,
    *,
    aggressive: bool = False,
    strip_emoji_glue: bool = False,
) -> TextInspectReport:
    buckets: dict[tuple[int, str], list[int]] = {}
    prev_kept: str | None = None
    valid_flag_tags = _valid_flag_tag_indices(text)
    valid_bidi_embeddings = _valid_bidi_embedding_indices(text)
    for i, ch in enumerate(text):
        action, out_char, kind = _decide(
            ch,
            prev_kept,
            text[i - 1] if i > 0 else None,
            text[i + 1] if i + 1 < len(text) else None,
            valid_flag_tag=i in valid_flag_tags,
            valid_bidi_embedding=i in valid_bidi_embeddings,
            normalize_spaces=True,
            treat_confusables=aggressive,
            strip_emoji_glue=strip_emoji_glue,
            strip_bidi=True,
        )
        if kind is None:
            # Kept; glue (emoji/script joiner/tag) does not advance the
            # "previous kept" base so ZWJ chains and flag runs stay bound.
            if not _is_glue(ord(ch)):
                prev_kept = out_char
            continue
        key = (ord(ch), kind)
        buckets.setdefault(key, []).append(i)
        if action == "replace":
            prev_kept = out_char
        # strip: prev_kept unchanged

    hits: list[CharHit] = []
    total = 0
    for (cp, kind), offsets in sorted(buckets.items(), key=lambda x: (-len(x[1]), x[0][0])):
        ch = chr(cp)
        hits.append(
            CharHit(
                codepoint=cp,
                char=ch,
                label=_char_label(ch),
                count=len(offsets),
                kind=kind,
                samples=offsets[:10],
            )
        )
        total += len(offsets)

    notes = [
        "Layer A only: invisible/format Unicode and space homoglyphs (edit-based carriers).",
        "Statistical (token-sampling) watermarks are not detectable here; use Layer B rewrite.",
        "Inspect kinds: strip, bidi, tag_chars, variation_selector, zwj_family, private_use, space, confusable, other_cf.",
        "Load-bearing invisibles are preserved by default during cleaning: emoji glue, CJK/Mongolian variation selectors, script joiners, complete flag tag sequences, same-script fillers/selectors (Mongolian FVS, Khmer inherent vowels, Hangul jamo fillers), RTL directional marks/paired embeddings, orthographic Arabic/Syriac Cf marks, and visible-layout format controls next to their own script (Egyptian hieroglyph quadrat, Duployan shorthand, musical beaming). Inspection still reports bidi controls. Use explicit strip flags only after review.",
    ]
    if not hits:
        notes.append(
            "No deterministic Layer A (invisible Unicode/format) carriers detected; "
            "statistical and pixel-domain marks are out of scope here."
        )
    return TextInspectReport(length=len(text), suspicious_total=total, hits=hits, notes=notes)


def clean_text(
    text: str,
    *,
    nfkc: bool = False,
    aggressive_homoglyphs: bool = False,
    normalize_spaces: bool = True,
    strip_emoji_glue: bool = False,
    strip_bidi: bool = False,
) -> tuple[str, dict]:
    """Return cleaned text and a stats dict."""
    removed: Counter[str] = Counter()
    replaced: Counter[str] = Counter()
    out_chars: list[str] = []
    prev_kept: str | None = None
    valid_flag_tags = _valid_flag_tag_indices(text)
    valid_bidi_embeddings = _valid_bidi_embedding_indices(text)

    for i, ch in enumerate(text):
        action, out_char, _kind = _decide(
            ch,
            prev_kept,
            text[i - 1] if i > 0 else None,
            text[i + 1] if i + 1 < len(text) else None,
            valid_flag_tag=i in valid_flag_tags,
            valid_bidi_embedding=i in valid_bidi_embeddings,
            normalize_spaces=normalize_spaces,
            treat_confusables=aggressive_homoglyphs,
            strip_emoji_glue=strip_emoji_glue,
            strip_bidi=strip_bidi,
        )
        if action == "keep":
            out_chars.append(out_char)
            # Glue (emoji/script joiner/tag) does not advance the "previous
            # kept" base, so ZWJ chains (❤️‍🔥) and flag runs stay bound.
            if not _is_glue(ord(ch)):
                prev_kept = out_char
        elif action == "replace":
            out_chars.append(out_char)
            replaced[_char_label(ch)] += 1
            prev_kept = out_char
        else:  # strip
            removed[_char_label(ch)] += 1
            # prev_kept unchanged

    result = "".join(out_chars)
    nfkc_changed = False
    if nfkc:
        before = result
        result = unicodedata.normalize("NFKC", result)
        if result != before:
            nfkc_changed = True
            changed_inputs = sum(
                end - start
                for operation, start, end, _new_start, _new_end in SequenceMatcher(
                    None, before, result, autojunk=False
                ).get_opcodes()
                if operation != "equal"
            )
            replaced["NFKC_normalize"] += changed_inputs or 1

    # Collapse runs of spaces only if we introduced space replacements? Keep conservative: no.

    stats = {
        "input_length": len(text),
        "output_length": len(result),
        "removed": dict(removed),
        "replaced": dict(replaced),
        "removed_count": sum(removed.values()),
        "replaced_count": sum(replaced.values()),
        "nfkc_changed": nfkc_changed,
    }
    return result, stats


def human_report(report: TextInspectReport) -> str:
    lines = [
        f"Length: {report.length} chars",
        f"Suspicious: {report.suspicious_total}",
    ]
    if report.hits:
        lines.append("Hits:")
        for h in report.hits:
            lines.append(
                f"  [{h.kind}/{_hit_confidence(h.kind)}] {h.label} x{h.count} @ {h.samples[:5]}"
            )
    for n in report.notes:
        lines.append(f"Note: {n}")
    return "\n".join(lines)