src/fix_ws_errors.py

# /// script
# requires-python = ">=3.9"
# dependencies = []
# ///
"""Fix known word segmentation errors in UDD-1.1 BIO files.

Seven fix passes:
1.   Split cross-boundary merges (uppercase mid-token signals)
1.5  Split long tokens (5+ syllables) via vocab-based greedy decomposition
2.   Merge always-split compounds (dictionary compounds + inconsistent forms)
2.5  Split foreign word merges (Latin-script tokens without Vietnamese diacritics)
2.75 Split proper name boundary merges (uppercase→lowercase transitions within words)
3.   Validate BIO invariants

Usage:
    uv run src/fix_ws_errors.py                # Fix all splits, write report
    uv run src/fix_ws_errors.py --dry-run      # Report only, no file changes
"""

import argparse
import re
import sys
from collections import Counter, defaultdict
from os.path import dirname, isfile, join

# ============================================================================
# Constants
# ============================================================================

# Compounds that should ALWAYS be merged (conservative curated list)
# Source: SEGMENTATION_EVAL.md sections 2c, 3, 6c + annotation guidelines
# Stored as tuples of lowercase syllables
MERGE_TERMS = {
    # Always-split dictionary compounds (high confidence from 6c)
    ("vụ", "án"),               # 892× split, legal compound
    ("phạt", "tù"),             # 422× split
    ("hủy", "bỏ"),              # 147× split
    ("chữa", "bệnh"),           # 112× split
    ("lời", "khai"),             # 102× split
    ("kèm", "theo"),             # 101× split
    ("ghi", "rõ"),               # 99× split
    ("trả", "lại"),              # 94× split
    ("khám", "bệnh"),            # 57× split
    ("rút", "gọn"),              # 51× split
    ("giấy", "chứng", "nhận"),   # 41× split, 3 syllables
    ("tù", "chung", "thân"),     # 38× split, 3 syllables
    ("quá", "hạn"),              # 31× split
    ("làm", "chủ"),              # 30× split
    ("ô", "nhiễm", "môi", "trường"),  # 26× split, 4 syllables
    # Inconsistent forms — majority is split, should be single
    ("phiên", "tòa"),            # 576 split vs 18 single
    ("hàng", "hóa"),             # 175 split vs 6 single
    ("chủ", "tọa"),              # 125 split vs 7 single
    ("bị", "hại"),               # 96 split vs 6 single
    ("tiền", "công"),            # 62 split vs 2 single
    ("thuê", "khoán"),           # 62 split vs 2 single
    ("hòa", "giải"),             # 53 split vs 30 single
    ("bốc", "hàng"),             # 35 split vs 1 single
    # ---- Cycle 1 gold corrections: new compound merges ----
    ("ủy", "ban"),               # committee
    ("lính", "thú"),             # soldier
    ("mu", "rùa"),               # turtle shell
    ("trêu", "ghẹo"),           # tease
    ("sương", "mai"),            # morning dew
    ("mái", "nhà"),              # roof
    ("nghiến", "răng"),          # gnash teeth
    ("nheo", "nheo"),            # squint
    ("dơn", "dớt"),              # pale/sickly
    ("xua", "tay"),              # wave hand
    ("nói", "gở"),               # say unlucky things
    ("bơi", "chó"),              # dog paddle
    ("người", "thương"),         # beloved
    ("chăn", "lợn"),             # pig herding
    ("khay", "trà"),             # tea tray
    ("đồng", "tự"),              # homograph
    ("tại", "ngũ"),              # in service (military)
    ("hành", "chánh"),           # administration
    ("lượng", "tử"),             # quantum
    ("tích", "lũy"),             # accumulate
    ("siêu", "máy", "tính"),     # supercomputer
    ("đường", "thẳng"),          # straight line
    ("đầm", "đuôi", "cá"),      # fishtail dress
    ("như", "điên"),              # like crazy
    ("tẩy", "chay"),             # boycott
}

# Build index for efficient longest-match lookup: {length: [term, ...]}
_MERGE_BY_LENGTH = defaultdict(list)
for _term in MERGE_TERMS:
    _MERGE_BY_LENGTH[len(_term)].append(_term)
MERGE_MAX_LEN = max(len(t) for t in MERGE_TERMS)

# Tokens with uppercase mid-token that are LEGITIMATE (not errors).
# Stored as lowercase strings (space-joined syllables) for comparison.
# Source: SEGMENTATION_EVAL.md section 2b — proper names and titles.
CROSS_BOUNDARY_WHITELIST = {
    "xã hội chủ nghĩa việt nam",
    "bộ tư pháp",
    "mặt trận tổ quốc việt nam",
    "đảng cộng sản việt nam",
    "tổng liên đoàn lao động",
    "hội đồng trọng tài",
    "chủ tịch",               # all-caps title
    "đại lý",                 # all-caps title
    "nguyễn sinh hùng",       # personal name
    "luật bảo hiểm xã hội",
    "luật bảo vệ",
    "bộ luật lao động",
    "pháp lệnh dân số",
    "bộ tài nguyên và môi trường",
    # Roman numeral sessions
    "khóa xiii",
    "khóa xv",
    "khóa xiv",
    "khóa xii",
    "khóa xi",
}


# ============================================================================
# BIO file I/O
# ============================================================================

def parse_bio_file(filepath):
    """Parse BIO file into list of sentences.

    Returns list of dicts with keys: sent_id, text, syllables, tags.
    """
    sentences = []
    current = {"sent_id": "", "text": "", "syllables": [], "tags": []}

    with open(filepath, "r", encoding="utf-8") as f:
        for line in f:
            line = line.rstrip("\n")
            if line.startswith("# sent_id = "):
                current["sent_id"] = line.split("= ", 1)[1]
                continue
            if line.startswith("# text = "):
                current["text"] = line.split("= ", 1)[1]
                continue
            if line.startswith("#"):
                continue
            if not line:
                if current["syllables"]:
                    sentences.append(dict(current))
                    current = {"sent_id": "", "text": "", "syllables": [], "tags": []}
                continue
            parts = line.split("\t")
            if len(parts) == 2:
                current["syllables"].append(parts[0])
                current["tags"].append(parts[1])

    if current["syllables"]:
        sentences.append(dict(current))

    return sentences


def write_bio_file(sentences, filepath):
    """Write sentences back to BIO format."""
    with open(filepath, "w", encoding="utf-8") as f:
        for sent in sentences:
            f.write(f"# sent_id = {sent['sent_id']}\n")
            f.write(f"# text = {sent['text']}\n")
            for syl, tag in zip(sent["syllables"], sent["tags"]):
                f.write(f"{syl}\t{tag}\n")
            f.write("\n")


def bio_to_words(syllables, tags):
    """Convert syllable-level BIO tags to word list."""
    words = []
    current = []
    for syl, tag in zip(syllables, tags):
        if tag == "B-W":
            if current:
                words.append(" ".join(current))
            current = [syl]
        else:
            current.append(syl)
    if current:
        words.append(" ".join(current))
    return words


def write_conllu(sentences, filepath):
    """Write sentences to CoNLL-U format (word-level, no syntactic annotation)."""
    with open(filepath, "w", encoding="utf-8") as f:
        for sent in sentences:
            f.write(f"# sent_id = {sent['sent_id']}\n")
            f.write(f"# text = {sent['text']}\n")
            words = bio_to_words(sent["syllables"], sent["tags"])
            for i, word in enumerate(words, 1):
                f.write(f"{i}\t{word}\t_\t_\t_\t_\t_\t_\t_\t_\n")
            f.write("\n")


# ============================================================================
# Vocab for long-token splitting
# ============================================================================

def build_split_vocab(all_sentences, min_count=5):
    """Build vocab of 2-4 syllable words for decomposing long tokens.

    Counts every 2-4 syllable word in the dataset (case-insensitive).
    Returns the set of forms that appear at least `min_count` times.
    Excludes entries with function words at boundaries (e.g. "tài nguyên và").
    """
    # Function words that should never be at the edge of a compound
    boundary_stopwords = {"và", "hoặc"}

    vocab = Counter()
    for sent in all_sentences:
        words = bio_to_words(sent["syllables"], sent["tags"])
        for w in words:
            syls = w.split()
            if 2 <= len(syls) <= 4:
                form = " ".join(s.lower() for s in syls)
                vocab[form] += 1
    return {
        form for form, count in vocab.items()
        if count >= min_count
        and form.split()[0] not in boundary_stopwords
        and form.split()[-1] not in boundary_stopwords
    }


def build_viet_syllables(all_sentences, min_count=50):
    """Build set of common Vietnamese syllables for foreign word filtering.

    Counts individual syllables across all sentences and returns those
    appearing at least `min_count` times (lowercased). These are used to
    distinguish Vietnamese multi-syllable words (like "kinh doanh") from
    truly foreign tokens (like "Max Planck").
    """
    counts = Counter()
    for sent in all_sentences:
        for syl in sent["syllables"]:
            counts[syl.lower()] += 1
    return {syl for syl, c in counts.items() if c >= min_count}


# ============================================================================
# Fix passes
# ============================================================================

def fix_cross_boundary(syllables, tags):
    """Pass 1: Split cross-boundary merges.

    Detects transitions from a non-uppercase syllable to an uppercase syllable
    within a multi-syllable word. This catches errors like "tố tụng Người"
    (lowercase "tụng" → uppercase "Người") while preserving proper names like
    "Việt Nam" (both uppercase, no transition).

    If the word (lowercased) is in CROSS_BOUNDARY_WHITELIST, skip it.

    Returns (new_tags, list of change descriptions).
    """
    new_tags = list(tags)
    changes = []

    # Reconstruct word spans: list of (start_idx, end_idx) for each word
    word_spans = []
    current_start = 0
    for i in range(len(tags)):
        if tags[i] == "B-W" and i > 0:
            word_spans.append((current_start, i))
            current_start = i
    word_spans.append((current_start, len(tags)))

    for start, end in word_spans:
        if end - start < 2:
            continue  # single-syllable word

        # Check for lowercase→uppercase transitions within the word.
        # A transition is: preceding syllable does NOT start with uppercase,
        # AND current syllable starts with uppercase. This catches real
        # cross-boundary merges (e.g., "tụng" → "Người") while ignoring
        # proper names where all syllables are uppercase (e.g., "Việt Nam").
        has_transition = False
        for j in range(start + 1, end):
            prev_syl = syllables[j - 1]
            curr_syl = syllables[j]
            if (curr_syl and curr_syl[0].isupper() and
                    prev_syl and not prev_syl[0].isupper()):
                has_transition = True
                break

        if not has_transition:
            continue

        # Check whitelist
        word_lower = " ".join(s.lower() for s in syllables[start:end])
        if word_lower in CROSS_BOUNDARY_WHITELIST:
            continue

        # Split at each lowercase→uppercase transition
        word_before = " ".join(syllables[start:end])
        for j in range(start + 1, end):
            prev_syl = syllables[j - 1]
            curr_syl = syllables[j]
            if (curr_syl and curr_syl[0].isupper() and
                    prev_syl and not prev_syl[0].isupper()):
                new_tags[j] = "B-W"

        word_parts = bio_to_words(syllables[start:end], new_tags[start:end])
        changes.append(f"split \"{word_before}\" → {' + '.join(repr(p) for p in word_parts)}")

    return new_tags, changes


def fix_split_long_tokens(syllables, tags, vocab):
    """Pass 1.5: Split 5+ syllable tokens into sub-words via vocab decomposition.

    For each word with 5+ syllables, apply greedy left-to-right longest-match
    against the vocab (trying 4→3→2 syllable matches). Unmatched syllables
    become single-syllable words.

    Returns (new_tags, list of change descriptions).
    """
    new_tags = list(tags)
    changes = []

    # Reconstruct word spans
    word_spans = []
    current_start = 0
    for i in range(len(tags)):
        if tags[i] == "B-W" and i > 0:
            word_spans.append((current_start, i))
            current_start = i
    word_spans.append((current_start, len(tags)))

    for start, end in word_spans:
        n_syls = end - start
        if n_syls < 5:
            continue

        # Greedy left-to-right longest-match decomposition
        word_before = " ".join(syllables[start:end])
        pos = start
        sub_words = []  # list of (sub_start, sub_end) index pairs

        while pos < end:
            matched = False
            # Try longest match first (4 → 3 → 2 syllables)
            for length in range(min(4, end - pos), 1, -1):
                candidate = " ".join(
                    s.lower() for s in syllables[pos:pos + length]
                )
                if candidate in vocab:
                    sub_words.append((pos, pos + length))
                    pos += length
                    matched = True
                    break
            if not matched:
                sub_words.append((pos, pos + 1))
                pos += 1

        # Only change if we actually split into multiple sub-words
        if len(sub_words) <= 1:
            continue

        # Update tags: B-W at start of each sub-word, I-W within
        for sw_start, sw_end in sub_words:
            new_tags[sw_start] = "B-W"
            for j in range(sw_start + 1, sw_end):
                new_tags[j] = "I-W"

        word_parts = bio_to_words(
            syllables[start:end], new_tags[start:end]
        )
        changes.append(
            f"split \"{word_before}\" → "
            f"{' + '.join(repr(p) for p in word_parts)}"
        )

    return new_tags, changes


def fix_merge_compounds(syllables, tags):
    """Pass 2: Merge always-split compounds.

    Scan syllables left-to-right. At each B-W position, check if the next N
    syllables (all at B-W positions) match a MERGE_TERMS entry (case-insensitive).
    Longest match first. If so, change subsequent B-W tags to I-W.

    Returns (new_tags, list of change descriptions).
    """
    new_tags = list(tags)
    changes = []
    n = len(syllables)
    i = 0

    while i < n:
        if new_tags[i] != "B-W":
            i += 1
            continue

        matched = False
        # Try longest match first
        for length in range(min(MERGE_MAX_LEN, n - i), 1, -1):
            if length not in _MERGE_BY_LENGTH:
                continue

            # Check all syllables in range are B-W (separate words)
            all_bw = True
            for j in range(i, i + length):
                if j > i and new_tags[j] != "B-W":
                    all_bw = False
                    break
            if not all_bw:
                continue

            # Check if syllables match any MERGE_TERMS entry
            candidate = tuple(s.lower() for s in syllables[i:i + length])
            if candidate in MERGE_TERMS:
                # Merge: change B-W to I-W for positions after the first
                parts_before = [syllables[j] for j in range(i, i + length)]
                for j in range(i + 1, i + length):
                    new_tags[j] = "I-W"
                merged = " ".join(parts_before)
                changes.append(f"merge \"{merged}\"")
                i += length
                matched = True
                break

        if not matched:
            i += 1

    return new_tags, changes


def _is_latin_no_vietnamese(s):
    """Check if a string is purely Latin-script without Vietnamese diacritics.

    Returns True for ASCII Latin (a-z, A-Z, 0-9, hyphen) and common Latin
    extensions BUT NOT Vietnamese-specific characters (ă, â, đ, ê, ô, ơ, ư
    and their tone marks).
    """
    # Vietnamese diacritics pattern: any character with Vietnamese-specific marks
    vietnamese_chars = re.compile(
        r'[àáảãạăắằẳẵặâấầẩẫậèéẻẽẹêếềểễệìíỉĩịòóỏõọôốồổỗộơớờởỡợ'
        r'ùúủũụưứừửữựỳýỷỹỵđÀÁẢÃẠĂẮẰẲẴẶÂẤẦẨẪẬÈÉẺẼẸÊẾỀỂỄỆÌÍỈĨỊ'
        r'ÒÓỎÕỌÔỐỒỔỖỘƠỚỜỞỠỢÙÚỦŨỤƯỨỪỬỮỰỲÝỶỸỴĐ]'
    )
    if vietnamese_chars.search(s):
        return False
    # Must contain at least one Latin letter
    return bool(re.search(r'[a-zA-Z]', s))


# Known foreign proper names that should stay merged (whitelist)
FOREIGN_NAME_WHITELIST = {
    "beethoven", "homer", "odysseus", "cecelia", "ahern", "holly",
    "hideoshi", "gurth", "euler", "hilbert", "rydberg", "bohr",
    "frankael-zermelo", "giambattista", "valli", "dachau",
    "habsburg", "newton", "einstein", "darwin", "shakespeare",
}


def fix_foreign_words(syllables, tags, viet_syllables):
    """Pass 2.5: Split foreign word merges.

    Detects multi-syllable tokens where ALL syllables are Latin-script only
    (no Vietnamese diacritics) AND none of the syllables are common Vietnamese
    syllables. Each such foreign syllable becomes its own word (B-W).

    Args:
        syllables: list of syllable strings.
        tags: list of BIO tag strings.
        viet_syllables: set of common Vietnamese syllables (lowercase) for
            filtering out false positives like "kinh doanh".

    Returns (new_tags, list of change descriptions).
    """
    new_tags = list(tags)
    changes = []

    # Reconstruct word spans
    word_spans = []
    current_start = 0
    for i in range(len(tags)):
        if tags[i] == "B-W" and i > 0:
            word_spans.append((current_start, i))
            current_start = i
    word_spans.append((current_start, len(tags)))

    for start, end in word_spans:
        n_syls = end - start
        if n_syls < 2:
            continue

        # Check if ALL syllables are Latin-only (no Vietnamese diacritics)
        all_latin = all(_is_latin_no_vietnamese(syllables[j]) for j in range(start, end))
        if not all_latin:
            continue

        # Check if ANY syllable is a common Vietnamese syllable → skip
        has_viet = any(
            syllables[j].lower() in viet_syllables for j in range(start, end)
        )
        if has_viet:
            continue

        # Check whitelist: if the whole token is a known name, skip
        token_lower = " ".join(syllables[start:end]).lower()
        if token_lower in FOREIGN_NAME_WHITELIST:
            continue

        # Split: make each syllable its own word
        word_before = " ".join(syllables[start:end])
        for j in range(start + 1, end):
            new_tags[j] = "B-W"

        parts = [syllables[j] for j in range(start, end)]
        changes.append(f"split-foreign \"{word_before}\" → {' + '.join(repr(p) for p in parts)}")

    return new_tags, changes


# Vietnamese institutional compound prefixes that should NOT be split by
# the name-boundary pass. Lowercased prefix tuples → the compound is legitimate.
# First-syllable prefixes that start Vietnamese institutional compounds.
# Any multi-syllable word starting with one of these + lowercase continuation
# is likely a legitimate compound, not a proper name boundary error.
NAME_BOUNDARY_WHITELIST_S1 = {
    "ủy",      # Ủy ban (nhân dân / thường vụ / ...)
    "viện",    # Viện kiểm sát / Viện nghiên cứu
    "tổng",    # Tổng giám đốc / Tổng thư ký / ...
    "nhà",     # Nhà khoa học / Nhà xuất bản / Nhà đầu tư
    "phòng",   # Phòng thí nghiệm
    "cảng",    # Cảng hàng không
    "xuất",    # Xuất nhập khẩu
    "sách",    # Sách (title compounds)
    "thuế",    # Thuế thu nhập
    "cây",     # Cây lương thực
    "nói",     # Nói tóm lại
    "bộ",      # Bộ luật dân sự / Bộ Tài chính
    "đại",     # Đại hội đồng
    "lò",      # Lò phản ứng
    "ngay",    # Ngay lập tức
    "việc",    # Việc làm ăn
    "vùng",    # Vùng kinh tế
    "sân",     # Sân vận động
    "tiểu",    # Tiểu văn hóa
    "trang",   # Trang thiết bị
    "tết",     # Tết dương lịch
    "thuyết",  # Thuyết sinh vật học
    "điểm",    # Điểm nóng chảy
    "lý",      # Lý thuyết
    "hệ",      # Hệ tiên đề
}


def fix_proper_name_boundary(syllables, tags, vocab):
    """Pass 2.75: Split proper name boundary merges.

    Detects multi-syllable tokens where uppercase syllables are followed by
    a lowercase common word (in vocab). Pattern: [Uppercase...][lowercase_common]
    → split before the lowercase word.

    This catches cases like "Tống_tiêu_diệt" → "Tống" + "tiêu_diệt" where
    a proper name is merged with the following verb/noun.

    Skips known Vietnamese institutional compounds (NAME_BOUNDARY_WHITELIST_PREFIXES).

    Returns (new_tags, list of change descriptions).
    """
    new_tags = list(tags)
    changes = []

    # Reconstruct word spans
    word_spans = []
    current_start = 0
    for i in range(len(tags)):
        if tags[i] == "B-W" and i > 0:
            word_spans.append((current_start, i))
            current_start = i
    word_spans.append((current_start, len(tags)))

    for start, end in word_spans:
        n_syls = end - start
        if n_syls < 3:
            # Need at least 3 syllables: Name + common_word(s)
            continue

        # Check whitelist: if the first syllable is a known institutional prefix, skip
        if syllables[start].lower() in NAME_BOUNDARY_WHITELIST_S1:
            continue

        # Find the transition point: last uppercase syllable before lowercase
        # Look for pattern: [Title/Upper...][lower...]
        # where the lowercase portion forms a known vocab word
        split_pos = None
        for j in range(start + 1, end):
            curr_syl = syllables[j]
            prev_syl = syllables[j - 1]

            # Transition: previous is title/upper, current is lowercase
            if (prev_syl and prev_syl[0].isupper() and
                    curr_syl and not curr_syl[0].isupper()):
                # Check if remaining syllables form a vocab word
                remaining = " ".join(s.lower() for s in syllables[j:end])
                if remaining in vocab:
                    split_pos = j
                    break
                # Also check if just 2 syllables from here form a vocab word
                if end - j >= 2:
                    two_syl = " ".join(s.lower() for s in syllables[j:j+2])
                    if two_syl in vocab:
                        split_pos = j
                        break

        if split_pos is None:
            continue

        word_before = " ".join(syllables[start:end])
        new_tags[split_pos] = "B-W"
        word_parts = bio_to_words(syllables[start:end], new_tags[start:end])
        changes.append(
            f"split-name-boundary \"{word_before}\" → "
            f"{' + '.join(repr(p) for p in word_parts)}"
        )

    return new_tags, changes


def validate_sentence(syllables, tags):
    """Pass 3: Validate BIO invariants.

    Returns list of error descriptions (empty if valid).
    """
    errors = []
    if not syllables:
        return errors

    if tags[0] != "B-W":
        errors.append(f"sentence starts with {tags[0]} instead of B-W")

    for i, tag in enumerate(tags):
        if tag not in ("B-W", "I-W"):
            errors.append(f"position {i}: invalid tag '{tag}'")

    return errors


# ============================================================================
# Report generation
# ============================================================================

def generate_report(all_stats, output_path=None):
    """Generate markdown report of all changes."""
    lines = []
    lines.append("# WS Fix Report")
    lines.append("")
    lines.append("Fixes applied by `src/fix_ws_errors.py` to UDD-1.1 word segmentation BIO files.")
    lines.append("")

    # Summary table
    lines.append("## Summary")
    lines.append("")
    lines.append("| File | Cross-boundary | Long token | Compound merges | Foreign splits | Name boundary | Validation errors |")
    lines.append("|------|---------------:|-----------:|----------------:|---------------:|--------------:|------------------:|")
    total_splits = 0
    total_long_splits = 0
    total_merges = 0
    total_foreign = 0
    total_name_boundary = 0
    total_errors = 0
    for fname, stats in all_stats.items():
        n_splits = stats["n_cross_boundary"]
        n_long = stats["n_split_long"]
        n_merges = stats["n_merge"]
        n_foreign = stats.get("n_foreign", 0)
        n_name_boundary = stats.get("n_name_boundary", 0)
        n_errors = stats["n_validation_errors"]
        total_splits += n_splits
        total_long_splits += n_long
        total_merges += n_merges
        total_foreign += n_foreign
        total_name_boundary += n_name_boundary
        total_errors += n_errors
        lines.append(f"| {fname} | {n_splits:,} | {n_long:,} | {n_merges:,} | {n_foreign:,} | {n_name_boundary:,} | {n_errors:,} |")
    lines.append(f"| **TOTAL** | **{total_splits:,}** | **{total_long_splits:,}** | **{total_merges:,}** | **{total_foreign:,}** | **{total_name_boundary:,}** | **{total_errors:,}** |")
    lines.append("")

    # Merge term frequency across all files
    lines.append("## Merge Frequency by Term")
    lines.append("")
    merge_counts = Counter()
    for stats in all_stats.values():
        merge_counts += stats["merge_term_counts"]
    lines.append("| Term | Count |")
    lines.append("|:-----|------:|")
    for term, count in merge_counts.most_common():
        lines.append(f"| {term} | {count:,} |")
    lines.append("")

    # Cross-boundary split examples
    lines.append("## Cross-Boundary Split Examples")
    lines.append("")
    for fname, stats in all_stats.items():
        if stats["cross_boundary_examples"]:
            lines.append(f"### {fname}")
            lines.append("")
            for ex in stats["cross_boundary_examples"][:20]:
                lines.append(f"- {ex}")
            if len(stats["cross_boundary_examples"]) > 20:
                lines.append(f"- ... and {len(stats['cross_boundary_examples']) - 20} more")
            lines.append("")

    # Long token split examples
    lines.append("## Long Token Split Examples")
    lines.append("")
    for fname, stats in all_stats.items():
        if stats["split_long_examples"]:
            lines.append(f"### {fname}")
            lines.append("")
            for ex in stats["split_long_examples"][:30]:
                lines.append(f"- {ex}")
            if len(stats["split_long_examples"]) > 30:
                lines.append(f"- ... and {len(stats['split_long_examples']) - 30} more")
            lines.append("")

    # Foreign word split examples
    lines.append("## Foreign Word Split Examples")
    lines.append("")
    for fname, stats in all_stats.items():
        examples = stats.get("foreign_examples", [])
        if examples:
            lines.append(f"### {fname}")
            lines.append("")
            for ex in examples[:30]:
                lines.append(f"- {ex}")
            if len(examples) > 30:
                lines.append(f"- ... and {len(examples) - 30} more")
            lines.append("")

    # Name boundary split examples
    lines.append("## Name Boundary Split Examples")
    lines.append("")
    for fname, stats in all_stats.items():
        examples = stats.get("name_boundary_examples", [])
        if examples:
            lines.append(f"### {fname}")
            lines.append("")
            for ex in examples[:30]:
                lines.append(f"- {ex}")
            if len(examples) > 30:
                lines.append(f"- ... and {len(examples) - 30} more")
            lines.append("")

    report = "\n".join(lines)

    if output_path:
        with open(output_path, "w", encoding="utf-8") as f:
            f.write(report)
        print(f"\nReport written to {output_path}")

    return report


# ============================================================================
# Main
# ============================================================================

def process_file(filepath, vocab=None, viet_syllables=None, sentences=None, dry_run=False):
    """Process a single BIO file: apply fixes, optionally write back.

    Args:
        filepath: Path to BIO file.
        vocab: Set of known 2-4 syllable words for long-token splitting.
            If None, Pass 1.5 and 2.75 are skipped.
        viet_syllables: Set of common Vietnamese syllables for foreign word
            filtering. If None, Pass 2.5 is skipped.
        sentences: Pre-parsed sentences (avoids re-parsing if already loaded).
        dry_run: If True, report changes without modifying files.

    Returns (sentences, stats_dict).
    """
    print(f"\nProcessing {filepath}...")
    if sentences is None:
        sentences = parse_bio_file(filepath)
    print(f"  Loaded {len(sentences):,} sentences")

    total_syllables_before = sum(len(s["syllables"]) for s in sentences)
    total_words_before = sum(
        sum(1 for t in s["tags"] if t == "B-W") for s in sentences
    )

    n_cross_boundary = 0
    n_split_long = 0
    n_merge = 0
    n_foreign = 0
    n_name_boundary = 0
    n_validation_errors = 0
    cross_boundary_examples = []
    split_long_examples = []
    foreign_examples = []
    name_boundary_examples = []
    merge_term_counts = Counter()

    for sent in sentences:
        syls = sent["syllables"]

        # Pass 1: Cross-boundary splits
        tags, cb_changes = fix_cross_boundary(syls, sent["tags"])
        n_cross_boundary += len(cb_changes)
        for ch in cb_changes:
            cross_boundary_examples.append(f"[{sent['sent_id']}] {ch}")

        # Pass 1.5: Split long tokens (5+ syllables)
        if vocab is not None:
            tags, split_changes = fix_split_long_tokens(syls, tags, vocab)
            n_split_long += len(split_changes)
            for ch in split_changes:
                split_long_examples.append(f"[{sent['sent_id']}] {ch}")

        # Pass 2: Merge compounds
        tags, merge_changes = fix_merge_compounds(syls, tags)
        n_merge += len(merge_changes)
        for ch in merge_changes:
            # Extract the merged term for counting
            # Format: 'merge "term"'
            term = ch.split('"')[1] if '"' in ch else ch
            merge_term_counts[term.lower()] += 1

        # Pass 2.5: Split foreign word merges
        if viet_syllables is not None:
            tags, fw_changes = fix_foreign_words(syls, tags, viet_syllables)
            n_foreign += len(fw_changes)
            for ch in fw_changes:
                foreign_examples.append(f"[{sent['sent_id']}] {ch}")

        # Pass 2.75: Split proper name boundary merges
        if vocab is not None:
            tags, nb_changes = fix_proper_name_boundary(syls, tags, vocab)
            n_name_boundary += len(nb_changes)
            for ch in nb_changes:
                name_boundary_examples.append(f"[{sent['sent_id']}] {ch}")

        # Pass 3: Validate
        errors = validate_sentence(syls, tags)
        n_validation_errors += len(errors)
        if errors:
            print(f"  WARN [{sent['sent_id']}]: {'; '.join(errors)}")

        sent["tags"] = tags

    total_syllables_after = sum(len(s["syllables"]) for s in sentences)
    total_words_after = sum(
        sum(1 for t in s["tags"] if t == "B-W") for s in sentences
    )

    print(f"  Cross-boundary splits:    {n_cross_boundary:,}")
    print(f"  Long token splits:        {n_split_long:,}")
    print(f"  Compound merges:          {n_merge:,}")
    print(f"  Foreign word splits:      {n_foreign:,}")
    print(f"  Name boundary splits:     {n_name_boundary:,}")
    print(f"  Validation errors:        {n_validation_errors:,}")
    print(f"  Words: {total_words_before:,} → {total_words_after:,} "
          f"(Δ{total_words_after - total_words_before:+,})")
    assert total_syllables_before == total_syllables_after, \
        f"Syllable count changed: {total_syllables_before} → {total_syllables_after}"
    print(f"  Syllables: {total_syllables_before:,} (unchanged)")

    if not dry_run:
        write_bio_file(sentences, filepath)
        print(f"  Written: {filepath}")

        # Also regenerate CoNLL-U
        conllu_path = filepath.replace(".txt", ".conllu")
        write_conllu(sentences, conllu_path)
        print(f"  Written: {conllu_path}")

    stats = {
        "n_cross_boundary": n_cross_boundary,
        "n_split_long": n_split_long,
        "n_merge": n_merge,
        "n_foreign": n_foreign,
        "n_name_boundary": n_name_boundary,
        "n_validation_errors": n_validation_errors,
        "cross_boundary_examples": cross_boundary_examples,
        "split_long_examples": split_long_examples,
        "foreign_examples": foreign_examples,
        "name_boundary_examples": name_boundary_examples,
        "merge_term_counts": merge_term_counts,
        "words_before": total_words_before,
        "words_after": total_words_after,
    }

    return sentences, stats


def main():
    parser = argparse.ArgumentParser(
        description="Fix known word segmentation errors in UDD-1.1 BIO files."
    )
    parser.add_argument(
        "--dry-run", action="store_true",
        help="Report changes without modifying files"
    )
    args = parser.parse_args()

    base_dir = dirname(dirname(__file__))
    bio_files = [
        join(base_dir, f"udd-ws-v1.1-{split}.txt")
        for split in ("train", "dev", "test")
    ]

    # Check all files exist
    for path in bio_files:
        if not isfile(path):
            print(f"ERROR: {path} not found", file=sys.stderr)
            sys.exit(1)

    if args.dry_run:
        print("=== DRY RUN — no files will be modified ===")

    # Phase 1: Parse all files
    all_sentences_by_file = {}
    for path in bio_files:
        print(f"Loading {path}...")
        all_sentences_by_file[path] = parse_bio_file(path)
        print(f"  {len(all_sentences_by_file[path]):,} sentences")

    # Phase 2: Build vocab from all sentences
    all_sents = [s for sents in all_sentences_by_file.values() for s in sents]
    vocab = build_split_vocab(all_sents)
    print(f"\nBuilt split vocab: {len(vocab):,} entries "
          f"(2-4 syllable words with count >= 5)")
    viet_syllables = build_viet_syllables(all_sents)
    print(f"Built Vietnamese syllable set: {len(viet_syllables):,} entries "
          f"(syllables with count >= 50)")

    # Phase 3: Process each file
    all_stats = {}
    for path in bio_files:
        fname = path.rsplit("/", 1)[-1]
        _, stats = process_file(
            path,
            vocab=vocab,
            viet_syllables=viet_syllables,
            sentences=all_sentences_by_file[path],
            dry_run=args.dry_run,
        )
        all_stats[fname] = stats

    # Generate report
    report_path = join(base_dir, "WS_FIX_REPORT.md")
    if not args.dry_run:
        generate_report(all_stats, report_path)
    else:
        report = generate_report(all_stats)
        print("\n" + report)

    # Final summary
    total_splits = sum(s["n_cross_boundary"] for s in all_stats.values())
    total_long = sum(s["n_split_long"] for s in all_stats.values())
    total_merges = sum(s["n_merge"] for s in all_stats.values())
    total_foreign = sum(s.get("n_foreign", 0) for s in all_stats.values())
    total_name_boundary = sum(s.get("n_name_boundary", 0) for s in all_stats.values())
    total_errors = sum(s["n_validation_errors"] for s in all_stats.values())
    print(f"\n{'='*50}")
    print(f"TOTAL: {total_splits:,} cross-boundary splits, "
          f"{total_long:,} long token splits, "
          f"{total_merges:,} compound merges, "
          f"{total_foreign:,} foreign word splits, "
          f"{total_name_boundary:,} name boundary splits, "
          f"{total_errors:,} validation errors")
    if args.dry_run:
        print("(dry run — no files modified)")


if __name__ == "__main__":
    main()