code/gemination.py

"""Amharic gemination from HornMorpho analyses.

Amharic gemination (consonant doubling) changes meaning but is not written in
Ge'ez script. HornMorpho (Michael Gasser, https://github.com/hltdi/HornMorpho)
computes it while analysing a word, and keeps it in the `seg` field if and only
if you call

    hm.anal('a', word, degem=False)

With the default degem=True the marks are stripped. With degem=False, the
character `/` stands immediately before every geminated character of the
morphemic segmentation, whatever caused the doubling: the root template, the
passive/reciprocal prefix t- assimilating to the first root consonant, a
suffix such as the auxiliary -all, a lexicon entry, or reduplication.

Example segs (degem=False):

    ይገኛል  passive imperfect   ----ይ</ገ/ኝ>---ኣ/ል---   ገ (t- prefix), ኛ (root), ል (suffix)
    ክልል   noun                -<ክ/ልል>------          ል (lexicon)
    የሚገኙ  relative            የ--/ም--ይ</ገ/ኝ>ኡ------  ሚ (prefix), ገ (t- prefix), ኙ (root)

The seg is morphemic, not a copy of the surface word: vowels merge across
morpheme boundaries (ቀም + ኣል gives ቀማል), palatalisation changes letters
(ን + ኢ gives ኝ), and the glottal letter of a vowel-initial suffix disappears.
This module therefore aligns the seg letters to the surface word by consonant
series and moves each `/` to the surface character it aligned with.

Do not read gemination from the `+gemN` feature instead. It only describes the
root template, so it misses every geminate created by a prefix or suffix, and
in reduplicated stems N counts template slots, not root consonants.

Usage:
    python gemination.py ይገኛል ክልል መለወጥ          (needs HornMorpho, see INSTALL.md)

    >>> from gemination import reading_gemination
    >>> reading_gemination("ይገኛል", {"seg": "----ይ</ገ/ኝ>---ኣ/ል---"})["pos"]
    [1, 2]

Positions are 0-based indices into the word's Unicode characters (one Ge'ez
fidel per index).

Lexicon v3 rules (on by default; pass rules=False for the v2 behaviour). Each
is backed by more than one independent source, see the dataset card:
  causative_glottal  a causative prefix ስ- or ስተ- on a glottal-initial root
                     holds the next root consonant (ማሳደ፟ግ, አስታው፟ስ);
                     HornMorpho leaves it out of many segs
  relative_m_light   the relative prefix's ም before a subject prefix
                     (የሚ-, እንደሚ-, በሚ-, የምን-, የማይ-) is not held
  relative_exist     with relative የ-, the reading of አለ "exist" (ለ held)
                     is ranked above አለ "say" (ያለው, ያሉት)
"""
import difflib
import re
import sys

GEM_PRE = "/"
GEM_MARK = "፟"          # ETHIOPIC COMBINING GEMINATION MARK
BOUNDARY = set("-<>")
GEEZ = re.compile(r"[ሀ-፿]")
GLOTTAL = {(0x12A0 - 0x1200) // 8, (0x12D0 - 0x1200) // 8}      # አ and ዐ series
# palatalised surface letter -> base consonant it comes from
PALATAL = {"ሽ": "ስ", "ች": "ት", "ጭ": "ጥ", "ኝ": "ን", "ዥ": "ዝ", "ጅ": "ድ", "ይ": "ል"}
# letters pronounced the same in Amharic, spelled either way (ሣ/ሳ, ሐ/ሀ, ፀ/ጸ)
HOMOPHONE = {"ሥ": "ስ", "ሕ": "ህ", "ኅ": "ህ", "ፅ": "ጽ", "ኽ": "ህ"}
# labialised series (ቈ ኰ ጐ ኈ ዀ) are the base consonant plus w: ቅ + ዋ gives ቋ
LABIAL_SERIES = {0x1248: 0x1240, 0x12B0: 0x12A8, 0x1310: 0x1308, 0x1288: 0x1280, 0x12C0: 0x12B8}

SOURCES = ("root", "t-prefix", "prefix", "suffix", "lexicon", "reduplication")


def series(ch):
    return (ord(ch) - 0x1200) // 8


def _key(ch):
    """Alignment key: consonant series, with labialised, homophone and palatal
    spellings folded to their base and both glottal series merged."""
    base = 0x1200 + series(ch) * 8
    base = LABIAL_SERIES.get(base, base)
    sixth = chr(base + 5)
    sixth = HOMOPHONE.get(sixth, sixth)
    sixth = PALATAL.get(sixth, sixth)
    s = series(sixth)
    return "G" if s in GLOTTAL else s


def parse_seg(seg):
    """Seg string -> list of (char, geminated, region, source) for its Ge'ez
    characters. region: 'pre' before '<', 'stem' inside <...>, 'suf' after '>'.

    source (only for geminated characters) is inferred from the seg alone:
      prefix        '/' before '<' (for example the relative yä-m- in የሚ)
      suffix        '/' after '>' (the auxiliary -all, plural -očč, -nna)
      t-prefix      '/' opens the stem ('</X'), sits on a boundary ('/-X'),
                    or doubles an unassimilated ተ- ('/ተ-'): the passive or
                    reciprocal t- merging into the next consonant
      lexicon       stem without internal boundaries in a noun-shaped seg: an
                    unanalysed dictionary entry that stores the gemination
      reduplication the same consonant series occurs earlier in the same
                    morpheme (frequentative stems such as ገለባ/በጥ). Roots
                    whose second half repeats the first (ግልግል, ስብስብ) also
                    land here.
      root          any other stem geminate: the root's template
    """
    stem = seg[seg.find("<") + 1:seg.find(">")] if "<" in seg and ">" in seg else ""
    lexical = "<" in seg and "-" not in stem and seg[:seg.find("<")].count("-") <= 2
    out, pending, opens, region, last, morph = [], False, False, "pre", "", []
    for i, ch in enumerate(seg):
        if ch == GEM_PRE:
            pending = True
            nxt = seg[i + 1:i + 3]
            opens = last == "<" or nxt[:1] == "-" or nxt == "ተ-"
        elif ch == "<":
            region, morph = "stem", []
        elif ch == ">":
            region = "suf"
        elif ch == "-":
            if region == "stem":
                morph = []
        elif GEEZ.match(ch):
            src = None
            if pending:
                if region == "pre":
                    src = "prefix"
                elif region == "suf":
                    src = "suffix"
                elif opens:
                    src = "t-prefix"
                elif lexical:
                    src = "lexicon"
                elif series(ch) in {series(c) for c in morph}:
                    src = "reduplication"
                else:
                    src = "root"
            out.append((ch, pending, region, src))
            if region == "stem":
                morph.append(ch)
            pending = opens = False
        if ch != "-":
            last = ch
    return out


def seg_to_positions(word, seg):
    """-> ([(surface index, region, source)], ok). ok is False when a geminated
    seg character could not be aligned to the surface word."""
    segc = parse_seg(seg)
    a = [_key(c) for c, _, _, _ in segc]
    b = [_key(c) for c in word]
    sm = difflib.SequenceMatcher(None, a, b, autojunk=False)
    m = {}
    for tag, i1, i2, j1, j2 in sm.get_opcodes():
        if tag == "equal" or (tag == "replace" and i2 - i1 == j2 - j1):
            for k in range(i2 - i1):
                m[i1 + k] = j1 + k
    pos, ok = {}, True
    for i, (_, gem, region, src) in enumerate(segc):
        if not gem:
            continue
        if i in m:
            pos.setdefault(m[i], (region, src))
        else:
            ok = False
    return sorted((p, r, s) for p, (r, s) in pos.items()), ok


CAUSATIVE_GLOTTAL = re.compile(r"(ስተ?-ኣ)([ሀ-፿])")
RELATIVE_M = re.compile(r"/ም(?=-+(?:ይ|እን|ት|ኣ))")


def apply_rules(seg):
    """Apply the v3 seg rules. -> (new seg, names of the rules that fired)."""
    if not seg:
        return seg, []
    fired = []
    new = CAUSATIVE_GLOTTAL.sub(r"\1/\2", seg)
    if new != seg:
        fired.append("causative_glottal")
    if "<" in new:
        pre, rest = new.split("<", 1)
        light = RELATIVE_M.sub("ም", pre)
        if light != pre:
            fired.append("relative_m_light")
            new = light + "<" + rest
    return new, fired


def relative_exist_first(word, patterns):
    """v3: with relative የ-, put the existence reading of አለ (ለ held) first.
    Bare ያለ is left alone: it can also be privative 'without', which holds nothing."""
    if word == "ያለ":
        return patterns
    for i, p in enumerate(patterns):
        if any("<ኣ/ለ>" in s and s.split("<")[0].replace("-", "") == "የ" for s in p["segs"]):
            if i:
                p["rules"] = sorted(set(p.get("rules", [])) | {"relative_exist"})
                patterns = [p] + patterns[:i] + patterns[i + 1:]
            return patterns
    return patterns


def native_first(word, patterns, taps):
    """Put a native speaker's tapped positions first. taps: word -> positions."""
    if word not in taps:
        return patterns
    pos = sorted(taps[word])
    for i, p in enumerate(patterns):
        if p["pos"] == pos:
            p["native"] = True
            return [p] + patterns[:i] + patterns[i + 1:]
    return [{"pos": pos, "letters": [word[k] for k in pos], "sources": ["native"] * len(pos), "freq": None,
             "pos_tags": [], "ok": True, "segs": [], "rules": [], "native": True}] + patterns


def reading_gemination(word, reading, final="suffix", rules=True):
    """Geminated surface positions for one HornMorpho reading (a dict with a
    'seg' from hm.anal(..., degem=False)).

    final: what to do with a geminate on the last character.
      "suffix" (default) drop it only if it comes from a suffix and the last
               letter is sixth order, so no vowel follows. In practice this is
               the auxiliary -all of ይገኛል: it is not audible before a pause
               and Armbruster never marks it. Vowel-final suffixes (-allu) and
               stem-final geminates (ይሰ፟ጥ፟) are kept.
      "keep"   keep every geminate.
      "drop"   drop any word-final geminate.
    """
    seg = reading.get("seg") or ""
    used, fired = apply_rules(seg) if rules else (seg, [])
    items, ok = seg_to_positions(word, used)
    last = len(word) - 1
    if final == "suffix" and word:
        sixth = (ord(word[last]) - 0x1200) % 8 == 5
        items = [x for x in items if not (x[0] == last and x[1] == "suf" and sixth)]
    elif final == "drop":
        items = [x for x in items if x[0] != last]
    return {"pos": [p for p, _, _ in items], "letters": [word[p] for p, _, _ in items],
            "sources": [s for _, _, s in items], "ok": ok, "seg": seg, "rules": fired}


def word_gemination(word, readings, final="suffix", rules=True):
    """Distinct gemination patterns over all readings of a word, most frequent
    root first (HornMorpho's 'freq'). Readings that differ only in grammar but
    geminate the same positions share one pattern."""
    pats = {}
    for r in readings:
        g = reading_gemination(word, r, final, rules)
        f = r.get("freq") or 0
        e = pats.get(tuple(g["pos"]))
        if e is None:
            e = pats[tuple(g["pos"])] = {"pos": g["pos"], "letters": g["letters"], "sources": g["sources"],
                                         "freq": f, "pos_tags": set(), "ok": True, "segs": [], "rules": set()}
        elif f > e["freq"]:
            e["freq"], e["sources"] = f, g["sources"]
        e["pos_tags"].add(str(r.get("pos")))
        e["segs"].append(g["seg"])
        e["ok"] = e["ok"] and g["ok"]
        e["rules"].update(g["rules"])
    out = sorted(pats.values(), key=lambda e: -e["freq"])
    for e in out:
        e["pos_tags"], e["rules"] = sorted(e["pos_tags"]), sorted(e["rules"])
    return relative_exist_first(word, out) if rules else out


def mark(word, pos):
    """Write the gemination mark U+135F after each geminated character."""
    s = set(pos)
    return "".join(c + (GEM_MARK if i in s else "") for i, c in enumerate(word))


def analyze(word, final="suffix", rules=True):
    """Run HornMorpho on one word and return its gemination patterns."""
    import hm
    try:
        rs = list(hm.anal("a", word, degem=False))
    except Exception:
        rs = []
    return word_gemination(word, rs, final, rules)


if __name__ == "__main__":
    for w in sys.argv[1:] or ["ይገኛል", "ክልል", "መለወጥ"]:
        pats = analyze(w)
        if not pats:
            print(f"{w}\tno analysis")
        for p in pats:
            print(f"{w}\t{mark(w, p['pos'])}\tpositions={p['pos']}\tsources={p['sources']}\t"
                  f"pos={','.join(p['pos_tags'])}\troot_freq={p['freq']}\tseg={p['segs'][0]}")