#!/usr/bin/env python3
"""Generate extension/src/codepage/codepage_tables.inc from Microsoft's WindowsBestFit tables.

The port emulates MultiByteToWideChar / WideCharToMultiByte off Windows. Instead of the host iconv
(Android's bionic has no GBK, and iconv tables differ from Windows in the corners), the conversions
use Microsoft's own code page definitions, published by unicode.org:

    https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/bestfit<cp>.txt

Each file has an MBTABLE (single bytes), DBCSRANGE/DBCSTABLE (lead byte + trail byte) and a WCTABLE
(Unicode -> bytes, including the many-to-one "best fit" entries WideCharToMultiByte uses without
WC_NO_BEST_FIT_CHARS). The generated data keeps the byte -> Unicode side and only the WCTABLE entries
that differ from its first-match inverse, so the runtime can rebuild the encoder.

Usage: python3 script/gen_codepage_tables.py [--cache DIR] [--output FILE]
Downloads missing files into the cache (build/bestfit by default) and checks their SHA-256.
"""
import argparse
import hashlib
import re
import sys
import urllib.request
from pathlib import Path

REPO = Path(__file__).resolve().parent.parent
URL = "https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WindowsBestFit/bestfit{}.txt"

# Every code page 40250 EterLib/Util.cpp names (1252 included; CP_ACP maps to it).
SHA256 = {
    874: "663f43ca662e037c4534cb16298b560f29ce29c27b49b3589601ec3d97dd89fd",
    932: "2614cfea35c3c86c41d33198793a84ca44edee3cf0ee0013a61a43fba4ece331",
    936: "e5070a2d6ad26619f5872ddbe64d3381c11620af5adbb04cda0f0abb1a91fdae",
    949: "50e13b60ea8fda66a8223ecc85270e0f182303222244e2345d3d57f3e839d20a",
    950: "cf8c23389a42a226ea707f7ec32c665556d1fc3364db25bd765ce64d54eaee2a",
    1250: "cef9f171e67b09445bcb3f9ffccdc89418250ff825f1bd2d29a92d2074d7a53b",
    1251: "59ec85612ff908d9da0e877893c935941e56b13a2882b4fb9c9599be3d1ce4e7",
    1252: "72ea23c939c5b26fae7aded0207b327e2f3902d7d3c168d7087f5cfc38ee76a9",
    1253: "ea80c442aff7f09b36da6335f85f8e527f51c146beeb9825ec00d1b6ca99a99e",
    1254: "3d02512087634dc493b720992b590277736ffb2d5b0b665d69b6b9727e2c361a",
    1255: "fdd4bdda74f6571d89171b0070ac052cd3714c395dc3d1799bcd5e4a4da6f83a",
    1256: "745c447ada04a838da8bea406c13f446c7453b6371e8c6c7863a632443d56007",
    1257: "b8c5d7f3b8c25c3d5625d44dd3d6ee7a06e652ddf77373d050282c1cb7517366",
    1258: "5d52a9357b7d6b5b5014ed5a51be0ff9809b0c33625793d2a4feaf502e0682f1",
}

NONE = 0xFFFF
PAIR = re.compile(rb"^\s*0x([0-9a-fA-F]+)\s+0x([0-9a-fA-F]+)")


def fetch(cp: int, cache: Path) -> bytes:
    path = cache / f"bestfit{cp}.txt"
    if not path.is_file():
        cache.mkdir(parents=True, exist_ok=True)
        with urllib.request.urlopen(URL.format(cp)) as response:
            path.write_bytes(response.read())
    data = path.read_bytes()
    digest = hashlib.sha256(data).hexdigest()
    if digest != SHA256[cp]:
        raise SystemExit(f"{path}: SHA-256 {digest} != {SHA256[cp]}")
    return data


def parse(cp: int, data: bytes):
    single = [NONE] * 256
    leads = []            # [(lo, hi)]
    dbcs = {}             # lead -> {trail: wc}
    wctable = {}          # wc -> mb
    mb_default = None
    section = None
    lead = None
    for raw in data.splitlines():
        line = raw.split(b";", 1)[0].strip()
        if not line:
            continue
        head = line.split()[0]
        if head == b"CODEPAGE":
            if int(line.split()[1]) != cp:
                raise SystemExit(f"bestfit{cp}.txt declares {line!r}")
            continue
        if head == b"CPINFO":
            fields = line.split()
            if int(fields[2], 16) != 0x3F:
                raise SystemExit(f"cp{cp}: byte default char {fields[2]!r} is not '?'")
            mb_default = int(fields[3], 16)
            continue
        if head in (b"MBTABLE", b"WCTABLE", b"DBCSRANGE"):
            section = head
            continue
        if head == b"DBCSTABLE":
            section = head
            match = re.search(rb"LeadByte\s*=\s*0x([0-9a-fA-F]+)", raw)
            lead = int(match.group(1), 16)
            dbcs.setdefault(lead, {})
            continue
        if head == b"ENDCODEPAGE":
            break
        match = PAIR.match(line)
        if not match:
            raise SystemExit(f"cp{cp}: unexpected line {raw!r}")
        a, b = int(match.group(1), 16), int(match.group(2), 16)
        # cp932 lists its second lead range (0xe0-0xfc) after the first range's DBCSTABLEs.
        if b"Lead Byte Range" in raw and section in (b"DBCSRANGE", b"DBCSTABLE"):
            leads.append((a, b))
            continue
        if section == b"MBTABLE":
            single[a] = b
        elif section == b"DBCSRANGE":
            leads.append((a, b))
        elif section == b"DBCSTABLE":
            dbcs[lead][a] = b
        elif section == b"WCTABLE":
            wctable[a] = b
    if mb_default is None:
        raise SystemExit(f"cp{cp}: no CPINFO")
    for lead in dbcs:
        if not any(lo <= lead <= hi for lo, hi in leads):
            raise SystemExit(f"cp{cp}: DBCSTABLE 0x{lead:02x} outside the lead ranges {leads}")
    return single, leads, dbcs, wctable, mb_default


def decode_map(single, dbcs):
    """bytes -> wc, bytes as int (single byte < 0x100, pair = lead << 8 | trail), ascending."""
    out = {}
    for b, wc in enumerate(single):
        if wc != NONE:
            out[b] = wc
    for lead in sorted(dbcs):
        for trail in sorted(dbcs[lead]):
            out[lead << 8 | trail] = dbcs[lead][trail]
    return out


def default_inverse(decoded):
    """The encoder the runtime builds: the first byte sequence (ascending) that decodes to wc."""
    inverse = {}
    for mb in sorted(decoded):
        inverse.setdefault(decoded[mb], mb)
    return inverse


def encode_overrides(decoded, wctable):
    """WCTABLE entries the default inverse gets wrong: 0 round-trip, 1 best fit, 2 not encodable."""
    inverse = default_inverse(decoded)
    out = []
    for wc in sorted(set(inverse) | set(wctable)):
        want = wctable.get(wc)
        if want is None:
            out.append((wc, 0, 2))
        elif decoded.get(want) != wc:
            out.append((wc, want, 1))
        elif inverse.get(wc) != want:
            out.append((wc, want, 0))
    return out


def rows(values, per_line=16):
    return "\n".join("\t" + ", ".join(values[i:i + per_line]) + "," for i in range(0, len(values), per_line))


def emit(cp, single, leads, dbcs, wctable, mb_default):
    decoded = decode_map(single, dbcs)
    overrides = encode_overrides(decoded, wctable)
    # Sanity: the rebuilt encoder must reproduce WCTABLE exactly.
    inverse = default_inverse(decoded)
    for wc, mb, kind in overrides:
        if kind == 2:
            inverse.pop(wc, None)
        else:
            inverse[wc] = mb
    if inverse != wctable:
        raise SystemExit(f"cp{cp}: encoder rebuild does not match WCTABLE")

    name = f"kCp{cp}"
    text = [f"// Code page {cp}: {len(decoded)} byte sequences, {len(wctable)} WCTABLE entries."]
    text.append(f"const uint16_t {name}Single[256] = {{\n{rows([f'0x{v:04X}' for v in single])}\n}};")
    lead_ranges = "nullptr"
    dbcs_rows = "nullptr"
    dbcs_data = "nullptr"
    if leads:
        lead_ranges = f"{name}Leads"
        text.append(f"const uint8_t {name}Leads[] = {{" + ", ".join(f"0x{lo:02X}, 0x{hi:02X}" for lo, hi in leads) + "};")
        row_defs = []
        data = []
        for lead in sorted(dbcs):
            trails = dbcs[lead]
            lo, hi = min(trails), max(trails)
            row_defs.append(f"\t{{0x{lead:02X}, 0x{lo:02X}, 0x{hi:02X}, {len(data)}}},")
            data.extend(trails.get(t, NONE) for t in range(lo, hi + 1))
        dbcs_rows = f"{name}Rows"
        dbcs_data = f"{name}Dbcs"
        text.append(f"const DbcsRow {name}Rows[] = {{\n" + "\n".join(row_defs) + "\n};")
        text.append(f"const uint16_t {name}Dbcs[] = {{\n{rows([f'0x{v:04X}' for v in data])}\n}};")
    text.append(f"const EncodeOverride {name}Overrides[] = {{\n"
                + rows([f"{{0x{wc:04X}, 0x{mb:04X}, {kind}}}" for wc, mb, kind in overrides], 6)
                + "\n};" if overrides else f"const EncodeOverride {name}Overrides[] = {{{{0, 0, 2}}}};")
    count = f"sizeof({name}Overrides) / sizeof({name}Overrides[0])" if overrides else "0"
    entry = (f"\t{{{cp}, 0x{mb_default:04X}, {name}Single, {lead_ranges}, "
             f"{len(leads)}, {dbcs_rows}, {len(dbcs) if leads else 0}, {dbcs_data}, "
             f"{name}Overrides, {count}}},")
    return "\n".join(text) + "\n", entry, len(overrides)


def main():
    parser = argparse.ArgumentParser(description=__doc__.split("\n")[0])
    parser.add_argument("--cache", type=Path, default=REPO / "build/bestfit")
    parser.add_argument("--output", type=Path, default=REPO / "extension/src/codepage/codepage_tables.inc")
    args = parser.parse_args()

    body = []
    entries = []
    for cp in sorted(SHA256):
        parsed = parse(cp, fetch(cp, args.cache))
        text, entry, n_over = emit(cp, *parsed)
        body.append(text)
        entries.append(entry)
        print(f"cp{cp}: {n_over} encode overrides", file=sys.stderr)
    header = ("// Generated by script/gen_codepage_tables.py from Microsoft's WindowsBestFit tables\n"
              "// (unicode.org MAPPINGS/VENDORS/MICSFT/WindowsBestFit). Do not edit.\n"
              "// 0xFFFF marks a byte / pair with no mapping. Included by codepage.cpp only.\n")
    table = "const CodePageTable kTables[] = {\n" + "\n".join(entries) + "\n};\n"
    args.output.parent.mkdir(parents=True, exist_ok=True)
    args.output.write_text(header + "\n" + "\n".join(body) + "\n" + table, encoding="ascii")
    print(f"wrote {args.output}", file=sys.stderr)


if __name__ == "__main__":
    main()