#!/usr/bin/env python3
"""Losslessly package the Room Server page for browser gzip decoding.

RoomWebHtml.h remains the reviewed page source and native UI fixture. Only
Room Server's ESP32 WebConfig callback references the compressed asset. Other
roles and nRF52 builds do not include either page in their firmware.
"""
from __future__ import annotations

import argparse
import gzip
import hashlib
from pathlib import Path
import re
import zlib

SOURCE = "src/helpers/esp32/RoomWebHtml.h"
OUTPUT = "src/helpers/esp32/RoomWebHtmlGzip.h"
MARKER = "// room-page-source-sha256: "


def source_page(header: str) -> bytes:
    matches = re.findall(
        r'static const char ROOM_WEB_HTML\[\] PROGMEM = R"roomhtml\(([\s\S]*?)\)roomhtml";',
        header,
    )
    if len(matches) != 1:
        raise ValueError("expected one RoomWebHtml.h page source")
    return matches[0].encode("ascii")


def page_bytes(header: str) -> bytes:
    matches = re.findall(
        r"static const uint8_t ROOM_WEB_HTML_GZ\[\] PROGMEM = \{([\s\S]*?)\};", header
    )
    if len(matches) != 1:
        raise ValueError("expected one compressed Room page")
    return bytes(int(value, 16) for value in re.findall(r"0x([0-9a-f]{2})", matches[0]))


def render(raw: bytes, encoded: bytes) -> str:
    if gzip.decompress(encoded) != raw:
        raise ValueError("compressed Room page differs from source")
    digest = hashlib.sha256(raw).hexdigest()
    lines = [
        "// Auto-generated by scripts/generate_room_web_html.py; DO NOT EDIT.",
        "// Lossless gzip of RoomWebHtml.h, decoded by the browser.",
        MARKER + digest,
        "#pragma once",
        "#include <stdint.h>",
        "#include <pgmspace.h>",
        "",
        "static const uint8_t ROOM_WEB_HTML_GZ[] PROGMEM = {",
    ]
    for index in range(0, len(encoded), 16):
        lines.append("  " + "".join("0x%02x," % value for value in encoded[index:index + 16]))
    lines.extend(["};", ""])
    return "\n".join(lines)


def generate(root: Path, *, check: bool = False) -> bool:
    raw = source_page((root / SOURCE).read_text(encoding="ascii"))
    destination = root / OUTPUT
    existing = destination.read_text(encoding="ascii") if destination.exists() else ""
    # Validate the actual bytes rather than trusting a marker or file mtime.
    try:
        encoded = page_bytes(existing)
        intact = gzip.decompress(encoded) == raw and render(raw, encoded) == existing
    except (ValueError, OSError, EOFError, zlib.error):
        intact = False
    if intact:
        return False
    if check:
        raise ValueError("compressed Room page is missing, stale or invalid; regenerate it")
    from zopfli_compress import gzip_compress
    encoded = gzip_compress(raw)
    destination.write_text(render(raw, encoded), encoding="ascii")
    print("Room Web HTML: %d source bytes -> %d gzip bytes" % (len(raw), len(encoded)))
    return True


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--check", action="store_true")
    arguments = parser.parse_args()
    root = Path(__file__).resolve().parents[1] if "__file__" in globals() else Path.cwd()
    generate(root, check=arguments.check)


if __name__ == "__main__":
    main()
elif "Import" in globals():
    generate(Path.cwd())