"""Build the content-addressed browser shell served by the dashboard."""

from __future__ import annotations

import gzip
import hashlib
import re
from dataclasses import dataclass
from pathlib import Path


SCRIPT_TAG = re.compile(r'^<script src="(static/[^"?]+\.js)"></script>$', re.MULTILINE)
WORKER_RUNTIME_SOURCE = "static/background-issue-sync.js"


@dataclass(frozen=True)
class FrontendBuild:
    dashboard_html: str
    runtime_bytes: bytes
    runtime_gzip_bytes: bytes
    runtime_digest: str
    runtime_name: str
    page_sources: tuple[str, ...]
    service_worker_source: str


def _bundle(frontend_dir: Path, sources: tuple[str, ...]) -> bytes:
    chunks = []
    for source in sources:
        path = frontend_dir / source.removeprefix("static/")
        chunks.append(f"/* {source} */\n".encode() + path.read_bytes() + b"\n;\n")
    return b"".join(chunks)


def build_frontend(frontend_dir: Path) -> FrontendBuild:
    """Return one internally consistent HTML, runtime, and offline-worker build."""
    source_html = (frontend_dir / "index.html").read_text()
    sources = tuple(SCRIPT_TAG.findall(source_html))
    if not sources:
        raise ValueError("dashboard entry document has no page scripts")

    runtime = _bundle(frontend_dir, sources)
    runtime_gzip = gzip.compress(runtime, compresslevel=6, mtime=0)
    digest = hashlib.sha256(runtime).hexdigest()[:16]
    runtime_name = f"runtime-{digest}.js"
    dashboard_html = SCRIPT_TAG.sub("", source_html)
    dashboard_html = dashboard_html.replace(
        "</body>", f'<script src="{runtime_name}"></script>\n</body>'
    )

    worker = (frontend_dir / "service-worker.js").read_text()
    for source in sources:
        if source != WORKER_RUNTIME_SOURCE:
            worker = worker.replace(f"  BASE + '{source}',\n", "")
    worker = worker.replace(
        "  BASE + 'static/dashboard.css',\n",
        f"  BASE + 'static/dashboard.css',\n  BASE + '{runtime_name}',\n",
    )
    worker = re.sub(
        r"const CACHE = 'stackchain-dashboard-shell-v\d+';",
        f"const CACHE = 'stackchain-dashboard-shell-{digest}';",
        worker,
        count=1,
    )

    return FrontendBuild(
        dashboard_html=dashboard_html,
        runtime_bytes=runtime,
        runtime_gzip_bytes=runtime_gzip,
        runtime_digest=digest,
        runtime_name=runtime_name,
        page_sources=sources,
        service_worker_source=worker,
    )