// wasm/python/lumbda-py.js
// Python tier loader — Pyodide (CPython-in-WASM) hosting lumbda.py.
//
// ES module form so it works in both window and Web Worker contexts.
// Exports createPythonTier() -> Promise<{ evalLisp(src) -> Promise<string>,
//                                          setBendUrl(url) -> void,
//                                          heapStats() -> {used,total} }>.

const PYODIDE_VERSION = "0.27.2";
const PYODIDE_INDEX_URL = `https://cdn.jsdelivr.net/pyodide/v${PYODIDE_VERSION}/full/`;

async function _bootstrap() {
    // Dynamic ES-module import works in both window and Worker (module type)
    // contexts. The CDN ships pyodide.mjs alongside pyodide.js.
    const { loadPyodide } = await import(PYODIDE_INDEX_URL + "pyodide.mjs");
    const pyodide = await loadPyodide({ indexURL: PYODIDE_INDEX_URL });

    // Pull lumbda.py + stdlib.lsp into Pyodide's virtual FS. Paths resolve
    // relative to THIS loader (under python/) for both window and Worker.
    const pyURL = new URL("./lumbda.py", import.meta.url).href;
    const stdlibURL = new URL("./stdlib.lsp", import.meta.url).href;
    const lumbdaSrc = await (await fetch(pyURL)).text();
    const stdlibSrc = await (await fetch(stdlibURL)).text();
    pyodide.FS.writeFile("/home/pyodide/lumbda.py", lumbdaSrc);
    pyodide.FS.writeFile("/home/pyodide/stdlib.lsp", stdlibSrc);

    // bend dispatch closure. Browser can't open raw TCP, so we POST
    // the S-expression payload to the configured worker URL and read
    // the response text back. Sync XHR is the only sync HTTP available
    // in a Web Worker; perfect for the blocking eval model lumbda
    // primitives expect.
    const refs = { bendUrl: null };
    globalThis._lumbdaPyBendCall = (payload) => {
        if (!refs.bendUrl) return "no bend URL configured";
        try {
            const xhr = new XMLHttpRequest();
            xhr.open("POST", refs.bendUrl, false);  // sync
            xhr.setRequestHeader("Content-Type", "text/plain; charset=utf-8");
            xhr.send(payload);
            return xhr.responseText || "";
        } catch (e) {
            return `bend error: ${e.message || String(e)}`;
        }
    };

    await pyodide.runPythonAsync(`
import sys, io
sys.path.insert(0, "/home/pyodide")
import lumbda
_env = lumbda.make_global_env()
for _e in lumbda.read_all(lumbda.PRELUDE):
    lumbda.leval(_e, _env)

# bend!-call primitive — bridges to JS XHR via globalThis._lumbdaPyBendCall.
# Argument: a string payload (the S-expression text). Returns response text.
from js import _lumbdaPyBendCall as _js_bend_call
def _bend_call_prim(args, env):
    if not args:
        return ""
    payload = args[0]
    if not isinstance(payload, str):
        payload = lumbda.show(payload)
    return str(_js_bend_call(payload))
_env.define(lumbda.S('bend!-call'), _bend_call_prim)

def _lumbda_eval(src):
    buf = io.StringIO()
    old = sys.stdout
    sys.stdout = buf
    last = None
    try:
        for e in lumbda.read_all(src):
            last = lumbda.leval(e, _env)
    except Exception as ex:
        sys.stdout = old
        return f"{buf.getvalue()}error: {ex}"
    sys.stdout = old
    out = buf.getvalue()
    if last is not None and not isinstance(last, lumbda._Void):
        rep = lumbda.show(last)
        if out and not out.endswith("\\n"):
            out += "\\n"
        out += rep
    return out
`);

    return {
        async evalLisp(src) {
            pyodide.globals.set("_src_in", src);
            return await pyodide.runPythonAsync("_lumbda_eval(_src_in)");
        },
        setBendUrl(url) { refs.bendUrl = url || null; },
        heapStats() {
            // Pyodide's runtime memory is the Emscripten linear memory.
            // CPython's GC reclaims behind the scenes, so this number
            // rises and falls naturally as objects die.
            const total = pyodide._module.HEAPU8.byteLength;
            return { used: total, total };
        },
    };
}

// Closure-encapsulated singleton (see lumbda-c.loader.js for rationale).
export const createPythonTier = (() => {
    let tier = null;
    return async () => {
        if (!tier) tier = await _bootstrap();
        return tier;
    };
})();