/**
 * lib.js — FFI wrapper around libarboricx.so via koffi.
 *
 * Exports low-level C ABI bindings and high-level helpers.
 */

import { existsSync } from 'node:fs';
import { dirname, join, resolve } from 'node:path';
import { fileURLToPath } from 'node:url';
import koffi from 'koffi';

const __dirname = dirname(fileURLToPath(import.meta.url));

koffi.opaque('arb_ctx_t');

// ── Library discovery ───────────────────────────────────────────────────────

export function findLib() {
  const env = process.env.ARBORICX_LIB;
  if (env) {
    if (existsSync(env)) return env;
    throw new Error(`ARBORICX_LIB set but file not found: ${env}`);
  }

  const candidates = [
    resolve(__dirname, 'libarboricx.so'),
    'libarboricx.so',
    './libarboricx.so',
    '/usr/local/lib/libarboricx.so',
    '/usr/lib/libarboricx.so',
  ];

  for (const p of candidates) {
    if (existsSync(p)) return p;
  }

  throw new Error('libarboricx.so not found. Set ARBORICX_LIB to its full path.');
}

// ── FFI setup ───────────────────────────────────────────────────────────────

let _lib = null;
let _libPath = null;

function ensureLib() {
  if (_lib) return _lib;
  const path = findLib();
  _lib = koffi.load(path);
  _libPath = path;
  return _lib;
}

export function loadLib(path) {
  if (_lib && _libPath === path) return;
  _lib = koffi.load(path);
  _libPath = path;
}

function getLib() {
  if (_lib) return _lib;
  return ensureLib();
}

// ── Context lifecycle ───────────────────────────────────────────────────────

export function init(libPath) {
  if (libPath) loadLib(libPath);
  const lib = getLib();
  const ctx = lib.func('arb_ctx_t *arboricx_init(void)')();
  if (!ctx) throw new Error('arboricx_init failed');
  return ctx;
}

export function free(ctx) {
  getLib().func('void arboricx_free(arb_ctx_t *ctx)')(ctx);
}

// ── Bundle loading ──────────────────────────────────────────────────────────

export function loadBundle(ctx, bytes, name) {
  const result = getLib().func('uint32_t arb_load_bundle(arb_ctx_t *ctx, _In_ uint8_t *bytes, size_t len, const char *name)')(ctx, bytes, bytes.length, name);
  if (result === 0) throw new Error(`arb_load_bundle failed for export "${name}"`);
  return result;
}

export function loadBundleDefault(ctx, bytes) {
  const result = getLib().func('uint32_t arb_load_bundle_default(arb_ctx_t *ctx, _In_ uint8_t *bytes, size_t len)')(ctx, bytes, bytes.length);
  if (result === 0) throw new Error('arb_load_bundle_default failed');
  return result;
}

// ── Reduction ───────────────────────────────────────────────────────────────

export function reduce(ctx, root, fuel = 1_000_000_000n) {
  const f = getLib().func('uint32_t arb_reduce(arb_ctx_t *ctx, uint32_t root, uint64_t fuel)');
  return f(ctx, root, typeof fuel === 'bigint' ? fuel : BigInt(fuel));
}

// ── Tree construction ───────────────────────────────────────────────────────

export function leaf(ctx) {
  return getLib().func('uint32_t arb_leaf(arb_ctx_t *ctx)')(ctx);
}

export function stem(ctx, child) {
  return getLib().func('uint32_t arb_stem(arb_ctx_t *ctx, uint32_t child)')(ctx, child);
}

export function fork(ctx, left, right) {
  return getLib().func('uint32_t arb_fork(arb_ctx_t *ctx, uint32_t left, uint32_t right)')(ctx, left, right);
}

export function app(ctx, func, arg) {
  return getLib().func('uint32_t arb_app(arb_ctx_t *ctx, uint32_t func, uint32_t arg)')(ctx, func, arg);
}

// ── Codec constructors ──────────────────────────────────────────────────────

export function ofNumber(ctx, n) {
  const big = typeof n === 'bigint' ? n : BigInt(n);
  return getLib().func('uint32_t arb_of_number(arb_ctx_t *ctx, uint64_t n)')(ctx, big);
}

export function ofString(ctx, s) {
  return getLib().func('uint32_t arb_of_string(arb_ctx_t *ctx, const char *s)')(ctx, s);
}

export function ofBytes(ctx, bytes) {
  return getLib().func('uint32_t arb_of_bytes(arb_ctx_t *ctx, _In_ uint8_t *bytes, size_t len)')(ctx, bytes, bytes.length);
}

export function ofList(ctx, items) {
  const arr = new Uint32Array(items);
  return getLib().func('uint32_t arb_of_list(arb_ctx_t *ctx, _In_ uint32_t *items, size_t len)')(ctx, arr, arr.length);
}

// ── Codec destructors ───────────────────────────────────────────────────────

export function toNumber(ctx, root) {
  const out = [0];
  const ok = getLib().func('int arb_to_number(arb_ctx_t *ctx, uint32_t root, _Out_ uint64_t *out)')(ctx, root, out);
  if (!ok) throw new Error('arb_to_number failed');
  return typeof out[0] === 'bigint' ? Number(out[0]) : out[0];
}

export function toString(ctx, root) {
  const ptrOut = [null];
  const lenOut = [0];
  const ok = getLib().func('int arb_to_string(arb_ctx_t *ctx, uint32_t root, _Out_ uint8_t **out_ptr, _Out_ size_t *out_len)')(ctx, root, ptrOut, lenOut);
  if (!ok) throw new Error('arb_to_string failed');

  const bytes = koffi.decode(ptrOut[0], 'uint8_t', lenOut[0]);
  const str = Buffer.from(bytes).toString('utf-8');
  getLib().func('void arboricx_free_buf(arb_ctx_t *ctx, uint8_t *ptr, size_t len)')(ctx, ptrOut[0], lenOut[0]);
  return str;
}

export function toBytes(ctx, root) {
  const ptrOut = [null];
  const lenOut = [0];
  const ok = getLib().func('int arb_to_bytes(arb_ctx_t *ctx, uint32_t root, _Out_ uint8_t **out_ptr, _Out_ size_t *out_len)')(ctx, root, ptrOut, lenOut);
  if (!ok) throw new Error('arb_to_bytes failed');

  const bytes = Buffer.from(koffi.decode(ptrOut[0], 'uint8_t', lenOut[0]));
  getLib().func('void arboricx_free_buf(arb_ctx_t *ctx, uint8_t *ptr, size_t len)')(ctx, ptrOut[0], lenOut[0]);
  return bytes;
}

export function toBool(ctx, root) {
  const out = [0];
  const ok = getLib().func('int arb_to_bool(arb_ctx_t *ctx, uint32_t root, _Out_ int *out)')(ctx, root, out);
  if (!ok) throw new Error('arb_to_bool failed');
  return out[0] !== 0;
}

// ── Result unwrapping ───────────────────────────────────────────────────────

export function unwrapResult(ctx, root) {
  const outOk = [0];
  const outValue = [0];
  const outRest = [0];
  const ok = getLib().func('int arb_unwrap_result(arb_ctx_t *ctx, uint32_t root, _Out_ int *out_ok, _Out_ uint32_t *out_value, _Out_ uint32_t *out_rest)')(ctx, root, outOk, outValue, outRest);
  if (!ok) throw new Error('arb_unwrap_result failed');
  return { ok: outOk[0] !== 0, value: outValue[0], rest: outRest[0] };
}

export function unwrapHostValue(ctx, root) {
  const outTag = [0n];
  const outPayload = [0];
  const ok = getLib().func('int arb_unwrap_host_value(arb_ctx_t *ctx, uint32_t root, _Out_ uint64_t *out_tag, _Out_ uint32_t *out_payload)')(ctx, root, outTag, outPayload);
  if (!ok) throw new Error('arb_unwrap_host_value failed');
  return { tag: outTag[0], payload: outPayload[0] };
}

// ── Kernel ──────────────────────────────────────────────────────────────────

export function kernelRoot(ctx) {
  return getLib().func('uint32_t arb_kernel_root(arb_ctx_t *ctx)')(ctx);
}

// ── High-level helpers ──────────────────────────────────────────────────────

export function decode(ctx, root) {
  try {
    return toBool(ctx, root) ? 'true' : 'false';
  } catch {
    try {
      return toString(ctx, root);
    } catch {
      try {
        return String(toNumber(ctx, root));
      } catch {
        throw new Error('could not decode result');
      }
    }
  }
}

export function decodeType(ctx, root) {
  try { toBool(ctx, root); return 'bool'; } catch {}
  try { toString(ctx, root); return 'string'; } catch {}
  try { toNumber(ctx, root); return 'number'; } catch {}
  return 'unknown (raw tree)';
}