#!/usr/bin/env node
/* Writes packages/runtime/src/scr_dyn_methods.h: the method-name ids the
 * checked-dynamic dispatch in scr_dyn_invoke.c compares (DYN_M_<name>), the
 * names, and an open-addressed hash table mapping a name to its id. The ids
 * are the DYN_M_ names scr_dyn_invoke.c uses, so the header follows the
 * dispatch code.
 *
 *   node scripts/gen-dyn-methods.mjs           write the header
 *   node scripts/gen-dyn-methods.mjs --check   fail when it is out of date */
import { readFileSync, writeFileSync } from "node:fs";

const source = new URL("../packages/runtime/src/scr_dyn_invoke.c", import.meta.url);
const target = new URL("../packages/runtime/src/scr_dyn_methods.h", import.meta.url);
const SLOTS = 256;

const used = new Set();
for (const match of readFileSync(source, "utf8").matchAll(/\bDYN_M_([A-Za-z][A-Za-z0-9]*)\b/g))
  if (match[1] !== "NONE" && match[1] !== "COUNT") used.add(match[1]);
const names = [...used].sort((a, b) => (a < b ? -1 : a > b ? 1 : 0));
if (names.length >= SLOTS / 2) throw new Error("too many method names for the hash table");

// The slot dyn_method_of in the header computes.
const slotOf = (name) =>
  (name.length * 7 + name.charCodeAt(0) * 31 + name.charCodeAt(name.length - 1)) & (SLOTS - 1);
const slots = new Array(SLOTS).fill(0);
names.forEach((name, i) => {
  let slot = slotOf(name);
  while (slots[slot] !== 0) slot = (slot + 1) & (SLOTS - 1);
  slots[slot] = i + 1;
});

const rows = (values, width) => {
  const out = [];
  for (let i = 0; i < values.length; i += width)
    out.push(`  ${values.slice(i, i + width).join(", ")},`);
  return out;
};
const text = [
  "/* Generated by scripts/gen-dyn-methods.mjs from the DYN_M_ ids scr_dyn_invoke.c",
  " * uses. Do not edit by hand. */",
  "#ifndef SCR_DYN_METHODS_H",
  "#define SCR_DYN_METHODS_H",
  "",
  "#include <stddef.h>",
  "#include <string.h>",
  "",
  "enum {",
  "  DYN_M_NONE,",
  ...names.map((name) => `  DYN_M_${name},`),
  "  DYN_M_COUNT",
  "};",
  "",
  "static const char *const dyn_method_names[DYN_M_COUNT] = {",
  "  NULL,",
  ...names.map((name) => `  ${JSON.stringify(name)},`),
  "};",
  "",
  "static const unsigned char dyn_method_lengths[DYN_M_COUNT] = {",
  ...rows([0, ...names.map((name) => name.length)], 16),
  "};",
  "",
  `/* Each name's id at its slot (or the next free one); 0 ends a probe. */`,
  `static const unsigned char dyn_method_slots[${SLOTS}] = {`,
  ...rows(slots, 16),
  "};",
  "",
  `#define DYN_METHOD_MAX_LENGTH ${Math.max(...names.map((name) => name.length))}`,
  "",
  "/* The id of a method name, compared by content; DYN_M_NONE for any other",
  " * name. */",
  "static inline int dyn_method_of(const char *m) {",
  "  size_t length = strlen(m);",
  "  if (length == 0 || length > DYN_METHOD_MAX_LENGTH) return DYN_M_NONE;",
  "  unsigned slot = (unsigned)(length * 7 + (unsigned char)m[0] * 31 +",
  `                             (unsigned char)m[length - 1]) & ${SLOTS - 1};`,
  "  for (;;) {",
  "    unsigned id = dyn_method_slots[slot];",
  "    if (id == 0) return DYN_M_NONE;",
  "    if (dyn_method_lengths[id] == length && memcmp(m, dyn_method_names[id], length) == 0) return (int)id;",
  `    slot = (slot + 1) & ${SLOTS - 1};`,
  "  }",
  "}",
  "",
  "#endif",
  "",
].join("\n");

if (process.argv.includes("--check")) {
  let current = "";
  try {
    current = readFileSync(target, "utf8");
  } catch {}
  if (current !== text) {
    console.error(
      "packages/runtime/src/scr_dyn_methods.h is out of date: run node scripts/gen-dyn-methods.mjs",
    );
    process.exit(1);
  }
} else {
  writeFileSync(target, text);
}