import fs from "node:fs";
import path from "node:path";

/**
 * Entity models (`entities/models/<x>.ts`) are pure domain logic — schemas,
 * invariants, derivations. They are the cheapest layer to test and the most
 * expensive to get wrong, so every model file must carry a sibling test.
 *
 * Scope is `entities/models/` only. Error classes (`entities/errors/`) are
 * conventionally covered by a consolidated `errors.test.ts`, and barrels
 * (`index.ts`) hold no logic — both are excluded.
 */
function isEntityModelFile(filename) {
  const normalized = filename.replace(/\\/g, "/");
  if (!normalized.includes("/entities/models/")) return false;
  if (!normalized.endsWith(".ts")) return false;
  if (normalized.endsWith(".test.ts")) return false;
  if (normalized.endsWith(".d.ts")) return false;
  if (normalized.endsWith("/index.ts")) return false;
  return true;
}

/** @type {import("eslint").Rule.RuleModule} */
export default {
  meta: {
    type: "problem",
    docs: {
      description:
        "Every entity model file (entities/models/<x>.ts) must have a sibling <x>.test.ts.",
    },
    schema: [],
    messages: {
      missingTest:
        "Entity model {{filename}} has no sibling test at {{expected}}. Entity models are pure domain logic — cover them with a unit test.",
    },
  },
  create(context) {
    return {
      Program(node) {
        const filename = context.filename;
        if (!isEntityModelFile(filename)) return;
        const expected = filename.replace(/\.ts$/, ".test.ts");
        if (fs.existsSync(expected)) return;
        context.report({
          node,
          messageId: "missingTest",
          data: {
            filename: path.basename(filename),
            expected: path.basename(expected),
          },
        });
      },
    };
  },
};