import {
  ArrayPrototypeJoin,
  ArrayPrototypePush,
  ArrayPrototypeSplice,
  Error,
  ErrorGetStack,
  ObjectCreate,
  Promise,
  String,
  TypeError,
  uncurryThis,
} from "ext:core/primordials";
import { op_test_config, op_test_event } from "ext:core/ops";
import type { TestEvent } from "ext:core/ops";
import type { TestContext } from "./main.js";
import { clearTimeout, setTimeout } from "ext:timers/timers.js";
import { required, usv } from "ext:web/idl.js";
import { flag, optionsOf, registry, type Definition, type ParsedStep } from "./shared.js";

type Report = (event: TestEvent) => void;
interface Shared {
  settled: boolean;
  test: string;
}
interface Local {
  running: boolean;
  pending: Promise<boolean>[];
  failed: number;
}
const indexOf = uncurryThis(String.prototype.indexOf);
const { now: dateNow } = Date;

function parseStep(nameOrOptions: unknown, fn: unknown, count: number): ParsedStep {
  required(count, 1);
  if (typeof nameOrOptions === "string") {
    if (count > 2 || (count === 2 && typeof fn !== "function")) {
      throw new TypeError("Expected step(name, fn)");
    }
    // The string form cannot express ignore, so a missing function is always
    // an error here rather than a late internal TypeError.
    if (fn === undefined) throw new TypeError(`Step "${usv(nameOrOptions)}" requires a function`);
    return { name: usv(nameOrOptions), fn, ignore: false } as ParsedStep;
  }
  if (count > 1) throw new TypeError("Expected step(options)");
  const options = optionsOf(nameOrOptions, ["name", "fn", "ignore"], "step");
  if (options.name === undefined) throw new TypeError("Step requires a name");
  const ignore = flag(options, "ignore", "Step");
  const func = options.fn;
  if (func === undefined) {
    if (!ignore) throw new TypeError(`Step "${usv(options.name)}" requires a function`);
  } else if (typeof func !== "function") {
    throw new TypeError(`Step "${usv(options.name)}" requires a function`);
  }
  return { name: usv(options.name), fn: func, ignore } as ParsedStep;
}

function formatError(error: unknown): string {
  let text;
  try {
    if (error instanceof Error) {
      const stack = ErrorGetStack(error);
      text = typeof stack === "string" && stack !== "" ? stack : String(error);
    } else {
      text = String(error);
    }
  } catch {
    return "Unknown error";
  }
  // The runner's own frames never explain a failure.
  const lines = text.split("\n");
  const kept = [lines[0]];
  for (let index = 1; index < lines.length; index++) {
    if (
      indexOf(lines[index], "ext:test/runner.js") === -1 &&
      indexOf(lines[index], "ext:test/main.js") === -1 &&
      indexOf(lines[index], "ext:test/shared.js") === -1
    ) {
      ArrayPrototypePush(kept, lines[index]);
    }
  }
  return ArrayPrototypeJoin(kept, "\n");
}

function withTimeout(work: () => Promise<void>, ms: number, name: string): Promise<void> {
  let timer: number | undefined;
  const started = (() => {
    try {
      return { failed: false, value: work() };
    } catch (error) {
      return { failed: true, error };
    }
  })();
  const attempt = started.failed
    ? Promise.reject(started.error)
    : Promise.resolve(started.value);
  if (!(ms < Infinity)) return attempt;
  const expired = new Promise<never>((_, reject) => {
    timer = setTimeout(
      () => reject(new Error(`Test "${name}" timed out after ${ms}ms`)),
      ms,
    );
  });
  return Promise.race([attempt, expired]).then(
    (value) => {
      clearTimeout(timer);
      return value;
    },
    (error) => {
      clearTimeout(timer);
      throw error;
    },
  );
}

// One test's contexts: `shared` observes the whole test (its name for
// stale-step errors and the settled flag), while each `local` tracks only
// its own running step, pending children, and failed children — so a
// concurrent violation fails its caller and ancestors, never its victim.
function context(name: string, depth: number, report: Report, shared: Shared, local: Local): TestContext {
  const self: { name: string; step: TestContext["step"] } = ObjectCreate(null);
  self.name = name;
  self.step = function step(nameOrOptions: unknown, fn?: unknown): Promise<boolean> {
    required(arguments.length, 1);
    const parsed = parseStep(nameOrOptions, fn, arguments.length);
    if (shared.settled) {
      throw new TypeError(`Step "${parsed.name}" called after "${shared.test}" settled`);
    }
    if (local.running) {
      local.failed += 1;
      report({
        kind: "fail",
        name: parsed.name,
        depth: depth + 1,
        elapsedMs: 0,
        text: `Error: Started step "${parsed.name}" while another step was running`,
      });
      return Promise.resolve(false);
    }
    local.running = true;
    const outcome = runStep(local, parsed, depth + 1, report, shared);
    ArrayPrototypePush(local.pending, outcome);
    return outcome;
  };
  return self;
}

// Waits out every step a body started without awaiting: an unawaited step
// still decides its parent. Loops so a step spawned from a step callback
// joins the same drain; the test timeout bounds evasive patterns.
async function drainSteps(local: Local): Promise<void> {
  let waited = 0;
  while (waited < local.pending.length) {
    waited = local.pending.length;
    await Promise.all(local.pending);
  }
}

function failedStepsText(failed: number): string {
  return `due to ${failed} failed step${failed === 1 ? "" : "s"}`;
}

// A step never throws its body's failure: it reports and resolves false,
// while the failure still fails every ancestor up to the test.
async function runStep(owner: Local, parsed: ParsedStep, depth: number, report: Report, shared: Shared): Promise<boolean> {
  const local: Local = { running: false, pending: [], failed: 0 };
  const start = dateNow();
  try {
    if (parsed.ignore) {
      report({ kind: "ignore", name: parsed.name, depth });
      return false;
    }
    await parsed.fn(context(parsed.name, depth, report, shared, local));
    await drainSteps(local);
    // A completion after the test settled (a timed-out body waking up) has
    // no parent left to report under, so it is dropped.
    if (shared.settled) return false;
    if (local.failed > 0) throw new Error(failedStepsText(local.failed));
    report({ kind: "pass", name: parsed.name, depth, elapsedMs: dateNow() - start });
    return true;
  } catch (error) {
    if (shared.settled) return false;
    report({
      kind: "fail",
      name: parsed.name,
      depth,
      elapsedMs: dateNow() - start,
      text: formatError(error),
    });
    owner.failed += 1;
    return false;
  } finally {
    owner.running = false;
  }
}

async function runTest(definition: Definition, report: Report): Promise<void> {
  if (definition.ignore) {
    report({ kind: "ignore", name: definition.name, depth: 0 });
    return;
  }
  const shared = { settled: false, test: definition.name };
  const local: Local = { running: false, pending: [], failed: 0 };
  const start = dateNow();
  try {
    await withTimeout(async () => {
      await definition.fn(context(definition.name, 0, report, shared, local));
      await drainSteps(local);
      if (local.failed > 0) throw new Error(failedStepsText(local.failed));
    }, definition.timeout, definition.name);
    report({
      kind: "pass",
      name: definition.name,
      depth: 0,
      elapsedMs: dateNow() - start,
    });
  } catch (error) {
    report({
      kind: "fail",
      name: definition.name,
      depth: 0,
      elapsedMs: dateNow() - start,
      text: formatError(error),
    });
  } finally {
    shared.settled = true;
  }
}

export async function runTests(): Promise<void> {
  registry.sealed = true;
  const config = op_test_config();
  const filter = config.filter ?? null;
  const matches = (name: string): boolean =>
    filter === null || indexOf(name, filter) !== -1;
  const selected: Definition[] = [];
  for (let index = 0; index < registry.definitions.length; index++) {
    if (matches(registry.definitions[index].name)) {
      ArrayPrototypePush(selected, registry.definitions[index]);
    } else {
      op_test_event({ kind: "filtered", name: registry.definitions[index].name, depth: 0 });
    }
  }
  if (config.noRun) {
    for (let index = 0; index < selected.length; index++) {
      const definition = selected[index];
      op_test_event({
        kind: definition.ignore ? "ignore" : "found",
        name: definition.name,
        depth: 0,
      });
    }
    op_test_event({ kind: "done" });
    return;
  }
  let focused = false;
  for (let index = 0; index < selected.length; index++) {
    if (selected[index].only) focused = true;
  }
  // Rejections nobody handles would otherwise abort the file through the
  // host with no attribution, or vanish once the run resolves. Collect them
  // under the running test and fail the file with the full list instead.
  const strays: { promise: Promise<unknown>; reason: unknown; test: string | null }[] = [];
  let current: string | null = null;
  function onUnhandled(event: PromiseRejectionEvent): void {
    try {
      event.preventDefault();
    } catch {
      // The host decides; the list below still records what was lost.
    }
    ArrayPrototypePush(
      strays,
      { promise: event.promise, reason: event.reason, test: current },
    );
  }
  function onHandled(event: PromiseRejectionEvent): void {
    for (let index = 0; index < strays.length; index++) {
      if (strays[index].promise === event.promise) {
        ArrayPrototypeSplice(strays, index, 1);
        break;
      }
    }
  }
  globalThis.addEventListener("unhandledrejection", onUnhandled);
  globalThis.addEventListener("rejectionhandled", onHandled);
  try {
    for (let index = 0; index < selected.length; index++) {
      const definition = selected[index];
      if (focused && !definition.only) {
        op_test_event({ kind: "filtered", name: definition.name, depth: 0 });
        continue;
      }
      op_test_event({
        kind: "start",
        name: definition.name,
        depth: 0,
        timeoutMs: definition.timeout === Infinity ? null : definition.timeout,
      });
      current = definition.name;
      await runTest(definition, op_test_event);
      current = null;
    }
    op_test_event({ kind: "done" });
    // Let strays queued during the run surface before judging them.
    await new Promise<void>((resolve) => setTimeout(resolve, 0));
    await new Promise<void>((resolve) => setTimeout(resolve, 0));
    if (strays.length > 0) {
      const lines = ["Unhandled rejections during the test run:"];
      for (let index = 0; index < strays.length; index++) {
        const entry = strays[index];
        const during = entry.test === null ? "after the run" : `during "${entry.test}"`;
        ArrayPrototypePush(lines, `  ${during}:`);
        const text = formatError(entry.reason).split("\n");
        for (let line = 0; line < text.length; line++) {
          ArrayPrototypePush(lines, `    ${text[line]}`);
        }
      }
      throw new Error(ArrayPrototypeJoin(lines, "\n"));
    }
  } finally {
    globalThis.removeEventListener("unhandledrejection", onUnhandled);
    globalThis.removeEventListener("rejectionhandled", onHandled);
  }
}