import { describe, it, expect, beforeEach } from "vitest";
import { Value } from "@alkdev/typebox/value";
import { h } from "../src/core/h.js";
import { createRoot as createHostRoot } from "../src/host/config.js";
import type { HostConfig } from "../src/host/config.js";
import type { Fiber } from "../src/host/fiber.js";
import { reconcileProps, commitEffects, commitHashes, resetUpdateQueue, wireSignalToFiber } from "../src/host/reconcile.js";
import { signal } from "../src/core/reactive.js";

function makeTrackingHost() {
  const prepareUpdateCalls: { instance: string; tag: string; prevProps: Record<string, unknown>; nextProps: Record<string, unknown> }[] = [];
  const commitUpdateCalls: { instance: string; payload: unknown; tag: string; prevProps: Record<string, unknown>; nextProps: Record<string, unknown> }[] = [];

  const host: HostConfig<string, string, Record<string, unknown>> = {
    name: "tracking",
    createRootContext: () => ({}),
    createInstance: (tag, props) => `${tag}_${tag}_inst`,
    createTextInstance: (text) => `text:${text}`,
    appendChild: () => {},
    prepareUpdate: (_instance, _tag, prevProps, nextProps) => {
      prepareUpdateCalls.push({ instance: _instance as string, tag: _tag as string, prevProps: { ...prevProps }, nextProps: { ...nextProps } });
      const changed: Record<string, unknown> = {};
      let hasChanges = false;
      for (const key of Object.keys(nextProps)) {
        if (prevProps[key] !== nextProps[key]) {
          changed[key] = nextProps[key];
          hasChanges = true;
        }
      }
      for (const key of Object.keys(prevProps)) {
        if (!(key in nextProps)) {
          changed[key] = undefined;
          hasChanges = true;
        }
      }
      return hasChanges ? changed : null;
    },
    commitUpdate: (instance, payload, tag, prevProps, nextProps) => {
      commitUpdateCalls.push({ instance: instance as string, payload, tag: tag as string, prevProps: { ...prevProps }, nextProps: { ...nextProps } });
    },
  };

  return { host, prepareUpdateCalls, commitUpdateCalls };
}

describe("Value.Hash O(1) change detection", () => {
  beforeEach(() => {
    resetUpdateQueue();
  });

  describe("fiber has hash field", () => {
    it("fibers created during mount have hash field initialized to null", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      expect(divFiber.hash).toBeNull();
    });

    it("commitHashes caches hash on each fiber", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

      commitHashes(root.rootFiber!);

      const divFiber = root.rootFiber!.children[0]!;
      expect(divFiber.hash).not.toBeNull();
      expect(typeof divFiber.hash).toBe("bigint");

      const spanFiber = divFiber.children[0]!;
      expect(spanFiber.hash).not.toBeNull();
      expect(typeof spanFiber.hash).toBe("bigint");
    });
  });

  describe("hash match skips subtree (fast path)", () => {
    it("identical re-render with cached hash skips prepareUpdate", () => {
      const { host, prepareUpdateCalls, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      commitHashes(root.rootFiber!);

      const divFiber = root.rootFiber!.children[0]!;
      expect(divFiber.hash).not.toBeNull();

      prepareUpdateCalls.length = 0;
      commitUpdateCalls.length = 0;

      root.render(h("div", { color: "red" }));

      expect(prepareUpdateCalls.length).toBe(0);
      expect(commitUpdateCalls.length).toBe(0);
    });

    it("identical re-render with children and cached hash skips all prepareUpdate", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

      commitHashes(root.rootFiber!);

      prepareUpdateCalls.length = 0;

      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

      expect(prepareUpdateCalls.length).toBe(0);
    });

    it("deeply nested unchanged subtree with hashes skips all prepareUpdate", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(
        h("div", { id: "1" },
          h("section", { class: "outer" },
            h("p", { align: "center" }, "text"),
          ),
        ),
      );

      commitHashes(root.rootFiber!);

      prepareUpdateCalls.length = 0;

      root.render(
        h("div", { id: "1" },
          h("section", { class: "outer" },
            h("p", { align: "center" }, "text"),
          ),
        ),
      );

      expect(prepareUpdateCalls.length).toBe(0);
    });
  });

  describe("hash mismatch falls through to Value.Equal / reconciliation", () => {
    it("hash mismatch with changed prop triggers commitUpdate", () => {
      const { host, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      commitHashes(root.rootFiber!);

      commitUpdateCalls.length = 0;

      root.render(h("div", { color: "blue" }));

      expect(commitUpdateCalls.length).toBeGreaterThanOrEqual(1);
    });

    it("hash mismatch for child triggers commitUpdate for child only", () => {
      const { host, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

      commitHashes(root.rootFiber!);

      commitUpdateCalls.length = 0;

      root.render(h("div", { color: "red" }, h("span", { label: "b" })));

      const spanCalls = commitUpdateCalls.filter((c) => c.tag === "span");
      expect(spanCalls.length).toBe(1);
      expect(spanCalls[0]!.prevProps.label).toBe("a");
      expect(spanCalls[0]!.nextProps.label).toBe("b");
    });
  });

  describe("hash is computed outside reactive computations", () => {
    it("Value.Hash is never called from within a computed or effect callback", async () => {
      const { host, commitUpdateCalls } = makeTrackingHost();
      const s = signal("red");

      const root = createHostRoot(host, {});
      root.render(h("div", { color: s.value }));

      const divFiber = root.rootFiber!.children[0]!;
      commitHashes(root.rootFiber!);

      wireSignalToFiber(
        divFiber,
        () => h("div", { color: s.value }),
        host as HostConfig<string, string, unknown>,
        {},
      );

      commitUpdateCalls.length = 0;

      s.value = "blue";

      await new Promise<void>((resolve) => {
        queueMicrotask(() => resolve());
      });

      expect(commitUpdateCalls.length).toBeGreaterThanOrEqual(1);
      expect(divFiber.props.color).toBe("blue");

      const newHash = divFiber.hash;
      expect(newHash).not.toBeNull();

      commitUpdateCalls.length = 0;

      s.value = "blue";

      await new Promise<void>((resolve) => {
        queueMicrotask(() => resolve());
      });

      expect(commitUpdateCalls.length).toBe(0);
    });

    it("commitHashes caches hash after commitEffects (commit phase)", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      expect(divFiber.hash).toBeNull();

      commitEffects(root.rootFiber!, host as HostConfig<string, string, unknown>, {});
      commitHashes(root.rootFiber!);

      expect(divFiber.hash).not.toBeNull();
    });
  });

  describe("reconcileProps direct call with hash comparison", () => {
    it("reconcileProps with hash match skips when fiber has cached hash", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      commitHashes(root.rootFiber!);

      expect(divFiber.hash).not.toBeNull();

      prepareUpdateCalls.length = 0;

      reconcileProps(divFiber, h("div", { color: "red" }), host as HostConfig<string, string, unknown>, {});

      expect(prepareUpdateCalls.length).toBe(0);
      expect(divFiber.effect).toBeNull();
    });

    it("reconcileProps with hash mismatch and Value.Equal match still bails out", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      commitHashes(root.rootFiber!);

      divFiber.hash = BigInt(-1);

      prepareUpdateCalls.length = 0;

      reconcileProps(divFiber, h("div", { color: "red" }), host as HostConfig<string, string, unknown>, {});

      expect(prepareUpdateCalls.length).toBe(0);
    });
  });

  describe("hash updated after commit", () => {
    it("hash is updated after re-render with new props", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      commitHashes(root.rootFiber!);

      const divFiber = root.rootFiber!.children[0]!;
      const originalHash = divFiber.hash;
      expect(originalHash).not.toBeNull();

      root.render(h("div", { color: "blue" }));

      const newHash = Value.Hash(h("div", { color: "blue" }));
      expect(divFiber.hash).toBe(newHash);
    });
  });
});