import { describe, it, expect, beforeEach } from "vitest";
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, resetUpdateQueue } from "../src/host/reconcile.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 instances: { tag: string; props: Record<string, unknown> }[] = [];
  const texts: string[] = [];
  const appends: { parent: string; child: string }[] = [];

  const host: HostConfig<string, string, Record<string, unknown>> = {
    name: "tracking",
    createRootContext: () => ({}),
    createInstance: (tag, props) => {
      const id = `${tag}_${instances.length}`;
      instances.push({ tag, props });
      return id;
    },
    createTextInstance: (text) => {
      texts.push(text);
      return `text_${texts.length - 1}`;
    },
    appendChild: (parent, child) => {
      appends.push({ parent, child });
    },
    prepareUpdate: (instance, tag, prevProps, nextProps) => {
      prepareUpdateCalls.push({ instance, tag, 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, payload, tag, prevProps: { ...prevProps }, nextProps: { ...nextProps } });
    },
  };

  return { host, prepareUpdateCalls, commitUpdateCalls, instances, texts, appends };
}

describe("Value.Equal bail-out", () => {
  beforeEach(() => {
    resetUpdateQueue();
  });

  describe("unchanged subtree skips prepareUpdate/commitUpdate", () => {
    it("identical re-render skips prepareUpdate for unchanged element", () => {
      const { host, prepareUpdateCalls, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      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 skips prepareUpdate for parent and children", () => {
      const { host, prepareUpdateCalls, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

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

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

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

  describe("changed prop still triggers prepareUpdate", () => {
    it("changed prop on parent triggers prepareUpdate", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      prepareUpdateCalls.length = 0;

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

      expect(prepareUpdateCalls.length).toBeGreaterThanOrEqual(1);
      const divCall = prepareUpdateCalls.find((c) => c.tag === "div");
      expect(divCall).toBeDefined();
      expect(divCall!.prevProps.color).toBe("red");
      expect(divCall!.nextProps.color).toBe("blue");
    });

    it("changed child prop triggers prepareUpdate only for child", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

      prepareUpdateCalls.length = 0;

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

      const spanCalls = prepareUpdateCalls.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("deeply nested unchanged subtree is fully skipped", () => {
    it("three levels of unchanged elements are all skipped", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(
        h("div", { id: "1" },
          h("section", { class: "outer" },
            h("p", { align: "center" }, "text"),
          ),
        ),
      );

      prepareUpdateCalls.length = 0;

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

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

    it("deep subtree with one change only commitUpdates the changed node", () => {
      const { host, commitUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(
        h("div", { id: "1" },
          h("section", { class: "outer" },
            h("p", { align: "center" }),
          ),
        ),
      );

      commitUpdateCalls.length = 0;

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

      const pCommit = commitUpdateCalls.filter((c) => c.tag === "p");
      expect(pCommit.length).toBe(1);
      expect(pCommit[0]!.prevProps.align).toBe("center");
      expect(pCommit[0]!.nextProps.align).toBe("left");
    });
  });

  describe("cachedNode is set on mount", () => {
    it("fibers created during mount have cachedNode set", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }, h("span", { label: "a" })));

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

    it("cachedNode matches the node used to create the fiber", () => {
      const { host } = makeTrackingHost();
      const root = createHostRoot(host, {});
      const divNode = h("div", { color: "red" });
      root.render(divNode);

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

  describe("reconcileProps direct call with Value.Equal bail-out", () => {
    it("reconcileProps with identical node does not call prepareUpdate", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      expect(divFiber.cachedNode).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 changed node calls prepareUpdate", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});
      root.render(h("div", { color: "red" }));

      const divFiber = root.rootFiber!.children[0]!;
      prepareUpdateCalls.length = 0;

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

      expect(prepareUpdateCalls.length).toBe(1);
    });
  });

  describe("Value.Equal deep equality", () => {
    it("deep-equal props with different object references still bail out", () => {
      const { host, prepareUpdateCalls } = makeTrackingHost();
      const root = createHostRoot(host, {});

      root.render(h("div", { style: { color: "red", size: 10 } }));
      prepareUpdateCalls.length = 0;

      root.render(h("div", { style: { color: "red", size: 10 } }));

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