/**
 * App — the citation-evidence MVP shell.
 *
 * Composes the two top-level layouts:
 *
 *   - Review mode (CE-WP-0002): collection list / viewer / evidence sidebar.
 *   - Forms mode (CE-WP-0003): form renderer / viewer / evidence strip,
 *     with click-to-link interaction.
 *
 * Mode selection is driven by `location.hash`: `#/forms/demo` lands in
 * Forms mode; anything else (including empty) lands in Review mode. The
 * top bar toggles between them. We keep the hash sync so reload + deep
 * links work; T08's E2E asserts the `/forms/demo` navigation path.
 *
 * Engine and binder providers are both mounted at the App root so
 * evidence/annotations/links survive switching tabs.
 */

import { useEffect, useState } from "react";

import { BinderProvider } from "@binder/index";
import {
  EngineProvider,
  useEngine,
} from "@work/index";

import { FormsApp } from "./forms/FormsApp";
import { ReviewLayout } from "./ReviewLayout";

type Mode = "review" | "forms";

const FORMS_HASH = "#/forms/demo";

function readModeFromHash(): Mode {
  if (typeof window === "undefined") return "review";
  return window.location.hash === FORMS_HASH ? "forms" : "review";
}

function writeModeToHash(mode: Mode) {
  if (typeof window === "undefined") return;
  const target = mode === "forms" ? FORMS_HASH : "";
  if (window.location.hash !== target) {
    if (target) {
      window.location.hash = target;
    } else {
      // Clear hash without leaving "#" trailing in the URL bar.
      history.replaceState(null, "", window.location.pathname + window.location.search);
    }
  }
}

function ModeRouter() {
  const [mode, setMode] = useState<Mode>(() => readModeFromHash());

  useEffect(() => {
    function onHash() {
      setMode(readModeFromHash());
    }
    window.addEventListener("hashchange", onHash);
    return () => window.removeEventListener("hashchange", onHash);
  }, []);

  const handleModeChange = (next: Mode) => {
    writeModeToHash(next);
    setMode(next);
  };

  return (
    <div style={{ display: "flex", flexDirection: "column", height: "100vh", color: "#222" }}>
      <TopBar mode={mode} onModeChange={handleModeChange} />
      <div style={{ flex: 1, minHeight: 0 }}>
        {mode === "review" ? <ReviewLayout /> : <FormsApp />}
      </div>
    </div>
  );
}

function TopBar({ mode, onModeChange }: { mode: Mode; onModeChange: (m: Mode) => void }) {
  return (
    <header
      style={{
        display: "flex",
        gap: 8,
        padding: "6px 12px",
        borderBottom: "1px solid #ddd",
        background: "#fafafa",
        fontFamily: "system-ui, sans-serif",
        alignItems: "center",
      }}
    >
      <strong style={{ fontSize: 13, marginRight: 8 }}>citation-evidence</strong>
      <button
        onClick={() => onModeChange("review")}
        aria-pressed={mode === "review"}
        style={tabStyle(mode === "review")}
      >
        Review
      </button>
      <button
        onClick={() => onModeChange("forms")}
        aria-pressed={mode === "forms"}
        style={tabStyle(mode === "forms")}
      >
        Forms
      </button>
    </header>
  );
}

function tabStyle(active: boolean) {
  return {
    padding: "4px 12px",
    fontSize: 12,
    border: "1px solid #ccc",
    borderBottom: active ? "2px solid #0050b3" : "1px solid #ccc",
    background: active ? "#e8f0ff" : "white",
    cursor: "pointer" as const,
  };
}

function AppInner() {
  const engine = useEngine();
  return (
    <BinderProvider bus={engine.bus}>
      <ModeRouter />
    </BinderProvider>
  );
}

export function App() {
  return (
    <EngineProvider>
      <AppInner />
    </EngineProvider>
  );
}