import { onBeforeUnmount } from "vue";
import { Terminal } from "@xterm/xterm";
import { FitAddon } from "@xterm/addon-fit";
import { SearchAddon } from "@xterm/addon-search";
import { WebLinksAddon } from "@xterm/addon-web-links";
import { invoke } from "@tauri-apps/api/core";
import { listen, type UnlistenFn } from "@tauri-apps/api/event";
import { useSessionStore } from "@/stores/session.store";
import "@xterm/xterm/css/xterm.css";

/** MobaXTerm Classic–inspired terminal theme colors. */
const defaultTheme = {
  background: "#0d1117",
  foreground: "#e0e0e0",
  cursor: "#58a6ff",
  cursorAccent: "#0d1117",
  selectionBackground: "rgba(88, 166, 255, 0.3)",
  selectionForeground: "#ffffff",
  black: "#0d1117",
  red: "#f85149",
  green: "#3fb950",
  yellow: "#e3b341",
  blue: "#58a6ff",
  magenta: "#bc8cff",
  cyan: "#39c5cf",
  white: "#e0e0e0",
  brightBlack: "#484f58",
  brightRed: "#ff7b72",
  brightGreen: "#56d364",
  brightYellow: "#e3b341",
  brightBlue: "#79c0ff",
  brightMagenta: "#d2a8ff",
  brightCyan: "#56d4dd",
  brightWhite: "#f0f6fc",
};

export interface UseTerminalReturn {
  terminal: Terminal;
  fitAddon: FitAddon;
  searchAddon: SearchAddon;
  mount: (container: HTMLElement) => void;
  destroy: () => void;
  write: (data: string) => void;
  fit: () => void;
}

/**
 * Composable that manages an xterm.js Terminal lifecycle.
 *
 * Wires bidirectional I/O:
 *   - User keystrokes → ssh_write (via Tauri invoke)
 *   - SSH stdout → xterm.js (via Tauri listen, base64 encoded)
 *   - Terminal resize → ssh_resize (via Tauri invoke)
 */
export function useTerminal(sessionId: string, backend: 'ssh' | 'pty' = 'ssh'): UseTerminalReturn {
  const writeCmd = backend === 'ssh' ? 'ssh_write' : 'pty_write';
  const resizeCmd = backend === 'ssh' ? 'ssh_resize' : 'pty_resize';
  const dataEvent = backend === 'ssh' ? `ssh:data:${sessionId}` : `pty:data:${sessionId}`;

  const fitAddon = new FitAddon();
  const searchAddon = new SearchAddon();
  const webLinksAddon = new WebLinksAddon();

  const terminal = new Terminal({
    theme: defaultTheme,
    fontFamily: "'Cascadia Mono', 'Cascadia Code', Consolas, 'JetBrains Mono', 'Fira Code', Menlo, Monaco, 'Courier New', monospace",
    fontSize: 14,
    lineHeight: 1.2,
    cursorBlink: true,
    cursorStyle: "block",
    scrollback: 10000,
    allowProposedApi: true,
    convertEol: backend === 'ssh',
    rightClickSelectsWord: false,
  });

  terminal.loadAddon(fitAddon);
  terminal.loadAddon(searchAddon);
  terminal.loadAddon(webLinksAddon);

  // Forward typed data to the backend
  terminal.onData((data: string) => {
    invoke(writeCmd, { sessionId, data }).catch((err: unknown) => {
      console.error("Write error:", err);
    });
  });

  // Forward resize events to the backend
  terminal.onResize((size: { cols: number; rows: number }) => {
    invoke(resizeCmd, { sessionId, cols: size.cols, rows: size.rows }).catch((err: unknown) => {
      console.error("Resize error:", err);
    });
  });

  // MobaXTerm-style clipboard: highlight to copy, right-click to paste
  const selectionDisposable = terminal.onSelectionChange(() => {
    const sel = terminal.getSelection();
    if (sel) {
      navigator.clipboard.writeText(sel).catch(() => {});
    }
  });

  function handleRightClickPaste(e: MouseEvent): void {
    e.preventDefault();
    e.stopPropagation();
    navigator.clipboard.readText().then((text) => {
      if (text) {
        invoke(writeCmd, { sessionId, data: text }).catch(() => {});
      }
    }).catch(() => {});
  }

  // Listen for SSH output events from the Rust backend (base64 encoded)
  // Tauri listen() returns a Promise<UnlistenFn> — store both the promise and
  // the resolved unlisten function so we can clean up properly.
  let unlistenFn: UnlistenFn | null = null;
  let unlistenPromise: Promise<UnlistenFn> | null = null;

  let resizeObserver: ResizeObserver | null = null;

  // Streaming TextDecoder persists across events so split multi-byte UTF-8
  // sequences at chunk boundaries are decoded correctly (e.g. a 3-byte em-dash
  // split across two Rust read() calls).
  const utf8Decoder = new TextDecoder("utf-8", { fatal: false });

  // Write batching — accumulate chunks and flush once per animation frame.
  // Without this, every tiny SSH read (sometimes single characters) triggers
  // a separate terminal.write(), producing a laggy typewriter effect.
  let pendingData = "";
  let rafId: number | null = null;

  function flushPendingData(): void {
    rafId = null;
    if (pendingData) {
      terminal.write(pendingData);
      pendingData = "";
    }
  }

  function queueWrite(data: string): void {
    pendingData += data;
    if (rafId === null) {
      rafId = requestAnimationFrame(flushPendingData);
    }
  }

  function mount(container: HTMLElement): void {
    terminal.open(container);

    // Wait for fonts to load before measuring cell dimensions.
    // If the font (Cascadia Mono etc.) isn't loaded when fitAddon.fit()
    // runs, canvas.measureText() uses a fallback font and gets wrong
    // cell widths — producing tiny dashes and 200+ column terminals.
    document.fonts.ready.then(() => {
      fitAddon.fit();
    });

    // Right-click paste on the terminal's DOM element
    terminal.element?.addEventListener("contextmenu", handleRightClickPaste);

    // Subscribe to SSH output events for this session.
    // Tauri v2 listen() callback receives { payload: T } — the base64 string
    // is in event.payload (not event.data as in Wails).
    unlistenPromise = listen<string>(dataEvent, (event) => {
      // Mark tab activity for background sessions
      try { useSessionStore().markActivity(sessionId); } catch {}

      const b64data = event.payload;

      try {
        // atob() returns Latin-1 — each byte becomes a char code 0x00–0xFF.
        // Reconstruct raw bytes, then decode with the streaming TextDecoder
        // which buffers incomplete multi-byte sequences between calls.
        const binaryStr = atob(b64data);
        const bytes = new Uint8Array(binaryStr.length);
        for (let i = 0; i < binaryStr.length; i++) {
          bytes[i] = binaryStr.charCodeAt(i);
        }
        const decoded = utf8Decoder.decode(bytes, { stream: true });
        if (decoded) {
          queueWrite(decoded);
        }
      } catch {
        // Fallback: write raw if not valid base64
        queueWrite(b64data);
      }
    });

    // Capture the resolved unlisten function for synchronous cleanup
    unlistenPromise.then((fn) => {
      unlistenFn = fn;
    });

    // Auto-fit when the container resizes
    resizeObserver = new ResizeObserver(() => {
      fitAddon.fit();
    });
    resizeObserver.observe(container);
  }

  function destroy(): void {
    if (rafId !== null) {
      cancelAnimationFrame(rafId);
      rafId = null;
    }
    // Flush any remaining buffered data before teardown
    if (pendingData) {
      terminal.write(pendingData);
      pendingData = "";
    }
    terminal.element?.removeEventListener("contextmenu", handleRightClickPaste);
    selectionDisposable.dispose();

    // Clean up the Tauri event listener.
    // If the promise already resolved, call unlisten directly.
    // If it's still pending, wait for resolution then call it.
    if (unlistenFn) {
      unlistenFn();
      unlistenFn = null;
    } else if (unlistenPromise) {
      unlistenPromise.then((fn) => fn());
    }
    unlistenPromise = null;

    if (resizeObserver) {
      resizeObserver.disconnect();
      resizeObserver = null;
    }
    terminal.dispose();
  }

  function write(data: string): void {
    terminal.write(data);
  }

  function fit(): void {
    fitAddon.fit();
  }

  onBeforeUnmount(() => {
    destroy();
  });

  return { terminal, fitAddon, searchAddon, mount, destroy, write, fit };
}