// ──────────────────────────────────  ChatDrawer.jsx
import { useEffect, useRef, useState } from "react";
import { Sheet, SheetTrigger, SheetContent } from "./ui/sheet.js";
import { Button } from "./ui/button.js";
import { Input }   from "./ui/input.js";
import { MessageCircle } from "lucide-react";

/* ---------------------------------------------------------------
   Streams from  /api/chat/free  and executes UI-tool callbacks
----------------------------------------------------------------*/
export default function ChatDrawer({
  pageContext    = "Home",
  snapshot       = null,
}) {
  /* state */
  const [open, setOpen]         = useState(false);
  const [prompt, setPrompt]     = useState("");
  const [messages, setMessages] = useState([]);   // { role, content }
  const listRef = useRef(null);
  
  /* auto-scroll */
  useEffect(() => {
    listRef.current &&
      (listRef.current.scrollTop = listRef.current.scrollHeight);
  }, [messages]);

  /* helper: stream-friendly append */
  const pushAssistant = (chunk) =>
    setMessages((prev) => {
      const last = prev.at(-1);
      if (last?.role === "assistant") {
        const updated = [...prev];
        updated[updated.length - 1] = {
          ...last,
          content: last.content + chunk
        };
        return updated;
      }
      return [...prev, { role: "assistant", content: chunk }];
    });

  /* send prompt */
  async function sendPrompt() {
    const text = prompt.trim();
    if (!text) return;

    setMessages((m) => [...m, { role: "user", content: text }]);
    setPrompt("");

    const body = JSON.stringify({
      prompt:      text,
      pageContext,
      chatHistory: messages,
      snapshot
    });

    try {
      const token   = localStorage.getItem("token") || "";
      const headers = {
        "Content-Type": "application/json",
        Accept       : "text/event-stream",
        ...(token ? { Authorization: `Bearer ${token}` } : {})
      };

      const resp = await fetch("/api/chat/free", {
        method: "POST",
        headers,
        body
      });
      if (!resp.ok || !resp.body) throw new Error(`HTTP ${resp.status}`);

      const reader  = resp.body.getReader();
      const decoder = new TextDecoder();
      let buf = "";

      /* ─────────────── STREAM LOOP ─────────────── */
      while (true) {
        const { value, done } = await reader.read();
        if (done) break;
        if (!value) continue;

        buf += decoder.decode(value, { stream: true });

        let nl;
        while ((nl = buf.indexOf("\n")) !== -1) {
          const line = buf.slice(0, nl).trim(); // one full line
          buf = buf.slice(nl + 1);              // keep remainder

          /* 2️⃣  normal assistant text */
          if (line) pushAssistant(line + "\n");
        }
      }
      /* ───────── END STREAM LOOP ───────── */
      
       if (buf.trim()) pushAssistant(buf);
    } catch (err) {
      console.error("[ChatDrawer] stream error", err);
      pushAssistant("Sorry — something went wrong. Please try again later.");
    }
  }

  /* Enter submits */
  const handleKeyDown = (e) => {
    if (e.key === "Enter" && !e.shiftKey) {
      e.preventDefault();
      sendPrompt();
    }
  };

  /* UI */
  return (
    <Sheet open={open} onOpenChange={setOpen}>
      {/* floating button */}
      <SheetTrigger>
        <button
          aria-label="Open chat"
          className="fixed bottom-6 right-6 z-50 rounded-full bg-blue-600 p-3 text-white shadow-lg hover:bg-blue-700"
        >
          <MessageCircle size={24} />
        </button>
      </SheetTrigger>

      {/* drawer */}
      <SheetContent
        side="right"
        className="flex max-h-screen w-[380px] flex-col px-0 md:w-[420px]"
      >
        <div className="sticky top-0 z-10 border-b bg-white px-4 py-3 font-semibold">
          {pageContext}
        </div>

        {/* transcript */}
        <div
          ref={listRef}
          className="flex-1 space-y-4 overflow-y-auto px-4 py-2 text-sm"
        >
          {messages.map((m, i) => (
            <div
              key={i}
              className={
                m.role === "user" ? "text-right" : "text-left text-gray-800"
              }
            >
              {m.content}
            </div>
          ))}
        </div>

        {/* prompt box */}
        <div className="border-t p-4">
          <form
            onSubmit={(e) => {
              e.preventDefault();
              sendPrompt();
            }}
            className="flex gap-2"
          >
            <Input
              value={prompt}
              onChange={(e) => setPrompt(e.target.value)}
              onKeyDown={handleKeyDown}
              placeholder="Ask me anything…"
              className="flex-1"
            />
            <Button type="submit" disabled={!prompt.trim()}>
              Send
            </Button>
          </form>
        </div>
      </SheetContent>
    </Sheet>
  );
}