"use client";

import { useEffect, useRef } from "react";
import { useParams } from "next/navigation";
import { useChat } from "@ai-sdk/react";
import { AlertTriangle, Bot, Loader2, Send, Sparkles, User } from "lucide-react";

import { Button } from "@/components/ui/button";
import { cn } from "@/lib/utils";

export default function AIPage() {
  const params = useParams();
  const workspaceSlug =
    typeof params?.workspaceSlug === "string" ? params.workspaceSlug : "";

  const scrollRef = useRef<HTMLDivElement>(null);
  const inputRef = useRef<HTMLTextAreaElement>(null);

  const {
    messages,
    input,
    handleInputChange,
    handleSubmit,
    status,
    error,
    setInput,
  } = useChat({
    api: "/api/chat",
    body: { workspace: workspaceSlug },
  });

  const isBusy = status === "submitted" || status === "streaming";

  useEffect(() => {
    if (scrollRef.current) {
      scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
    }
  }, [messages, status]);

  return (
    <div className="flex h-full min-h-0 flex-col">
      <div className="flex shrink-0 items-center gap-3 border-b px-6 py-4">
        <div className="flex h-9 w-9 items-center justify-center rounded-lg bg-primary/10">
          <Sparkles className="size-5 text-primary" />
        </div>
        <div>
          <h1 className="text-lg font-semibold">AI Assistant</h1>
          <p className="text-xs text-muted-foreground">
            Ask me anything about your workspace
          </p>
        </div>
      </div>

      <div ref={scrollRef} className="min-h-0 flex-1 overflow-y-auto">
        {messages.length === 0 ? (
          <div className="flex h-full min-h-[12rem] flex-col items-center justify-center gap-4 text-muted-foreground">
            <div className="flex h-16 w-16 items-center justify-center rounded-2xl bg-primary/10">
              <Bot className="size-8 text-primary" />
            </div>
            <div className="text-center">
              <p className="text-base font-medium">How can I help you today?</p>
              <p className="mt-1 text-sm">
                Ask me to break down a task, draft an outline, or summarize what
                you have open.
              </p>
            </div>
            <div className="mt-2 flex flex-wrap justify-center gap-2">
              {[
                "Break this project into subtasks",
                "Summarize my open tasks",
                "Draft a sprint plan for this week",
              ].map((suggestion) => (
                <button
                  key={suggestion}
                  type="button"
                  onClick={() => setInput(suggestion)}
                  className="rounded-full border px-3 py-1.5 text-xs transition-colors hover:bg-muted"
                >
                  {suggestion}
                </button>
              ))}
            </div>
          </div>
        ) : (
          <div className="mx-auto max-w-3xl space-y-4 px-4 py-6">
            {messages.map((msg) => (
              <div
                key={msg.id}
                className={cn(
                  "flex gap-3",
                  msg.role === "user" && "flex-row-reverse",
                )}
              >
                <div
                  className={cn(
                    "flex h-8 w-8 shrink-0 items-center justify-center rounded-full",
                    msg.role === "user"
                      ? "bg-primary text-primary-foreground"
                      : "bg-muted",
                  )}
                >
                  {msg.role === "user" ? (
                    <User className="size-4" />
                  ) : (
                    <Bot className="size-4" />
                  )}
                </div>
                <div
                  className={cn(
                    "max-w-[80%] rounded-xl px-4 py-2.5 text-sm whitespace-pre-wrap",
                    msg.role === "user"
                      ? "bg-primary text-primary-foreground"
                      : "bg-muted",
                  )}
                >
                  {msg.content}
                </div>
              </div>
            ))}
            {status === "submitted" && (
              <div className="flex gap-3">
                <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-full bg-muted">
                  <Bot className="size-4" />
                </div>
                <div className="rounded-xl bg-muted px-4 py-2.5">
                  <Loader2 className="size-4 animate-spin" />
                </div>
              </div>
            )}
          </div>
        )}

        {error ? <ChatErrorBanner error={error} /> : null}
      </div>

      <div className="shrink-0 border-t bg-background p-4">
        <form
          onSubmit={handleSubmit}
          className="mx-auto flex max-w-3xl gap-2"
        >
          <textarea
            ref={inputRef}
            value={input}
            onChange={handleInputChange}
            onKeyDown={(e) => {
              if (e.key === "Enter" && !e.shiftKey) {
                e.preventDefault();
                if (input.trim() && !isBusy) {
                  // Cast: handleSubmit accepts FormEvent | KeyboardEvent; the
                  // useChat helper unwraps either.
                  handleSubmit(
                    e as unknown as React.FormEvent<HTMLFormElement>,
                  );
                }
              }
            }}
            placeholder="Ask anything..."
            className="flex-1 resize-none rounded-lg border bg-background px-4 py-2.5 text-sm focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
            rows={1}
          />
          <Button
            type="submit"
            size="icon"
            disabled={!input.trim() || isBusy || !workspaceSlug}
          >
            <Send className="size-4" />
          </Button>
        </form>
      </div>
    </div>
  );
}

function ChatErrorBanner({ error }: { error: Error }) {
  const message = parseErrorMessage(error);
  const isUnavailable = /AI is unavailable/i.test(message);
  return (
    <div
      className={cn(
        "mx-auto mb-4 mt-2 flex max-w-3xl items-start gap-3 rounded-lg border px-4 py-3 text-sm",
        isUnavailable
          ? "border-amber-500/40 bg-amber-500/10 text-amber-900 dark:text-amber-200"
          : "border-destructive/40 bg-destructive/10 text-destructive",
      )}
      role="alert"
    >
      <AlertTriangle className="mt-0.5 size-4 shrink-0" />
      <div className="min-w-0">
        <p className="font-medium">
          {isUnavailable ? "AI is unavailable" : "Something went wrong"}
        </p>
        <p className="mt-1 break-words text-xs opacity-90">{message}</p>
      </div>
    </div>
  );
}

/**
 * `useChat` wraps fetch errors in a generic Error; the route handler returns
 * a JSON body with `{ error: string }`. Try to surface that to the user; fall
 * back to whatever message the SDK gave us.
 */
function parseErrorMessage(error: Error): string {
  const raw = error.message || "";
  try {
    const parsed = JSON.parse(raw) as { error?: string };
    if (parsed?.error) return parsed.error;
  } catch {
    // not JSON; fall through
  }
  return raw || "Unknown error";
}