"use client";

import { useCallback, useRef, useState } from "react";
import type { Model } from "@/lib/data";
import { elideMiddle } from "./elide";

// The field is a fixed 420px with 14px of padding either side. It does not
// grow with the name: a field that resized would shove the rest of the
// sentence around on every keystroke.
const TEXT_PX = 420 - 28;
const TRACKING = "-1.6px"; // -0.04em at 40px

/**
 * The canvas cannot resolve `var(--font-geist-sans)`, so take the font the
 * browser actually resolved on the field itself.
 */
function fontOf(el: HTMLInputElement | null): string | null {
  if (!el) return null;
  const s = getComputedStyle(el);
  return s.font || `${s.fontWeight} ${s.fontSize} ${s.fontFamily}`;
}

interface Props {
  onResolve: (model: Model | null) => void;
}

type Status =
  | { kind: "empty" }
  | { kind: "loading" }
  | { kind: "error"; message: string }
  | { kind: "ok" };

/**
 * A free-text field for a Hub repo id. There are millions of models on the
 * Hub, so there is no list to pick from — the id is typed, and the sizes come
 * back from /api/model.
 */
export default function ModelInput({ onResolve }: Props) {
  const [text, setText] = useState("");
  const [status, setStatus] = useState<Status>({ kind: "empty" });
  const [focused, setFocused] = useState(false);
  const [font, setFont] = useState<string | null>(null);
  // A callback ref runs at commit, which is where the resolved font can be read.
  const attachInput = useCallback((el: HTMLInputElement | null) => {
    if (el) setFont(fontOf(el));
  }, []);
  const timer = useRef<ReturnType<typeof setTimeout> | undefined>(undefined);
  // Only the newest lookup may write state; earlier ones lose the race.
  const latest = useRef(0);

  async function lookup(id: string, ticket: number) {
    try {
      const res = await fetch(`/api/model?id=${encodeURIComponent(id)}`);
      const body = await res.json();
      if (ticket !== latest.current) return;
      if (!res.ok) {
        setStatus({ kind: "error", message: body.error ?? "Lookup failed." });
        onResolve(null);
        return;
      }
      setStatus({ kind: "ok" });
      onResolve(body as Model);
    } catch {
      if (ticket !== latest.current) return;
      setStatus({ kind: "error", message: "Could not reach the Hub." });
      onResolve(null);
    }
  }

  function handleChange(next: string) {
    setText(next);
    clearTimeout(timer.current);
    const id = next.trim();
    const ticket = ++latest.current;

    if (!id) {
      setStatus({ kind: "empty" });
      onResolve(null);
      return;
    }

    setStatus({ kind: "loading" });
    timer.current = setTimeout(() => lookup(id, ticket), 400);
  }

  // While the field is not being edited, a name too long for the box shows its
  // middle elided so the tail — the part that names the checkpoint — stays
  // visible. The input keeps the real value throughout.
  const elided =
    focused || !font ? text : elideMiddle(text, TEXT_PX, font, TRACKING);
  const isElided = elided !== text;

  return (
    <span className="relative inline-flex flex-col">
      <input
        ref={attachInput}
        aria-label="Model"
        value={text}
        onChange={(e) => handleChange(e.target.value)}
        onFocus={() => setFocused(true)}
        onBlur={() => setFocused(false)}
        placeholder="Qwen/Qwen3-32B"
        spellCheck={false}
        autoCapitalize="off"
        autoComplete="off"
        title={isElided ? text : undefined}
        className={`h-[52px] w-[420px] rounded-md bg-paper px-3.5 text-[40px] font-medium leading-[44px] tracking-[-0.04em] ring-raised outline-none placeholder:text-ash ${
          isElided ? "text-transparent" : "text-obsidian"
        }`}
      />
      {isElided && (
        <span
          aria-hidden
          className="pointer-events-none absolute inset-y-0 left-3.5 flex items-center text-[40px] font-medium leading-[44px] tracking-[-0.04em] text-obsidian"
        >
          {elided}
        </span>
      )}
      <span
        className="label absolute top-[56px] left-1 whitespace-nowrap text-graphite"
        role={status.kind === "error" ? "alert" : undefined}
      >
        {status.kind === "loading" && "Looking up"}
        {status.kind === "error" && status.message}
      </span>
    </span>
  );
}