"use client";

import { useCallback, useEffect, useId, useRef, useState } from "react";
import dynamic from "next/dynamic";
import Link from "next/link";
import { useRouter } from "next/navigation";
import type { EditorView } from "@uiw/react-codemirror";
import { api, ApiError } from "@/lib/client";
import { categoryLabel, slugify, todayIso, validatePost } from "@/lib/validate";
import type { BlogPost, GalleryImage, ImageFile, PostInput } from "@/lib/types";
import TagInput from "./TagInput";
import PreviewFrame from "./PreviewFrame";
import ImagePanel from "./ImagePanel";
import { insertText } from "./MarkdownEditor";

// CodeMirror touches the DOM on load; render it client-side only.
const MarkdownEditor = dynamic(() => import("./MarkdownEditor"), {
  ssr: false,
  loading: () => <div className="pane" />,
});

type Props = {
  /** Absent for a new post. */
  post?: BlogPost;
  revision: string;
  files?: ImageFile[];
  categories: string[];
  tags: string[];
};

type Form = PostInput & { images: GalleryImage[] };

function toForm(post?: BlogPost): Form {
  return {
    slug: post?.slug ?? "",
    title: post?.title ?? "",
    description: post?.description ?? "",
    date: post?.date ?? todayIso(),
    category: post?.category ?? "",
    tags: post?.tags ?? [],
    images: post?.images ?? [],
    details: post?.details ?? "",
  };
}

export default function PostEditor({ post, revision: initialRevision, files: initialFiles, categories, tags }: Props) {
  const router = useRouter();
  const categoryListId = useId();
  const viewRef = useRef<EditorView | null>(null);

  const [form, setForm] = useState<Form>(() => toForm(post));
  const [baseline, setBaseline] = useState(() => JSON.stringify(toForm(post)));
  const [savedSlug, setSavedSlug] = useState<string | null>(post?.slug ?? null);
  const [slugTouched, setSlugTouched] = useState(Boolean(post));
  const [revision, setRevision] = useState(initialRevision);
  const [files, setFiles] = useState<ImageFile[]>(initialFiles ?? []);
  const [saving, setSaving] = useState(false);
  const [message, setMessage] = useState<{ kind: "ok" | "error"; text: string } | null>(null);
  const [conflict, setConflict] = useState(false);

  const dirty = JSON.stringify(form) !== baseline;

  const update = <K extends keyof Form>(key: K, value: Form[K]) => setForm((f) => ({ ...f, [key]: value }));

  function setTitle(title: string) {
    setForm((f) => ({ ...f, title, slug: slugTouched ? f.slug : slugify(title) }));
  }

  const save = useCallback(
    async (opts: { close?: boolean; force?: boolean } = {}) => {
      const { post: input, errors } = validatePost(form);
      if (!input) {
        setMessage({ kind: "error", text: errors.join("; ") });
        return;
      }
      setSaving(true);
      setMessage(null);
      try {
        const body = { post: input, revision: opts.force ? undefined : revision };
        const res = savedSlug
          ? await api<{ post: BlogPost; revision: string }>(`/api/posts/${savedSlug}`, { method: "PUT", json: body })
          : await api<{ post: BlogPost; revision: string }>("/api/posts", { method: "POST", json: body });
        setRevision(res.revision);
        setBaseline(JSON.stringify(form));
        setConflict(false);
        const slugChanged = res.post.slug !== savedSlug;
        setSavedSlug(res.post.slug);
        setMessage({ kind: "ok", text: `Saved ${new Date().toLocaleTimeString()}` });
        if (opts.close) router.push("/");
        else if (slugChanged) router.replace(`/posts/${res.post.slug}`);
        router.refresh();
      } catch (err) {
        if (err instanceof ApiError && err.status === 409 && /changed on disk/.test(err.message)) setConflict(true);
        else setMessage({ kind: "error", text: (err as Error).message });
      } finally {
        setSaving(false);
      }
    },
    [form, revision, savedSlug, router]
  );

  // Ctrl/Cmd+S saves.
  useEffect(() => {
    const onKey = (e: KeyboardEvent) => {
      if ((e.ctrlKey || e.metaKey) && e.key.toLowerCase() === "s") {
        e.preventDefault();
        if (!saving) save();
      }
    };
    window.addEventListener("keydown", onKey);
    return () => window.removeEventListener("keydown", onKey);
  }, [save, saving]);

  // Warn before losing unsaved edits: tab close/reload, and in-app links.
  useEffect(() => {
    if (!dirty) return;
    const onBeforeUnload = (e: BeforeUnloadEvent) => e.preventDefault();
    const onClick = (e: MouseEvent) => {
      const a = (e.target as HTMLElement).closest("a[href]");
      if (a && !a.closest(".preview-frame") && !window.confirm("Discard unsaved changes?")) {
        e.preventDefault();
        e.stopPropagation();
      }
    };
    window.addEventListener("beforeunload", onBeforeUnload);
    document.addEventListener("click", onClick, true);
    return () => {
      window.removeEventListener("beforeunload", onBeforeUnload);
      document.removeEventListener("click", onClick, true);
    };
  }, [dirty]);

  function insertImage(file: ImageFile) {
    const view = viewRef.current;
    if (!view) return;
    const src = "/" + file.src;
    const snippet = /\.mp4$/i.test(file.name)
      ? `<video src="${src}" controls></video>`
      : `![${file.name.replace(/\.[^.]+$/, "").replace(/[-_]+/g, " ")}](${src})`;
    insertText(view, snippet, true);
  }

  const isNew = !savedSlug;

  return (
    <main>
      <div className="editor-head">
        <h1>{isNew ? "New post" : form.title || savedSlug}</h1>
        {dirty && <span className="badge warn">unsaved</span>}
        <Link href="/" className="button">
          Back
        </Link>
        <button disabled={saving} onClick={() => save()}>
          {saving ? "Saving…" : "Save"}
        </button>
        <button className="primary" disabled={saving} onClick={() => save({ close: true })}>
          Save &amp; close
        </button>
      </div>

      {conflict && (
        <div className="notice warn">
          blog-posts.json changed on disk since this page loaded (another edit, or a git pull).
          <button onClick={() => window.location.reload()}>Reload (discard my edits)</button>
          <button className="danger" onClick={() => save({ force: true })}>
            Save anyway (overwrite this post)
          </button>
        </div>
      )}
      {message && <div className={`notice ${message.kind}`}>{message.text}</div>}

      <div className="meta-grid">
        <label className="field">
          <span>title</span>
          <input value={form.title} onChange={(e) => setTitle(e.target.value)} placeholder="Post title" />
        </label>
        <label className="field">
          <span>slug</span>
          <input
            className="mono"
            value={form.slug}
            onChange={(e) => {
              setSlugTouched(true);
              update("slug", e.target.value);
            }}
            onBlur={() => update("slug", slugify(form.slug))}
            placeholder="post-slug"
          />
          <span className="field-hint">
            /blog/{form.slug || "…"}
            {savedSlug && form.slug !== savedSlug && " · renaming moves the image folder"}
          </span>
        </label>
        <label className="field">
          <span>date</span>
          <input type="date" value={form.date} onChange={(e) => update("date", e.target.value)} />
        </label>

        <label className="field span-2">
          <span>description</span>
          <textarea
            rows={2}
            value={form.description}
            onChange={(e) => update("description", e.target.value)}
            placeholder="1–2 sentence excerpt shown on the post card"
          />
          <span className="field-hint">{form.description.length} characters</span>
        </label>
        <label className="field">
          <span>category</span>
          <input
            list={categoryListId}
            value={form.category}
            onChange={(e) => update("category", e.target.value)}
            onBlur={() => update("category", slugify(form.category))}
            placeholder="pick or type a new one"
          />
          <datalist id={categoryListId}>
            {categories.map((c) => (
              <option key={c} value={c}>
                {categoryLabel(c)}
              </option>
            ))}
          </datalist>
          <span className="field-hint">
            {form.category
              ? `shown as “${categoryLabel(form.category)}”${categories.includes(form.category) ? "" : " · new category"}`
              : "one per post"}
          </span>
        </label>

        <div className="field span-all">
          <span className="mono small muted">tags</span>
          <TagInput value={form.tags} onChange={(t) => update("tags", t)} suggestions={tags} />
        </div>
      </div>

      <div className="split">
        <MarkdownEditor
          value={form.details}
          onChange={(v) => update("details", v)}
          onView={(v) => (viewRef.current = v)}
        />
        <PreviewFrame markdown={form.details} category={form.category} images={form.images} title={form.title} />
      </div>

      <ImagePanel
        slug={savedSlug && savedSlug === form.slug ? savedSlug : null}
        files={files}
        onFilesChange={setFiles}
        gallery={form.images}
        onGalleryChange={(g) => update("images", g)}
        onInsert={insertImage}
      />
    </main>
  );
}