"use client";

import { useMemo, useState } from "react";
import CodeMirror, { EditorSelection, EditorView, keymap } from "@uiw/react-codemirror";
import { markdown, markdownLanguage } from "@codemirror/lang-markdown";
import { languages } from "@codemirror/language-data";
import { useSystemDark } from "@/lib/useSystemDark";

/* Markdown source editor with a formatting toolbar. Source (not WYSIWYG) on
 * purpose: posts embed raw HTML blocks that rich-text editors would mangle.
 * The live preview beside it is what makes it visual. */

type Props = {
  value: string;
  onChange: (value: string) => void;
  /** Receives the EditorView so the parent can insert text (e.g. images). */
  onView?: (view: EditorView | null) => void;
};

/** Wrap each selection in `before`/`after`, or unwrap if already wrapped. */
export function wrap(view: EditorView, before: string, after = before, placeholder = "text") {
  view.dispatch(
    view.state.changeByRange((range) => {
      const doc = view.state.doc;
      const outerFrom = range.from - before.length;
      const outerTo = range.to + after.length;
      const isWrapped =
        outerFrom >= 0 &&
        outerTo <= doc.length &&
        doc.sliceString(outerFrom, range.from) === before &&
        doc.sliceString(range.to, outerTo) === after;
      if (isWrapped) {
        return {
          changes: [
            { from: outerFrom, to: range.from, insert: "" },
            { from: range.to, to: outerTo, insert: "" },
          ],
          range: EditorSelection.range(outerFrom, range.to - before.length),
        };
      }
      const text = range.empty ? placeholder : doc.sliceString(range.from, range.to);
      return {
        changes: { from: range.from, to: range.to, insert: before + text + after },
        range: EditorSelection.range(range.from + before.length, range.from + before.length + text.length),
      };
    })
  );
  view.focus();
}

/** Toggle a prefix on every line touched by the selection ("# ", "> ", "- "...). */
export function prefixLines(view: EditorView, prefix: string | ((i: number) => string)) {
  const { state } = view;
  const changes: { from: number; to?: number; insert: string }[] = [];
  const seen = new Set<number>();
  for (const range of state.selection.ranges) {
    const first = state.doc.lineAt(range.from).number;
    const last = state.doc.lineAt(range.to).number;
    for (let n = first, i = 0; n <= last; n++, i++) {
      if (seen.has(n)) continue;
      seen.add(n);
      const line = state.doc.line(n);
      const p = typeof prefix === "function" ? prefix(i) : prefix;
      // Strip any existing heading/quote/list marker so prefixes replace each other.
      const existing = /^(#{1,6} |> |- |\d+\. )/.exec(line.text)?.[0] ?? "";
      if (existing === p) changes.push({ from: line.from, to: line.from + existing.length, insert: "" });
      else changes.push({ from: line.from, to: line.from + existing.length, insert: p });
    }
  }
  view.dispatch({ changes });
  view.focus();
}

/** Replace the selection with `text` (on its own lines when `block`). */
export function insertText(view: EditorView, text: string, block = false) {
  const { state } = view;
  const range = state.selection.main;
  let insert = text;
  if (block) {
    const before = state.doc.sliceString(Math.max(0, range.from - 2), range.from);
    const after = state.doc.sliceString(range.to, range.to + 1);
    if (range.from > 0 && !before.endsWith("\n\n")) insert = (before.endsWith("\n") ? "\n" : "\n\n") + insert;
    if (after !== "\n") insert += "\n";
  }
  view.dispatch({
    changes: { from: range.from, to: range.to, insert },
    selection: EditorSelection.cursor(range.from + insert.length),
  });
  view.focus();
}

function link(view: EditorView) {
  const url = window.prompt("Link URL", "https://");
  if (!url) return;
  wrap(view, "[", `](${url})`, "link text");
}

const BLOCKQUOTE_HTML = "<blockquote>\nQuote text\n</blockquote>";

export default function MarkdownEditor({ value, onChange, onView }: Props) {
  const [view, setView] = useState<EditorView | null>(null);
  const dark = useSystemDark();

  const extensions = useMemo(
    () => [
      markdown({ base: markdownLanguage, codeLanguages: languages }),
      EditorView.lineWrapping,
      keymap.of([
        { key: "Mod-b", run: (v) => (wrap(v, "**"), true) },
        { key: "Mod-i", run: (v) => (wrap(v, "*"), true) },
        { key: "Mod-k", run: (v) => (link(v), true) },
      ]),
    ],
    []
  );

  const tools: ({ label: string; title: string; run: (v: EditorView) => void } | "sep")[] = [
    { label: "H1", title: "Heading 1", run: (v) => prefixLines(v, "# ") },
    { label: "H2", title: "Heading 2", run: (v) => prefixLines(v, "## ") },
    { label: "H3", title: "Heading 3", run: (v) => prefixLines(v, "### ") },
    "sep",
    { label: "B", title: "Bold (Ctrl+B)", run: (v) => wrap(v, "**") },
    { label: "I", title: "Italic (Ctrl+I)", run: (v) => wrap(v, "*") },
    { label: "</>", title: "Inline code", run: (v) => wrap(v, "`", "`", "code") },
    { label: "link", title: "Link (Ctrl+K)", run: link },
    "sep",
    { label: "• list", title: "Bullet list", run: (v) => prefixLines(v, "- ") },
    { label: "1. list", title: "Numbered list", run: (v) => prefixLines(v, (i) => `${i + 1}. `) },
    { label: "> quote", title: "Markdown quote", run: (v) => prefixLines(v, "> ") },
    { label: "<quote>", title: "HTML blockquote (the site's raised style)", run: (v) => insertText(v, BLOCKQUOTE_HTML, true) },
    { label: "```", title: "Code block", run: (v) => wrap(v, "```\n", "\n```", "code") },
    { label: "—", title: "Horizontal rule", run: (v) => insertText(v, "---", true) },
  ];

  return (
    <div className="pane">
      <div className="pane-head">
        {tools.map((tool, i) =>
          tool === "sep" ? (
            <span key={i} className="tb-sep" />
          ) : (
            <button
              key={tool.label}
              type="button"
              title={tool.title}
              disabled={!view}
              onMouseDown={(e) => e.preventDefault()}
              onClick={() => view && tool.run(view)}
            >
              {tool.label}
            </button>
          )
        )}
        <span className="spacer" />
        <span>markdown</span>
      </div>
      <div className="pane-body">
        <CodeMirror
          value={value}
          onChange={onChange}
          extensions={extensions}
          theme={dark ? "dark" : "light"}
          height="100%"
          style={{ position: "absolute", inset: 0 }}
          basicSetup={{ foldGutter: false, highlightActiveLine: false }}
          onCreateEditor={(v) => {
            setView(v);
            onView?.(v);
          }}
        />
      </div>
    </div>
  );
}