"use client";

import { useCallback, useLayoutEffect, useMemo, useRef } from "react";
import { DiffEditor, type DiffOnMount } from "@monaco-editor/react";
import type { editor as monacoEditor } from "monaco-editor";
import { useTheme } from "next-themes";
import { cn } from "@/lib/utils";
import type { FileDiffData } from "@/lib/diff/types";
import { getMonacoLanguage } from "@/lib/editor/language-map";
import { EDITOR_FONT_FAMILY } from "@/lib/theme/editor-theme";
import { initMonacoThemes } from "./monaco-init";

initMonacoThemes();

type MonacoInlineDiffProps = {
  data: FileDiffData;
  className?: string;
};

/** Parse original/modified content from diff data. */
function parseDiffData(data: FileDiffData): { original: string; modified: string } {
  if (data.oldContent || data.newContent) {
    return { original: data.oldContent ?? "", modified: data.newContent ?? "" };
  }
  if (data.diff) {
    return parsePatchToSides(data.diff);
  }
  return { original: "", modified: "" };
}

/** Reconstruct original/modified sides from a unified diff patch. */
function parsePatchToSides(diff: string): { original: string; modified: string } {
  const originalLines: string[] = [];
  const modifiedLines: string[] = [];
  for (const line of diff.split("\n")) {
    if (
      line.startsWith("diff ") ||
      line.startsWith("index ") ||
      line.startsWith("--- ") ||
      line.startsWith("+++ ") ||
      line.startsWith("@@") ||
      line.startsWith("\\")
    )
      continue;
    if (line.startsWith("-")) {
      originalLines.push(line.slice(1));
    } else if (line.startsWith("+")) {
      modifiedLines.push(line.slice(1));
    } else {
      const content = line.startsWith(" ") ? line.slice(1) : line;
      originalLines.push(content);
      modifiedLines.push(content);
    }
  }
  return { original: originalLines.join("\n"), modified: modifiedLines.join("\n") };
}

export function MonacoInlineDiff({ data, className }: MonacoInlineDiffProps) {
  const { resolvedTheme } = useTheme();
  const language = getMonacoLanguage(data.filePath);
  const diffEditorRef = useRef<monacoEditor.IStandaloneDiffEditor | null>(null);

  const handleMount: DiffOnMount = useCallback((editor) => {
    diffEditorRef.current = editor;
  }, []);

  // Fix: reset model before @monaco-editor/react's cleanup disposes models
  useLayoutEffect(() => {
    return () => {
      try {
        diffEditorRef.current?.setModel(null);
      } catch {
        /* already disposed */
      }
    };
  }, []);

  const { original, modified } = useMemo(() => parseDiffData(data), [data]);

  const lineCount = Math.max(original.split("\n").length, modified.split("\n").length);
  const height = Math.min(Math.max(lineCount * 16 + 8, 48), 300);

  return (
    <div
      className={cn(
        "mt-3 rounded-md border border-border/50 bg-background/60 px-3 py-2 text-xs overflow-hidden",
        className,
      )}
    >
      <DiffEditor
        height={height}
        language={language}
        original={original}
        modified={modified}
        theme={resolvedTheme === "dark" ? "kandev-dark" : "kandev-light"}
        onMount={handleMount}
        options={{
          readOnly: true,
          fontSize: 11,
          fontFamily: EDITOR_FONT_FAMILY,
          lineHeight: 16,
          minimap: { enabled: false },
          wordWrap: "on",
          renderSideBySide: false,
          scrollBeyondLastLine: false,
          lineNumbers: "off",
          glyphMargin: false,
          folding: false,
          renderOverviewRuler: false,
          scrollbar: { vertical: "hidden", horizontal: "hidden", alwaysConsumeMouseWheel: false },
          automaticLayout: true,
          domReadOnly: true,
          contextmenu: false,
          padding: { top: 2, bottom: 2 },
        }}
        loading={null}
      />
    </div>
  );
}