/**
 * POST /api/apply-changes
 *
 * Lets the user manually override the LLM's heading classifications.
 * Accepts the user's corrected heading indices and regenerates the enriched docx.
 *
 * Body: {
 *   sessionId: string,
 *   headingIndices: number[],  // paragraph indices to mark as headings
 *   headingFontSize?: number   // font size in pt, default 18
 * }
 */
import { NextResponse } from "next/server";
import { applyHeadingChanges } from "@/lib/docx-service";
import fileStore from "@/lib/file-store";

export async function POST(request) {
  try {
    const body = await request.json();
    const { sessionId, headingIndices, headingFontSize = 18 } = body;

    if (!sessionId) {
      return NextResponse.json(
        { error: "sessionId is required" },
        { status: 400 }
      );
    }

    if (!Array.isArray(headingIndices)) {
      return NextResponse.json(
        { error: "headingIndices must be an array of paragraph indices" },
        { status: 400 }
      );
    }

    const session = fileStore.get(sessionId);
    if (!session) {
      return NextResponse.json(
        { error: "Session not found or expired. Please re-upload the file." },
        { status: 404 }
      );
    }

    // Build changes from user-specified heading indices
    const headingChanges = headingIndices.map((index) => ({
      index,
      headingFontSize,
      bold: true,
    }));

    // Apply formatting changes
    const enrichedBuffer = applyHeadingChanges(
      session.originalBuffer,
      headingChanges
    );

    // Update the session
    const updatedClassifications = (session.paragraphs || []).map((p) => ({
      index: p.index,
      text: p.text,
      isHeading: headingIndices.includes(p.index),
    }));

    fileStore.update(sessionId, {
      enrichedBuffer: enrichedBuffer,
      headingIndices: headingIndices,
      classifications: updatedClassifications,
      headingFontSize: headingFontSize,
    });

    return NextResponse.json({
      sessionId,
      classifications: updatedClassifications,
      headingsApplied: headingIndices.length,
      headingFontSize,
    });
  } catch (err) {
    console.error("Apply changes error:", err);
    return NextResponse.json(
      { error: "Failed to apply changes: " + err.message },
      { status: 500 }
    );
  }
}