import "server-only";

import { fetchImageBufferFromUrl } from "@/lib/ai/rmbg/service";

export type CanvasLayoutReplaceSourceProfile = {
  boundingHeight: number;
  boundingWidth: number;
  silhouetteAspectRatio: number;
  sourceHeight: number;
  sourceWidth: number;
  transparentPixelRatio: number;
};

export async function resolveCanvasLayoutReplaceSourceProfile(
  sourceImageUrl: string,
): Promise<CanvasLayoutReplaceSourceProfile | null> {
  try {
    const sharp = (await import("sharp")).default;
    const sourceBuffer = await fetchImageBufferFromUrl(sourceImageUrl);
    const { data, info } = await sharp(sourceBuffer, { failOn: "none" })
      .rotate()
      .ensureAlpha()
      .raw()
      .toBuffer({ resolveWithObject: true });
    const pixelCount = info.width * info.height;
    if (pixelCount <= 0 || info.channels < 4) return null;

    let transparentPixelCount = 0;
    let minX = info.width;
    let minY = info.height;
    let maxX = -1;
    let maxY = -1;

    for (let pixelIndex = 0; pixelIndex < pixelCount; pixelIndex += 1) {
      const alpha = data[pixelIndex * info.channels + 3] || 0;
      if (alpha < 250) transparentPixelCount += 1;
      if (alpha < 24) continue;

      const x = pixelIndex % info.width;
      const y = Math.floor(pixelIndex / info.width);
      if (x < minX) minX = x;
      if (x > maxX) maxX = x;
      if (y < minY) minY = y;
      if (y > maxY) maxY = y;
    }

    const transparentPixelRatio = transparentPixelCount / pixelCount;
    if (transparentPixelRatio < 0.01 || maxX < minX || maxY < minY) {
      return null;
    }

    const boundingWidth = maxX - minX + 1;
    const boundingHeight = maxY - minY + 1;
    if (boundingWidth < 2 || boundingHeight < 2) return null;

    return {
      boundingHeight,
      boundingWidth,
      silhouetteAspectRatio: boundingWidth / boundingHeight,
      sourceHeight: info.height,
      sourceWidth: info.width,
      transparentPixelRatio,
    };
  } catch (error) {
    console.warn("[Canvas Layout Replace] Failed to resolve source profile:", {
      error: error instanceof Error ? error.message : String(error),
    });
    return null;
  }
}