import {
  AbortMultipartUploadCommand,
  CompleteMultipartUploadCommand,
  CreateMultipartUploadCommand,
  HeadObjectCommand,
  PutObjectCommand,
  UploadPartCommand,
} from "@aws-sdk/client-s3";
import { getSignedUrl } from "@aws-sdk/s3-request-presigner";
import { NextResponse } from "next/server";
import { z } from "zod";

import { auth } from "@/app/(auth)/auth";
import { upsertMediaAsset } from "@/lib/db/queries";
import {
  buildS3PublicUrl,
  buildStorageObjectKey,
  createS3Client,
  getContentType,
  maybeEnqueueStorageMigrationTask,
  resolveS3UploadTarget,
} from "@/lib/storage/service";

const DIRECT_UPLOAD_MAX_BYTES = 500 * 1024 * 1024;
const MULTIPART_THRESHOLD_BYTES = 50 * 1024 * 1024;
const DEFAULT_PART_SIZE_BYTES = 8 * 1024 * 1024;
const PRESIGNED_URL_EXPIRES_SECONDS = 15 * 60;
const DIRECT_UPLOAD_PREFIX = "uploads/direct";

const allowedDirectUploadTypes = new Set([
  "image/jpeg",
  "image/jpg",
  "image/png",
  "image/webp",
]);

const InitiateSchema = z.object({
  action: z.literal("initiate"),
  filename: z.string().min(1).max(256),
  contentType: z.string().min(1).max(128),
  size: z.number().int().positive().max(DIRECT_UPLOAD_MAX_BYTES),
  purpose: z.string().max(64).optional(),
});

const CompleteSchema = z.object({
  action: z.literal("complete"),
  key: z.string().min(1).max(512),
  uploadId: z.string().min(1).max(512).optional(),
  filename: z.string().min(1).max(256),
  contentType: z.string().min(1).max(128),
  size: z.number().int().positive().max(DIRECT_UPLOAD_MAX_BYTES),
  parts: z
    .array(
      z.object({
        ETag: z.string().min(1),
        PartNumber: z.number().int().positive(),
      })
    )
    .optional(),
  purpose: z.string().max(64).optional(),
});

const AbortSchema = z.object({
  action: z.literal("abort"),
  key: z.string().min(1).max(512),
  uploadId: z.string().min(1).max(512),
});

const RequestSchema = z.discriminatedUnion("action", [
  InitiateSchema,
  CompleteSchema,
  AbortSchema,
]);

function normalizeContentType(contentType: string, filename: string) {
  const trimmed = contentType.trim().toLowerCase();
  return trimmed || getContentType(filename);
}

function sanitizeDisplayName(filename: string) {
  return (
    filename
      .trim()
      .replace(/[^\u4e00-\u9fa5a-zA-Z0-9._-]+/g, "-")
      .replace(/^-+|-+$/g, "")
      .slice(0, 120) || `upload-${Date.now()}`
  );
}

function userUploadPrefix(userId: string) {
  return `${DIRECT_UPLOAD_PREFIX}/${userId}`;
}

function assertUserOwnedKey(key: string, userId: string) {
  const normalized = String(key || "").replace(/^\/+/, "");
  const prefix = `${userUploadPrefix(userId)}/`;
  if (!normalized.startsWith(prefix)) {
    throw new Error("Invalid upload object key");
  }
  return normalized;
}

function isAllowedDirectUpload(contentType: string) {
  return allowedDirectUploadTypes.has(contentType);
}

function computePartSize(size: number) {
  if (size <= 100 * 1024 * 1024) return DEFAULT_PART_SIZE_BYTES;
  if (size <= 300 * 1024 * 1024) return 12 * 1024 * 1024;
  return 16 * 1024 * 1024;
}

async function createPartUrls(params: {
  client: ReturnType<typeof createS3Client>;
  bucket: string;
  key: string;
  uploadId: string;
  partCount: number;
}) {
  const urls = [];
  for (let partNumber = 1; partNumber <= params.partCount; partNumber += 1) {
    const command = new UploadPartCommand({
      Bucket: params.bucket,
      Key: params.key,
      UploadId: params.uploadId,
      PartNumber: partNumber,
    });
    urls.push({
      partNumber,
      url: await getSignedUrl(params.client, command, {
        expiresIn: PRESIGNED_URL_EXPIRES_SECONDS,
      }),
    });
  }
  return urls;
}

export async function POST(request: Request) {
  const session = await auth();
  if (!session?.user?.id) {
    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
  }

  let payload: z.infer<typeof RequestSchema>;
  try {
    payload = RequestSchema.parse(await request.json());
  } catch (error) {
    return NextResponse.json(
      {
        error: "Invalid direct upload request",
        details: error instanceof Error ? error.message : String(error),
      },
      { status: 400 }
    );
  }

  const target = await resolveS3UploadTarget().catch((error) => {
    console.error("[DirectUpload] Failed to resolve storage target:", error);
    return null;
  });

  if (!target) {
    return NextResponse.json(
      { error: "Direct upload is not available for current storage backend" },
      { status: 409 }
    );
  }

  const client = createS3Client(target.config);
  const bucket = target.config.bucket;

  try {
    if (payload.action === "initiate") {
      const contentType = normalizeContentType(
        payload.contentType,
        payload.filename
      );

      if (!isAllowedDirectUpload(contentType)) {
        return NextResponse.json(
          { error: "Direct upload only supports JPG, PNG and WebP images" },
          { status: 400 }
        );
      }

      const displayName = sanitizeDisplayName(payload.filename);
      const key = buildStorageObjectKey(
        displayName,
        userUploadPrefix(session.user.id)
      );

      if (payload.size < MULTIPART_THRESHOLD_BYTES) {
        const command = new PutObjectCommand({
          Bucket: bucket,
          Key: key,
          ContentType: contentType,
          ACL: "public-read",
        });
        const url = await getSignedUrl(client, command, {
          expiresIn: PRESIGNED_URL_EXPIRES_SECONDS,
        });

        return NextResponse.json({
          mode: "single",
          key,
          url,
          headers: {
            "Content-Type": contentType,
            "x-amz-acl": "public-read",
          },
          expiresIn: PRESIGNED_URL_EXPIRES_SECONDS,
        });
      }

      const createResult = await client.send(
        new CreateMultipartUploadCommand({
          Bucket: bucket,
          Key: key,
          ContentType: contentType,
          ACL: "public-read",
        })
      );

      const uploadId = createResult.UploadId;
      if (!uploadId) {
        throw new Error("Storage provider did not return uploadId");
      }

      const partSize = computePartSize(payload.size);
      const partCount = Math.ceil(payload.size / partSize);
      const parts = await createPartUrls({
        client,
        bucket,
        key,
        uploadId,
        partCount,
      });

      return NextResponse.json({
        mode: "multipart",
        key,
        uploadId,
        partSize,
        partCount,
        parts,
        expiresIn: PRESIGNED_URL_EXPIRES_SECONDS,
      });
    }

    if (payload.action === "abort") {
      const key = assertUserOwnedKey(payload.key, session.user.id);
      await client.send(
        new AbortMultipartUploadCommand({
          Bucket: bucket,
          Key: key,
          UploadId: payload.uploadId,
        })
      );
      return NextResponse.json({ ok: true });
    }

    const key = assertUserOwnedKey(payload.key, session.user.id);
    const contentType = normalizeContentType(payload.contentType, payload.filename);
    if (!isAllowedDirectUpload(contentType)) {
      return NextResponse.json(
        { error: "Direct upload only supports JPG, PNG and WebP images" },
        { status: 400 }
      );
    }

    if (payload.uploadId) {
      const parts = [...(payload.parts || [])].sort(
        (a, b) => a.PartNumber - b.PartNumber
      );
      if (parts.length === 0) {
        return NextResponse.json(
          { error: "Missing multipart upload parts" },
          { status: 400 }
        );
      }

      await client.send(
        new CompleteMultipartUploadCommand({
          Bucket: bucket,
          Key: key,
          UploadId: payload.uploadId,
          MultipartUpload: {
            Parts: parts,
          },
        })
      );
    }

    const head = await client.send(
      new HeadObjectCommand({
        Bucket: bucket,
        Key: key,
      })
    );

    const actualSize =
      typeof head.ContentLength === "number" ? head.ContentLength : null;
    if (actualSize !== null && actualSize <= 0) {
      throw new Error("Uploaded object is empty");
    }

    const url = buildS3PublicUrl(target.config, key);
    const resolvedContentType =
      head.ContentType || contentType || getContentType(payload.filename);
    const asset = await upsertMediaAsset({
      userId: session.user.id,
      mediaType: "image",
      sourceType: "upload",
      status: "ready",
      originalUrl: url,
      previewUrl: url,
      thumbnailUrl: url,
      mimeType: resolvedContentType,
      displayName: payload.filename,
      sourceTable: "direct_upload",
      metadata: {
        pathname: key,
        size: actualSize ?? payload.size,
        expectedSize: payload.size,
        uploadMode: payload.uploadId ? "multipart" : "single",
        purpose: payload.purpose || null,
      },
    });

    await maybeEnqueueStorageMigrationTask({
      uploaded: { url, pathname: key },
      storageConfig: target.storageConfig,
      migrationConfig: target.migrationConfig,
    }).catch((error) => {
      console.error("[DirectUpload] Failed to enqueue OSS migration task:", error);
    });

    return NextResponse.json({
      url,
      pathname: key,
      contentType: resolvedContentType,
      assetId: asset?.id ?? null,
    });
  } catch (error) {
    console.error("[DirectUpload] Request failed:", error);
    return NextResponse.json(
      {
        error: "Direct upload failed",
        details: error instanceof Error ? error.message : String(error),
      },
      { status: 500 }
    );
  }
}