prisma-offset-cursor-pagination.ts

// pagination.input.ts
import { Field, InputType } from '@nestjs/graphql';
import { IsInt, IsOptional, Max, Min } from 'class-validator';

@InputType()
export class PaginationInput {
  // cursor field name
  @Field({ nullable: true })
  @IsOptional()
  cursorName?: string;

  // pagination cursor, object id
  @Field({ nullable: true })
  @IsOptional()
  cursor?: number;

  // take number, backward from cursor, exclude forward
  @Field({
    nullable: true,
    description: 'forward from cursor, value is page size',
  })
  @IsOptional()
  @IsInt()
  @Min(1)
  @Max(200)
  backward?: number;

  // take number, forward from cursor, exclude backward
  @Field({
    nullable: true,
    description: 'backward from cursor, value is page size',
  })
  @IsOptional()
  @IsInt()
  @Min(1)
  @Max(200)
  forward?: number;

  // skip page number
  @Field({ nullable: true })
  @IsOptional()
  @IsInt()
  @Min(1)
  @Max(5)
  skipPage?: number;
}



// pagination.ts
import { PaginationInput } from './entities/pagination.input';

interface PaginationArgs {
  cursor?: any;
  skip?: number;
  take?: number;
}

export const parsePaginationArgs = (
  input: PaginationInput,
  totalCount?: number,
): PaginationArgs => {
  // forward & backward check, only one should & must exist
  if ((input.forward && input.backward) || (!input.forward && !input.backward))
    return {};

  let result = {};

  // parse cursor
  if (input.cursorName && input.cursor) {
    result = { cursor: { [input.cursorName]: input.cursor } };
  }

  let take = 0;
  let skip = 0;
  let pageSize = 0;

  // forward page
  if (input.forward) {
    pageSize = input.forward;
    take = pageSize;

    if (input.skipPage) {
      skip = input.skipPage * pageSize;
    }
  }

  // backward page
  if (input.backward) {
    pageSize = input.backward;
    take = pageSize;

    // last page, try get actual last page size
    if (!input.cursor && !input.cursorName && totalCount) {
      take = totalCount % take;
    }

    if (input.skipPage) {
      skip = (input.skipPage - 1) * pageSize + take;
      take = -pageSize;
    } else {
      take = -take;
    }
  }

  // skip cursor itself
  if (input.cursorName && input.cursor) skip += 1;

  result = { ...result, take, skip };
  return result;
};