lib.rs

use borsh::{BorshDeserialize, BorshSerialize};
use std::collections::HashMap;
use std::convert::TryInto;

use solana_program::{
    account_info::{next_account_info, AccountInfo},
    entrypoint,
    entrypoint::ProgramResult,
    msg,
    program_error::ProgramError,
    pubkey::Pubkey,
};

#[derive(BorshSerialize, BorshDeserialize, Debug)]
pub struct CampaignAccount {
    pub campaign_owner: Pubkey,
    pub campaign_amount: u64,
    pub campaign_description: String,
    pub campaign_fulfilled: u64,
}

entrypoint!(process_instruction);

pub fn process_instruction(
    program_id: &Pubkey, 
    accounts: &[AccountInfo], 
    data: &[u8], 
) -> ProgramResult {

    let accounts_iter = &mut accounts.iter();
    let campaign_account = next_account_info(accounts_iter)?;

    let (instruction_byte, rest_of_data) = data.split_first().unwrap();

    let amount = rest_of_data
      .get(..8)
      .and_then(|slice| slice.try_into().ok())
      .map(u64::from_le_bytes)
      .unwrap();
      
    let description = String::from_utf8(rest_of_data[9..].to_vec()).unwrap();      

    if *instruction_byte == 0 {
      let campaign_owner_account = next_account_info(accounts_iter)?;
      let mut campaign_account_data = CampaignAccount::try_from_slice(&campaign_account.data.borrow())?;
      campaign_account_data.campaign_owner = *campaign_owner_account.owner;
      campaign_account_data.campaign_amount = amount;
      campaign_account_data.campaign_description = description;
      campaign_account_data.campaign_fulfilled = 0;
      campaign_account_data.serialize(&mut &mut campaign_account.data.borrow_mut()[..])?;
    }

    if *instruction_byte == 1 {
      //get campaign status 

      let mut campaign_account_data = CampaignAccount::try_from_slice(&campaign_account.data.borrow())?;
      msg!("{}",campaign_account_data.campaign_amount - campaign_account_data.campaign_fulfilled);

    }

    if *instruction_byte == 2 {

    }

    if *instruction_byte == 3 {

    }
    

    Ok(())
}