Implement Tier-Based Rewards

[jdnichollsc]

Add Tier-Based Reward Logic

Definition of Done:

• Campaign creators can define tiers with price, limits, and rewards.
• Contributions can be linked to specific tiers.
• Validate tier limits before accepting contributions.

Tasks:

• Define the Tier struct.
• Add an instruction for creators to create tiers.
• Update contribution logic to support tiers.
• Validate tier limits during contributions.

Code Example:

#[account]
pub struct Tier {
    pub campaign: Pubkey,             // Associated campaign
    pub title: String,                // Tier title
    pub price: u64,                   // Tier price in lamports
    pub max_backers: u32,             // Maximum number of backers
    pub current_backers: u32,         // Current number of backers
}

#[derive(Accounts)]
pub struct CreateTier<'info> {
    #[account(mut)]
    pub campaign: Account<'info, Campaign>,
    #[account(init, payer = creator, space = 8 + Tier::MAX_SIZE, seeds = [b"tier", campaign.key().as_ref(), title.as_bytes()], bump)]
    pub tier: Account<'info, Tier>,
    #[account(mut)]
    pub creator: Signer<'info>,
    pub system_program: Program<'info, System>,
}

pub fn create_tier(
    ctx: Context<CreateTier>,
    title: String,
    price: u64,
    max_backers: u32,
) -> Result<()> {
    let tier = &mut ctx.accounts.tier;
    tier.campaign = ctx.accounts.campaign.key();
    tier.title = title;
    tier.price = price;
    tier.max_backers = max_backers;
    tier.current_backers = 0;
    Ok(())
}