use serde::{Deserialize, Serialize};

use crate::account::{Account, AccountWithMetadata};

pub type ProgramId = [u32; 8];

/// A trait to be implemented by inner programs.
pub trait Program {
    const PROGRAM_ID: ProgramId;
    const PROGRAM_ELF: &[u8];
    type InstructionData: Serialize + for<'de> Deserialize<'de>;
}

/// Validates well-behaved program execution
///
/// # Parameters
/// - `pre_states`: The list of input accounts, each annotated with authorization metadata.
/// - `post_states`: The list of resulting accounts after executing the program logic.
/// - `executing_program_id`: The identifier of the program that was executed.
pub fn validate_constraints(
    pre_states: &[AccountWithMetadata],
    post_states: &[Account],
    executing_program_id: ProgramId,
) -> Result<(), ()> {
    // 1. Lengths must match
    if pre_states.len() != post_states.len() {
        return Err(());
    }

    for (pre, post) in pre_states.iter().zip(post_states) {
        // 2. Nonce must remain unchanged
        if pre.account.nonce != post.nonce {
            return Err(());
        }

        // 3. Ownership change only allowed from default accounts
        if pre.account.program_owner != post.program_owner && pre.account != Account::default() {
            return Err(());
        }

        // 4. Decreasing balance only allowed if owned by executing program
        if post.balance < pre.account.balance && pre.account.program_owner != executing_program_id {
            return Err(());
        }

        // 5. Data changes only allowed if owned by executing program
        if pre.account.data != post.data
            && (executing_program_id != pre.account.program_owner
                || executing_program_id != post.program_owner)
        {
            return Err(());
        }
    }

    // 6. Total balance is preserved
    let total_balance_pre_states: u128 = pre_states.iter().map(|pre| pre.account.balance).sum();
    let total_balance_post_states: u128 = post_states.iter().map(|post| post.balance).sum();
    if total_balance_pre_states != total_balance_post_states {
        return Err(());
    }

    Ok(())
}