agb/examples/hyperspace-roll/src/level_generation.rs

use agb::{hash_map::HashMap, rng};
use alloc::vec::Vec;

use crate::{battle::EnemyAttack, Face};

pub struct GeneratedAttack {
    pub attack: EnemyAttack,
    pub cooldown: u32,
}

fn roll_dice(number_of_dice: u32, bits_per_dice: u32) -> u32 {
    assert!(
        32 % bits_per_dice == 0,
        "the number of bits per dice should be a multiple of 32"
    );

    assert!(
        number_of_dice % (32 / bits_per_dice) == 0,
        "number of dice should be a multiple of 32 / bits per dice"
    );

    fn roll_dice_inner(number_of_random_values: u32, bits_per_dice: u32) -> u32 {
        let mut count = 0;
        let bit_mask = 1u32.wrapping_shl(bits_per_dice).wrapping_sub(1);

        for _ in 0..number_of_random_values {
            let n = agb::rng::gen() as u32;
            for idx in 0..(32 / bits_per_dice) {
                count += (n >> (bits_per_dice * idx)) & bit_mask;
            }
        }

        count
    }

    roll_dice_inner(number_of_dice / (32 / bits_per_dice), bits_per_dice)
}

// uses multiple dice rolls to generate a random value with a specified mean and width
fn roll_dice_scaled(number_of_dice: u32, bits_per_dice: u32, width: u32) -> i32 {
    let dice = roll_dice(number_of_dice, bits_per_dice) as i32;

    let current_width = (number_of_dice * ((1 << bits_per_dice) - 1)) as i32;
    let current_mean = current_width / 2;

    let dice_around_zero = dice - current_mean;

    fn divide_nearest(numerator: i32, denominator: i32) -> i32 {
        if (numerator < 0) ^ (denominator < 0) {
            (numerator - denominator / 2) / denominator
        } else {
            (numerator + denominator / 2) / denominator
        }
    }
    divide_nearest(dice_around_zero * width as i32, current_width)
}

fn default_roll(width: u32) -> i32 {
    roll_dice_scaled(2, 16, width)
}

pub fn generate_attack(current_level: u32) -> Option<GeneratedAttack> {
    if (rng::gen().rem_euclid(1024) as u32) < current_level * 2 {
        Some(GeneratedAttack {
            attack: generate_enemy_attack(current_level),
            cooldown: generate_cooldown(current_level),
        })
    } else {
        None
    }
}

pub fn generate_enemy_health(current_level: u32) -> u32 {
    (5 + current_level as i32 * 2 + default_roll(current_level * 4)) as u32
}

fn generate_enemy_attack(current_level: u32) -> EnemyAttack {
    let attack_id = rng::gen().rem_euclid(10) as u32;

    if attack_id < 7 {
        EnemyAttack::Shoot(rng::gen().rem_euclid(((current_level + 2) / 3) as i32) as u32 + 1)
    } else if attack_id < 9 {
        EnemyAttack::Shield(
            (rng::gen().rem_euclid(((current_level + 4) / 5) as i32) as u32 + 1).min(5),
        )
    } else {
        EnemyAttack::Heal(rng::gen().rem_euclid(((current_level + 1) / 2) as i32) as u32)
    }
}

fn generate_cooldown(current_level: u32) -> u32 {
    rng::gen().rem_euclid((5 * 60 - current_level as i32 * 10).max(1)) as u32 + 2 * 60
}

pub fn generate_upgrades(level: u32, call: &mut dyn FnMut()) -> Vec<Face> {
    let mut upgrade_values = HashMap::new();

    upgrade_values.insert(Face::Shoot, 5);
    upgrade_values.insert(Face::DoubleShot, 10);
    upgrade_values.insert(Face::DoubleShotValue, 15);
    upgrade_values.insert(Face::TripleShot, 20);
    upgrade_values.insert(Face::TripleShotValue, 30);
    upgrade_values.insert(Face::Shield, 5);
    upgrade_values.insert(Face::DoubleShield, 10);
    upgrade_values.insert(Face::TripleShield, 20);
    upgrade_values.insert(Face::DoubleShieldValue, 25);
    upgrade_values.insert(Face::Malfunction, -2);
    upgrade_values.insert(Face::Bypass, 7);
    upgrade_values.insert(Face::Disrupt, 10);
    upgrade_values.insert(Face::MalfunctionShot, 15);
    upgrade_values.insert(Face::Heal, 8);
    upgrade_values.insert(Face::BurstShield, 30);
    upgrade_values.insert(Face::Invert, 30);

    let potential_upgrades: Vec<Face> = upgrade_values.keys().cloned().collect();

    let mut upgrades = Vec::new();

    let upgrade_value = |upgrades: &[Face], potential_upgrade: Face| -> i32 {
        upgrades
            .iter()
            .map(|x| upgrade_values.get(x).unwrap())
            .sum::<i32>()
            + upgrade_values.get(&potential_upgrade).unwrap()
    };

    let max_upgrade_value = 15 + (rng::gen().rem_euclid(level as i32 * 5));
    let mut attempts = 0;

    while upgrades.len() != 3 {
        call();

        attempts += 1;
        let next = potential_upgrades[rng::gen() as usize % potential_upgrades.len()];
        let number_of_malfunctions = upgrades
            .iter()
            .chain(core::iter::once(&next))
            .filter(|&x| *x == Face::Malfunction)
            .count();
        let maximum_number_of_malfunctions = (level >= 5).into();
        if upgrade_value(&upgrades, next) <= max_upgrade_value
            && number_of_malfunctions <= maximum_number_of_malfunctions
        {
            upgrades.push(next);
            attempts = 0;
        }

        if attempts > 100 {
            attempts = 0;
            upgrades.clear();
        }
    }

    upgrades
}