veloren/common/src/lottery.rs

// Example for calculating a drop rate:
//
// On every roll an f32 between 0 and 1 is created.
// For every loot table a total range is created by the sum of the individual
// ranges per item.
//
// This range is the sum of all single ranges defined per item in a table.
//                                                   // Individual Range
// (3, "common.items.food.cheese"),                  // 0.0..3.0
// (3, "common.items.food.apple"),                   // 3.0..6.0
// (3, "common.items.food.mushroom"),                // 6.0..9.0
// (1, "common.items.food.coconut"),                 // 9.0..10.0
// (0.05, "common.items.food.apple_mushroom_curry"), // 10.0..10.05
// (0.10, "common.items.food.apple_stick"),          // 10.05..10.15
// (0.10, "common.items.food.mushroom_stick"),       // 10.15..10.25
//
// The f32 is multiplied by the max. value needed to drop an item in this
// particular table. X = max. value needed = 10.15
//
// Example roll
// [Random Value 0..1] * X = Number inside the table's total range
// 0.45777 * X = 4.65
// 4.65 is in the range of 3.0..6.0 => Apple drops
//
// Example drop chance calculation
// Cheese drop rate = 3/X = 29.6%
// Coconut drop rate = 1/X = 9.85%

use crate::{
    assets::{self, AssetExt},
    comp::Item,
};
use rand::prelude::*;
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use tracing::warn;

#[derive(Clone, Debug, PartialEq, Deserialize)]
pub struct Lottery<T> {
    items: Vec<(f32, T)>,
    total: f32,
}

impl<T: DeserializeOwned + Send + Sync + 'static> assets::Asset for Lottery<T> {
    type Loader = assets::LoadFrom<Vec<(f32, T)>, assets::RonLoader>;

    const EXTENSION: &'static str = "ron";
}

impl<T> From<Vec<(f32, T)>> for Lottery<T> {
    fn from(mut items: Vec<(f32, T)>) -> Lottery<T> {
        let mut total = 0.0;

        for (rate, _) in &mut items {
            total += *rate;
            *rate = total - *rate;
        }

        Self { items, total }
    }
}

impl<T> Lottery<T> {
    pub fn choose_seeded(&self, seed: u32) -> &T {
        let x = ((seed % 65536) as f32 / 65536.0) * self.total;
        &self.items[self
            .items
            .binary_search_by(|(y, _)| y.partial_cmp(&x).unwrap())
            .unwrap_or_else(|i| i.saturating_sub(1))]
        .1
    }

    pub fn choose(&self) -> &T { self.choose_seeded(thread_rng().gen()) }

    pub fn iter(&self) -> impl Iterator<Item = &(f32, T)> { self.items.iter() }

    pub fn total(&self) -> f32 { self.total }
}

#[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
pub enum LootSpec<T: AsRef<str>> {
    /// Asset specifier
    Item(T),
    /// Asset specifier, lower range, upper range
    ItemQuantity(T, u32, u32),
    /// Loot table
    LootTable(T),
    /// No loot given
    None,
}

impl<T: AsRef<str>> LootSpec<T> {
    pub fn to_item(&self) -> Option<Item> {
        match self {
            Self::Item(item) => Item::new_from_asset(item.as_ref()).ok(),
            Self::ItemQuantity(item, lower, upper) => {
                let range = *lower..=*upper;
                let quantity = thread_rng().gen_range(range);
                if let Ok(mut item) = Item::new_from_asset(item.as_ref()) {
                    // TODO: Handle multiple of an item that is unstackable
                    if item.set_amount(quantity).is_err() {
                        warn!("Tried to set quantity on non stackable item");
                    }
                    Some(item)
                } else {
                    None
                }
            },
            Self::LootTable(table) => Lottery::<LootSpec<String>>::load_expect(table.as_ref())
                .read()
                .choose()
                .to_item(),
            Self::None => None,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{assets, comp::Item};

    #[test]
    fn test_loot_tables() {
        fn validate_table_contents(table: Lottery<LootSpec<String>>) {
            for (_, item) in table.iter() {
                match item {
                    LootSpec::Item(item) => {
                        Item::new_from_asset_expect(item);
                    },
                    LootSpec::ItemQuantity(item, lower, upper) => {
                        assert!(
                            *lower > 0,
                            "Lower quantity must be more than 0. It is {}.",
                            lower
                        );
                        assert!(
                            upper >= lower,
                            "Upper quantity must be at least the value of lower quantity. Upper \
                             value: {}, low value: {}.",
                            upper,
                            lower
                        );
                        Item::new_from_asset_expect(item);
                    },
                    LootSpec::LootTable(loot_table) => {
                        let loot_table =
                            Lottery::<LootSpec<String>>::load_expect_cloned(loot_table);
                        validate_table_contents(loot_table);
                    },
                    LootSpec::None => {},
                }
            }
        }

        let loot_tables =
            assets::read_expect_dir::<Lottery<LootSpec<String>>>("common.loot_tables", true);
        for loot_table in loot_tables {
            validate_table_contents(loot_table.clone());
        }
    }
}