skara-brae-server/crates/sb-core/src/combat.rs

use rand::Rng;
use sb_shared::{AttackType, CombatLog, CombatRound, CritEntry, CritResult};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::LazyLock;

const CRIT_TABLES_JSON: &str =
    include_str!("../../../../skara-brae-common/data/crit-tables/combat.json");

static CRIT_TABLES: LazyLock<HashMap<String, HashMap<String, CritEntry>>> = LazyLock::new(|| {
    serde_json::from_str(CRIT_TABLES_JSON).expect("failed to parse crit tables")
});

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CombatStats {
    pub name: String,
    pub hp: i32,
    pub level: i32,
    pub strength: i64,
    pub dexterity: i64,
    pub constitution: i64,
    pub luck: i64,
    pub ob_base: i32,
    pub db_base: i32,
    pub attack_type: AttackType,
}

impl CombatStats {
    pub fn offensive_bonus(&self) -> i32 {
        let str_bonus = super::character::stat_bonus(self.strength) as i32;
        str_bonus + self.ob_base
    }

    pub fn defensive_bonus(&self) -> i32 {
        let dex_bonus = super::character::stat_bonus(self.dexterity) as i32;
        let con_bonus = (super::character::stat_bonus(self.constitution) as i32) / 2;
        dex_bonus + con_bonus + self.db_base
    }
}

pub fn parse_attack_type(s: &str) -> AttackType {
    match s {
        "slash" => AttackType::Slash,
        "crush" => AttackType::Crush,
        "puncture" => AttackType::Puncture,
        _ => AttackType::Crush,
    }
}

pub fn crit_damage_cap(attacker_level: i32, defender_level: i32, defender_hp: i32) -> Option<i32> {
    let diff = defender_level - attacker_level;
    if diff <= 0 {
        return None;
    }
    let cap_pct = match diff {
        1..=9 => return None,
        10..=19 => 0.60,
        20..=49 => 0.40,
        50..=99 => 0.15,
        _ => 0.05,
    };
    Some((defender_hp as f64 * cap_pct) as i32)
}

pub fn open_ended_roll(rng: &mut impl Rng) -> i32 {
    let roll: i32 = rng.random_range(1..=100);
    let mut total = roll;
    if roll >= 96 {
        total += open_ended_roll(rng);
    } else if roll <= 5 {
        total -= open_ended_roll(rng);
    }
    total
}

pub fn resolve_attack(
    rng: &mut impl Rng,
    attacker: &CombatStats,
    defender: &CombatStats,
) -> CombatRound {
    let raw_roll = open_ended_roll(rng);
    let ob = attacker.offensive_bonus();
    let db = defender.defensive_bonus();
    let attack_total = raw_roll + ob;
    let result = attack_total - db;

    let mut damage = 0;
    let mut crit = None;

    if result > 0 {
        damage = result;
        if let Some(severity) = crit_severity(result)
            && let Some(crit_entry) = lookup_crit(&attacker.attack_type, &severity)
        {
            let crit_damage = (damage as f64 * crit_entry.damage_multiplier) as i32;
            let capped = if let Some(cap) = crit_damage_cap(attacker.level, defender.level, defender.hp) {
                crit_damage.min(cap)
            } else {
                crit_damage
            };
            damage = capped;
            crit = Some(CritResult {
                severity: severity.clone(),
                crit: crit_entry,
            });
        }
    }

    CombatRound {
        attacker: attacker.name.clone(),
        defender: defender.name.clone(),
        raw_roll,
        ob,
        db,
        result,
        damage,
        crit,
        defender_hp: 0,
    }
}

pub fn crit_severity(result: i32) -> Option<String> {
    if result >= 151 {
        Some("D".into())
    } else if result >= 101 {
        Some("C".into())
    } else if result >= 51 {
        Some("B".into())
    } else if result >= 21 {
        Some("A".into())
    } else {
        None
    }
}

pub fn lookup_crit(attack_type: &AttackType, severity: &str) -> Option<CritEntry> {
    let type_key = format!("{:?}", attack_type).to_lowercase();
    CRIT_TABLES.get(&type_key)?.get(severity).cloned()
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SpellEffect {
    pub combat_effect: String,
    pub damage_min: i32,
    pub damage_max: i32,
    pub heal_min: i32,
    pub heal_max: i32,
}

pub fn resolve_combat(
    attacker: CombatStats,
    defender: CombatStats,
    xp_reward: i32,
    gold_min: i32,
    gold_max: i32,
    rng: &mut impl Rng,
) -> CombatLog {
    resolve_combat_full(attacker, defender, xp_reward, gold_min, gold_max, None, None, rng)
}

pub fn resolve_combat_with_song(
    attacker: CombatStats,
    defender: CombatStats,
    xp_reward: i32,
    gold_min: i32,
    gold_max: i32,
    song_effect: Option<&str>,
    rng: &mut impl Rng,
) -> CombatLog {
    resolve_combat_full(attacker, defender, xp_reward, gold_min, gold_max, song_effect, None, rng)
}

#[allow(clippy::too_many_arguments)]
pub fn resolve_combat_full(
    attacker: CombatStats,
    defender: CombatStats,
    xp_reward: i32,
    gold_min: i32,
    gold_max: i32,
    song_effect: Option<&str>,
    spell: Option<&SpellEffect>,
    rng: &mut impl Rng,
) -> CombatLog {
    let mut rng = rng;
    let mut a_hp = attacker.hp;
    let mut d_hp = defender.hp;
    let mut rounds = Vec::new();

    loop {
        let mut round = resolve_attack(&mut rng, &apply_song_to_attacker(&attacker, song_effect), &apply_song_to_defender(&defender, song_effect));

        if let Some(sp) = spell
            && sp.combat_effect == "damage"
        {
            let spell_dmg = rng.random_range(sp.damage_min..=sp.damage_max);
            round.damage += spell_dmg;
        }

        d_hp = (d_hp - round.damage).max(0);
        round.defender_hp = d_hp;
        rounds.push(round);

        if d_hp <= 0 {
            let gold = rng.random_range(gold_min..=gold_max);
            return CombatLog {
                rounds,
                winner: attacker.name.clone(),
                loser: defender.name.clone(),
                xp_gained: xp_reward,
                gold_gained: gold,
            };
        }

        let mut round = resolve_attack(&mut rng, &defender, &apply_song_to_defender(&make_temp_stats(&attacker, a_hp), song_effect));
        a_hp = (a_hp - round.damage).max(0);
        round.defender_hp = a_hp;
        rounds.push(round);

        if a_hp <= 0 {
            return CombatLog {
                rounds,
                winner: defender.name.clone(),
                loser: attacker.name.clone(),
                xp_gained: 0,
                gold_gained: 0,
            };
        }

        if song_effect == Some("heal") && a_hp > 0 && a_hp < attacker.hp {
            let heal_amt = (attacker.hp as f64 * 0.03).ceil() as i32;
            a_hp = (a_hp + heal_amt).min(attacker.hp);
        }

        if let Some(sp) = spell
            && sp.combat_effect == "heal" && a_hp > 0 && a_hp < attacker.hp
        {
            let heal_amt = rng.random_range(sp.heal_min..=sp.heal_max);
            a_hp = (a_hp + heal_amt).min(attacker.hp);
        }
    }
}

fn apply_song_to_attacker(stats: &CombatStats, song_effect: Option<&str>) -> CombatStats {
    let mut s = stats.clone();
    match song_effect {
        Some("accuracy") => { s.ob_base += 15; }
        Some("damage") => { s.ob_base += 20; }
        _ => {}
    }
    s
}

fn apply_song_to_defender(stats: &CombatStats, song_effect: Option<&str>) -> CombatStats {
    let mut s = stats.clone();
    match song_effect {
        Some("defense") | Some("magic_resist") => { s.db_base += 10; }
        Some("weaken") => { s.ob_base = (s.ob_base as f64 * 0.7) as i32; }
        _ => {}
    }
    s
}

fn make_temp_stats(original: &CombatStats, hp: i32) -> CombatStats {
    let mut s = original.clone();
    s.hp = hp;
    s
}

#[cfg(test)]
mod tests {
    use super::*;

    fn attacker() -> CombatStats {
        CombatStats {
            name: "Hero".into(), hp: 100, level: 1,
            strength: 50, dexterity: 40, constitution: 40, luck: 20,
            ob_base: 20, db_base: 10,
            attack_type: AttackType::Slash,
        }
    }

    fn defender() -> CombatStats {
        CombatStats {
            name: "Goblin".into(), hp: 50, level: 1,
            strength: 30, dexterity: 30, constitution: 30, luck: 10,
            ob_base: 10, db_base: 5,
            attack_type: AttackType::Crush,
        }
    }

    #[test]
    fn open_ended_roll_stays_in_range() {
        use rand::SeedableRng;
        let mut rng = rand::rngs::StdRng::seed_from_u64(42);
        for _ in 0..1000 {
            let roll = open_ended_roll(&mut rng);
            assert!(roll > -500 && roll < 500, "roll out of expected range: {}", roll);
        }
    }

    #[test]
    fn offensive_bonus_includes_stat_and_base() {
        let a = attacker();
        let ob = a.offensive_bonus();
        assert!(ob > a.ob_base);
    }

    #[test]
    fn defensive_bonus_includes_stat_and_base() {
        let d = defender();
        let db = d.defensive_bonus();
        assert!(db > d.db_base);
    }

    #[test]
    fn crit_damage_cap_equal_level_is_none() {
        assert_eq!(crit_damage_cap(5, 5, 100), None);
        assert_eq!(crit_damage_cap(1, 1, 100), None);
    }

    #[test]
    fn crit_damage_cap_higher_defender_reduces() {
        let cap = crit_damage_cap(1, 15, 100).unwrap();
        assert!(cap < 100);
    }

    #[test]
    fn crit_damage_cap_scaling() {
        let cap_10 = crit_damage_cap(1, 11, 100).unwrap();
        let cap_50 = crit_damage_cap(1, 51, 100).unwrap();
        let cap_100 = crit_damage_cap(1, 101, 100).unwrap();
        assert!(cap_100 < cap_50);
        assert!(cap_50 < cap_10);
    }

    #[test]
    fn resolve_attack_can_hit_or_miss() {
        use rand::SeedableRng;
        let mut rng = rand::rngs::StdRng::seed_from_u64(42);
        let a = attacker();
        let d = defender();
        for _ in 0..100 {
            let round = resolve_attack(&mut rng, &a, &d);
            assert_eq!(round.attacker, "Hero");
            assert_eq!(round.defender, "Goblin");
            assert!(round.defender_hp <= d.hp);
            assert!(round.defender_hp >= 0);
        }
    }

    #[test]
    fn resolve_combat_produces_winner() {
        use rand::SeedableRng;
        let mut rng = rand::rngs::StdRng::seed_from_u64(42);
        let a = attacker();
        let d = defender();
        let log = resolve_combat(a.clone(), d.clone(), 10, 5, 10, &mut rng);
        assert!(!log.rounds.is_empty());
        assert!(log.winner == a.name || log.winner == d.name);
        assert!(log.loser != log.winner);
    }

    #[test]
    fn parse_attack_type_maps_known_types() {
        assert!(matches!(parse_attack_type("slash"), AttackType::Slash));
        assert!(matches!(parse_attack_type("crush"), AttackType::Crush));
        assert!(matches!(parse_attack_type("puncture"), AttackType::Puncture));
        assert!(matches!(parse_attack_type("unarmed"), AttackType::Crush));
        assert!(matches!(parse_attack_type("unknown"), AttackType::Crush));
    }
}