pokeductor 0.3.0

//! Team-level type analysis.
//!
//! `typechart` answers a question about one species: what is *this* weak to?
//! A party of six asks a different one. What actually decides whether a team
//! holds together is not any single member's weaknesses but the overlap
//! between them:
//!
//! - an attacking type that hits **several** members hard is a hole an
//!   opponent will aim at, while one that hits a single member is just that
//!   member's problem;
//! - an attacking type **nobody** resists is a hit the team has to take on the
//!   chin every time;
//! - a defending type nobody hits back hard is a wall the team cannot break.
//!
//! All three fall straight out of the members' typings, so this stays as
//! offline and as instant as the single-species card.

use std::cmp::Reverse;

use crate::models::PokemonDetail;
use crate::typechart::{self, TYPES};

/// Largest party the analyser accepts, matching the games.
pub const MAX_MEMBERS: usize = 6;

/// How many members an attacking type must hit super-effectively before it
/// counts as a *shared* weakness rather than one member's own business.
const SHARED_WEAKNESS_MIN: usize = 2;

/// Abilities that grant an outright immunity to a whole damage type, and the
/// type each one answers.
///
/// Only true immunities are listed. Abilities that merely soften a type (Thick
/// Fat halving Fire and Ice, say) belong to the multipliers the chart already
/// knows nothing about, and abilities keyed to a *class* of move rather than a
/// type (Soundproof, Bulletproof) cannot be expressed as a type at all.
const ABILITY_IMMUNITIES: [(&str, &str); 11] = [
    ("levitate", "ground"),
    ("earth-eater", "ground"),
    ("flash-fire", "fire"),
    ("well-baked-body", "fire"),
    ("water-absorb", "water"),
    ("storm-drain", "water"),
    ("dry-skin", "water"),
    ("volt-absorb", "electric"),
    ("lightning-rod", "electric"),
    ("motor-drive", "electric"),
    ("sap-sipper", "grass"),
];

/// The type `ability` grants immunity to, if any.
fn immunity_from(ability: &str) -> Option<&'static str> {
    ABILITY_IMMUNITIES
        .iter()
        .find(|(slug, _)| *slug == ability)
        .map(|(_, immune_to)| *immune_to)
}

/// One attacking type, weighed against the whole team.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ThreatRow {
    pub attacker: &'static str,
    /// Members taking super-effective damage (×2 or ×4) from it.
    pub weak: usize,
}

/// An immunity a member owes to an ability rather than to its typing.
///
/// These are deliberately kept out of the numbers above. A species has one of
/// its listed abilities, not all of them, so an immunity is only guaranteed
/// when there is nothing else it could have had — anything else would make the
/// chart claim a certainty the data does not support.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct AbilityImmunity {
    /// API name of the member that has it.
    pub member: String,
    /// API slug of the ability granting it.
    pub ability: String,
    pub immune_to: &'static str,
    /// True when the ability is the species' only one, so it cannot not have
    /// it. False when the species could have had a different ability instead.
    pub certain: bool,
}

/// What the team card reports. Every list is in canonical type order, and
/// empty lists are the good news: nothing to worry about in that category.
#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct TeamAnalysis {
    /// Attacking types hitting at least [`SHARED_WEAKNESS_MIN`] members
    /// super-effectively, most members first.
    pub shared_weaknesses: Vec<ThreatRow>,
    /// Attacking types no member resists or is immune to.
    pub unresisted: Vec<&'static str>,
    /// Defending types no member hits super-effectively with a same-type move.
    pub offense_gaps: Vec<&'static str>,
    /// Immunities the members' abilities grant, which the type chart cannot
    /// see. Reported alongside the lists above rather than folded into them.
    pub ability_immunities: Vec<AbilityImmunity>,
}

/// Analyses a party. An empty team yields an empty analysis rather than
/// "weak to everything": with nothing to defend, there is nothing to report.
pub fn analyse(team: &[&PokemonDetail]) -> TeamAnalysis {
    if team.is_empty() {
        return TeamAnalysis::default();
    }

    let mut shared_weaknesses = Vec::new();
    let mut unresisted = Vec::new();

    for attacker in TYPES {
        let multipliers = team.iter().map(|m| typechart::combined(attacker, &m.types));

        let mut weak = 0;
        let mut resisted_by_anyone = false;
        for multiplier in multipliers {
            // The same thresholds `typechart` uses: every value the chart can
            // produce is an exact binary fraction, so these never sit near a
            // boundary.
            if multiplier > 1.5 {
                weak += 1;
            } else if multiplier < 0.9 {
                resisted_by_anyone = true;
            }
        }

        if weak >= SHARED_WEAKNESS_MIN {
            shared_weaknesses.push(ThreatRow { attacker, weak });
        }
        if !resisted_by_anyone {
            unresisted.push(attacker);
        }
    }

    // Stable, so types sharing a count keep canonical order.
    shared_weaknesses.sort_by_key(|row| Reverse(row.weak));

    let offense_gaps = TYPES
        .into_iter()
        .filter(|defender| {
            !team.iter().any(|member| {
                member
                    .types
                    .iter()
                    .any(|attacker| typechart::effectiveness(attacker, defender) > 1.5)
            })
        })
        .collect();

    let ability_immunities = team
        .iter()
        .flat_map(|member| {
            // Certain only when the species has nowhere else to land: with one
            // possible ability it must have this one.
            let certain = member.abilities.len() == 1;
            member.abilities.iter().filter_map(move |ability| {
                Some(AbilityImmunity {
                    member: member.name.clone(),
                    ability: ability.name.clone(),
                    immune_to: immunity_from(&ability.name)?,
                    certain,
                })
            })
        })
        .collect();

    TeamAnalysis {
        shared_weaknesses,
        unresisted,
        offense_gaps,
        ability_immunities,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::models::Ability;
    use std::collections::HashMap;

    fn member(name: &str, types: &[&str]) -> PokemonDetail {
        with_abilities(name, types, &[])
    }

    fn with_abilities(name: &str, types: &[&str], abilities: &[&str]) -> PokemonDetail {
        PokemonDetail {
            name: name.to_string(),
            species: name.to_string(),
            dex_number: 0,
            is_legendary: false,
            is_mythical: false,
            is_baby: false,
            types: types.iter().map(|t| t.to_string()).collect(),
            abilities: abilities
                .iter()
                .map(|a| Ability {
                    name: a.to_string(),
                    is_hidden: false,
                })
                .collect(),
            stats: Vec::new(),
            height: 0,
            weight: 0,
            sprite_url: None,
            shiny_sprite_url: None,
            genera: HashMap::new(),
            flavors: HashMap::new(),
        }
    }

    fn weakness_count(analysis: &TeamAnalysis, attacker: &str) -> usize {
        analysis
            .shared_weaknesses
            .iter()
            .find(|row| row.attacker == attacker)
            .map_or(0, |row| row.weak)
    }

    #[test]
    fn an_empty_team_reports_nothing() {
        assert_eq!(analyse(&[]), TeamAnalysis::default());
    }

    #[test]
    fn one_members_weakness_is_not_shared() {
        let charizard = member("charizard", &["fire", "flying"]);
        let analysis = analyse(&[&charizard]);
        // Rock is ×4 on Charizard, but a party of one has nothing to share it
        // with, so it is that member's problem and not the team's.
        assert!(analysis.shared_weaknesses.is_empty());
    }

    #[test]
    fn a_weakness_two_members_share_is_reported() {
        // Both are hit ×2 by Electric and neither resists it.
        let gyarados = member("gyarados", &["water", "flying"]);
        let pelipper = member("pelipper", &["water", "flying"]);
        let analysis = analyse(&[&gyarados, &pelipper]);

        assert_eq!(weakness_count(&analysis, "electric"), 2);
        assert!(analysis.unresisted.contains(&"electric"));
    }

    #[test]
    fn the_worst_shared_weakness_comes_first() {
        // Three Water/Flying bodies: Electric hits all three, Rock only ×2 on
        // each of them as well — but Electric is ×4, and more to the point
        // every member is weak to both, so ordering falls back to the count.
        let team: Vec<PokemonDetail> = ["gyarados", "pelipper", "mantine"]
            .iter()
            .map(|n| member(n, &["water", "flying"]))
            .collect();
        let refs: Vec<&PokemonDetail> = team.iter().collect();
        let analysis = analyse(&refs);

        let counts: Vec<usize> = analysis.shared_weaknesses.iter().map(|r| r.weak).collect();
        let mut sorted = counts.clone();
        sorted.sort_by(|a, b| b.cmp(a));
        assert_eq!(counts, sorted, "rows must be ordered worst-first");
        assert_eq!(weakness_count(&analysis, "electric"), 3);
    }

    #[test]
    fn a_type_someone_resists_is_not_unresisted() {
        let magnezone = member("magnezone", &["electric", "steel"]);
        let gyarados = member("gyarados", &["water", "flying"]);
        let analysis = analyse(&[&magnezone, &gyarados]);

        // Magnezone resists Electric (Steel ×½ · Electric ×½), so the team has
        // an answer to it even though Gyarados is weak.
        assert!(!analysis.unresisted.contains(&"electric"));
        // And with only one member weak to it, it is not a *shared* weakness.
        assert_eq!(weakness_count(&analysis, "electric"), 0);
    }

    #[test]
    fn offense_gaps_are_what_nobody_hits_hard() {
        let charizard = member("charizard", &["fire", "flying"]);
        let analysis = analyse(&[&charizard]);

        // Fire hits Grass/Ice/Bug/Steel; Flying hits Grass/Fighting/Bug.
        for covered in ["grass", "ice", "bug", "steel", "fighting"] {
            assert!(
                !analysis.offense_gaps.contains(&covered),
                "{covered} is covered"
            );
        }
        // Nothing it carries is strong against Water or Dragon.
        assert!(analysis.offense_gaps.contains(&"water"));
        assert!(analysis.offense_gaps.contains(&"dragon"));
    }

    #[test]
    fn a_sole_ability_grants_a_certain_immunity() {
        // Rotom has nothing but Levitate, so the Ground immunity is a fact.
        let rotom = with_abilities("rotom", &["electric", "ghost"], &["levitate"]);
        let analysis = analyse(&[&rotom]);

        assert_eq!(
            analysis.ability_immunities,
            vec![AbilityImmunity {
                member: "rotom".to_string(),
                ability: "levitate".to_string(),
                immune_to: "ground",
                certain: true,
            }]
        );
    }

    #[test]
    fn one_of_several_abilities_is_only_a_possibility() {
        // Vaporeon can have Water Absorb — or Hydration instead.
        let vaporeon = with_abilities("vaporeon", &["water"], &["water-absorb", "hydration"]);
        let analysis = analyse(&[&vaporeon]);

        assert_eq!(analysis.ability_immunities.len(), 1);
        assert_eq!(analysis.ability_immunities[0].immune_to, "water");
        assert!(!analysis.ability_immunities[0].certain);
    }

    #[test]
    fn abilities_that_grant_no_immunity_are_ignored() {
        let bulbasaur = with_abilities("bulbasaur", &["grass"], &["overgrow", "chlorophyll"]);
        let analysis = analyse(&[&bulbasaur]);
        assert!(analysis.ability_immunities.is_empty());
    }

    #[test]
    fn an_ability_immunity_does_not_touch_the_type_numbers() {
        // Levitate answers Ground, but the chart-level lists stay chart-level:
        // Gengar's typing alone still has no Ground resistance to report.
        let levitator = with_abilities("gengar", &["ghost", "poison"], &["levitate"]);
        let analysis = analyse(&[&levitator]);

        assert!(analysis.unresisted.contains(&"ground"));
        assert_eq!(analysis.ability_immunities[0].immune_to, "ground");
    }

    #[test]
    fn a_broad_team_closes_most_gaps() {
        let team = [
            member("charizard", &["fire", "flying"]),
            member("gyarados", &["water", "flying"]),
            member("magnezone", &["electric", "steel"]),
            member("gengar", &["ghost", "poison"]),
            member("garchomp", &["dragon", "ground"]),
            member("machamp", &["fighting"]),
        ];
        let refs: Vec<&PokemonDetail> = team.iter().collect();
        let analysis = analyse(&refs);

        assert_eq!(refs.len(), MAX_MEMBERS);
        // Six well-spread typings should leave few types untouched offensively.
        assert!(
            analysis.offense_gaps.len() <= 3,
            "unexpected gaps: {:?}",
            analysis.offense_gaps
        );
    }
}