//! Squad evaluation, behind a game-rules boundary.
//!
//! # Why this is a trait and not a function in `squad.rs`
//!
//! Chemistry, rating and star rating are **game-specific**. FUT chemistry
//! changed substantially between FIFA generations, so a single formula
//! compiled into generic Core would quietly make Core a FIFA-something server.
//! Core is allowed to understand that a squad *has* an evaluation; it is not
//! allowed to know how any particular game computes one.
//!
//! ```text
//!   Core                  owns the squad, slots, items, persistence
//!     |                   and the SEMANTIC concept of an evaluation
//!     v
//!   SquadRules            how a specific game computes it
//!     |
//!     +-- DefaultSquadRules   OpenFUT's own rules (the implementation that
//!     |                       already existed in Core)
//!     +-- Fifa17SquadRules    NOT YET WRITTEN. The FIFA 17 algorithm is not
//!                             proven, and inventing one would be worse than
//!                             having none.
//! ```
//!
//! # Pure data in, evaluation out
//!
//! Rules take a [`SquadSnapshot`] — already resolved by Core from the database
//! — rather than a pool and a card database. That keeps every rules
//! implementation synchronous, dependency-free and testable without fixtures,
//! and it stops a game's rules from reaching into Core's storage.
//!
//! # Client-reported values are not evaluations
//!
//! FIFA 17 sends its own `chemistry`, `rating` and `starRating` on every squad
//! save. Those are observations about what the client believes, captured for
//! shadow validation, and they are deliberately a *different type* from
//! [`SquadEvaluation`] so no later code can pass one where the other belongs.

use serde::{Deserialize, Serialize};

/// One player in a squad, reduced to the attributes rules are allowed to see.
///
/// Deliberately not `OwnedCard` + `CardDefinition`: rules should not be able to
/// reach storage identifiers, loan state or acquisition history.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SquadPlayerCard {
    /// Core's owned-card id. Present so an evaluation can attribute per-player
    /// results; rules must not interpret its contents.
    pub owned_card_id: String,
    pub card_id: String,
    pub name: String,
    pub overall: u8,
    pub position: String,
    pub nation: String,
    pub league: String,
    pub club: String,
    /// Slot this player occupies, in Core's numbering.
    pub slot: i64,
    pub on_bench: bool,
}

/// Everything a rules implementation may consider.
#[derive(Debug, Clone, Default)]
pub struct SquadSnapshot {
    pub formation: String,
    pub players: Vec<SquadPlayerCard>,
}

impl SquadSnapshot {
    pub fn starters(&self) -> impl Iterator<Item = &SquadPlayerCard> {
        self.players.iter().filter(|p| !p.on_bench)
    }
}

/// The semantic result Core understands.
///
/// `chemistry` has no fixed scale here on purpose — `chemistry_max` travels
/// with it, because a later game may not use 100.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct SquadEvaluation {
    pub chemistry: i64,
    pub chemistry_max: i64,
    pub rating: i64,
    pub star_rating: i64,
    /// Per-player detail, for UIs and for diagnosing a rules mismatch.
    pub players: Vec<PlayerEvaluation>,
    /// Which rules produced this, so a stored or logged evaluation is never
    /// ambiguous about its own provenance.
    pub rules: String,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct PlayerEvaluation {
    pub owned_card_id: String,
    pub chemistry: i64,
    pub detail: Vec<(String, i64)>,
}

/// What a game client claimed about a squad it sent.
///
/// **Never canonical.** A separate type from [`SquadEvaluation`] specifically so
/// that assigning one to the other does not compile. A modified client can put
/// anything here; OpenFUT has no independent knowledge of what it means until
/// its own rules run.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Default)]
pub struct ClientReportedEvaluation {
    pub client_reported_chemistry: Option<i64>,
    pub client_reported_rating: Option<i64>,
    pub client_reported_star_rating: Option<i64>,
}

/// Result of comparing what the client claimed against what the server derived.
///
/// A mismatch is **not** silently reconciled in either direction: the server's
/// value stands as canonical and the disagreement is reported so the rules
/// model can be investigated against the exact squad that produced it.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct EvaluationComparison {
    pub field: String,
    pub client: i64,
    pub server: i64,
}

impl ClientReportedEvaluation {
    /// Fields where the client and the server disagree. Empty means agreement
    /// on every field the client actually sent.
    pub fn compare(&self, server: &SquadEvaluation) -> Vec<EvaluationComparison> {
        let mut out = Vec::new();
        let mut check = |field: &str, client: Option<i64>, srv: i64| {
            if let Some(c) = client {
                if c != srv {
                    out.push(EvaluationComparison {
                        field: field.to_string(),
                        client: c,
                        server: srv,
                    });
                }
            }
        };
        check(
            "chemistry",
            self.client_reported_chemistry,
            server.chemistry,
        );
        check("rating", self.client_reported_rating, server.rating);
        check(
            "star_rating",
            self.client_reported_star_rating,
            server.star_rating,
        );
        out
    }
}

/// How a specific game evaluates a squad.
pub trait SquadRules: Send + Sync {
    /// Stable identifier recorded in [`SquadEvaluation::rules`].
    fn name(&self) -> &'static str;
    fn evaluate(&self, snapshot: &SquadSnapshot) -> SquadEvaluation;
}

/// OpenFUT's own rules — the implementation that already lived in Core.
///
/// Moved here unchanged in behaviour rather than rewritten: it is the default
/// for clients that have no game-specific rules, and changing its numbers while
/// relocating it would have made the move unreviewable.
///
/// Link scoring: club +3 each (max 6), league +1 each (max 4), nation +1 each
/// (max 3), per player capped at 10, team total capped at 100.
pub struct DefaultSquadRules;

impl SquadRules for DefaultSquadRules {
    fn name(&self) -> &'static str {
        "openfut-default-v2"
    }

    fn evaluate(&self, snapshot: &SquadSnapshot) -> SquadEvaluation {
        let starters: Vec<&SquadPlayerCard> = snapshot.starters().collect();

        let mut players = Vec::with_capacity(starters.len());
        let mut total: i64 = 0;

        for (i, p) in starters.iter().enumerate() {
            let count = |f: fn(&SquadPlayerCard) -> &String, v: &String| {
                starters
                    .iter()
                    .enumerate()
                    .filter(|(j, o)| *j != i && f(o) == v)
                    .count() as i64
            };
            let club_links = count(|c| &c.club, &p.club);
            let league_links = count(|c| &c.league, &p.league);
            let nation_links = count(|c| &c.nation, &p.nation);

            let club_pts = (club_links * 3).min(6);
            let league_pts = league_links.min(4);
            let nation_pts = nation_links.min(3);
            let chem = (club_pts + league_pts + nation_pts).min(10);
            total += chem;

            players.push(PlayerEvaluation {
                owned_card_id: p.owned_card_id.clone(),
                chemistry: chem,
                detail: vec![
                    ("club_links".into(), club_links),
                    ("league_links".into(), league_links),
                    ("nation_links".into(), nation_links),
                    ("club_pts".into(), club_pts),
                    ("league_pts".into(), league_pts),
                    ("nation_pts".into(), nation_pts),
                ],
            });
        }

        // Mean overall of the starters, rounded down. Empty squad rates 0
        // rather than dividing by zero.
        let rating = if starters.is_empty() {
            0
        } else {
            starters.iter().map(|p| p.overall as i64).sum::<i64>() / starters.len() as i64
        };

        SquadEvaluation {
            chemistry: total.min(100),
            chemistry_max: 100,
            rating,
            // 0-5 from the rating band. Coarse on purpose: this is OpenFUT's
            // own presentation value, not a reconstruction of any game's.
            star_rating: match rating {
                0 => 0,
                1..=64 => 1,
                65..=74 => 2,
                75..=81 => 3,
                82..=87 => 4,
                _ => 5,
            },
            players,
            rules: self.name().to_string(),
        }
    }
}

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

    fn p(slot: i64, club: &str, league: &str, nation: &str, overall: u8) -> SquadPlayerCard {
        SquadPlayerCard {
            owned_card_id: format!("owned-{slot}"),
            card_id: format!("card-{slot}"),
            name: format!("P{slot}"),
            overall,
            position: "ST".into(),
            nation: nation.into(),
            league: league.into(),
            club: club.into(),
            slot,
            on_bench: false,
        }
    }

    #[test]
    fn an_empty_squad_evaluates_without_dividing_by_zero() {
        let e = DefaultSquadRules.evaluate(&SquadSnapshot::default());
        assert_eq!(e.chemistry, 0);
        assert_eq!(e.rating, 0);
        assert_eq!(e.star_rating, 0);
        assert!(e.players.is_empty());
    }

    #[test]
    fn bench_players_do_not_contribute() {
        let mut snap = SquadSnapshot {
            formation: "4-4-2".into(),
            players: vec![p(0, "A", "L", "N", 80), p(1, "A", "L", "N", 80)],
        };
        let with_both = DefaultSquadRules.evaluate(&snap);
        snap.players[1].on_bench = true;
        let with_bench = DefaultSquadRules.evaluate(&snap);
        assert!(
            with_bench.chemistry < with_both.chemistry,
            "a benched team-mate must not create links: {with_bench:?}"
        );
        assert_eq!(with_bench.players.len(), 1);
    }

    #[test]
    fn links_are_capped_per_category_and_per_player() {
        // Eleven identical players: club links alone would be 30 pts uncapped.
        let players: Vec<_> = (0..11).map(|i| p(i, "A", "L", "N", 90)).collect();
        let e = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "4-4-2".into(),
            players,
        });
        for pe in &e.players {
            assert_eq!(pe.chemistry, 10, "per-player cap is 10: {pe:?}");
        }
        assert_eq!(e.chemistry, 100);
        assert_eq!(e.chemistry_max, 100);
    }

    #[test]
    fn team_chemistry_is_capped_at_the_maximum() {
        // 15 starters would total 150 uncapped.
        let players: Vec<_> = (0..15).map(|i| p(i, "A", "L", "N", 90)).collect();
        let e = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "x".into(),
            players,
        });
        assert_eq!(e.chemistry, 100);
    }

    #[test]
    fn unrelated_players_earn_no_chemistry() {
        let players = vec![
            p(0, "A", "L1", "N1", 80),
            p(1, "B", "L2", "N2", 80),
            p(2, "C", "L3", "N3", 80),
        ];
        let e = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "x".into(),
            players,
        });
        assert_eq!(e.chemistry, 0);
        assert_eq!(e.rating, 80);
    }

    #[test]
    fn the_evaluation_names_the_rules_that_produced_it() {
        let e = DefaultSquadRules.evaluate(&SquadSnapshot::default());
        assert_eq!(e.rules, "openfut-default-v2");
        assert_eq!(DefaultSquadRules.name(), "openfut-default-v2");
    }

    /// The comparison must report disagreement rather than reconcile it.
    #[test]
    fn a_client_that_disagrees_is_reported_not_reconciled() {
        let server = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "x".into(),
            players: vec![p(0, "A", "L", "N", 80)],
        });
        let claimed = ClientReportedEvaluation {
            client_reported_chemistry: Some(52),
            client_reported_rating: Some(server.rating),
            client_reported_star_rating: None,
        };
        let diff = claimed.compare(&server);
        assert_eq!(diff.len(), 1, "{diff:?}");
        assert_eq!(diff[0].field, "chemistry");
        assert_eq!(diff[0].client, 52);
        assert_eq!(diff[0].server, server.chemistry);
        // And the server's own value is untouched by the comparison.
        assert_eq!(server.chemistry, 0);
    }

    /// A field the client did not send cannot disagree.
    #[test]
    fn absent_client_fields_are_not_treated_as_zero() {
        let server = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "x".into(),
            players: vec![p(0, "A", "L", "N", 80)],
        });
        assert!(ClientReportedEvaluation::default()
            .compare(&server)
            .is_empty());
    }

    #[test]
    fn agreement_reports_nothing() {
        let server = DefaultSquadRules.evaluate(&SquadSnapshot {
            formation: "x".into(),
            players: vec![p(0, "A", "L", "N", 80)],
        });
        let claimed = ClientReportedEvaluation {
            client_reported_chemistry: Some(server.chemistry),
            client_reported_rating: Some(server.rating),
            client_reported_star_rating: Some(server.star_rating),
        };
        assert!(claimed.compare(&server).is_empty());
    }
}