//! Level 6 — anchors. Two rooms share the same trap — define it once.
//!
//! Paired design note: `l06.md`.
//!
//! Note: serde_yaml resolves aliases at parse time, so the target is
//! emitted **expanded** (the trap dict appears in each room). Players
//! who use anchors/aliases will produce the same parsed `Value` and
//! pass via the semantic short-circuit. Players who paste the dict
//! verbatim also pass.

use rand::seq::SliceRandom;
use rand::{Rng, SeedableRng};
use rand_chacha::ChaCha8Rng;
use serde::Serialize;
use serde_yaml::{Mapping, Value};

use crate::describe::Describer;

use super::{Generated, Level};

pub struct Anchors;

const ROOM_NAMES: &[&str] = &["north", "south", "east", "west"];
const TRAP_TYPES: &[&str] = &["pit", "snare", "dart", "rune"];

#[derive(Serialize)]
struct DescCtx {
    trap_type: String,
    trap_depth: i64,
    trap_spikes: bool,
    rooms: Vec<String>,
}

impl Level for Anchors {
    fn id(&self) -> u8 {
        6
    }

    fn name(&self) -> &'static str {
        "Anchors"
    }

    fn generate(&self, seed: u64) -> Generated {
        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_0006);
        let trap_type = *TRAP_TYPES.choose(&mut rng).expect("non-empty");
        let trap_depth = rng.gen_range(10..=30i64);
        let trap_spikes = rng.gen_bool(0.5);
        let n_rooms = rng.gen_range(2..=3);
        let rooms: Vec<&'static str> = ROOM_NAMES
            .choose_multiple(&mut rng, n_rooms)
            .copied()
            .collect();

        let mut trap = Mapping::new();
        trap.insert(
            Value::String("type".to_string()),
            Value::String(trap_type.to_string()),
        );
        trap.insert(Value::String("depth".to_string()), Value::from(trap_depth));
        trap.insert(
            Value::String("spikes".to_string()),
            Value::Bool(trap_spikes),
        );

        let mut rooms_map = Mapping::new();
        for r in &rooms {
            rooms_map.insert(
                Value::String((*r).to_string()),
                Value::Mapping(trap.clone()),
            );
        }

        let mut top = Mapping::new();
        top.insert(Value::String("trap".to_string()), Value::Mapping(trap));
        top.insert(
            Value::String("rooms".to_string()),
            Value::Mapping(rooms_map),
        );

        let target_yaml =
            serde_yaml::to_string(&Value::Mapping(top)).expect("serialise mapping");

        let mut d = Describer::new();
        d.register(
            "l06",
            "A single trap recurs through these halls:\n\
             - type: {{ trap_type }}\n\
             - depth: {{ trap_depth }}\n\
             - spikes: {{ trap_spikes }}\n\
             \n\
             Reuse it for these rooms: {% for r in rooms %}{{ r }}{% if not loop.last %}, {% endif %}{% endfor %}.\n\
             💡 Define `trap: &name` once and reference it as `*name` in every room.",
        )
        .expect("register template");
        let description = d
            .render(
                "l06",
                &DescCtx {
                    trap_type: trap_type.to_string(),
                    trap_depth,
                    trap_spikes,
                    rooms: rooms.iter().map(|s| s.to_string()).collect(),
                },
            )
            .expect("render template");

        Generated {
            target_yaml,
            description,
            flavor: "🪤 A trap recurs through these halls.".to_string(),
        }
    }
}