//! Level 11 — advanced anchors. Anchor shapes inside a list, alias
//! them elsewhere.
//!
//! Paired design note: `l11.md`.
//!
//! Like L6, serde_yaml expands aliases on parse, so the emitted target
//! is the fully-inlined form. Players who use `&anchor` / `*alias`
//! produce the same `Value` and pass via the semantic short-circuit.

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

use crate::describe::Describer;

use super::{Generated, Level};

pub struct AdvAnchors;

const SHAPES: &[(&str, i64)] = &[
    ("triangle", 3),
    ("square", 4),
    ("pentagon", 5),
    ("hexagon", 6),
    ("heptagon", 7),
    ("octagon", 8),
];

#[derive(Serialize)]
struct DescCtx {
    shapes: Vec<ShapeDesc>,
    copies: Vec<String>,
}

#[derive(Serialize)]
struct ShapeDesc {
    name: String,
    sides: i64,
    interior_angle_sum: i64,
}

fn shape_value(name: &str, sides: i64) -> Value {
    let mut m = Mapping::new();
    m.insert(
        Value::String("name".to_string()),
        Value::String(name.to_string()),
    );
    m.insert(Value::String("sides".to_string()), Value::from(sides));
    m.insert(
        Value::String("interior".to_string()),
        Value::from((sides - 2) * 180),
    );
    Value::Mapping(m)
}

impl Level for AdvAnchors {
    fn id(&self) -> u8 {
        11
    }

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

    fn generate(&self, seed: u64) -> Generated {
        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_000B);

        let n = rng.gen_range(2..=3);
        let picked: Vec<(&'static str, i64)> = SHAPES
            .choose_multiple(&mut rng, n)
            .copied()
            .collect();

        // The defining `shapes:` list.
        let shapes_seq: Sequence = picked
            .iter()
            .map(|(name, sides)| shape_value(name, *sides))
            .collect();

        // `copies:` — random selections with possible repetition.
        let m = rng.gen_range(3..=4);
        let mut copies_seq = Sequence::new();
        let mut copy_names = Vec::new();
        for _ in 0..m {
            let (name, sides) = picked.choose(&mut rng).unwrap();
            copies_seq.push(shape_value(name, *sides));
            copy_names.push((*name).to_string());
        }

        let mut top = Mapping::new();
        top.insert(
            Value::String("shapes".to_string()),
            Value::Sequence(shapes_seq),
        );
        top.insert(
            Value::String("copies".to_string()),
            Value::Sequence(copies_seq),
        );

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

        let shape_descs: Vec<ShapeDesc> = picked
            .iter()
            .map(|(name, sides)| ShapeDesc {
                name: (*name).to_string(),
                sides: *sides,
                interior_angle_sum: (sides - 2) * 180,
            })
            .collect();

        let mut d = Describer::new();
        d.register(
            "l11",
            "Shapes are defined once and reused.\n\
             Definitions:\n\
             {% for s in shapes %}- {{ s.name }}: sides={{ s.sides }}, interior={{ s.interior_angle_sum }}\n\
             {% endfor %}\n\
             Copies, in order: {% for c in copies %}{{ c }}{% if not loop.last %}, {% endif %}{% endfor %}\n\
             💡 Anchor each shape in the list with `- &name`, then alias by `*name` in copies.",
        )
        .expect("register template");
        let description = d
            .render(
                "l11",
                &DescCtx {
                    shapes: shape_descs,
                    copies: copy_names,
                },
            )
            .expect("render template");

        Generated {
            target_yaml,
            description,
            flavor: "🔺 The geometry chamber repeats its forms.".to_string(),
        }
    }
}