//! Drift detection between the AST and `specs/form_a.md`.
//!
//! The spec is hand-curated, but it cannot silently fall behind the
//! language. Every AST enum (`Term`, `Pattern`, `Type`, `Def`, `Literal`,
//! `ParamMode`) discriminates on a `#[serde(rename = "...")]` tag.
//! These tests construct a sample of every variant, then check that the
//! corresponding tag string (or its parenthesised Form-A keyword) appears
//! in the spec.
//!
//! The exhaustive `match` is the load-bearing piece: adding a new variant
//! without a spec entry fails compilation here long before the test runs.
//! Once the variant is matched, the test asserts the spec mentions it.

use std::collections::BTreeMap;

use ailang_core::ast::{
    ConstDef, Ctor, Def, FnDef, Literal, NewArg, Pattern, Suppress, Term, Type, TypeDef,
};
use ailang_core::FORM_A_SPEC;

/// Every `Term` variant must be reachable from the spec. The Form-A
/// keyword for each variant is what the spec is supposed to teach an
/// LLM; if it is missing here, the LLM cannot produce that term.
#[test]
fn spec_mentions_every_term_variant() {
    let exemplars: Vec<(&str, Term)> = vec![
        ("(lit-unit", Term::Lit { lit: Literal::Unit }),
        // The Var form has no parenthesised keyword (a bare ident is a
        // var-ref). The spec calls it out under "Atom forms"; we look for
        // that anchor.
        ("Atom forms", Term::Var { name: "x".into() }),
        (
            "(app",
            Term::App {
                callee: Box::new(Term::Var { name: "f".into() }),
                args: vec![Term::Var { name: "x".into() }],
                tail: false,
            },
        ),
        (
            "(let ",
            Term::Let {
                name: "x".into(),
                value: Box::new(Term::Lit { lit: Literal::Int { value: 1 } }),
                body: Box::new(Term::Var { name: "x".into() }),
            },
        ),
        (
            "(let-rec",
            Term::LetRec {
                name: "f".into(),
                ty: Type::fn_owned(vec![], Type::int(), vec![]),
                params: vec![],
                body: Box::new(Term::Lit { lit: Literal::Int { value: 0 } }),
                in_term: Box::new(Term::Var { name: "f".into() }),
            },
        ),
        (
            "(if",
            Term::If {
                cond: Box::new(Term::Lit { lit: Literal::Bool { value: true } }),
                then: Box::new(Term::Lit { lit: Literal::Int { value: 1 } }),
                else_: Box::new(Term::Lit { lit: Literal::Int { value: 0 } }),
            },
        ),
        (
            "(do ",
            Term::Do {
                op: "io/print_str".into(),
                args: vec![],
                tail: false,
            },
        ),
        (
            "(term-ctor",
            Term::Ctor {
                type_name: "List".into(),
                ctor: "Nil".into(),
                args: vec![],
            },
        ),
        (
            "(match",
            Term::Match {
                scrutinee: Box::new(Term::Var { name: "x".into() }),
                arms: vec![],
            },
        ),
        (
            "(lam",
            Term::Lam {
                params: vec![],
                param_tys: vec![],
                ret_ty: Box::new(Type::int()),
                effects: vec![],
                body: Box::new(Term::Lit { lit: Literal::Int { value: 0 } }),
            },
        ),
        (
            "(seq",
            Term::Seq {
                lhs: Box::new(Term::Var { name: "a".into() }),
                rhs: Box::new(Term::Var { name: "b".into() }),
            },
        ),
        (
            "(clone",
            Term::Clone {
                value: Box::new(Term::Var { name: "x".into() }),
            },
        ),
        (
            "(reuse-as",
            Term::ReuseAs {
                source: Box::new(Term::Var { name: "x".into() }),
                body: Box::new(Term::Var { name: "y".into() }),
            },
        ),
        (
            "(loop",
            Term::Loop {
                binders: Vec::new(),
                body: Box::new(Term::Lit { lit: Literal::Unit }),
            },
        ),
        (
            "(recur",
            Term::Recur { args: vec![] },
        ),
        (
            "(new",
            Term::New {
                type_name: "T".into(),
                args: vec![NewArg::Value(Term::Lit {
                    lit: Literal::Int { value: 0 },
                })],
            },
        ),
        ("(intrinsic", Term::Intrinsic),
    ];

    for (anchor, term) in exemplars {
        // Force the exhaustive match: the body is just a tag string that
        // we will not actually use, but the compiler will refuse to
        // compile this file once a new Term variant is added without a
        // matching arm.
        let _: &'static str = match term {
            Term::Lit { .. } => "lit",
            Term::Var { .. } => "var",
            Term::App { .. } => "app",
            Term::Let { .. } => "let",
            Term::LetRec { .. } => "letrec",
            Term::If { .. } => "if",
            Term::Do { .. } => "do",
            Term::Ctor { .. } => "ctor",
            Term::Match { .. } => "match",
            Term::Lam { .. } => "lam",
            Term::Seq { .. } => "seq",
            Term::Clone { .. } => "clone",
            Term::ReuseAs { .. } => "reuse-as",
            Term::Loop { .. } => "loop",
            Term::Recur { .. } => "recur",
            Term::New { .. } => "new",
            Term::Intrinsic => "intrinsic",
        };
        assert!(
            FORM_A_SPEC.contains(anchor),
            "spec is missing anchor `{anchor}` for a Term variant — \
             update crates/ailang-core/specs/form_a.md"
        );
    }
}

/// Every `Pattern` variant must appear in the spec.
#[test]
fn spec_mentions_every_pattern_variant() {
    let exemplars: Vec<(&str, Pattern)> = vec![
        ("_", Pattern::Wild),
        // pat-var is again the bare-ident form. The spec discusses it
        // under "Patterns". Use the heading as the anchor.
        ("## Patterns", Pattern::Var { name: "x".into() }),
        ("(pat-lit", Pattern::Lit { lit: Literal::Int { value: 0 } }),
        (
            "(pat-ctor",
            Pattern::Ctor { ctor: "Nil".into(), fields: vec![] },
        ),
    ];

    for (anchor, pat) in exemplars {
        let _: &'static str = match pat {
            Pattern::Wild => "wild",
            Pattern::Var { .. } => "var",
            Pattern::Lit { .. } => "lit",
            Pattern::Ctor { .. } => "ctor",
        };
        assert!(
            FORM_A_SPEC.contains(anchor),
            "spec is missing anchor `{anchor}` for a Pattern variant"
        );
    }
}

/// Every `Type` variant must appear in the spec.
#[test]
fn spec_mentions_every_type_variant() {
    let exemplars: Vec<(&str, Type)> = vec![
        ("(con ", Type::int()),
        (
            "(fn-type",
            Type::fn_owned(vec![], Type::unit(), vec![]),
        ),
        (
            "TYVAR-NAME",
            Type::Var { name: "a".into() },
        ),
        (
            "(forall",
            Type::Forall {
                vars: vec!["a".into()],
                constraints: vec![],
                body: Box::new(Type::Var { name: "a".into() }),
            },
        ),
    ];

    for (anchor, ty) in exemplars {
        let _: &'static str = match ty {
            Type::Con { .. } => "con",
            Type::Fn { .. } => "fn",
            Type::Var { .. } => "var",
            Type::Forall { .. } => "forall",
        };
        assert!(
            FORM_A_SPEC.contains(anchor),
            "spec is missing anchor `{anchor}` for a Type variant"
        );
    }
}

/// Every `Literal` variant must appear in the spec.
#[test]
fn spec_mentions_every_literal_variant() {
    // Anchors describe how the literal renders in Form-A.
    let exemplars: Vec<(&str, Literal)> = vec![
        ("`INT`", Literal::Int { value: 0 }),
        ("`true`, `false`", Literal::Bool { value: true }),
        ("`STRING`", Literal::Str { value: "x".into() }),
        ("(lit-unit)", Literal::Unit),
        ("`FLOAT`", Literal::Float { bits: 0 }),
    ];

    for (anchor, lit) in exemplars {
        let _: &'static str = match lit {
            Literal::Int { .. } => "int",
            Literal::Bool { .. } => "bool",
            Literal::Str { .. } => "str",
            Literal::Unit => "unit",
            Literal::Float { .. } => "float",
        };
        assert!(
            FORM_A_SPEC.contains(anchor),
            "spec is missing anchor `{anchor}` for a Literal variant"
        );
    }
}

/// Every `Def` kind must appear in the spec.
#[test]
fn spec_mentions_every_def_kind() {
    let fn_def = FnDef {
        name: "f".into(),
        doc: None,
        suppress: vec![],
        ty: Type::fn_owned(vec![], Type::int(), vec![]),
        params: vec![],
        body: Term::Lit { lit: Literal::Int { value: 0 } },
    export: None,
    };
    let const_def = ConstDef {
        name: "k".into(),
        doc: None,
        ty: Type::int(),
        value: Term::Lit { lit: Literal::Int { value: 0 } },
    };
    let type_def = TypeDef {
        name: "T".into(),
        doc: None,
        vars: vec![],
        ctors: vec![Ctor {
            name: "C".into(),
            fields: vec![],
        }],
        drop_iterative: false,
        param_in: BTreeMap::new(),
    };
    let exemplars: Vec<(&str, Def)> = vec![
        ("(fn ", Def::Fn(fn_def)),
        ("(const ", Def::Const(const_def)),
        ("(data ", Def::Type(type_def)),
    ];

    for (anchor, def) in exemplars {
        let _: &'static str = match def {
            Def::Fn(_) => "fn",
            Def::Const(_) => "const",
            Def::Type(_) => "type",
            // class/instance Def variants exist but are
            // not yet anchored in the prose-spec block. Once 22b.4
            // adds prose projection for them, the FORM_A_SPEC text
            // gains `(class ` / `(instance ` anchors and this match
            // will be exercised. For 22b.1 the exemplars list above
            // does not produce these variants.
            Def::Class(_) => "class",
            Def::Instance(_) => "instance",
        };
        assert!(
            FORM_A_SPEC.contains(anchor),
            "spec is missing anchor `{anchor}` for a Def kind"
        );
    }
}

/// The mode keywords (the RC memory model) must appear so an LLM knows the
/// Form-A wrapper syntax.
#[test]
fn spec_mentions_mode_keywords() {
    assert!(FORM_A_SPEC.contains("(own"), "spec missing `(own ...)`");
    assert!(FORM_A_SPEC.contains("(borrow"), "spec missing `(borrow ...)`");
}

/// `tail-app` and `tail-do` are distinct keywords from `app`/`do`. The
/// spec must mention both, otherwise an LLM cannot produce tail-correct
/// code at scale.
#[test]
fn spec_mentions_tail_variants() {
    assert!(FORM_A_SPEC.contains("tail-app"), "spec missing `tail-app`");
    assert!(FORM_A_SPEC.contains("tail-do"), "spec missing `tail-do`");
}

/// `suppress` is part of the surface and the LLM must know how to
/// preserve it. Empty-because is itself a diagnostic; the spec calls
/// it out so the LLM does not produce empty justifications.
#[test]
fn spec_mentions_suppress_clause() {
    assert!(FORM_A_SPEC.contains("(suppress"), "spec missing `(suppress ...)`");
    assert!(
        FORM_A_SPEC.contains("empty-suppress-reason"),
        "spec missing the empty-suppress-reason diagnostic"
    );
    // Make sure `Suppress` in the AST can still be constructed — the
    // exhaustive-match property carries through to the surface.
    let _ = Suppress {
        code: "x".into(),
        because: "y".into(),
    };
}