reddb-io-types 1.21.0

//! Agent-facing type & multi-model knowledge reference — generated from the
//! engine's own type-system authorities (ADR 0061, "Agent-Facing Knowledge &
//! MCP Surface").
//!
//! Where [`crate::knowledge`]'s sibling in `reddb-io-rql` emits the RQL grammar
//! surface, this module emits the **value-type catalog** and the **multi-model
//! map**. The volatile facts come straight from the source of truth so the
//! reference cannot drift from the engine:
//!
//! - the value types come from the three type-system authorities in this crate
//!   — [`function_catalog::FUNCTION_CATALOG`], [`operator_catalog::OPERATOR_CATALOG`],
//!   and [`cast_catalog::CAST_CATALOG`] (every concrete type they reference), and
//! - the operators and casts are likewise read live from those tables.
//!
//! Layered over that per-model type catalog is the **multi-model map**: the
//! paradigms RedDB stores (documents, key-value, queues, graph nodes/edges,
//! vault secrets, config, and RQL-tabular collections). The map is the
//! conceptual narrative — hand-authored because it is judgment, not extractable
//! — but it points into the generated type catalog by [`TypeCategory`], so the
//! two layers stay coupled.
//!
//! Nothing here hand-maintains *which* value types exist — that is read from
//! the catalogs above. The same generated content is served two ways from this
//! one source: as the `reddb://knowledge/types` MCP resource and as the type
//! section of the generated `docs/llms.txt`. The anti-drift tests at the bottom
//! pin the "generated, exhaustive, in-sync" contract.

use crate::cast_catalog::{CastContext, CAST_CATALOG};
use crate::function_catalog::FUNCTION_CATALOG;
use crate::json::{Map, Value as JsonValue};
use crate::operator_catalog::{OperatorKind, OPERATOR_CATALOG};
use crate::types::{DataType, TypeCategory};

/// Canonical URI for the type & multi-model knowledge resource served over MCP.
pub const RESOURCE_URI: &str = "reddb://knowledge/types";

/// Short human title for the type knowledge resource.
pub const RESOURCE_TITLE: &str = "RedDB Type & Multi-Model Reference";

/// One-line description of the type knowledge resource.
pub const RESOURCE_DESCRIPTION: &str =
    "Generated value-type catalog (function/operator/cast authorities) plus the multi-model map.";

/// Markers delimiting the generated type block inside `docs/llms.txt`. The
/// `docs/llms.txt` sync test reads the text between these markers and asserts
/// it equals [`type_reference_markdown`], so the file is generated, not
/// hand-maintained.
pub const LLMS_BEGIN_MARKER: &str = "<!-- BEGIN GENERATED: types -->";
/// Closing marker for the generated type block in `docs/llms.txt`.
pub const LLMS_END_MARKER: &str = "<!-- END GENERATED: types -->";

/// One paradigm in RedDB's multi-model surface. The narrative (`summary`) is
/// hand-authored judgment; `categories` points into the generated value-type
/// catalog so the map is layered over — not duplicated from — the type system.
pub struct ModelParadigm {
    /// Display name of the paradigm (e.g. "Documents", "Graph nodes & edges").
    pub name: &'static str,
    /// One-sentence description of what the paradigm stores and how it is shaped.
    pub summary: &'static str,
    /// The [`TypeCategory`] families this paradigm predominantly holds, linking
    /// the map back into the per-model type catalog above it.
    pub categories: &'static [TypeCategory],
}

/// The multi-model map: the paradigms RedDB stores, layered over the value-type
/// catalog. Hand-authored narrative (ADR 0061 §3), but each entry references the
/// generated [`TypeCategory`] families it predominantly holds.
pub const MULTI_MODEL_MAP: &[ModelParadigm] = &[
    ModelParadigm {
        name: "Documents",
        summary: "Schemaless JSON-shaped entities addressed by collection + entity id; \
nested fields are typed value-by-value from the catalog below.",
        categories: &[
            TypeCategory::Json,
            TypeCategory::String,
            TypeCategory::Numeric,
            TypeCategory::Boolean,
        ],
    },
    ModelParadigm {
        name: "Key-value",
        summary: "Flat collection + key → value pairs for caches and counters; any \
catalogued value type can be the stored payload.",
        categories: &[
            TypeCategory::String,
            TypeCategory::Numeric,
            TypeCategory::Json,
        ],
    },
    ModelParadigm {
        name: "Queues",
        summary: "Ordered FIFO/priority message streams (LPUSH/RPUSH/LPOP/RPOP, ACK/NACK); \
each message body is a catalogued value, usually text or JSON.",
        categories: &[
            TypeCategory::String,
            TypeCategory::Json,
            TypeCategory::TimeSpan,
        ],
    },
    ModelParadigm {
        name: "Graph nodes & edges",
        summary: "Property graph of nodes and edges; references between them are first-class \
value types and properties draw from the full catalog.",
        categories: &[
            TypeCategory::Reference,
            TypeCategory::String,
            TypeCategory::Numeric,
        ],
    },
    ModelParadigm {
        name: "Vault secrets",
        summary: "Encrypted secrets and password hashes that the expression layer treats as \
opaque — coercion must be opted into explicitly.",
        categories: &[TypeCategory::Opaque, TypeCategory::String],
    },
    ModelParadigm {
        name: "Config",
        summary: "Hierarchical, resolvable configuration entries; values are catalogued \
scalars and JSON resolved per environment.",
        categories: &[
            TypeCategory::String,
            TypeCategory::Boolean,
            TypeCategory::Numeric,
            TypeCategory::Json,
        ],
    },
    ModelParadigm {
        name: "RQL-tabular",
        summary: "Relational tables with typed columns queried through RQL; columns bind \
directly to the value types and categories of the catalog below.",
        categories: &[
            TypeCategory::Numeric,
            TypeCategory::String,
            TypeCategory::Boolean,
            TypeCategory::DateTime,
            TypeCategory::Domain,
        ],
    },
];

/// Push a concrete value type into `acc`, skipping the catalog sentinels.
///
/// `DataType::Unknown` (the function-catalog "any" placeholder) and
/// `DataType::Nullable` (the operator-catalog prefix "don't care" marker) are
/// matching markers in the authorities, not real value types, so they are
/// filtered out of the published catalog.
fn push_value_type(acc: &mut Vec<DataType>, candidate: DataType) {
    if matches!(candidate, DataType::Unknown | DataType::Nullable) {
        return;
    }
    if !acc.contains(&candidate) {
        acc.push(candidate);
    }
}

/// Every concrete value type referenced by the type-system authorities
/// (function / operator / cast catalogs), sorted by discriminant and
/// deduplicated.
///
/// This is read live from the three catalogs, so adding a type to any of them
/// flows automatically into the generated reference; the anti-drift test
/// [`tests::catalog_matches_authorities`] independently re-derives the same set
/// and pins the equality.
pub fn catalogued_value_types() -> Vec<DataType> {
    let mut types: Vec<DataType> = Vec::new();
    for entry in FUNCTION_CATALOG {
        for &arg in entry.arg_types {
            push_value_type(&mut types, arg);
        }
        push_value_type(&mut types, entry.return_type);
    }
    for entry in OPERATOR_CATALOG {
        push_value_type(&mut types, entry.lhs_type);
        push_value_type(&mut types, entry.rhs_type);
        push_value_type(&mut types, entry.return_type);
    }
    for entry in CAST_CATALOG {
        push_value_type(&mut types, entry.src);
        push_value_type(&mut types, entry.target);
    }
    types.sort_by_key(|ty| *ty as u8);
    types
}

/// Distinct operator symbols, sorted, taken from the engine's static
/// [`OPERATOR_CATALOG`]. The catalog carries one row per overload, so a symbol
/// (e.g. `-`, which is both infix and prefix) can appear several times — this
/// collapses them.
pub fn operator_symbols() -> Vec<&'static str> {
    let mut names: Vec<&'static str> = OPERATOR_CATALOG.iter().map(|entry| entry.name).collect();
    names.sort_unstable();
    names.dedup();
    names
}

/// The implicit (always-allowed, lossless) casts the engine inserts silently,
/// sorted by `(src, target)` discriminant. These are the widenings an agent can
/// rely on without writing `CAST(...)`.
pub fn implicit_casts() -> Vec<(DataType, DataType)> {
    let mut pairs: Vec<(DataType, DataType)> = CAST_CATALOG
        .iter()
        .filter(|cast| cast.context == CastContext::Implicit)
        .map(|cast| (cast.src, cast.target))
        .collect();
    pairs.sort_by_key(|(src, target)| (*src as u8, *target as u8));
    pairs
}

/// Human label for a [`TypeCategory`], used by the generated map.
fn category_label(category: TypeCategory) -> &'static str {
    match category {
        TypeCategory::Numeric => "Numeric",
        TypeCategory::String => "String",
        TypeCategory::Boolean => "Boolean",
        TypeCategory::DateTime => "DateTime",
        TypeCategory::TimeSpan => "TimeSpan",
        TypeCategory::Array => "Array",
        TypeCategory::Network => "Network",
        TypeCategory::Geo => "Geo",
        TypeCategory::Domain => "Domain",
        TypeCategory::Uuid => "Uuid",
        TypeCategory::Opaque => "Opaque",
        TypeCategory::Reference => "Reference",
        TypeCategory::Vector => "Vector",
        TypeCategory::Json => "Json",
        TypeCategory::Unknown => "Unknown",
    }
}

/// The order in which value-type categories are presented in the reference.
const CATEGORY_ORDER: &[TypeCategory] = &[
    TypeCategory::Numeric,
    TypeCategory::String,
    TypeCategory::Boolean,
    TypeCategory::DateTime,
    TypeCategory::TimeSpan,
    TypeCategory::Domain,
    TypeCategory::Network,
    TypeCategory::Geo,
    TypeCategory::Uuid,
    TypeCategory::Json,
    TypeCategory::Vector,
    TypeCategory::Array,
    TypeCategory::Reference,
    TypeCategory::Opaque,
];

fn render_code_list<I, S>(items: I) -> String
where
    I: IntoIterator<Item = S>,
    S: AsRef<str>,
{
    items
        .into_iter()
        .map(|item| format!("`{}`", item.as_ref()))
        .collect::<Vec<_>>()
        .join(", ")
}

/// Generate the canonical type & multi-model reference as Markdown, sourced
/// entirely from the engine's type-system authorities (for the type catalog)
/// plus the hand-authored multi-model narrative. This single string is what the
/// MCP `reddb://knowledge/types` resource serves and what `docs/llms.txt` embeds.
pub fn type_reference_markdown() -> String {
    let types = catalogued_value_types();
    let operators = operator_symbols();
    let casts = implicit_casts();

    let mut out = String::new();
    out.push_str("# RedDB Type & Multi-Model Reference\n\n");
    out.push_str(
        "RedDB is a multi-model store (documents, key-value, queues, graph, vault, \
config, and RQL-tabular collections) layered over one logical type system.\n\n",
    );
    out.push_str(
        "This reference is generated from the `reddb-io-types` function, operator, and \
cast catalogs. Do not edit by hand — regenerate from the engine.\n\n",
    );

    // ── Value types, grouped by category ──
    out.push_str(&format!("## Value types ({})\n\n", types.len()));
    out.push_str(
        "Every concrete value type the engine's type-system authorities reference, \
grouped by coercion category:\n\n",
    );
    for &category in CATEGORY_ORDER {
        let mut names: Vec<String> = types
            .iter()
            .filter(|ty| ty.category() == category)
            .map(|ty| ty.to_string())
            .collect();
        names.dedup();
        if names.is_empty() {
            continue;
        }
        out.push_str(&format!("### {} types\n\n", category_label(category)));
        out.push_str(&render_code_list(&names));
        out.push_str("\n\n");
    }

    // ── Operators ──
    out.push_str(&format!("## Operators ({})\n\n", operators.len()));
    out.push_str("The type system resolves these built-in operators:\n\n");
    out.push_str(&render_code_list(&operators));
    out.push_str("\n\n");

    // ── Implicit casts ──
    out.push_str(&format!("## Implicit casts ({})\n\n", casts.len()));
    out.push_str(
        "Lossless widenings the engine inserts silently — usable anywhere without an \
explicit `CAST`:\n\n",
    );
    for (src, target) in &casts {
        out.push_str(&format!("- `{src}` → `{target}`\n"));
    }
    out.push('\n');

    // ── Multi-model map, layered over the type catalog ──
    out.push_str("## Multi-model map\n\n");
    out.push_str(
        "RedDB stores several paradigms over the value-type catalog above. Each \
paradigm's `Type families` point back into that catalog by category:\n\n",
    );
    for paradigm in MULTI_MODEL_MAP {
        out.push_str(&format!("### {}\n\n", paradigm.name));
        out.push_str(paradigm.summary);
        out.push_str("\n\n");
        let families: Vec<&str> = paradigm
            .categories
            .iter()
            .map(|&category| category_label(category))
            .collect();
        out.push_str(&format!(
            "Type families: {}\n\n",
            render_code_list(&families)
        ));
    }

    // Trim the trailing blank line so the body ends with exactly one newline.
    while out.ends_with("\n\n") {
        out.pop();
    }
    out
}

/// The type block as embedded in `docs/llms.txt`: the generated reference fenced
/// by the begin/end markers. Emitting the markers here keeps `docs/llms.txt` and
/// the MCP resource fed by one source.
pub fn type_llms_section() -> String {
    format!(
        "{begin}\n{body}\n{end}",
        begin = LLMS_BEGIN_MARKER,
        body = type_reference_markdown(),
        end = LLMS_END_MARKER,
    )
}

// ─────────────────────────────────────────────────────────────────────────
// Active type/cast lookup (ADR 0061 §4 — the `reddb_type_of` MCP tool seam)
//
// Where the markdown reference above is the *passive* knowledge resource, the
// functions below answer a *targeted* question — "what is this value or type
// name, and what can I cast/operate it to?" — by reading the same three
// catalogs live. The MCP `reddb_type_of` tool is a thin wrapper over
// [`type_of_json`]: it owns no type knowledge of its own.
// ─────────────────────────────────────────────────────────────────────────

/// Resolve a type *name* (canonical reddb spelling or a common SQL alias, both
/// case-insensitive — e.g. `INTEGER`, `int`, `string`) to its [`DataType`].
///
/// Delegates to [`DataType::from_sql_name`] so the accepted spellings stay in
/// lockstep with the engine's own SQL type parser; returns `None` for names the
/// engine does not recognise.
pub fn resolve_type_name(name: &str) -> Option<DataType> {
    DataType::from_sql_name(name)
}

/// Infer the [`DataType`] of a bare JSON literal as the engine would type it on
/// the wire: `null → NULLABLE`, booleans → `BOOLEAN`, integral numbers →
/// `INTEGER`, fractional numbers → `FLOAT`, strings → `TEXT`, arrays → `ARRAY`,
/// objects → `JSON`.
///
/// This is deliberately the *structural* type of the literal, not a re-parse
/// into a richer domain type (an email-shaped string is still `TEXT` here);
/// callers wanting the domain type pass the type name explicitly.
pub fn infer_literal_type(value: &JsonValue) -> DataType {
    match value {
        JsonValue::Null => DataType::Nullable,
        JsonValue::Bool(_) => DataType::Boolean,
        JsonValue::Number(n) => {
            if n.fract() == 0.0 && *n >= i64::MIN as f64 && *n <= i64::MAX as f64 {
                DataType::Integer
            } else {
                DataType::Float
            }
        }
        JsonValue::String(_) => DataType::Text,
        JsonValue::Array(_) => DataType::Array,
        JsonValue::Object(_) => DataType::Json,
    }
}

/// Human label for a [`CastContext`], matching the engine's coercion vocabulary.
fn cast_context_label(context: CastContext) -> &'static str {
    match context {
        CastContext::Implicit => "implicit",
        CastContext::Assignment => "assignment",
        CastContext::Explicit => "explicit",
    }
}

/// Human label for an [`OperatorKind`].
fn operator_kind_label(kind: OperatorKind) -> &'static str {
    match kind {
        OperatorKind::Infix => "infix",
        OperatorKind::Prefix => "prefix",
        OperatorKind::Postfix => "postfix",
    }
}

/// Every cast *out of* `ty` registered in [`CAST_CATALOG`], in catalog order.
/// Each tuple is `(target, context, lossy)` read straight from the catalog row.
pub fn casts_from(ty: DataType) -> Vec<(DataType, CastContext, bool)> {
    CAST_CATALOG
        .iter()
        .filter(|cast| cast.src == ty)
        .map(|cast| (cast.target, cast.context, cast.lossy))
        .collect()
}

/// Every operator overload in [`OPERATOR_CATALOG`] that accepts `ty` as one of
/// its operands, in catalog order. The `Nullable` left-operand marker on prefix
/// operators is treated as "no left operand", so a prefix `-` matches only when
/// `ty` is its (right) operand, never via the marker.
pub fn operators_for(ty: DataType) -> Vec<&'static crate::operator_catalog::OperatorEntry> {
    OPERATOR_CATALOG
        .iter()
        .filter(|entry| {
            let lhs_matches = entry.kind != OperatorKind::Prefix && entry.lhs_type == ty;
            lhs_matches || entry.rhs_type == ty
        })
        .collect()
}

/// Build the structured `reddb_type_of` answer for a resolved [`DataType`]: its
/// canonical name + category, the casts available out of it, and the operator
/// overloads that accept it — all read live from the catalogs.
pub fn type_facts_json(ty: DataType) -> JsonValue {
    let casts: Vec<JsonValue> = casts_from(ty)
        .into_iter()
        .map(|(target, context, lossy)| {
            let mut obj = Map::new();
            obj.insert("target".to_string(), JsonValue::String(target.to_string()));
            obj.insert(
                "context".to_string(),
                JsonValue::String(cast_context_label(context).to_string()),
            );
            obj.insert("lossy".to_string(), JsonValue::Bool(lossy));
            JsonValue::Object(obj)
        })
        .collect();

    let operators: Vec<JsonValue> = operators_for(ty)
        .into_iter()
        .map(|entry| {
            let mut obj = Map::new();
            obj.insert(
                "symbol".to_string(),
                JsonValue::String(entry.name.to_string()),
            );
            obj.insert(
                "kind".to_string(),
                JsonValue::String(operator_kind_label(entry.kind).to_string()),
            );
            // Prefix operators carry a `Nullable` left-operand marker, not a real
            // operand — surface that as JSON null rather than leaking the marker.
            let lhs = if entry.kind == OperatorKind::Prefix {
                JsonValue::Null
            } else {
                JsonValue::String(entry.lhs_type.to_string())
            };
            obj.insert("lhs".to_string(), lhs);
            obj.insert(
                "rhs".to_string(),
                JsonValue::String(entry.rhs_type.to_string()),
            );
            obj.insert(
                "returns".to_string(),
                JsonValue::String(entry.return_type.to_string()),
            );
            JsonValue::Object(obj)
        })
        .collect();

    let mut obj = Map::new();
    obj.insert(
        "canonical_type".to_string(),
        JsonValue::String(ty.to_string()),
    );
    obj.insert(
        "category".to_string(),
        JsonValue::String(category_label(ty.category()).to_string()),
    );
    obj.insert(
        "is_preferred".to_string(),
        JsonValue::Bool(ty.is_preferred()),
    );
    obj.insert("casts".to_string(), JsonValue::Array(casts));
    obj.insert("operators".to_string(), JsonValue::Array(operators));
    JsonValue::Object(obj)
}

/// Answer a `reddb_type_of` query. Exactly one of `type_name` or `value` should
/// carry the lookup subject: a type name (resolved with [`resolve_type_name`])
/// or a JSON literal whose structural type is inferred with
/// [`infer_literal_type`]. Returns the structured facts from [`type_facts_json`]
/// wrapped with the resolved canonical type, or `None` when a supplied type name
/// is unknown to the engine.
pub fn type_of_json(type_name: Option<&str>, value: Option<&JsonValue>) -> Option<JsonValue> {
    let ty = match (type_name, value) {
        (Some(name), _) => resolve_type_name(name)?,
        (None, Some(literal)) => infer_literal_type(literal),
        (None, None) => return None,
    };
    Some(type_facts_json(ty))
}

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

    /// Independently re-derive the concrete value types from the three
    /// authorities and assert the published catalog equals that set — the
    /// anti-drift guarantee: the reference stays in sync with the
    /// function/operator/cast catalogs.
    #[test]
    fn catalog_matches_authorities() {
        let mut expected: Vec<DataType> = Vec::new();
        let mut record = |ty: DataType| {
            if matches!(ty, DataType::Unknown | DataType::Nullable) {
                return;
            }
            if !expected.contains(&ty) {
                expected.push(ty);
            }
        };
        for entry in FUNCTION_CATALOG {
            for &arg in entry.arg_types {
                record(arg);
            }
            record(entry.return_type);
        }
        for entry in OPERATOR_CATALOG {
            record(entry.lhs_type);
            record(entry.rhs_type);
            record(entry.return_type);
        }
        for entry in CAST_CATALOG {
            record(entry.src);
            record(entry.target);
        }
        expected.sort_by_key(|ty| *ty as u8);

        assert_eq!(
            catalogued_value_types(),
            expected,
            "the published value-type catalog drifted from the function/operator/cast \
authorities in reddb-io-types"
        );
    }

    /// The published catalog excludes the catalog sentinels and is non-empty.
    #[test]
    fn catalog_excludes_sentinels() {
        let types = catalogued_value_types();
        assert!(!types.is_empty(), "value-type catalog must not be empty");
        assert!(
            !types.contains(&DataType::Unknown),
            "Unknown is a catalog placeholder, not a value type"
        );
        assert!(
            !types.contains(&DataType::Nullable),
            "Nullable is a prefix-operator marker, not a value type"
        );
    }

    /// The catalog is sorted by discriminant, so the generated reference is
    /// stable and reviewable.
    #[test]
    fn catalog_is_sorted_and_unique() {
        let types = catalogued_value_types();
        let mut sorted = types.clone();
        sorted.sort_by_key(|ty| *ty as u8);
        assert_eq!(types, sorted, "catalogued_value_types must be sorted");
        let mut deduped = types.clone();
        deduped.dedup();
        assert_eq!(
            deduped.len(),
            types.len(),
            "catalog must not contain duplicates"
        );
    }

    /// authorities ⊆ reference: every catalogued value type appears, by its
    /// display name, in the generated reference.
    #[test]
    fn reference_lists_every_value_type() {
        let reference = type_reference_markdown();
        for ty in catalogued_value_types() {
            assert!(
                reference.contains(&format!("`{ty}`")),
                "value type {ty} from the catalogs is missing from the generated type \
reference"
            );
        }
    }

    /// Every operator symbol from the catalog appears in the reference.
    #[test]
    fn reference_lists_every_operator() {
        let reference = type_reference_markdown();
        for symbol in operator_symbols() {
            assert!(
                reference.contains(&format!("`{symbol}`")),
                "operator {symbol:?} is missing from the generated type reference"
            );
        }
    }

    /// The multi-model map enumerates all seven paradigms RedDB stores, and each
    /// is layered over the type catalog by at least one category family.
    #[test]
    fn multi_model_map_covers_every_paradigm() {
        let names: Vec<&str> = MULTI_MODEL_MAP.iter().map(|m| m.name).collect();
        for expected in [
            "Documents",
            "Key-value",
            "Queues",
            "Graph nodes & edges",
            "Vault secrets",
            "Config",
            "RQL-tabular",
        ] {
            assert!(
                names.contains(&expected),
                "multi-model map is missing the {expected:?} paradigm"
            );
        }
        for paradigm in MULTI_MODEL_MAP {
            assert!(
                !paradigm.categories.is_empty(),
                "paradigm {:?} must link to at least one type category",
                paradigm.name
            );
        }
    }

    /// Every paradigm and its category families render into the reference.
    #[test]
    fn reference_includes_multi_model_map() {
        let reference = type_reference_markdown();
        for paradigm in MULTI_MODEL_MAP {
            assert!(
                reference.contains(paradigm.name),
                "paradigm {:?} is missing from the generated reference",
                paradigm.name
            );
            for &category in paradigm.categories {
                assert!(
                    reference.contains(category_label(category)),
                    "category {:?} for paradigm {:?} is missing from the reference",
                    category_label(category),
                    paradigm.name
                );
            }
        }
    }

    /// The reference is deterministic (pure function of the catalogs + map).
    #[test]
    fn reference_is_deterministic() {
        assert_eq!(type_reference_markdown(), type_reference_markdown());
    }

    /// The `docs/llms.txt` block wraps exactly the reference between markers.
    #[test]
    fn llms_section_wraps_reference() {
        let section = type_llms_section();
        assert!(section.starts_with(LLMS_BEGIN_MARKER));
        assert!(section.ends_with(LLMS_END_MARKER));
        assert!(section.contains(&type_reference_markdown()));
    }

    /// Type names resolve through the engine's own SQL parser — canonical
    /// spelling and common aliases, case-insensitively.
    #[test]
    fn resolve_type_name_accepts_canonical_and_aliases() {
        assert_eq!(resolve_type_name("INTEGER"), Some(DataType::Integer));
        assert_eq!(resolve_type_name("int"), Some(DataType::Integer));
        assert_eq!(resolve_type_name("string"), Some(DataType::Text));
        assert_eq!(resolve_type_name("TEXT"), Some(DataType::Text));
        assert_eq!(resolve_type_name("not-a-type"), None);
    }

    /// Bare JSON literals are typed structurally, the way the wire sees them.
    #[test]
    fn infer_literal_type_maps_json_shapes() {
        assert_eq!(infer_literal_type(&JsonValue::Null), DataType::Nullable);
        assert_eq!(
            infer_literal_type(&JsonValue::Bool(true)),
            DataType::Boolean
        );
        assert_eq!(
            infer_literal_type(&JsonValue::Number(42.0)),
            DataType::Integer
        );
        assert_eq!(infer_literal_type(&JsonValue::Number(3.5)), DataType::Float);
        assert_eq!(
            infer_literal_type(&JsonValue::String("hi".to_string())),
            DataType::Text
        );
        assert_eq!(
            infer_literal_type(&JsonValue::Array(vec![])),
            DataType::Array
        );
        assert_eq!(
            infer_literal_type(&JsonValue::Object(Map::new())),
            DataType::Json
        );
    }

    /// `casts_from` reports exactly the catalog rows whose `src` is the type,
    /// and the catalog says INTEGER widens to FLOAT implicitly and losslessly.
    #[test]
    fn casts_from_reads_catalog_rows() {
        let casts = casts_from(DataType::Integer);
        let widen = casts
            .iter()
            .find(|(target, _, _)| *target == DataType::Float)
            .expect("INTEGER → FLOAT cast present in catalog");
        assert_eq!(widen.1, CastContext::Implicit);
        assert!(!widen.2, "INTEGER → FLOAT must be lossless");
        // Every returned row genuinely has INTEGER as its source.
        for (target, _, _) in &casts {
            assert!(CAST_CATALOG
                .iter()
                .any(|c| c.src == DataType::Integer && c.target == *target));
        }
    }

    /// `operators_for` matches a type as either operand, and skips the prefix
    /// `Nullable` left-operand marker.
    #[test]
    fn operators_for_matches_either_operand() {
        let ops = operators_for(DataType::Integer);
        assert!(
            ops.iter().any(|e| e.name == "+"),
            "INTEGER should accept the + operator"
        );
        // The prefix-`-` overload (unary negation) carries a Nullable lhs marker;
        // it is matched via its (right) operand, never via the marker. So every
        // matched entry that *does* carry a Nullable lhs must be a prefix whose
        // right operand is the looked-up type.
        for entry in &ops {
            if entry.lhs_type == DataType::Nullable {
                assert_eq!(entry.kind, OperatorKind::Prefix);
                assert_eq!(entry.rhs_type, DataType::Integer);
            } else {
                assert!(entry.lhs_type == DataType::Integer || entry.rhs_type == DataType::Integer);
            }
        }
    }

    /// The structured answer carries the canonical type, category, casts and
    /// operators — all sourced from the catalogs.
    #[test]
    fn type_facts_json_reports_canonical_casts_and_operators() {
        let facts = type_facts_json(DataType::Integer);
        assert_eq!(
            facts.get("canonical_type").and_then(JsonValue::as_str),
            Some("INTEGER")
        );
        assert_eq!(
            facts.get("category").and_then(JsonValue::as_str),
            Some("Numeric")
        );
        let casts = facts.get("casts").and_then(JsonValue::as_array).unwrap();
        assert!(
            casts
                .iter()
                .any(|c| c.get("target").and_then(JsonValue::as_str) == Some("FLOAT")),
            "INTEGER → FLOAT must appear in the casts"
        );
        let operators = facts
            .get("operators")
            .and_then(JsonValue::as_array)
            .unwrap();
        assert!(
            operators
                .iter()
                .any(|o| o.get("symbol").and_then(JsonValue::as_str) == Some("+")),
            "the + operator must appear in the operators"
        );
    }

    /// The query entry point resolves by type name, infers from a value, and
    /// rejects an unknown type name.
    #[test]
    fn type_of_json_resolves_name_and_value() {
        // By type name (alias).
        let by_name = type_of_json(Some("int"), None).expect("known type name");
        assert_eq!(
            by_name.get("canonical_type").and_then(JsonValue::as_str),
            Some("INTEGER")
        );
        // By JSON value literal.
        let by_value = type_of_json(None, Some(&JsonValue::Bool(false))).expect("value");
        assert_eq!(
            by_value.get("canonical_type").and_then(JsonValue::as_str),
            Some("BOOLEAN")
        );
        // Unknown name → None so the caller can surface a parse error.
        assert!(type_of_json(Some("frobnicate"), None).is_none());
        // Nothing supplied → None.
        assert!(type_of_json(None, None).is_none());
    }
}