clapfig 0.21.1

//! JSON Schema generation from a config schema.
//!
//! Entry point is [`generate_schema::<C>()`](generate_schema): it walks the
//! compile-time `confique::meta::Meta` tree and produces a JSON Schema
//! document. Useful for auto-generating UI editors, external validation
//! tools, or IDE integrations.
//!
//! Internally the walker consumes a crate-private `SchemaRef` view so the
//! same generator will serve runtime-supplied schemas (issue #36) without
//! a separate code path.
//!
//! # What is in the schema
//!
//! - **Structure**: every nested config struct becomes a JSON `object` with
//!   `properties`; non-`Option<T>` fields are listed in `required`.
//! - **Docs**: struct and field `///` doc comments become `description`.
//! - **Types**: inferred from each field's `#[config(default = ...)]`
//!   expression. String → `"string"`, integer → `"integer"`, float →
//!   `"number"`, bool → `"boolean"`, array → `"array"`, map → `"object"`.
//! - **Defaults**: the literal default value (when present) is emitted as
//!   `default` on the property.
//! - **Env vars**: when a field maps to an env var, the name is attached as
//!   the non-standard `x-env` extension.
//!
//! # Limitation: types without defaults
//!
//! Confique's `Meta` tree does not carry Rust type information directly — it
//! only records the default-value *expression*. A field without a default and
//! without an explicit type hint therefore gets no `type` key in the schema
//! (i.e. any JSON value is accepted). This is acceptable for UI generation:
//! a form generator will still see the field and its docs, and users supply
//! values anyway.
//!
//! # Example
//!
//! ```ignore
//! use clapfig::schema;
//!
//! let value = schema::generate_schema::<MyConfig>();
//! println!("{}", serde_json::to_string_pretty(&value).unwrap());
//! ```

use confique::Config;
use confique::meta::{Expr, MapEntry, MapKey};
use serde_json::{Map, Value, json};

use crate::runtime::LeafType;
use crate::spec::{DocSource, FieldKindRef, FieldRef, LeafDefault, LeafRef, SchemaRef};

/// JSON Schema dialect emitted in the root `$schema` field.
const SCHEMA_DIALECT: &str = "https://json-schema.org/draft/2020-12/schema";

/// Generate a JSON Schema document from a confique config type.
///
/// Returns a `serde_json::Value` — the caller serializes it to a string,
/// writes it to a file, or embeds it wherever needed.
pub fn generate_schema<C: Config>() -> Value {
    generate_schema_from_ref(SchemaRef::from_meta(&C::META))
}

/// Internal entry point. Walks any `SchemaRef`-backed schema and emits the
/// JSON Schema document. Phase 2's runtime adapter calls this directly with
/// its own `SchemaRef` variant.
pub(crate) fn generate_schema_from_ref(schema: SchemaRef<'_>) -> Value {
    let mut root = schema_to_object(schema);
    if let Value::Object(map) = &mut root {
        map.insert("$schema".into(), Value::String(SCHEMA_DIALECT.into()));
    }
    root
}

/// Convert a schema node into a JSON Schema object.
fn schema_to_object(schema: SchemaRef<'_>) -> Value {
    let mut obj = Map::new();
    obj.insert("type".into(), Value::String("object".into()));
    obj.insert("title".into(), Value::String(schema.name().into()));
    let schema_doc = schema.doc();
    if !schema_doc.is_empty() {
        obj.insert("description".into(), Value::String(join_doc(schema_doc)));
    }

    let mut properties = Map::new();
    let mut required = Vec::new();

    for field in schema.fields() {
        let (name, prop, is_required) = field_to_property(field);
        if is_required {
            required.push(Value::String(name.clone()));
        }
        properties.insert(name, prop);
    }

    obj.insert("properties".into(), Value::Object(properties));
    if !required.is_empty() {
        obj.insert("required".into(), Value::Array(required));
    }
    obj.insert("additionalProperties".into(), Value::Bool(false));

    Value::Object(obj)
}

/// Convert a [`FieldRef`] into a `(name, schema, required)` triple.
///
/// `required` is `true` for non-optional leaves and for all nested structs
/// (a nested struct has its own internal required list).
fn field_to_property(field: FieldRef<'_>) -> (String, Value, bool) {
    match field.kind {
        FieldKindRef::Nested { schema: nested } => {
            let mut schema = schema_to_object(nested);
            if !field.doc.is_empty()
                && let Value::Object(map) = &mut schema
            {
                map.insert("description".into(), Value::String(join_doc(field.doc)));
            }
            (field.name.into(), schema, true)
        }
        FieldKindRef::ArrayOf { schema: item } => {
            // JSON Schema for a TOML `[[name]]` array of items: `type: array`
            // with `items: <item schema>`. Each runtime array entry is itself
            // typed against `item`, so the per-item schema is the natural
            // place to declare structure.
            //
            // Not marked required: `DynamicSpec::finalize` treats an absent
            // array-of as the empty list (no entries), so a JSON Schema
            // requiring the property would reject configs clapfig accepts.
            let mut prop = Map::new();
            if !field.doc.is_empty() {
                prop.insert("description".into(), Value::String(join_doc(field.doc)));
            }
            prop.insert("type".into(), Value::String("array".into()));
            prop.insert("items".into(), schema_to_object(item));
            (field.name.into(), Value::Object(prop), false)
        }
        FieldKindRef::Leaf(leaf) => {
            let mut prop = Map::new();
            if !field.doc.is_empty() {
                prop.insert("description".into(), Value::String(join_doc(field.doc)));
            }
            populate_leaf(&mut prop, leaf);
            (field.name.into(), Value::Object(prop), !leaf.optional)
        }
    }
}

/// Apply a leaf's declared type, default, env hint, and allowed-value set
/// onto its JSON Schema object.
fn populate_leaf(prop: &mut Map<String, Value>, leaf: LeafRef<'_>) {
    // Phase 2 runtime path supplies an explicit `LeafType`; emit a faithful
    // JSON Schema `type` from it without depending on whether a default
    // happens to be present.
    if let Some(ty) = leaf.ty
        && let Some(name) = leaf_type_json_name(ty)
    {
        prop.insert("type".into(), Value::String(name.into()));
        if let LeafType::Array(item) = ty
            && let Some(item_name) = leaf_type_json_name(item)
        {
            let mut items = Map::new();
            items.insert("type".into(), Value::String(item_name.into()));
            prop.insert("items".into(), Value::Object(items));
        }
    }

    if let Some(default) = leaf.default {
        match default {
            LeafDefault::Expr(expr) => {
                // Confique's `Meta` doesn't carry an explicit type; infer
                // from the default expression if a `LeafType` wasn't already
                // emitted above.
                if leaf.ty.is_none()
                    && let Some(ty) = infer_type(expr)
                {
                    prop.insert("type".into(), Value::String(ty.into()));
                }
                if let Some(default_value) = expr_to_json(expr) {
                    prop.insert("default".into(), default_value);
                }
            }
            LeafDefault::Toml(value) => {
                if let Some(default_value) = toml_value_to_json(value) {
                    prop.insert("default".into(), default_value);
                }
            }
        }
    }

    if let Some(env_name) = leaf.env {
        prop.insert("x-env".into(), Value::String(env_name.into()));
    }

    if let Some(values) = leaf.allowed_values {
        let enum_array: Vec<Value> = values.iter().filter_map(toml_value_to_json).collect();
        if !enum_array.is_empty() {
            prop.insert("enum".into(), Value::Array(enum_array));
        }
    }
}

/// JSON Schema `type` name for a runtime [`LeafType`]. `Enum` returns the
/// underlying primitive type implied by the first allowed value (callers
/// also emit `enum: [...]` separately).
fn leaf_type_json_name(ty: &LeafType) -> Option<&'static str> {
    match ty {
        LeafType::String => Some("string"),
        LeafType::Integer => Some("integer"),
        LeafType::Float => Some("number"),
        LeafType::Bool => Some("boolean"),
        LeafType::DateTime => Some("string"),
        LeafType::Array(_) => Some("array"),
        LeafType::Map(_) => Some("object"),
        LeafType::Enum { values } => values.first().and_then(toml_value_json_type),
        // Unconstrained: JSON Schema convention is to omit `type` entirely,
        // signalling that any value is acceptable. Callers reading the
        // schema are expected to validate the value themselves.
        LeafType::Value => None,
    }
}

/// Map a `toml::Value` to its JSON Schema `type` name.
fn toml_value_json_type(value: &toml::Value) -> Option<&'static str> {
    match value {
        toml::Value::String(_) => Some("string"),
        toml::Value::Integer(_) => Some("integer"),
        toml::Value::Float(_) => Some("number"),
        toml::Value::Boolean(_) => Some("boolean"),
        _ => None,
    }
}

/// Infer a JSON Schema `type` string from a confique default expression.
fn infer_type(expr: &Expr) -> Option<&'static str> {
    match expr {
        Expr::Str(_) => Some("string"),
        Expr::Integer(_) => Some("integer"),
        Expr::Float(_) => Some("number"),
        Expr::Bool(_) => Some("boolean"),
        Expr::Array(_) => Some("array"),
        Expr::Map(_) => Some("object"),
        _ => None,
    }
}

/// Convert a confique `Expr` (default value) into a JSON value.
///
/// Returns `None` for variants we can't faithfully represent (confique's
/// `Expr` is `#[non_exhaustive]`), so the caller can omit the `default` key
/// entirely rather than emitting a misleading `null`.
fn expr_to_json(expr: &Expr) -> Option<Value> {
    match expr {
        Expr::Str(s) => Some(Value::String((*s).into())),
        Expr::Integer(i) => Some(json!(i)),
        Expr::Float(f) => Some(json!(f)),
        Expr::Bool(b) => Some(Value::Bool(*b)),
        Expr::Array(items) => Some(Value::Array(
            items.iter().filter_map(expr_to_json).collect(),
        )),
        Expr::Map(entries) => {
            let mut obj = Map::new();
            for MapEntry { key, value } in *entries {
                let Some(key_str) = map_key_to_string(key) else {
                    continue;
                };
                let Some(val) = expr_to_json(value) else {
                    continue;
                };
                obj.insert(key_str, val);
            }
            Some(Value::Object(obj))
        }
        _ => None,
    }
}

/// Render a `MapKey` as a JSON object key. Returns `None` for variants we
/// can't faithfully represent, so the caller can skip the entry rather than
/// collapsing distinct keys onto an empty string.
fn map_key_to_string(key: &MapKey) -> Option<String> {
    match key {
        MapKey::Str(s) => Some((*s).into()),
        MapKey::Integer(i) => Some(i.to_string()),
        MapKey::Float(f) => Some(f.to_string()),
        MapKey::Bool(b) => Some(b.to_string()),
        _ => None,
    }
}

/// Convert a `toml::Value` into a JSON value for the `enum` slot.
///
/// Currently only used by the (Phase-1-dormant) `allowed_values` path on
/// `LeafRef`. The static spec never populates it; Phase 2 will.
///
/// Complex variants (`Array`, `Table`, `Datetime`) are dropped today. The
/// runtime enum surface in Phase 2 is scalar-only (`Field::enum_of(...)`
/// over TOML primitives — log levels, modes, format names), so this is the
/// faithful set for v1. Revisit if Phase 2 widens `enum_of` to accept
/// container values.
fn toml_value_to_json(value: &toml::Value) -> Option<Value> {
    match value {
        toml::Value::String(s) => Some(Value::String(s.clone())),
        toml::Value::Integer(i) => Some(json!(i)),
        toml::Value::Float(f) => Some(json!(f)),
        toml::Value::Boolean(b) => Some(Value::Bool(*b)),
        _ => None,
    }
}

fn join_doc(source: DocSource<'_>) -> String {
    source
        .iter()
        .map(|l| l.trim())
        .collect::<Vec<_>>()
        .join(" ")
        .trim()
        .to_string()
}

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

    fn schema() -> Value {
        generate_schema::<TestConfig>()
    }

    #[test]
    fn root_has_schema_dialect_and_type_object() {
        let s = schema();
        assert_eq!(s["$schema"], SCHEMA_DIALECT);
        assert_eq!(s["type"], "object");
        assert_eq!(s["title"], "TestConfig");
    }

    #[test]
    fn root_lists_top_level_properties() {
        let s = schema();
        let props = s["properties"].as_object().unwrap();
        assert!(props.contains_key("host"));
        assert!(props.contains_key("port"));
        assert!(props.contains_key("debug"));
        assert!(props.contains_key("database"));
    }

    #[test]
    fn types_inferred_from_defaults() {
        let s = schema();
        let props = &s["properties"];
        assert_eq!(props["host"]["type"], "string");
        assert_eq!(props["port"]["type"], "integer");
        assert_eq!(props["debug"]["type"], "boolean");
    }

    #[test]
    fn defaults_emitted_on_properties() {
        let s = schema();
        let props = &s["properties"];
        assert_eq!(props["host"]["default"], "localhost");
        assert_eq!(props["port"]["default"], 8080);
        assert_eq!(props["debug"]["default"], false);
    }

    #[test]
    fn doc_comments_become_descriptions() {
        let s = schema();
        let props = &s["properties"];
        assert!(
            props["host"]["description"]
                .as_str()
                .unwrap()
                .contains("host")
        );
        assert!(
            props["port"]["description"]
                .as_str()
                .unwrap()
                .contains("port")
        );
    }

    #[test]
    fn nested_struct_becomes_object_with_own_properties() {
        let s = schema();
        let db = &s["properties"]["database"];
        assert_eq!(db["type"], "object");
        assert_eq!(db["title"], "TestDbConfig");
        let db_props = db["properties"].as_object().unwrap();
        assert!(db_props.contains_key("url"));
        assert!(db_props.contains_key("pool_size"));
        assert_eq!(db_props["pool_size"]["type"], "integer");
        assert_eq!(db_props["pool_size"]["default"], 5);
    }

    #[test]
    fn required_array_excludes_optional_fields() {
        let s = schema();
        let root_required: Vec<&str> = s["required"]
            .as_array()
            .unwrap()
            .iter()
            .map(|v| v.as_str().unwrap())
            .collect();
        assert!(root_required.contains(&"host"));
        assert!(root_required.contains(&"port"));
        assert!(root_required.contains(&"debug"));
        assert!(root_required.contains(&"database"));

        let db_required: Vec<&str> = s["properties"]["database"]["required"]
            .as_array()
            .unwrap()
            .iter()
            .map(|v| v.as_str().unwrap())
            .collect();
        assert!(db_required.contains(&"pool_size"));
        // url is Option<String> — must NOT be required.
        assert!(!db_required.contains(&"url"));
    }

    #[test]
    fn optional_field_still_appears_in_properties() {
        let s = schema();
        let db_props = s["properties"]["database"]["properties"]
            .as_object()
            .unwrap();
        assert!(db_props.contains_key("url"));
        // No default and Option<T>, so no `type` and no `default`.
        assert!(!db_props["url"].as_object().unwrap().contains_key("type"));
        assert!(!db_props["url"].as_object().unwrap().contains_key("default"));
    }

    #[test]
    fn additional_properties_false_on_objects() {
        let s = schema();
        assert_eq!(s["additionalProperties"], false);
        assert_eq!(s["properties"]["database"]["additionalProperties"], false);
    }

    #[test]
    fn optional_field_has_no_null_default_key() {
        // Regression guard: expr_to_json must not fabricate a `default: null`
        // for fields that have no default (Option<T> / unrepresentable Expr).
        let s = schema();
        let url = &s["properties"]["database"]["properties"]["url"];
        let url_obj = url.as_object().unwrap();
        assert!(
            !url_obj.contains_key("default"),
            "optional field must not have a default key: {url}"
        );
    }

    #[test]
    fn schema_serializes_to_valid_json() {
        let s = schema();
        let json_text = serde_json::to_string_pretty(&s).unwrap();
        let reparsed: Value = serde_json::from_str(&json_text).unwrap();
        assert_eq!(reparsed, s);
    }
}