openapi_model_generator/

parser.rs

use crate::{
    models::{
        CompositionModel, EnumModel, Field, Model, ModelType, RequestModel, ResponseModel,
        TypeAliasModel, UnionModel, UnionType, UnionVariant,
    },
    Result,
};
use indexmap::IndexMap;
use openapiv3::{
    AdditionalProperties, OpenAPI, ReferenceOr, Schema, SchemaKind, StringFormat, Type,
    VariantOrUnknownOrEmpty,
};
use std::collections::HashSet;

const X_RUST_TYPE: &str = "x-rust-type";
const X_RUST_ATTRS: &str = "x-rust-attrs";

/// Information about a field extracted from OpenAPI schema
#[derive(Debug)]
struct FieldInfo {
    field_type: String,
    format: String,
    is_nullable: bool,
    is_array_ref: bool,
    description: Option<String>,
    custom_attrs: Option<Vec<String>>,
    validation_rules: Option<crate::models::ValidationRules>,
}

/// Converts camelCase to PascalCase
/// Example: "createRole" -> "CreateRole", "listRoles" -> "ListRoles", "listRoles-Input" -> "ListRolesInput"
pub(crate) fn to_pascal_case(input: &str) -> String {
    input
        .split(&['-', '_'][..])
        .filter(|s| !s.is_empty())
        .map(|s| {
            let mut chars = s.chars();
            match chars.next() {
                Some(first) => first.to_ascii_uppercase().to_string() + chars.as_str(),
                None => String::new(),
            }
        })
        .collect::<String>()
}

/// Extracts custom Rust attributes from x-rust-attrs extension
fn extract_custom_attrs(schema: &Schema) -> Option<Vec<String>> {
    schema
        .schema_data
        .extensions
        .get(X_RUST_ATTRS)
        .and_then(|value| {
            if let Some(arr) = value.as_array() {
                let attrs: Vec<String> = arr
                    .iter()
                    .filter_map(|v| v.as_str().map(|s| s.to_string()))
                    .collect();
                if attrs.is_empty() {
                    None
                } else {
                    Some(attrs)
                }
            } else {
                tracing::warn!(
                    "x-rust-attrs should be an array of strings, got: {:?}",
                    value
                );
                None
            }
        })
}

pub fn parse_openapi(
    openapi: &OpenAPI,
) -> Result<(Vec<ModelType>, Vec<RequestModel>, Vec<ResponseModel>)> {
    let mut models = Vec::new();
    let mut requests = Vec::new();
    let mut responses = Vec::new();

    let mut added_models = HashSet::new();

    let empty_schemas = IndexMap::new();
    let empty_request_bodies = IndexMap::new();

    let (schemas, request_bodies) = if let Some(components) = &openapi.components {
        (&components.schemas, &components.request_bodies)
    } else {
        (&empty_schemas, &empty_request_bodies)
    };

    // Parse components/schemas
    if let Some(components) = &openapi.components {
        for (name, schema) in &components.schemas {
            let model_types = parse_schema_to_model_type(name, schema, &components.schemas)?;
            for model_type in model_types {
                if added_models.insert(model_type.name().to_string()) {
                    models.push(model_type);
                }
            }
        }

        // Parse components/requestBodies - extract schemas and create models
        for (name, request_body_ref) in &components.request_bodies {
            if let ReferenceOr::Item(request_body) = request_body_ref {
                for media_type in request_body.content.values() {
                    if let Some(schema) = &media_type.schema {
                        let model_types =
                            parse_schema_to_model_type(name, schema, &components.schemas)?;
                        for model_type in model_types {
                            if added_models.insert(model_type.name().to_string()) {
                                models.push(model_type);
                            }
                        }
                    }
                }
            }
        }
    }

    // Parse paths
    for (_path, path_item) in openapi.paths.iter() {
        let path_item = match path_item {
            ReferenceOr::Item(item) => item,
            ReferenceOr::Reference { .. } => continue,
        };

        let operations = [
            &path_item.get,
            &path_item.post,
            &path_item.put,
            &path_item.delete,
            &path_item.patch,
        ];

        for op in operations.iter().filter_map(|o| o.as_ref()) {
            let inline_models =
                process_operation(op, &mut requests, &mut responses, schemas, request_bodies)?;
            for model_type in inline_models {
                if added_models.insert(model_type.name().to_string()) {
                    models.push(model_type);
                }
            }
        }
    }

    Ok((models, requests, responses))
}

fn process_operation(
    operation: &openapiv3::Operation,
    requests: &mut Vec<RequestModel>,
    responses: &mut Vec<ResponseModel>,
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
    request_bodies: &IndexMap<String, ReferenceOr<openapiv3::RequestBody>>,
) -> Result<Vec<ModelType>> {
    let mut inline_models = Vec::new();

    // Parse request body
    if let Some(request_body_ref) = &operation.request_body {
        let (request_body_data, is_inline) = match request_body_ref {
            ReferenceOr::Item(request_body) => (Some((request_body, request_body.required)), true),
            ReferenceOr::Reference { reference } => {
                if let Some(rb_name) = reference.strip_prefix("#/components/requestBodies/") {
                    (
                        request_bodies.get(rb_name).and_then(|rb_ref| match rb_ref {
                            ReferenceOr::Item(rb) => Some((rb, false)),
                            ReferenceOr::Reference { .. } => None,
                        }),
                        false,
                    )
                } else {
                    (None, false)
                }
            }
        };

        if let Some((request_body, is_required)) = request_body_data {
            for (content_type, media_type) in &request_body.content {
                if let Some(schema) = &media_type.schema {
                    let operation_name =
                        to_pascal_case(operation.operation_id.as_deref().unwrap_or("Unknown"));

                    let schema_type = if is_inline {
                        if let ReferenceOr::Item(schema_item) = schema {
                            if matches!(schema_item.schema_kind, SchemaKind::Type(Type::Object(_)))
                            {
                                let model_name = format!("{operation_name}RequestBody");
                                let model_types =
                                    parse_schema_to_model_type(&model_name, schema, all_schemas)?;
                                inline_models.extend(model_types);
                                model_name
                            } else {
                                extract_type_and_format(schema, all_schemas)?.0
                            }
                        } else {
                            extract_type_and_format(schema, all_schemas)?.0
                        }
                    } else {
                        extract_type_and_format(schema, all_schemas)?.0
                    };

                    let request = RequestModel {
                        name: format!("{operation_name}Request"),
                        content_type: content_type.clone(),
                        schema: schema_type,
                        is_required,
                    };
                    requests.push(request);
                }
            }
        }
    }

    // Parse responses
    for (status, response_ref) in operation.responses.responses.iter() {
        if let ReferenceOr::Item(response) = response_ref {
            for (content_type, media_type) in &response.content {
                if let Some(schema) = &media_type.schema {
                    let response = ResponseModel {
                        name: format!(
                            "{}Response",
                            to_pascal_case(operation.operation_id.as_deref().unwrap_or("Unknown"))
                        ),
                        status_code: status.to_string(),
                        content_type: content_type.clone(),
                        schema: extract_type_and_format(schema, all_schemas)?.0,
                        description: Some(response.description.clone()),
                    };
                    responses.push(response);
                }
            }
        }
    }
    Ok(inline_models)
}

fn parse_schema_to_model_type(
    name: &str,
    schema: &ReferenceOr<Schema>,
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<Vec<ModelType>> {
    match schema {
        ReferenceOr::Reference { .. } => Ok(Vec::new()),
        ReferenceOr::Item(schema) => {
            if let Some(rust_type) = schema.schema_data.extensions.get(X_RUST_TYPE) {
                if let Some(type_str) = rust_type.as_str() {
                    return Ok(vec![ModelType::TypeAlias(TypeAliasModel {
                        name: to_pascal_case(name),
                        target_type: type_str.to_string(),
                        description: schema.schema_data.description.clone(),
                        custom_attrs: extract_custom_attrs(schema),
                    })]);
                }
            }

            match &schema.schema_kind {
                // regular objects
                SchemaKind::Type(Type::Object(obj)) => {
                    // Special case: object with only additionalProperties (no regular properties)
                    if obj.properties.is_empty() && obj.additional_properties.is_some() {
                        let hashmap_type = match &obj.additional_properties {
                            Some(additional_props) => match additional_props {
                                openapiv3::AdditionalProperties::Any(_) => {
                                    "std::collections::HashMap<String, serde_json::Value>"
                                        .to_string()
                                }
                                openapiv3::AdditionalProperties::Schema(schema_ref) => {
                                    let (inner_type, _) =
                                        extract_type_and_format(schema_ref, all_schemas)?;
                                    format!("std::collections::HashMap<String, {inner_type}>")
                                }
                            },
                            None => {
                                "std::collections::HashMap<String, serde_json::Value>".to_string()
                            }
                        };
                        return Ok(vec![ModelType::TypeAlias(TypeAliasModel {
                            name: to_pascal_case(name),
                            target_type: hashmap_type,
                            description: schema.schema_data.description.clone(),
                            custom_attrs: extract_custom_attrs(schema),
                        })]);
                    }

                    let mut fields = Vec::new();
                    let mut inline_models = Vec::new();

                    // Process regular properties
                    for (field_name, field_schema) in &obj.properties {
                        if let ReferenceOr::Item(boxed_schema) = field_schema {
                            if matches!(boxed_schema.schema_kind, SchemaKind::Type(Type::Object(_)))
                            {
                                let struct_name = to_pascal_case(field_name);
                                let wrapped_schema = ReferenceOr::Item((**boxed_schema).clone());
                                let nested_models = parse_schema_to_model_type(
                                    &struct_name,
                                    &wrapped_schema,
                                    all_schemas,
                                )?;
                                inline_models.extend(nested_models);
                            }
                        }

                        let (field_info, inline_model) = match field_schema {
                            ReferenceOr::Item(boxed_schema) => extract_field_info(
                                name,
                                field_name,
                                &ReferenceOr::Item((**boxed_schema).clone()),
                                all_schemas,
                            )?,
                            ReferenceOr::Reference { reference } => extract_field_info(
                                name,
                                field_name,
                                &ReferenceOr::Reference {
                                    reference: reference.clone(),
                                },
                                all_schemas,
                            )?,
                        };
                        if let Some(inline_model) = inline_model {
                            inline_models.push(inline_model);
                        }
                        let is_required = obj.required.contains(field_name);
                        fields.push(Field {
                            name: field_name.clone(),
                            field_type: field_info.field_type,
                            format: field_info.format,
                            is_required,
                            is_array_ref: field_info.is_array_ref,
                            is_nullable: field_info.is_nullable,
                            description: field_info.description,
                            custom_attrs: field_info.custom_attrs,
                            validation_rules: field_info.validation_rules,
                        });
                    }

                    let mut models = inline_models;
                    if obj.properties.is_empty() && obj.additional_properties.is_none() {
                        models.push(ModelType::Struct(Model {
                            name: to_pascal_case(name),
                            fields: vec![],
                            custom_attrs: extract_custom_attrs(schema),
                            description: schema.schema_data.description.clone(),
                        }));
                    } else if !fields.is_empty() {
                        models.push(ModelType::Struct(Model {
                            name: to_pascal_case(name),
                            fields,
                            custom_attrs: extract_custom_attrs(schema),
                            description: schema.schema_data.description.clone(),
                        }));
                    }
                    Ok(models)
                }

                // allOf
                SchemaKind::AllOf { all_of } => {
                    let (all_fields, inline_models) =
                        resolve_all_of_fields(name, all_of, all_schemas)?;
                    let mut models = inline_models;

                    if !all_fields.is_empty() {
                        models.push(ModelType::Composition(CompositionModel {
                            name: to_pascal_case(name),
                            all_fields,
                            custom_attrs: extract_custom_attrs(schema),
                        }));
                    }

                    Ok(models)
                }

                // oneOf
                SchemaKind::OneOf { one_of } => {
                    let (variants, inline_models) =
                        resolve_union_variants(name, one_of, all_schemas)?;
                    let mut models = inline_models;

                    models.push(ModelType::Union(UnionModel {
                        name: to_pascal_case(name),
                        variants,
                        union_type: UnionType::OneOf,
                        custom_attrs: extract_custom_attrs(schema),
                    }));

                    Ok(models)
                }

                // anyOf
                SchemaKind::AnyOf { any_of } => {
                    let (variants, inline_models) =
                        resolve_union_variants(name, any_of, all_schemas)?;
                    let mut models = inline_models;

                    models.push(ModelType::Union(UnionModel {
                        name: to_pascal_case(name),
                        variants,
                        union_type: UnionType::AnyOf,
                        custom_attrs: extract_custom_attrs(schema),
                    }));

                    Ok(models)
                }

                // enum strings
                SchemaKind::Type(Type::String(string_type)) => {
                    if !string_type.enumeration.is_empty() {
                        let variants: Vec<String> = string_type
                            .enumeration
                            .iter()
                            .filter_map(|value| value.clone())
                            .collect();

                        if !variants.is_empty() {
                            let models = vec![ModelType::Enum(EnumModel {
                                name: to_pascal_case(name),
                                variants,
                                description: schema.schema_data.description.clone(),
                                custom_attrs: extract_custom_attrs(schema),
                            })];

                            return Ok(models);
                        }
                    }
                    Ok(Vec::new())
                }

                SchemaKind::Type(Type::Array(array)) => {
                    let mut models = Vec::new();
                    let array_name = to_pascal_case(name);

                    let items = match &array.items {
                        Some(items) => items,
                        None => return Ok(Vec::new()),
                    };

                    match items {
                        ReferenceOr::Item(item_schema) => match &item_schema.schema_kind {
                            SchemaKind::OneOf { one_of } => {
                                let item_type_name = format!("{array_name}Item");

                                let (variants, inline_models) =
                                    resolve_union_variants(&item_type_name, one_of, all_schemas)?;

                                models.extend(inline_models);

                                models.push(ModelType::Union(UnionModel {
                                    name: item_type_name.clone(),
                                    variants,
                                    union_type: UnionType::OneOf,
                                    custom_attrs: extract_custom_attrs(item_schema),
                                }));

                                models.push(ModelType::TypeAlias(TypeAliasModel {
                                    name: array_name,
                                    target_type: format!("Vec<{item_type_name}>"),
                                    description: schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(schema),
                                }));
                            }

                            SchemaKind::Type(Type::String(s)) if !s.enumeration.is_empty() => {
                                let item_type_name = format!("{array_name}Item");

                                let variants: Vec<String> =
                                    s.enumeration.iter().filter_map(|v| v.clone()).collect();

                                models.push(ModelType::Enum(EnumModel {
                                    name: item_type_name.clone(),
                                    variants,
                                    description: item_schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(item_schema),
                                }));

                                models.push(ModelType::TypeAlias(TypeAliasModel {
                                    name: array_name,
                                    target_type: format!("Vec<{item_type_name}>"),
                                    description: schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(schema),
                                }));
                            }

                            SchemaKind::Type(Type::Integer(n)) if !n.enumeration.is_empty() => {
                                let item_type_name = format!("{array_name}Item");

                                let variants: Vec<String> = n
                                    .enumeration
                                    .iter()
                                    .filter_map(|v| v.map(|num| format!("Value{num}")))
                                    .collect();

                                models.push(ModelType::Enum(EnumModel {
                                    name: item_type_name.clone(),
                                    variants,
                                    description: item_schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(item_schema),
                                }));

                                models.push(ModelType::TypeAlias(TypeAliasModel {
                                    name: array_name,
                                    target_type: format!("Vec<{item_type_name}>"),
                                    description: schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(schema),
                                }));
                            }

                            _ => {
                                let normalized_items = match items {
                                    ReferenceOr::Item(boxed_schema) => {
                                        ReferenceOr::Item((**boxed_schema).clone())
                                    }
                                    ReferenceOr::Reference { reference } => {
                                        ReferenceOr::Reference {
                                            reference: reference.clone(),
                                        }
                                    }
                                };

                                let (inner_type, _) =
                                    extract_type_and_format(&normalized_items, all_schemas)?;

                                models.push(ModelType::TypeAlias(TypeAliasModel {
                                    name: array_name,
                                    target_type: format!("Vec<{inner_type}>"),
                                    description: schema.schema_data.description.clone(),
                                    custom_attrs: extract_custom_attrs(schema),
                                }));
                            }
                        },

                        ReferenceOr::Reference { .. } => {
                            let normalized_items = match items {
                                ReferenceOr::Item(boxed_schema) => {
                                    ReferenceOr::Item((**boxed_schema).clone())
                                }
                                ReferenceOr::Reference { reference } => ReferenceOr::Reference {
                                    reference: reference.clone(),
                                },
                            };

                            let (inner_type, _) =
                                extract_type_and_format(&normalized_items, all_schemas)?;

                            models.push(ModelType::TypeAlias(TypeAliasModel {
                                name: array_name,
                                target_type: format!("Vec<{inner_type}>"),
                                description: schema.schema_data.description.clone(),
                                custom_attrs: extract_custom_attrs(schema),
                            }));
                        }
                    }

                    Ok(models)
                }

                _ => Ok(Vec::new()),
            }
        }
    }
}

fn extract_validation_rules(schema: &Schema) -> Option<crate::models::ValidationRules> {
    use crate::models::ValidationRules;

    let mut rules = ValidationRules::default();

    // Extract type-specific validation rules
    match &schema.schema_kind {
        openapiv3::SchemaKind::Type(openapiv3::Type::String(string_type)) => {
            // Extract format-based validation rules for strings
            match &string_type.format {
                openapiv3::VariantOrUnknownOrEmpty::Item(_fmt) => {
                    // Standard formats like DateTime, Date are handled elsewhere
                    // For email/url validation, rely on Unknown format strings
                }
                openapiv3::VariantOrUnknownOrEmpty::Unknown(unknown_format) => {
                    match unknown_format.to_lowercase().as_str() {
                        "email" => rules.email = true,
                        "uri" | "url" => rules.url = true,
                        _ => {}
                    }
                }
                _ => {}
            }

            // Extract string-specific validation rules
            rules.min_length = string_type.min_length;
            rules.max_length = string_type.max_length;
            rules.pattern = string_type.pattern.clone();
        }
        openapiv3::SchemaKind::Type(openapiv3::Type::Integer(integer_type)) => {
            rules.minimum = integer_type.minimum.map(|v| v as f64);
            rules.maximum = integer_type.maximum.map(|v| v as f64);
            rules.exclusive_minimum = integer_type.exclusive_minimum;
            rules.exclusive_maximum = integer_type.exclusive_maximum;
            rules.multiple_of = integer_type.multiple_of.map(|v| v as f64);
        }
        openapiv3::SchemaKind::Type(openapiv3::Type::Number(number_type)) => {
            rules.minimum = number_type.minimum;
            rules.maximum = number_type.maximum;
            rules.exclusive_minimum = number_type.exclusive_minimum;
            rules.exclusive_maximum = number_type.exclusive_maximum;
            rules.multiple_of = number_type.multiple_of;
        }
        openapiv3::SchemaKind::Type(openapiv3::Type::Array(array_type)) => {
            rules.min_items = array_type.min_items;
            rules.max_items = array_type.max_items;
            rules.unique_items = array_type.unique_items;
        }
        _ => {}
    }

    if rules.has_any() {
        Some(rules)
    } else {
        None
    }
}

fn extract_type_and_format(
    schema: &ReferenceOr<Schema>,
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<(String, String)> {
    match schema {
        ReferenceOr::Reference { reference } => {
            let type_name = reference.split('/').next_back().unwrap_or("Unknown");

            if let Some(ReferenceOr::Item(schema)) = all_schemas.get(type_name) {
                if matches!(schema.schema_kind, SchemaKind::OneOf { .. }) {
                    return Ok((to_pascal_case(type_name), "oneOf".to_string()));
                }
            }
            Ok((to_pascal_case(type_name), "reference".to_string()))
        }

        ReferenceOr::Item(schema) => match &schema.schema_kind {
            SchemaKind::Type(Type::String(string_type)) => match &string_type.format {
                VariantOrUnknownOrEmpty::Item(fmt) => match fmt {
                    StringFormat::DateTime => {
                        Ok(("DateTime<Utc>".to_string(), "date-time".to_string()))
                    }
                    StringFormat::Date => Ok(("NaiveDate".to_string(), "date".to_string())),
                    _ => Ok(("String".to_string(), format!("{fmt:?}"))),
                },
                VariantOrUnknownOrEmpty::Unknown(unknown_format) => {
                    if unknown_format.to_lowercase() == "uuid" {
                        Ok(("Uuid".to_string(), "uuid".to_string()))
                    } else {
                        Ok(("String".to_string(), unknown_format.clone()))
                    }
                }
                _ => Ok(("String".to_string(), "string".to_string())),
            },
            SchemaKind::Type(Type::Integer(_)) => Ok(("i64".to_string(), "integer".to_string())),
            SchemaKind::Type(Type::Number(_)) => Ok(("f64".to_string(), "number".to_string())),
            SchemaKind::Type(Type::Boolean(_)) => Ok(("bool".to_string(), "boolean".to_string())),
            SchemaKind::Type(Type::Array(arr)) => {
                if let Some(items) = &arr.items {
                    match items {
                        ReferenceOr::Item(boxed_schema) => extract_type_and_format(
                            &ReferenceOr::Item((**boxed_schema).clone()),
                            all_schemas,
                        ),

                        ReferenceOr::Reference { reference } => extract_type_and_format(
                            &ReferenceOr::Reference {
                                reference: reference.clone(),
                            },
                            all_schemas,
                        ),
                    }
                } else {
                    Ok(("serde_json::Value".to_string(), "array".to_string()))
                }
            }
            SchemaKind::Type(Type::Object(_obj)) => {
                Ok(("serde_json::Value".to_string(), "object".to_string()))
            }
            _ => Ok(("serde_json::Value".to_string(), "unknown".to_string())),
        },
    }
}

/// Extracts field information including type, format, and nullable flag from OpenAPI schema
fn extract_field_info(
    parent_name: &str,
    field_name: &str,
    schema: &ReferenceOr<Schema>,
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<(FieldInfo, Option<ModelType>)> {
    let (mut field_type, format) = extract_type_and_format(schema, all_schemas)?;

    let (is_nullable, is_array_ref, en, description, custom_attrs, validation_rules) = match schema
    {
        ReferenceOr::Reference { reference } => {
            let is_array_ref = false;
            let mut is_nullable = false;
            let mut validation_rules = None;

            if let Some(type_name) = reference.strip_prefix("#/components/schemas/") {
                if let Some(ReferenceOr::Item(schema)) = all_schemas.get(type_name) {
                    is_nullable = schema.schema_data.nullable;
                    // x-rust-attrs on the referenced schema are type-level attributes
                    // already applied to that type's own definition. Do not propagate
                    // them to the field that references it.
                    validation_rules = extract_validation_rules(schema);
                }
            }

            (
                is_nullable,
                is_array_ref,
                None,
                None,
                None,
                validation_rules,
            )
        }

        ReferenceOr::Item(schema) => {
            if let Some(rust_type) = schema.schema_data.extensions.get(X_RUST_TYPE) {
                if let Some(type_str) = rust_type.as_str() {
                    field_type = type_str.to_string();
                }
            }

            let is_nullable = schema.schema_data.nullable;
            let is_array_ref = matches!(schema.schema_kind, SchemaKind::Type(Type::Array(_)));
            let description = schema.schema_data.description.clone();
            let validation_rules = extract_validation_rules(schema);

            let maybe_enum = match &schema.schema_kind {
                SchemaKind::Type(Type::String(s)) if !s.enumeration.is_empty() => {
                    let variants: Vec<String> =
                        s.enumeration.iter().filter_map(|v| v.clone()).collect();
                    let enum_name = format!("{}{}", parent_name, to_pascal_case(field_name));
                    field_type = enum_name.clone();
                    Some(ModelType::Enum(EnumModel {
                        name: enum_name,
                        variants,
                        description: schema.schema_data.description.clone(),
                        custom_attrs: extract_custom_attrs(schema),
                    }))
                }
                SchemaKind::Type(Type::Object(obj)) => {
                    if obj.properties.is_empty() {
                        if let Some(additional_props) = &obj.additional_properties {
                            match additional_props {
                                AdditionalProperties::Schema(schema) => {
                                    let (value_type, _) =
                                        extract_type_and_format(&schema.clone(), all_schemas)?;

                                    field_type = format!(
                                        "std::collections::HashMap<String, {}>",
                                        value_type
                                    );
                                }

                                AdditionalProperties::Any(true) => {
                                    field_type =
                                        "std::collections::HashMap<String, serde_json::Value>"
                                            .to_string();
                                }

                                AdditionalProperties::Any(false) => {
                                    // technically: no additional props allowed
                                    field_type = "serde_json::Value".to_string();
                                }
                            }
                            None
                        } else {
                            field_type = "serde_json::Value".to_string();
                            None
                        }
                    } else {
                        let struct_name = to_pascal_case(field_name);
                        field_type = struct_name.clone();

                        let wrapped_schema = ReferenceOr::Item(schema.clone());
                        let models =
                            parse_schema_to_model_type(&struct_name, &wrapped_schema, all_schemas)?;

                        models
                            .into_iter()
                            .find(|m| matches!(m, ModelType::Struct(_)))
                    }
                }
                _ => None,
            };
            // When an inline enum is generated from this field, x-rust-attrs belong
            // on the enum type (already captured in the EnumModel above). Don't
            // also emit them as struct field attributes.
            let field_custom_attrs = if maybe_enum.is_some() {
                None
            } else {
                extract_custom_attrs(schema)
            };
            (
                is_nullable,
                is_array_ref,
                maybe_enum,
                description,
                field_custom_attrs,
                validation_rules,
            )
        }
    };

    Ok((
        FieldInfo {
            field_type,
            format,
            is_nullable,
            is_array_ref,
            description,
            custom_attrs,
            validation_rules,
        },
        en,
    ))
}

fn resolve_all_of_fields(
    name: &str,
    all_of: &[ReferenceOr<Schema>],
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<(Vec<Field>, Vec<ModelType>)> {
    let mut all_fields: IndexMap<String, Field> = IndexMap::new();
    let mut models = Vec::new();
    let mut all_required_fields = HashSet::new();

    for schema_ref in all_of {
        let schema_to_check = match schema_ref {
            ReferenceOr::Reference { reference } => reference
                .strip_prefix("#/components/schemas/")
                .and_then(|schema_name| all_schemas.get(schema_name)),
            ReferenceOr::Item(_) => Some(schema_ref),
        };

        if let Some(ReferenceOr::Item(schema)) = schema_to_check {
            if let SchemaKind::Type(Type::Object(obj)) = &schema.schema_kind {
                all_required_fields.extend(obj.required.iter().cloned());
            }
        }
    }

    // Primitive Rust types that a base schema may use as a placeholder. A later
    // allOf component that re-declares the same field with a different type is
    // narrowing the field (e.g. a plain `string` base narrowed to a string enum),
    // so the more specific incoming type should win.
    const PRIMITIVE_TYPES: &[&str] = &["String", "i64", "f64", "bool"];

    // Try hard to replace all_fields entries that are serde_json::Value or a
    // primitive placeholder with a more specific type provided by a later allOf
    // component.
    // Notes:
    //  - Most of the substitions are fairly straightforward, Value, Optional Value.
    //  - HashMap is more complex to understand, we are replacing a Value HashMap
    //    with an actual structure type
    //  - A base schema may declare a field as a primitive (e.g. `String`) while a
    //    composing schema narrows it to a named type (e.g. an inline string enum).
    //    The named type (more specific) wins.
    fn less_value(fields: Vec<Field>, all_fields: &mut IndexMap<String, Field>) {
        for field in fields {
            if let Some(existing_field) = all_fields.get_mut(&field.name) {
                // Value
                if existing_field.field_type == "serde_json::Value" {
                    *existing_field = field;
                } else if existing_field.field_type == "Option<serde_json::Value>" {
                    existing_field.field_type = format!("Option<{}>", field.field_type);
                // HashMap Value
                } else if existing_field.field_type
                    == "std::collections::HashMap<String, serde_json::Value>"
                {
                    *existing_field = field;
                } else if existing_field.field_type
                    == "Option<std::collections::HashMap<String, serde_json::Value>>"
                {
                    existing_field.field_type = format!("Option<{}>", field.field_type);
                // Vec Value
                } else if existing_field.field_type == "Vec<serde_json::Value>" {
                    existing_field.field_type = format!("Vec<{}>", field.field_type);
                } else if existing_field.field_type == "Option<Vec<serde_json::Value>>" {
                    existing_field.field_type = format!("Option<Vec<{}>>", field.field_type);
                // Primitive narrowed to a more specific named type by a later
                // allOf component (e.g. `String` -> a string enum type).
                // serde_json::Value is a generic fallback, not a narrowing -
                // a primitive must not be replaced by something less specific.
                } else if PRIMITIVE_TYPES.contains(&existing_field.field_type.as_str())
                    && !PRIMITIVE_TYPES.contains(&field.field_type.as_str())
                    && field.field_type != "serde_json::Value"
                {
                    existing_field.field_type = field.field_type;
                }
            } else {
                all_fields.insert(field.name.clone(), field);
            }
        }
    }

    // Now collect fields from all schemas
    for schema_ref in all_of {
        match schema_ref {
            ReferenceOr::Reference { reference } => {
                if let Some(schema_name) = reference.strip_prefix("#/components/schemas/") {
                    if let Some(referenced_schema) = all_schemas.get(schema_name) {
                        let (fields, inline_models) =
                            extract_fields_from_schema(name, referenced_schema, all_schemas)?;
                        // If we have an all_fields entry that is of type serde_json::Value, then we should replace it.
                        less_value(fields, &mut all_fields);
                        models.extend(inline_models);
                    }
                }
            }
            ReferenceOr::Item(_schema) => {
                let (fields, inline_models) =
                    extract_fields_from_schema(name, schema_ref, all_schemas)?;
                // If we have an all_fields entry that is of type serde_json::Value, then we should replace it.
                less_value(fields, &mut all_fields);
                models.extend(inline_models);
            }
        }
    }

    // Update is_required for fields based on the merged required set
    for field in all_fields.values_mut() {
        if all_required_fields.contains(&field.name) {
            field.is_required = true;
        }
    }

    Ok((all_fields.into_values().collect(), models))
}

fn resolve_union_variants(
    name: &str,
    schemas: &[ReferenceOr<Schema>],
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<(Vec<UnionVariant>, Vec<ModelType>)> {
    use std::collections::BTreeSet;

    let mut variants = Vec::new();
    let mut models = Vec::new();
    let mut enum_values: BTreeSet<String> = BTreeSet::new();
    let mut is_all_simple_enum = true;

    for schema_ref in schemas {
        let resolved = match schema_ref {
            ReferenceOr::Reference { reference } => reference
                .strip_prefix("#/components/schemas/")
                .and_then(|n| all_schemas.get(n)),
            ReferenceOr::Item(_) => Some(schema_ref),
        };

        let Some(resolved_schema) = resolved else {
            is_all_simple_enum = false;
            continue;
        };

        match resolved_schema {
            ReferenceOr::Item(schema) => match &schema.schema_kind {
                SchemaKind::Type(Type::String(s)) if !s.enumeration.is_empty() => {
                    enum_values.extend(s.enumeration.iter().filter_map(|v| v.as_ref().cloned()));
                }
                SchemaKind::Type(Type::Integer(n)) if !n.enumeration.is_empty() => {
                    enum_values.extend(
                        n.enumeration
                            .iter()
                            .filter_map(|v| v.map(|num| format!("Value{num}"))),
                    );
                }

                _ => is_all_simple_enum = false,
            },
            ReferenceOr::Reference { reference } => {
                if let Some(n) = reference.strip_prefix("#/components/schemas/") {
                    if let Some(ReferenceOr::Item(inner)) = all_schemas.get(n) {
                        if let SchemaKind::Type(Type::String(s)) = &inner.schema_kind {
                            let values: Vec<String> = s
                                .enumeration
                                .iter()
                                .filter_map(|v| v.as_ref().cloned())
                                .collect();
                            enum_values.extend(values);
                        } else {
                            is_all_simple_enum = false;
                        }
                    }
                }
            }
        }
    }
    if is_all_simple_enum && !enum_values.is_empty() {
        let enum_name = to_pascal_case(name);
        let enum_model = ModelType::Enum(EnumModel {
            name: enum_name.clone(),
            variants: enum_values.iter().map(|v| to_pascal_case(v)).collect(),
            description: None,
            custom_attrs: None, // Collective enum from multiple schemas, no single source for attrs
        });

        return Ok((vec![], vec![enum_model]));
    }

    // fallback for usual union-schemas
    for (index, schema_ref) in schemas.iter().enumerate() {
        match schema_ref {
            ReferenceOr::Reference { reference } => {
                if let Some(schema_name) = reference.strip_prefix("#/components/schemas/") {
                    if let Some(referenced_schema) = all_schemas.get(schema_name) {
                        if let ReferenceOr::Item(schema) = referenced_schema {
                            if matches!(schema.schema_kind, SchemaKind::OneOf { .. }) {
                                variants.push(UnionVariant {
                                    name: to_pascal_case(schema_name),
                                    fields: vec![],
                                    primitive_type: None,
                                });
                            } else {
                                let (fields, inline_models) = extract_fields_from_schema(
                                    schema_name,
                                    referenced_schema,
                                    all_schemas,
                                )?;
                                variants.push(UnionVariant {
                                    name: to_pascal_case(schema_name),
                                    fields,
                                    primitive_type: None,
                                });
                                models.extend(inline_models);
                            }
                        }
                    }
                }
            }
            ReferenceOr::Item(schema) => match &schema.schema_kind {
                SchemaKind::Type(Type::String(_)) => {
                    variants.push(UnionVariant {
                        name: "String".to_string(),
                        fields: vec![],
                        primitive_type: Some("String".to_string()),
                    });
                }

                SchemaKind::Type(Type::Integer(_)) => {
                    variants.push(UnionVariant {
                        name: "Integer".to_string(),
                        fields: vec![],
                        primitive_type: Some("i64".to_string()),
                    });
                }

                SchemaKind::Type(Type::Number(_)) => {
                    variants.push(UnionVariant {
                        name: "Number".to_string(),
                        fields: vec![],
                        primitive_type: Some("f64".to_string()),
                    });
                }

                SchemaKind::Type(Type::Boolean(_)) => {
                    variants.push(UnionVariant {
                        name: "Boolean".to_string(),
                        fields: vec![],
                        primitive_type: Some("Boolean".to_string()),
                    });
                }

                _ => {
                    let (fields, inline_models) =
                        extract_fields_from_schema(name, schema_ref, all_schemas)?;
                    let variant_name = format!("Variant{index}");
                    variants.push(UnionVariant {
                        name: variant_name,
                        fields,
                        primitive_type: None,
                    });
                    models.extend(inline_models);
                }
            },
        }
    }

    Ok((variants, models))
}

fn extract_fields_from_schema(
    parent_name: &str,
    schema_ref: &ReferenceOr<Schema>,
    all_schemas: &IndexMap<String, ReferenceOr<Schema>>,
) -> Result<(Vec<Field>, Vec<ModelType>)> {
    let mut fields = Vec::new();
    let mut inline_models = Vec::new();

    match schema_ref {
        ReferenceOr::Reference { .. } => Ok((fields, inline_models)),
        ReferenceOr::Item(schema) => {
            match &schema.schema_kind {
                SchemaKind::Type(Type::Object(obj)) => {
                    for (field_name, field_schema) in &obj.properties {
                        let (field_info, inline_model) = match field_schema {
                            ReferenceOr::Item(boxed_schema) => extract_field_info(
                                parent_name,
                                field_name,
                                &ReferenceOr::Item((**boxed_schema).clone()),
                                all_schemas,
                            )?,
                            ReferenceOr::Reference { reference } => extract_field_info(
                                parent_name,
                                field_name,
                                &ReferenceOr::Reference {
                                    reference: reference.clone(),
                                },
                                all_schemas,
                            )?,
                        };

                        let is_nullable = field_info.is_nullable
                            || field_name == "value"
                            || field_name == "default_value";

                        let field_type = field_info.field_type.clone();

                        let is_required = obj.required.contains(field_name);
                        fields.push(Field {
                            name: field_name.clone(),
                            field_type,
                            format: field_info.format,
                            is_required,
                            is_nullable,
                            is_array_ref: field_info.is_array_ref,
                            description: field_info.description,
                            custom_attrs: field_info.custom_attrs,
                            validation_rules: field_info.validation_rules,
                        });
                        if let Some(inline_model) = inline_model {
                            match &inline_model {
                                ModelType::Struct(m) if m.fields.is_empty() => {}
                                _ => inline_models.push(inline_model),
                            }
                        }
                    }
                }
                SchemaKind::Type(Type::String(s)) if !s.enumeration.is_empty() => {
                    let name = schema
                        .schema_data
                        .title
                        .clone()
                        .unwrap_or_else(|| "AnonymousStringEnum".to_string());

                    let enum_model = ModelType::Enum(EnumModel {
                        name,
                        variants: s
                            .enumeration
                            .iter()
                            .filter_map(|v| v.as_ref().map(|s| to_pascal_case(s)))
                            .collect(),
                        description: schema.schema_data.description.clone(),
                        custom_attrs: extract_custom_attrs(schema),
                    });

                    inline_models.push(enum_model);
                }
                SchemaKind::Type(Type::Integer(n)) if !n.enumeration.is_empty() => {
                    let name = schema
                        .schema_data
                        .title
                        .clone()
                        .unwrap_or_else(|| "AnonymousIntEnum".to_string());

                    let enum_model = ModelType::Enum(EnumModel {
                        name,
                        variants: n
                            .enumeration
                            .iter()
                            .filter_map(|v| v.map(|num| format!("Value{num}")))
                            .collect(),
                        description: schema.schema_data.description.clone(),
                        custom_attrs: extract_custom_attrs(schema),
                    });

                    inline_models.push(enum_model);
                }

                _ => {}
            }

            Ok((fields, inline_models))
        }
    }
}

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

    #[test]
    fn test_parse_inline_request_body_generates_model() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {
                "/items": {
                    "post": {
                        "operationId": "createItem",
                        "requestBody": {
                            "content": {
                                "application/json": {
                                    "schema": {
                                        "type": "object",
                                        "properties": {
                                            "name": { "type": "string" },
                                            "value": { "type": "integer" }
                                        },
                                        "required": ["name"]
                                    }
                                }
                            }
                        },
                        "responses": { "200": { "description": "OK" } }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, requests, _responses) =
            parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // 1. Verify that request model was created
        assert_eq!(requests.len(), 1);
        let request_model = &requests[0];
        assert_eq!(request_model.name, "CreateItemRequest");

        // 2. Verify that request schema references a NEW model, not Value
        assert_eq!(request_model.schema, "CreateItemRequestBody");

        // 3. Verify that the request body model itself was generated
        let inline_model = models.iter().find(|m| m.name() == "CreateItemRequestBody");
        assert!(
            inline_model.is_some(),
            "Expected a model named 'CreateItemRequestBody' to be generated"
        );

        if let Some(ModelType::Struct(model)) = inline_model {
            assert_eq!(model.fields.len(), 2);
            assert_eq!(model.fields[0].name, "name");
            assert_eq!(model.fields[0].field_type, "String");
            assert!(model.fields[0].is_required);

            assert_eq!(model.fields[1].name, "value");
            assert_eq!(model.fields[1].field_type, "i64");
            assert!(!model.fields[1].is_required);
        } else {
            panic!("Expected a Struct model for CreateItemRequestBody");
        }
    }

    #[test]
    fn test_parse_ref_request_body_works() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "components": {
                "schemas": {
                    "ItemData": {
                        "type": "object",
                        "properties": {
                            "name": { "type": "string" }
                        }
                    }
                },
                "requestBodies": {
                    "CreateItem": {
                        "content": {
                            "application/json": {
                                "schema": { "$ref": "#/components/schemas/ItemData" }
                            }
                        }
                    }
                }
            },
            "paths": {
                "/items": {
                    "post": {
                        "operationId": "createItem",
                        "requestBody": { "$ref": "#/components/requestBodies/CreateItem" },
                        "responses": { "200": { "description": "OK" } }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, requests, _responses) =
            parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Verify that request model was created
        assert_eq!(requests.len(), 1);
        let request_model = &requests[0];
        assert_eq!(request_model.name, "CreateItemRequest");

        // Verify that schema references an existing model
        assert_eq!(request_model.schema, "ItemData");

        // Verify that ItemData model exists in the models list
        assert!(models.iter().any(|m| m.name() == "ItemData"));
    }

    #[test]
    fn test_parse_no_request_body() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {
                "/items": {
                    "get": {
                        "operationId": "listItems",
                        "responses": { "200": { "description": "OK" } }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (_models, requests, _responses) =
            parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Verify that no request models were created
        assert!(requests.is_empty());
    }

    #[test]
    fn test_nullable_reference_field() {
        // Test verifies that nullable is correctly read from the target schema when using $ref
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "NullableUser": {
                        "type": "object",
                        "nullable": true,
                        "properties": {
                            "name": { "type": "string" }
                        }
                    },
                    "Post": {
                        "type": "object",
                        "properties": {
                            "author": {
                                "$ref": "#/components/schemas/NullableUser"
                            }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Find Post model
        let post_model = models.iter().find(|m| m.name() == "Post");
        assert!(post_model.is_some(), "Expected Post model to be generated");

        if let Some(ModelType::Struct(post)) = post_model {
            let author_field = post.fields.iter().find(|f| f.name == "author");
            assert!(author_field.is_some(), "Expected author field");

            // Verify that nullable is correctly handled for reference type
            // (nullable is taken from the target schema NullableUser)
            let author = author_field.unwrap();
            assert!(
                author.is_nullable,
                "Expected author field to be nullable (from referenced schema)"
            );
        } else {
            panic!("Expected Post to be a Struct");
        }
    }

    #[test]
    fn test_allof_required_fields_merge() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "BaseEntity": {
                        "type": "object",
                        "properties": {
                            "id": { "type": "string" },
                            "created": { "type": "string" }
                        },
                        "required": ["id"]
                    },
                    "Person": {
                        "allOf": [
                            { "$ref": "#/components/schemas/BaseEntity" },
                            {
                                "type": "object",
                                "properties": {
                                    "name": { "type": "string" },
                                    "age": { "type": "integer" }
                                },
                                "required": ["name"]
                            }
                        ]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Find Person model
        let person_model = models.iter().find(|m| m.name() == "Person");
        assert!(
            person_model.is_some(),
            "Expected Person model to be generated"
        );

        if let Some(ModelType::Composition(person)) = person_model {
            // Verify that id (from BaseEntity) is required
            let id_field = person.all_fields.iter().find(|f| f.name == "id");
            assert!(id_field.is_some(), "Expected id field");
            assert!(
                id_field.unwrap().is_required,
                "Expected id to be required from BaseEntity"
            );

            // Verify that name (from second object) is required
            let name_field = person.all_fields.iter().find(|f| f.name == "name");
            assert!(name_field.is_some(), "Expected name field");
            assert!(
                name_field.unwrap().is_required,
                "Expected name to be required from inline object"
            );

            // Verify that created and age are not required
            let created_field = person.all_fields.iter().find(|f| f.name == "created");
            assert!(created_field.is_some(), "Expected created field");
            assert!(
                !created_field.unwrap().is_required,
                "Expected created to be optional"
            );

            let age_field = person.all_fields.iter().find(|f| f.name == "age");
            assert!(age_field.is_some(), "Expected age field");
            assert!(
                !age_field.unwrap().is_required,
                "Expected age to be optional"
            );
        } else {
            panic!("Expected Person to be a Composition");
        }
    }

    #[test]
    fn test_x_rust_type_generates_type_alias() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "User": {
                        "type": "object",
                        "x-rust-type": "crate::domain::User",
                        "description": "Custom domain user type",
                        "properties": {
                            "name": { "type": "string" },
                            "age": { "type": "integer" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Verify that TypeAlias is created, not Struct
        let user_model = models.iter().find(|m| m.name() == "User");
        assert!(user_model.is_some(), "Expected User model");

        match user_model.unwrap() {
            ModelType::TypeAlias(alias) => {
                assert_eq!(alias.name, "User");
                assert_eq!(alias.target_type, "crate::domain::User");
                assert_eq!(
                    alias.description,
                    Some("Custom domain user type".to_string())
                );
            }
            _ => panic!("Expected TypeAlias, got different type"),
        }
    }

    #[test]
    fn test_x_rust_type_works_with_enum() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Status": {
                        "type": "string",
                        "enum": ["active", "inactive"],
                        "x-rust-type": "crate::domain::Status"
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let status_model = models.iter().find(|m| m.name() == "Status");
        assert!(status_model.is_some(), "Expected Status model");

        // Should be TypeAlias, not Enum
        assert!(
            matches!(status_model.unwrap(), ModelType::TypeAlias(_)),
            "Expected TypeAlias for enum with x-rust-type"
        );
    }

    #[test]
    fn test_x_rust_type_works_with_oneof() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Payment": {
                        "oneOf": [
                            { "type": "object", "properties": { "card": { "type": "string" } } },
                            { "type": "object", "properties": { "cash": { "type": "number" } } }
                        ],
                        "x-rust-type": "payments::Payment"
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let payment_model = models.iter().find(|m| m.name() == "Payment");
        assert!(payment_model.is_some(), "Expected Payment model");

        // Should be TypeAlias, not Union
        match payment_model.unwrap() {
            ModelType::TypeAlias(alias) => {
                assert_eq!(alias.target_type, "payments::Payment");
            }
            _ => panic!("Expected TypeAlias for oneOf with x-rust-type"),
        }
    }

    #[test]
    fn test_x_rust_attrs_on_struct() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "User": {
                        "type": "object",
                        "x-rust-attrs": [
                            "#[derive(Serialize, Deserialize)]",
                            "#[serde(rename_all = \"camelCase\")]"
                        ],
                        "properties": {
                            "name": { "type": "string" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let user_model = models.iter().find(|m| m.name() == "User");
        assert!(user_model.is_some(), "Expected User model");

        match user_model.unwrap() {
            ModelType::Struct(model) => {
                assert!(model.custom_attrs.is_some(), "Expected custom_attrs");
                let attrs = model.custom_attrs.as_ref().unwrap();
                assert_eq!(attrs.len(), 2);
                assert_eq!(attrs[0], "#[derive(Serialize, Deserialize)]");
                assert_eq!(attrs[1], "#[serde(rename_all = \"camelCase\")]");
            }
            _ => panic!("Expected Struct model"),
        }
    }

    #[test]
    fn test_x_rust_attrs_on_enum() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Status": {
                        "type": "string",
                        "enum": ["active", "inactive"],
                        "x-rust-attrs": ["#[serde(rename_all = \"UPPERCASE\")]"]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let status_model = models.iter().find(|m| m.name() == "Status");
        assert!(status_model.is_some(), "Expected Status model");

        match status_model.unwrap() {
            ModelType::Enum(enum_model) => {
                assert!(enum_model.custom_attrs.is_some());
                let attrs = enum_model.custom_attrs.as_ref().unwrap();
                assert_eq!(attrs.len(), 1);
                assert_eq!(attrs[0], "#[serde(rename_all = \"UPPERCASE\")]");
            }
            _ => panic!("Expected Enum model"),
        }
    }

    #[test]
    fn test_x_rust_attrs_with_x_rust_type() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "User": {
                        "type": "object",
                        "x-rust-type": "crate::domain::User",
                        "x-rust-attrs": ["#[cfg_attr(test, derive(Default))]"],
                        "properties": {
                            "name": { "type": "string" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let user_model = models.iter().find(|m| m.name() == "User");
        assert!(user_model.is_some(), "Expected User model");

        // Should be TypeAlias with attributes
        match user_model.unwrap() {
            ModelType::TypeAlias(alias) => {
                assert_eq!(alias.target_type, "crate::domain::User");
                assert!(alias.custom_attrs.is_some());
                let attrs = alias.custom_attrs.as_ref().unwrap();
                assert_eq!(attrs.len(), 1);
                assert_eq!(attrs[0], "#[cfg_attr(test, derive(Default))]");
            }
            _ => panic!("Expected TypeAlias with custom attrs"),
        }
    }

    #[test]
    fn test_x_rust_attrs_empty_array() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "User": {
                        "type": "object",
                        "x-rust-attrs": [],
                        "properties": {
                            "name": { "type": "string" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let user_model = models.iter().find(|m| m.name() == "User");
        assert!(user_model.is_some());

        match user_model.unwrap() {
            ModelType::Struct(model) => {
                // Empty array should result in None
                assert!(model.custom_attrs.is_none());
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_x_rust_type_on_string_property() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Document": {
                        "type": "object",
                        "description": "Document with custom version type",
                        "properties": {
                            "title": { "type": "string", "description": "Document title." },
                            "content": { "type": "string", "description": "Document content." },
                            "version": {
                                "type": "string",
                                "format": "semver",
                                "x-rust-type": "semver::Version",
                                "description": "Semantic version."
                            }
                        },
                        "required": ["title", "content", "version"]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let document_model = models.iter().find(|m| m.name() == "Document");
        assert!(document_model.is_some(), "Expected Document model");

        match document_model.unwrap() {
            ModelType::Struct(model) => {
                // Verify that version field has custom type
                let version_field = model.fields.iter().find(|f| f.name == "version");
                assert!(version_field.is_some(), "Expected version field");
                assert_eq!(version_field.unwrap().field_type, "semver::Version");

                // Verify other fields have regular types
                let title_field = model.fields.iter().find(|f| f.name == "title");
                assert_eq!(title_field.unwrap().field_type, "String");

                let content_field = model.fields.iter().find(|f| f.name == "content");
                assert_eq!(content_field.unwrap().field_type, "String");
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_x_rust_type_on_integer_property() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Configuration": {
                        "type": "object",
                        "description": "Configuration with custom duration type",
                        "properties": {
                            "timeout": {
                                "type": "integer",
                                "x-rust-type": "std::time::Duration",
                                "description": "Timeout duration."
                            },
                            "retries": { "type": "integer" }
                        },
                        "required": ["timeout", "retries"]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let config_model = models.iter().find(|m| m.name() == "Configuration");
        assert!(config_model.is_some(), "Expected Configuration model");

        match config_model.unwrap() {
            ModelType::Struct(model) => {
                // Verify that timeout field has custom type
                let timeout_field = model.fields.iter().find(|f| f.name == "timeout");
                assert!(timeout_field.is_some(), "Expected timeout field");
                assert_eq!(timeout_field.unwrap().field_type, "std::time::Duration");

                // Verify other field has regular i64 type
                let retries_field = model.fields.iter().find(|f| f.name == "retries");
                assert_eq!(retries_field.unwrap().field_type, "i64");
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_x_rust_type_on_number_property() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Product": {
                        "type": "object",
                        "description": "Product with custom decimal type",
                        "properties": {
                            "price": {
                                "type": "number",
                                "x-rust-type": "decimal::Decimal",
                                "description": "Product price."
                            },
                            "quantity": { "type": "number" }
                        },
                        "required": ["price", "quantity"]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let product_model = models.iter().find(|m| m.name() == "Product");
        assert!(product_model.is_some(), "Expected Product model");

        match product_model.unwrap() {
            ModelType::Struct(model) => {
                // Verify that price field has custom type
                let price_field = model.fields.iter().find(|f| f.name == "price");
                assert!(price_field.is_some(), "Expected price field");
                assert_eq!(price_field.unwrap().field_type, "decimal::Decimal");

                // Verify other field has regular f64 type
                let quantity_field = model.fields.iter().find(|f| f.name == "quantity");
                assert_eq!(quantity_field.unwrap().field_type, "f64");
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_x_rust_type_on_nullable_property() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Settings": {
                        "type": "object",
                        "description": "Settings with nullable custom type",
                        "properties": {
                            "settings": {
                                "type": "string",
                                "x-rust-type": "serde_json::Value",
                                "nullable": true,
                                "description": "Optional settings."
                            }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let settings_model = models.iter().find(|m| m.name() == "Settings");
        assert!(settings_model.is_some(), "Expected Settings model");

        match settings_model.unwrap() {
            ModelType::Struct(model) => {
                let settings_field = model.fields.iter().find(|f| f.name == "settings");
                assert!(settings_field.is_some(), "Expected settings field");

                let field = settings_field.unwrap();
                assert_eq!(field.field_type, "serde_json::Value");
                assert!(field.is_nullable, "Expected field to be nullable");
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_multiple_properties_with_x_rust_type() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "ComplexModel": {
                        "type": "object",
                        "description": "Model with multiple custom-typed properties",
                        "properties": {
                            "id": {
                                "type": "string",
                                "format": "uuid",
                                "x-rust-type": "uuid::Uuid"
                            },
                            "price": {
                                "type": "number",
                                "x-rust-type": "decimal::Decimal"
                            },
                            "timeout": {
                                "type": "integer",
                                "x-rust-type": "std::time::Duration"
                            },
                            "regular_field": { "type": "string" }
                        },
                        "required": ["id", "price", "timeout"]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let model = models.iter().find(|m| m.name() == "ComplexModel");
        assert!(model.is_some(), "Expected ComplexModel model");

        match model.unwrap() {
            ModelType::Struct(struct_model) => {
                // Verify all custom types
                let id_field = struct_model.fields.iter().find(|f| f.name == "id");
                assert_eq!(id_field.unwrap().field_type, "uuid::Uuid");

                let price_field = struct_model.fields.iter().find(|f| f.name == "price");
                assert_eq!(price_field.unwrap().field_type, "decimal::Decimal");

                let timeout_field = struct_model.fields.iter().find(|f| f.name == "timeout");
                assert_eq!(timeout_field.unwrap().field_type, "std::time::Duration");

                // Verify regular field
                let regular_field = struct_model
                    .fields
                    .iter()
                    .find(|f| f.name == "regular_field");
                assert_eq!(regular_field.unwrap().field_type, "String");

                // Verify nullable flags for required/optional fields
                assert!(!id_field.unwrap().is_nullable, "id should not be nullable");
                assert!(
                    !price_field.unwrap().is_nullable,
                    "price should not be nullable"
                );
                assert!(
                    !timeout_field.unwrap().is_nullable,
                    "timeout should not be nullable"
                );
                // regular_field is not in required, but generator doesn't mark it as nullable
                // (this is expected behavior - nullable only for explicitly nullable fields)
            }
            _ => panic!("Expected Struct"),
        }
    }

    #[test]
    fn test_x_rust_attrs_on_field() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "FrontendEvent": {
                        "type": "object",
                        "properties": {
                            "field": {
                                "type": "integer",
                                "minimum": 0,
                                "maximum": 100,
                                "nullable": true,
                                "x-rust-attrs": ["#[validate(range(min = 0, max = 100))]"]
                            },
                            "name": { "type": "string" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let model = models.iter().find(|m| m.name() == "FrontendEvent");
        assert!(model.is_some(), "Expected FrontendEvent model");

        match model.unwrap() {
            ModelType::Struct(struct_model) => {
                let field = struct_model.fields.iter().find(|f| f.name == "field");
                assert!(field.is_some(), "Expected progress_percent field");
                let field = field.unwrap();
                assert_eq!(field.field_type, "i64");
                assert!(
                    field.custom_attrs.is_some(),
                    "Expected field-level x-rust-attrs"
                );
                let attrs = field.custom_attrs.as_ref().unwrap();
                assert_eq!(attrs.len(), 1);
                assert_eq!(attrs[0], "#[validate(range(min = 0, max = 100))]");

                let name_field = struct_model.fields.iter().find(|f| f.name == "name");
                assert!(name_field.unwrap().custom_attrs.is_none());
            }
            _ => panic!("Expected Struct"),
        }
    }

    // Two structs each having a field named `type` with different inline enum values.
    // The generator must produce two distinct enum types rather than colliding on the
    // shared name `Type`.
    #[test]
    fn test_inline_enum_fields_on_different_structs_get_unique_names() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "SignalA": {
                        "type": "object",
                        "properties": {
                            "type": {
                                "type": "string",
                                "enum": ["variant_a"]
                            }
                        }
                    },
                    "SignalB": {
                        "type": "object",
                        "properties": {
                            "type": {
                                "type": "string",
                                "enum": ["variant_b"]
                            }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // Both enum types must be generated - neither should be dropped by deduplication.
        let signal_a_type = models.iter().find(|m| m.name() == "SignalAType");
        let signal_b_type = models.iter().find(|m| m.name() == "SignalBType");

        assert!(
            signal_a_type.is_some(),
            "Expected SignalAType enum to be generated"
        );
        assert!(
            signal_b_type.is_some(),
            "Expected SignalBType enum to be generated"
        );

        // Each enum must contain only its own variant.
        match signal_a_type.unwrap() {
            ModelType::Enum(e) => {
                assert_eq!(e.variants, vec!["variant_a"]);
            }
            _ => panic!("Expected Enum for SignalAType"),
        }
        match signal_b_type.unwrap() {
            ModelType::Enum(e) => {
                assert_eq!(e.variants, vec!["variant_b"]);
            }
            _ => panic!("Expected Enum for SignalBType"),
        }

        // The struct fields must reference the qualified enum names.
        let signal_a = models.iter().find(|m| m.name() == "SignalA");
        assert!(signal_a.is_some(), "Expected SignalA struct");
        if let Some(ModelType::Struct(s)) = signal_a {
            let type_field = s.fields.iter().find(|f| f.name == "type").unwrap();
            assert_eq!(type_field.field_type, "SignalAType");
        }

        let signal_b = models.iter().find(|m| m.name() == "SignalB");
        assert!(signal_b.is_some(), "Expected SignalB struct");
        if let Some(ModelType::Struct(s)) = signal_b {
            let type_field = s.fields.iter().find(|f| f.name == "type").unwrap();
            assert_eq!(type_field.field_type, "SignalBType");
        }
    }

    // x-rust-attrs on an inline enum property (e.g. derive macros for the generated
    // enum type) must not leak into the parent struct as field-level attributes.
    // Before the fix this caused `#[derive(...)]` to appear inside the struct body,
    // which is invalid Rust.
    #[test]
    fn test_x_rust_attrs_on_inline_enum_field_go_to_enum_not_field() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Signal": {
                        "type": "object",
                        "properties": {
                            "kind": {
                                "type": "string",
                                "enum": ["started", "stopped"],
                                "x-rust-attrs": [
                                    "#[derive(derive_more::Display, Debug, Clone)]"
                                ]
                            },
                            "name": { "type": "string" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // The generated enum must carry the custom attrs.
        let kind_enum = models.iter().find(|m| m.name() == "SignalKind");
        assert!(
            kind_enum.is_some(),
            "Expected SignalKind enum to be generated"
        );
        match kind_enum.unwrap() {
            ModelType::Enum(e) => {
                assert!(
                    e.custom_attrs.is_some(),
                    "x-rust-attrs should be on the generated enum"
                );
                let attrs = e.custom_attrs.as_ref().unwrap();
                assert!(attrs.iter().any(|a| a.contains("derive")));
            }
            _ => panic!("Expected Enum for SignalKind"),
        }

        // The parent struct field must NOT carry the attrs - emitting derive macros
        // as field attributes is invalid Rust.
        let signal = models.iter().find(|m| m.name() == "Signal");
        assert!(signal.is_some(), "Expected Signal struct");
        if let Some(ModelType::Struct(s)) = signal {
            let kind_field = s.fields.iter().find(|f| f.name == "kind").unwrap();
            assert!(
                kind_field.custom_attrs.is_none(),
                "x-rust-attrs must not appear on the struct field when they target a generated inline enum"
            );
        }
    }

    // A base schema declares fields as plain primitives (String, i64). A composing
    // schema narrows those same fields to specific named types via allOf. The
    // composed struct must use the more specific types, not the primitive placeholders.
    #[test]
    fn test_allof_primitive_field_narrowed_to_specific_type() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "BaseSignal": {
                        "type": "object",
                        "required": ["type"],
                        "properties": {
                            "type": {
                                "type": "string",
                                "description": "The signal type identifier."
                            },
                            "name": {
                                "type": "string",
                                "description": "Human-readable label."
                            }
                        }
                    },
                    "ConcreteSignal": {
                        "allOf": [
                            { "$ref": "#/components/schemas/BaseSignal" },
                            {
                                "type": "object",
                                "required": ["type"],
                                "properties": {
                                    "type": {
                                        "type": "string",
                                        "enum": ["concrete"]
                                    }
                                }
                            }
                        ]
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        // The inline enum for `type` must be generated.
        let type_enum = models.iter().find(|m| m.name() == "ConcreteSignalType");
        assert!(
            type_enum.is_some(),
            "Expected ConcreteSignalType enum to be generated"
        );
        match type_enum.unwrap() {
            ModelType::Enum(e) => assert_eq!(e.variants, vec!["concrete"]),
            _ => panic!("Expected Enum for ConcreteSignalType"),
        }

        // The composed struct must use the specific enum type, not plain String.
        let concrete = models.iter().find(|m| m.name() == "ConcreteSignal");
        assert!(concrete.is_some(), "Expected ConcreteSignal model");
        if let Some(ModelType::Composition(c)) = concrete {
            let type_field = c.all_fields.iter().find(|f| f.name == "type").unwrap();
            assert_eq!(
                type_field.field_type, "ConcreteSignalType",
                "allOf should narrow plain String to the more specific enum type"
            );
        } else {
            panic!("Expected ConcreteSignal to be a Composition");
        }
    }

    // x-rust-attrs on a $ref target schema are type-level attributes that belong
    // to the type definition. They must NOT be propagated to the field that
    // references that type, as emitting #[derive(...)] at field position is
    // invalid Rust.
    #[test]
    fn test_x_rust_attrs_from_ref_target_not_propagated_to_field() {
        let openapi_spec: OpenAPI = serde_json::from_value(json!({
            "openapi": "3.0.0",
            "info": { "title": "Test API", "version": "1.0.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Address": {
                        "type": "object",
                        "x-rust-attrs": ["#[derive(Hash, Eq, PartialEq)]"],
                        "properties": {
                            "street": { "type": "string" }
                        }
                    },
                    "Person": {
                        "type": "object",
                        "properties": {
                            "name": { "type": "string" },
                            "address": { "$ref": "#/components/schemas/Address" }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let person = models.iter().find(|m| m.name() == "Person");
        assert!(person.is_some(), "Expected Person model");

        if let Some(ModelType::Struct(s)) = person {
            let address_field = s.fields.iter().find(|f| f.name == "address").unwrap();
            assert_eq!(address_field.field_type, "Address");
            assert!(
                address_field.custom_attrs.is_none(),
                "x-rust-attrs from the referenced Address type must not appear on the Person.address field"
            );
        } else {
            panic!("Expected Person to be a Struct");
        }
    }

    #[test]
    fn test_schema_level_nullable_ref_makes_field_optional() {
        // A field whose $ref target schema has `nullable: true` at the schema level
        // must produce is_nullable = true, resulting in Option<T> in the output.
        let openapi_spec: OpenAPI = serde_json::from_value(serde_json::json!({
            "openapi": "3.0.3",
            "info": { "title": "Test", "version": "0.1.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "NullableString": {
                        "type": "string",
                        "nullable": true
                    },
                    "Container": {
                        "type": "object",
                        "required": ["value"],
                        "properties": {
                            "value": {
                                "$ref": "#/components/schemas/NullableString"
                            }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let container = models.iter().find(|m| m.name() == "Container");
        assert!(container.is_some(), "Expected Container model");

        if let Some(ModelType::Struct(s)) = container {
            let value_field = s.fields.iter().find(|f| f.name == "value").unwrap();
            assert!(
                value_field.is_nullable,
                "Field referencing a nullable schema must be marked is_nullable"
            );
        } else {
            panic!("Expected Container to be a Struct");
        }
    }

    #[test]
    fn test_inline_nullable_field_is_optional() {
        // An inline field with `nullable: true` directly on the property must be is_nullable.
        let openapi_spec: OpenAPI = serde_json::from_value(serde_json::json!({
            "openapi": "3.0.3",
            "info": { "title": "Test", "version": "0.1.0" },
            "paths": {},
            "components": {
                "schemas": {
                    "Widget": {
                        "type": "object",
                        "properties": {
                            "label": {
                                "type": "string",
                                "nullable": true
                            }
                        }
                    }
                }
            }
        }))
        .expect("Failed to deserialize OpenAPI spec");

        let (models, _, _) = parse_openapi(&openapi_spec).expect("Failed to parse OpenAPI spec");

        let widget = models.iter().find(|m| m.name() == "Widget");
        assert!(widget.is_some(), "Expected Widget model");

        if let Some(ModelType::Struct(s)) = widget {
            let label_field = s.fields.iter().find(|f| f.name == "label").unwrap();
            assert!(
                label_field.is_nullable,
                "Inline field with nullable: true must be marked is_nullable"
            );
        } else {
            panic!("Expected Widget to be a Struct");
        }
    }
}