Creating Custom Models

Overview

Custom models allow you to extend Stremio Core with your own stateful components. By implementing the Model trait, you can integrate seamlessly with the runtime system and benefit from automatic effect handling, state propagation, and UI updates.

The Model Trait

The Model trait is the foundation for all stateful components:

use stremio_core::runtime::{Model, Env, Msg, Effect};
use serde::{Serialize, Deserialize};

pub trait Model<E: Env>: Clone {
    type Field: Send + Sync + Serialize + for<'de> Deserialize<'de>;

    fn update(&mut self, msg: &Msg) -> (Vec<Effect>, Vec<Self::Field>);
    fn update_field(&mut self, msg: &Msg, field: &Self::Field) -> (Vec<Effect>, Vec<Self::Field>);
}

See src/runtime/update.rs:8

Manual Implementation

Step 1: Define Your Model

use serde::{Serialize, Deserialize};
use stremio_core::models::common::Loadable;

#[derive(Clone, Serialize, Debug)]
pub struct MyCustomModel {
    pub data: Loadable<Vec<String>, String>,
    pub filter: Option<String>,
    pub page: u32,
}

impl Default for MyCustomModel {
    fn default() -> Self {
        Self {
            data: Loadable::Loading,
            filter: None,
            page: 0,
        }
    }
}

Step 2: Define Field Enum

The Field enum represents all mutable fields in your model:

#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
#[serde(rename_all = "snake_case")]
pub enum MyCustomModelField {
    Data,
    Filter,
    Page,
}

Step 3: Implement the Model Trait

use stremio_core::runtime::{Model, Env, Msg, Effect, Effects};
use stremio_core::runtime::msg::{Action, Internal};

impl<E: Env + 'static> Model<E> for MyCustomModel {
    type Field = MyCustomModelField;

    fn update(&mut self, msg: &Msg) -> (Vec<Effect>, Vec<Self::Field>) {
        match msg {
            Msg::Action(Action::Load(request)) => {
                // Update state
                self.data = Loadable::Loading;
                self.page = 0;
                
                // Create effects
                let effects = Effects::future(EffectFuture::Concurrent(
                    fetch_data::<E>(request.clone()).boxed_env()
                ));
                
                // Return effects and changed fields
                let fields = vec![
                    MyCustomModelField::Data,
                    MyCustomModelField::Page,
                ];
                (effects.into_iter().collect(), fields)
            }
            Msg::Internal(Internal::DataLoaded(data)) => {
                self.data = Loadable::Ready(data.clone());
                let fields = vec![MyCustomModelField::Data];
                (vec![], fields)
            }
            _ => {
                // No changes
                (vec![], vec![])
            }
        }
    }

    fn update_field(&mut self, msg: &Msg, field: &Self::Field) -> (Vec<Effect>, Vec<Self::Field>) {
        match field {
            MyCustomModelField::Data => {
                // Update only the data field
                match msg {
                    Msg::Internal(Internal::DataLoaded(data)) => {
                        self.data = Loadable::Ready(data.clone());
                        (vec![], vec![MyCustomModelField::Data])
                    }
                    _ => (vec![], vec![])
                }
            }
            MyCustomModelField::Filter => {
                // Update only the filter field
                match msg {
                    Msg::Action(Action::UpdateFilter(filter)) => {
                        self.filter = filter.clone();
                        (vec![], vec![MyCustomModelField::Filter])
                    }
                    _ => (vec![], vec![])
                }
            }
            MyCustomModelField::Page => {
                (vec![], vec![])
            }
        }
    }
}

See src/runtime/update.rs:8 for trait definition

Using the Model Derive Macro

For complex models with multiple fields, use the #[derive(Model)] macro:

Step 1: Enable the Derive Feature

[dependencies]
stremio-core = { version = "*", features = ["derive"] }

Step 2: Structure Your Model

The model must have a ctx field:

use stremio_core::Model;
use stremio_core::models::ctx::Ctx;
use serde::Serialize;

#[derive(Model, Clone, Serialize)]
#[model(Env)]  // Specify your Env type
pub struct MyAppModel {
    pub ctx: Ctx,
    pub catalog: CatalogModel,
    pub player: PlayerModel,
    pub library: LibraryModel,
}

See stremio-derive/src/lib.rs:14

Generated Code

The derive macro generates:

Field enum with variants for each field
Model implementation that coordinates updates across fields
Automatic effect composition combining effects from all fields

See stremio-derive/src/lib.rs:113

Context-Aware Models

Many models need access to user context. Use the UpdateWithCtx trait:

use stremio_core::runtime::{UpdateWithCtx, Env, Msg, Effects};
use stremio_core::models::ctx::Ctx;

#[derive(Clone, Serialize)]
pub struct CatalogModel {
    pub items: Loadable<Vec<MetaItem>, String>,
    pub selected_addon: Option<String>,
}

impl<E: Env + 'static> UpdateWithCtx<E> for CatalogModel {
    fn update(&mut self, msg: &Msg, ctx: &Ctx) -> Effects {
        match msg {
            Msg::Action(Action::Load(request)) => {
                // Access user's installed addons
                let addons = &ctx.profile.addons;
                
                // Filter by user preferences
                let auth_key = ctx.profile.auth_key();
                
                // Build request with context
                self.items = Loadable::Loading;
                Effects::future(EffectFuture::Concurrent(
                    fetch_catalog::<E>(request, addons, auth_key).boxed_env()
                ))
            }
            _ => Effects::none().unchanged()
        }
    }
}

See src/runtime/update.rs:22 and src/models/catalog_with_filters.rs:149

Complete Example: Custom Favorites Model

Here’s a complete example of a custom favorites model:

use serde::{Serialize, Deserialize};
use stremio_core::runtime::{
    Model, Env, Msg, Effect, Effects, EffectFuture, EnvFutureExt,
};
use stremio_core::runtime::msg::{Action, Internal};
use stremio_core::types::resource::MetaItemPreview;

// Define custom actions
#[derive(Clone, Debug)]
pub enum FavoritesAction {
    Load,
    Add(MetaItemPreview),
    Remove(String),  // ID to remove
}

// Model state
#[derive(Clone, Serialize, Debug)]
pub struct FavoritesModel {
    pub items: Vec<MetaItemPreview>,
    pub loading: bool,
}

impl Default for FavoritesModel {
    fn default() -> Self {
        Self {
            items: vec![],
            loading: false,
        }
    }
}

// Field enum
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq)]
#[serde(rename_all = "snake_case")]
pub enum FavoritesField {
    Items,
    Loading,
}

// Helper function to load from storage
fn load_favorites<E: Env>() -> impl Future<Output = Msg> {
    E::get_storage::<Vec<MetaItemPreview>>("favorites")
        .map(|result| match result {
            Ok(Some(items)) => Msg::Internal(Internal::FavoritesLoaded(items)),
            _ => Msg::Internal(Internal::FavoritesLoaded(vec![])),
        })
}

// Helper function to save to storage
fn save_favorites<E: Env>(items: Vec<MetaItemPreview>) -> impl Future<Output = Msg> {
    E::set_storage("favorites", Some(&items))
        .map(|_| Msg::Event(Event::FavoritesSaved))
}

// Model implementation
impl<E: Env + 'static> Model<E> for FavoritesModel {
    type Field = FavoritesField;

    fn update(&mut self, msg: &Msg) -> (Vec<Effect>, Vec<Self::Field>) {
        match msg {
            // Handle custom action (you'd extend Action enum)
            Msg::Action(Action::Favorites(FavoritesAction::Load)) => {
                self.loading = true;
                let effects = Effects::future(EffectFuture::Sequential(
                    load_favorites::<E>().boxed_env()
                ));
                (effects.into_iter().collect(), vec![FavoritesField::Loading])
            }
            
            Msg::Action(Action::Favorites(FavoritesAction::Add(item))) => {
                if !self.items.iter().any(|i| i.id == item.id) {
                    self.items.push(item.clone());
                    let items = self.items.clone();
                    let effects = Effects::future(EffectFuture::Sequential(
                        save_favorites::<E>(items).boxed_env()
                    ));
                    (effects.into_iter().collect(), vec![FavoritesField::Items])
                } else {
                    (vec![], vec![])
                }
            }
            
            Msg::Action(Action::Favorites(FavoritesAction::Remove(id))) => {
                self.items.retain(|item| &item.id != id);
                let items = self.items.clone();
                let effects = Effects::future(EffectFuture::Sequential(
                    save_favorites::<E>(items).boxed_env()
                ));
                (effects.into_iter().collect(), vec![FavoritesField::Items])
            }
            
            Msg::Internal(Internal::FavoritesLoaded(items)) => {
                self.items = items.clone();
                self.loading = false;
                (
                    vec![],
                    vec![FavoritesField::Items, FavoritesField::Loading]
                )
            }
            
            _ => (vec![], vec![])
        }
    }

    fn update_field(&mut self, msg: &Msg, field: &Self::Field) -> (Vec<Effect>, Vec<Self::Field>) {
        // Delegate to update() for simplicity
        self.update(msg)
    }
}

Integrating with Runtime

Once your model is defined, integrate it with the runtime:

use stremio_core::runtime::Runtime;

// Create your model
let model = FavoritesModel::default();

// Initialize with load effect
let initial_effects = vec![
    Effect::Msg(Box::new(Msg::Action(
        Action::Favorites(FavoritesAction::Load)
    )))
];

// Create runtime
let (runtime, mut rx) = Runtime::<MyEnv, FavoritesModel>::new(
    model,
    initial_effects,
    100,  // buffer size
);

// Dispatch actions
runtime.dispatch(RuntimeAction {
    field: None,
    action: Action::Favorites(FavoritesAction::Add(item)),
});

// Listen for state changes
tokio::spawn(async move {
    while let Some(event) = rx.next().await {
        match event {
            RuntimeEvent::NewState(fields, model) => {
                println!("Updated fields: {:?}", fields);
                println!("New state: {:?}", model);
            }
            RuntimeEvent::CoreEvent(event) => {
                println!("Core event: {:?}", event);
            }
        }
    }
});

See src/runtime/runtime.rs:39

Testing Custom Models

Test your models with the test environment:

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

    #[test]
    fn test_add_favorite() {
        let mut model = FavoritesModel::default();
        let item = MetaItemPreview {
            id: "tt123".to_string(),
            name: "Test Movie".to_string(),
            // ... other fields
        };
        
        let (effects, fields) = model.update(&Msg::Action(
            Action::Favorites(FavoritesAction::Add(item.clone()))
        ));
        
        assert_eq!(model.items.len(), 1);
        assert_eq!(fields, vec![FavoritesField::Items]);
        assert_eq!(effects.len(), 1);  // Save effect
    }

    #[test]
    fn test_remove_favorite() {
        let mut model = FavoritesModel {
            items: vec![MetaItemPreview {
                id: "tt123".to_string(),
                name: "Test Movie".to_string(),
                // ...
            }],
            loading: false,
        };
        
        let (effects, fields) = model.update(&Msg::Action(
            Action::Favorites(FavoritesAction::Remove("tt123".to_string()))
        ));
        
        assert_eq!(model.items.len(), 0);
        assert_eq!(fields, vec![FavoritesField::Items]);
    }
}

Best Practices

Keep Models Simple

Each model should have a clear, single responsibility. Compose complex models from simpler ones.

Use Type-Safe Actions

Define custom action enums for your model instead of using strings or generic types.

Handle All Message Types

Always include a catch-all pattern that returns empty effects and fields for unhandled messages.

Minimize Clones

Use Arc<T> for large data structures that are frequently cloned across messages.

Separate Concerns

Keep business logic in helper functions. The update method should focus on state transitions.

Common Patterns

Resource Loading Pattern

impl<E: Env> Model<E> for MyModel {
    fn update(&mut self, msg: &Msg) -> (Vec<Effect>, Vec<Self::Field>) {
        match msg {
            Msg::Action(Action::Load(request)) => {
                self.data = Loadable::Loading;
                (fetch_effects(request), vec![Field::Data])
            }
            Msg::Internal(Internal::LoadSuccess(data)) => {
                self.data = Loadable::Ready(data.clone());
                (vec![], vec![Field::Data])
            }
            Msg::Internal(Internal::LoadError(err)) => {
                self.data = Loadable::Err(err.clone());
                (vec![], vec![Field::Data])
            }
            _ => (vec![], vec![])
        }
    }
}

See src/models/common/loadable.rs:5

Pagination Pattern

impl<E: Env> Model<E> for PaginatedModel {
    fn update(&mut self, msg: &Msg) -> (Vec<Effect>, Vec<Self::Field>) {
        match msg {
            Msg::Action(Action::LoadNextPage) => {
                if self.has_next_page && !self.loading {
                    self.page += 1;
                    self.loading = true;
                    (fetch_page_effects(self.page), vec![Field::Page, Field::Loading])
                } else {
                    (vec![], vec![])
                }
            }
            Msg::Internal(Internal::PageLoaded(items)) => {
                self.items.extend(items.clone());
                self.loading = false;
                self.has_next_page = !items.is_empty();
                (vec![], vec![Field::Items, Field::Loading])
            }
            _ => (vec![], vec![])
        }
    }
}

See src/models/catalog_with_filters.rs:191

Next Steps

State Management

Deep dive into state management patterns

Environment Trait

Learn about the Env trait for side effects

Get Started

Core Concepts

Addon System

Models

Platform Integration

Advanced

Overview

The Model Trait

Manual Implementation

Step 1: Define Your Model

Step 2: Define Field Enum

Step 3: Implement the Model Trait

Using the Model Derive Macro

Step 1: Enable the Derive Feature

Step 2: Structure Your Model

Generated Code

Context-Aware Models

Complete Example: Custom Favorites Model

Integrating with Runtime

Testing Custom Models

Best Practices

Common Patterns

Resource Loading Pattern

Next Steps

State Management

Environment Trait

Build docs developers (and LLMs) love

Get Started

Core Concepts

Addon System

Models

Platform Integration

Advanced

​Overview

​The Model Trait

​Manual Implementation

​Step 1: Define Your Model

​Step 2: Define Field Enum

​Step 3: Implement the Model Trait

​Using the Model Derive Macro

​Step 1: Enable the Derive Feature

​Step 2: Structure Your Model

​Generated Code

​Context-Aware Models

​Complete Example: Custom Favorites Model

​Integrating with Runtime

​Testing Custom Models

​Best Practices

​Common Patterns

​Resource Loading Pattern

​Pagination Pattern

​Next Steps

State Management

Environment Trait

Build docs developers (and LLMs) love

Overview

The Model Trait

Manual Implementation

Step 1: Define Your Model

Step 2: Define Field Enum

Step 3: Implement the Model Trait

Using the Model Derive Macro

Step 1: Enable the Derive Feature

Step 2: Structure Your Model

Generated Code

Context-Aware Models

Complete Example: Custom Favorites Model

Integrating with Runtime

Testing Custom Models

Best Practices

Common Patterns

Resource Loading Pattern

Pagination Pattern

Next Steps