pub mod builders;

use crate::{
    effect::{Effect, Future},
    protocol::Visitor,
};

/// A buildable type.
pub trait Build<'ctx, M, E: Effect>: BuilderTypes<Value = Self> + Send {
    /// The builder that can be used to build a value of `Self`.
    type Builder: Builder<'ctx, E, Seed = Self::Seed, Error = Self::Error, Value = Self>;
}

pub trait BuilderTypes {
    type Seed: Send;

    /// Error that can happen during filling the builder with data.
    type Error: Send;

    /// Type to be built.
    type Value: Send;
}

/// Builder for a type.
///
/// The `'ctx` lifetime is some lifetime that is longer than the walker.
/// As such, the built value can borrow from other data with a `'ctx` lifetimes.
///
/// A builder allows creating a value of a type [`Self::Value`][BuilderTypes::Value].
/// The way to use a builder is as follows.
/// - Call [`Default::default()`] to create an instance of the builder.
/// - Call [`Self::as_visitor()`] and give it to a walker's
///     [`walk()`][crate::walk::Walker::walk]. The walker will then fill
///     the builder with data from it's walk.
/// - Call [`Self::build()`] to finish building the value and get any errors
///     that happened during filling it with data.
pub trait Builder<'ctx, E: Effect>: BuilderTypes + Sized + Send {
    fn from_seed<'a>(seed: Self::Seed) -> Future<'a, Self, E>
    where
        Self: 'a;

    /// Finish the value.
    ///
    /// If an error happened with the builder during the walk
    /// it will be reported here.
    fn build<'a>(self) -> Future<'a, Result<Self::Value, Self::Error>, E>
    where
        Self: 'a;

    /// Get the builder as a visitor that a walker can use.
    ///
    /// This is expected to just be `self`.
    fn as_visitor(&mut self) -> Visitor<'_, 'ctx>;
}