Using the Builder API

The following example demonstrates the builder interface to create the same service as the example above. Hopefully this is more readable as it tends to be less repetative, uses &str for identifiers, and includes helper functions for common traits for example. It provides this better construction experience (there are no read methods on builder objects) by compromising two aspects:

1. The API itself is very repetative; this means the same method may be on multiple objects, but makes it easier to use. For example, you want to add the documentation trait to a shape, so you can:
   1. construct a Trait entity using the core model and the Builder::add_trait method,
   2. use the TraitBuilder::documentation method which also takes the string to use as the trait value and returns a new TraitBuilder, or
   3. use the Builder::documentation method that hides all the details of a trait and just takes a string.
2. It hides a lot of the Identifier and ShapeID construction and so any of those calls to from_str may fail when the code unwraps the result. This means the builder can panic in ways the core model does not.

#![allow(unused_variables)]
fn main() {
use atelier_core::builder::traits::ErrorSource;
use atelier_core::builder::values::{ArrayBuilder, ObjectBuilder};
use atelier_core::builder::{
    traits, ListBuilder, MemberBuilder, ModelBuilder, OperationBuilder, ResourceBuilder,
    ServiceBuilder, ShapeTraits, SimpleShapeBuilder, StructureBuilder, TraitBuilder,
};
use atelier_core::model::{Identifier, Model, ShapeID};
use atelier_core::Version;
use std::convert::TryInto;

let model: Model = ModelBuilder::new(Version::V10, "example.motd")
    .service(
        ServiceBuilder::new("MessageOfTheDay", "2020-06-21")
            .documentation("Provides a Message of the day.")
            .resource("Message")
            .into(),
    )
    .resource(
        ResourceBuilder::new("Message")
            .identifier("date", "Date")
            .read("GetMessage")
            .into(),
    )
    .simple_shape(
        SimpleShapeBuilder::string("Date")
            .apply_trait(traits::pattern(r"^\d\d\d\d\-\d\d-\d\d$"))
            .into(),
    )
    .operation(
        OperationBuilder::new("GetMessage")
            .readonly()
            .input("GetMessageInput")
            .output("GetMessageOutput")
            .error("BadDateValue")
            .into(),
    )
    .structure(
        StructureBuilder::new("GetMessageInput")
            .member("date", "Date")
            .into(),
    )
    .structure(
        StructureBuilder::new("GetMessageOutput")
            .add_member(MemberBuilder::string("message").required().into())
            .into(),
    )
    .structure(
        StructureBuilder::new("BadDateValue")
            .error_source(ErrorSource::Client)
            .add_member(MemberBuilder::string("errorMessage").required().into())
            .into(),
    )
    .try_into().unwrap();
}