Move guide to readme

README.md

@@ -49,3 +49,141 @@ resource: this is achieved by constructing resource IDs only from responses,
 and static values. `DELETE` functions cause the resource ID argument to be
 _moved_ (while other methods only _borrow_) preventing it from being further
 used.
+
+## Getting started
+
+In order to start using tapioca in your project, the first step is to locate the OAS schema for the API you wish to use. Let's assume it's at `https://example.org/schema.yml`. Then, add the latest version to your `Cargo.toml` as usual, and import tapioca with macros:
+```rust
+#[macro_use]
+extern crate tapioca;
+```
+and invoke the `infer_api` macro to build a client for the API:
+```rust
+infer_api!(example, "https://example.org/schema.yml");
+```
+
+The macro expands at compile-time, building a typed client in-place; (almost) all the code it generates will be located under a module named `example`, or whatever we specify in the first argument. The only exception is two crates (which must be loaded at the root level) which are needed to be externed inside your crate in order to use their macros - at least for now, the Rust's macro system is seeing a lot of change, and this may be improved. These are `serde_derive` and `tapicoa_codegen`; consequently, they also need to be in your `Cargo.toml`, but any other crates used (not for macros) by tapicoa will _not_ need this treatment, or pollute your project's namespace.
+
+## Accessing the client
+
+The module built by `infer_api` contains modules with the names of each of the paths available on an API, and each of those contains a function for each of the HTTP methods valid for that resource. For example, to `GET /foobars`, the function ident is:
+```rust
+example::foobars::get
+```
+
+In order to call this function, we might need to supply some arguments for [authentication](#authentication), [query parameters](#query-parameters), [request body](#request-bodies), et al. - the types for these are located inside a module of the same name as the function, for example:
+```rust
+example::foobars::get::QueryParams
+```
+
+## Authentication
+
+Before we make a request, we need to introduce authentication - currently, authentication must be specified for every request, even if null.
+
+Authentication requirements in an OAS schema are specified at two levels: server-wide, and operation specific - `GET /foobars` can have different requirements to other operations, which may just inherit from the server requirement. Thus we have two `enum`s of acceptable authentication schemes:
+```rust
+example::ServerAuth
+example::foobars::get::OpAuth
+```
+which must be used depends on whether the operation `examples::foobars::get` overrides the server-wide authentication requirement - but the type-checker will tell us if we get it wrong.
+
+If there's no authentication required at all, we can just use:
+```rust
+example::ServerAuth::new();
+```
+
+If it's HTTP Basic, then (depending on whether it's a server or operation requirement):
+```rust
+example::ServerAuth::Basic(username: String, password:String);
+example::foobars::get::OpAuth::Basic(username: String, password:String);
+```
+
+If it's a custom header:
+```rust
+example::ServerAuth::ApiKey(api_key: String);
+example::foobars::get::OpAuth::ApiKey(api_key: String);
+```
+
+Though note that the variant identifier, e.g. `Basic` or `ApiKey`, depends on the name used in the OAS schema. This is because there may be multiple definitions of the same type.
+
+## Making a request
+
+Now that we've seen how to construct an authentication argument, we can actually `GET` some `foobars`!
+
+```rust
+let auth = examples::ServerAuth::new();
+let response = examples::foobars::get(&auth);
+```
+
+`response` is actually a `Result<Response, Response>`: if the response status code is an error, we get an `Err(response)`, otherwise it's an `Ok(response)`. This means we can use `response.is_ok`, `response.is_err`, and pattern matching:
+```rust
+match examples::foobars::get(&auth) {
+    Ok(response) => foobar_handler(response),
+    Err(response) => err_handler(response),
+}
+```
+
+We can use further pattern matching in each of these handlers, in order to respond differently to different status codes:
+```rust
+fn foobar_handler(response: Response) {
+    match response.body {
+        OkBody::Status200(body) => {
+            for foobar in body.the_foobars {
+                println!("Foobar {} is named {}", foobar.id, foobar.name);
+            }
+        },
+        OkBody::UnspecifiedCode(body)
+        | OkBody::MalformedJson(body) => something_else(),
+    }
+}
+```
+where we always have `UnspecifiedCode` (one not in the schema) and `MalformedJson` (invalid JSON, or did not match schema) as well as a `StatusXXX` for each of the possibilities specified in the schema. `err_handler` would look similar, with `ErrBody::Status403`, etc.
+
+## Request bodies
+
+Say this `example::foobars` collection also supports `POST`ing new `foobar`s, we can supply the request body to create one like this:
+```rust
+let body = example::foobars::post::RequestBody {
+    name: "Foobarry".into(),
+    age: 12,
+    email: None,
+};
+```
+
+The structure and field types of the body is fully defined by the schema, and may include:
+  - `i32`, `i64`
+  - `bool`
+  - `String`
+  - `Option<_>`
+  - `Vec<_>`
+  - further `struct`s
+
+## Query parameters
+
+Query parameters are supplied much like [request bodies](#request-bodies):
+```rust
+let query = example::foobars::get::QueryParams {
+    age: 34,
+};
+```
+
+## Path parameters
+
+Path parameters are slightly different. Because of the need to distinguish `example::foobars::get` from a `GET` on a single resource in that collection, the name of the path parameter is encoded in the path module name, for example:
+```rust
+example::foobars__id_::get
+```
+
+If the API specifies two resource identifiers in a row, this would be `foobars__id1___id2_`. This gets ugly, and may be changed in a future version.
+
+Path parameters can be constructed from the response, for example when creating a new resource and the server generated its ID, or from a static reference:
+```rust
+static provisioned_id = "fea3c8e91baa1";
+
+fn main() {
+    let auth = example::ServerAuth::new();
+    let resource = examples::foobars__id_::Resource_id::from_static(provisioned_id);
+
+    example::foobars__id_::get(&resource, &auth);
+}
+```