use axum::{
	body::Body,
	http::StatusCode,
	http::header,
	response::IntoResponse,
	response::Response,
};
#[cfg(feature="axum-view+cookie")]
use axum::http::header::SET_COOKIE;
use axum_extra::headers::HeaderValue;
use tera::Tera;
use toml::Table;

use std::marker::PhantomData;

use crate::HumusFormat;
use crate::HumusFormatFamily;
use crate::HumusProtoEngine;
use crate::HumusQuerySettings;
use crate::HumusView;

/* The engine itself */

/// 🌄 Tera based Templating Engine that writes out axum Response structs.
///
/// The engine uses logic and data from the configured [View] (V) type as well as
/// data and configuration provided by the [QuerySettings] (S) type to produce the
/// desired response with minimal code overhead inside your main logic.
///
/// <b>Note:</b> The private fields are [PhantomData] because the V, S and N
///              generics are only used for the implementation.
/// 
/// [PhantomData]: https://doc.rust-lang.org/std/marker/struct.PhantomData.html
/// 
/// The Engine operates in one of two modes determined by the [Format] (F) which
/// is [provided by the QuerySettings]:
/// * [Template Mode]: The [Format] describes which template to use for rendering
///                    the [View] to some kind of text using Tera templates.
/// * [API Mode]: The [View] [serializes itself], usually to a [Json Response].
///
/// # Template Mode
///
/// In template mode the following sequence of events happens:
/// * status code, format and cookies are fetched.
///   (The cookie functionality is enabled with the `axum-view+cookie` feature)
/// * Template name and MimeType are fetched.
/// * The Template context is populated with metadatam the [View] and `template_config`.
/// * The [QuerySettings] are given the chance to populate the context
///   with their own values using the `initalize_template_context()` hook.
/// * The template gets rendered, resulting in further processing or an error response.
/// * The response is constructed using the MimeType from earlier and
///   the text from the template.
/// * The [View] is given a chance to alter the Response
///   using the `update_response()` hook.
/// * If the status code of the Response is "200 OK" (the default)
///   the status code and cookies fetched earlier are applied.
///
/// ## Template Symbols
///
/// The symbols defined for inside templates are:
/// * `view` will contain the template name, that coincides with
///   the basename of the template file.
/// * `format` will contain the format name (i.e. `html`, `text`, `json`)
/// * `mime_type` will contain the serialized mime_type
///   (i.e. `text/plain; charset=utf-8` or `application/json`)
/// * `http_status` will contain the numeric HTTP status code.
/// * `data` will contain the serde serialized [View]
/// * `extra` will be set to `template_config` which usually comes
///   from an `extra.toml` file in the template directory or a
///   configured custom location.
/// * others that were added by the [QuerySettings] in `initalize_template_context()`
///
/// # API Mode
/// 
/// In API mode the following, simpler sequence of events happens:
/// * status code, format and cookies are fetched.
///   (The cookie functionality is enabled with the `axum-view+cookie` feature)
/// * The [View] [serializes itself] using the `get_api_response()` callback.
/// * If the status code of the Response is "200 OK" (the default)
///   the status code and cookies fetched earlier are applied.
/// 
/// 
/// [View]: ./trait.HumusView.html
/// [QuerySettings]: ./trait.HumusQuerySettings.html
/// [Format]: ./trait.HumusFormat.html
/// [provided by the QuerySettings]: ./trait.HumusQuerySettings.html#tymethod.get_format
/// [Template Mode]: ./enum.HumusFormatFamily.html#variant.Template
/// [API Mode]: ./enum.HumusFormatFamily.html#variant.API
/// [serializes itself]: ./trait.HumusView.html#method.get_api_response
/// [Json Response]: https://docs.rs/axum/0.6.20/axum/struct.Json.html
///
#[derive(Clone)]
pub struct HumusEngine<V, S, F>
where V: HumusView<S, F>, S: HumusQuerySettings<F>, F: HumusFormat {
	
	/// An instance of the tera templating engine.
	pub tera: Tera,
	
	/// If it was possible to read any extra configuration it will be stored here.
	pub template_config: Option<Table>,

	phantom_view: PhantomData<V>,
	phantom_settings: PhantomData<S>,
	phantom_format: PhantomData<F>,
}

impl<V, S, F> HumusEngine<V, S, F>
where V: HumusView<S, F>, S: HumusQuerySettings<F>, F: HumusFormat {

	/// Creates a new Templating Engine.
	///
	/// An alternative would be converting from a [HumusProtoEngine].
	///
	/// [HumusProtoEngine]: ./struct.HumusProtoEngine.html
	pub fn new(tera: Tera, template_config: Option<Table>) -> Self {
		Self {
			tera: tera,
			template_config: template_config,
			phantom_view: PhantomData,
			phantom_settings: PhantomData,
			phantom_format: PhantomData,
		}
	}

	/// Takes settings and a view, converting it to a serveable response.
	///
	/// Example:
	/// ```
	/// async fn hello_world_handler(
	/// 	State(arc_state): State<Arc<ServiceSharedState>>,
	/// 	Extension(settings): Extension<QuerySettings>,
	/// ) -> Response {
	/// 	let state = Arc::clone(&arc_state);
	///
	/// 	state.templating_engine.render_view(
	/// 		&settings,
	/// 		View::Message{
	/// 			title: "Hey There!".to_string(),
	/// 			message: "You are an awesome creature!".to_string()
	/// 		},
	/// 	)
	/// }
	///
	/// ```
	pub fn render_view(
		&self,
		settings: &S,
		view: V,
	) -> Response {
		let status_code = view.get_status_code(&settings);
		let format = settings.get_format();
		#[cfg(feature="axum-view+cookie")]
		let cookie_string = view.get_cookie_header(&settings);

		let mut response = match format.get_family() {
			HumusFormatFamily::Template => {
				let template_name = view.get_template_name();
				let mime_type = format.get_mime_type();
		
				let mut context = tera::Context::new();
				context.insert("view", &template_name);
				//intented for shared macros
				context.insert("format", &format.get_name());
				context.insert("mimetype", &mime_type.to_string());
				context.insert("http_status", &status_code.as_u16());
				context.insert("data", &view);
				context.insert("extra", &self.template_config);
				settings.initalize_template_context(&mut context);

				match self.tera.render(
					&(template_name.clone()+&format.get_file_extension()),
					&context
				) {
					Ok(text) => {
						let mut response = (
							[(
								header::CONTENT_TYPE,
								HeaderValue::from_str(mime_type.as_ref())
									.expect("MimeType should always be a valid header value.")
							)],
							Into::<Body>::into(text),
						).into_response();
						view.update_response(&mut response, &settings);
						response
					},
					Err(e) => {
						println!("There was an error while rendering template {}: {e:?}", template_name);
						(
							StatusCode::INTERNAL_SERVER_ERROR,
						format!("Template error in {}, contact owner or see logs.\n", template_name)
						).into_response()
					}
				}
			}
			HumusFormatFamily::API => {
				view.get_api_response(&settings)
			}
		};

		// Everything went well and nobody did the following work for us.
		if response.status() == StatusCode::OK {
			
			// Set status code
			if status_code != StatusCode::OK {
				*response.status_mut() = status_code;
			}

			// Set cookie header
			#[cfg(feature="axum-view+cookie")]
			if let Some(cookie_string) = cookie_string {
				if let Ok(header_value) = HeaderValue::from_str(&cookie_string) {
					response.headers_mut().append(
						SET_COOKIE,
						header_value,
					);
				}
			}
			
		}

		// return response
		response
	}
}

impl<V, S, F> From<HumusProtoEngine> for HumusEngine<V, S, F>
where V: HumusView<S, F>, S: HumusQuerySettings<F>, F: HumusFormat {
	fn from(e: HumusProtoEngine) -> Self {
		Self::new(e.tera, e.template_config)
	}
}

impl<V, S, F> From<HumusEngine<V, S, F>> for HumusProtoEngine
where V: HumusView<S, F>, S: HumusQuerySettings<F>, F: HumusFormat {
	fn from(e: HumusEngine<V, S, F>) -> Self {
		Self {
			tera: e.tera,
			template_config: e.template_config,
		}
	}
}