vorma 0.86.0-pre.6

//! Page and endpoint targets resolved to hrefs. A page target names one of
//! the application's view patterns; each loader at or above the pattern that
//! owns search fields must accept its own fields, and the href carries the
//! fields as the input supplied them. An endpoint target names an endpoint
//! pattern; the redirect's follow-up request must reach an endpoint with the
//! redirecting endpoint's types.

use std::fmt;
use std::sync::Arc;

use http::Method;
use serde_json::{Map, Value};
use vorma_path_wire::{
	DYNAMIC_PARAM_PREFIX, INDEX_SEGMENT, SPLAT_SEGMENT, canonicalize_pattern, encode_path_segment,
};

use crate::outcome::{RedirectingApiEndpoint, ResolveTarget};
use crate::plan::{ApiEndpointNode, ClassifiedRequest, CurrentPlan, Plan, ViewNode};
use crate::result::{ApiEndpointTarget, PageTarget, RedirectStatus};
use crate::search::{SearchShape, serialize_search_params};

/// Turns page targets into hrefs. Every handler context has one as
/// `page_hrefs`, and [`LoadedApp::page_hrefs`](crate::LoadedApp::page_hrefs)
/// returns one for code outside a request, such as host routes and background
/// jobs. Canonical links, `og:url` and hreflang alternates, pagination links,
/// and links in email can use it instead of formatting URLs by hand.
///
/// A [`Redirect`](crate::Redirect) to a [`PageTarget`] and
/// [`PageHrefs::to_href`] resolve the target by the same rules.
#[derive(Clone)]
pub struct PageHrefs {
	resolver: Arc<dyn ResolveTarget>,
}

impl PageHrefs {
	pub(crate) fn new(resolver: Arc<dyn ResolveTarget>) -> Self {
		Self { resolver }
	}

	/// Creates a `PageHrefs` that resolves every page target with
	/// `resolve_page_target`, which returns the href or the reason that the
	/// target is invalid. A test uses it to build a handler context without a
	/// loaded app.
	pub fn from_resolver(
		resolve_page_target: impl Fn(&PageTarget) -> Result<String, String> + Send + Sync + 'static,
	) -> Self {
		Self::new(Arc::new(FunctionResolver(resolve_page_target)))
	}

	/// Returns the page's path, search, and hash as a relative href.
	///
	/// The target's pattern must be a page in the current build, and the
	/// search input must fit the input of every loader at or above the
	/// pattern. Path segments and search parameters get Vorma's encoding, and
	/// the hash gets the URL standard's fragment encoding. The path that the
	/// target builds must reach the target's own page: when another page
	/// pattern or a `GET` API endpoint is more specific for that path, such as
	/// `/users/new` for the target `/users/:id` with `id` set to `new` when
	/// `/users/new` is also a page, the target is invalid. A target that does
	/// not meet these conditions returns an [`HrefError`].
	///
	/// The current build is the build that the request used, for a handler
	/// context, and the build that Vorma most recently planned, for
	/// [`LoadedApp::page_hrefs`](crate::LoadedApp::page_hrefs). A redirect
	/// resolves its target against the build that the request used.
	pub fn to_href(&self, target: &PageTarget) -> Result<String, HrefError> {
		self.resolver
			.resolve_page_target(target)
			.map_err(|problem| HrefError {
				message: format!("the page target {:?} is invalid: {problem}", target.pattern),
			})
	}
}

/// A page-target resolver from a function. It resolves no endpoint target.
struct FunctionResolver<Resolve>(Resolve);

impl<Resolve: Fn(&PageTarget) -> Result<String, String> + Send + Sync> ResolveTarget
	for FunctionResolver<Resolve>
{
	fn resolve_page_target(&self, target: &PageTarget) -> Result<String, String> {
		(self.0)(target)
	}

	fn resolve_api_endpoint_target(
		&self,
		_redirecting: &RedirectingApiEndpoint,
		_target: &ApiEndpointTarget,
		_status: RedirectStatus,
	) -> Result<String, String> {
		Err("a PageHrefs made from a function resolves page targets only".to_owned())
	}
}

impl fmt::Debug for PageHrefs {
	fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
		formatter.debug_struct("PageHrefs").finish_non_exhaustive()
	}
}

/// A [`PageTarget`] that cannot become an href: its pattern is not a page in
/// the current build, a parameter is missing, the search input does not fit
/// the loaders at or above the pattern, or the path that the target builds
/// belongs to a different page or to a `GET` API endpoint.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct HrefError {
	message: String,
}

impl fmt::Display for HrefError {
	fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
		formatter.write_str(&self.message)
	}
}

impl std::error::Error for HrefError {}

impl<State: Send + Sync + 'static> ResolveTarget for CurrentPlan<State> {
	fn resolve_page_target(&self, target: &PageTarget) -> Result<String, String> {
		self.get().resolve_page_target(target)
	}

	fn resolve_api_endpoint_target(
		&self,
		redirecting: &RedirectingApiEndpoint,
		target: &ApiEndpointTarget,
		status: RedirectStatus,
	) -> Result<String, String> {
		self.get()
			.resolve_api_endpoint_target(redirecting, target, status)
	}
}

impl<State: Send + Sync + 'static> ResolveTarget for Plan<State> {
	fn resolve_page_target(&self, target: &PageTarget) -> Result<String, String> {
		let node = self
			.find_view_node(target.pattern)
			.ok_or_else(|| "no view loader or view declares this pattern".to_owned())?;
		let search = resolve_search(node, target)?;
		let parts = HrefParts {
			kind: PatternKind::View,
			pattern: &node.pattern,
			params: &target.params,
			splat_values: &target.splat_values,
			search,
			hash: target.hash.as_deref(),
		};
		let mut href = build_path(&parts)?;
		self.check_path_reaches_view(&href, node)?;
		append_search_and_hash(&mut href, parts);
		Ok(href)
	}

	fn resolve_api_endpoint_target(
		&self,
		redirecting: &RedirectingApiEndpoint,
		target: &ApiEndpointTarget,
		status: RedirectStatus,
	) -> Result<String, String> {
		let follow_up = follow_up_method(status, &redirecting.method);
		let node = self
			.find_api_endpoint_node(&follow_up, target.pattern)
			.ok_or_else(|| {
				format!(
					"the follow-up request uses {follow_up}, and no {follow_up} API endpoint declares this pattern"
				)
			})?;
		let types = &node.declaration.types;
		if types.output != redirecting.types.output {
			return Err(
				"its output type differs from the redirecting endpoint's output type".to_owned(),
			);
		}
		if types.declared_error != redirecting.types.declared_error {
			return Err(
				"its declared error type differs from the redirecting endpoint's declared error type"
					.to_owned(),
			);
		}
		let search = if follow_up == redirecting.method && follow_up != Method::GET {
			if types.input != redirecting.types.input {
				return Err(format!(
					"the follow-up {follow_up} request carries this request's body, and its input type differs from the redirecting endpoint's input type"
				));
			}
			if target.input.is_some() {
				return Err(format!(
					"the follow-up {follow_up} request carries this request's body, so the target takes no search input"
				));
			}
			None
		} else {
			resolve_api_endpoint_search(node, target)?
		};
		let parts = HrefParts {
			kind: PatternKind::ApiEndpoint,
			pattern: node.declaration.pattern,
			params: &target.params,
			splat_values: &target.splat_values,
			search,
			hash: None,
		};
		let mut href = build_path(&parts)?;
		append_search_and_hash(&mut href, parts);
		Ok(href)
	}
}

impl<State> Plan<State> {
	/// Checks that a `GET` request for `path` reaches `node`. A path that
	/// the target's params and splat values build can belong to a more specific pattern, such
	/// as `/users/new` for the target `/users/:id` with `id` set to `new`
	/// when `/users/new` is also a view pattern, or to a `GET` endpoint.
	fn check_path_reaches_view(&self, path: &str, node: &ViewNode<State>) -> Result<(), String> {
		match self.classify(&Method::GET, path) {
			Ok(ClassifiedRequest::View { positions })
				if positions
					.last()
					.is_some_and(|leaf| std::ptr::eq(leaf.node, node)) =>
			{
				Ok(())
			}
			Ok(ClassifiedRequest::View { positions }) => Err(format!(
				"the path {path:?} belongs to the view pattern {:?}",
				positions
					.last()
					.map_or("", |leaf| leaf.node.pattern.as_str())
			)),
			Ok(ClassifiedRequest::ApiEndpoint { node, .. }) => Err(format!(
				"the path {path:?} belongs to the GET API endpoint {:?}",
				node.declaration.pattern
			)),
			Ok(ClassifiedRequest::Unmatched) => {
				Err(format!("the path {path:?} matches no view pattern"))
			}
			Err(error) => Err(format!("the path {path:?} is not a valid path: {error}")),
		}
	}
}

/// The method of the request that follows a redirect, as the Fetch standard
/// defines it: 303 turns any method except `HEAD` into `GET`, 302 turns `POST`
/// into `GET`, and 307 and 308 keep the method. An endpoint's declared method
/// is never `HEAD`, because the `GET` endpoint answers `HEAD` requests.
fn follow_up_method(status: RedirectStatus, method: &Method) -> Method {
	match status {
		RedirectStatus::SeeOther => Method::GET,
		RedirectStatus::Found if method == Method::POST => Method::GET,
		RedirectStatus::Found
		| RedirectStatus::TemporaryRedirect
		| RedirectStatus::PermanentRedirect => method.clone(),
	}
}

/// A follow-up `GET` request's search input, which must fit the target
/// endpoint's input type.
fn resolve_api_endpoint_search<State>(
	node: &ApiEndpointNode<State>,
	target: &ApiEndpointTarget,
) -> Result<Option<Map<String, Value>>, String> {
	let input = match &target.input {
		None => None,
		Some(Ok(input)) => Some(input),
		Some(Err(error)) => return Err(format!("the search input cannot be serialized: {error}")),
	};
	let Some(shape) = &node.search else {
		return match input {
			None => Ok(None),
			Some(_) => Err("the endpoint takes no search input".to_owned()),
		};
	};
	let empty = Map::new();
	let object = match input {
		// An omitted search is an empty one; the input type decides whether
		// that fits it.
		None => &empty,
		Some(Value::Object(object)) => object,
		Some(_) => return Err("the search input is not an object".to_owned()),
	};
	let projected: Map<String, Value> = field_names(shape)
		.filter_map(|name| {
			object
				.get(name)
				.map(|value| (name.to_owned(), value.clone()))
		})
		.collect();
	if !(node.declaration.is_search_input_valid_fn)(Value::Object(projected.clone())) {
		return Err("the search input does not fit the endpoint's input type".to_owned());
	}
	Ok(Some(projected))
}

fn field_names(shape: &SearchShape) -> impl Iterator<Item = &str> {
	let fields = match shape {
		SearchShape::Object { fields, .. } => fields.as_slice(),
		_ => &[],
	};
	fields.iter().map(|field| field.name.as_str())
}

/// The search fields that the pattern's owners accept, in owner order.
fn resolve_search<State>(
	node: &ViewNode<State>,
	target: &PageTarget,
) -> Result<Option<Map<String, Value>>, String> {
	let input = match &target.input {
		None => None,
		Some(Ok(input)) => Some(input),
		Some(Err(error)) => return Err(format!("the search input cannot be serialized: {error}")),
	};
	if node.search_owners.is_empty() {
		return match input {
			None => Ok(None),
			Some(_) => Err("no loader at or above this pattern declares search input".to_owned()),
		};
	}
	let empty = Map::new();
	let object = match input {
		// An omitted search is an empty one; each owner decides whether that
		// satisfies it.
		None => &empty,
		Some(Value::Object(object)) => object,
		Some(_) => return Err("the search input is not an object".to_owned()),
	};
	let mut search = Map::new();
	for owner in &node.search_owners {
		let Some(shape) = &owner.search else {
			continue;
		};
		let projected: Map<String, Value> = field_names(shape)
			.filter_map(|name| {
				object
					.get(name)
					.map(|value| (name.to_owned(), value.clone()))
			})
			.collect();
		if !(owner.declaration.is_search_input_valid_fn)(Value::Object(projected.clone())) {
			return Err(format!(
				"the search input does not satisfy the input of the view loader {:?}",
				owner.declaration.pattern
			));
		}
		search.extend(projected);
	}
	Ok(Some(search))
}

/// Which grammar a pattern uses: nested view patterns or flat endpoint
/// patterns.
#[derive(Clone, Copy, PartialEq, Eq)]
enum PatternKind {
	View,
	ApiEndpoint,
}

struct HrefParts<'a> {
	kind: PatternKind,
	pattern: &'a str,
	params: &'a [(String, String)],
	splat_values: &'a [String],
	search: Option<Map<String, Value>>,
	hash: Option<&'a str>,
}

/// The path of an href from a pattern, its params, and its splat values, by the rules of the
/// client's href builder (`packages/client/src/protocol/href.ts`). A `:name`
/// segment takes the param of that name and `*` takes the splat values. In a
/// view pattern, a trailing `_index` names its parent path and is omitted, and a
/// non-root splat needs a value. An API pattern keeps its trailing slash,
/// and an empty splat after other segments becomes a trailing slash.
fn build_path(parts: &HrefParts<'_>) -> Result<String, String> {
	let spelled = canonicalize_pattern(parts.pattern).map_err(|error| error.to_string())?;
	let has_trailing_slash =
		parts.kind == PatternKind::ApiEndpoint && spelled.len() > 1 && spelled.ends_with('/');
	let pattern_segments: Vec<&str> = if spelled == "/" {
		Vec::new()
	} else if has_trailing_slash {
		spelled[1..spelled.len() - 1].split('/').collect()
	} else {
		spelled[1..].split('/').collect()
	};
	let mut trailing_slash = has_trailing_slash;
	let mut segments = Vec::with_capacity(pattern_segments.len());
	let mut has_splat = false;
	for (index, segment) in pattern_segments.iter().enumerate() {
		let is_last = index + 1 == pattern_segments.len();
		if parts.kind == PatternKind::View && is_last && *segment == INDEX_SEGMENT {
			continue;
		}
		if segment.len() == SPLAT_SEGMENT.len_utf8() && segment.starts_with(SPLAT_SEGMENT) {
			has_splat = true;
			if parts.splat_values.is_empty() {
				match parts.kind {
					PatternKind::View if pattern_segments.len() > 1 => {
						return Err(format!(
							"the view pattern {:?} cannot select its non-root splat with no values",
							parts.pattern
						));
					}
					PatternKind::ApiEndpoint if !segments.is_empty() => trailing_slash = true,
					PatternKind::View | PatternKind::ApiEndpoint => {}
				}
			}
			for value in parts.splat_values {
				segments.push(encode_path_segment(value).map_err(|error| error.to_string())?);
			}
			continue;
		}
		if let Some(name) = segment.strip_prefix(DYNAMIC_PARAM_PREFIX) {
			let value = parts
				.params
				.iter()
				.find(|(param, _)| param == name)
				.map(|(_, value)| value)
				.ok_or_else(|| format!("the parameter {name} is missing"))?;
			segments.push(encode_path_segment(value).map_err(|error| error.to_string())?);
			continue;
		}
		segments.push((*segment).to_owned());
	}
	if !has_splat && !parts.splat_values.is_empty() {
		return Err(format!(
			"the pattern {:?} does not accept splat values",
			parts.pattern
		));
	}
	Ok(if segments.is_empty() {
		"/".to_owned()
	} else if trailing_slash {
		format!("/{}/", segments.join("/"))
	} else {
		format!("/{}", segments.join("/"))
	})
}

/// Appends the search and the hash of an href to its path.
fn append_search_and_hash(href: &mut String, parts: HrefParts<'_>) {
	if let Some(search) = parts.search.filter(|search| !search.is_empty()) {
		let entries = serialize_search_params(&Value::Object(search));
		let mut serializer = form_urlencoded::Serializer::new(String::new());
		serializer.extend_pairs(&entries);
		let query = serializer.finish();
		if !query.is_empty() {
			href.push('?');
			href.push_str(&query);
		}
	}
	if let Some(hash) = parts.hash.filter(|hash| !hash.is_empty()) {
		href.push('#');
		push_fragment(href, hash.strip_prefix('#').unwrap_or(hash));
	}
}

/// Percent-encodes a fragment with the URL standard's fragment percent-encode
/// set, as the `hash` setter of a URL does.
fn push_fragment(href: &mut String, fragment: &str) {
	for character in fragment.chars() {
		// The URL parser removes ASCII tabs and newlines before it encodes.
		if matches!(character, '\t' | '\n' | '\r') {
			continue;
		}
		let encode = matches!(character, '\u{0}'..='\u{1F}' | ' ' | '"' | '<' | '>' | '`')
			|| character > '\u{7E}';
		if !encode {
			href.push(character);
			continue;
		}
		let mut buffer = [0; 4];
		for byte in character.encode_utf8(&mut buffer).bytes() {
			href.push_str(&format!("%{byte:02X}"));
		}
	}
}