/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */

//! Presigned request types and configuration.

use std::fmt;
use std::time::{Duration, SystemTime};

const ONE_WEEK: Duration = Duration::from_secs(604800);

/// Presigning config values required for creating a presigned request.
#[non_exhaustive]
#[derive(Debug, Clone)]
pub struct PresigningConfig {
    start_time: SystemTime,
    expires_in: Duration,
}

impl PresigningConfig {
    /// Creates a `PresigningConfig` with the given `expires_in` duration.
    ///
    /// The `expires_in` duration is the total amount of time the presigned request should
    /// be valid for. Other config values are defaulted.
    ///
    /// Credential expiration time takes priority over the `expires_in` value.
    /// If the credentials used to sign the request expire before the presigned request is
    /// set to expire, then the presigned request will become invalid.
    pub fn expires_in(expires_in: Duration) -> Result<PresigningConfig, PresigningConfigError> {
        Self::builder().expires_in(expires_in).build()
    }

    /// Creates a new builder for creating a `PresigningConfig`.
    pub fn builder() -> PresigningConfigBuilder {
        PresigningConfigBuilder::default()
    }

    /// Returns the amount of time the presigned request should be valid for.
    pub fn expires(&self) -> Duration {
        self.expires_in
    }

    /// Returns the start time. The presigned request will be valid between this and the end
    /// time produced by adding the `expires()` value to it.
    pub fn start_time(&self) -> SystemTime {
        self.start_time
    }
}

#[derive(Debug)]
enum ErrorKind {
    /// Presigned requests cannot be valid for longer than one week.
    ExpiresInDurationTooLong,

    /// The `PresigningConfig` builder requires a value for `expires_in`.
    ExpiresInRequired,
}

/// `PresigningConfig` build errors.
#[derive(Debug)]
pub struct PresigningConfigError {
    kind: ErrorKind,
}

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

impl fmt::Display for PresigningConfigError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.kind {
            ErrorKind::ExpiresInDurationTooLong => {
                write!(f, "`expires_in` must be no longer than one week")
            }
            ErrorKind::ExpiresInRequired => write!(f, "`expires_in` is required"),
        }
    }
}

impl From<ErrorKind> for PresigningConfigError {
    fn from(kind: ErrorKind) -> Self {
        Self { kind }
    }
}

/// Builder used to create `PresigningConfig`.
#[non_exhaustive]
#[derive(Default, Debug)]
pub struct PresigningConfigBuilder {
    start_time: Option<SystemTime>,
    expires_in: Option<Duration>,
}

impl PresigningConfigBuilder {
    /// Sets the start time for the presigned request.
    ///
    /// The request will start to be valid at this time, and will cease to be valid after
    /// the end time, which can be determined by adding the `expires_in` duration to this
    /// start time. If not specified, this will default to the current time.
    ///
    /// Optional.
    pub fn start_time(mut self, start_time: SystemTime) -> Self {
        self.set_start_time(Some(start_time));
        self
    }

    /// Sets the start time for the presigned request.
    ///
    /// The request will start to be valid at this time, and will cease to be valid after
    /// the end time, which can be determined by adding the `expires_in` duration to this
    /// start time. If not specified, this will default to the current time.
    ///
    /// Optional.
    pub fn set_start_time(&mut self, start_time: Option<SystemTime>) {
        self.start_time = start_time;
    }

    /// Sets how long the request should be valid after the `start_time` (which defaults
    /// to the current time).
    ///
    /// Credential expiration time takes priority over the `expires_in` value.
    /// If the credentials used to sign the request expire before the presigned request is
    /// set to expire, then the presigned request will become invalid.
    ///
    /// Required.
    pub fn expires_in(mut self, expires_in: Duration) -> Self {
        self.set_expires_in(Some(expires_in));
        self
    }

    /// Sets how long the request should be valid after the `start_time` (which defaults
    /// to the current time).
    ///
    /// Credential expiration time takes priority over the `expires_in` value.
    /// If the credentials used to sign the request expire before the presigned request is
    /// set to expire, then the presigned request will become invalid.
    ///
    /// Required.
    pub fn set_expires_in(&mut self, expires_in: Option<Duration>) {
        self.expires_in = expires_in;
    }

    /// Builds the `PresigningConfig`. This will error if `expires_in` is not
    /// given, or if it's longer than one week.
    pub fn build(self) -> Result<PresigningConfig, PresigningConfigError> {
        let expires_in = self.expires_in.ok_or(ErrorKind::ExpiresInRequired)?;
        if expires_in > ONE_WEEK {
            return Err(ErrorKind::ExpiresInDurationTooLong.into());
        }
        Ok(PresigningConfig {
            start_time: self.start_time.unwrap_or_else(SystemTime::now),
            expires_in,
        })
    }
}

/// Represents a presigned request. This only includes the HTTP request method, URI, and headers.
///
/// **This struct has conversion convenience functions:**
///
/// - [`PresignedRequest::to_http_request<B>`][Self::to_http_request] returns an [`http::Request<B>`](https://docs.rs/http/0.2.6/http/request/struct.Request.html)
/// - [`PresignedRequest::into`](#impl-From<PresignedRequest>) returns an [`http::request::Builder`](https://docs.rs/http/0.2.6/http/request/struct.Builder.html)
#[non_exhaustive]
pub struct PresignedRequest(http::Request<()>);

impl PresignedRequest {
    pub(crate) fn new(inner: http::Request<()>) -> Self {
        Self(inner)
    }

    /// Returns the HTTP request method.
    pub fn method(&self) -> &http::Method {
        self.0.method()
    }

    /// Returns the HTTP request URI.
    pub fn uri(&self) -> &http::Uri {
        self.0.uri()
    }

    /// Returns any HTTP headers that need to go along with the request, except for `Host`,
    /// which should be sent based on the endpoint in the URI by the HTTP client rather than
    /// added directly.
    pub fn headers(&self) -> &http::HeaderMap<http::HeaderValue> {
        self.0.headers()
    }

    /// Given a body, convert this `PresignedRequest` into an `http::Request`
    pub fn to_http_request<B>(self, body: B) -> Result<http::Request<B>, http::Error> {
        let builder: http::request::Builder = self.into();

        builder.body(body)
    }
}

impl fmt::Debug for PresignedRequest {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("PresignedRequest")
            .field("method", self.method())
            .field("uri", self.uri())
            .field("headers", self.headers())
            .finish()
    }
}

impl From<PresignedRequest> for http::request::Builder {
    fn from(req: PresignedRequest) -> Self {
        let mut builder = http::request::Builder::new()
            .uri(req.uri())
            .method(req.method());

        if let Some(headers) = builder.headers_mut() {
            *headers = req.headers().clone();
        }

        builder
    }
}

/// Tower middleware service for creating presigned requests
#[allow(dead_code)]
pub(crate) mod service {
    use super::PresignedRequest;
    use aws_smithy_http::operation;
    use http::header::USER_AGENT;
    use std::future::{ready, Ready};
    use std::marker::PhantomData;
    use std::task::{Context, Poll};

    /// Tower [`Service`](tower::Service) for generated a [`PresignedRequest`] from the AWS middleware.
    #[derive(Default, Debug)]
    #[non_exhaustive]
    pub(crate) struct PresignedRequestService<E> {
        _phantom: PhantomData<E>,
    }

    // Required because of the derive Clone on MapRequestService.
    // Manually implemented to avoid requiring errors to implement Clone.
    impl<E> Clone for PresignedRequestService<E> {
        fn clone(&self) -> Self {
            Self {
                _phantom: Default::default(),
            }
        }
    }

    impl<E> PresignedRequestService<E> {
        /// Creates a new `PresignedRequestService`
        pub(crate) fn new() -> Self {
            Self {
                _phantom: Default::default(),
            }
        }
    }

    impl<E> tower::Service<operation::Request> for PresignedRequestService<E> {
        type Response = PresignedRequest;
        type Error = E;
        type Future = Ready<Result<PresignedRequest, E>>;

        fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
            Poll::Ready(Ok(()))
        }

        fn call(&mut self, req: operation::Request) -> Self::Future {
            let (mut req, _) = req.into_parts();

            // Remove user agent headers since the request will not be executed by the AWS Rust SDK.
            req.headers_mut().remove(USER_AGENT);
            req.headers_mut().remove("X-Amz-User-Agent");

            ready(Ok(PresignedRequest::new(req.map(|_| ()))))
        }
    }
}
