// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

use crate::{
    env::Env, ClientAssertion, ClientAssertionCredential, ClientAssertionCredentialOptions,
};
use azure_core::{
    credentials::{AccessToken, Secret, TokenCredential, TokenRequestOptions},
    error::ErrorKind,
    http::{
        headers::{FromHeaders, HeaderName, Headers, AUTHORIZATION, CONTENT_LENGTH},
        request::Request,
        ClientMethodOptions, Method, Pipeline, PipelineSendOptions, StatusCode, Url,
    },
};
use serde::Deserialize;
use std::{borrow::Cow, convert::Infallible, fmt, sync::Arc};

// cspell:ignore fedauthredirect msedge oidcrequesturi
const OIDC_VARIABLE_NAME: &str = "SYSTEM_OIDCREQUESTURI";
const OIDC_VERSION: &str = "7.1";
const TFS_FEDAUTHREDIRECT_HEADER: HeaderName = HeaderName::from_static("x-tfs-fedauthredirect");

const ALLOWED_HEADERS: &[&str] = &["x-msedge-ref", "x-vss-e2eid"];

/// Authenticates an [Azure Pipelines service connection](https://learn.microsoft.com/azure/devops/pipelines/library/service-endpoints).
#[derive(Debug)]
pub struct AzurePipelinesCredential(ClientAssertionCredential<Client>);

/// Options for constructing a new [`AzurePipelinesCredential`].
#[derive(Debug, Default)]
pub struct AzurePipelinesCredentialOptions {
    /// Options for the [`ClientAssertionCredential`] used by the [`AzurePipelinesCredential`].
    pub credential_options: ClientAssertionCredentialOptions,

    #[cfg(test)]
    pub(crate) env: Option<Env>,
}

impl AzurePipelinesCredential {
    /// Creates a new `AzurePipelinesCredential`.
    ///
    /// # Arguments
    /// - `tenant_id`: The tenant (directory) ID of the service principal federated with the service connection.
    /// - `client_id`: The client (application) ID of that service principal.
    /// - `service_connection_id`: ID of the service connection to authenticate.
    /// - `system_access_token`: Security token for the running build. See
    ///   [Azure Pipelines documentation](https://learn.microsoft.com/azure/devops/pipelines/build/variables?view=azure-devops#systemaccesstoken)
    ///   for an example showing how to get this value.
    /// - `options`: Options for configuring the credential. If `None`, the credential uses its default options.
    ///
    pub fn new<T>(
        tenant_id: String,
        client_id: String,
        service_connection_id: &str,
        system_access_token: T,
        options: Option<AzurePipelinesCredentialOptions>,
    ) -> azure_core::Result<Arc<Self>>
    where
        T: Into<Secret>,
    {
        let system_access_token = system_access_token.into();

        crate::validate_tenant_id(&tenant_id)?;
        crate::validate_not_empty(&client_id, "no client ID specified")?;
        crate::validate_not_empty(service_connection_id, "no service connection ID specified")?;
        crate::validate_not_empty(
            system_access_token.secret(),
            "no system access token specified",
        )?;

        let mut options = options.unwrap_or_default();
        options
            .credential_options
            .client_options
            .logging
            .additional_allowed_header_names
            // the logging policy constructor will remove any duplicates
            .extend(ALLOWED_HEADERS.iter().map(|&s| Cow::Borrowed(s)));

        #[cfg(test)]
        let env = options.env.unwrap_or_default();
        #[cfg(not(test))]
        let env = Env::default();

        let endpoint = env
            .var(OIDC_VARIABLE_NAME)
            .map_err(|err| azure_core::Error::with_error(
                ErrorKind::Credential,
                err,
                format!("no value for environment variable {OIDC_VARIABLE_NAME}. This should be set by Azure Pipelines"),
            ))?;
        let mut endpoint: Url = endpoint.parse().map_err(|err| {
            azure_core::Error::with_error(
                ErrorKind::Credential,
                err,
                format!("invalid URL for environment variable {OIDC_VARIABLE_NAME}"),
            )
        })?;
        endpoint
            .query_pairs_mut()
            .append_pair("api-version", OIDC_VERSION)
            .append_pair("serviceConnectionId", service_connection_id);
        let pipeline = azure_core::http::Pipeline::new(
            option_env!("CARGO_PKG_NAME"),
            option_env!("CARGO_PKG_VERSION"),
            options.credential_options.client_options.clone(),
            Vec::default(),
            Vec::default(),
            None,
        );
        let client = Client {
            endpoint,
            pipeline: Arc::new(pipeline),
            system_access_token,
        };
        let credential = ClientAssertionCredential::new_exclusive(
            tenant_id,
            client_id,
            client,
            stringify!(AzurePipelinesCredential),
            Some(options.credential_options),
        )?;

        Ok(Arc::new(Self(credential)))
    }
}

#[async_trait::async_trait]
impl TokenCredential for AzurePipelinesCredential {
    async fn get_token(
        &self,
        scopes: &[&str],
        options: Option<TokenRequestOptions<'_>>,
    ) -> azure_core::Result<AccessToken> {
        self.0.get_token(scopes, options).await
    }
}

#[derive(Debug)]
struct Client {
    endpoint: Url,
    pipeline: Arc<Pipeline>,
    system_access_token: Secret,
}

#[async_trait::async_trait]
impl ClientAssertion for Client {
    async fn secret(&self, options: Option<ClientMethodOptions<'_>>) -> azure_core::Result<String> {
        let mut req = Request::new(self.endpoint.clone(), Method::Post);
        req.insert_header(
            AUTHORIZATION,
            String::from("Bearer ") + self.system_access_token.secret(),
        );
        req.insert_header(TFS_FEDAUTHREDIRECT_HEADER, "Suppress");
        req.insert_header(CONTENT_LENGTH, "0");

        let options = options.unwrap_or_default();
        let ctx = options.context.to_borrowed();
        let resp = self
            .pipeline
            .send(
                &ctx,
                &mut req,
                Some(PipelineSendOptions {
                    skip_checks: true,
                    ..Default::default()
                }),
            )
            .await?;
        let status = resp.status();
        if status != StatusCode::Ok {
            let err_headers: ErrorHeaders = resp.headers().get()?;
            return Err(azure_core::Error::with_message(
                ErrorKind::HttpResponse {
                    status,
                    error_code: Some(status.canonical_reason().to_string()),
                    raw_response: Some(Box::new(resp)),
                },
                format!(
                "{status} response from the OIDC endpoint. Check service connection ID and pipeline configuration. {err_headers}"
            ),
            ));
        }

        let assertion: Assertion = resp.into_body().json()?;
        Ok(assertion.oidc_token.secret().to_string())
    }
}

#[derive(Debug, Deserialize)]
struct Assertion {
    #[serde(rename = "oidcToken")]
    oidc_token: Secret,
}

#[derive(Debug)]
struct ErrorHeaders {
    msedge_ref: Option<String>,
    vss_e2eid: Option<String>,
}

const MSEDGE_REF: HeaderName = HeaderName::from_static("x-msedge-ref");
const VSS_E2EID: HeaderName = HeaderName::from_static("x-vss-e2eid");

impl FromHeaders for ErrorHeaders {
    type Error = Infallible;

    fn header_names() -> &'static [&'static str] {
        ALLOWED_HEADERS
    }

    fn from_headers(headers: &Headers) -> Result<Option<Self>, Self::Error> {
        Ok(Some(Self {
            msedge_ref: headers.get_optional_string(&MSEDGE_REF),
            vss_e2eid: headers.get_optional_string(&VSS_E2EID),
        }))
    }
}

impl fmt::Display for ErrorHeaders {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut v = f.debug_struct("Headers");
        if let Some(ref msedge_ref) = self.msedge_ref {
            v.field(MSEDGE_REF.as_str(), msedge_ref);
        }
        if let Some(ref vss_e2eid) = self.vss_e2eid {
            v.field(VSS_E2EID.as_str(), vss_e2eid);
        }
        v.finish()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::env::Env;
    use azure_core::{
        http::{AsyncRawResponse, ClientOptions, RawResponse, Transport},
        Bytes,
    };
    use azure_core_test::http::MockHttpClient;
    use futures::FutureExt as _;

    #[test]
    fn param_errors() {
        assert!(AzurePipelinesCredential::new("".into(), "".into(), "", "", None).is_err());
        assert!(AzurePipelinesCredential::new("_".into(), "".into(), "", "", None).is_err());
        assert!(AzurePipelinesCredential::new("a".into(), "".into(), "", "", None).is_err());
        assert!(AzurePipelinesCredential::new("a".into(), "b".into(), "", "", None).is_err());
        assert!(AzurePipelinesCredential::new("a".into(), "b".into(), "c", "", None).is_err());

        let options = AzurePipelinesCredentialOptions {
            env: Some(Env::from(
                &[(OIDC_VARIABLE_NAME, "http://localhost/get_token")][..],
            )),
            ..Default::default()
        };
        assert!(
            AzurePipelinesCredential::new("a".into(), "b".into(), "c", "d", Some(options)).is_ok()
        );
    }

    #[tokio::test]
    async fn error_response() {
        let expected_status = StatusCode::Forbidden;
        let body = Bytes::from_static(b"content");
        let mut headers = Headers::new();
        headers.insert(MSEDGE_REF, "foo");
        headers.insert(VSS_E2EID, "bar");
        let expected_response =
            RawResponse::from_bytes(expected_status, headers.clone(), body.clone());
        let headers_for_mock = headers.clone();
        let body_for_mock = body.clone();
        let mock_client = MockHttpClient::new(move |req| {
            assert_eq!(
                req.url().as_str(),
                "http://localhost/get_token?api-version=7.1&serviceConnectionId=c"
            );
            let headers = headers_for_mock.clone();
            let body = body_for_mock.clone();

            async move { Ok(AsyncRawResponse::from_bytes(expected_status, headers, body)) }.boxed()
        });
        let options = AzurePipelinesCredentialOptions {
            credential_options: ClientAssertionCredentialOptions {
                client_options: ClientOptions {
                    transport: Some(Transport::new(Arc::new(mock_client))),
                    ..Default::default()
                },
            },
            env: Some(Env::from(
                &[(OIDC_VARIABLE_NAME, "http://localhost/get_token")][..],
            )),
        };
        let err = AzurePipelinesCredential::new("a".into(), "b".into(), "c", "d", Some(options))
            .expect("credential")
            .get_token(&["default"], None)
            .await
            .expect_err("expected error");

        assert!(matches!(err.kind(), ErrorKind::Credential));
        assert_eq!(
            r#"AzurePipelinesCredential authentication failed. 403 response from the OIDC endpoint. Check service connection ID and pipeline configuration. Headers { x-msedge-ref: "foo", x-vss-e2eid: "bar" }
To troubleshoot, visit https://aka.ms/azsdk/rust/identity/troubleshoot#apc"#,
            err.to_string(),
        );
        match err
            .downcast_ref::<azure_core::Error>()
            .expect("returned error should wrap an azure_core::Error")
            .kind()
        {
            ErrorKind::HttpResponse {
                error_code: Some(reason),
                raw_response: Some(response),
                status,
                ..
            } => {
                assert_eq!(status.canonical_reason(), reason.as_str());
                assert_eq!(&expected_response, response.as_ref());
                assert_eq!(expected_status, *status);
            }
            err => panic!("unexpected {:?}", err),
        };
    }

    #[tokio::test]
    async fn mock_request() {
        let mock_client = MockHttpClient::new(|req| {
            async move {
                if req.url().as_str()
                    == "http://localhost/get_token?api-version=7.1&serviceConnectionId=c"
                {
                    assert!(matches!(
                        req.headers().get_str(&AUTHORIZATION),
                        Ok(value) if value == "Bearer d",
                    ));
                    assert!(matches!(
                        req.headers().get_str(&TFS_FEDAUTHREDIRECT_HEADER),
                        Ok(value) if value == "Suppress",
                    ));

                    let mut headers = Headers::new();
                    headers.insert(MSEDGE_REF, "foo");
                    headers.insert(VSS_E2EID, "bar");

                    return Ok(AsyncRawResponse::from_bytes(
                        StatusCode::Ok,
                        headers,
                        Bytes::from_static(br#"{"oidcToken":"baz"}"#),
                    ));
                }

                if req.url().as_str() == "https://login.microsoftonline.com/a/oauth2/v2.0/token" {
                    return Ok(AsyncRawResponse::from_bytes(
                        StatusCode::Ok,
                        Headers::new(),
                        Bytes::from_static(
                            br#"{"token_type":"test","expires_in":0,"ext_expires_in":0,"access_token":"qux"}"#,
                        ),
                    ));
                }

                panic!("not supported")
            }.boxed()
        });
        let options = AzurePipelinesCredentialOptions {
            credential_options: ClientAssertionCredentialOptions {
                client_options: ClientOptions {
                    transport: Some(Transport::new(Arc::new(mock_client))),
                    ..Default::default()
                },
            },
            env: Some(Env::from(
                &[(OIDC_VARIABLE_NAME, "http://localhost/get_token")][..],
            )),
        };
        let credential =
            AzurePipelinesCredential::new("a".into(), "b".into(), "c", "d", Some(options))
                .expect("valid AzurePipelinesCredential");
        let secret = credential
            .get_token(&["default"], None)
            .await
            .expect("valid response");
        assert_eq!(secret.token.secret(), "qux");
    }
}
