// Copyright 2022 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#![allow(clippy::module_name_repetitions)]

use std::collections::HashMap;

use axum::response::{Html, IntoResponse, Redirect, Response};
use mas_data_model::{AuthorizationGrant, StorageBackend};
use mas_templates::{FormPostContext, Templates};
use oauth2_types::requests::ResponseMode;
use serde::Serialize;
use thiserror::Error;
use url::Url;

#[derive(Debug, Clone)]
enum CallbackDestinationMode {
    Query {
        existing_params: HashMap<String, String>,
    },
    Fragment,
    FormPost,
}

#[derive(Debug, Clone)]
pub struct CallbackDestination {
    mode: CallbackDestinationMode,
    safe_redirect_uri: Url,
    state: Option<String>,
}

#[derive(Debug, Error)]
pub enum IntoCallbackDestinationError {
    #[error("Redirect URI can't have a fragment")]
    RedirectUriFragmentNotAllowed,

    #[error("Existing query parameters are not valid")]
    RedirectUriInvalidQueryParams(#[from] serde_urlencoded::de::Error),

    #[error("Requested response_mode is not supported")]
    UnsupportedResponseMode,
}

#[derive(Debug, Error)]
pub enum CallbackDestinationError {
    #[error("Failed to render the form_post template")]
    FormPostRender(#[from] mas_templates::TemplateError),

    #[error("Failed to serialize parameters query string")]
    ParamsSerialization(#[from] serde_urlencoded::ser::Error),
}

impl<S: StorageBackend> TryFrom<&AuthorizationGrant<S>> for CallbackDestination {
    type Error = IntoCallbackDestinationError;

    fn try_from(value: &AuthorizationGrant<S>) -> Result<Self, Self::Error> {
        Self::try_new(
            &value.response_mode,
            value.redirect_uri.clone(),
            value.state.clone(),
        )
    }
}

impl CallbackDestination {
    pub fn try_new(
        mode: &ResponseMode,
        mut redirect_uri: Url,
        state: Option<String>,
    ) -> Result<Self, IntoCallbackDestinationError> {
        if redirect_uri.fragment().is_some() {
            return Err(IntoCallbackDestinationError::RedirectUriFragmentNotAllowed);
        }

        let mode = match mode {
            ResponseMode::Query => {
                let existing_params = redirect_uri
                    .query()
                    .map(serde_urlencoded::from_str)
                    .transpose()?
                    .unwrap_or_default();

                // Remove the query from the URL
                redirect_uri.set_query(None);

                CallbackDestinationMode::Query { existing_params }
            }
            ResponseMode::Fragment => CallbackDestinationMode::Fragment,
            ResponseMode::FormPost => CallbackDestinationMode::FormPost,
            _ => return Err(IntoCallbackDestinationError::UnsupportedResponseMode),
        };

        Ok(Self {
            mode,
            safe_redirect_uri: redirect_uri,
            state,
        })
    }

    pub async fn go<T: Serialize + Send + Sync>(
        self,
        templates: &Templates,
        params: T,
    ) -> Result<Response, CallbackDestinationError> {
        #[derive(Serialize)]
        struct AllParams<'s, T> {
            #[serde(flatten, skip_serializing_if = "Option::is_none")]
            existing: Option<&'s HashMap<String, String>>,

            #[serde(skip_serializing_if = "Option::is_none")]
            state: Option<String>,

            #[serde(flatten)]
            params: T,
        }

        let mut redirect_uri = self.safe_redirect_uri;
        let state = self.state;

        match self.mode {
            CallbackDestinationMode::Query { existing_params } => {
                let merged = AllParams {
                    existing: Some(&existing_params),
                    state,
                    params,
                };

                let new_qs = serde_urlencoded::to_string(merged)?;

                redirect_uri.set_query(Some(&new_qs));

                Ok(Redirect::to(redirect_uri.as_str()).into_response())
            }

            CallbackDestinationMode::Fragment => {
                let merged = AllParams {
                    existing: None,
                    state,
                    params,
                };

                let new_qs = serde_urlencoded::to_string(merged)?;

                redirect_uri.set_fragment(Some(&new_qs));

                Ok(Redirect::to(redirect_uri.as_str()).into_response())
            }

            CallbackDestinationMode::FormPost => {
                let merged = AllParams {
                    existing: None,
                    state,
                    params,
                };
                let ctx = FormPostContext::new(redirect_uri, merged);
                let rendered = templates.render_form_post(&ctx).await?;
                Ok(Html(rendered).into_response())
            }
        }
    }
}