//

use std::{
    cell::RefCell,
    collections::HashMap,
    fmt::{Debug, Display},
    marker::PhantomData,
    ops::Deref,
    rc::Rc,
    sync::Arc,
};

use bytes::Bytes;
use derive_more::derive::{Display, From};
use http::StatusCode;
use reqwest::{Client, RequestBuilder};
use tokio::sync::Mutex;
use url::Url;

use crate::net::{Request, Response};

use super::{Error, Result};

/// A list of planned requests and responses
type Plans = Vec<Plan>;

/// A planned request and the response to return
///
/// Contains a list of the criteria that a request must meet before being considered a match.
#[derive(Debug)]
struct Plan {
    match_request: Vec<MatchRequest>,
    response: reqwest::Response,
}
impl Plan {
    fn matches(&self, request: &Request) -> bool {
        self.match_request.iter().all(|criteria| match criteria {
            MatchRequest::Method(method) => request.method() == http::Method::from(method),
            MatchRequest::Url(uri) => request.url() == uri,
            MatchRequest::Header { name, value } => {
                request
                    .headers()
                    .iter()
                    .any(|(request_header_name, request_header_value)| {
                        let Ok(request_header_value) = request_header_value.to_str() else {
                            return false;
                        };
                        request_header_name.as_str() == name && request_header_value == value
                    })
            }
            MatchRequest::Body(body) => {
                request.body().and_then(reqwest::Body::as_bytes) == Some(body)
            }
        })
    }
}
impl Display for Plan {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for m in &self.match_request {
            write!(f, "{m} ")?;
        }
        writeln!(f, "=> {:?}", self.response)
    }
}

/// An abstraction for the network
#[derive(Debug, Clone, Default)]
pub struct Net {
    plans: Option<Arc<Mutex<RefCell<Plans>>>>,
}
impl Net {
    /// Creates a new unmocked [Net] for creating real network requests.
    pub(super) const fn new() -> Self {
        Self { plans: None }
    }
}
impl Net {
    /// Helper to create a default [Client].
    ///
    /// # Example
    ///
    /// ```rust
    /// # use kxio::net::Result;
    /// let net = kxio::net::new();
    /// let client = net.client();
    /// let request = client.get("https://hyper.rs");
    /// ```
    #[must_use]
    pub fn client(&self) -> Client {
        Default::default()
    }

    /// Constructs the Request and sends it to the target URL, returning a
    /// future Response.
    ///
    /// However, if this request is from a [Net] that was created from a [MockNet],
    /// then the request will be matched and any stored response returned, or an
    /// error if no matched request was found.
    ///
    /// # Errors
    ///
    /// This method fails if there was an error while sending request,
    /// redirect loop was detected or redirect limit was exhausted.
    /// If the response has a Status Code of `4xx` or `5xx` then the
    /// response will be returned as an [Error::ResponseError].
    ///
    /// # Example
    ///
    /// ```no_run
    /// # use kxio::net::Result;
    /// # async fn run() -> Result<()> {
    /// let net = kxio::net::new();
    /// let request = net.client().get("https://hyper.rs");
    /// let response = net.send(request).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn send(&self, request: impl Into<RequestBuilder>) -> Result<Response> {
        let Some(plans) = &self.plans else {
            return request.into().send().await.map_err(Error::from);
        };
        let request = request.into().build()?;
        eprintln!(
            "? {} {} {:?}",
            request.method(),
            request.url(),
            request.headers()
        );
        let index = plans
            .lock()
            .await
            .deref()
            .borrow()
            .iter()
            .position(|plan| plan.matches(&request));
        match index {
            Some(i) => {
                let plan = plans.lock().await.borrow_mut().remove(i);
                eprintln!("- matched: {plan}");
                let response = plan.response;
                if response.status().is_success() {
                    Ok(response)
                } else {
                    Err(crate::net::Error::ResponseError { response })
                }
            }
            None => Err(Error::UnexpectedMockRequest(request)),
        }
    }

    /// Starts building an http DELETE request for the URL.
    #[must_use]
    pub fn delete(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Delete, url)
    }

    /// Starts building an http GET request for the URL.
    #[must_use]
    pub fn get(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Get, url)
    }

    /// Starts building an http HEAD request for the URL.
    #[must_use]
    pub fn head(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Head, url)
    }

    /// Starts building an http PATCH request for the URL.
    #[must_use]
    pub fn patch(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Patch, url)
    }

    /// Starts building an http POST request for the URL.
    #[must_use]
    pub fn post(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Post, url)
    }

    /// Starts building an http PUT request for the URL.
    #[must_use]
    pub fn put(&self, url: impl Into<String>) -> ReqBuilder {
        ReqBuilder::new(self, NetMethod::Put, url)
    }
}
impl MockNet {
    pub async fn try_from(net: Net) -> std::result::Result<Self, super::Error> {
        match &net.plans {
            Some(plans) => Ok(MockNet {
                plans: Rc::new(RefCell::new(plans.lock().await.take())),
            }),
            None => Err(super::Error::NetIsNotAMock),
        }
    }
}

#[derive(Debug, Clone, Display, PartialEq, Eq)]
pub enum NetMethod {
    Delete,
    Get,
    Head,
    Patch,
    Post,
    Put,
}
impl From<&NetMethod> for http::Method {
    fn from(value: &NetMethod) -> Self {
        match value {
            NetMethod::Delete => http::Method::DELETE,
            NetMethod::Get => http::Method::GET,
            NetMethod::Head => http::Method::HEAD,
            NetMethod::Patch => http::Method::PATCH,
            NetMethod::Post => http::Method::POST,
            NetMethod::Put => http::Method::PUT,
        }
    }
}

/// A builder for an http request.
pub struct ReqBuilder<'net> {
    net: &'net Net,
    url: String,
    method: NetMethod,
    headers: Vec<(String, String)>,
    body: Option<Bytes>,
}
impl<'net> ReqBuilder<'net> {
    #[must_use]
    fn new(net: &'net Net, method: NetMethod, url: impl Into<String>) -> Self {
        Self {
            net,
            url: url.into(),
            method,
            headers: vec![],
            body: None,
        }
    }

    /// Constructs the Request and sends it to the target URL, returning a
    /// future Response.
    ///
    /// However, if this request is from a [Net] that was created from a [MockNet],
    /// then the request will be matched and any stored response returned, or an
    /// error if no matched request was found.
    ///
    /// # Errors
    ///
    /// This method fails if there was an error while sending request,
    /// redirect loop was detected or redirect limit was exhausted.
    /// If the response has a Status Code of `4xx` or `5xx` then the
    /// response will be returned as an [Error::ResponseError].
    ///
    /// # Example
    ///
    /// ```no_run
    /// # use kxio::net::Result;
    /// # async fn run() -> Result<()> {
    /// let net = kxio::net::new();
    /// let response = net.get("https://hyper.rs")
    ///   .header("foo", "bar")
    ///   .body("{}")
    ///   .send().await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn send(self) -> Result<Response> {
        let client = self.net.client();
        // Method
        let mut req = match self.method {
            NetMethod::Delete => client.delete(self.url),
            NetMethod::Get => client.get(self.url),
            NetMethod::Head => client.head(self.url),
            NetMethod::Patch => client.patch(self.url),
            NetMethod::Post => client.post(self.url),
            NetMethod::Put => client.put(self.url),
        };
        // Headers
        for (name, value) in self.headers.into_iter() {
            req = req.header(name, value);
        }
        // Body
        if let Some(bytes) = self.body {
            req = req.body(bytes);
        }

        self.net.send(req).await
    }

    /// Adds the header and value to the request.
    #[must_use]
    pub fn header(mut self, name: impl Into<String>, value: impl Into<String>) -> Self {
        self.headers.push((name.into(), value.into()));
        self
    }

    /// Adds the headers to the request.
    #[must_use]
    pub fn headers(mut self, headers: HashMap<String, String>) -> Self {
        self.headers.extend(headers);
        self
    }

    /// Sets the request body.
    #[must_use]
    pub fn body(mut self, bytes: impl Into<Bytes>) -> Self {
        self.body = Some(bytes.into());
        self
    }
}

/// A struct for defining the expected requests and their responses that should be made
/// during a test.
///
/// When the [MockNet] goes out of scope it will verify that all expected requests were consumed,
/// otherwise it will `panic`.
///
/// # Example
///
/// ```rust
/// # use kxio::net::Result;
/// use kxio::net::StatusCode;
/// # #[tokio::main]
/// # async fn run() -> Result<()> {
/// let mock_net = kxio::net::mock();
/// let client = mock_net.client();
/// // define an expected requet, and the response that should be returned
/// mock_net.on().get("https://hyper.rs")
///     .respond(StatusCode::OK).body("Ok");
/// let net: kxio::net::Net = mock_net.into();
/// // use 'net' in your program, by passing it as a reference
///
/// // In some rare cases you don't want to assert that all expected requests were made.
/// // You should recover the `MockNet` from the `Net` and `MockNet::reset` it.
/// let mock_net = kxio::net::MockNet::try_from(net).await?;
/// mock_net.reset(); // only if explicitly needed
/// # Ok(())
/// # }
/// ```
#[derive(Debug, Clone, Default)]
pub struct MockNet {
    plans: Rc<RefCell<Plans>>,
}
impl MockNet {
    /// Helper to create a default [Client].
    ///
    /// # Example
    ///
    /// ```rust
    /// let mock_net = kxio::net::mock();
    /// let client = mock_net.client();
    /// let request = client.get("https://hyper.rs");
    /// ```
    pub fn client(&self) -> Client {
        Default::default()
    }

    /// Specify an expected request.
    ///
    /// # Example
    ///
    /// ```rust
    /// use kxio::net::StatusCode;
    /// # use kxio::net::Result;
    /// # fn run() -> Result<()> {
    /// let mock_net = kxio::net::mock();
    /// let client = mock_net.client();
    /// mock_net.on().get("https://hyper.rs")
    ///     .respond(StatusCode::OK).body("Ok");
    /// # Ok(())
    /// # }
    /// ```
    #[must_use]
    pub fn on(&self) -> WhenRequest<WhenBuildRequest> {
        WhenRequest::new(self)
    }

    fn _when(&self, plan: Plan) {
        self.plans.borrow_mut().push(plan);
    }

    /// Clears all the expected requests and responses from the [MockNet].
    ///
    /// When the [MockNet] goes out of scope it will assert that all expected requests and
    /// responses were consumed. If there are any left unconsumed, then it will `panic`.
    ///
    /// # Example
    ///
    /// ```rust
    /// # use kxio::net::Result;
    /// # #[tokio::main]
    /// # async fn run() -> Result<()> {
    /// # let mock_net = kxio::net::mock();
    /// # let net: kxio::net::Net = mock_net.into();
    /// let mock_net = kxio::net::MockNet::try_from(net).await?;
    /// mock_net.reset(); // only if explicitly needed
    /// # Ok(())
    /// # }
    /// ```
    pub fn reset(&self) {
        self.plans.take();
    }
}
impl From<MockNet> for Net {
    fn from(mock_net: MockNet) -> Self {
        Self {
            // keep the original `inner` around to allow it's Drop impelmentation to run when we go
            // out of scope at the end of the test
            plans: Some(Arc::new(Mutex::new(RefCell::new(mock_net.plans.take())))),
        }
    }
}

impl Drop for MockNet {
    fn drop(&mut self) {
        let unused = self.plans.take();
        if unused.is_empty() {
            return; // all good
        }
        panic_with_unused_plans(unused);
    }
}
impl Drop for Net {
    fn drop(&mut self) {
        if let Some(plans) = &self.plans {
            let unused = plans.try_lock().expect("lock plans").take();
            if unused.is_empty() {
                return; // all good
            }
            panic_with_unused_plans(unused);
        }
    }
}

fn panic_with_unused_plans(unused: Vec<Plan>) {
    eprintln!("These requests were expected, but not made:");
    for plan in unused {
        eprintln!("- {plan}");
    }
    panic!("There were expected requests that were not made.");
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum MatchRequest {
    Method(NetMethod),
    Url(Url),
    Header { name: String, value: String },
    Body(bytes::Bytes),
}
impl Display for MatchRequest {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Method(method) => write!(f, "{method}"),
            Self::Url(url) => write!(f, "{url}"),
            Self::Header { name, value } => write!(f, "({name}: {value})"),
            Self::Body(body) => write!(f, "Body: {body:?}"),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum RespondWith {
    Status(StatusCode),
    Header { name: String, value: String },
    Body(bytes::Bytes),
}

#[derive(Clone, Debug, Display, From)]
pub enum MockError {
    #[display("url parse: {}", 0)]
    UrlParse(#[from] url::ParseError),
}
impl std::error::Error for MockError {}

pub trait WhenState {}

pub struct WhenBuildRequest;
impl WhenState for WhenBuildRequest {}

pub struct WhenBuildResponse;
impl WhenState for WhenBuildResponse {}

#[derive(Debug, Clone)]
pub struct WhenRequest<'net, State>
where
    State: WhenState,
{
    _state: PhantomData<State>,
    net: &'net MockNet,
    match_on: Vec<MatchRequest>,
    respond_with: Vec<RespondWith>,
    error: Option<MockError>,
}

impl<'net> WhenRequest<'net, WhenBuildRequest> {
    fn new(net: &'net MockNet) -> Self {
        Self {
            _state: PhantomData,
            net,
            match_on: vec![],
            respond_with: vec![],
            error: None,
        }
    }

    /// Starts mocking a GET http request.
    #[must_use]
    pub fn get(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Get, url)
    }

    /// Starts mocking a POST http request.
    #[must_use]
    pub fn post(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Post, url)
    }

    /// Starts mocking a PUT http request.
    #[must_use]
    pub fn put(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Put, url)
    }

    /// Starts mocking a DELETE http request.
    #[must_use]
    pub fn delete(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Delete, url)
    }

    /// Starts mocking a HEAD http request.
    #[must_use]
    pub fn head(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Head, url)
    }

    /// Starts mocking a PATCH http request.
    #[must_use]
    pub fn patch(self, url: impl Into<String>) -> Self {
        self._url(NetMethod::Patch, url)
    }

    fn _url(mut self, method: NetMethod, url: impl Into<String>) -> Self {
        self.match_on.push(MatchRequest::Method(method));
        match Url::parse(&url.into()) {
            Ok(url) => {
                self.match_on.push(MatchRequest::Url(url));
            }
            Err(err) => {
                self.error.replace(err.into());
            }
        }
        self
    }

    /// Specifies a header that the mock will match against.
    ///
    /// Any request that does not have this header will not match the mock.
    #[must_use]
    pub fn header(mut self, name: impl Into<String>, value: impl Into<String>) -> Self {
        self.match_on.push(MatchRequest::Header {
            name: name.into(),
            value: value.into(),
        });
        self
    }

    /// Specifies headers that the mock will match against.
    ///
    /// Any request that does not have this header will not match the mock.
    #[must_use]
    pub fn headers(mut self, headers: HashMap<String, String>) -> Self {
        for (name, value) in headers {
            self.match_on.push(MatchRequest::Header { name, value });
        }
        self
    }

    /// Specifies the body that the mock will match against.
    ///
    /// Any request that does not have this body will not match the mock.
    #[must_use]
    pub fn body(mut self, body: impl Into<bytes::Bytes>) -> Self {
        self.match_on.push(MatchRequest::Body(body.into()));
        self
    }

    /// Specifies the http Status Code that will be returned for the matching request.
    #[must_use]
    pub fn respond(self, status: StatusCode) -> WhenRequest<'net, WhenBuildResponse> {
        WhenRequest::<WhenBuildResponse> {
            _state: PhantomData,
            net: self.net,
            match_on: self.match_on,
            respond_with: vec![RespondWith::Status(status)],
            error: self.error,
        }
    }
}
impl<'net> WhenRequest<'net, WhenBuildResponse> {
    /// Specifies a header that will be on the response sent for the matching request.
    #[must_use]
    pub fn header(mut self, name: impl Into<String>, value: impl Into<String>) -> Self {
        let name = name.into();
        let value = value.into();
        self.respond_with.push(RespondWith::Header { name, value });
        self
    }

    /// Specifies headers that will be on the response sent for the matching request.
    #[must_use]
    pub fn headers(mut self, headers: impl Into<HashMap<String, String>>) -> Self {
        let h: HashMap<String, String> = headers.into();
        for (name, value) in h.into_iter() {
            self.respond_with.push(RespondWith::Header { name, value });
        }
        self
    }

    /// Specifies the body of the response sent for the matching request.
    pub fn body(mut self, body: impl Into<bytes::Bytes>) -> Result<()> {
        self.respond_with.push(RespondWith::Body(body.into()));
        self.mock()
    }

    /// Marks a response that has no body as complete.
    pub fn mock(self) -> Result<()> {
        if let Some(error) = self.error {
            return Err(crate::net::Error::InvalidMock(error));
        }
        let mut builder = http::response::Builder::default();
        let mut response_body = None;
        for part in self.respond_with {
            builder = match part {
                RespondWith::Status(status) => builder.status(status),
                RespondWith::Header { name, value } => builder.header(name, value),
                RespondWith::Body(body) => {
                    response_body.replace(body);
                    builder
                }
            }
        }

        let body = response_body.unwrap_or_default();
        let response = builder.body(body)?;
        self.net._when(Plan {
            match_request: self.match_on,
            response: response.into(),
        });
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn is_normal<T: Sized + Send + Sync + Unpin>() {}

    #[test]
    fn normal_types() {
        is_normal::<Net>();
        // is_normal::<MockNet>(); // only used in test setup - no need to be Send or Sync
        is_normal::<MatchRequest>();
        is_normal::<Plan>();
        // is_normal::<WhenRequest>(); // only used in test setup - no need to be Send or Sync
    }

    #[test]
    fn plan_display() {
        let plan = Plan {
            match_request: vec![
                MatchRequest::Method(NetMethod::Put),
                MatchRequest::Header {
                    name: "alpha".into(),
                    value: "1".into(),
                },
                MatchRequest::Body("req body".into()),
            ],
            response: http::response::Builder::default()
                .status(204)
                .header("foo", "bar")
                .header("baz", "buck")
                .body("contents")
                .expect("body")
                .into(),
        };
        let result = plan.to_string();

        let expected = [
            "Put",
            "(alpha: 1)",
            "Body: b\"req body\"",
            "=>",
            "Response {",
            "url: \"http://no.url.provided.local/\",",
            "status: 204,",
            "headers: {\"foo\": \"bar\", \"baz\": \"buck\"}",
            "}\n",
        ]
        .join(" ");
        assert_eq!(result, expected);
    }
}