//! Mattermost's JSON, typed: the posts and users we read, the events that arrive over the
//! WebSocket, and the requests we send over it. Mattermost's JSON is not ours: unknown fields are
//! ignored, but every id we keep must be a valid id.

pub mod rest;

use std::time::Duration;

use serde::Deserialize;

use crate::config::valid_id;

/// At most this many changed posts come back from one `posts?since` call (Mattermost v11.11.0,
/// `SqlPostStore::GetPostsSince`); a full answer may have left some out.
pub const SINCE_LIMIT: usize = 1000;

#[derive(Debug)]
pub enum MmError {
    /// No answer: connecting, TLS, or the HTTP exchange failed.
    Net(String),
    /// 401 or 403: the token is refused.
    Auth(u16),
    /// 429, still, after waiting as asked.
    RateLimited(Duration),
    /// Any other status that is not 2xx, with the start of the body.
    Status(u16, String),
    /// The answer is not the JSON we expect.
    Json(String),
}

impl std::fmt::Display for MmError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            MmError::Net(why) => write!(f, "{why}"),
            MmError::Auth(status) => write!(f, "Mattermost refused the token ({status})"),
            MmError::RateLimited(wait) => {
                write!(f, "rate limited; asked to wait {} s", wait.as_secs())
            }
            // Quoted: the body is the server's text, and must not forge a log line.
            MmError::Status(status, body) => write!(f, "status {status}: {body:?}"),
            MmError::Json(why) => write!(f, "unexpected JSON: {why}"),
        }
    }
}

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

/// This bot, from `GET /users/me`.
#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
pub struct Me {
    pub id: String,
    pub username: String,
}

/// The fields of a post that `gatewayd` uses.
#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
pub struct Post {
    pub id: String,
    pub user_id: String,
    pub channel_id: String,
    #[serde(default)]
    pub root_id: String,
    #[serde(default)]
    pub message: String,
    pub create_at: i64,
    #[serde(default)]
    pub delete_at: i64,
    /// Empty for a message a user wrote; anything else is a system message.
    #[serde(default, rename = "type")]
    pub kind: String,
}

impl Post {
    /// Every id is a Mattermost id (the root may be empty): they end up in session ids and paths.
    pub(crate) fn check(self) -> Result<Post, MmError> {
        // id, user_id and channel_id must be `valid_id`, and root_id empty or `valid_id`; otherwise
        // Json("a post with an invalid id: <id quoted with {:?}>").
        todo!()
    }
}

/// An event from the WebSocket.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Event {
    Hello,
    /// A new post, and the type of its channel: `D` direct, `G` group, `O` open, `P` private.
    Posted {
        post: Post,
        channel_type: String,
    },
    /// Any other event, or a reply to one of our requests, by its name (empty for a reply).
    Other(String),
}

#[derive(Deserialize)]
struct RawEvent {
    #[serde(default)]
    event: String,
    #[serde(default)]
    data: serde_json::Map<String, serde_json::Value>,
}

pub(crate) fn json<T: serde::de::DeserializeOwned>(bytes: &[u8]) -> Result<T, MmError> {
    // `serde_json::from_slice`; its error becomes Json(e.to_string()).
    todo!()
}

/// One WebSocket text message as an event. `posted` carries the post as a JSON **string**.
pub fn parse_event(text: &str) -> Result<Event, MmError> {
    // Parse into RawEvent. "hello" -> Hello. "posted" -> data.post must be a JSON *string*; parse
    // that string as a Post and `check` it (a missing or non-string post is Json). channel_type is
    // data.channel_type when it is a string, else "". Any other event name -> Other(name) (a reply
    // has no event: Other("")).
    todo!()
}

/// The WebSocket request that shows this bot as typing in a thread (`parent` is the root).
pub fn typing(seq: u64, channel: &str, parent: &str) -> String {
    // serde_json::json!({"action": "user_typing", "seq": seq, "data": {"channel_id": channel,
    // "parent_id": parent}}) as a string.
    todo!()
}

/// What a `posts?since` call gave back.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Since {
    /// Posts created after the time, not deleted, oldest first.
    pub posts: Vec<Post>,
    /// Mattermost's limit was reached: some posts may be missing.
    pub full: bool,
}

#[derive(Deserialize)]
struct PostList {
    #[serde(default)]
    order: Vec<String>,
    #[serde(default)]
    posts: std::collections::HashMap<String, Post>,
}

/// The body of `GET /channels/{id}/posts?since=<since>`. Only ids in `order` changed after
/// `since`; `posts` also holds the roots of their threads, which may be older. Edited and deleted
/// posts come back too: only new posts count.
pub fn since_list(body: &[u8], since: i64) -> Result<Since, MmError> {
    // Parse a PostList. full = order.len() >= SINCE_LIMIT. For each id in `order` (never the keys
    // of `posts`), skip it if it is not in `posts`; keep the post if create_at > since and
    // delete_at == 0, after `check`. Sort by (create_at, id), remove repeated ids.
    todo!()
}