// SPDX-FileCopyrightText: 2025 Tomasz Kramkowski <tomasz@kramkow.ski>
// SPDX-License-Identifier: GPL-3.0-or-later

use std::{
    collections::HashMap, fmt, fs::File, io::Read, os::unix::fs::PermissionsExt, path::Path,
    process, time::Duration,
};

use anyhow::bail;
use rumqttc::{AsyncClient, EventLoop, MqttOptions, QoS};
use serde::{
    de::{self, Visitor},
    Deserialize, Deserializer,
};

use crate::PROGRAM;

#[derive(Deserialize, Debug)]
pub struct Credentials {
    pub username: String,
    pub password: String,
}

fn default_host() -> String {
    "localhost".to_string()
}

fn default_port() -> u16 {
    1883
}

fn default_qos() -> QoS {
    QoS::ExactlyOnce
}

fn default_id() -> String {
    PROGRAM.to_string()
}

fn default_timeout() -> Duration {
    Duration::from_secs(60)
}

#[allow(clippy::enum_variant_names)]
#[derive(Deserialize, Debug)]
#[serde(remote = "QoS", rename_all = "kebab-case")]
#[repr(u8)]
pub enum QoSDef {
    AtMostOnce = 0,
    AtLeastOnce = 1,
    ExactlyOnce = 2,
}

pub fn deserialize_qos_opt<'de, D>(deserializer: D) -> Result<Option<QoS>, D::Error>
where
    D: Deserializer<'de>,
{
    #[derive(Deserialize)]
    struct Helper(#[serde(with = "QoSDef")] QoS);

    let helper = Option::deserialize(deserializer)?;
    Ok(helper.map(|Helper(external)| external))
}

#[derive(Debug)]
pub struct Route {
    // TODO: Figure out a way to allow arbitrary unix paths (arbitrary
    // non-unicode) without base64
    pub programs: Vec<Vec<String>>,
    pub qos: Option<QoS>,
}

impl<'de> Deserialize<'de> for Route {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        struct VecOrRoute;

        impl<'de> Visitor<'de> for VecOrRoute {
            type Value = Route;

            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("map or seq")
            }

            fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
            where
                A: serde::de::SeqAccess<'de>,
            {
                let vec: Vec<Vec<String>> =
                    Deserialize::deserialize(de::value::SeqAccessDeserializer::new(seq))?;
                Ok(Route {
                    programs: vec,
                    qos: None,
                })
            }

            fn visit_map<A>(self, map: A) -> Result<Self::Value, A::Error>
            where
                A: serde::de::MapAccess<'de>,
            {
                #[derive(Deserialize)]
                struct RouteHelper {
                    programs: Vec<Vec<String>>,
                    #[serde(default, deserialize_with = "deserialize_qos_opt")]
                    qos: Option<QoS>,
                }

                let helper: RouteHelper =
                    Deserialize::deserialize(de::value::MapAccessDeserializer::new(map))?;
                Ok(Route {
                    programs: helper.programs,
                    qos: helper.qos,
                })
            }
        }

        deserializer.deserialize_any(VecOrRoute)
    }
}

pub fn deserialize_timeout<'de, D>(deserializer: D) -> Result<Duration, D::Error>
where
    D: Deserializer<'de>,
{
    struct DurationVisitor;

    impl<'de> de::Visitor<'de> for DurationVisitor {
        type Value = Duration;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("a positive number")
        }

        fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            if v < 0 {
                return Err(de::Error::invalid_value(
                    de::Unexpected::Signed(v),
                    &"a non-negative number",
                ));
            }
            if v == 0 {
                Ok(Duration::MAX)
            } else {
                Ok(Duration::from_secs(v as u64))
            }
        }

        fn visit_f64<E>(self, v: f64) -> Result<Self::Value, E>
        where
            E: de::Error,
        {
            if v < 0.0 {
                return Err(de::Error::invalid_value(
                    de::Unexpected::Float(v),
                    &"a non-negative number",
                ));
            }
            if v == 0.0 {
                Ok(Duration::MAX)
            } else {
                Ok(Duration::from_secs_f64(v))
            }
        }
    }

    deserializer.deserialize_any(DurationVisitor)
}

#[derive(Deserialize, Debug)]
pub struct Config {
    #[serde(default = "default_host")]
    pub host: String,
    #[serde(default = "default_port")]
    pub port: u16,
    #[serde(with = "QoSDef", default = "default_qos")]
    pub qos: QoS,
    #[serde(default = "default_timeout", deserialize_with = "deserialize_timeout")]
    pub timeout: Duration,
    pub credentials: Option<Credentials>,
    #[serde(default = "default_id")]
    pub id: String,
    pub routes: HashMap<String, Route>,
}

impl Config {
    pub fn mqtt_client(&self) -> (AsyncClient, EventLoop) {
        let client_id = format!("{}_{}", self.id, process::id());
        let mut options = MqttOptions::new(client_id, &self.host, self.port);
        if let Some(credentials) = &self.credentials {
            options.set_credentials(&credentials.username, &credentials.password);
        }
        // TODO: Make configurable
        options.set_keep_alive(Duration::from_secs(5));
        options.set_max_packet_size(10 * 1024 * 1024, 10 * 1024 * 1024);
        AsyncClient::new(options, 10)
    }
}

pub fn load<P: AsRef<Path>>(path: P) -> anyhow::Result<Config> {
    let mut f = File::open(path)?;
    let mut config = String::new();
    f.read_to_string(&mut config)?;
    let config: Config = toml::from_str(&config)?;
    if config.credentials.is_some() {
        let mode = f.metadata()?.permissions().mode();
        if mode & 0o044 != 0o000 {
            bail!("Config file contains credentials while being group or world readable.");
        }
    }
    Ok(config)
}