use std::any::type_name;
use std::ops::{Deref, DerefMut};

use mlua::{AnyUserData, Lua, Result, Table, TableExt, ToLua, UserData, Value, Variadic};

use crate::{Channel, Core, HttpMessage, LogLevel, Txn};

/// Represents methods available to call in [`UserFilter`].
pub struct FilterMethod;

impl FilterMethod {
    pub const START_ANALYZE: u8 = 0b00000001;
    pub const END_ANALYZE: u8 = 0b00000010;
    pub const HTTP_HEADERS: u8 = 0b00000100;
    pub const HTTP_PAYLOAD: u8 = 0b00001000;
    pub const HTTP_END: u8 = 0b00010000;

    pub const ALL: u8 = u8::MAX;
}

/// A code that filter callback functions may return.
pub enum FilterResult {
    /// A filtering step is finished for filter.
    Continue,
    /// A filtering step must be paused, waiting for more data or for an external event depending on filter.
    Wait,
    /// Trigger a error
    Error,
}

impl FilterResult {
    fn code(&self) -> i8 {
        match self {
            FilterResult::Continue => 1,
            FilterResult::Wait => 0,
            FilterResult::Error => -1,
        }
    }
}

/// A flag corresponding to the filter flag FLT_CFG_FL_HTX.
/// When it is set for a filter, it means the filter is able to filter HTTP streams.
const FLT_CFG_FL_HTX: u8 = 1;

/// A trait that defines all required callback functions to implement filters.
pub trait UserFilter: Sized {
    /// Sets methods available for this filter.
    /// By default ALL
    const METHODS: u8 = FilterMethod::ALL;

    /// Continue execution if a filter callback returns an error.
    const CONTINUE_IF_ERROR: bool = true;

    /// Creates a new instance of filter.
    fn new(lua: &Lua, args: Table) -> Result<Self>;

    /// Called when the analysis starts on the channel `chn`.
    fn start_analyze(&mut self, lua: &Lua, txn: Txn, chn: Channel) -> Result<FilterResult> {
        let _ = (lua, txn, chn);
        Ok(FilterResult::Continue)
    }

    /// Called when the analysis ends on the channel `chn`.
    fn end_analyze(&mut self, lua: &Lua, txn: Txn, chn: Channel) -> Result<FilterResult> {
        let _ = (lua, txn, chn);
        Ok(FilterResult::Continue)
    }

    /// Called just before the HTTP payload analysis and after any processing on the HTTP message `msg`.
    fn http_headers(&mut self, lua: &Lua, txn: Txn, msg: HttpMessage) -> Result<FilterResult> {
        let _ = (lua, txn, msg);
        Ok(FilterResult::Continue)
    }

    /// Called during the HTTP payload analysis on the HTTP message `msg`.
    fn http_payload(&mut self, lua: &Lua, txn: Txn, msg: HttpMessage) -> Result<Option<usize>> {
        let _ = (lua, txn, msg);
        Ok(None)
    }

    /// Called after the HTTP payload analysis on the HTTP message `msg`.
    fn http_end(&mut self, lua: &Lua, txn: Txn, msg: HttpMessage) -> Result<FilterResult> {
        let _ = (lua, txn, msg);
        Ok(FilterResult::Continue)
    }

    //
    // HAProxy provided methods
    //

    /// Enable the data filtering on the channel `chn` for the current filter.
    /// It may be called at any time from any callback functions proceeding the data analysis.
    fn register_data_filter(lua: &Lua, txn: Txn, chn: Channel) -> Result<()> {
        let global_filter = lua.globals().raw_get::<_, Table>("filter")?;
        global_filter.call_function("register_data_filter", (txn.r#priv, chn))?;
        Ok(())
    }

    /// Disable the data filtering on the channel `chn` for the current filter.
    /// It may be called at any time from any callback functions.
    fn unregister_data_filter(lua: &Lua, txn: Txn, chn: Channel) -> Result<()> {
        let filter = lua.globals().raw_get::<_, Table>("filter")?;
        filter.call_function("unregister_data_filter", (txn.r#priv, chn))?;
        Ok(())
    }
}

pub(crate) struct UserFilterWrapper<T>(T);

impl<T> UserFilterWrapper<T>
where
    T: UserFilter + 'static,
{
    pub(crate) fn make_class(lua: &Lua) -> Result<Table> {
        let class = lua.create_table()?;
        class.raw_set("__index", class.clone())?;

        // Attributes
        class.raw_set("id", type_name::<T>())?;
        class.raw_set("flags", FLT_CFG_FL_HTX)?;

        //
        // Methods
        //
        let class_key = lua.create_registry_value(class.clone())?;
        class.raw_set(
            "new",
            lua.create_function(move |lua, class: Table| {
                let args = class.raw_get("args")?;
                let filter = match T::new(lua, args) {
                    Ok(filter) => filter,
                    Err(err) => {
                        let core = Core::new(lua)?;
                        let msg = format!("Filter '{}': {err}", type_name::<T>());
                        core.log(LogLevel::Err, &msg)?;
                        return Ok(Value::Nil);
                    }
                };
                let this = lua.create_sequence_from([Self(filter)])?;
                let class = lua.registry_value::<Table>(&class_key)?;
                this.set_metatable(Some(class));
                Ok(Value::Table(this))
            })?,
        )?;

        if T::METHODS & FilterMethod::START_ANALYZE != 0 {
            class.raw_set(
                "start_analyze",
                lua.create_function(|lua, (t, mut txn, chn): (Table, Txn, Channel)| {
                    let ud = t.raw_get::<_, AnyUserData>(1)?;
                    let mut this = ud.borrow_mut::<Self>()?;
                    txn.r#priv = Value::Table(t);
                    Self::process_result(lua, this.start_analyze(lua, txn, chn))
                })?,
            )?;
        }

        if T::METHODS & FilterMethod::END_ANALYZE != 0 {
            class.raw_set(
                "end_analyze",
                lua.create_function(|lua, (t, mut txn, chn): (Table, Txn, Channel)| {
                    let ud = t.raw_get::<_, AnyUserData>(1)?;
                    let mut this = ud.borrow_mut::<Self>()?;
                    txn.r#priv = Value::Table(t);
                    Self::process_result(lua, this.end_analyze(lua, txn, chn))
                })?,
            )?;
        }

        if T::METHODS & FilterMethod::HTTP_HEADERS != 0 {
            class.raw_set(
                "http_headers",
                lua.create_function(|lua, (t, mut txn, msg): (Table, Txn, HttpMessage)| {
                    let ud = t.raw_get::<_, AnyUserData>(1)?;
                    let mut this = ud.borrow_mut::<Self>()?;
                    txn.r#priv = Value::Table(t);
                    Self::process_result(lua, this.http_headers(lua, txn, msg))
                })?,
            )?;
        }

        if T::METHODS & FilterMethod::HTTP_PAYLOAD != 0 {
            class.raw_set(
                "http_payload",
                lua.create_function(|lua, (t, mut txn, msg): (Table, Txn, HttpMessage)| {
                    let ud = t.raw_get::<_, AnyUserData>(1)?;
                    let mut this = ud.borrow_mut::<Self>()?;
                    txn.r#priv = Value::Table(t);
                    let mut res = Variadic::new();
                    match this.http_payload(lua, txn, msg) {
                        Ok(Some(len)) => {
                            res.push(len.to_lua(lua)?);
                        }
                        Ok(None) => {}
                        Err(err) if T::CONTINUE_IF_ERROR => {
                            if let Ok(core) = Core::new(lua) {
                                let _ = core.log(
                                    LogLevel::Err,
                                    &format!("Filter '{}': {}", type_name::<T>(), err),
                                );
                            }
                        }
                        Err(err) => return Err(err),
                    };
                    Ok(res)
                })?,
            )?;
        }

        if T::METHODS & FilterMethod::HTTP_END != 0 {
            class.raw_set(
                "http_end",
                lua.create_function(|lua, (t, mut txn, msg): (Table, Txn, HttpMessage)| {
                    let ud = t.raw_get::<_, AnyUserData>(1)?;
                    let mut this = ud.borrow_mut::<Self>()?;
                    txn.r#priv = Value::Table(t);
                    Self::process_result(lua, this.http_end(lua, txn, msg))
                })?,
            )?;
        }

        Ok(class)
    }

    #[inline]
    fn process_result(lua: &Lua, res: Result<FilterResult>) -> Result<i8> {
        match res {
            Ok(res) => Ok(res.code()),
            Err(err) if T::CONTINUE_IF_ERROR => {
                if let Ok(core) = Core::new(lua) {
                    let _ = core.log(
                        LogLevel::Err,
                        &format!("Filter '{}': {}", type_name::<T>(), err),
                    );
                }
                Ok(FilterResult::Continue.code())
            }
            Err(err) => Err(err),
        }
    }
}

impl<T> UserData for UserFilterWrapper<T> where T: UserFilter + 'static {}

impl<T> Deref for UserFilterWrapper<T> {
    type Target = T;

    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> DerefMut for UserFilterWrapper<T> {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}