/*
 * This file is part of espanso.
 *
 * Copyright (C) 2019-2021 Federico Terzi
 *
 * espanso is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * espanso is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with espanso.  If not, see <https://www.gnu.org/licenses/>.
 */

use log::trace;
use std::{
  cell::RefCell,
  collections::{HashMap, VecDeque},
};

use super::super::Middleware;
use crate::event::{
  input::{Key, Status},
  internal::{DetectedMatch, MatchesDetectedEvent},
  Event, EventType,
};

pub trait Matcher<'a, State> {
  fn process(
    &'a self,
    prev_state: Option<&State>,
    event: &MatcherEvent,
  ) -> (State, Vec<MatchResult>);
}

#[derive(Debug)]
pub enum MatcherEvent {
  Key { key: Key, chars: Option<String> },
  VirtualSeparator,
}

#[derive(Debug, Clone, PartialEq)]
pub struct MatchResult {
  pub id: i32,
  pub trigger: String,
  pub left_separator: Option<String>,
  pub right_separator: Option<String>,
  pub args: HashMap<String, String>,
}

pub trait MatcherMiddlewareConfigProvider {
  fn max_history_size(&self) -> usize;
}

pub trait ModifierStateProvider {
  fn get_modifier_state(&self) -> ModifierState;
}

#[derive(Debug, Clone)]
pub struct ModifierState {
  pub is_ctrl_down: bool,
  pub is_alt_down: bool,
  pub is_meta_down: bool,
}

pub struct MatcherMiddleware<'a, State> {
  matchers: &'a [&'a dyn Matcher<'a, State>],

  matcher_states: RefCell<VecDeque<Vec<State>>>,

  max_history_size: usize,

  modifier_status_provider: &'a dyn ModifierStateProvider,
}

impl<'a, State> MatcherMiddleware<'a, State> {
  pub fn new(
    matchers: &'a [&'a dyn Matcher<'a, State>],
    options_provider: &'a dyn MatcherMiddlewareConfigProvider,
    modifier_status_provider: &'a dyn ModifierStateProvider,
  ) -> Self {
    let max_history_size = options_provider.max_history_size();

    Self {
      matchers,
      matcher_states: RefCell::new(VecDeque::new()),
      max_history_size,
      modifier_status_provider,
    }
  }
}

impl<'a, State> Middleware for MatcherMiddleware<'a, State> {
  fn name(&self) -> &'static str {
    "matcher"
  }

  fn next(&self, event: Event, _: &mut dyn FnMut(Event)) -> Event {
    if is_event_of_interest(&event.etype) {
      let mut matcher_states = self.matcher_states.borrow_mut();
      let prev_states = if !matcher_states.is_empty() {
        matcher_states.get(matcher_states.len() - 1)
      } else {
        None
      };

      if let EventType::Keyboard(keyboard_event) = &event.etype {
        // Backspace handling
        if keyboard_event.key == Key::Backspace {
          trace!("popping the last matcher state");
          matcher_states.pop_back();
          return event;
        }

        // We need to filter out some keyboard events if they are generated
        // while some modifier keys are pressed, otherwise we could have
        // wrong matches being detected.
        // See: https://github.com/federico-terzi/espanso/issues/725
        if should_skip_key_event_due_to_modifier_press(
          &self.modifier_status_provider.get_modifier_state(),
        ) {
          trace!("skipping keyboard event because incompatible modifiers are pressed");
          return event;
        }
      }

      // Some keys (such as the arrow keys) and mouse clicks prevent espanso from building
      // an accurate key buffer, so we need to invalidate it.
      if is_invalidating_event(&event.etype) {
        trace!("invalidating event detected, clearing matching state");
        matcher_states.clear();
        return event;
      }

      let mut all_results = Vec::new();

      if let Some(matcher_event) = convert_to_matcher_event(&event.etype) {
        let mut new_states = Vec::new();
        for (i, matcher) in self.matchers.iter().enumerate() {
          let prev_state = prev_states.and_then(|states| states.get(i));

          let (state, results) = matcher.process(prev_state, &matcher_event);
          all_results.extend(results);

          new_states.push(state);
        }

        matcher_states.push_back(new_states);
        if matcher_states.len() > self.max_history_size {
          matcher_states.pop_front();
        }

        if !all_results.is_empty() {
          return Event::caused_by(
            event.source_id,
            EventType::MatchesDetected(MatchesDetectedEvent {
              matches: all_results
                .into_iter()
                .map(|result| DetectedMatch {
                  id: result.id,
                  trigger: Some(result.trigger),
                  right_separator: result.right_separator,
                  left_separator: result.left_separator,
                  args: result.args,
                })
                .collect(),
              is_search: false,
            }),
          );
        }
      }
    }

    event
  }
}

fn is_event_of_interest(event_type: &EventType) -> bool {
  match event_type {
    EventType::Keyboard(keyboard_event) => {
      if keyboard_event.status != Status::Pressed {
        // Skip non-press events
        false
      } else {
        // Skip linux Keyboard (XKB) Extension function and modifier keys
        // In hex, they have the byte 3 = 0xfe
        // See list in "keysymdef.h" file
        if cfg!(target_os = "linux") {
          if let Key::Other(raw_code) = &keyboard_event.key {
            if (65025..=65276).contains(raw_code) {
              return false;
            }
          }
        }

        // Skip modifier keys
        !matches!(
          keyboard_event.key,
          Key::Alt | Key::Shift | Key::CapsLock | Key::Meta | Key::NumLock | Key::Control
        )
      }
    }
    EventType::Mouse(mouse_event) => mouse_event.status == Status::Pressed,
    EventType::MatchInjected => true,
    _ => false,
  }
}

fn convert_to_matcher_event(event_type: &EventType) -> Option<MatcherEvent> {
  match event_type {
    EventType::Keyboard(keyboard_event) => Some(MatcherEvent::Key {
      key: keyboard_event.key.clone(),
      chars: keyboard_event.value.clone(),
    }),
    EventType::Mouse(_) => Some(MatcherEvent::VirtualSeparator),
    EventType::MatchInjected => Some(MatcherEvent::VirtualSeparator),
    _ => None,
  }
}

fn is_invalidating_event(event_type: &EventType) -> bool {
  match event_type {
    EventType::Keyboard(keyboard_event) => matches!(
      keyboard_event.key,
      Key::ArrowDown
        | Key::ArrowLeft
        | Key::ArrowRight
        | Key::ArrowUp
        | Key::End
        | Key::Home
        | Key::PageDown
        | Key::PageUp
        | Key::Escape
    ),
    EventType::Mouse(_) => true,
    _ => false,
  }
}

fn should_skip_key_event_due_to_modifier_press(modifier_state: &ModifierState) -> bool {
  if cfg!(target_os = "macos") {
    modifier_state.is_meta_down
  } else if cfg!(target_os = "windows") {
    modifier_state.is_alt_down
  } else if cfg!(target_os = "linux") {
    modifier_state.is_alt_down || modifier_state.is_meta_down
  } else {
    unreachable!()
  }
}

// TODO: test