use std::collections::HashMap;

use syscall::data::Stat;
use syscall::error::{Error, Result, EBADF, EINVAL, ENOENT};
use syscall::flag::{MODE_DIR, MODE_FILE};

#[derive(Clone, Debug, Default)]
struct InputState {
    composing: bool,
    preedit: String,
    committed: String,
}

enum HandleKind {
    Root,
    State,
    Compose,
    Candidates,
}

struct Handle {
    kind: HandleKind,
    offset: usize,
}

pub struct ImeScheme {
    next_id: usize,
    handles: HashMap<usize, Handle>,
    state: InputState,
    engine: Box<dyn ImeEngine>,
}

trait ImeEngine {
    fn feed_key(&mut self, scancode: u8, pressed: bool, shift: bool, altgr: bool) -> ImeResult;
    fn reset(&mut self);
    fn candidates(&self) -> &[String];
}

#[derive(Clone, Debug)]
struct ImeResult {
    committed: Option<char>,
    preedit: String,
    candidates_changed: bool,
}

struct BasicLatinEngine {
    dead_key: Option<char>,
    candidates: Vec<String>,
    compose_scancode: u8,
    dead_key_index: usize,
}

impl BasicLatinEngine {
    fn new() -> Self {
        BasicLatinEngine {
            dead_key: None,
            candidates: Vec::new(),
            compose_scancode: 0x5D,
            dead_key_index: 0,
        }
    }

    fn compose_dead(&self, base: char) -> Option<char> {
        let dk = self.dead_key?;
        match (dk, base) {
            ('\u{0300}', 'a') => Some('à'),
            ('\u{0300}', 'e') => Some('è'),
            ('\u{0300}', 'i') => Some('ì'),
            ('\u{0300}', 'o') => Some('ò'),
            ('\u{0300}', 'u') => Some('ù'),
            ('\u{0301}', 'a') => Some('á'),
            ('\u{0301}', 'e') => Some('é'),
            ('\u{0301}', 'i') => Some('í'),
            ('\u{0301}', 'o') => Some('ó'),
            ('\u{0301}', 'u') => Some('ú'),
            ('\u{0302}', 'a') => Some('â'),
            ('\u{0302}', 'e') => Some('ê'),
            ('\u{0302}', 'i') => Some('î'),
            ('\u{0302}', 'o') => Some('ô'),
            ('\u{0302}', 'u') => Some('û'),
            ('\u{0308}', 'a') => Some('ä'),
            ('\u{0308}', 'e') => Some('ë'),
            ('\u{0308}', 'i') => Some('ï'),
            ('\u{0308}', 'o') => Some('ö'),
            ('\u{0308}', 'u') => Some('ü'),
            ('\u{030C}', 'a') => Some('ǎ'),
            ('\u{030C}', 'e') => Some('ě'),
            ('\u{030C}', 'i') => Some('ǐ'),
            ('\u{030C}', 'o') => Some('ǒ'),
            ('\u{030C}', 'u') => Some('ǔ'),
            _ => None,
        }
    }
    fn scancode_to_char(scancode: u8, shift: bool) -> Option<char> {
        let lower = match scancode {
            0x02 => '1',
            0x03 => '2',
            0x04 => '3',
            0x05 => '4',
            0x06 => '5',
            0x07 => '6',
            0x08 => '7',
            0x09 => '8',
            0x0A => '9',
            0x0B => '0',
            0x10 => 'q',
            0x11 => 'w',
            0x12 => 'e',
            0x13 => 'r',
            0x14 => 't',
            0x15 => 'y',
            0x16 => 'u',
            0x17 => 'i',
            0x18 => 'o',
            0x19 => 'p',
            0x1E => 'a',
            0x1F => 's',
            0x20 => 'd',
            0x21 => 'f',
            0x22 => 'g',
            0x23 => 'h',
            0x24 => 'j',
            0x25 => 'k',
            0x26 => 'l',
            0x2C => 'z',
            0x2D => 'x',
            0x2E => 'c',
            0x2F => 'v',
            0x30 => 'b',
            0x31 => 'n',
            0x32 => 'm',
            0x27 => ';',
            0x28 => '\'',
            0x29 => '`',
            0x33 => ',',
            0x34 => '.',
            0x35 => '/',
            0x0C => '-',
            0x0D => '=',
            _ => return None,
        };
        if shift {
            Some(lower.to_ascii_uppercase())
        } else {
            Some(lower)
        }
    }
}

impl ImeEngine for BasicLatinEngine {
    fn feed_key(&mut self, scancode: u8, pressed: bool, shift: bool, _altgr: bool) -> ImeResult {
        if !pressed {
            return ImeResult {
                committed: None,
                preedit: String::new(),
                candidates_changed: false,
            };
        }

        if let Some(current_dead) = self.dead_key.take() {
            if let Some(base) = Self::scancode_to_char(scancode, shift) {
                match self.compose_dead(base) {
                    Some(composed) => {
                        self.candidates.clear();
                        return ImeResult {
                            committed: Some(composed),
                            preedit: String::new(),
                            candidates_changed: true,
                        };
                    }
                    None => {
                        self.dead_key = None;
                        return ImeResult {
                            committed: Some(current_dead),
                            preedit: String::new(),
                            candidates_changed: false,
                        };
                    }
                }
            } else {
                self.dead_key = Some(current_dead);
                return ImeResult {
                    committed: None,
                    preedit: current_dead.to_string(),
                    candidates_changed: false,
                };
            }
        }

        let is_dead_trigger = scancode == self.compose_scancode;
        if is_dead_trigger {
            let dead_keys = [
                ('\u{0300}', "grave"),
                ('\u{0301}', "acute"),
                ('\u{0302}', "circumflex"),
                ('\u{0308}', "diaeresis"),
                ('\u{030C}', "caron"),
            ];
            let (dk, _name) = dead_keys[self.dead_key_index % dead_keys.len()];
            self.dead_key_index = (self.dead_key_index + 1) % dead_keys.len();
            self.dead_key = Some(dk);
            self.candidates = vec![dk.to_string()];
            return ImeResult {
                committed: None,
                preedit: dk.to_string(),
                candidates_changed: true,
            };
        }

        ImeResult {
            committed: None,
            preedit: String::new(),
            candidates_changed: false,
        }
    }

    fn reset(&mut self) {
        self.dead_key = None;
        self.candidates.clear();
    }

    fn candidates(&self) -> &[String] {
        &self.candidates
    }
}

impl ImeScheme {
    pub fn new() -> Self {
        ImeScheme {
            next_id: 1,
            handles: HashMap::new(),
            state: InputState::default(),
            engine: Box::new(BasicLatinEngine::new()),
        }
    }

    pub fn feed(&mut self, scancode: u8, pressed: bool, shift: bool, altgr: bool) {
        let result = self.engine.feed_key(scancode, pressed, shift, altgr);
        if let Some(ch) = result.committed {
            self.state.committed.push(ch);
            self.state.composing = false;
            self.state.preedit.clear();
        }
        if result.candidates_changed {
            self.state.composing = !self.engine.candidates().is_empty();
        }
        if !result.preedit.is_empty() {
            self.state.composing = true;
            self.state.preedit = result.preedit;
        }
    }
}

impl redox_scheme::SchemeBlockMut for ImeScheme {
    fn open(&mut self, path: &str, _flags: usize, _uid: u32, _gid: u32) -> Result<Option<usize>> {
        let cleaned = path.trim_matches('/');
        let kind = match cleaned {
            "" => HandleKind::Root,
            "state" => HandleKind::State,
            "compose" => HandleKind::Compose,
            "candidates" => HandleKind::Candidates,
            _ => return Err(Error::new(ENOENT)),
        };

        let id = self.next_id;
        self.next_id += 1;
        self.handles.insert(id, Handle { kind, offset: 0 });
        Ok(Some(id))
    }

    fn read(&mut self, id: usize, buf: &mut [u8]) -> Result<Option<usize>> {
        let handle = self.handles.get_mut(&id).ok_or(Error::new(EBADF))?;

        let content: Vec<u8> = match &handle.kind {
            HandleKind::Root => "state\ncompose\ncandidates\n".as_bytes().to_vec(),
            HandleKind::State => format!(
                "composing={}\npreedit={}\ncommitted={}\n",
                self.state.composing, self.state.preedit, self.state.committed
            )
            .into_bytes(),
            HandleKind::Compose => "basic-latin\n".as_bytes().to_vec(),
            HandleKind::Candidates => {
                let mut out = String::new();
                for (i, c) in self.engine.candidates().iter().enumerate() {
                    out.push_str(&format!("{}\t{}\n", i, c));
                }
                out.into_bytes()
            }
        };

        if handle.offset >= content.len() {
            return Ok(Some(0));
        }
        let remaining = &content[handle.offset..];
        let to_copy = remaining.len().min(buf.len());
        buf[..to_copy].copy_from_slice(&remaining[..to_copy]);
        handle.offset += to_copy;
        Ok(Some(to_copy))
    }

    fn write(&mut self, id: usize, buf: &[u8]) -> Result<Option<usize>> {
        let handle = self.handles.get(&id).ok_or(Error::new(EBADF))?;
        match &handle.kind {
            HandleKind::Compose => {
                let input = String::from_utf8_lossy(buf);
                for line in input.lines() {
                    let line = line.trim();
                    if line == "reset" {
                        self.engine.reset();
                        self.state = InputState::default();
                        continue;
                    }
                    let mut fields = line.split_whitespace();
                    let Some("feed") = fields.next() else {
                        continue;
                    };
                    let Some(scancode) = fields.next().and_then(|field| field.parse::<u8>().ok())
                    else {
                        continue;
                    };
                    let Some(pressed) = fields.next().and_then(|field| field.parse::<bool>().ok())
                    else {
                        continue;
                    };
                    let shift = fields
                        .next()
                        .and_then(|field| field.parse::<bool>().ok())
                        .unwrap_or(false);
                    let altgr = fields
                        .next()
                        .and_then(|field| field.parse::<bool>().ok())
                        .unwrap_or(false);
                    self.feed(scancode, pressed, shift, altgr);
                }
                Ok(Some(buf.len()))
            }
            _ => Err(Error::new(EINVAL)),
        }
    }

    fn fstat(&mut self, id: usize, stat: &mut Stat) -> Result<Option<usize>> {
        let handle = self.handles.get(&id).ok_or(Error::new(EBADF))?;
        match &handle.kind {
            HandleKind::Root => stat.st_mode = MODE_DIR | 0o555,
            _ => stat.st_mode = MODE_FILE | 0o644,
        }
        Ok(Some(0))
    }

    fn close(&mut self, id: usize) -> Result<Option<usize>> {
        self.handles.remove(&id);
        Ok(Some(0))
    }
}