use std::env;
use std::fmt;
use std::ptr;
use std::sync::Arc;
use std::os::raw::c_char;
use std::ffi::{CStr, CString, IntoStringError};

use parking_lot::Mutex;

use super::{ffi, util, XConnection, XError};

lazy_static! {
    static ref GLOBAL_LOCK: Mutex<()> = Default::default();
}

unsafe fn open_im(
    xconn: &Arc<XConnection>,
    locale_modifiers: &CStr,
) -> Option<ffi::XIM> {
    let _lock = GLOBAL_LOCK.lock();

    // XSetLocaleModifiers returns...
    // * The current locale modifiers if it's given a NULL pointer.
    // * The new locale modifiers if we succeeded in setting them.
    // * NULL if the locale modifiers string is malformed.
    (xconn.xlib.XSetLocaleModifiers)(locale_modifiers.as_ptr());

    let im = (xconn.xlib.XOpenIM)(
        xconn.display,
        ptr::null_mut(),
        ptr::null_mut(),
        ptr::null_mut(),
    );

    if im.is_null() {
        None
    } else {
        Some(im)
    }
}

#[derive(Debug)]
pub struct InputMethod {
    pub im: ffi::XIM,
    name: String,
}

impl InputMethod {
    fn new(im: ffi::XIM, name: String) -> Self {
        InputMethod { im, name }
    }
}

#[derive(Debug)]
pub enum InputMethodResult {
    /// Input method used locale modifier from `XMODIFIERS` environment variable.
    XModifiers(InputMethod),
    /// Input method used internal fallback locale modifier.
    Fallback(InputMethod),
    /// Input method could not be opened using any locale modifier tried.
    Failure,
}

impl InputMethodResult {
    pub fn is_fallback(&self) -> bool {
        if let &InputMethodResult::Fallback(_) = self {
            true
        } else {
            false
        }
    }

    pub fn ok(self) -> Option<InputMethod> {
        use self::InputMethodResult::*;
        match self {
            XModifiers(im) | Fallback(im) => Some(im),
            Failure => None,
        }
    }
}

#[derive(Debug, Clone)]
enum GetXimServersError {
    XError(XError),
    GetPropertyError(util::GetPropertyError),
    InvalidUtf8(IntoStringError),
}

// The root window has a property named XIM_SERVERS, which contains a list of atoms represeting
// the availabile XIM servers. For instance, if you're using ibus, it would contain an atom named
// "@server=ibus". It's possible for this property to contain multiple atoms, though presumably
// rare. Note that we replace "@server=" with "@im=" in order to match the format of locale
// modifiers, since we don't want a user who's looking at logs to ask "am I supposed to set
// XMODIFIERS to `@server=ibus`?!?"
unsafe fn get_xim_servers(xconn: &Arc<XConnection>) -> Result<Vec<String>, GetXimServersError> {
    let servers_atom = xconn.get_atom_unchecked(b"XIM_SERVERS\0");

    let root = (xconn.xlib.XDefaultRootWindow)(xconn.display);

    let mut atoms: Vec<ffi::Atom> = xconn.get_property(
        root,
        servers_atom,
        ffi::XA_ATOM,
    ).map_err(GetXimServersError::GetPropertyError)?;

    let mut names: Vec<*const c_char> = Vec::with_capacity(atoms.len());
    (xconn.xlib.XGetAtomNames)(
        xconn.display,
        atoms.as_mut_ptr(),
        atoms.len() as _,
        names.as_mut_ptr() as _,
    );
    names.set_len(atoms.len());

    let mut formatted_names = Vec::with_capacity(names.len());
    for name in names {
        let string = CStr::from_ptr(name)
            .to_owned()
            .into_string()
            .map_err(GetXimServersError::InvalidUtf8)?;
        (xconn.xlib.XFree)(name as _);
        formatted_names.push(string.replace("@server=", "@im="));
    }
    xconn.check_errors().map_err(GetXimServersError::XError)?;
    Ok(formatted_names)
}

#[derive(Clone)]
struct InputMethodName {
    c_string: CString,
    string: String,
}

impl InputMethodName {
    pub fn from_string(string: String) -> Self {
        let c_string = CString::new(string.clone())
            .expect("String used to construct CString contained null byte");
        InputMethodName {
            c_string,
            string,
        }
    }

    pub fn from_str(string: &str) -> Self {
        let c_string = CString::new(string)
            .expect("String used to construct CString contained null byte");
        InputMethodName {
            c_string,
            string: string.to_owned(),
        }
    }
}

impl fmt::Debug for InputMethodName {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.string.fmt(f)
    }
}

#[derive(Debug, Clone)]
struct PotentialInputMethod {
    name: InputMethodName,
    successful: Option<bool>,
}

impl PotentialInputMethod {
    pub fn from_string(string: String) -> Self {
        PotentialInputMethod {
            name: InputMethodName::from_string(string),
            successful: None,
        }
    }

    pub fn from_str(string: &str) -> Self {
        PotentialInputMethod {
            name: InputMethodName::from_str(string),
            successful: None,
        }
    }

    pub fn reset(&mut self) {
        self.successful = None;
    }

    pub fn open_im(&mut self, xconn: &Arc<XConnection>) -> Option<InputMethod> {
        let im = unsafe { open_im(xconn, &self.name.c_string) };
        self.successful = Some(im.is_some());
        im.map(|im| InputMethod::new(im, self.name.string.clone()))
    }
}

// By logging this struct, you get a sequential listing of every locale modifier tried, where it
// came from, and if it succceeded.
#[derive(Debug, Clone)]
pub struct PotentialInputMethods {
    // On correctly configured systems, the XMODIFIERS environemnt variable tells us everything we
    // need to know.
    xmodifiers: Option<PotentialInputMethod>,
    // We have some standard options at our disposal that should ostensibly always work. For users
    // who only need compose sequences, this ensures that the program launches without a hitch
    // For users who need more sophisticated IME features, this is more or less a silent failure.
    // Logging features should be added in the future to allow both audiences to be effectively
    // served.
    fallbacks: [PotentialInputMethod; 2],
    // For diagnostic purposes, we include the list of XIM servers that the server reports as
    // being available.
    _xim_servers: Result<Vec<String>, GetXimServersError>,
}

impl PotentialInputMethods {
    pub fn new(xconn: &Arc<XConnection>) -> Self {
        let xmodifiers = env::var("XMODIFIERS")
            .ok()
            .map(PotentialInputMethod::from_string);
        PotentialInputMethods {
            // Since passing "" to XSetLocaleModifiers results in it defaulting to the value of
            // XMODIFIERS, it's worth noting what happens if XMODIFIERS is also "". If simply
            // running the program with `XMODIFIERS="" cargo run`, then assuming XMODIFIERS is
            // defined in the profile (or parent environment) then that parent XMODIFIERS is used.
            // If that XMODIFIERS value is also "" (i.e. if you ran `export XMODIFIERS=""`), then
            // XSetLocaleModifiers uses the default local input method. Note that defining
            // XMODIFIERS as "" is different from XMODIFIERS not being defined at all, since in
            // that case, we get `None` and end up skipping ahead to the next method.
            xmodifiers,
            fallbacks: [
                // This is a standard input method that supports compose equences, which should
                // always be available. `@im=none` appears to mean the same thing.
                PotentialInputMethod::from_str("@im=local"),
                // This explicitly specifies to use the implementation-dependent default, though
                // that seems to be equivalent to just using the local input method.
                PotentialInputMethod::from_str("@im="),
            ],
            // The XIM_SERVERS property can have surprising values. For instance, when I exited
            // ibus to run fcitx, it retained the value denoting ibus. Even more surprising is
            // that the fcitx input method could only be successfully opened using "@im=ibus".
            // Presumably due to this quirk, it's actually possible to alternate between ibus and
            // fcitx in a running application.
            _xim_servers: unsafe { get_xim_servers(xconn) },
        }
    }

    // This resets the `successful` field of every potential input method, ensuring we have
    // accurate information when this struct is re-used by the destruction/instantiation callbacks.
    fn reset(&mut self) {
        if let Some(ref mut input_method) = self.xmodifiers {
            input_method.reset();
        }

        for input_method in &mut self.fallbacks {
            input_method.reset();
        }
    }

    pub fn open_im(
        &mut self,
        xconn: &Arc<XConnection>,
        callback: Option<&dyn Fn() -> ()>,
    ) -> InputMethodResult {
        use self::InputMethodResult::*;

        self.reset();

        if let Some(ref mut input_method) = self.xmodifiers {
            let im = input_method.open_im(xconn);
            if let Some(im) = im {
                return XModifiers(im);
            } else {
                if let Some(ref callback) = callback {
                    callback();
                }
            }
        }

        for input_method in &mut self.fallbacks {
            let im = input_method.open_im(xconn);
            if let Some(im) = im {
                return Fallback(im);
            }
        }

        Failure
    }
}