/*!
 * Layout-related data.
 *
 * The `View` contains `Row`s and each `Row` contains `Button`s.
 * They carry data relevant to their positioning only,
 * except the Button, which also carries some data
 * about its appearance and function.
 *
 * The layout is determined bottom-up, by measuring `Button` sizes,
 * deriving `Row` sizes from them, and then centering them within the `View`.
 *
 * That makes the `View` position immutable,
 * and therefore different than the other positions.
 *
 * Note that it might be a better idea
 * to make `View` position depend on its contents,
 * and let the renderer scale and center it within the widget.
 */

use std::cmp;
use std::collections::HashMap;
use std::ffi::CString;
use std::fmt;
use std::vec::Vec;

use crate::action::Action;
use crate::actors;
use crate::drawing;
use crate::float_ord::FloatOrd;
use crate::keyboard::{KeyState, KeyCode, PressType};
use crate::logging;
use crate::popover;
use crate::receiver;
use crate::submission::{ Submission, SubmitData, Timestamp };
use crate::util::find_max_double;

use crate::imservice::ContentPurpose;

// Traits
use crate::logging::Warn;

/// Gathers stuff defined in C or called by C
pub mod c {
    use super::*;
    
    use crate::receiver;
    use crate::submission::c::Submission as CSubmission;

    use gtk_sys;
    use std::ops::{ Add, Sub };
    use std::os::raw::c_void;
    
    use crate::util::CloneOwned;
    
    // The following defined in C
    #[repr(transparent)]
    #[derive(Copy, Clone)]
    pub struct EekGtkKeyboard(pub *const gtk_sys::GtkWidget);

    extern "C" {
        #[allow(improper_ctypes)]
        pub fn eek_gtk_keyboard_emit_feedback(
            keyboard: EekGtkKeyboard,
        );
    }

    /// Defined in eek-types.h
    #[repr(C)]
    #[derive(Clone, Debug, PartialEq)]
    pub struct Point {
        pub x: f64,
        pub y: f64,
    }

    impl Add for Point {
        type Output = Self;
        fn add(self, other: Self) -> Self {
            &self + other
        }
    }

    impl Add<Point> for &Point {
        type Output = Point;
        fn add(self, other: Point) -> Point {
            Point {
                x: self.x + other.x,
                y: self.y + other.y,
            }
        }
    }

    impl Sub<&Point> for Point {
        type Output = Point;
        fn sub(self, other: &Point) -> Point {
            Point {
                x: self.x - other.x,
                y: self.y - other.y,
            }
        }
    }

    /// Defined in eek-types.h
    #[repr(C)]
    #[derive(Clone, Debug, PartialEq)]
    pub struct Bounds {
        pub x: f64,
        pub y: f64,
        pub width: f64,
        pub height: f64
    }

    impl Bounds {
        pub fn contains(&self, point: &Point) -> bool {
            point.x > self.x && point.x < self.x + self.width
                && point.y > self.y && point.y < self.y + self.height
        }
    }

    /// Translate and then scale
    #[repr(C)]
    pub struct Transformation {
        pub origin_x: f64,
        pub origin_y: f64,
        pub scale_x: f64,
        pub scale_y: f64,
    }

    impl Transformation {
        /// Applies the new transformation after this one
        pub fn chain(self, next: Transformation) -> Transformation {
            Transformation {
                origin_x: self.origin_x + self.scale_x * next.origin_x,
                origin_y: self.origin_y + self.scale_y * next.origin_y,
                scale_x: self.scale_x * next.scale_x,
                scale_y: self.scale_y * next.scale_y,
            }
        }
        fn forward(&self, p: Point) -> Point {
            Point {
                x: (p.x - self.origin_x) / self.scale_x,
                y: (p.y - self.origin_y) / self.scale_y,
            }
        }
        fn reverse(&self, p: Point) -> Point {
            Point {
                x: p.x * self.scale_x + self.origin_x,
                y: p.y * self.scale_y + self.origin_y,
            }
        }
        pub fn reverse_bounds(&self, b: Bounds) -> Bounds {
            let start = self.reverse(Point { x: b.x, y: b.y });
            let end = self.reverse(Point {
                x: b.x + b.width,
                y: b.y + b.height,
            });
            Bounds {
                x: start.x,
                y: start.y,
                width: end.x - start.x,
                height: end.y - start.y,
            }
        }
    }

    // This is constructed only in C, no need for warnings
    #[allow(dead_code)]
    #[repr(transparent)]
    pub struct LevelKeyboard(*const c_void);

    // The following defined in Rust. TODO: wrap naked pointers to Rust data inside RefCells to prevent multiple writers

    /// Positions the layout contents within the available space.
    /// The origin of the transformation is the point inside the margins.
    #[no_mangle]
    pub extern "C"
    fn squeek_layout_calculate_transformation(
        layout: *const Layout,
        allocation_width: f64,
        allocation_height: f64,
    ) -> Transformation {
        let layout = unsafe { &*layout };
        layout.shape.calculate_transformation(Size {
            width: allocation_width,
            height: allocation_height,
        })
    }

    #[no_mangle]
    pub extern "C"
    fn squeek_layout_get_kind(layout: *const Layout) -> u32 {
        let layout = unsafe { &*layout };
        layout.shape.kind.clone() as u32
    }

    #[no_mangle]
    pub extern "C"
    fn squeek_layout_get_purpose(layout: *const Layout) -> u32 {
        let layout = unsafe { &*layout };
        layout.shape.purpose.clone() as u32
    }

    #[no_mangle]
    pub extern "C"
    fn squeek_layout_free(layout: *mut Layout) {
        unsafe { Box::from_raw(layout) };
    }

    /// Entry points for more complex procedures and algorithms which span multiple modules
    pub mod procedures {
        use super::*;

        /// Release pointer in the specified position
        #[no_mangle]
        pub extern "C"
        fn squeek_layout_release(
            layout: *mut Layout,
            submission: CSubmission,
            widget_to_layout: Transformation,
            time: u32,
            popover: actors::popover::c::Actor,
            app_state: receiver::c::State,
            ui_keyboard: EekGtkKeyboard,
        ) {
            let time = Timestamp(time);
            let layout = unsafe { &mut *layout };
            let submission = submission.clone_ref();
            let mut submission = submission.borrow_mut();
            let app_state = app_state.clone_owned();
            let popover_state = popover.clone_owned();
            
            let ui_backend = UIBackend {
                widget_to_layout,
                keyboard: ui_keyboard,
            };

            // The list must be copied,
            // because it will be mutated in the loop
            let pressed_buttons
                = layout.state.active_buttons.clone();
            for (button, _key_state) in pressed_buttons.iter_pressed() {
                seat::handle_release_key(
                    layout,
                    &mut submission,
                    Some(&ui_backend),
                    time,
                    Some((&popover_state, app_state.clone())),
                    button,
                );
            }
            drawing::queue_redraw(ui_keyboard);
        }

        /// Release all buttons but don't redraw
        #[no_mangle]
        pub extern "C"
        fn squeek_layout_release_all_only(
            layout: *mut Layout,
            submission: CSubmission,
            time: u32,
        ) {
            let layout = unsafe { &mut *layout };
            let submission = submission.clone_ref();
            let mut submission = submission.borrow_mut();
            // The list must be copied,
            // because it will be mutated in the loop
            let pressed_buttons = layout.state.active_buttons.clone();
            for (button, _key_state) in pressed_buttons.iter_pressed() {
                seat::handle_release_key(
                    layout,
                    &mut submission,
                    None, // don't update UI
                    Timestamp(time),
                    None, // don't switch layouts
                    button,
                );
            }
        }

        #[no_mangle]
        pub extern "C"
        fn squeek_layout_depress(
            layout: *mut Layout,
            submission: CSubmission,
            x_widget: f64, y_widget: f64,
            widget_to_layout: Transformation,
            time: u32,
            ui_keyboard: EekGtkKeyboard,
        ) {
            let layout = unsafe { &mut *layout };
            let submission = submission.clone_ref();
            let mut submission = submission.borrow_mut();
            let point = widget_to_layout.forward(
                Point { x: x_widget, y: y_widget }
            );

            let index = layout.find_index_by_position(point);

            if let Some((row, position_in_row)) = index {
                let button = ButtonPosition {
                    view: layout.state.current_view.clone(),
                    row,
                    position_in_row,
                };
                seat::handle_press_key(
                    layout,
                    &mut submission,
                    Timestamp(time),
                    &button,
                );
                // maybe TODO: draw on the display buffer here
                drawing::queue_redraw(ui_keyboard);
                unsafe {
                    eek_gtk_keyboard_emit_feedback(ui_keyboard);
                }
            };
        }

        // FIXME: this will work funny
        // when 2 touch points are on buttons and moving one after another
        // Solution is to have separate pressed lists for each point
        #[no_mangle]
        pub extern "C"
        fn squeek_layout_drag(
            layout: *mut Layout,
            submission: CSubmission,
            x_widget: f64, y_widget: f64,
            widget_to_layout: Transformation,
            time: u32,
            popover: actors::popover::c::Actor,
            app_state: receiver::c::State,
            ui_keyboard: EekGtkKeyboard,
        ) {
            let time = Timestamp(time);
            let layout = unsafe { &mut *layout };
            let submission = submission.clone_ref();
            let mut submission = submission.borrow_mut();
            // We only need to query state here, not update.
            // A copy is enough.
            let popover_state = popover.clone_owned();
            let app_state = app_state.clone_owned();
            let ui_backend = UIBackend {
                widget_to_layout,
                keyboard: ui_keyboard,
            };
            let point = ui_backend.widget_to_layout.forward(
                Point { x: x_widget, y: y_widget }
            );

            let pressed_buttons = layout.state.active_buttons.clone();
            let pressed_buttons = pressed_buttons.iter_pressed();
            let button_info = layout.find_index_by_position(point);

            if let Some((row, position_in_row)) = button_info {
                let current_pos = ButtonPosition {
                    view: layout.state.current_view.clone(),
                    row,
                    position_in_row,
                };
                let mut found = false;
                for (button, _key_state) in pressed_buttons {
                    if button == &current_pos {
                        found = true;
                    } else {
                        seat::handle_release_key(
                            layout,
                            &mut submission,
                            Some(&ui_backend),
                            time,
                            Some((&popover_state, app_state.clone())),
                            button,
                        );
                    }
                }
                if !found {
                    let button = ButtonPosition {
                        view: layout.state.current_view.clone(),
                        row,
                        position_in_row,
                    };
                    seat::handle_press_key(
                        layout,
                        &mut submission,
                        time,
                        &button,
                    );
                    // maybe TODO: draw on the display buffer here
                    unsafe {
                        eek_gtk_keyboard_emit_feedback(ui_keyboard);
                    }
                }
            } else {
                for (button, _key_state) in pressed_buttons {
                    seat::handle_release_key(
                        layout,
                        &mut submission,
                        Some(&ui_backend),
                        time,
                        Some((&popover_state, app_state.clone())),
                        button,
                    );
                }
            }
            drawing::queue_redraw(ui_keyboard);
        }

        #[cfg(test)]
        mod test {
            use super::*;

            fn near(a: f64, b: f64) -> bool {
                (a - b).abs() < ((a + b) * 0.001f64).abs()
            }

            #[test]
            fn transform_back() {
                let transform = Transformation {
                    origin_x: 10f64,
                    origin_y: 11f64,
                    scale_x: 12f64,
                    scale_y: 13f64,
                };
                let point = Point { x: 1f64, y: 1f64 };
                let transformed = transform.reverse(transform.forward(point.clone()));
                assert!(near(point.x, transformed.x));
                assert!(near(point.y, transformed.y));
            }
        }
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Size {
    pub width: f64,
    pub height: f64,
}

#[derive(Debug, Clone, PartialEq)]
pub enum Label {
    /// Text used to display the symbol
    Text(CString),
    /// Icon name used to render the symbol
    IconName(CString),
}

/// The definition of an interactive button
#[derive(Clone, Debug, PartialEq)]
pub struct Button {
    /// ID string, e.g. for CSS
    pub name: CString,
    /// Label to display to the user
    pub label: Label,
    pub size: Size,
    /// The name of the visual class applied
    pub outline_name: CString,
    // action-related stuff
    /// A cache of raw keycodes derived from Action::Submit given a keymap
    pub keycodes: Vec<KeyCode>,
    /// Static description of what the key does when pressed or released
    pub action: Action,
}

impl Button {
    pub fn get_bounds(&self) -> c::Bounds {
        c::Bounds {
            x: 0.0, y: 0.0,
            width: self.size.width, height: self.size.height,
        }
    }
}

/// The representation of a row of buttons
#[derive(Clone, Debug)]
pub struct Row {
    /// Buttons together with their offset from the left relative to the row.
    /// ie. the first button always start at 0.
    buttons: Vec<(f64, Button)>,

    /// Total size of the row
    size: Size,
}

impl Row {
    pub fn new(buttons: Vec<(f64, Button)>) -> Row {
        // Make sure buttons are sorted by offset.
        debug_assert!({
            let mut sorted = buttons.clone();
            sorted.sort_by(|(f1, _), (f2, _)| f1.partial_cmp(f2).unwrap());

            sorted.iter().map(|(f, _)| *f).collect::<Vec<_>>()
                == buttons.iter().map(|(f, _)| *f).collect::<Vec<_>>()
        });

        let width = buttons.iter().next_back()
            .map(|(x_offset, button)| button.size.width + x_offset)
            .unwrap_or(0.0);

        let height = find_max_double(
            buttons.iter(),
            |(_offset, button)| button.size.height,
        );

        Row { buttons, size: Size { width, height } }
    }

    pub fn get_size(&self) -> Size {
        self.size.clone()
    }

    pub fn get_buttons(&self) -> &Vec<(f64, Button)> {
        &self.buttons
    }

    /// Finds the first button that covers the specified point
    /// relative to row's position's origin.
    /// Returns its index too.
    fn find_button_by_position(&self, x: f64) -> (&Button, usize)
    {
        // Buttons are sorted so we can use a binary search to find the clicked
        // button. Note this doesn't check whether the point is actually within
        // a button. This is on purpose as we want a click past the left edge of
        // the left-most button to register as a click.
        let result = self.buttons.binary_search_by(
            |&(f, _)| f.partial_cmp(&x).unwrap()
        );

        let index = result.unwrap_or_else(|r| r);
        let index = if index > 0 { index - 1 } else { 0 };

        (&self.buttons[index].1, index)
    }
}

#[derive(Clone, Debug)]
pub struct Spacing {
    pub row: f64,
    pub button: f64,
}

#[derive(Clone)]
pub struct View {
    /// Rows together with their offsets from the top left
    rows: Vec<(c::Point, Row)>,

    /// Total size of the view
    size: Size,
}

impl View {
    pub fn new(rows: Vec<(f64, Row)>) -> View {
        // Make sure rows are sorted by offset.
        debug_assert!({
            let mut sorted = rows.clone();
            sorted.sort_by(|(f1, _), (f2, _)| f1.partial_cmp(f2).unwrap());

            sorted.iter().map(|(f, _)| *f).collect::<Vec<_>>()
                == rows.iter().map(|(f, _)| *f).collect::<Vec<_>>()
        });

        // No need to call `get_rows()`,
        // as the biggest row is the most far reaching in both directions
        // because they are all centered.
        let width = find_max_double(rows.iter(), |(_offset, row)| row.size.width);

        let height = rows.iter().next_back()
            .map(|(y_offset, row)| row.size.height + y_offset)
            .unwrap_or(0.0);

        // Center the rows
        let rows = rows.into_iter().map(|(y_offset, row)| {(
                c::Point {
                    x: (width - row.size.width) / 2.0,
                    y: y_offset,
                },
                row,
            )}).collect::<Vec<_>>();

        View { rows, size: Size { width, height } }
    }
    /// Finds the first button that covers the specified point
    /// relative to view's position's origin.
    /// Returns also (row, column) index.
    fn find_button_by_position(&self, point: c::Point)
        -> Option<(&Button, (usize, usize))>
    {
        // Only test bounds of the view here, letting rows/column search extend
        // to the edges of these bounds.
        let bounds = c::Bounds {
            x: 0.0,
            y: 0.0,
            width: self.size.width,
            height: self.size.height,
        };
        if !bounds.contains(&point) {
            return None;
        }

        // Rows are sorted so we can use a binary search to find the row.
        let result = self.rows.binary_search_by(
            |(f, _)| f.y.partial_cmp(&point.y).unwrap()
        );

        let index = result.unwrap_or_else(|r| r);
        let index = if index > 0 { index - 1 } else { 0 };

        let row = &self.rows[index];
        let (button, button_index)
            = row.1.find_button_by_position(point.x - row.0.x);

        Some((
            &button,
            (index, button_index),
        ))
    }

    pub fn get_size(&self) -> Size {
        self.size.clone()
    }

    /// Returns positioned rows, with appropriate x offsets (centered)
    pub fn get_rows(&self) -> &Vec<(c::Point, Row)> {
        &self.rows
    }

    /// Returns a size which contains all the views
    /// if they are all centered on the same point.
    pub fn calculate_super_size(views: Vec<&View>) -> Size {
        Size {
            height: find_max_double(
                views.iter(),
                |view| view.size.height,
            ),
            width: find_max_double(
                views.iter(),
                |view| view.size.width,
            ),
        }
    }
}

/// The physical characteristic of layout for the purpose of styling
#[derive(Clone, Copy, PartialEq, Debug)]
pub enum ArrangementKind {
    Base = 0,
    Wide = 1,
}

#[derive(Debug, PartialEq)]
pub struct Margins {
    pub top: f64,
    pub bottom: f64,
    pub left: f64,
    pub right: f64,
}

#[derive(Clone, Debug, PartialEq)]
pub enum LatchedState {
    /// Holds view to return to.
    FromView(String),
    Not,
}

/// Associates the state of a layout with its definition.
/// Contains everything necessary to present this layout to the user
/// and to determine its reactions to inputs.
pub struct Layout {
    pub state: LayoutState,
    pub shape: LayoutData,
}

/// Button position for the pressed buttons list
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct ButtonPosition {
    // There's only ever going to be a handul of pressed buttons,
    // so as inefficient as String is, it won't make a difference.
    // In the worst case, views can turn into indices in the description.
    pub view: String,
    /// Index to the view's row.
    pub row: usize,
    /// Index to the row's button.
    pub position_in_row: usize,
}

#[derive(Clone)]
pub struct ActiveButtons(HashMap<ButtonPosition, KeyState>);

enum Presence {
    Missing,
    Present,
}

static RELEASED: KeyState = KeyState { pressed: PressType::Released };

impl ActiveButtons {
    fn insert(&mut self, button: ButtonPosition, state: KeyState) -> Presence {
        match self.0.insert(button, state) {
            Some(_) => Presence::Present,
            None => Presence::Missing,
        }
    }
    
    pub fn get(&self, button: &ButtonPosition) -> &KeyState {
        self.0.get(button)
            .unwrap_or(&RELEASED)
    }
    fn remove(&mut self, button: &ButtonPosition) -> Presence {
        match self.0.remove(button) {
            Some(_) => Presence::Present,
            None => Presence::Missing,
        }
    }
    fn iter_pressed(&self) -> impl Iterator<Item=(&ButtonPosition, &KeyState)> {
        self.0.iter().filter(|(_p, s)| s.pressed == PressType::Pressed)
    }
}

/// Changeable state that can't be derived from the definition of the layout.
pub struct LayoutState {
    pub current_view: String,

    // If current view is latched,
    // clicking any button that emits an action (erase, submit, set modifier)
    // will cause lock buttons to unlatch.
    view_latched: LatchedState,
    // a Vec would be enough, but who cares, this will be small & fast enough
    // TODO: turn those into per-input point *_buttons to track dragging.
    // The renderer doesn't need the list of pressed keys any more,
    // because it needs to iterate
    // through all buttons of the current view anyway.
    // When the list tracks actual location,
    // it becomes possible to place popovers and other UI accurately.
    /// Buttons not in this list are in their base state:
    /// not pressed.
    /// Latched/locked appearance is derived from current view
    /// and button metadata.
    pub active_buttons: ActiveButtons,
}

/// A builder structure for picking up layout data from storage
pub struct LayoutParseData {
    /// Point is the offset within the panel
    /// (transformed to layout's coordinate space).
    pub views: HashMap<String, (c::Point, View)>,
    /// xkb keymaps applicable to the contained keys
    pub keymaps: Vec<CString>,
    pub margins: Margins,
}

/// Static, cacheable information for the layout
pub struct LayoutData {
    pub margins: Margins,
    pub kind: ArrangementKind,
    pub purpose: ContentPurpose,

    // Views own the actual buttons which have state
    // Maybe they should own UI only,
    // and keys should be owned by a dedicated non-UI-State?
    /// Point is the offset within the layout
    pub views: HashMap<String, (c::Point, View)>,

    // Non-UI stuff
    /// xkb keymaps applicable to the contained keys. Unchangeable
    pub keymaps: Vec<CString>,
}

#[derive(Debug)]
struct NoSuchView;

impl fmt::Display for NoSuchView {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "No such view")
    }
}


impl LayoutData {
    fn get_button(&self, button: &ButtonPosition) -> Option<&Button> {
        let (_, view) = self.views.get(&button.view)?;
        let (_, row) = view.rows.get(button.row)?;
        let (_, key) = row.buttons.get(button.position_in_row)?;
        Some(key)
    }

    fn find_button_place(&self, button: &ButtonPosition) -> Option<procedures::Place> {
        let (_, view) = self.views.get(&button.view)?;
        procedures::find_button_place(view, (button.row, button.position_in_row))
    }
    
    /// Calculates size without margins
    fn calculate_inner_size(&self) -> Size {
        View::calculate_super_size(
            self.views.iter().map(|(_, (_offset, v))| v).collect()
        )
    }

    /// Size including margins
    fn calculate_size(&self) -> Size {
        let inner_size = self.calculate_inner_size();
        Size {
            width: self.margins.left + inner_size.width + self.margins.right,
            height: (
                self.margins.top
                + inner_size.height
                + self.margins.bottom
            ),
        }
    }

    pub fn calculate_transformation(
        &self,
        available: Size,
    ) -> c::Transformation {
        let size = self.calculate_size();
        let h_scale = available.width / size.width;
        let v_scale = available.height / size.height;
        // Allow up to 5% (and a bit more) horizontal stretching for filling up available space
        let scale_x = if (h_scale / v_scale) < 1.055 { h_scale } else { v_scale };
        let scale_y = cmp::min(FloatOrd(h_scale), FloatOrd(v_scale)).0;
        let outside_margins = c::Transformation {
            origin_x: (available.width - (scale_x * size.width)) / 2.0,
            origin_y: (available.height - (scale_y * size.height)) / 2.0,
            scale_x: scale_x,
            scale_y: scale_y,
        };
        outside_margins.chain(c::Transformation {
            origin_x: self.margins.left,
            origin_y: self.margins.top,
            scale_x: 1.0,
            scale_y: 1.0,
        })
    }
}

// Unfortunately, changes are not atomic due to mutability :(
// An error will not be recoverable
// The usage of &mut on Rc<RefCell<KeyState>> doesn't mean anything special.
// Cloning could also be used.
impl Layout {
    pub fn new(data: LayoutParseData, kind: ArrangementKind, purpose: ContentPurpose) -> Layout {
        Layout {
            shape: LayoutData {
                kind,
                views: data.views,
                keymaps: data.keymaps,
                margins: data.margins,
                purpose,
            },
            state: LayoutState {
                current_view: "base".to_owned(),
                view_latched: LatchedState::Not,
                active_buttons: ActiveButtons(HashMap::new()),
            },
        }
    }

    pub fn get_current_view_position(&self) -> &(c::Point, View) {
        &self.shape.views
            .get(&self.state.current_view).expect("Selected nonexistent view")
    }

    pub fn get_current_view(&self) -> &View {
        &self.shape.views.get(&self.state.current_view).expect("Selected nonexistent view").1
    }

    fn set_view(&mut self, view: String) -> Result<(), NoSuchView> {
        if self.shape.views.contains_key(&view) {
            self.state.current_view = view;
            Ok(())
        } else {
            Err(NoSuchView)
        }
    }

    // Layout is passed around mutably,
    // so better keep the field away from direct access.
    pub fn get_view_latched(&self) -> &LatchedState {
        &self.state.view_latched
    }
    
    /// Returns index within current view
    fn find_index_by_position(&self, point: c::Point) -> Option<(usize, usize)> {
        let (offset, view) = self.get_current_view_position();
        view.find_button_by_position(point - offset)
            .map(|(_b, i)| i)
    }

    /// Returns index within current view too.
    pub fn foreach_visible_button<F>(&self, mut f: F)
        where F: FnMut(c::Point, &Button, (usize, usize))
    {
        let (view_offset, view) = self.get_current_view_position();
        let rows = view.get_rows().iter().enumerate();
        for (row_idx, (row_offset, row)) in rows {
            let buttons = row.buttons.iter().enumerate();
            for (button_idx, (x_offset, button)) in buttons {
                let offset = view_offset
                    + row_offset.clone()
                    + c::Point { x: *x_offset, y: 0.0 };
                f(offset, button, (row_idx, button_idx));
            }
        }
    }

    fn apply_view_transition(
        &mut self,
        action: &Action,
    ) {
        let (transition, new_latched) = Layout::process_action_for_view(
            action,
            &self.state.current_view,
            &self.state.view_latched,
        );

        match transition {
            ViewTransition::UnlatchAll => self.unstick_locks(),
            ViewTransition::ChangeTo(view) => try_set_view(self, view.into()),
            ViewTransition::NoChange => {},
        };

        self.state.view_latched = new_latched;
    }

    /// Unlatch all latched keys,
    /// so that the new view is the one before first press.
    fn unstick_locks(&mut self) {
        if let LatchedState::FromView(name) = self.state.view_latched.clone() {
            match self.set_view(name.clone()) {
                Ok(_) => { self.state.view_latched = LatchedState::Not; }
                Err(e) => log_print!(
                    logging::Level::Bug,
                    "Bad view {}, can't unlatch ({:?})",
                    name,
                    e,
                ),
            }
        }
    }

    /// Last bool is new latch state.
    /// It doesn't make sense when the result carries UnlatchAll,
    /// but let's not be picky.
    ///
    /// Although the state is not defined at the keys
    /// (it's in the relationship between view and action),
    /// keys go through the following stages when clicked repeatedly:
    /// unlocked+unlatched -> locked+latched -> locked+unlatched
    /// -> unlocked+unlatched
    fn process_action_for_view<'a>(
        action: &'a Action,
        current_view: &str,
        latched: &LatchedState,
    ) -> (ViewTransition<'a>, LatchedState) {
        match action {
            Action::Submit { text: _, keys: _ }
                | Action::Erase
                | Action::ApplyModifier(_)
            => {
                let t = match latched {
                    LatchedState::FromView(_) => ViewTransition::UnlatchAll,
                    LatchedState::Not => ViewTransition::NoChange,
                };
                (t, LatchedState::Not)
            },
            Action::SetView(view) => (
                ViewTransition::ChangeTo(view),
                LatchedState::Not,
            ),
            Action::LockView { lock, unlock, latches, looks_locked_from: _ } => {
                use self::ViewTransition as VT;
                let locked = action.is_locked(current_view);
                match (locked, latched, latches) {
                    // Was unlocked, now make locked but latched.
                    (false, LatchedState::Not, true) => (
                        VT::ChangeTo(lock),
                        LatchedState::FromView(current_view.into()),
                    ),
                    // Layout is latched for reason other than this button.
                    (false, LatchedState::FromView(view), true) => (
                        VT::ChangeTo(lock),
                        LatchedState::FromView(view.clone()),
                    ),
                    // Was latched, now only locked.
                    (true, LatchedState::FromView(_), true)
                        => (VT::NoChange, LatchedState::Not),
                    // Was unlocked, can't latch so now make fully locked.
                    (false, _, false)
                        => (VT::ChangeTo(lock), LatchedState::Not),
                    // Was locked, now make unlocked.
                    (true, _, _)
                        => (VT::ChangeTo(unlock), LatchedState::Not),
                }
            },
            _ => (ViewTransition::NoChange, latched.clone()),
        }
    }
}

#[derive(Debug, PartialEq)]
enum ViewTransition<'a> {
    ChangeTo(&'a str),
    UnlatchAll,
    NoChange,
}

fn try_set_view(layout: &mut Layout, view_name: &str) {
    layout.set_view(view_name.into())
        .or_print(
            logging::Problem::Bug,
            &format!("Bad view {}, ignoring", view_name),
        );
}


mod procedures {
    use super::*;

    pub type Place<'v> = (c::Point, &'v Button);

    /// Finds the canvas offset of the button.
    pub fn find_button_place<'v>(
        view: &'v View,
        (row, position_in_row): (usize, usize),
    ) -> Option<Place<'v>> {
        let (row_offset, row) = view.get_rows().get(row)?;
        let (x_offset, button) = row.get_buttons()
            .get(position_in_row)?;
        Some((
            row_offset + c::Point { x: *x_offset, y: 0.0 },
            button,
        ))
    }

    #[cfg(test)]
    mod test {
        use super::*;

        use crate::layout::test::*;

        /// Checks indexing of buttons
        #[test]
        fn view_has_button() {
            let button = make_button("1".into());

            let row = Row::new(vec!((0.1, button)));

            let view = View::new(vec!((1.2, row)));

            assert_eq!(
                find_button_place(&view, (0, 0)),
                Some((
                    c::Point { x: 0.1, y: 1.2 },
                    &make_button("1".into()),
                ))
            );

            let view = View::new(vec![]);
            assert_eq!(
                find_button_place(&view, (0, 0)),
                None,
            );
        }
    }
}

pub struct UIBackend {
    widget_to_layout: c::Transformation,
    keyboard: c::EekGtkKeyboard,
}

/// Top level procedures, dispatching to everything
mod seat {
    use super::*;

    fn handle_press_key_cleaner(
        shape: &LayoutData,
        submission: &mut Submission,
        time: Timestamp,
        button_pos: &ButtonPosition,
    ) {
        let button = shape.get_button(button_pos).unwrap();
        let action = button.action.clone();
        match action {
            Action::Submit {
                text: Some(text),
                keys: _,
            } => submission.handle_press(
                button_pos.into(),
                SubmitData::Text(&text),
                &button.keycodes,
                time,
            ),
            Action::Submit {
                text: None,
                keys: _,
            } => submission.handle_press(
                button_pos.into(),
                SubmitData::Keycodes,
                &button.keycodes,
                time,
            ),
            Action::Erase => submission.handle_press(
                button_pos.into(),
                SubmitData::Erase,
                &button.keycodes,
                time,
            ),
            _ => {},
        };
    }
    
    pub fn handle_press_key(
        layout: &mut Layout,
        submission: &mut Submission,
        time: Timestamp,
        button_pos: &ButtonPosition,
    ) {
        // Send messages
        handle_press_key_cleaner(&layout.shape, submission, time, button_pos);
    
        // Update state
        let find = layout.state.active_buttons.get(button_pos);
        if let KeyState { pressed: PressType::Pressed } = find {
            log_print!(
                logging::Level::Bug,
                "Button {:?} was already pressed", button_pos,
            );
        } else {
            layout.state.active_buttons.insert(
                button_pos.clone(),
                KeyState { pressed: PressType::Pressed },
            );
        }
    }

    fn handle_release_key_cleaner(
        shape: &LayoutData,
        submission: &mut Submission,
        ui: Option<&UIBackend>,
        time: Timestamp,
        // TODO: intermediate measure:
        // passing state conditionally because it's only used for popover.
        // Eventually, it should be used for sumitting button events,
        // and passed always.
        manager: Option<(&actors::popover::State, receiver::State)>,
        button_pos: &ButtonPosition,
    ) -> Action{
        let button = shape.get_button(&button_pos).unwrap();
        let action = button.action.clone();

        // process non-view switching
        match action.clone() {
            Action::Submit { text: _, keys: _ }
                | Action::Erase
            => {
                submission.handle_release(button_pos.into(), time);
            },
            Action::ApplyModifier(modifier) => {
                // FIXME: key id is unneeded with stateless locks
                let key_id = button_pos.into();
                let gets_locked = !submission.is_modifier_active(modifier);
                match gets_locked {
                    true => submission.handle_add_modifier(
                        key_id,
                        modifier, time,
                    ),
                    false => submission.handle_drop_modifier(key_id, time),
                }
            }
            // only show when UI is present
            Action::ShowPreferences => if let Some(ui) = &ui {
                // only show when layout manager is available
                if let Some((manager, app_state)) = manager {
                    let place = shape.find_button_place(button_pos);

                    if let Some((position, button)) = place {
                        let bounds = c::Bounds {
                            x: position.x,
                            y: position.y,
                            width: button.size.width,
                            height: button.size.height,
                        };
                        popover::show(
                            ui.keyboard,
                            ui.widget_to_layout.reverse_bounds(bounds),
                            manager,
                            app_state,
                        );
                    }
                }
            },
            // Other keys are handled in view switcher before.
            _ => {}
        };
        
        action
    }
    
    /// Mutates layout and sends events.
    /// This split away from handle_release_key
    /// in order to pull at least some of the mutation away
    /// from what should some day be core functional logic.
    pub fn handle_release_key(
        layout: &mut Layout,
        submission: &mut Submission,
        ui: Option<&UIBackend>,
        time: Timestamp,
        // TODO: intermediate measure:
        // passing state conditionally because it's only used for popover.
        // Eventually, it should be used for sumitting button events,
        // and passed always.
        manager: Option<(&actors::popover::State, receiver::State)>,
        button_pos: &ButtonPosition,
    ) {
        // Send events
        let action = handle_release_key_cleaner(
            &layout.shape,
            submission,
            ui,
            time,
            manager,
            button_pos,
        );
        
        // Apply state changes
        layout.apply_view_transition(&action);
        
        if let Presence::Missing = layout.state.active_buttons.remove(&button_pos) {
            log_print!(
                logging::Level::Bug,
                "No button to remove from pressed list: {:?}", button_pos
            );
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    use std::ffi::CString;

    pub fn make_button(
        name: String,
    ) -> Button {
        Button {
            name: CString::new(name.clone()).unwrap(),
            size: Size { width: 0f64, height: 0f64 },
            outline_name: CString::new("test").unwrap(),
            label: Label::Text(CString::new(name).unwrap()),
            action: Action::SetView("default".into()),
            keycodes: Vec::new(),
        }
    }

    #[test]
    fn latch_lock_unlock() {
        let action = Action::LockView {
            lock: "lock".into(),
            unlock: "unlock".into(),
            latches: true,
            looks_locked_from: vec![],
        };

        assert_eq!(
            Layout::process_action_for_view(&action, "unlock", &LatchedState::Not),
            (ViewTransition::ChangeTo("lock"), LatchedState::FromView("unlock".into())),
        );

        assert_eq!(
            Layout::process_action_for_view(&action, "lock", &LatchedState::FromView("unlock".into())),
            (ViewTransition::NoChange, LatchedState::Not),
        );

        assert_eq!(
            Layout::process_action_for_view(&action, "lock", &LatchedState::Not),
            (ViewTransition::ChangeTo("unlock"), LatchedState::Not),
        );

        assert_eq!(
            Layout::process_action_for_view(&Action::Erase, "lock", &LatchedState::FromView("base".into())),
            (ViewTransition::UnlatchAll, LatchedState::Not),
        );
    }

    #[test]
    fn latch_pop_layout() {
        let switch = Action::LockView {
            lock: "locked".into(),
            unlock: "base".into(),
            latches: true,
            looks_locked_from: vec![],
        };

        let submit = Action::Erase;

        let view = View::new(vec![(
            0.0,
            Row::new(vec![
                (
                    0.0,
                    Button {
                        action: switch.clone(),
                        ..make_button("switch".into())
                    },
                ),
                (
                    1.0,
                    Button {
                        action: submit.clone(),
                        ..make_button("submit".into())
                    },
                ),
            ]),
        )]);

        let mut layout = Layout {
            state: LayoutState {
                current_view: "base".into(),
                view_latched: LatchedState::Not,
                active_buttons: ActiveButtons(HashMap::new()),
            },
            shape: LayoutData {
                keymaps: Vec::new(),
                kind: ArrangementKind::Base,
                margins: Margins {
                    top: 0.0,
                    left: 0.0,
                    right: 0.0,
                    bottom: 0.0,
                },
                views: hashmap! {
                    // Both can use the same structure.
                    // Switching doesn't depend on the view shape
                    // as long as the switching button is present.
                    "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
                    "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view),
                },
                purpose: ContentPurpose::Normal,
            },
        };

        // Basic cycle
        layout.apply_view_transition(&switch);
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&switch);
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&submit);
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&switch);
        assert_eq!(&layout.state.current_view, "base");
        layout.apply_view_transition(&switch);
        // Unlatch
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&submit);
        assert_eq!(&layout.state.current_view, "base");
    }

    #[test]
    fn reverse_unlatch_layout() {
        let switch = Action::LockView {
            lock: "locked".into(),
            unlock: "base".into(),
            latches: true,
            looks_locked_from: vec![],
        };

        let unswitch = Action::LockView {
            lock: "locked".into(),
            unlock: "unlocked".into(),
            latches: false,
            looks_locked_from: vec![],
        };

        let submit = Action::Erase;

        let view = View::new(vec![(
            0.0,
            Row::new(vec![
                (
                    0.0,
                    Button {
                        action: switch.clone(),
                        ..make_button("switch".into())
                    },
                ),
                (
                    1.0,
                    Button {
                        action: submit.clone(),
                        ..make_button("submit".into())
                    },
                ),
            ]),
        )]);

        let mut layout = Layout {
            state: LayoutState {
                current_view: "base".into(),
                view_latched: LatchedState::Not,
                active_buttons: ActiveButtons(HashMap::new()),
            },
            shape: LayoutData {
                keymaps: Vec::new(),
                kind: ArrangementKind::Base,
                margins: Margins {
                    top: 0.0,
                    left: 0.0,
                    right: 0.0,
                    bottom: 0.0,
                },
                views: hashmap! {
                    // Both can use the same structure.
                    // Switching doesn't depend on the view shape
                    // as long as the switching button is present.
                    "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
                    "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
                    "unlocked".into() => (c::Point { x: 0.0, y: 0.0 }, view),
                },
                purpose: ContentPurpose::Normal,
            },
        };

        layout.apply_view_transition(&switch);
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&unswitch);
        assert_eq!(&layout.state.current_view, "unlocked");
    }

    #[test]
    fn latch_twopop_layout() {
        let switch = Action::LockView {
            lock: "locked".into(),
            unlock: "base".into(),
            latches: true,
            looks_locked_from: vec![],
        };

        let switch_again = Action::LockView {
            lock: "ĄĘ".into(),
            unlock: "locked".into(),
            latches: true,
            looks_locked_from: vec![],
        };

        let submit = Action::Erase;

        let view = View::new(vec![(
            0.0,
            Row::new(vec![
                (
                    0.0,
                    Button {
                        action: switch.clone(),
                        ..make_button("switch".into())
                    },
                ),
                (
                    1.0,
                    Button {
                        action: submit.clone(),
                        ..make_button("submit".into())
                    },
                ),
            ]),
        )]);

        let mut layout = Layout {
            state: LayoutState {
                current_view: "base".into(),
                view_latched: LatchedState::Not,
                active_buttons: ActiveButtons(HashMap::new()),
            },
            shape: LayoutData {
                keymaps: Vec::new(),
                kind: ArrangementKind::Base,
                margins: Margins {
                    top: 0.0,
                    left: 0.0,
                    right: 0.0,
                    bottom: 0.0,
                },
                views: hashmap! {
                    // All can use the same structure.
                    // Switching doesn't depend on the view shape
                    // as long as the switching button is present.
                    "base".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
                    "locked".into() => (c::Point { x: 0.0, y: 0.0 }, view.clone()),
                    "ĄĘ".into() => (c::Point { x: 0.0, y: 0.0 }, view),
                },
                purpose: ContentPurpose::Normal,
            },
        };

        // Latch twice, then Ąto-unlatch across 2 levels
        layout.apply_view_transition(&switch);
        println!("{:?}", layout.state.view_latched);
        assert_eq!(&layout.state.current_view, "locked");
        layout.apply_view_transition(&switch_again);
        println!("{:?}", layout.state.view_latched);
        assert_eq!(&layout.state.current_view, "ĄĘ");
        layout.apply_view_transition(&submit);
        println!("{:?}", layout.state.view_latched);
        assert_eq!(&layout.state.current_view, "base");
    }

    #[test]
    fn check_centering() {
        //    A B
        // ---bar---
        let view = View::new(vec![
            (
                0.0,
                Row::new(vec![
                    (
                        0.0,
                        Button {
                            size: Size { width: 5.0, height: 10.0 },
                            ..make_button("A".into())
                        },
                    ),
                    (
                        5.0,
                        Button {
                            size: Size { width: 5.0, height: 10.0 },
                            ..make_button("B".into())
                        },
                    ),
                ]),
            ),
            (
                10.0,
                Row::new(vec![
                    (
                        0.0,
                        Button {
                            size: Size { width: 30.0, height: 10.0 },
                            ..make_button("bar".into())
                        },
                    ),
                ]),
            )
        ]);
        assert!(
            view.find_button_by_position(c::Point { x: 5.0, y: 5.0 })
                .unwrap().0.name.to_str().unwrap() == "A"
        );
        assert!(
            view.find_button_by_position(c::Point { x: 14.99, y: 5.0 })
                .unwrap().0.name.to_str().unwrap() == "A"
        );
        assert!(
            view.find_button_by_position(c::Point { x: 15.01, y: 5.0 })
                .unwrap().0.name.to_str().unwrap() == "B"
        );
        assert!(
            view.find_button_by_position(c::Point { x: 25.0, y: 5.0 })
                .unwrap().0.name.to_str().unwrap() == "B"
        );
    }

    #[test]
    fn check_bottom_margin() {
        // just one button
        let view = View::new(vec![
            (
                0.0,
                Row::new(vec![(
                    0.0,
                    Button {
                        size: Size { width: 1.0, height: 1.0 },
                        ..make_button("foo".into())
                    },
                )]),
            ),
        ]);
        let layout = LayoutData {
            keymaps: Vec::new(),
            kind: ArrangementKind::Base,
            // Lots of bottom margin
            margins: Margins {
                top: 0.0,
                left: 0.0,
                right: 0.0,
                bottom: 1.0,
            },
            views: hashmap! {
                String::new() => (c::Point { x: 0.0, y: 0.0 }, view),
            },
            purpose: ContentPurpose::Normal,
        };
        assert_eq!(
            layout.calculate_inner_size(),
            Size { width: 1.0, height: 1.0 }
        );
        assert_eq!(
            layout.calculate_size(),
            Size { width: 1.0, height: 2.0 }
        );
        // Don't change those values randomly!
        // They take advantage of incidental precise float representation
        // to even be comparable.
        let transformation = layout.calculate_transformation(
            Size { width: 2.0, height: 2.0 }
        );
        assert_eq!(transformation.scale_x, 1.0);
        assert_eq!(transformation.scale_y, 1.0);
        assert_eq!(transformation.origin_x, 0.5);
        assert_eq!(transformation.origin_y, 0.0);
    }

    #[test]
    fn check_stretching() {
        // just one button
        let view = View::new(vec![
            (
                0.0,
                Row::new(vec![(
                    0.0,
                    Button {
                        size: Size { width: 1.0, height: 1.0 },
                        ..make_button("foo".into())
                    },
                )]),
            ),
        ]);
        let layout = LayoutData {
            keymaps: Vec::new(),
            kind: ArrangementKind::Base,
            margins: Margins {
                top: 0.0,
                left: 0.0,
                right: 0.0,
                bottom: 0.0,
            },
            views: hashmap! {
                String::new() => (c::Point { x: 0.0, y: 0.0 }, view),
            },
            purpose: ContentPurpose::Normal,
        };
        let transformation = layout.calculate_transformation(
            Size { width: 100.0, height: 100.0 }
        );
        assert_eq!(transformation.scale_x, 100.0);
        assert_eq!(transformation.scale_y, 100.0);
        let transformation = layout.calculate_transformation(
            Size { width: 95.0, height: 100.0 }
        );
        assert_eq!(transformation.scale_x, 95.0);
        assert_eq!(transformation.scale_y, 95.0);
        let transformation = layout.calculate_transformation(
            Size { width: 105.0, height: 100.0 }
        );
        assert_eq!(transformation.scale_x, 105.0);
        assert_eq!(transformation.scale_y, 100.0);
        let transformation = layout.calculate_transformation(
            Size { width: 106.0, height: 100.0 }
        );
        assert_eq!(transformation.scale_x, 100.0);
        assert_eq!(transformation.scale_y, 100.0);
    }
}