use crate::*;

#[derive(Clone, Copy, Debug, PartialEq)]
pub enum FocusState<T: Copy + Debug + PartialEq> {
    Exited(T),
    Focused(T),
    Entered(T),
}

impl<T: Copy + Debug + PartialEq> FocusState<T> {
    pub fn inner (&self) -> T {
        match self {
            Self::Exited(inner)  => *inner,
            Self::Focused(inner) => *inner,
            Self::Entered(inner) => *inner,
        }
    }
    pub fn set_inner (&mut self, inner: T) {
        *self = match self {
            Self::Exited(_)  => Self::Exited(inner),
            Self::Focused(_) => Self::Focused(inner),
            Self::Entered(_) => Self::Entered(inner),
        }
    }
    pub fn is_exited (&self) -> bool {
        if let Self::Exited(_) = self { true } else { false }
    }
    pub fn is_focused (&self) -> bool {
        if let Self::Focused(_) = self { true } else { false }
    }
    pub fn is_entered (&self) -> bool {
        if let Self::Entered(_) = self { true } else { false }
    }
    pub fn to_exited (&mut self) {
        *self = Self::Exited(self.inner())
    }
    pub fn to_focused (&mut self) {
        *self = Self::Focused(self.inner())
    }
    pub fn to_entered (&mut self) {
        *self = Self::Entered(self.inner())
    }
}

#[derive(Copy, Clone, PartialEq, Debug)]
pub enum FocusCommand {
    Next,
    Prev,
    Up,
    Down,
    Left,
    Right,
    Enter,
    Exit
}

impl<F: HasFocus + FocusGrid> Command<F> for FocusCommand {
    fn execute (self, state: &mut F) -> Perhaps<FocusCommand> {
        use FocusCommand::*;
        match self {
            Next  => { state.focus_next();  },
            Prev  => { state.focus_prev();  },
            Up    => { state.focus_up();    },
            Down  => { state.focus_down();  },
            Left  => { state.focus_left();  },
            Right => { state.focus_right(); },
            Enter => { state.focus_enter(); },
            Exit  => { state.focus_exit();  },
            _    => {}
        }
        Ok(None)
    }
}

/// Trait for things that have ordered focusable subparts.
pub trait HasFocus {
    /// Type that identifies of focused item.
    type Item: Copy + PartialEq + Debug;
    /// Get the currently focused item.
    fn focused (&self) -> Self::Item;
    /// Focus the next item.
    fn focus_next (&mut self);
    /// Focus the previous item.
    fn focus_prev (&mut self);
    /// Loop forward until a specific item is focused.
    fn focus (&mut self, target: Self::Item) {
        while self.focused() != target {
            self.focus_next()
        }
    }
    /// Enter the focused item
    fn focus_enter (&mut self) {}
    /// Exit the focused item
    fn focus_exit (&mut self) {}
    /// Return the focused item, if any
    fn focus_entered (&self) -> Option<Self::Item> { None }
}

/// Trait for things that implement directional focus.
pub trait FocusGrid {
    type Item: Copy + PartialEq + Debug;
    fn focus_layout (&self) -> &[&[Self::Item]];
    fn focus_cursor (&self) -> (usize, usize);
    fn focus_cursor_mut (&mut self) -> &mut (usize, usize);
    fn focus_update (&mut self) {}
    fn focus_up (&mut self) {
        let layout = self.focus_layout();
        let (x, y) = self.focus_cursor();
        let next_y = if y == 0 { layout.len().saturating_sub(1) } else { y - 1 };
        let next_x = if layout[y].len() == layout[next_y].len() { x } else {
            ((x as f32 / layout[y].len() as f32) * layout[next_y].len() as f32) as usize
        };
        *self.focus_cursor_mut() = (next_x, next_y);
        self.focus_update();
    }
    fn focus_down (&mut self) {
        let layout = self.focus_layout();
        let (x, y) = self.focus_cursor();
        let next_y = if y >= layout.len().saturating_sub(1) { 0 } else { y + 1 };
        let next_x = if layout[y].len() == layout[next_y].len() { x } else {
            ((x as f32 / layout[y].len() as f32) * layout[next_y].len() as f32) as usize
        };
        *self.focus_cursor_mut() = (next_x, next_y);
        self.focus_update();
    }
    fn focus_left (&mut self) {
        let layout = self.focus_layout();
        let (x, y) = self.focus_cursor();
        let next_x = if x == 0 { layout[y].len().saturating_sub(1) } else { x - 1 };
        *self.focus_cursor_mut() = (next_x, y);
        self.focus_update();
    }
    fn focus_right (&mut self) {
        let layout = self.focus_layout();
        let (x, y) = self.focus_cursor();
        let next_x = if x >= layout[y].len().saturating_sub(1) { 0 } else { x + 1 };
        *self.focus_cursor_mut() = (next_x, y);
        self.focus_update();
    }
}

impl<T, U> HasFocus for U
where
    T: Copy + PartialEq + Debug,
    U: FocusGrid<Item = T>
{
    type Item = T;
    fn focused (&self) -> Self::Item {
        let (x, y) = self.focus_cursor();
        self.focus_layout()[y][x]
    }
    fn focus_next (&mut self) {
        let current = self.focused();
        let (x, y) = self.focus_cursor();
        if x < self.focus_layout()[y].len().saturating_sub(1) {
            self.focus_right();
        } else {
            self.focus_down();
            self.focus_cursor_mut().0 = 0;
        }
        if self.focused() == current { // FIXME: prevent infinite loop
            self.focus_next()
        }
        self.focus_exit();
        self.focus_update();
    }
    fn focus_prev (&mut self) {
        let current = self.focused();
        let (x, _) = self.focus_cursor();
        if x > 0 {
            self.focus_left();
        } else {
            self.focus_up();
            let (_, y) = self.focus_cursor();
            let next_x = self.focus_layout()[y].len().saturating_sub(1);
            self.focus_cursor_mut().0 = next_x;
        }
        if self.focused() == current { // FIXME: prevent infinite loop
            self.focus_prev()
        }
        self.focus_exit();
        self.focus_update();
    }
}