/// Determines if the cursor should be incremented or decremented on write
#[derive(Debug, PartialEq, Eq)]
pub enum CursorMode {
    Increment,
    Decrement,
}

impl Default for CursorMode {
    fn default() -> CursorMode {
        CursorMode::Increment
    }
}

/// Determines if the screen should be shifted on write
#[derive(Debug, PartialEq, Eq)]
pub enum ShiftMode {
    Enabled,
    Disabled,
}

impl From<bool> for ShiftMode {
    fn from(b: bool) -> ShiftMode {
        if b {
            ShiftMode::Enabled
        } else {
            ShiftMode::Disabled
        }
    }
}

impl Default for ShiftMode {
    fn default() -> ShiftMode {
        ShiftMode::Disabled
    }
}

#[derive(Default)]
pub struct EntryMode {
    pub cursor_mode: CursorMode,
    pub shift_mode: ShiftMode,
}

impl EntryMode {
    pub fn as_byte(&self) -> u8 {
        let cursor_bits = match self.cursor_mode {
            CursorMode::Increment => 0b0000_0010,
            CursorMode::Decrement => 0,
        };

        let shift_bits = match self.shift_mode {
            ShiftMode::Enabled => 0b0000_0001,
            ShiftMode::Disabled => 0,
        };

        0b0000_0100 | cursor_bits | shift_bits
    }
}

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn cursor_mode() {
        let em = EntryMode {
            cursor_mode: CursorMode::Increment,
            shift_mode: Default::default(),
        };

        assert!(em.as_byte() & 0b0000_0010 != 0);

        let em = EntryMode {
            cursor_mode: CursorMode::Decrement,
            shift_mode: Default::default(),
        };

        assert!(em.as_byte() & 0b0000_0010 == 0);
    }

    #[test]
    fn shift_mode() {
        let em = EntryMode {
            cursor_mode: Default::default(),
            shift_mode: ShiftMode::Enabled,
        };

        assert!(em.as_byte() & 0b0000_0001 != 0);

        let em = EntryMode {
            cursor_mode: Default::default(),
            shift_mode: ShiftMode::Disabled,
        };

        assert!(em.as_byte() & 0b0000_0001 == 0);
    }
}