morse_codec/

message.rs

//! Message struct to hold decoded message or message to be encoded.
//!
//! Client code can use this to access and manipulate the
//! internal message of MorseDecoder or MorseEncoder:
//!
//! ```ignore
//! // Get a decoded message
//! let decoded_message = decoder.message.as_str();
//! let decoded_message_chars = decoder.message.as_charray();
//! // ...Do something with the message...
//!
//! // Clear the message
//! decoder.message.clear();
//!
//! // Set message to something different
//! // and continue decoding from the end
//! decoder.message.set_message("SOME INITIAL MESSAGE", true);
//!
//! // We continue sending signals
//! decoder.signal_event(125, true);
//! decoder.signal_event(200, false);
//! ....
//!
//! // To show an editing cursor on the screen
//! let editing_position = decoder.message.get_edit_pos();
//! ```

use crate::{
    FILLER,
    FILLER_CHAR,
    Character,
};

#[cfg(feature = "utf8")]
use core::fmt::Display;

#[cfg(feature = "utf8")]
#[derive(Debug)]
/// When "utf8" feature is enabled, instead of &str
/// we return this new type struct as a placeholder for &str,
/// because it's still hard to use arithmetic operations in
/// const expressions. In the future if this PR gets merged:
/// <https://github.com/rust-lang/rust/issues/76560>
/// We might update the code to do stuff like:
/// let chars: [0; MSG_MAX * 4] = ...
pub struct Utf8Charray<'a>(&'a [char]);

#[cfg(feature = "utf8")]
impl Display for Utf8Charray<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        for ch in self.0 {
            write!(f, "{}", ch)?;
        }

        Ok(())
    }
}

#[cfg(feature = "utf8")]
impl PartialEq<&str> for Utf8Charray<'_> {
    fn eq(&self, other: &&str) -> bool {
        let mut other_chars = other.chars();
        for &ch in self.0.iter() {
            let other_char = other_chars.next();
            if other_char.is_none() || ch != other_char.unwrap() {
                return false;
            }
        }

        true
    }
}

#[cfg(feature = "utf8")]
impl Utf8Charray<'_> {
    pub fn iter(&self) -> impl Iterator<Item = &char> {
        self.0.iter()
    }
}

/// This struct holds the message in human readable format.
///
/// It also provides functions to do edit position manipulation,
/// getting or setting characters at index positions.
pub struct Message<const MSG_MAX: usize> {
    chars: [Character; MSG_MAX],
    edit_pos: usize,
    last_change_index: usize,
    clamp_edit_pos: bool,
}

impl<const MSG_MAX: usize> Default for Message<MSG_MAX> {
    fn default() -> Self {
        Self {
            chars: [FILLER; MSG_MAX],
            edit_pos: 0,
            last_change_index: 0,
            clamp_edit_pos: false,
        }
    }
}

// Constructor with a starter string
impl<const MSG_MAX: usize> Message<MSG_MAX> {
    /// Maximum index editing position can be at
    pub const POS_MAX: usize = MSG_MAX - 1;

    /// Get an instance of Message starting from an &str.
    ///
    /// edit_pos_end means client code wants to continue editing this
    /// text at the end.
    pub fn new(message_str: &str, edit_pos_end: bool, clamp_edit_pos: bool) -> Self {
        let mut new_self = Self {
            chars: Self::str_to_chars(message_str),
            clamp_edit_pos,
            ..Self::default()
        };

        if edit_pos_end {
            new_self.edit_pos = new_self.len().clamp(0, Self::POS_MAX);
        }

        new_self
    }

    #[cfg(not(feature = "utf8"))]
    // Static member utility function to convert an &str to character array internal format.
    fn str_to_chars(str: &str) -> [u8; MSG_MAX] {
        let mut str_iter = str.chars()
            .take(MSG_MAX)
            .filter(|ch| ch.is_ascii());

        core::array::from_fn(|_|
            str_iter.next()
                .unwrap_or(FILLER_CHAR)
                .to_ascii_uppercase() as u8
        )
    }

    #[cfg(feature = "utf8")]
    // Static member utility function to convert an &str to charray internal format.
    fn str_to_chars(str: &str) -> [Character; MSG_MAX] {
        let mut str_iter = str.chars()
            .take(MSG_MAX);

        core::array::from_fn(|_|
            str_iter.next()
                .unwrap_or(FILLER_CHAR)
                .to_uppercase()
                .next()
                .unwrap()
        )
    }
}

// Private stuff
impl<const MSG_MAX: usize> Message<MSG_MAX> {
    // Index of last character before the last FILLERs
    fn last_char_index(&self) -> Option<usize> {
        self.chars.iter().rposition(|ch| *ch != FILLER)
    }

    // Check if any FILLER characters are between normal chars
    // and convert them to ' ' space characters.
    fn update_empty_chars(&mut self) {
        if let Some(last_index) = self.last_char_index() {
            self.chars.iter_mut().enumerate().for_each(|(index, ch)| {
                if *ch == FILLER && index < last_index {
                    *ch = ' ' as Character;
                }
            });
        }
    }
}

// Public API
impl<const MSG_MAX: usize> Message<MSG_MAX> {
    /// Get an iterator to the message chars contained within.
    pub fn iter(&self) -> MessageIterator<MSG_MAX> {
        MessageIterator {
            message: self,
            index: 0,
        }
    }

    /// Sets current editing position to given value.
    pub fn set_edit_pos(&mut self, pos: usize) {
        self.edit_pos = pos.clamp(0, Self::POS_MAX);
    }

    /// Change the clamping behaviour of the edit position to
    /// wrapping (default) or clamping.
    ///
    /// With clamping set, when edit position is shifted to left or right,
    /// it won't cycle forward to maximum position or revert back to zero position,
    /// effectively remaining within the limits of the message no matter current position is.
    pub fn set_edit_position_clamp(&mut self, clamp: bool) {
        self.clamp_edit_pos = clamp;
    }

    pub fn is_edit_clamped(&self) -> bool {
        self.clamp_edit_pos
    }

    /// Returns current editing position.
    pub fn get_edit_pos(&self) -> usize {
        self.edit_pos
    }

    pub fn get_last_changed_index(&self) -> usize {
        self.last_change_index
    }

    pub fn get_last_changed_char(&self) -> Character {
        self.chars[self.last_change_index]
    }

    /// Move editing position to the left.
    /// By default it will wrap to the end if position is 0
    pub fn shift_edit_left(&mut self) {
        self.edit_pos = match self.edit_pos {
            0 => if self.clamp_edit_pos { 0 } else { Self::POS_MAX },
            p => p - 1,
        }
    }

    /// Move editing position to the right.
    /// By default it will wrap to the beginning if position is POS_MAX
    pub fn shift_edit_right(&mut self) {
        self.edit_pos = match self.edit_pos {
            p if p == Self::POS_MAX => if self.clamp_edit_pos { Self::POS_MAX } else { 0 },
            p => p + 1,
        }
    }

    /// Insert character at the editing position.
    ///
    /// If any characters before the character are [FILLER]s
    /// They'll automatically be converted to empty characters ' '
    /// which means the user wants some space between words.
    pub fn add_char(&mut self, ch: Character) {
        self.chars[self.edit_pos] = ch;
        // This is only necessary if client code sets edit position
        // manually and adds a character after it, but hey.
        self.update_empty_chars();
        self.last_change_index = self.edit_pos;
    }

    /// Insert character at index.
    ///
    /// If any characters before the character are [FILLER]s
    /// They'll automatically be converted to empty characters ' '
    /// which means the user wants some space between words.
    pub fn put_char_at(&mut self, index: usize, ch: Character) -> Result<(), &str> {
        if index < MSG_MAX {
            self.chars[index] = ch;
            self.update_empty_chars();
            self.last_change_index = index;

            Ok(())
        } else {
            Err("Put char index doesn't fit into message length")
        }
    }

    /// Returns character at an index
    pub fn char_at(&self, index: usize) -> Character {
        self.chars[index]
    }

    /// Returns current length of the message discarding empty FILLER characters at the end.
    ///
    /// This is useful for creating ranged loops of actual characters decoded or can be encoded.
    pub fn len(&self) -> usize {
        let index = self.last_char_index();
        match index {
            Some(i) if i < MSG_MAX => i + 1,
            Some(i) if i == MSG_MAX => MSG_MAX,
            _ => 0,
        }
    }

    /// Returns true if the message is empty, false otherwise.
    ///
    /// This method discards FILLER characters and only takes into
    /// account normal characters.
    pub fn is_empty(&self) -> bool {
        self.last_char_index().is_none()
    }

    /// Manually set the message from an &str.
    ///
    /// edit_pos_end flag means we'll continue from the end of this string when
    /// we continue decoding or encoding.
    pub fn set_message(&mut self, message_str: &str, edit_pos_end: bool) -> Result<(), &str> {
        if message_str.len() > MSG_MAX {
            Err("Message string can't be longer than MSG_MAX.")
        } else {
            self.chars = Self::str_to_chars(message_str);

            if edit_pos_end {
                self.edit_pos = self.len().clamp(0, Self::POS_MAX);
            } else {
                self.edit_pos = 0;
            }

            self.last_change_index = self.edit_pos;

            Ok(())
        }
    }

    /// Returns the message as it is now in a character array format.
    ///
    /// Note that this also includes 'empty' [FILLER] characters.
    /// Client code can use return value of len() which is the actual length
    /// to loop through it or filter the fillers manually in a loop or iterator.
    pub fn as_charray(&self) -> [Character; MSG_MAX] {
        self.chars
    }

    /// Returns the message as it is now as &str slice.
    /// Or as a [Utf8Charray] if "utf8" feature is enabled.
    ///
    /// Note that this *does not* include empty [FILLER] characters.
    #[cfg(not(feature = "utf8"))]
    pub fn as_str(&self) -> &str {
        core::str::from_utf8(self.chars[0..self.len()].as_ref()).unwrap()
    }

    #[cfg(feature = "utf8")]
    pub fn as_str(&self) -> Utf8Charray {
        // Fixme: Update the code to use buffer copy,
        // after const generic expressions become stable in Rust.
        // https://github.com/rust-lang/rust/issues/76560
        //
        // let mut buffer = [0u8; MSG_MAX * 4];
        // let mut pos: usize = 0;
        // for ch in self.chars {
        //      pos += ch.encode_utf8(&mut buffer).len();
        // }
        //
        // core::str::from_utf8(buffer[0..pos].asref()).unwrap()

        Utf8Charray(self.chars[..self.len()].as_ref())
    }

    /// Clear the message and start over.
    pub fn clear(&mut self) {
        self.chars = [FILLER; MSG_MAX];
        self.edit_pos = 0;
    }
}

/// Message iterator provides a convenient way to iterate over
/// message characters. This doesn't include empty FILLER chars.
pub struct MessageIterator<'a, const MSG_MAX: usize> {
    message: &'a Message<MSG_MAX>,
    index: usize,
}

impl<'a, const MSG_MAX: usize> Iterator for MessageIterator<'a, MSG_MAX> {
    type Item = &'a Character;

    fn next(&mut self) -> Option<Self::Item> {
        if self.index < self.message.len() {
            let result = Some(&self.message.chars[self.index]);
            self.index += 1;

            result
        } else {
            None
        }
    }
}