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// License: see LICENSE file at root directory of `master` branch

//! # Encoder

use alloc::{
    string::String,
};

use super::{
    PAD_CHAR,
    Kind,
};

/// # Adds a char to a string
///
/// Line column will be updated based on max line length and line separators.
fn add_char(s: &mut String, chr: &char, max_line_len: &usize, line_separators: &Option<&[char]>, line_column: &mut usize) {
    s.push(*chr);

    if *max_line_len == 0 {
        return;
    }

    if let Some(line_separators) = line_separators {
        *line_column = (*line_column).saturating_add(1);
        if *line_column >= *max_line_len {
            for chr in line_separators.iter() {
                s.push(*chr);
            }
            *line_column = 0;
        }
    }
}

/// # Encodes
pub fn encode(bytes: impl AsRef<[u8]>, kind: Kind) -> String {
    let bytes = bytes.as_ref();

    let mut result = String::with_capacity(kind.estimate_encoding_capacity(bytes));

    let max_line_len = kind.max_line_len().unwrap_or(0);
    let line_separators = kind.line_separators();
    let mut line_column = 0;

    let must_use_pad = kind.must_use_pad();
    let last_chars = kind.last_chars();
    let len = bytes.len();
    let mut index = 0;

    loop {
        // First
        let byte = match index < len {
            true => bytes[index],
            false => break,
        };
        add_char(&mut result, Kind::get_char((byte >> 2) as usize, last_chars), &max_line_len, &line_separators, &mut line_column);
        index += 1;

        // Second
        let bits = (byte << 6) >> 2;
        match index < len {
            true => {
                let byte = bytes[index];
                index += 1;
                add_char(
                    &mut result, Kind::get_char((bits | (byte >> 4)) as usize, last_chars), &max_line_len, &line_separators, &mut line_column
                );

                // Third
                let bits = (byte << 4) >> 2;
                match index < len {
                    true => {
                        let byte = bytes[index];
                        index += 1;

                        add_char(
                            &mut result, Kind::get_char((bits | (byte >> 6)) as usize, last_chars), &max_line_len, &line_separators,
                            &mut line_column
                        );
                        add_char(
                            &mut result, Kind::get_char(((byte << 2) >> 2) as usize, last_chars), &max_line_len, &line_separators,
                            &mut line_column
                        );
                    },
                    false => {
                        add_char(&mut result, Kind::get_char(bits as usize, last_chars), &max_line_len, &line_separators, &mut line_column);
                        if must_use_pad {
                            result.push(PAD_CHAR);
                        }
                        break;
                    },
                };
            },
            false => {
                add_char(&mut result, Kind::get_char(bits as usize, last_chars), &max_line_len, &line_separators, &mut line_column);
                if must_use_pad {
                    for _ in 0..2 {
                        add_char(&mut result, &PAD_CHAR, &max_line_len, &line_separators, &mut line_column);
                    }
                }
                break;
            },
        };
    }

    result
}

/// # Encodes bytes via [`Standard`][debt64::Kind::Standard]
///
/// [debt64::Kind::Standard]: enum.Kind.html#variant.Standard
pub fn encode_standard(bytes: impl AsRef<[u8]>) -> String {
    encode(bytes, Kind::Standard)
}

/// # Encodes bytes via [`IMAP`][debt64::Kind::IMAP]
///
/// [debt64::Kind::IMAP]: enum.Kind.html#variant.IMAP
pub fn encode_imap(bytes: impl AsRef<[u8]>) -> String {
    encode(bytes, Kind::IMAP)
}

/// # Encodes bytes via [`MIME`][debt64::Kind::MIME]
///
/// [debt64::Kind::MIME]: enum.Kind.html#variant.MIME
pub fn encode_mime(bytes: impl AsRef<[u8]>) -> String {
    encode(bytes, Kind::MIME)
}

/// # Encodes bytes via [`URL`][debt64::Kind::URL]
///
/// [debt64::Kind::URL]: enum.Kind.html#variant.URL
pub fn encode_url(bytes: impl AsRef<[u8]>) -> String {
    encode(bytes, Kind::URL)
}

/// # Encodes bytes via [`FreenetURL`][debt64::Kind::FreenetURL]
///
/// [debt64::Kind::FreenetURL]: enum.Kind.html#variant.FreenetURL
pub fn encode_freenet_url(bytes: impl AsRef<[u8]>) -> String {
    encode(bytes, Kind::FreenetURL)
}