io-email 0.1.0

Email client library
Documentation 
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//! Shared helpers for the Maildir coroutines: flag conversions,
//! mailbox-name validation, and `paginate` shared with m2dir.

use alloc::{
    string::{String, ToString},
    vec::Vec,
};

use io_maildir::{
    flag::types::{MaildirFlag, MaildirFlags},
    path::MaildirPath,
};
use thiserror::Error;

use crate::flag::types::{Flag, IanaFlag};

/// Errors produced by the mailbox-name validator.
#[derive(Clone, Debug, Error)]
#[error("invalid Maildir mailbox `{0}`")]
pub struct InvalidMailboxName(pub String);

/// Validates a logical mailbox `name`; rejects `..` segments so
/// callers cannot escape the store. Empty name maps to the store root
/// (INBOX-equivalent under Maildir++).
pub(crate) fn mailbox_path(name: &str) -> Result<MaildirPath, InvalidMailboxName> {
    if name.split('/').any(|seg| seg == "..") {
        return Err(InvalidMailboxName(name.to_string()));
    }
    Ok(MaildirPath::from(name))
}

/// Maps a shared [`Flag`] to a [`MaildirFlag`]; non-IANA keywords go
/// through [`MaildirFlag::Keyword`] for the dovecot-keywords sidecar.
pub(crate) fn flag_to_maildir(flag: &Flag) -> MaildirFlag {
    match flag.iana() {
        Some(IanaFlag::Seen) => MaildirFlag::Seen,
        Some(IanaFlag::Answered) => MaildirFlag::Replied,
        Some(IanaFlag::Flagged) => MaildirFlag::Flagged,
        Some(IanaFlag::Draft) => MaildirFlag::Draft,
        Some(IanaFlag::Deleted) => MaildirFlag::Trashed,
        Some(IanaFlag::Forwarded) => MaildirFlag::Passed,
        Some(_) | None => MaildirFlag::Keyword(flag.raw().to_string()),
    }
}

/// Shared flag slice to [`MaildirFlags`].
pub(crate) fn flags_to_maildir(flags: &[Flag]) -> MaildirFlags {
    flags.iter().map(flag_to_maildir).collect()
}

/// Maildir info-section letter (S/R/F/D/T/P) to shared [`Flag`];
/// `None` for letters outside the standard six.
pub(crate) fn flag_from_char(c: char) -> Option<Flag> {
    match c {
        'S' => Some(Flag::from_iana(IanaFlag::Seen)),
        'R' => Some(Flag::from_iana(IanaFlag::Answered)),
        'F' => Some(Flag::from_iana(IanaFlag::Flagged)),
        'D' => Some(Flag::from_iana(IanaFlag::Draft)),
        'T' => Some(Flag::from_iana(IanaFlag::Deleted)),
        'P' => Some(Flag::from_iana(IanaFlag::Forwarded)),
        _ => None,
    }
}

/// 1-indexed in-memory pagination shared with m2dir; `page_size = None`
/// returns the full slice; size 0 or a page past the end returns empty.
pub(crate) fn paginate<T>(items: Vec<T>, page: Option<u32>, page_size: Option<u32>) -> Vec<T> {
    let Some(size) = page_size else {
        return items;
    };
    if size == 0 {
        return Vec::new();
    }
    let page = page.unwrap_or(1).max(1);
    let skip = ((page - 1) as usize).saturating_mul(size as usize);
    if skip >= items.len() {
        return Vec::new();
    }
    items.into_iter().skip(skip).take(size as usize).collect()
}