daaki-message 0.2.0

//! Public API types for parsed and outgoing email messages.
//!
//! All types are fully owned (`String` / `Vec<u8>`) with no lifetime parameters,
//! per workspace conventions.
//!
//! # References
//! - RFC 5322 (Internet Message Format — address, date-time)
//! - RFC 2045 (MIME — Content-Transfer-Encoding)
//! - RFC 2183 (Content-Disposition)
//! - RFC 3501 Section 6.4.5 (IMAP MIME section numbers)

// ---------------------------------------------------------------------------
// Validated newtypes
// ---------------------------------------------------------------------------

/// Error returned when constructing a validated protocol type from an invalid string.
///
/// Shared across `daaki-imap` and `daaki-smtp` for validated newtypes
/// such as `SequenceSet`, `MailboxName`, `Domain`, `ForwardPath`, etc.
/// Each crate's [`Error`] type provides a blanket `From<ValidationError>`
/// conversion so these can be used with `?` in application code.
#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[error("{0}")]
pub struct ValidationError(String);

impl ValidationError {
    /// Create a new validation error with the given message.
    pub fn new(message: impl Into<String>) -> Self {
        Self(message.into())
    }

    /// Return the error message as a string slice.
    pub fn message(&self) -> &str {
        &self.0
    }
}

/// A validated RFC 5322 header field name.
///
/// RFC 5322 Section 2.2 defines a field name as `1*ftext`, where
/// `ftext = %d33-57 / %d59-126` — printable US-ASCII excluding the colon
/// (`:`). This newtype enforces that constraint at construction time so
/// that downstream code can rely on the name being well-formed.
///
/// # Case Insensitivity
///
/// Comparison and hashing are case-insensitive per RFC 5322 Section 2.2,
/// so `HeaderName::new("Subject")` and `HeaderName::new("subject")` are equal.
///
/// # References
/// - RFC 5322 Section 2.2 (header field syntax)
#[non_exhaustive]
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "serde", serde(try_from = "String", into = "String"))]
pub struct HeaderName(String);

impl HeaderName {
    /// Creates a new `HeaderName` after validating ftext syntax
    /// (RFC 5322 Section 2.2).
    ///
    /// The name must be non-empty and consist solely of printable US-ASCII
    /// characters (33..=126) excluding colon (58).
    ///
    /// # Errors
    ///
    /// Returns [`crate::error::Error::InvalidHeaderName`] if the name is
    /// empty or contains invalid characters.
    ///
    /// # References
    /// - RFC 5322 Section 2.2
    pub fn new(s: impl Into<String>) -> crate::Result<Self> {
        let s = s.into();
        validate_ftext(&s)?;
        Ok(Self(s))
    }

    /// Creates a `HeaderName` without validation — test-only.
    #[cfg(test)]
    pub(crate) fn new_unchecked(s: impl Into<String>) -> Self {
        Self(s.into())
    }

    /// Returns the header name as a string slice.
    pub fn as_str(&self) -> &str {
        &self.0
    }

    /// Consumes self and returns the inner `String`.
    pub fn into_inner(self) -> String {
        self.0
    }
}

impl AsRef<str> for HeaderName {
    fn as_ref(&self) -> &str {
        &self.0
    }
}

/// Internet message field names are case-insensitive during comparison.
///
/// RFC 822 Section 3.4.7 states this rule explicitly, and RFC 5322 retains
/// the same `field-name` model for message headers.
impl PartialEq for HeaderName {
    fn eq(&self, other: &Self) -> bool {
        self.0.eq_ignore_ascii_case(&other.0)
    }
}

impl Eq for HeaderName {}

/// Hash header names case-insensitively so hashing matches equality.
///
/// RFC 822 Section 3.4.7: field-name case is not distinguished. RFC 5322
/// continues the same header field model.
impl std::hash::Hash for HeaderName {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        for byte in self.0.as_bytes() {
            byte.to_ascii_lowercase().hash(state);
        }
    }
}

/// Order header names case-insensitively (RFC 5322 Section 2.2).
impl PartialOrd for HeaderName {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

/// Total ordering on header names, case-insensitive (RFC 5322 Section 2.2).
impl Ord for HeaderName {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        let a = self.0.as_bytes().iter().map(u8::to_ascii_lowercase);
        let b = other.0.as_bytes().iter().map(u8::to_ascii_lowercase);
        a.cmp(b)
    }
}

impl std::fmt::Display for HeaderName {
    /// Displays the header name verbatim (RFC 5322 Section 2.2).
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0)
    }
}

impl TryFrom<String> for HeaderName {
    type Error = crate::error::Error;

    /// Converts a `String` into a validated `HeaderName` (RFC 5322 Section 2.2).
    fn try_from(s: String) -> Result<Self, Self::Error> {
        Self::new(s)
    }
}

impl TryFrom<&str> for HeaderName {
    type Error = crate::error::Error;

    /// Converts a `&str` into a validated `HeaderName` (RFC 5322 Section 2.2).
    fn try_from(s: &str) -> Result<Self, Self::Error> {
        Self::new(s)
    }
}

impl From<HeaderName> for String {
    fn from(h: HeaderName) -> Self {
        h.into_inner()
    }
}

/// Validates that `s` is a valid `ftext` sequence per RFC 5322 Section 2.2.
///
/// `field-name = 1*ftext` where `ftext = %d33-57 / %d59-126` — printable
/// US-ASCII characters excluding colon (`:`).
///
/// # References
/// - RFC 5322 Section 2.2
fn validate_ftext(s: &str) -> crate::Result<()> {
    if s.is_empty() {
        return Err(crate::error::Error::InvalidHeaderName(
            "header name must not be empty".into(),
        ));
    }
    if let Some(bad) = s.chars().find(|&c| {
        // ftext: printable ASCII (33..=126) excluding ':' (58)
        let b = c as u32;
        !(33..=126).contains(&b) || c == ':'
    }) {
        return Err(crate::error::Error::InvalidHeaderName(format!(
            "header name contains invalid character {bad:?} (RFC 5322 Section 2.2)"
        )));
    }
    Ok(())
}

/// A validated RFC 5322 message-ID (bare, without angle brackets).
///
/// RFC 5322 Section 3.6.4 defines `msg-id = "<" id-left "@" id-right ">"`.
/// This type stores only the bare `id-left "@" id-right` content. Angle
/// brackets are added by the builder when emitting wire format.
///
/// # Validation rules
/// - Non-empty
/// - Exactly one `@` separator
/// - `id-left` and `id-right` must each be non-empty
/// - No whitespace, angle brackets, or control characters
///
/// # References
/// - RFC 5322 Section 3.6.4 (message identification)
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[cfg_attr(feature = "serde", serde(try_from = "String", into = "String"))]
pub struct MessageId(String);

impl MessageId {
    /// Creates a new `MessageId` after validation (RFC 5322 Section 3.6.4).
    ///
    /// The value must be a bare message-ID (no angle brackets) containing
    /// exactly one `@` with non-empty parts on each side, and no
    /// whitespace, angle brackets, or control characters.
    ///
    /// # Errors
    ///
    /// Returns [`crate::error::Error::InvalidMessageId`] if validation fails.
    ///
    /// # References
    /// - RFC 5322 Section 3.6.4
    pub fn new(s: impl Into<String>) -> crate::Result<Self> {
        let s = s.into();
        validate_message_id(&s)?;
        Ok(Self(s))
    }

    /// Creates a `MessageId` without validation — test-only.
    #[cfg(test)]
    pub(crate) fn new_unchecked(s: impl Into<String>) -> Self {
        Self(s.into())
    }

    /// Returns the message-ID as a string slice.
    pub fn as_str(&self) -> &str {
        &self.0
    }

    /// Consumes self and returns the inner `String`.
    pub fn into_inner(self) -> String {
        self.0
    }
}

impl AsRef<str> for MessageId {
    fn as_ref(&self) -> &str {
        &self.0
    }
}

impl std::fmt::Display for MessageId {
    /// Displays the bare message-ID (RFC 5322 Section 3.6.4).
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0)
    }
}

impl TryFrom<String> for MessageId {
    type Error = crate::error::Error;

    /// Converts a `String` into a validated `MessageId` (RFC 5322 Section 3.6.4).
    fn try_from(s: String) -> Result<Self, Self::Error> {
        Self::new(s)
    }
}

impl TryFrom<&str> for MessageId {
    type Error = crate::error::Error;

    /// Converts a `&str` into a validated `MessageId` (RFC 5322 Section 3.6.4).
    fn try_from(s: &str) -> Result<Self, Self::Error> {
        Self::new(s)
    }
}

impl From<MessageId> for String {
    fn from(m: MessageId) -> Self {
        m.into_inner()
    }
}

/// Validates a bare message-ID per RFC 5322 Section 3.6.4.
///
/// The value must contain exactly one `@`. For outbound/public API values,
/// RFC 5322 Section 3.6.4 permits only modern generated forms:
/// `id-left = dot-atom-text` and `id-right = dot-atom-text / no-fold-literal`.
/// Obsolete parser-only forms remain accepted by the inbound parser via
/// separate recovery helpers.
///
/// RFC 6532 Section 3.2 extends the relevant `atext`, `qtext`, and `dtext`
/// productions to permit UTF-8 non-ASCII.
///
/// # References
/// - RFC 5322 Section 3.6.4
/// - RFC 5322 Section 3.2.3
/// - RFC 5322 Section 3.2.4
/// - RFC 6532 Section 3.2
fn validate_message_id(s: &str) -> crate::Result<()> {
    if s.is_empty() {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID must not be empty".into(),
        ));
    }

    let Some((id_left, id_right)) = split_strict_message_id_parts(s) else {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID must contain exactly one '@' \
             (RFC 5322 Section 3.6.4)"
                .into(),
        ));
    };

    if id_left.is_empty() {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID id-left (before '@') must not be empty \
             (RFC 5322 Section 3.6.4)"
                .into(),
        ));
    }
    if id_right.is_empty() {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID id-right (after '@') must not be empty \
             (RFC 5322 Section 3.6.4)"
                .into(),
        ));
    }

    // RFC 5322 Section 3.6.4 prose says generated msg-id syntax "only permits
    // the dot-atom-text form on the left-hand side of the @". Appendix A notes
    // that no-fold-quote was removed from the modern msg-id syntax, even
    // though obsolete parser forms still exist in Section 4.5.4.
    if !is_message_id_dot_atom_text(id_left) {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID id-left must be dot-atom-text \
             (RFC 5322 Section 3.6.4)"
                .into(),
        ));
    }
    if !(is_message_id_dot_atom_text(id_right) || is_message_id_no_fold_literal(id_right)) {
        return Err(crate::error::Error::InvalidMessageId(
            "message-ID id-right must be dot-atom-text or no-fold-literal \
             (RFC 5322 Sections 3.6.4 and 3.2.3)"
                .into(),
        ));
    }

    Ok(())
}

/// Returns `true` when `s` is a syntactically valid bare message-ID body for
/// liberal inbound parsing.
///
/// RFC 5322 Section 4.5.4 still defines obsolete `obs-id-left` /
/// `obs-id-right` forms that parsers may recover from inbound messages, even
/// though generators and strict public validators should not emit them.
///
/// # References
/// - RFC 5322 Section 3.6.4
/// - RFC 5322 Section 4.5.4
/// - RFC 5322 Section 3.2.3
/// - RFC 5322 Section 3.2.4
/// - RFC 6532 Section 3.2
pub(crate) fn is_valid_bare_message_id_body(s: &str) -> bool {
    split_liberal_message_id_parts(s).is_some_and(|(id_left, id_right)| {
        !id_left.is_empty()
            && !id_right.is_empty()
            && (is_message_id_dot_atom_text(id_left) || is_message_id_no_fold_quote(id_left))
            && (is_message_id_dot_atom_text(id_right) || is_message_id_no_fold_literal(id_right))
    })
}

/// Returns `true` when `s` is a syntactically valid bare message-ID body for
/// generated output and strict public API validation.
///
/// Unlike liberal parser recovery, this follows the modern generation rule
/// from RFC 5322 Section 3.6.4: `id-left` is limited to `dot-atom-text`.
///
/// # References
/// - RFC 5322 Section 3.6.4
/// - RFC 5322 Section 3.2.3
/// - RFC 6532 Section 3.2
pub(crate) fn is_strict_bare_message_id_body(s: &str) -> bool {
    split_strict_message_id_parts(s).is_some_and(|(id_left, id_right)| {
        !id_left.is_empty()
            && !id_right.is_empty()
            && is_message_id_dot_atom_text(id_left)
            && (is_message_id_dot_atom_text(id_right) || is_message_id_no_fold_literal(id_right))
    })
}

/// Split a bare message-ID body into `id-left` and `id-right` at the single
/// `@` separator for strict/generated validation.
///
/// RFC 5322 Section 3.6.4 limits generated `msg-id` values to dot-atom
/// `id-left`, so any additional `@` character makes the identifier invalid.
///
/// # References
/// - RFC 5322 Section 3.6.4
fn split_strict_message_id_parts(s: &str) -> Option<(&str, &str)> {
    let (id_left, id_right) = s.split_once('@')?;
    if id_right.contains('@') {
        return None;
    }
    Some((id_left, id_right))
}

/// Split a bare message-ID body into `id-left` and `id-right` at the single
/// unquoted `@` separator for liberal inbound parsing.
///
/// RFC 5322 Section 4.5.4 allows obsolete local-part syntax on the left-hand
/// side, so `@` characters inside quoted strings are not treated as
/// separators during parser recovery.
///
/// # References
/// - RFC 5322 Section 3.6.4
/// - RFC 5322 Section 4.5.4
/// - RFC 5322 Section 3.2.4
fn split_liberal_message_id_parts(s: &str) -> Option<(&str, &str)> {
    let bytes = s.as_bytes();
    let mut in_quotes = false;
    let mut escaped = false;
    let mut at_pos = None;

    for (index, &byte) in bytes.iter().enumerate() {
        if in_quotes {
            if escaped {
                escaped = false;
                continue;
            }

            match byte {
                b'\\' => escaped = true,
                b'"' => in_quotes = false,
                _ => {}
            }
            continue;
        }

        match byte {
            b'"' => in_quotes = true,
            b'@' => {
                if at_pos.is_some() {
                    return None;
                }
                at_pos = Some(index);
            }
            _ => {}
        }
    }

    if in_quotes || escaped {
        return None;
    }

    at_pos.map(|index| (&s[..index], &s[index + 1..]))
}

/// Returns `true` when `s` matches RFC 5322 Section 3.2.3 `dot-atom-text`.
///
/// RFC 6532 Section 3.2 extends `atext` to include UTF-8 non-ASCII octets.
///
/// # References
/// - RFC 5322 Section 3.2.3
/// - RFC 6532 Section 3.2
fn is_message_id_dot_atom_text(s: &str) -> bool {
    if s.is_empty() || s.starts_with('.') || s.ends_with('.') || s.contains("..") {
        return false;
    }

    s.bytes()
        .all(|byte| is_message_id_atext(byte) || byte == b'.' || byte >= 0x80)
}

/// Returns `true` when `s` matches the quoted-string form allowed by obsolete
/// `obs-id-left` parser recovery.
///
/// RFC 6532 Section 3.2 extends `qtext` to include UTF-8 non-ASCII octets.
///
/// # References
/// - RFC 5322 Section 4.5.4
/// - RFC 5322 Section 3.4.1
/// - RFC 5322 Section 3.2.4
/// - RFC 6532 Section 3.2
fn is_message_id_no_fold_quote(s: &str) -> bool {
    let Some(inner) = s
        .strip_prefix('"')
        .and_then(|value| value.strip_suffix('"'))
    else {
        return false;
    };

    let bytes = inner.as_bytes();
    let mut index = 0;
    while index < bytes.len() {
        let byte = bytes[index];
        if byte == b'\\' {
            index += 1;
            if index >= bytes.len() {
                return false;
            }

            let escaped = bytes[index];
            if !(escaped == b'\t' || (0x20..=0x7E).contains(&escaped)) {
                return false;
            }
        } else if !(matches!(byte, 33 | 35..=91 | 93..=126) || byte >= 0x80) {
            return false;
        }
        index += 1;
    }

    true
}

/// Returns `true` when `s` matches RFC 5322 Section 3.6.4 `no-fold-literal`.
///
/// RFC 6532 Section 3.2 extends `dtext` to include UTF-8 non-ASCII octets.
///
/// # References
/// - RFC 5322 Section 3.6.4
/// - RFC 6532 Section 3.2
fn is_message_id_no_fold_literal(s: &str) -> bool {
    let Some(inner) = s
        .strip_prefix('[')
        .and_then(|value| value.strip_suffix(']'))
    else {
        return false;
    };

    inner
        .bytes()
        .all(|byte| matches!(byte, 33..=90 | 94..=126) || byte >= 0x80)
}

/// Returns `true` when `byte` is RFC 5322 `atext`.
///
/// # References
/// - RFC 5322 Section 3.2.3
fn is_message_id_atext(byte: u8) -> bool {
    byte.is_ascii_alphanumeric()
        || matches!(
            byte,
            b'!' | b'#'
                | b'$'
                | b'%'
                | b'&'
                | b'\''
                | b'*'
                | b'+'
                | b'-'
                | b'/'
                | b'='
                | b'?'
                | b'^'
                | b'_'
                | b'`'
                | b'{'
                | b'|'
                | b'}'
                | b'~'
        )
}

// ---------------------------------------------------------------------------

/// A parsed email message.
///
/// Produced by [`crate::parse_email`]. All fields are owned.
/// Missing or unparseable optional fields are `None`.
///
/// # References
/// - RFC 5322 (message structure)
/// - RFC 2045–2046 (MIME body parts)
#[non_exhaustive]
#[derive(Debug, Clone, Default, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct ParsedEmail {
    /// Message-ID with angle brackets stripped (RFC 5322 Section 3.6.4).
    ///
    /// This field uses `String` rather than [`MessageId`] because parsed
    /// messages may originate from non-conformant sources whose message IDs
    /// do not pass strict RFC 5322 validation. The parser follows Postel's
    /// law: accept what you can, even if the value is technically malformed.
    /// [`OutgoingEmail::in_reply_to`] and [`OutgoingEmail::references`] use
    /// the validated [`MessageId`] type to ensure outgoing messages are
    /// strictly conformant.
    pub message_id: Option<String>,
    /// All `In-Reply-To` message-ids, angle brackets stripped (RFC 5322 Section 3.6.4).
    ///
    /// RFC 5322: `in-reply-to = "In-Reply-To:" 1*msg-id CRLF` — multiple
    /// message-IDs are valid. Each element is a single message-ID without
    /// angle brackets.
    ///
    /// Uses `String` rather than [`MessageId`] for the same reason as
    /// [`message_id`](Self::message_id): parsed messages may contain
    /// non-conformant IDs that would fail strict validation.
    pub in_reply_to: Vec<String>,
    /// All `References` message-ids, angle brackets stripped (RFC 5322 Section 3.6.4).
    ///
    /// RFC 5322: `references = "References:" 1*msg-id CRLF`. Each element is
    /// a single message-ID without angle brackets.
    ///
    /// Uses `String` rather than [`MessageId`] for the same reason as
    /// [`message_id`](Self::message_id): parsed messages may contain
    /// non-conformant IDs that would fail strict validation.
    pub references: Vec<String>,
    /// Decoded subject (RFC 5322 Section 3.6.5, RFC 2047 encoded words decoded).
    pub subject: Option<String>,
    /// Originator mailboxes (RFC 5322 Section 3.6.2: `from = "From:" mailbox-list`).
    pub from: Vec<Address>,
    /// The agent responsible for actual transmission of the message
    /// (RFC 5322 Section 3.6.2: `sender = "Sender:" mailbox`).
    ///
    /// Contains exactly one mailbox. Required when `From` contains multiple
    /// addresses; otherwise optional. `None` when the header is absent.
    pub sender: Option<Address>,
    /// To recipients (RFC 5322 Section 3.6.3).
    pub to: Vec<Address>,
    /// Cc recipients (RFC 5322 Section 3.6.3).
    pub cc: Vec<Address>,
    /// Bcc recipients (RFC 5322 Section 3.6.3).
    pub bcc: Vec<Address>,
    /// Reply-To addresses (RFC 5322 Section 3.6.2).
    pub reply_to: Vec<Address>,
    /// Parsed date with original timezone offset preserved (RFC 5322 Section 3.3).
    pub date: Option<DateTime>,
    /// First `text/plain` body part, decoded to UTF-8.
    pub body_text: Option<String>,
    /// First `text/html` body part, decoded to UTF-8.
    pub body_html: Option<String>,
    /// Detected attachments with IMAP section numbers.
    pub attachments: Vec<ParsedAttachment>,
    /// Raw header bytes as a `String` (everything before the header/body separator).
    pub raw_headers: String,
    /// Optional fields not defined by RFC 5322 (RFC 5322 Section 3.6.8).
    ///
    /// Contains all headers that are not one of the well-known structured
    /// headers (From, To, Cc, Bcc, Reply-To, Subject, Date, Message-ID,
    /// In-Reply-To, References, Sender, Content-Type,
    /// Content-Transfer-Encoding, MIME-Version), plus any top-level
    /// `Content-Disposition` or `Content-ID` field preserved for RFC 2183
    /// Section 2.10 and RFC 2045 Section 7 consumers. Each entry is a
    /// `(lowercase-name, decoded-value)` pair, preserving the order they
    /// appeared in the message.
    pub extra_headers: Vec<(String, String)>,
    /// Total byte count of the input.
    pub size: u64,
}

impl ParsedEmail {
    /// Convert extra headers to validated `(HeaderName, String)` pairs
    /// suitable for use in [`OutgoingEmail::extra_headers`].
    ///
    /// Headers whose names fail RFC 5322 Section 2.2 validation are
    /// silently dropped — such names originate from non-conformant
    /// messages and cannot be reproduced in well-formed output.
    pub fn validated_extra_headers(&self) -> Vec<(HeaderName, String)> {
        self.extra_headers
            .iter()
            .filter_map(|(name, value)| {
                HeaderName::new(name.clone())
                    .ok()
                    .map(|hn| (hn, value.clone()))
            })
            .collect()
    }
}

/// An email address with optional display name.
///
/// # References
/// - RFC 5322 Section 3.4 (address specification)
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct Address {
    /// Display name, decoded from RFC 2047 encoded words if present.
    pub name: Option<String>,
    /// Email address (`addr-spec` form).
    pub email: String,
}

impl Address {
    /// Creates an address with only an email, validating the syntax.
    ///
    /// # Errors
    ///
    /// Returns [`crate::Error::InvalidAddress`] if the email is not valid
    /// per RFC 5322 Section 3.4.
    pub fn new(email: impl Into<String>) -> crate::Result<Self> {
        let addr = Self {
            name: None,
            email: email.into(),
        };
        crate::builder::validate_address(&addr)?;
        Ok(addr)
    }

    /// Creates an address with a display name and email, validating the syntax.
    ///
    /// # Errors
    ///
    /// Returns [`crate::Error::InvalidAddress`] if the email is not valid
    /// per RFC 5322 Section 3.4.
    pub fn with_name(name: impl Into<String>, email: impl Into<String>) -> crate::Result<Self> {
        let addr = Self {
            name: Some(name.into()),
            email: email.into(),
        };
        crate::builder::validate_address(&addr)?;
        Ok(addr)
    }

    /// Creates an `Address` **without validating** the email syntax.
    ///
    /// # You almost certainly want [`Address::new`] or [`Address::with_name`] instead
    ///
    /// Those constructors validate the email address against RFC 5322
    /// Section 3.4 and reject malformed input. An `Address` built with
    /// `new_unchecked` may contain syntax that is invalid for outgoing
    /// mail, which can cause:
    ///
    /// - Rejected `RCPT TO` commands at the SMTP layer.
    /// - Malformed `From`/`To`/`Cc` headers that downstream MTAs or MUAs
    ///   cannot parse.
    /// - Messages that silently disappear into spam filters or bounce
    ///   queues.
    ///
    /// # When this method is appropriate
    ///
    /// This exists for **parser and protocol-conversion code** that must
    /// accept addresses already received from the network, where Postel's
    /// law applies (RFC 5322 Section 3.4): be liberal in what you accept.
    /// For example, an IMAP ENVELOPE address or a `From:` header parsed
    /// from an incoming message may contain syntax that is technically
    /// non-conformant but still meaningful. Rejecting it would discard
    /// data the user needs to see.
    ///
    /// If you are **building a new outgoing message**, use [`Address::new`]
    /// or [`Address::with_name`] — they enforce the same validation the
    /// message builder applies and will catch mistakes at construction
    /// time rather than at send time.
    pub fn new_unchecked(name: Option<String>, email: String) -> Self {
        Self { name, email }
    }
}

/// RFC 5322 specials that require a display name to be quoted.
const SPECIALS: &[char] = &[
    '(', ')', '<', '>', '[', ']', ':', ';', '@', '\\', ',', '.', '"',
];

impl std::fmt::Display for Address {
    /// Formats the address per RFC 5322 Section 3.4.
    ///
    /// - Non-ASCII display names are RFC 2047 encoded (RFC 5322 Section 2.2
    ///   requires header field bodies to be US-ASCII; RFC 2047 Section 5
    ///   defines the encoded-word mechanism for non-ASCII text).
    /// - ASCII display names containing specials are quoted per RFC 5322 Section 3.2.4.
    /// - Without display name: bare `email`
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.name {
            // RFC 5322 Section 3.4: display-name is a `phrase` (`1*word`).
            // Whitespace alone does not form a valid word, so treat it as absent.
            Some(name) if !name.trim().is_empty() => {
                if !name.is_ascii() || name.bytes().any(|b| (b < 0x20 && b != b'\t') || b == 0x7F) {
                    // RFC 5322 Section 2.2: field bodies must be US-ASCII printable.
                    // RFC 5322 Section 3.2.3: atext excludes control characters.
                    // HTAB (0x09) is valid WSP per RFC 5322 Section 2.2.
                    // RFC 2047 Section 5: use encoded-words for non-ASCII/non-printable text.
                    let encoded = crate::builder::encode_rfc2047_if_needed(name);
                    write!(f, "{encoded} <{}>", self.email)
                } else if name.contains("=?") {
                    // RFC 2047 Section 5: an unquoted phrase may contain
                    // encoded-words. A display name that literally contains
                    // `=?` would be mis-decoded by the parser. Quoting
                    // prevents this: RFC 2047 Section 5 says encoded-words
                    // MUST NOT appear inside a quoted-string.
                    let escaped = name.replace('\\', "\\\\").replace('"', "\\\"");
                    write!(f, "\"{escaped}\" <{}>", self.email)
                } else if name.chars().any(|c| SPECIALS.contains(&c)) {
                    let escaped = name.replace('\\', "\\\\").replace('"', "\\\"");
                    write!(f, "\"{escaped}\" <{}>", self.email)
                } else {
                    write!(f, "{name} <{}>", self.email)
                }
            }
            _ => write!(f, "{}", self.email),
        }
    }
}

impl std::str::FromStr for Address {
    type Err = crate::error::Error;

    /// Parses an address from a string (RFC 5322 Section 3.4).
    ///
    /// Accepts both `Display Name <email>` and bare `email` forms.
    /// Decodes RFC 2047 encoded words in the display name (RFC 2047 Section 5).
    #[allow(clippy::too_many_lines)]
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let s = s.trim();
        if s.is_empty() {
            return Err(crate::error::Error::InvalidAddress(
                "empty address string".into(),
            ));
        }

        // Try "Display Name <email>" form
        if let Some(angle_start) = s.rfind('<') {
            if let Some(angle_end) = s.rfind('>') {
                if angle_end > angle_start {
                    let trailing = &s[angle_end + 1..];
                    validate_trailing_cfws(
                        trailing,
                        s,
                        "angle-addr",
                        "RFC 5322 Section 3.4 / Section 3.2.2",
                    )?;
                    let mut email = s[angle_start + 1..angle_end].trim().to_string();
                    // RFC 5322 Section 4.4: strip obsolete source route
                    // (obs-route = obs-domain-list ":"). Example:
                    // `<@hop1,@hop2:user@domain>` → `user@domain`.
                    if email.starts_with('@') {
                        if let Some(colon) = email.find(':') {
                            email = email[colon + 1..].trim().to_string();
                        }
                    }
                    let name_part = s[..angle_start].trim();
                    let name = crate::parser::normalize_display_name_phrase(name_part);
                    if email.is_empty() {
                        return Err(crate::error::Error::InvalidAddress(
                            "empty email in angle brackets".into(),
                        ));
                    }
                    let addr = Self { name, email };
                    // RFC 5322 Section 3.4.1 / RFC 6531 Section 3.3: parse
                    // the display name leniently, but validate the addr-spec
                    // with the same rules the builder enforces for emission.
                    crate::builder::validate_address(&addr)?;
                    return Ok(addr);
                }
            }
        }

        // Bare email — RFC 5322 Section 3.4.1: `addr-spec = local-part "@" domain`.
        // Both local-part and domain must be non-empty.
        //
        // Also handles comments (RFC 5322 Section 3.2.2) before or after the
        // addr-spec: `addr-spec (comment)` or `(comment) addr-spec`.  The
        // comment text is extracted as the display name, matching the behavior
        // of `parse_single_address` in the parser.
        if s.find('@').is_some() {
            // Check for a parenthesized comment: `user@host (Name)` (trailing)
            // or `(Name) user@host` (leading).
            // RFC 5322 Section 3.2.2: `comment = "(" *([FWS] ccontent) [FWS] ")"`.
            let (addr_part, comment_name) = if let Some(paren_start) =
                crate::parser::find_paren_outside_quotes(s)
            {
                let before_paren = s[..paren_start].trim();
                let comment_and_rest = &s[paren_start..];
                // Extract comment content, handling nested parentheses
                // (RFC 5322 Section 3.2.2).
                let after_paren = &s[paren_start + 1..];
                let name = strip_comment_delimiters(after_paren);
                let comment_name = if name.is_empty() { None } else { Some(name) };

                if !before_paren.is_empty() && before_paren.contains('@') {
                    // Trailing comment: `user@host (Name)`
                    validate_trailing_cfws(
                        comment_and_rest,
                        s,
                        "addr-spec comment",
                        "RFC 5322 Section 3.4.1 / Section 3.2.2",
                    )?;
                    (before_paren, comment_name)
                } else {
                    // Leading comment: `(Name) user@host`
                    // RFC 5322 Section 3.2.2: CFWS (including comments) may
                    // appear before the addr-spec.
                    // Find the text after the closing paren for the addr-spec.
                    let close_paren = find_matching_close_paren(&s[paren_start..]);
                    let after_comment = s.get(paren_start + close_paren + 1..).unwrap_or("").trim();
                    if !after_comment.is_empty() && after_comment.contains('@') {
                        (after_comment, comment_name)
                    } else {
                        // `@` was inside the comment, not in the address
                        (before_paren, comment_name)
                    }
                }
            } else {
                (s, None)
            };

            // Find `@` in the addr_part (not in the original string `s`),
            // since `addr_part` may be a shorter substring when a comment
            // was stripped. Fall back to the full addr_part length if there
            // is no `@` in addr_part (which means the `@` was inside the
            // comment, not in the address).
            let at_in_addr = addr_part.find('@').unwrap_or(addr_part.len());
            let local = &addr_part[..at_in_addr];
            let domain = addr_part.get(at_in_addr + 1..).unwrap_or("");
            if local.is_empty() || domain.is_empty() {
                return Err(crate::error::Error::InvalidAddress(format!(
                    "invalid bare email (empty local-part or domain): {s} \
                     (RFC 5322 Section 3.4.1)"
                )));
            }
            let addr = Self {
                name: comment_name,
                email: addr_part.to_string(),
            };
            // RFC 5322 Section 3.4.1 / RFC 6531 Section 3.3: bare addr-spec
            // syntax must satisfy the same validation rules used by the
            // message builder so public parsing and emission stay aligned.
            crate::builder::validate_address(&addr)?;
            return Ok(addr);
        }

        Err(crate::error::Error::InvalidAddress(format!(
            "cannot parse address: {s}"
        )))
    }
}

/// Finds the offset (from the start of `s`) of the closing `)` that matches
/// the opening `(` at position 0, respecting nesting and backslash escapes.
///
/// Returns `s.len() - 1` if no matching close paren is found (Postel's law:
/// treat the rest of the string as the comment body).
///
/// # References
/// - RFC 5322 Section 3.2.2 (nested comments, quoted-pair in comments)
fn find_matching_close_paren(s: &str) -> usize {
    let bytes = s.as_bytes();
    if bytes.is_empty() || bytes[0] != b'(' {
        return 0;
    }
    let mut depth: u32 = 0;
    let mut i = 0;
    while i < bytes.len() {
        match bytes[i] {
            b'\\' => {
                // Skip escaped character (RFC 5322 Section 3.2.4 quoted-pair).
                i += 2;
                continue;
            }
            b'(' => {
                depth = depth.saturating_add(1);
            }
            b')' => {
                depth = depth.saturating_sub(1);
                if depth == 0 {
                    return i;
                }
            }
            _ => {}
        }
        i += 1;
    }
    // No matching close paren found — use end of string.
    s.len().saturating_sub(1)
}

/// Extracts the text content from inside a parenthesized comment, handling
/// nested parentheses and backslash escaping per RFC 5322 Section 3.2.2.
///
/// `input` should be the text AFTER the opening `(`.  Returns the trimmed
/// content with the trailing `)` stripped.  Nested parentheses are preserved
/// in the output.
///
/// # References
/// - RFC 5322 Section 3.2.2 (comment = "(" *([FWS] ccontent) [FWS] ")")
/// - RFC 5322 Section 3.2.4 (quoted-pair = "\" (VCHAR / WSP))
fn strip_comment_delimiters(input: &str) -> String {
    let bytes = input.as_bytes();
    let mut depth: u32 = 1;
    let mut end = input.len();
    let mut i = 0;
    while i < bytes.len() {
        match bytes[i] {
            b'\\' => {
                // Skip the next character (quoted-pair per RFC 5322 Section 3.2.4).
                i += 2;
                continue;
            }
            b'(' => {
                depth = depth.saturating_add(1);
            }
            b')' => {
                depth = depth.saturating_sub(1);
                if depth == 0 {
                    end = i;
                    break;
                }
            }
            _ => {}
        }
        i += 1;
    }
    // RFC 5322 Section 3.2.2: resolve quoted-pair escapes (`\X` → `X`)
    // within the extracted comment content.
    unescape_quoted_string(input[..end].trim())
}

/// Returns `true` if the input contains only CFWS after trimming leading FWS.
///
/// Used to validate text after an `angle-addr` where RFC 5322 Section 3.4
/// permits only trailing CFWS, not arbitrary atoms or phrases.
///
/// # References
/// - RFC 5322 Section 3.2.2 (comments / CFWS)
/// - RFC 5322 Section 3.4 (angle-addr)
fn is_cfws_only(mut input: &str) -> bool {
    loop {
        input = input.trim_start();
        if input.is_empty() {
            return true;
        }
        if !input.starts_with('(') {
            return false;
        }

        let close = find_matching_close_paren(input);
        if input.as_bytes().get(close) != Some(&b')') {
            return false;
        }
        input = &input[close + 1..];
    }
}

/// Reject trailing non-CFWS text after a parsed address component.
///
/// # References
/// - RFC 5322 Section 3.2.2 (comments / CFWS)
/// - RFC 5322 Sections 3.4-3.4.1 (address forms)
fn validate_trailing_cfws(
    trailing: &str,
    original: &str,
    context: &str,
    rfc_sections: &str,
) -> Result<(), crate::error::Error> {
    if trailing.is_empty() || is_cfws_only(trailing) {
        return Ok(());
    }
    Err(crate::error::Error::InvalidAddress(format!(
        "invalid trailing text after {context}: {original} ({rfc_sections})"
    )))
}

/// Unescapes a quoted-string: removes backslash from `\\` → `\` and `\"` → `"`.
///
/// Per RFC 5322 Section 3.2.4, a `quoted-pair` is `"\" (VCHAR / WSP)`.
fn unescape_quoted_string(input: &str) -> String {
    let mut result = String::with_capacity(input.len());
    let mut chars = input.chars();
    while let Some(c) = chars.next() {
        if c == '\\' {
            if let Some(next) = chars.next() {
                result.push(next);
            } else {
                result.push(c);
            }
        } else {
            result.push(c);
        }
    }
    result
}

/// Metadata for an attachment found during parsing.
///
/// Does not contain the attachment binary data — use the `section` field
/// to fetch the content on-demand via IMAP `BODY.PEEK[section]`.
///
/// # References
/// - RFC 2183 (Content-Disposition)
/// - RFC 3501 Section 6.4.5 (MIME section numbers)
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct ParsedAttachment {
    /// Filename from `Content-Disposition` or `Content-Type` name parameter.
    pub filename: Option<String>,
    /// MIME content type (e.g., `"application/pdf"`).
    pub content_type: String,
    /// Content-ID header value, stripped of angle brackets (RFC 2392).
    pub content_id: Option<String>,
    /// `true` if `Content-Disposition: inline` or has a `Content-ID`.
    pub is_inline: bool,
    /// Size of the MIME part body in bytes (if available).
    pub size: Option<u64>,
    /// IMAP MIME section number (e.g., `"2"`, `"1.2"`) for on-demand fetch.
    pub section: Option<String>,
}

/// Day-of-week abbreviations per RFC 5322 Section 3.3.
const DOW_NAMES: [&str; 7] = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];

/// Month abbreviations per RFC 5322 Section 3.3.
const MONTH_NAMES: [&str; 12] = [
    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
];

/// Date-time with timezone offset preserved.
///
/// # Equality and Ordering
///
/// `PartialEq`, `Eq`, `Hash`, `PartialOrd`, and `Ord` are implemented manually
/// rather than derived. All comparisons normalize to UTC first, so two values
/// representing the same instant with different timezone offsets are considered
/// equal (e.g., `2025-01-01T00:00:00+0000` == `2024-12-31T19:00:00-0500`).
///
/// # References
/// - RFC 5322 Section 3.3 (date-time specification)
#[non_exhaustive]
#[derive(Debug, Clone)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct DateTime {
    /// Year (e.g., 2025).
    pub(crate) year: u16,
    /// Month (1–12).
    pub(crate) month: u8,
    /// Day of month (1–31).
    pub(crate) day: u8,
    /// Hour (0–23).
    pub(crate) hour: u8,
    /// Minute (0–59).
    pub(crate) minute: u8,
    /// Second (0–59).
    pub(crate) second: u8,
    /// Timezone offset from UTC in minutes (e.g., +0530 → 330, −0800 → −480).
    pub(crate) tz_offset_minutes: i16,
}

impl DateTime {
    /// Creates a new `DateTime` from individual components.
    ///
    /// Fields are stored as-is; clamping to valid ranges happens at
    /// formatting / comparison time (see [`Self::to_rfc5322_string`],
    /// [`Self::to_unix_timestamp`]).
    ///
    /// # References
    /// - RFC 5322 Section 3.3 (date-time specification)
    pub fn new(
        year: u16,
        month: u8,
        day: u8,
        hour: u8,
        minute: u8,
        second: u8,
        tz_offset_minutes: i16,
    ) -> Self {
        Self {
            year,
            month,
            day,
            hour,
            minute,
            second,
            tz_offset_minutes,
        }
    }

    /// Returns the year (e.g., 2025).
    pub fn year(&self) -> u16 {
        self.year
    }

    /// Returns the month, clamped to 1–12 (RFC 5322 Section 3.3).
    pub fn month(&self) -> u8 {
        self.month.clamp(1, 12)
    }

    /// Returns the day of month, clamped to a valid range for the
    /// current month and year (RFC 5322 Section 3.3).
    pub fn day(&self) -> u8 {
        let month = self.month.clamp(1, 12);
        let max_day = Self::days_in_month(month, self.year);
        self.day.clamp(1, max_day)
    }

    /// Returns the hour, clamped to 0–23 (RFC 5322 Section 3.3).
    pub fn hour(&self) -> u8 {
        self.hour.clamp(0, 23)
    }

    /// Returns the minute, clamped to 0–59 (RFC 5322 Section 3.3).
    pub fn minute(&self) -> u8 {
        self.minute.clamp(0, 59)
    }

    /// Returns the second, clamped to 0–60 (60 is valid for leap
    /// seconds per RFC 5322 Section 3.3).
    pub fn second(&self) -> u8 {
        self.second.clamp(0, 60)
    }

    /// Returns the timezone offset from UTC in minutes (e.g., +0530 → 330,
    /// −0800 → −480), clamped to ±1439 (RFC 5322 Section 3.3).
    pub fn tz_offset_minutes(&self) -> i16 {
        self.tz_offset_minutes.clamp(-1439, 1439)
    }

    /// Converts this date-time to a Unix timestamp (seconds since 1970-01-01T00:00:00Z).
    ///
    /// The timezone offset is applied so the result is always UTC-based.
    /// Uses the same civil-to-days algorithm as the builder.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    pub fn to_unix_timestamp(&self) -> i64 {
        // Clamp all fields to valid ranges, consistent with the string
        // formatters (RFC 5322 §3.3). This ensures the timestamp matches
        // the date-time that would be printed by to_rfc5322_string().
        let (month, day, hour, minute, second) = self.clamped_fields();
        let days = Self::civil_to_days(i32::from(self.year), u32::from(month), u32::from(day));
        // RFC 5322 Section 3.3 allows second=60 (leap second), but Unix
        // timestamps have no leap-second representation.  Clamp to 59 so
        // the timestamp stays within the correct minute (RFC 5322 §3.3).
        let second = if second >= 60 { 59 } else { second };
        let secs =
            days * 86400 + i64::from(hour) * 3600 + i64::from(minute) * 60 + i64::from(second);
        // Clamp timezone offset to the valid RFC 5322 Section 3.3 range
        // (±23:59 = ±1439 minutes), consistent with tz_parts() used by
        // to_rfc5322_string(). Without this clamp, an out-of-range offset
        // produces a timestamp that disagrees with the formatted string.
        let tz = i64::from(self.tz_offset_minutes.clamp(-1439, 1439));
        secs - tz * 60
    }

    /// Creates a `DateTime` from a Unix timestamp (seconds since epoch) and a
    /// timezone offset in minutes.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
    pub fn from_unix_timestamp(timestamp: i64, tz_offset_minutes: i16) -> Self {
        // Clamp timezone offset to the valid RFC 5322 Section 3.3 range
        // (±23:59 = ±1439 minutes) before computing local time. This
        // ensures the stored offset matches what to_rfc5322_string() and
        // to_unix_timestamp() will use, preserving round-trip consistency.
        let tz_offset_minutes = tz_offset_minutes.clamp(-1439, 1439);
        // Apply timezone offset to get local time
        let local_secs = timestamp + i64::from(tz_offset_minutes) * 60;
        let days = local_secs.div_euclid(86400);
        let time_secs = local_secs.rem_euclid(86400) as u64;

        let (year, month, day) = Self::civil_from_days(days);

        // Clamp year to 0–9999 to prevent silent truncation when casting
        // i32 → u16. Negative years (BCE dates) and years above 9999 are
        // outside the RFC 5322 Section 3.3 representable range (year =
        // 4*DIGIT). Without this clamp, negative years wrap to large u16
        // values, corrupting the date and breaking round-trips.
        let year = year.clamp(0, 9999) as u16;

        Self {
            year,
            month: month as u8,
            day: day as u8,
            hour: (time_secs / 3600) as u8,
            minute: ((time_secs % 3600) / 60) as u8,
            second: (time_secs % 60) as u8,
            tz_offset_minutes,
        }
    }

    /// Returns the current UTC time as a `DateTime`.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    #[allow(
        clippy::cast_possible_truncation,
        clippy::cast_sign_loss,
        clippy::cast_possible_wrap
    )]
    pub fn now() -> Self {
        use std::time::{SystemTime, UNIX_EPOCH};

        let secs = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();

        Self::from_unix_timestamp(secs as i64, 0)
    }

    /// Returns the number of days in the given month, accounting for leap years.
    ///
    /// The RFC 5322 Section 3.3 grammar allows day values 1-31 for all months,
    /// but calendar-valid dates require per-month limits (e.g., Feb has 28 or 29).
    ///
    /// # References
    /// - RFC 5322 Section 3.3 (date-time specification)
    fn days_in_month(month: u8, year: u16) -> u8 {
        match month {
            2 => {
                // Leap year: divisible by 4, except centuries unless divisible by 400
                let y = u32::from(year);
                if (y % 4 == 0 && y % 100 != 0) || (y % 400 == 0) {
                    29
                } else {
                    28
                }
            }
            4 | 6 | 9 | 11 => 30,
            // Months 1, 3, 5, 7, 8, 10, 12 all have 31 days.
            // month is clamped to 1-12 before calling; wildcard covers 31-day months.
            _ => 31,
        }
    }

    /// Returns clamped date-time fields conforming to RFC 5322 Section 3.3.
    ///
    /// Clamps each field to its valid range:
    /// - month: 1–12
    /// - day: 1–`days_in_month(month, year)` (accounts for per-month limits and
    ///   leap years, so invalid dates like Feb 31 are clamped to Feb 28/29)
    /// - hour: 0–23
    /// - minute: 0–59
    /// - second: 0–60 (60 is valid for leap seconds per RFC 5322 Section 3.3)
    ///
    /// # References
    /// - RFC 5322 Section 3.3 (date-time specification)
    fn clamped_fields(&self) -> (u8, u8, u8, u8, u8) {
        let month = self.month.clamp(1, 12);
        // Clamp day against the actual number of days in the clamped month
        // and year, not a flat 31 (RFC 5322 Section 3.3).
        let max_day = Self::days_in_month(month, self.year);
        let day = self.day.clamp(1, max_day);
        (
            month,
            day,
            self.hour.clamp(0, 23),
            self.minute.clamp(0, 59),
            self.second.clamp(0, 60),
        )
    }

    /// Returns the day of week for this date.
    ///
    /// Returns 0 for Sunday, 1 for Monday, ..., 6 for Saturday.
    /// Uses clamped month/day values for consistency with `to_rfc5322_string()`
    /// (RFC 5322 Section 3.3).
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    #[allow(clippy::cast_sign_loss)]
    pub fn weekday(&self) -> u8 {
        let (month, day, _, _, _) = self.clamped_fields();
        let days = Self::civil_to_days(i32::from(self.year), u32::from(month), u32::from(day));
        // 1970-01-01 was Thursday (4); result is always in [0, 6]
        (((days % 7) + 4 + 7) % 7) as u8
    }

    /// Formats this date-time as an RFC 5322 date-time string.
    ///
    /// Produces the format: `day-of-week, DD Mon YYYY HH:MM:SS ±HHMM`
    /// (e.g., `"Thu, 13 Feb 2025 15:47:33 +0000"`).
    ///
    /// All fields are clamped to their valid ranges per RFC 5322 Section 3.3
    /// to ensure well-formed output (Postel's law: be conservative in what
    /// you send).
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    pub fn to_rfc5322_string(&self) -> String {
        let (month, day, hour, minute, second) = self.clamped_fields();
        let dow = self.weekday();
        let dow_name = DOW_NAMES[dow as usize];
        // month is already clamped to [1, 12] by clamped_fields()
        let month_name = MONTH_NAMES[(month - 1) as usize];
        let (sign, tz_h, tz_m) = self.tz_parts();
        format!(
            "{dow_name}, {:02} {month_name} {:04} {:02}:{:02}:{:02} {sign}{tz_h:02}{tz_m:02}",
            day, self.year, hour, minute, second,
        )
    }

    /// Formats this date-time as an ISO 8601 / RFC 3339 string.
    ///
    /// Produces the format: `YYYY-MM-DDTHH:MM:SS±HH:MM`
    /// (e.g., `"2025-02-13T15:47:33+00:00"`).
    ///
    /// All fields are clamped to their valid ranges for consistency with
    /// `to_rfc5322_string()`.
    ///
    /// This format is widely used in JSON APIs and structured data exchange.
    ///
    /// # References
    /// - ISO 8601 (date-time representation)
    /// - RFC 3339 (date-time on the Internet)
    pub fn to_iso8601_string(&self) -> String {
        let (month, day, hour, minute, second) = self.clamped_fields();
        let (sign, tz_h, tz_m) = self.tz_parts();
        format!(
            "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}{sign}{tz_h:02}:{tz_m:02}",
            self.year, month, day, hour, minute, second,
        )
    }

    /// Parses an RFC 5322 date-time string into a `DateTime`.
    ///
    /// Accepts: `[day-of-week ","] day month year hour ":" minute [":" second] zone`
    ///
    /// Strips CFWS (comments and folding white space) before parsing, as
    /// allowed by the obsolete date syntax (RFC 5322 Section 4.3).
    ///
    /// Returns `None` if the input is not a valid RFC 5322 date-time.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    /// - RFC 5322 Section 4.3 (obsolete syntax)
    pub fn parse_rfc5322(input: &str) -> Option<Self> {
        crate::parser::parse_rfc5322_date(input)
    }

    /// Returns the timezone offset decomposed as `(sign, hours, minutes)`.
    ///
    /// # References
    /// - RFC 5322 Section 3.3 (zone = ("+" / "-") 4DIGIT)
    fn tz_parts(&self) -> (char, u16, u16) {
        // Clamp to the valid RFC 5322 range: zone hours 0-23, minutes 0-59,
        // so the maximum magnitude is 23*60+59 = 1439 (RFC 5322 Section 3.3).
        let clamped = self.tz_offset_minutes.clamp(-1439, 1439);
        let sign = if clamped >= 0 { '+' } else { '-' };
        let abs = clamped.unsigned_abs();
        (sign, abs / 60, abs % 60)
    }

    /// Converts days since Unix epoch to `(year, month, day)`.
    ///
    /// Algorithm from Howard Hinnant's date algorithms.
    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
    fn civil_from_days(z: i64) -> (i32, u32, u32) {
        let z = z + 719_468;
        let era = (if z >= 0 { z } else { z - 146_096 }) / 146_097;
        let doe = (z - era * 146_097) as u32;
        let yoe = (doe - doe / 1460 + doe / 36524 - doe / 146_096) / 365;
        let y = i64::from(yoe) + era * 400;
        let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
        let mp = (5 * doy + 2) / 153;
        let d = doy - (153 * mp + 2) / 5 + 1;
        let m = if mp < 10 { mp + 3 } else { mp - 9 };
        let y = if m <= 2 { y + 1 } else { y };
        (y as i32, m, d)
    }

    /// Converts `(year, month, day)` to days since Unix epoch.
    ///
    /// Algorithm from Howard Hinnant's date algorithms.
    #[allow(clippy::cast_sign_loss, clippy::cast_possible_wrap)]
    fn civil_to_days(year: i32, month: u32, day: u32) -> i64 {
        let y = if month <= 2 {
            i64::from(year) - 1
        } else {
            i64::from(year)
        };
        let m = if month <= 2 { month + 9 } else { month - 3 };
        let era = (if y >= 0 { y } else { y - 399 }) / 400;
        let yoe = (y - era * 400) as u64;
        let doy = (153 * u64::from(m) + 2) / 5 + u64::from(day) - 1;
        let doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;
        era * 146_097 + doe as i64 - 719_468
    }
}

impl PartialEq for DateTime {
    /// Compares two `DateTime` values by their UTC-normalized timestamps,
    /// consistent with the `Ord` implementation.
    ///
    /// # References
    /// - RFC 5322 Section 3.3 (date-time specification)
    fn eq(&self, other: &Self) -> bool {
        self.to_unix_timestamp() == other.to_unix_timestamp()
    }
}

impl Eq for DateTime {}

impl std::hash::Hash for DateTime {
    /// Hashes by UTC-normalized timestamp, consistent with `Eq` and `Ord`.
    ///
    /// Two `DateTime` values representing the same UTC instant (but with
    /// different timezone offsets) will produce the same hash, matching the
    /// `Eq` behavior.
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.to_unix_timestamp().hash(state);
    }
}

impl PartialOrd for DateTime {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for DateTime {
    /// Compares two `DateTime` values by their UTC-normalized timestamps.
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.to_unix_timestamp().cmp(&other.to_unix_timestamp())
    }
}

impl std::fmt::Display for DateTime {
    /// Formats this date-time for human-readable display.
    ///
    /// All fields are clamped to their valid ranges, consistent with
    /// `to_rfc5322_string()` and `to_iso8601_string()` (RFC 5322 §3.3).
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let (month, day, hour, minute, second) = self.clamped_fields();
        let (sign, tz_h, tz_m) = self.tz_parts();
        write!(
            f,
            "{:04}-{:02}-{:02} {:02}:{:02}:{:02} {sign}{tz_h:02}{tz_m:02}",
            self.year, month, day, hour, minute, second,
        )
    }
}

impl std::str::FromStr for DateTime {
    type Err = crate::error::Error;

    /// Parses an RFC 5322 date-time string into a `DateTime`.
    ///
    /// Accepts: `[day-of-week ","] day month year hour ":" minute [":" second] zone`
    ///
    /// This enables the ergonomic `"Thu, 13 Feb 2025 15:47:33 +0000".parse::<DateTime>()`
    /// pattern via the standard `FromStr` trait.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    /// - RFC 5322 Section 4.3 (obsolete syntax)
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::parse_rfc5322(s).ok_or_else(|| {
            crate::error::Error::InvalidDate(format!("cannot parse RFC 5322 date: {s}"))
        })
    }
}

/// An outgoing email to be built into raw RFC 5322 bytes.
///
/// Used as input to [`crate::build_message`].
///
/// # References
/// - RFC 5322 (message format)
/// - RFC 2046 (MIME multipart)
#[non_exhaustive]
#[derive(Debug, Default, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct OutgoingEmail {
    /// Originator mailboxes (RFC 5322 Section 3.6.2: `from = "From:" mailbox-list`).
    ///
    /// Must contain at least one address. When multiple addresses are present,
    /// `sender` **must** be set per RFC 5322 Section 3.6.2:
    /// "If the from field contains more than one mailbox specification in the
    /// mailbox-list, then the sender field, containing the field value
    /// corresponding to the responsible agent, MUST appear in the message."
    pub from: Vec<Address>,
    /// The agent responsible for actual transmission of the message
    /// (RFC 5322 Section 3.6.2: `sender = "Sender:" mailbox`).
    ///
    /// Required when `from` contains more than one address. Optional when
    /// `from` contains exactly one address.
    pub sender: Option<Address>,
    /// To recipients (RFC 5322 Section 3.6.3).
    pub to: Vec<Address>,
    /// Cc recipients (RFC 5322 Section 3.6.3).
    pub cc: Vec<Address>,
    /// Bcc recipients — included in SMTP envelope (`RCPT TO`) but **must not**
    /// appear in message headers (RFC 5322 Section 3.6.3).
    pub bcc: Vec<Address>,
    /// Reply-To addresses (RFC 5322 Section 3.6.2: `address-list`).
    pub reply_to: Vec<Address>,
    /// Explicit origination date (RFC 5322 Section 3.6.1).
    ///
    /// When `None`, [`crate::build_message`] uses the current UTC time.
    /// Set this when building drafts, re-sending, or importing messages
    /// that require a specific date.
    pub date: Option<DateTime>,
    /// Subject line (RFC 5322 Section 3.6.5).
    pub subject: String,
    /// Plain text body.
    pub body_text: Option<String>,
    /// HTML body.
    pub body_html: Option<String>,
    /// In-Reply-To message-IDs — bare `addr-spec` values (no angle brackets),
    /// builder wraps each in angle brackets for the wire format and silently
    /// drops malformed IDs (RFC 5322 Section 3.6.4: `in-reply-to = 1*msg-id`).
    ///
    /// Accepts plain strings so that parsed message-IDs (which may be
    /// non-conformant) can flow directly from [`ParsedEmail`] into a reply
    /// without fallible conversion.
    pub in_reply_to: Vec<String>,
    /// References message-IDs — bare `addr-spec` values (no angle brackets),
    /// builder wraps each in angle brackets for the wire format and silently
    /// drops malformed IDs (RFC 5322 Section 3.6.4: `references = 1*msg-id`).
    ///
    /// Accepts plain strings for the same reason as [`in_reply_to`](Self::in_reply_to).
    pub references: Vec<String>,
    /// File attachments.
    pub attachments: Vec<OutgoingAttachment>,
    /// Additional headers to include verbatim (RFC 5322 Section 3.6.8).
    ///
    /// Each entry is a `(field-name, unstructured-value)` pair. The
    /// [`HeaderName`] newtype enforces RFC 5322 Section 2.2 ftext syntax at
    /// construction time. Values are sanitized (CR/LF stripped) and long
    /// lines are folded per RFC 5322 Section 2.2.3. Headers are emitted
    /// after the standard headers (From, To, Subject, etc.) in the order
    /// they appear here.
    pub extra_headers: Vec<(HeaderName, String)>,
}

/// An attachment to include in an outgoing email.
///
/// # References
/// - RFC 2183 (Content-Disposition: attachment / inline)
/// - RFC 2392 (Content-ID)
/// - RFC 2045 (Content-Transfer-Encoding: base64)
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct OutgoingAttachment {
    /// Filename for the `Content-Disposition` header.
    pub filename: String,
    /// MIME content type (e.g., `"application/pdf"`).
    pub content_type: String,
    /// Raw file data — will be base64-encoded in the message.
    pub data: Vec<u8>,
    /// When `true`, the part uses `Content-Disposition: inline` instead of
    /// `attachment` (RFC 2183 Section 2).  Typically used for images
    /// embedded in HTML via `cid:` URLs.
    pub is_inline: bool,
    /// Optional `Content-ID` header value (RFC 2392).  Should be a bare
    /// `addr-spec` (e.g., `"image001@example.com"`); the builder wraps it
    /// in angle brackets.  Required for HTML-embedded inline images that
    /// are referenced as `<img src="cid:image001@example.com">`.
    pub content_id: Option<String>,
}

impl OutgoingAttachment {
    /// Creates a regular (non-inline) attachment.
    ///
    /// # References
    /// - RFC 2183 (Content-Disposition: attachment)
    /// - RFC 2045 (Content-Transfer-Encoding: base64)
    pub fn new(
        filename: impl Into<String>,
        content_type: impl Into<String>,
        data: impl Into<Vec<u8>>,
    ) -> Self {
        Self {
            filename: filename.into(),
            content_type: content_type.into(),
            data: data.into(),
            is_inline: false,
            content_id: None,
        }
    }

    /// Creates an inline attachment with a Content-ID for embedding in HTML.
    ///
    /// Inline attachments use `Content-Disposition: inline` (RFC 2183
    /// Section 2) and are referenced by the HTML body via `cid:` URLs
    /// (RFC 2392).
    ///
    /// # References
    /// - RFC 2183 Section 2 (Content-Disposition: inline)
    /// - RFC 2392 (Content-ID)
    pub fn inline(
        filename: impl Into<String>,
        content_type: impl Into<String>,
        data: impl Into<Vec<u8>>,
        content_id: impl Into<String>,
    ) -> Self {
        Self {
            filename: filename.into(),
            content_type: content_type.into(),
            data: data.into(),
            is_inline: true,
            content_id: Some(content_id.into()),
        }
    }
}

/// The result of building an email message.
///
/// # References
/// - RFC 5322 (message format)
/// - RFC 5321 (SMTP envelope)
#[non_exhaustive]
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct BuiltMessage {
    /// Raw RFC 5322 message bytes (headers + body). BCC excluded from headers.
    pub raw: Vec<u8>,
    /// All envelope recipients (to + cc + bcc) for SMTP `RCPT TO`.
    pub envelope_recipients: Vec<String>,
    /// The generated Message-ID (bare `addr-spec`, no angle brackets).
    pub message_id: String,
}

/// TLS mode for the initial connection (RFC 8314).
///
/// This type lives in `daaki-message` rather than in the protocol crates
/// because both `daaki-imap` and `daaki-smtp` need it, and `daaki-message`
/// is already the shared dependency in the workspace. Both protocol crates
/// re-export it at their crate root.
#[non_exhaustive]
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum TlsMode {
    /// Connect directly over TLS (RFC 8314 Section 3.3).
    Implicit,
    /// Connect in cleartext, then upgrade via STARTTLS.
    StartTls,
    /// No TLS (testing only — should not be used in production).
    None,
}

#[cfg(test)]
#[path = "types_tests.rs"]
mod tests;