daaki-message 0.1.0

//! 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)

/// 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)
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ParsedEmail {
    /// Message-ID with angle brackets stripped (RFC 5322 Section 3.6.4).
    pub message_id: Option<String>,
    /// First `In-Reply-To` message-id only (RFC 5322 Section 3.6.4).
    pub in_reply_to: Option<String>,
    /// All `References` message-ids, space-joined (RFC 5322 Section 3.6.4).
    pub references: Option<String>,
    /// Decoded subject (RFC 5322 Section 3.6.5, RFC 2047 encoded words decoded).
    pub subject: Option<String>,
    /// Sender address (RFC 5322 Section 3.6.2).
    pub from: 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,
    /// Total byte count of the input.
    pub size: u64,
}

/// An email address with optional display name.
///
/// # References
/// - RFC 5322 Section 3.4 (address specification)
#[derive(Debug, Clone, PartialEq, Eq)]
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,
}

/// 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 {
            Some(name) if !name.is_empty() => {
                if !name.is_ascii() {
                    // RFC 5322 Section 2.2: field bodies must be US-ASCII.
                    // RFC 2047 Section 5: use encoded-words for non-ASCII text.
                    let encoded = crate::builder::encode_rfc2047_if_needed(name);
                    write!(f, "{encoded} <{}>", 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).
    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 email = s[angle_start + 1..angle_end].trim().to_string();
                    let name_part = s[..angle_start].trim();
                    let name = if name_part.is_empty() {
                        None
                    } else {
                        // Strip only the outer pair of quotes from a quoted-string
                        // (RFC 5322 Section 3.2.4). Using trim_matches('"') would
                        // greedily strip multiple quotes and corrupt escaped quotes
                        // like `\"` at the end of the display name.
                        let stripped = strip_outer_quotes(name_part);
                        let name = stripped.trim().to_string();
                        if name.is_empty() {
                            None
                        } else {
                            // Decode RFC 2047 encoded words in display name
                            // (RFC 2047 Section 5, RFC 5322 Section 2.2).
                            let unescaped = unescape_quoted_string(&name);
                            let decoded = crate::parser::decode_encoded_words(&unescaped);
                            Some(decoded)
                        }
                    };
                    if email.is_empty() {
                        return Err(crate::error::Error::InvalidAddress(
                            "empty email in angle brackets".into(),
                        ));
                    }
                    return Ok(Self { name, email });
                }
            }
        }

        // Bare email
        if s.contains('@') {
            return Ok(Self {
                name: None,
                email: s.to_string(),
            });
        }

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

/// Strips only the outer pair of quotes from a quoted-string.
///
/// If `input` starts with `"` and ends with `"`, removes those two characters.
/// Otherwise returns the input unchanged. Unlike `trim_matches('"')`, this does
/// not greedily strip multiple consecutive quotes, which is critical when the
/// display name ends with an escaped quote like `"She said \"hello\""`.
///
/// # References
/// - RFC 5322 Section 3.2.4 (quoted-string structure)
fn strip_outer_quotes(input: &str) -> &str {
    if input.len() >= 2 && input.starts_with('"') && input.ends_with('"') {
        &input[1..input.len() - 1]
    } else {
        input
    }
}

/// 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)
#[derive(Debug, Clone, PartialEq, Eq)]
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.
///
/// # References
/// - RFC 5322 Section 3.3 (date-time specification)
#[derive(Debug, Clone)]
pub struct DateTime {
    /// Year (e.g., 2025).
    pub year: u16,
    /// Month (1–12).
    pub month: u8,
    /// Day of month (1–31).
    pub day: u8,
    /// Hour (0–23).
    pub hour: u8,
    /// Minute (0–59).
    pub minute: u8,
    /// Second (0–59).
    pub second: u8,
    /// Timezone offset from UTC in minutes (e.g., +0530 → 330, −0800 → −480).
    pub tz_offset_minutes: i16,
}

impl DateTime {
    /// 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 {
        let days = Self::civil_to_days(
            i32::from(self.year),
            u32::from(self.month),
            u32::from(self.day),
        );
        let secs = days * 86400
            + i64::from(self.hour) * 3600
            + i64::from(self.minute) * 60
            + i64::from(self.second);
        // Subtract timezone offset to normalize to UTC
        secs - i64::from(self.tz_offset_minutes) * 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 {
        // 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);

        Self {
            year: year as u16,
            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 day of week for this date.
    ///
    /// Returns 0 for Sunday, 1 for Monday, ..., 6 for Saturday.
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    #[allow(clippy::cast_sign_loss)]
    pub fn weekday(&self) -> u8 {
        let days = Self::civil_to_days(
            i32::from(self.year),
            u32::from(self.month),
            u32::from(self.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"`).
    ///
    /// # References
    /// - RFC 5322 Section 3.3
    pub fn to_rfc5322_string(&self) -> String {
        let dow = self.weekday();
        let dow_name = DOW_NAMES[dow as usize];
        // Clamp month to valid range [1, 12] to prevent index-out-of-bounds
        // panic on malformed DateTime values (RFC 5322 Section 3.3: month = 1–12).
        let month_idx = self.month.clamp(1, 12).saturating_sub(1) as usize;
        let month_name = MONTH_NAMES[month_idx];
        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}",
            self.day, self.year, self.hour, self.minute, self.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"`).
    ///
    /// 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 (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, self.month, self.day, self.hour, self.minute, self.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) {
        let sign = if self.tz_offset_minutes >= 0 {
            '+'
        } else {
            '-'
        };
        let abs = self.tz_offset_minutes.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 {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        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, self.month, self.day, self.hour, self.minute, self.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)
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct OutgoingEmail {
    /// Sender address (RFC 5322 Section 3.6.2).
    pub from: 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 address (RFC 5322 Section 3.6.2).
    pub reply_to: Option<Address>,
    /// 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 ID — bare `addr-spec`, builder wraps in angle brackets.
    pub in_reply_to: Option<String>,
    /// References — space-separated bare message-ids, builder wraps each in angle brackets.
    pub references: Option<String>,
    /// File attachments.
    pub attachments: Vec<OutgoingAttachment>,
}

/// An attachment to include in an outgoing email.
///
/// # References
/// - RFC 2183 (Content-Disposition: attachment)
/// - RFC 2045 (Content-Transfer-Encoding: base64)
#[derive(Debug, Clone, PartialEq, Eq)]
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>,
}

/// The result of building an email message.
///
/// # References
/// - RFC 5322 (message format)
/// - RFC 5321 (SMTP envelope)
#[derive(Debug, Clone, PartialEq, Eq)]
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,
}

#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests {
    use super::*;

    #[test]
    fn address_display_bare_email() {
        let addr = Address {
            name: None,
            email: "user@example.com".into(),
        };
        assert_eq!(addr.to_string(), "user@example.com");
    }

    #[test]
    fn address_display_with_name() {
        let addr = Address {
            name: Some("John Doe".into()),
            email: "john@example.com".into(),
        };
        assert_eq!(addr.to_string(), "John Doe <john@example.com>");
    }

    #[test]
    fn address_display_name_with_specials_quoted() {
        let addr = Address {
            name: Some("Doe, John".into()),
            email: "john@example.com".into(),
        };
        assert_eq!(addr.to_string(), "\"Doe, John\" <john@example.com>");
    }

    #[test]
    fn address_display_name_with_quotes_escaped() {
        let addr = Address {
            name: Some("John \"Doc\" Doe".into()),
            email: "john@example.com".into(),
        };
        assert_eq!(
            addr.to_string(),
            "\"John \\\"Doc\\\" Doe\" <john@example.com>"
        );
    }

    #[test]
    fn address_from_str_bare_email() {
        let addr: Address = "user@example.com".parse().unwrap();
        assert_eq!(addr.email, "user@example.com");
        assert!(addr.name.is_none());
    }

    #[test]
    fn address_from_str_with_name() {
        let addr: Address = "John Doe <john@example.com>".parse().unwrap();
        assert_eq!(addr.email, "john@example.com");
        assert_eq!(addr.name.as_deref(), Some("John Doe"));
    }

    #[test]
    fn address_from_str_quoted_name() {
        let addr: Address = "\"Doe, John\" <john@example.com>".parse().unwrap();
        assert_eq!(addr.email, "john@example.com");
        assert_eq!(addr.name.as_deref(), Some("Doe, John"));
    }

    #[test]
    fn address_from_str_escaped_quotes_in_name() {
        let addr: Address = "\"John \\\"Doc\\\" Doe\" <john@example.com>"
            .parse()
            .unwrap();
        assert_eq!(addr.email, "john@example.com");
        assert_eq!(addr.name.as_deref(), Some("John \"Doc\" Doe"));
    }

    #[test]
    fn address_from_str_empty_rejected() {
        let result: Result<Address, _> = "".parse();
        assert!(result.is_err());
    }

    #[test]
    fn address_from_str_no_at_rejected() {
        let result: Result<Address, _> = "not-an-email".parse();
        assert!(result.is_err());
    }

    #[test]
    fn address_round_trip_display_from_str() {
        let original = Address {
            name: Some("Doe, John".into()),
            email: "john@example.com".into(),
        };
        let displayed = original.to_string();
        let parsed: Address = displayed.parse().unwrap();
        assert_eq!(original, parsed);
    }

    #[test]
    fn datetime_now_returns_plausible_date() {
        let now = DateTime::now();
        // Year should be 2025 or later (test written in 2026)
        assert!(now.year >= 2025, "DateTime::now() year is {}", now.year);
        assert!((1..=12).contains(&now.month));
        assert!((1..=31).contains(&now.day));
        assert!(now.hour <= 23);
        assert!(now.minute <= 59);
        assert!(now.second <= 60);
        assert_eq!(now.tz_offset_minutes, 0, "now() should return UTC");
    }

    #[test]
    fn datetime_weekday_known_dates() {
        // 2025-02-13 is a Thursday (4)
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 0,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        assert_eq!(dt.weekday(), 4, "2025-02-13 should be Thursday (4)");

        // 1970-01-01 is a Thursday (4)
        let epoch = DateTime::from_unix_timestamp(0, 0);
        assert_eq!(epoch.weekday(), 4, "1970-01-01 should be Thursday (4)");

        // 2025-03-16 is a Sunday (0)
        let sunday = DateTime {
            year: 2025,
            month: 3,
            day: 16,
            hour: 0,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        assert_eq!(sunday.weekday(), 0, "2025-03-16 should be Sunday (0)");
    }

    #[test]
    fn datetime_eq_consistent_with_ord() {
        // Two DateTime values representing the same UTC instant (2025-01-15 12:00:00 UTC)
        // but with different timezone offsets.
        let utc = DateTime {
            year: 2025,
            month: 1,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        let plus_five = DateTime {
            year: 2025,
            month: 1,
            day: 15,
            hour: 17,
            minute: 0,
            second: 0,
            tz_offset_minutes: 300, // +0500
        };

        // Both should have the same UTC timestamp
        assert_eq!(utc.to_unix_timestamp(), plus_five.to_unix_timestamp());

        // Ord says they are equal
        assert_eq!(
            utc.cmp(&plus_five),
            std::cmp::Ordering::Equal,
            "cmp should consider same-UTC-instant values equal"
        );

        // PartialEq must agree with Ord — this is the Rust contract
        assert_eq!(
            utc, plus_five,
            "PartialEq must agree with Ord: same UTC instant should be =="
        );
    }

    #[test]
    fn datetime_hash_consistent_with_eq() {
        use std::collections::hash_map::DefaultHasher;
        use std::hash::{Hash, Hasher};

        fn hash_of(dt: &DateTime) -> u64 {
            let mut hasher = DefaultHasher::new();
            dt.hash(&mut hasher);
            hasher.finish()
        }

        // Two DateTime values representing the same UTC instant
        // (2025-01-15 12:00:00 UTC) but with different timezone offsets.
        let utc = DateTime {
            year: 2025,
            month: 1,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        let plus_five = DateTime {
            year: 2025,
            month: 1,
            day: 15,
            hour: 17,
            minute: 0,
            second: 0,
            tz_offset_minutes: 300,
        };

        // Eq says they are equal
        assert_eq!(utc, plus_five);

        // Hash MUST agree: equal values must produce equal hashes
        assert_eq!(
            hash_of(&utc),
            hash_of(&plus_five),
            "Hash must be consistent with Eq: same UTC instant must hash the same"
        );
    }

    #[test]
    fn datetime_to_rfc5322_string_utc() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 15,
            minute: 47,
            second: 33,
            tz_offset_minutes: 0,
        };
        // 2025-02-13 is a Thursday
        assert_eq!(dt.to_rfc5322_string(), "Thu, 13 Feb 2025 15:47:33 +0000");
    }

    #[test]
    fn datetime_to_rfc5322_string_positive_offset() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 21,
            minute: 17,
            second: 33,
            tz_offset_minutes: 330, // +0530
        };
        assert_eq!(dt.to_rfc5322_string(), "Thu, 13 Feb 2025 21:17:33 +0530");
    }

    #[test]
    fn datetime_to_rfc5322_string_negative_offset() {
        let dt = DateTime {
            year: 2025,
            month: 3,
            day: 16,
            hour: 9,
            minute: 0,
            second: 0,
            tz_offset_minutes: -480, // -0800
        };
        // 2025-03-16 is a Sunday
        assert_eq!(dt.to_rfc5322_string(), "Sun, 16 Mar 2025 09:00:00 -0800");
    }

    #[test]
    fn datetime_parse_rfc5322_basic() {
        let dt = DateTime::parse_rfc5322("Thu, 13 Feb 2025 15:47:33 +0000").unwrap();
        assert_eq!(dt.year, 2025);
        assert_eq!(dt.month, 2);
        assert_eq!(dt.day, 13);
        assert_eq!(dt.hour, 15);
        assert_eq!(dt.minute, 47);
        assert_eq!(dt.second, 33);
        assert_eq!(dt.tz_offset_minutes, 0);
    }

    #[test]
    fn datetime_parse_rfc5322_with_offset() {
        let dt = DateTime::parse_rfc5322("Fri, 14 Feb 2025 09:15:00 -0800").unwrap();
        assert_eq!(dt.year, 2025);
        assert_eq!(dt.tz_offset_minutes, -480);
    }

    #[test]
    fn datetime_parse_rfc5322_round_trip() {
        let original = DateTime {
            year: 2025,
            month: 12,
            day: 25,
            hour: 0,
            minute: 0,
            second: 0,
            tz_offset_minutes: 330,
        };
        let s = original.to_rfc5322_string();
        let parsed = DateTime::parse_rfc5322(&s).unwrap();
        assert_eq!(original, parsed);
    }

    #[test]
    fn datetime_parse_rfc5322_invalid() {
        assert!(DateTime::parse_rfc5322("not a date").is_none());
        assert!(DateTime::parse_rfc5322("").is_none());
    }

    #[test]
    fn datetime_to_iso8601_string_utc() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 15,
            minute: 47,
            second: 33,
            tz_offset_minutes: 0,
        };
        assert_eq!(dt.to_iso8601_string(), "2025-02-13T15:47:33+00:00");
    }

    #[test]
    fn datetime_to_iso8601_string_positive_offset() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 21,
            minute: 17,
            second: 33,
            tz_offset_minutes: 330, // +05:30
        };
        assert_eq!(dt.to_iso8601_string(), "2025-02-13T21:17:33+05:30");
    }

    #[test]
    fn datetime_to_iso8601_string_negative_offset() {
        let dt = DateTime {
            year: 2025,
            month: 3,
            day: 16,
            hour: 9,
            minute: 0,
            second: 0,
            tz_offset_minutes: -480, // -08:00
        };
        assert_eq!(dt.to_iso8601_string(), "2025-03-16T09:00:00-08:00");
    }

    /// `Address::Display` must RFC 2047 encode non-ASCII display
    /// names, since RFC 5322 Section 2.2 requires header field bodies to be
    /// US-ASCII (RFC 2047 Section 5 defines the encoded-word mechanism).
    #[test]
    fn address_display_non_ascii_is_rfc2047_encoded() {
        let addr = Address {
            name: Some("José García".into()),
            email: "jose@example.com".into(),
        };
        let displayed = addr.to_string();

        // RFC 5322 Section 2.2: field bodies must be US-ASCII
        assert!(
            displayed.is_ascii(),
            "Display output must be pure ASCII, got: {displayed}"
        );
        // RFC 2047 Base64 encoded word marker
        assert!(
            displayed.contains("=?UTF-8?B?"),
            "Non-ASCII name must be RFC 2047 encoded, got: {displayed}"
        );
        // Email must still appear in angle brackets
        assert!(
            displayed.contains("<jose@example.com>"),
            "Email must appear in angle brackets, got: {displayed}"
        );
    }

    /// ASCII display names must NOT be RFC 2047 encoded — encoding is only
    /// needed for non-ASCII characters (RFC 2047 Section 5).
    #[test]
    fn address_display_ascii_name_unchanged() {
        let addr = Address {
            name: Some("John Doe".into()),
            email: "john@example.com".into(),
        };
        let displayed = addr.to_string();
        assert_eq!(displayed, "John Doe <john@example.com>");
        // Must not contain encoded-word markers
        assert!(
            !displayed.contains("=?"),
            "ASCII name should not be RFC 2047 encoded, got: {displayed}"
        );
    }

    /// Round-trip: non-ASCII name formatted with Display, then parsed back
    /// with `FromStr`, must recover the original name (RFC 2047 encode/decode).
    #[test]
    fn address_display_non_ascii_round_trip() {
        let original = Address {
            name: Some("José García".into()),
            email: "jose@example.com".into(),
        };
        let displayed = original.to_string();
        let parsed: Address = displayed.parse().unwrap();
        assert_eq!(
            original, parsed,
            "Round-trip failed: displayed as '{displayed}', parsed name = {:?}",
            parsed.name
        );
    }

    /// `DateTime` with out-of-range month must not panic in
    /// `to_rfc5322_string()` or `weekday()` — violates "no panics" rule and
    /// RFC 5322 Section 3.3 (month is 1–12).
    #[test]
    fn datetime_invalid_month_no_panic() {
        // Month 0 (below valid range)
        let dt_zero = DateTime {
            year: 2025,
            month: 0,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        // Must not panic — should produce a clamped/fallback string
        let _ = dt_zero.to_rfc5322_string();
        let _ = dt_zero.weekday();

        // Month 13 (above valid range)
        let dt_thirteen = DateTime {
            year: 2025,
            month: 13,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        // Must not panic
        let _ = dt_thirteen.to_rfc5322_string();
        let _ = dt_thirteen.weekday();

        // Month 255 (u8::MAX)
        let dt_max = DateTime {
            year: 2025,
            month: 255,
            day: 15,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 0,
        };
        // Must not panic
        let _ = dt_max.to_rfc5322_string();
        let _ = dt_max.weekday();
    }

    #[test]
    fn datetime_from_str_basic() {
        let dt: DateTime = "Thu, 13 Feb 2025 15:47:33 +0000".parse().unwrap();
        assert_eq!(dt.year, 2025);
        assert_eq!(dt.month, 2);
        assert_eq!(dt.day, 13);
        assert_eq!(dt.hour, 15);
        assert_eq!(dt.minute, 47);
        assert_eq!(dt.second, 33);
        assert_eq!(dt.tz_offset_minutes, 0);
    }

    #[test]
    fn datetime_from_str_with_offset() {
        let dt: DateTime = "Fri, 14 Feb 2025 09:15:00 -0800".parse().unwrap();
        assert_eq!(dt.year, 2025);
        assert_eq!(dt.tz_offset_minutes, -480);
    }

    #[test]
    fn datetime_from_str_invalid() {
        let result: Result<DateTime, _> = "not a date".parse();
        assert!(result.is_err());
    }

    #[test]
    fn datetime_from_str_empty() {
        let result: Result<DateTime, _> = "".parse();
        assert!(result.is_err());
    }

    #[test]
    fn datetime_from_str_round_trip() {
        let original = DateTime {
            year: 2025,
            month: 7,
            day: 4,
            hour: 12,
            minute: 30,
            second: 0,
            tz_offset_minutes: -300,
        };
        let s = original.to_rfc5322_string();
        let parsed: DateTime = s.parse().unwrap();
        assert_eq!(original, parsed);
    }

    #[test]
    fn datetime_display_utc() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 15,
            minute: 47,
            second: 33,
            tz_offset_minutes: 0,
        };
        assert_eq!(dt.to_string(), "2025-02-13 15:47:33 +0000");
    }

    #[test]
    fn datetime_display_positive_offset() {
        let dt = DateTime {
            year: 2025,
            month: 2,
            day: 13,
            hour: 21,
            minute: 17,
            second: 33,
            tz_offset_minutes: 330, // +0530
        };
        assert_eq!(dt.to_string(), "2025-02-13 21:17:33 +0530");
    }

    #[test]
    fn datetime_display_negative_offset() {
        let dt = DateTime {
            year: 2025,
            month: 3,
            day: 16,
            hour: 9,
            minute: 0,
            second: 0,
            tz_offset_minutes: -480, // -0800
        };
        assert_eq!(dt.to_string(), "2025-03-16 09:00:00 -0800");
    }

    #[test]
    fn datetime_display_non_half_hour_offset() {
        // Nepal Standard Time: UTC+05:45
        let dt = DateTime {
            year: 2025,
            month: 6,
            day: 1,
            hour: 12,
            minute: 0,
            second: 0,
            tz_offset_minutes: 345, // +0545
        };
        assert_eq!(dt.to_string(), "2025-06-01 12:00:00 +0545");
    }

    #[test]
    fn datetime_display_extreme_offset() {
        // +1200 (e.g. Fiji)
        let dt = DateTime {
            year: 2025,
            month: 1,
            day: 1,
            hour: 0,
            minute: 0,
            second: 0,
            tz_offset_minutes: 720, // +1200
        };
        assert_eq!(dt.to_string(), "2025-01-01 00:00:00 +1200");

        // -1200 (Baker Island)
        let dt_neg = DateTime {
            year: 2025,
            month: 1,
            day: 1,
            hour: 0,
            minute: 0,
            second: 0,
            tz_offset_minutes: -720, // -1200
        };
        assert_eq!(dt_neg.to_string(), "2025-01-01 00:00:00 -1200");
    }

    /// Parsing `<>` must return `Err(InvalidAddress("empty email in angle brackets"))`.
    /// Covers the empty-email guard at L139-142 (RFC 5322 Section 3.4).
    #[test]
    fn address_from_str_empty_angle_brackets_rejected() {
        let result: Result<Address, _> = "<>".parse();
        let err = result.unwrap_err();
        let msg = err.to_string();
        assert!(
            msg.contains("empty email in angle brackets"),
            "expected 'empty email in angle brackets' error, got: {msg}"
        );
    }

    /// Parsing `<user@example.com>` (no display name) must yield `name: None`.
    /// Covers the empty `name_part` branch at L120-121 (RFC 5322 Section 3.4).
    #[test]
    fn address_from_str_angle_brackets_no_name() {
        let addr: Address = "<user@example.com>".parse().unwrap();
        assert_eq!(addr.email, "user@example.com");
        assert!(
            addr.name.is_none(),
            "expected name to be None for bare angle-bracket address, got: {:?}",
            addr.name
        );
    }

    /// Parsing `"" <user@example.com>` (quoted empty display name) must yield `name: None`.
    /// After stripping outer quotes, the name is empty, so it becomes `None` at L129-130
    /// (RFC 5322 Section 3.2.4 — quoted-string, RFC 5322 Section 3.4).
    #[test]
    fn address_from_str_quoted_empty_name_is_none() {
        let addr: Address = "\"\" <user@example.com>".parse().unwrap();
        assert_eq!(addr.email, "user@example.com");
        assert!(
            addr.name.is_none(),
            "expected name to be None for quoted empty name, got: {:?}",
            addr.name
        );
    }

    /// Parsing `"   " <user@example.com>` (whitespace-only prefix before `<`) must
    /// yield `name: None`. The whitespace-only `name_part` is trimmed to empty at L119-121
    /// (RFC 5322 Section 3.4).
    #[test]
    fn address_from_str_whitespace_only_name_is_none() {
        let addr: Address = "   <user@example.com>".parse().unwrap();
        assert_eq!(addr.email, "user@example.com");
        assert!(
            addr.name.is_none(),
            "expected name to be None for whitespace-only prefix, got: {:?}",
            addr.name
        );
    }

    /// Parsing `<user@example.com` (unclosed angle bracket) must fall through to
    /// the bare email path or error, since `rfind('>')` fails or returns a position
    /// before `<`. Covers L116/L145-146 (RFC 5322 Section 3.4).
    #[test]
    fn address_from_str_unclosed_angle_bracket() {
        // The `>` is never found, so the angle-bracket branch is skipped.
        // The input does contain `@`, so it parses as a bare email.
        let result: Result<Address, _> = "<user@example.com".parse();
        // Either it parses as a (malformed) bare email or errors — either is acceptable.
        // It must NOT panic.
        if let Ok(addr) = result {
            // Bare email path was taken; name must be None
            assert!(addr.name.is_none());
            assert!(addr.email.contains("user@example.com"));
        }
        // Err is also acceptable — malformed input rejected
    }

    /// `Display` impl must quote and escape backslash and double-quote in
    /// display names containing RFC 5322 specials.
    /// Covers the `replace('\\', "\\\\").replace('"', "\\\"")` path at L88
    /// (RFC 5322 Section 3.2.4 — quoted-pair).
    #[test]
    fn address_display_name_with_special_chars() {
        let addr = Address {
            name: Some("O'Brien \\test".into()),
            email: "obrien@example.com".into(),
        };
        let displayed = addr.to_string();
        // Backslash is a special char, so the name must be quoted and backslash escaped
        assert!(
            displayed.contains("\\\\"),
            "backslash should be escaped in quoted name, got: {displayed}"
        );
        assert!(
            displayed.starts_with('"'),
            "name with specials should be quoted, got: {displayed}"
        );
        assert!(
            displayed.contains("<obrien@example.com>"),
            "email must appear in angle brackets, got: {displayed}"
        );
    }

    /// `unescape_quoted_string` with a trailing backslash (no following character)
    /// must preserve the backslash rather than dropping it.
    /// Covers the `else` branch at L190-192 (RFC 5322 Section 3.2.4 — quoted-pair).
    #[test]
    fn unescape_trailing_backslash() {
        let result = unescape_quoted_string("hello\\");
        assert_eq!(
            result, "hello\\",
            "trailing backslash with no following char should be preserved"
        );
    }
}