use regex::Regex;
use crate::config::Config;
use crate::connect::ImapSession;
use crate::{connect, Email};

const MAX_FETCH: u32 = 50;

/// Refresh inbox using NOOP + fetch. Reconnects on error.
pub(crate) fn refresh(
    session: &mut Option<ImapSession>,
    config: &Config,
) -> Result<Vec<Email>, String> {
    // If we have a session, try NOOP to keep alive / detect changes
    if let Some(s) = session.as_mut() {
        if s.noop().is_ok() {
            return fetch_inbox(s);
        }
    }

    // Session is dead or missing — reconnect
    *session = None;
    let mut new_session = connect::connect(config)?;
    let result = fetch_inbox(&mut new_session);
    *session = Some(new_session);
    result
}


fn fetch_range(exists: u32) -> String {
    let start = exists.saturating_sub(MAX_FETCH - 1).max(1);
    format!("{}:{}", start, exists)
}

fn fetch_inbox(session: &mut ImapSession) -> Result<Vec<Email>, String> {
    match session {
        ImapSession::Plain(s) => {
            let mailbox = s.select("INBOX").map_err(|e| e.to_string())?;
            if mailbox.exists == 0 {
                return Ok(Vec::new());
            }
            let range = fetch_range(mailbox.exists);
            let messages = s
                .fetch(range, "BODY.PEEK[HEADER.FIELDS (SUBJECT FROM DATE)]")
                .map_err(|e| e.to_string())?;
            let mut emails = parse_emails(&messages);
            emails.reverse();
            Ok(emails)
        }
        ImapSession::Tls(s) => {
            let mailbox = s.select("INBOX").map_err(|e| e.to_string())?;
            if mailbox.exists == 0 {
                return Ok(Vec::new());
            }
            let range = fetch_range(mailbox.exists);
            let messages = s
                .fetch(range, "BODY.PEEK[HEADER.FIELDS (SUBJECT FROM DATE)]")
                .map_err(|e| e.to_string())?;
            let mut emails = parse_emails(&messages);
            emails.reverse();
            Ok(emails)
        }
    }
}

fn parse_emails(fetches: &[imap::types::Fetch]) -> Vec<Email> {
    let mut emails = Vec::new();
    for message in fetches {
        if let Some(body) = message.header() {
            let header = String::from_utf8_lossy(body);
            let mut subject = String::new();
            let mut from = String::new();
            let mut date = String::new();

            for line in header.lines() {
                if let Some(val) = line.strip_prefix("Subject: ") {
                    subject = val.to_string();
                } else if let Some(val) = line.strip_prefix("From: ") {
                    from = val.to_string();
                } else if let Some(val) = line.strip_prefix("Date: ") {
                    date = Regex::new(r#" \(...\)$"#).unwrap().replace_all(val, "").to_string();
                }
            }

            emails.push(Email { subject, from, date });
        }
    }
    emails
}