/// T.30 session state machine for Group 3 fax.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum T30State {
    Idle,
    Dialing,
    HandshakeTransmitting,   // Phase B - sending DIS/DCS
    HandshakeReceiving,      // Phase B - receiving DIS/DCS
    DcsSent,                 // DCS has been sent, waiting for CFR
    CfrReceived,             // Received CFR, ready to send pages
    PageTransmitting,        // Phase C - sending page data
    PageReceiving,
    PostPageHandshake,        // Phase D - MCF, EOP, MPS
    Disconnecting,            // Phase E - DCN
    Completed,
    Error,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum T30Event {
    Connected,
    DisReceived,
    DisSent,
    DcsReceived,
    DcsSent,
    TcfSent,
    TcfReceived,
    CfrReceived,
    CfrSent,
    PageSent,
    PageReceived,
    McfReceived,
    McfSent,
    EopReceived,
    EopSent,
    DcnReceived,
    DcnSent,
    Timeout,
    Error,
    Retrain,
}

pub struct T30Session {
    state: T30State,
    retry_count: u8,
    max_retries: u8,
}

impl T30Session {
    pub fn new() -> Self {
        Self {
            state: T30State::Idle,
            retry_count: 0,
            max_retries: 3,
        }
    }

    pub fn state(&self) -> T30State {
        self.state
    }

    pub fn start_receive(&mut self) {
        self.state = T30State::HandshakeReceiving;
    }

    pub fn transition(&mut self, event: T30Event) {
        match (self.state, event) {
            // Send flow
            (T30State::Idle, T30Event::Connected) => {
                // Default to transmitting; caller can override with start_receive()
                self.state = T30State::HandshakeTransmitting;
            }
            (T30State::HandshakeTransmitting, T30Event::DisReceived) => {
                self.state = T30State::DcsSent;
            }
            (T30State::DcsSent, T30Event::CfrReceived) => self.state = T30State::PageTransmitting,
            (T30State::PageTransmitting, T30Event::PageSent) => self.state = T30State::PostPageHandshake,
            (T30State::PostPageHandshake, T30Event::McfReceived) => self.state = T30State::Disconnecting,
            (T30State::PostPageHandshake, T30Event::EopReceived) => self.state = T30State::Disconnecting,
            (T30State::Disconnecting, T30Event::DcnSent) => self.state = T30State::Completed,

            // Receive flow
            (T30State::HandshakeReceiving, T30Event::DcsReceived) => self.state = T30State::PageReceiving,
            (T30State::PageReceiving, T30Event::PageReceived) => self.state = T30State::PostPageHandshake,
            (T30State::PostPageHandshake, T30Event::McfSent) => self.state = T30State::Disconnecting,
            (T30State::Disconnecting, T30Event::DcnReceived) => self.state = T30State::Completed,

            // Error handling
            (_, T30Event::Timeout) | (_, T30Event::Error) => {
                if self.retry_count < self.max_retries {
                    self.retry_count += 1;
                    // Stay in same state for retry
                } else {
                    self.state = T30State::Error;
                }
            }

            _ => {
                // Unexpected transition - log and set error
                self.state = T30State::Error;
            }
        }
    }
}