/*
 * RS232 IRQ handler
 *
 * portSet is a parameter passed by the assembly ISR wrapper: It's set to 1 for ports
 * COM2 and 4, and set to 0 for COM1 and 3.
 */
void rs232_irq_handler(uint32_t portSet) {
    uint16_t port_addr[2][2] = {
        {rs232_to_io_map[0], rs232_to_io_map[2]},
        {rs232_to_io_map[1], rs232_to_io_map[3]}
    };

    sys_pic_irq_eoi((portSet == 0) ? 3 : 4); // send int ack to PIC

    // Read IRQ registers
    uint8_t irq_port1 = io_inb(port_addr[portSet & 0x01][0]+2);
    uint8_t irq_port2 = io_inb(port_addr[portSet & 0x01][1]+2);

process_irq: ; // gcc is stupid
    // Determine which port triggered it
    uint8_t triggered_port = 0;
    if((irq_port2 & 0x01)) triggered_port = 0;
    else if((irq_port1 & 0x01)) triggered_port = 1;
    else return; // none of the two ports wants to ack the interrupt

    // Shift the entire value right one bit, and get low 3 bits only
    // We could use the high two bits to determine if FIFOs are on, but without
    // them we wouldn't have a working driver
    uint8_t irq = (((triggered_port == 0) ? irq_port1 : irq_port2) >> 0x01) & 0x07;
    uint16_t port = port_addr[portSet & 0x03][triggered_port];

    terminal_write_string("IRQ : 0x");
    terminal_write_byte(irq);

    // Get the struct
    rs232_buffer_t *port_info = &rs232_buffer_ptrs[portSet + (triggered_port << 1)];

    // Service appropriate IRQ
    switch(irq) {
        case 0: { // Modem bits have changed (Read MSR to service)
            port_info->delta_flags = io_inb(port + 6);
            break;
        }

        case 1: { // Transmitter FIFO empty (Write to THR/read IIR)
            // Check if we have any data in the TX buffer
            if(port_info->tx_buf_off == 0) break;

            int offset = port_info->tx_buf_off;
            uint8_t *data_read = port_info->tx_buf;

            // Write 14 bytes if more than 14 are pending
            int num_bytes_write = (offset > 14) ? 14 : offset;

            for(int i = 0; i < num_bytes_write; i++) {
                io_outb(port, *data_read++);
            }

            // Shift buffer
            rs232_shift_buffer(port_info, true, num_bytes_write);

            break;
        }

        case 2: { // RX FIFO threshold (14 bytes) reached (Read RBR to service)

            break;
        }

        case 3: { // Status changed (Read LSR to service)
            port_info->line_status = io_inb(port + 5);
            break;
        }

        case 6: { // No RX act for 4 words, but data avail (Read RBR to service)

            break;
        }

        // well son you dun fucked up good if you get here
        default:
            PANIC("Got unrecognised RS232 interrupt");
            break;
    }

    // Re-read the IRQ states for both ports
    irq_port1 = io_inb(port_addr[portSet & 0x01][0]+2);
    irq_port2 = io_inb(port_addr[portSet & 0x01][1]+2);

    // If any of them do NOT have bit 0 clear, process IRQ again
    if(!(irq_port1 & 0x01)) goto process_irq;
    if(!(irq_port2 & 0x01)) goto process_irq;
}