read-line.c

/*
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>



#define MAX_BUFFER_LINE 2048
#define BACKSPACE 8
#define ESC 27

extern int debug_mode;

int line_length;
char line_buffer[MAX_BUFFER_LINE];

int history_index = 0;
int history_access = 0;
char* history[30];
int history_length = sizeof(history)/sizeof(char *);

int position = 0;
int key_debug=0;

void read_line_print_usage()
{
  char * usage = "\n"
    "\tctrl-?   :    Print usage\n"
    "\tBackspace :   Deletes last character\n"
    "\tup arrow   :  See last command in the history\n"
    "\tleft arrow  key : Move the cursor to the left\n"
    "\tright arrow key: Move the cursor to the right\n"
    "\tdelete key(ctrl-D): delete current character.\n"
    "\tbackspace (ctrl-H)key: Removes the character at the position before the cursor.\n"
    "\tHome key (or ctrl-A): The cursor moves to the beginning of the line\n"
    "\tEnd key (or ctrl-E): The cursor moves to the end of the line\n";
  write(1, usage, strlen(usage));
}

void clear_line() //clears current console line
{
    if(line_length > 0)
    {
    	int i = 0;
        char ch;
        // Print backspaces
        if(debug_mode)
        	fprintf(stderr, "position before clear=%d\n", position);
        i = position;       
        while(i--) 
        {
            ch = BACKSPACE;
            write(1,&ch,1);
        }
        // Print spaces on top
        for (i =0; i < line_length; i++) 
        {
            ch = ' ';
            write(1,&ch,1);
        }
        // Print backspaces
        for (i =0; i < line_length; i++) 
        {
            ch = BACKSPACE;
            write(1,&ch,1);
        }
        line_length = 0;
        position = 0;
    }    
}
void delete_and_shift(int isBackspace) //0 = del, 1 = backspace
{
	int i, k; 
	char ch;          
    if( position >= 0 && position < line_length)
    {
    	int old_len = line_length, old_pos = position;
        if(isBackspace && old_pos > 0)
            old_pos--;

        clear_line(); //will set line_length and position to 0
        // modify line_buffer
        char new_line[MAX_BUFFER_LINE] = {0};
        
        if(key_debug | debug_mode)
			fprintf(stderr, "position=%d\n", position);
			
        for(i = 0, k = 0; i < old_len; i++, k++)
		{
		 	if( i == old_pos)
		 		new_line[k] = line_buffer[++i];
		 	else
		 		new_line[k] = line_buffer[i];
		}
		line_length = strlen(new_line);
		position = line_length;
		
		if(debug_mode)
			fprintf(stderr, "line_buff=%s\n", line_buffer);
		
		memset(line_buffer,0,sizeof(line_buffer));
		strncpy(line_buffer, new_line, line_length);
		
		if(debug_mode)
		{
			fprintf(stderr, "new_line=%s\n", new_line);
			fprintf(stderr, "line_buffer=%s\n", line_buffer);			
		}
			
		if(key_debug |debug_mode)
			fprintf(stderr, "position=%d\n", position);	
			
        write(1, line_buffer, line_length);
        // reset cursor
        i = position - old_pos;
        while(i--)
        {
            ch = BACKSPACE;
            write(1, &ch, 1);
            position--;
        }
    }
}
char * read_line() 
{
    int itr;
    if(debug_mode)
		for(itr = history_index; itr > 0; itr--)
      		fprintf(stderr, "\nhistory[%d]=%s", itr, history[itr]);

    // Set terminal in raw mode
    tty_raw_mode();
    line_length = 0;
    while (1) 
    {
      // Read one character in raw mode.
        char ch;
        read(0, &ch, 1);
        if (ch>=32 && ch != ESC && ch < 127 ) 
        {
            // It is a printable character. display it back
            write(1,&ch,1);
            // If max number of character reached return.
            if (line_length==MAX_BUFFER_LINE-2) 
              break; 
            // add char to buffer.
            line_buffer[line_length]=ch;
            line_length++;
            position++;
        }
        else if (ch==10) 
        {
            // <Enter> was typed. Return line. add current line to history
            if(line_length > 0)
            {
                history[history_index] = strdup(line_buffer);
                if(history_index == 29)
                    history_index = 0;
                else
                    history_index++;
                
                if(debug_mode)
                    for(itr = 0; itr < history_index; itr++)
                  fprintf(stderr, "\nhistory[%d]=%s\n", itr, history[itr]);
            }  
            write(1,&ch,1);
            break;
        }
        else if (ch == 31) 
        {
            // ctrl-?
            read_line_print_usage();
            line_buffer[0]=0;
            break;
        }
        else if (ch == BACKSPACE || ch==127) 
        {
            if(line_length>0 && position> 0)
            {
                // <backspace> or ctrl-H was typed. Remove previous character read.
                // Go back one character
                if(position == line_length)
                {
                    ch = BACKSPACE;
                    write(1,&ch,1);
                    // Write a space to erase the last character read
                    ch = ' ';
                    write(1,&ch,1);
                    // Go back one character
                    ch = BACKSPACE;
                    write(1,&ch,1);
                    // Remove one character from buffer
                    line_length--;
                    position--;
                }
                else
                    delete_and_shift(1);
            }            
        }
        else if(ch == 4)
        {
            /* ctrl-D:  Removes the character at the cursor. 
               The characters in the right side are shifted to the left. */
            delete_and_shift(0);                         
        }
        else if(ch == 1)
        {
            /*Home key (or ctrl-A): The cursor moves to the beginning of the line */
            if(position != 0 && position < line_length+1 && position > 0)
            {
                while(position != 0 )
                {
                    ch = BACKSPACE;
                    write(1, &ch, 1);
                    position--;
                }
            } 
        }
        else if(ch == 12)
        {
            /* Clear line (or ctrl-l): clear current line */
            clear_line();
        }
        else if(ch==5)
        {
            /*End key (or ctrl-E): The cursor moves to the end of the line */
            if( position < line_length && position >= 0)
            {
                while(position != line_length )
                {
                    ch = line_buffer[position];
                    write(1, &ch, 1);
                    position++;
                }
            }  
        }
        else if (ch==ESC)  // Esc. Read two chars more
        {
            char ch1; 
            char ch2;
            read(0, &ch1, 1);
            read(0, &ch2, 1);
            if (ch1==91 && ch2==65) // up
            {
                // Print previous line in history.
                // Erase old line
                clear_line();	
                // Copy line from history
                if(history_access > history_index)
                    history_access = history_index-1;
                else if(history_access < 0)
                    history_access = 0;
                if( history_access >= 0 &&  history[history_access] )
                {
                    memset(line_buffer,0,sizeof(line_buffer));
                    strcpy(line_buffer, history[history_access]);
                    line_length = strlen(line_buffer);
                    position= line_length-1;
                    history_access--;
                    if(debug_mode)
                        fprintf(stderr, "history_index after <up>=%d\n", history_index);
                    // echo line
                    write(1, line_buffer, line_length);
                }               
            }
            else if(ch1==91 && ch2==66) //down 
            {
                // Shows the next command in the history list
                // Print next line in history.
                // Erase old line
                clear_line();
                // Copy line from history
                if(history_access > history_index)
                    history_access = history_index-1;
                else if(history_access < 0)
                    history_access = 0;
               if(history_access >= 0 && history[history_access])
                {
                    memset(line_buffer,0,sizeof(line_buffer));
                    strcpy(line_buffer, history[history_access]);
                    line_length = strlen(line_buffer);
                    position= line_length-1;
                    history_access++;
                    if(debug_mode)
                        fprintf(stderr, "history_index=%d\n", history_index);
                    write(1, line_buffer, line_length);
                }
                    
            } 
            else if(ch1==91 && ch2==67) //right 
            {
                /* Move the cursor to the right and allow insertion at 
                that position. If the cursor is at the end  of the line it does nothing. */
                if(position >= 0 && position < line_length && line_length > 0 )
                {
                    ch= line_buffer[position];
                    write(1, &ch, 1);
                    position++;
                }
            } 
            else if(ch1==91 && ch2==68) //left 
            {
                /* Move the cursor to the left and allow insertion at that 
                position. If the cursor is at the beginning of the line it does nothing. */
                if(position > 0 && position <= line_length && line_length > 0)
                {
                    ch=BACKSPACE;
                    write(1, &ch, 1);
                    position--;
                } 
            }
            else if(ch1==91 && ch2==52) // <end>
            {
                //read char because end is ESC+91+52+126
                read(0, &ch1, 1);
                /* end key */
                if( position < line_length && position >= 0)
                {
                    while(position != line_length )
                    {
                        ch = line_buffer[position];
                        write(1, &ch, 1);
                        position++;
                    }
                }  
            }
            else if(ch1==91 && ch2==51) // <del>
            {
                //read char because del is ESC+91+51+126
                read(0, &ch1, 1);
                /* del key */   
                delete_and_shift(0);
            }
            else if(ch1==91 && ch2==49) // <HOME>
            {
                //read char because home is ESC+91+49+126
                read(0, &ch1, 1);
                /* home key */
                if(position > 0 && position <= line_length )
                {
                    while(position != 0 )
                    {
                        ch = BACKSPACE;
                        write(1, &ch, 1);
                        position--;
                    }
                }        
            }  
        }
    }
    // Add eol and null char at the end of string
    if(line_length < 0)
        return "";
    line_buffer[line_length]=10;
    line_length++;
    line_buffer[line_length]=0; 
    position = 0;
    return line_buffer;
}