Line editor for interactive editing of text lines/pages - LINEEDIT.BAS

'
' Edit a string until ENTER with LineEdit:
'
Sub Example1
  a$ = "text to edit"
  Do: k = LineEdit(a$): Loop Until k = 13 ' until ENTER
End Sub

'
' Edit a string until ENTER or ESC with ESC to restore the old string value:
'
Sub Example2
  a$ = "text to edit"
  b$ = a$ ' save old string value
  Do: k = LineEdit(a$): Loop Until k = 13 Or k = 27 ' until ENTER or ESC
  If k = 27 Then ' ESC pressed
    Print b$;
    If Len(a$) > Len(b$) Then Print Space$(Len(a$) - Len(b$));
    a$ = b$ ' restore old value on ESC
  EndIf
End Sub

'
' Interactive editing of 10 lines with up/down screen navigation:
'
Sub Example3
  Local a$(10) length 40
  Cls
  Print "Tiny edit | ESC to quit"
  For row = 1 To 10
    Print @(0,12*row) a$(row);Tab(11);"|"
  Next row
  row = 1  ' first row to edit
  cur = 0  ' cursor at begin of the line
  max = 40 ' max size of a$()
  win = 10 ' edit in window of 10 chars
  Do
    Print @(0,12*row); ' place cursor where we want to edit the line
    k = LineEdit(a$(row), cur, -1, max, win) ' -1: get next key press
    If k = 128 Then
      If row > 1 Then row = row - 1  ' UP key: move up
    ElseIf k = 13 Or k = 129 Then
      If row < 10 Then row = row + 1 ' DOWN key: move down
    EndIf
    Print @(0,132) "row:";row;" col:";cur;" key:";k;"  ";
  Loop Until k = 27 ' until ESC
End Sub

'
' Interactive editing with screen navigation while continuously updating the screen with the current time:
'
Sub Example4
  Local a$(10) length 120
  Cls
  Print "         | Editor | ESC to quit"
  For row = 1 To 10
    Print @(0,12*row) a$(row);
  Next row
  row = 1  ' first row to edit
  cur = 0  ' cursor at begin of the line
  max = 120 ' max size of a$()
  win = MM.HRes/6 ' edit in window up to window width
  ' show cursor
  Font 1,,1: Print @(0,12*row) Mid$(a$(row)+" ", 1, 1);Chr$(8);: Font 1,,0
  Do
    Print @(0,0) Time$; ' continuously show the current time
    k = Asc(Inkey$)
    If k Then
      Print @(0,12*row);
      k = LineEdit(a$(row), cur, k, max, win) ' pass in key to edit line
      If k = 128 Then ' UP key: move up
        If row > 1 Then row = row - 1
        Font 1,,1: Print @(0,12*row) Mid$(a$(row)+" ", 1, 1);Chr$(8);: Font 1,,0
        cur = 0
      ElseIf k = 13 Or k = 129 Then ' DOWN key: move down
        If row < 10 Then row = row + 1
        Font 1,,1: Print @(0,12*row) Mid$(a$(row)+" ", 1, 1);Chr$(8);: Font 1,,0
        cur = 0
      EndIf
    EndIf
  Loop Until k = 27 ' until ESC
End Sub

'
' Edit a string of digits, masking key presses to digits
'
Sub Example5
  a$ = "1234"
  Font 1,,1: Print Mid$(a$, 1, 1);: Font 1,,0: Print Mid$(a$, 2);Chr$(13);
  Do
    k = Asc(Inkey$)
    If k Then
      If k < 32 Or k > 126 Or Instr("0123456789", Chr$(k)) Then
        k = LineEdit(a$, cur, k)
      EndIf
    EndIf
  Loop Until k = 13 Or k = 27 ' until ENTER or ESC
End Sub

' LineEdit(a$, [cur [, key [, max [, win ]]]]) edit string a$ at position cur,
' use key parameter (when provided) to make the next edit of a$ and update cur, and
' return new key press, or if key press not provided (zero) keep editing until
' ESC, ENTER or special key such as F1, UP/DOWN etc. where max is the maximum
' string length and win is the "window" size. Use LEFT/RIGHT/HOME/END to
' navigate the line, BACKSPACE/DEL to delete a character.
'
' Supports three editing modes: key=0 (default) edit until ENTER or other
' special key, key=-1 wait for key and make one edit, returning the key value,
' key=X to pass a key press to LineEdit to make one edit, returning the key
' value.
'
' Curser position cur parameter is passed in and updated by LineEdit
'
' Use the max parameter when the string has a maximum length smaller than 255
'
' To edit within a smaller window, use the win parameter
'
Function LineEdit(a$, cur, key, max, win)
  Local x, y, size, from, done
  x = MM.HPos: y = MM.VPos
  If max <= 0 Then max = 255
  If win <= 0 Then win = 255
  size = Len(a$)
  If cur < 0 Then
    cur = 0
  ElseIf cur > size Then
    cur = size
  EndIf
  done = key
  Do
    If key >= 32 And key < 127 Then
      If size < max Then
        a$ = Left$(a$, cur) + Chr$(key) + Mid$(a$, cur + 1)
        cur = cur + 1
        size = size + 1
      EndIf
    ElseIf key = 8 Then
      If cur > 0 Then
        cur = cur - 1
        a$ = Left$(a$, cur) + Mid$(a$, cur + 2)
        size = size - 1
      EndIf
    ElseIf key = 127 Then
      If cur < size Then
        a$ = Left$(a$, cur) + Mid$(a$, cur + 2)
        size = size - 1
      EndIf
    ElseIf key = 130 Then
      If cur > 0 Then cur = cur - 1
    ElseIf key = 131 Then
      If cur < size Then cur = cur + 1
    ElseIf key = 134 Then
      cur = 0
    ElseIf key = 135 Then
      cur = size
    ElseIf key > 0 Then
      ' done editing, so print a clean line
      Print @(x,y) Left$(a$, win);
      ' remove the cursor from the end of the line
      If cur = size And size < win Then Print " ";
      Exit
    EndIf
    ' cursor cannot move beyond string max length
    If cur >= max Then cur = max - 1
    ' cursor is offset from window start
    If cur >= win Then from = cur - win + 2 Else from = 1
    If cur = size Then
      ' print the line constrained to the window size
      Print @(x,y) Mid$(a$, from);
      ' put the cursor at the end
      Font 1,,1: Print " ";: Font 1,,0
      ' BACKSPACE may require removing the cursor from the end of the line
      If key = 8 Then
        If cur + 1 < win And size < win Then Print " ";
      EndIf
    Else
      ' print the line constrained to window size
      Print @(x,y) Mid$(a$, from, cur - from + 1);
      ' invert character at the cursor
      Font 1,,1: Print Mid$(a$, cur + 1, 1);: Font 1,,0
      ' print the rest of the line
      Print Mid$(a$, cur + 2, win - cur + from - 2);
      If cur < win And size < win Then Print " ";
    EndIf
    ' if this is a non-blocking call then exit
    If done > 0 Then Exit
    ' wait on key press
    Do: key = Asc(Inkey$): Loop Until key
    done = -done
  Loop
  ' move cursor back to the start of the line before returning
  Print @(x,y);
  LineEdit = key
End Function