/* vim.c - a small vi/vim-style screen editor for the Commodore 64
 *
 * Core half of the program: text buffer, cursor motion, key handling
 * and saving. Drawing lives in vscreen.c because Power C's compiler
 * reports "program too big" when the whole editor is one unit. The two
 * halves share functions only - every piece of state stays private to
 * this file and is handed to draw() as arguments - because sharing
 * variables across Power C object files proved unreliable.
 *
 * Modal editing, like vi:
 *
 *   COMMAND mode            INSERT mode
 *     i   insert here         any key   type text
 *     a   append after char   RETURN    split the line
 *     o   open line below     DEL       backspace
 *     O   open line above     RUN/STOP  back to COMMAND mode
 *     x   delete character    cursor keys move
 *     h j k l or cursor keys  CLR/HOME  start of line
 *     0   start of line
 *     $   end of line
 *     :   command line
 *
 *   : commands
 *     :w      write "notes" to disk (SEQ file, drive 8)
 *     :wq     write and quit
 *     :q      quit
 *
 * Special C characters, on the same keys the Power C manual gives for ced:
 *
 *   {   SHIFT +        }   SHIFT -         \   English pound key
 *   ~   C= (logo) P     _   C= (logo) @     |   C= (logo) *
 *
 * The Kernal already produces the codes Power C expects for these
 * ($DB, $DD, $5C, $AF, $A4, $DF - read from the key tables at $EB81),
 * so insert mode only has to accept them. The character ROM has no
 * brace or bar glyphs, so on screen they appear as the nearest glyph.
 *
 * ESCAPE is the C64 RUN/STOP key, which the Kernal reports in the
 * zero-page STOP flag at $91.
 *
 * The text buffer holds 2000 bytes with 13 ($0D) as the line break.
 * Keys come from the Kernal keyboard buffer at $0277, count at $c6.
 *
 * Build with build.bat in this folder:
 *
 *   cc vim.c        ->  vim.o
 *   cc vscreen.c    ->  vscreen.o
 *   link -s
 *   > vim.o
 *   > vscreen.o
 *   > ^             (stdlib.l + syslib.l)
 *   >
 *   output file name: vim
 *
 * Then run with:  x64sc -autostart "vim.d81:vim"
 * or from BASIC:  LOAD"VIM",8,1 : RUN
 *
 * Note: this Power C build rejects both $7C and $DC as "illegal
 * character" for the | operator, so nested tests are used instead of ||.
 */

#include <stdio.h>

static char text[2000];         /* document, 13 = line break */
static int  tlen;               /* bytes in use */
static int  pos;                /* cursor, byte offset into text */
static int  mode;               /* 0 command, 1 insert, 2 : prompt */
static char fname[17];          /* file name used by :w */
static char cmd[9];             /* text after the ':' */
static int  cmdlen;
static int  quit;
static int  msgcode;            /* message for draw(): 0 none, 1-4 */

static char *defnam = "notes";

/* ---------- provided by vscreen.c ---------- */

int draw();
int clrscr();

/* ---------- buffer helpers ---------- */

static lstart(n)                /* offset of the first byte of line n */
int n;
{
    int i;
    int c;

    if (n <= 0) return 0;
    c = 0;
    i = 0;
    while (i < tlen) {
        if (text[i] == 13) {
            c = c + 1;
            if (c == n) return i + 1;
        }
        i = i + 1;
    }
    return tlen;
}

static lcount()                 /* number of line breaks */
{
    int i;
    int c;

    c = 0;
    for (i = 0; i < tlen; i++)
        if (text[i] == 13) c = c + 1;
    return c;
}

static lnof()                   /* line holding the cursor */
{
    int i;
    int c;

    c = 0;
    for (i = 0; i < pos && i < tlen; i++)
        if (text[i] == 13) c = c + 1;
    return c;
}

static intend(o)                /* offset of the line end */
int o;
{
    int e;

    e = o;
    while (e < tlen && text[e] != 13) e = e + 1;
    return e;
}

static inschr(ch)
int ch;
{
    int i;

    if (tlen >= 1999) {
        msgcode = 1;
        return;
    }
    for (i = tlen; i > pos; i--)
        text[i] = text[i - 1];
    text[pos] = ch;
    tlen = tlen + 1;
    pos = pos + 1;
}

static delat()
{
    int i;

    if (pos >= tlen) return;
    for (i = pos; i < tlen - 1; i++)
        text[i] = text[i + 1];
    tlen = tlen - 1;
}

static backsp()
{
    if (pos <= 0) return;
    pos = pos - 1;
    delat();
}

/* ---------- cursor motion ---------- */

static movleft()
{
    if (pos > 0) pos = pos - 1;
}

static movright()
{
    if (pos < tlen) pos = pos + 1;
}

static movdown()
{
    int ln;
    int cs;
    int o;
    int e;

    ln = lnof();
    if (ln + 1 > lcount()) return;
    cs = pos - lstart(ln);
    o = lstart(ln + 1);
    e = intend(o);
    pos = o + cs;
    if (pos > e) pos = e;
}

static movup()
{
    int ln;
    int cs;
    int o;
    int e;

    ln = lnof();
    if (ln <= 0) return;
    cs = pos - lstart(ln);
    o = lstart(ln - 1);
    e = intend(o);
    pos = o + cs;
    if (pos > e) pos = e;
}

static linehome()
{
    pos = lstart(lnof());
}

static lineend()
{
    pos = intend(lstart(lnof()));
}

/* ---------- saving ---------- */

static savfil()
{
    FILE *f;
    int i;

    f = fopen(fname, "w");
    if (!f) {
        msgcode = 2;
        return;
    }
    if (ferror(f)) {
        msgcode = 2;
        fclose(f);
        return;
    }
    for (i = 0; i < tlen; i++) fputc(text[i], f);
    fclose(f);
    msgcode = 3;
}

/* ---------- : command line ---------- */

static docmd()
{
    if (cmdlen == 0) return;
    if (cmd[0] == 'w') {
        if (cmdlen > 1 && cmd[1] == 'q') {
            savfil();
            quit = 1;
            return;
        }
        savfil();
        return;
    }
    if (cmd[0] == 'q') {
        quit = 1;
        return;
    }
    msgcode = 4;
}

/* ---------- key handlers ---------- */

static insk(k)
int k;
{
    if (k == 3) {                       /* ESC: leave insert mode */
        mode = 0;
        if (pos > 0) pos = pos - 1;
        return;
    }
    if (k == 13) { inschr(13); return; }
    if (k == 20) { backsp(); return; }
    if (k == 157) { movleft(); return; }
    if (k == 29)  { movright(); return; }
    if (k == 145) { movup(); return; }
    if (k == 17)  { movdown(); return; }
    if (k == 19)  { linehome(); return; }
    if (k >= 32 && k < 128) { inschr(k); return; }
    if (k == 219) { inschr(k); return; }   /* SHIFT + : { */
    if (k == 221) { inschr(k); return; }   /* SHIFT - : } */
    if (k == 223) { inschr(k); return; }   /* logo  * : | */
    if (k == 175) { inschr(k); return; }   /* logo  P : ~ */
    if (k == 164) { inschr(k); return; }   /* logo  @ : _ */
}

static cmdk(k)
int k;
{
    if (k >= 65 && k <= 90) k = k + 32;     /* letters arrive as PETSCII $41-$5A */
    if (k == ':') {
        mode = 2;
        cmdlen = 0;
        cmd[0] = 0;
        return;
    }
    if (k == 'i') { mode = 1; return; }
    if (k == 'a') {
        if (pos < tlen && text[pos] != 13) pos = pos + 1;
        mode = 1;
        return;
    }
    if (k == 'o') {
        pos = intend(lstart(lnof()));
        inschr(13);
        mode = 1;
        return;
    }
    if (k == 'O') {
        pos = lstart(lnof());
        inschr(13);
        pos = pos - 1;
        mode = 1;
        return;
    }
    if (k == 'x') { delat(); return; }
    if (k == 'h') { movleft(); return; }
    if (k == 157) { movleft(); return; }
    if (k == 'l') { movright(); return; }
    if (k == 29)  { movright(); return; }
    if (k == 'j') { movdown(); return; }
    if (k == 17)  { movdown(); return; }
    if (k == 'k') { movup(); return; }
    if (k == 145) { movup(); return; }
    if (k == '0') { linehome(); return; }
    if (k == 19)  { linehome(); return; }
    if (k == '$') { lineend(); return; }
}

/* ---------- keyboard ---------- */

static getkey()                         /* one byte from the Kernal keyboard
                                           buffer, $0277, count at $c6 */
{
    char *cnt;
    char *buf;
    int i;
    int k;

    cnt = (char *) 198;
    buf = (char *) 631;
    if (*cnt == 0) return 0;
    if (*cnt > 10) {
        *cnt = 0;
        return 0;
    }
    k = buf[0];
    for (i = 0; i < 9; i++) buf[i] = buf[i + 1];
    *cnt = *cnt - 1;
    return k;
}

static waitkey()
{
    char *stop;
    int k;

    for (;;) {
        stop = (char *) 145;            /* $91: RUN/STOP flag */
        if (*stop) {
            *stop = 0;
            return 3;
        }
        k = getkey();
        if (k) return k;
    }
}

/* ---------- main loop ---------- */

main()
{
    int k;
    int i;

    tlen = 0;
    pos = 0;
    mode = 0;
    cmdlen = 0;
    quit = 0;
    msgcode = 0;

    i = 0;
    while (defnam[i]) {
        fname[i] = defnam[i];
        i = i + 1;
    }
    fname[i] = 0;

    while (!quit) {
        draw(text, tlen, pos, mode, fname, cmd, cmdlen, msgcode);
        msgcode = 0;
        k = waitkey();
        if (mode == 2) {
            if (k == 13) {
                mode = 0;
                docmd();
            }
            else if (k == 20) {
                if (cmdlen > 0) cmdlen = cmdlen - 1;
            }
            else if (k >= 32 && cmdlen < 8) {
                if (k >= 65 && k <= 90) k = k + 32;
                cmd[cmdlen] = k;
                cmdlen = cmdlen + 1;
            }
            continue;
        }
        if (mode == 1) {
            insk(k);
            continue;
        }
        cmdk(k);
    }

    clrscr();
    printf("bye\n");
}