/*
 * Copyright (C) 1984-2012  Mark Nudelman
 * Modified for use with illumos by Garrett D'Amore.
 * Copyright 2014 Garrett D'Amore <garrett@damore.org>
 *
 * You may distribute under the terms of either the GNU General Public
 * License or the Less License, as specified in the README file.
 *
 * For more information, see the README file.
 */

/*
 * Low level character input from the input file.
 * We use these special purpose routines which optimize moving
 * both forward and backward from the current read pointer.
 */

#include <sys/stat.h>

#include "less.h"

extern dev_t curr_dev;
extern ino_t curr_ino;
extern int less_is_more;

typedef off_t BLOCKNUM;

int ignore_eoi;

/*
 * Pool of buffers holding the most recently used blocks of the input file.
 * The buffer pool is kept as a doubly-linked circular list,
 * in order from most- to least-recently used.
 * The circular list is anchored by the file state "thisfile".
 */
struct bufnode {
        struct bufnode *next, *prev;
        struct bufnode *hnext, *hprev;
};

#define LBUFSIZE        8192
struct buf {
        struct bufnode node;
        BLOCKNUM block;
        unsigned int datasize;
        unsigned char data[LBUFSIZE];
};
#define bufnode_buf(bn)  ((struct buf *)bn)

/*
 * The file state is maintained in a filestate structure.
 * A pointer to the filestate is kept in the ifile structure.
 */
#define BUFHASH_SIZE    64
struct filestate {
        struct bufnode buflist;
        struct bufnode hashtbl[BUFHASH_SIZE];
        int file;
        int flags;
        off_t fpos;
        int nbufs;
        BLOCKNUM block;
        unsigned int offset;
        off_t fsize;
};

#define ch_bufhead      thisfile->buflist.next
#define ch_buftail      thisfile->buflist.prev
#define ch_nbufs        thisfile->nbufs
#define ch_block        thisfile->block
#define ch_offset       thisfile->offset
#define ch_fpos         thisfile->fpos
#define ch_fsize        thisfile->fsize
#define ch_flags        thisfile->flags
#define ch_file         thisfile->file

#define END_OF_CHAIN    (&thisfile->buflist)
#define END_OF_HCHAIN(h) (&thisfile->hashtbl[h])
#define BUFHASH(blk)    ((blk) & (BUFHASH_SIZE-1))

/*
 * Macros to manipulate the list of buffers in thisfile->buflist.
 */
#define FOR_BUFS(bn) \
        for ((bn) = ch_bufhead; (bn) != END_OF_CHAIN; (bn) = (bn)->next)

#define BUF_RM(bn) \
        (bn)->next->prev = (bn)->prev; \
        (bn)->prev->next = (bn)->next;

#define BUF_INS_HEAD(bn) \
        (bn)->next = ch_bufhead; \
        (bn)->prev = END_OF_CHAIN; \
        ch_bufhead->prev = (bn); \
        ch_bufhead = (bn);

#define BUF_INS_TAIL(bn) \
        (bn)->next = END_OF_CHAIN; \
        (bn)->prev = ch_buftail; \
        ch_buftail->next = (bn); \
        ch_buftail = (bn);

/*
 * Macros to manipulate the list of buffers in thisfile->hashtbl[n].
 */
#define FOR_BUFS_IN_CHAIN(h, bn) \
        for ((bn) = thisfile->hashtbl[h].hnext; \
            (bn) != END_OF_HCHAIN(h); (bn) = (bn)->hnext)

#define BUF_HASH_RM(bn) \
        (bn)->hnext->hprev = (bn)->hprev; \
        (bn)->hprev->hnext = (bn)->hnext;

#define BUF_HASH_INS(bn, h) \
        (bn)->hnext = thisfile->hashtbl[h].hnext; \
        (bn)->hprev = END_OF_HCHAIN(h); \
        thisfile->hashtbl[h].hnext->hprev = (bn); \
        thisfile->hashtbl[h].hnext = (bn);

static struct filestate *thisfile;
static int ch_ungotchar = -1;
static int maxbufs = -1;

extern int autobuf;
extern int secure;
extern int screen_trashed;
extern int follow_mode;
extern IFILE curr_ifile;
extern int logfile;
extern char *namelogfile;

static int ch_addbuf(void);


/*
 * Get the character pointed to by the read pointer.
 */
int
ch_get(void)
{
        struct buf *bp;
        struct bufnode *bn;
        int n;
        int slept;
        int h;
        off_t pos;
        off_t len;

        if (thisfile == NULL)
                return (EOI);

        /*
         * Quick check for the common case where
         * the desired char is in the head buffer.
         */
        if (ch_bufhead != END_OF_CHAIN) {
                bp = bufnode_buf(ch_bufhead);
                if (ch_block == bp->block && ch_offset < bp->datasize)
                        return (bp->data[ch_offset]);
        }

        slept = FALSE;

        /*
         * Look for a buffer holding the desired block.
         */
        h = BUFHASH(ch_block);
        FOR_BUFS_IN_CHAIN(h, bn) {
                bp = bufnode_buf(bn);
                if (bp->block == ch_block) {
                        if (ch_offset >= bp->datasize)
                                /*
                                 * Need more data in this buffer.
                                 */
                                break;
                        goto found;
                }
        }
        if (bn == END_OF_HCHAIN(h)) {
                /*
                 * Block is not in a buffer.
                 * Take the least recently used buffer
                 * and read the desired block into it.
                 * If the LRU buffer has data in it,
                 * then maybe allocate a new buffer.
                 */
                if (ch_buftail == END_OF_CHAIN ||
                    bufnode_buf(ch_buftail)->block != -1) {
                        /*
                         * There is no empty buffer to use.
                         * Allocate a new buffer if:
                         * 1. We can't seek on this file and -b is not in
                         *    effect; or
                         * 2. We haven't allocated the max buffers for this
                         *    file yet.
                         */
                        if ((autobuf && !(ch_flags & CH_CANSEEK)) ||
                            (maxbufs < 0 || ch_nbufs < maxbufs))
                                if (ch_addbuf())
                                        /*
                                         * Allocation failed: turn off autobuf.
                                         */
                                        autobuf = OPT_OFF;
                }
                bn = ch_buftail;
                bp = bufnode_buf(bn);
                BUF_HASH_RM(bn); /* Remove from old hash chain. */
                bp->block = ch_block;
                bp->datasize = 0;
                BUF_HASH_INS(bn, h); /* Insert into new hash chain. */
        }

read_more:
        pos = (ch_block * LBUFSIZE) + bp->datasize;
        if ((len = ch_length()) != -1 && pos >= len)
                /*
                 * At end of file.
                 */
                return (EOI);

        if (pos != ch_fpos) {
                /*
                 * Not at the correct position: must seek.
                 * If input is a pipe, we're in trouble (can't seek on a pipe).
                 * Some data has been lost: just return "?".
                 */
                if (!(ch_flags & CH_CANSEEK))
                        return ('?');
                if (lseek(ch_file, (off_t)pos, SEEK_SET) == (off_t)-1) {
                        error("seek error", NULL);
                        clear_eol();
                        return (EOI);
                }
                ch_fpos = pos;
        }

        /*
         * Read the block.
         * If we read less than a full block, that's ok.
         * We use partial block and pick up the rest next time.
         */
        if (ch_ungotchar != -1) {
                bp->data[bp->datasize] = (unsigned char)ch_ungotchar;
                n = 1;
                ch_ungotchar = -1;
        } else {
                n = iread(ch_file, &bp->data[bp->datasize],
                    (unsigned int)(LBUFSIZE - bp->datasize));
        }

        if (n == READ_INTR)
                return (EOI);
        if (n < 0) {
                error("read error", NULL);
                clear_eol();
                n = 0;
        }

        /*
         * If we have a log file, write the new data to it.
         */
        if (!secure && logfile >= 0 && n > 0)
                (void) write(logfile, (char *)&bp->data[bp->datasize], n);

        ch_fpos += n;
        bp->datasize += n;

        /*
         * If we have read to end of file, set ch_fsize to indicate
         * the position of the end of file.
         */
        if (n == 0) {
                ch_fsize = pos;
                if (ignore_eoi) {
                        /*
                         * We are ignoring EOF.
                         * Wait a while, then try again.
                         */
                        if (!slept) {
                                PARG parg;
                                parg.p_string = wait_message();
                                ierror("%s", &parg);
                        }
                        sleep(1);
                        slept = TRUE;

                        if (follow_mode == FOLLOW_NAME) {
                                /*
                                 * See whether the file's i-number has changed.
                                 * If so, force the file to be closed and
                                 * reopened.
                                 */
                                struct stat st;
                                int r = stat(get_filename(curr_ifile), &st);
                                if (r == 0 && (st.st_ino != curr_ino ||
                                    st.st_dev != curr_dev)) {
                                        /*
                                         * screen_trashed=2 causes
                                         * make_display to reopen the file.
                                         */
                                        screen_trashed = 2;
                                        return (EOI);
                                }
                        }
                }
                if (any_sigs())
                        return (EOI);
        }

found:
        if (ch_bufhead != bn) {
                /*
                 * Move the buffer to the head of the buffer chain.
                 * This orders the buffer chain, most- to least-recently used.
                 */
                BUF_RM(bn);
                BUF_INS_HEAD(bn);

                /*
                 * Move to head of hash chain too.
                 */
                BUF_HASH_RM(bn);
                BUF_HASH_INS(bn, h);
        }

        if (ch_offset >= bp->datasize)
                /*
                 * After all that, we still don't have enough data.
                 * Go back and try again.
                 */
                goto read_more;

        return (bp->data[ch_offset]);
}

/*
 * ch_ungetchar is a rather kludgy and limited way to push
 * a single char onto an input file descriptor.
 */
void
ch_ungetchar(int c)
{
        if (c != -1 && ch_ungotchar != -1)
                error("ch_ungetchar overrun", NULL);
        ch_ungotchar = c;
}

/*
 * Close the logfile.
 * If we haven't read all of standard input into it, do that now.
 */
void
end_logfile(void)
{
        static int tried = FALSE;

        if (logfile < 0)
                return;
        if (!tried && ch_fsize == -1) {
                tried = TRUE;
                ierror("Finishing logfile", NULL);
                while (ch_forw_get() != EOI)
                        if (abort_sigs())
                                break;
        }
        close(logfile);
        logfile = -1;
        free(namelogfile);
        namelogfile = NULL;
}

/*
 * Start a log file AFTER less has already been running.
 * Invoked from the - command; see toggle_option().
 * Write all the existing buffered data to the log file.
 */
void
sync_logfile(void)
{
        struct buf *bp;
        struct bufnode *bn;
        int warned = FALSE;
        BLOCKNUM block;
        BLOCKNUM nblocks;

        nblocks = (ch_fpos + LBUFSIZE - 1) / LBUFSIZE;
        for (block = 0; block < nblocks; block++) {
                int wrote = FALSE;
                FOR_BUFS(bn) {
                        bp = bufnode_buf(bn);
                        if (bp->block == block) {
                                (void) write(logfile, (char *)bp->data,
                                    bp->datasize);
                                wrote = TRUE;
                                break;
                        }
                }
                if (!wrote && !warned) {
                        error("Warning: log file is incomplete", NULL);
                        warned = TRUE;
                }
        }
}

/*
 * Determine if a specific block is currently in one of the buffers.
 */
static int
buffered(BLOCKNUM block)
{
        struct buf *bp;
        struct bufnode *bn;
        int h;

        h = BUFHASH(block);
        FOR_BUFS_IN_CHAIN(h, bn) {
                bp = bufnode_buf(bn);
                if (bp->block == block)
                        return (TRUE);
        }
        return (FALSE);
}

/*
 * Seek to a specified position in the file.
 * Return 0 if successful, non-zero if can't seek there.
 */
int
ch_seek(off_t pos)
{
        BLOCKNUM new_block;
        off_t len;

        if (thisfile == NULL)
                return (0);

        len = ch_length();
        if (pos < ch_zero() || (len != -1 && pos > len))
                return (1);

        new_block = pos / LBUFSIZE;
        if (!(ch_flags & CH_CANSEEK) && pos != ch_fpos &&
            !buffered(new_block)) {
                if (ch_fpos > pos)
                        return (1);
                while (ch_fpos < pos) {
                        if (ch_forw_get() == EOI)
                                return (1);
                        if (abort_sigs())
                                return (1);
                }
                return (0);
        }
        /*
         * Set read pointer.
         */
        ch_block = new_block;
        ch_offset = pos % LBUFSIZE;
        return (0);
}

/*
 * Seek to the end of the file.
 */
int
ch_end_seek(void)
{
        off_t len;

        if (thisfile == NULL)
                return (0);

        if (ch_flags & CH_CANSEEK)
                ch_fsize = filesize(ch_file);

        len = ch_length();
        if (len != -1)
                return (ch_seek(len));

        /*
         * Do it the slow way: read till end of data.
         */
        while (ch_forw_get() != EOI)
                if (abort_sigs())
                        return (1);
        return (0);
}

/*
 * Seek to the beginning of the file, or as close to it as we can get.
 * We may not be able to seek there if input is a pipe and the
 * beginning of the pipe is no longer buffered.
 */
int
ch_beg_seek(void)
{
        struct bufnode *bn;
        struct bufnode *firstbn;

        /*
         * Try a plain ch_seek first.
         */
        if (ch_seek(ch_zero()) == 0)
                return (0);

        /*
         * Can't get to position 0.
         * Look thru the buffers for the one closest to position 0.
         */
        firstbn = ch_bufhead;
        if (firstbn == END_OF_CHAIN)
                return (1);
        FOR_BUFS(bn) {
                if (bufnode_buf(bn)->block < bufnode_buf(firstbn)->block)
                        firstbn = bn;
        }
        ch_block = bufnode_buf(firstbn)->block;
        ch_offset = 0;
        return (0);
}

/*
 * Return the length of the file, if known.
 */
off_t
ch_length(void)
{
        if (thisfile == NULL)
                return (-1);
        if (ignore_eoi)
                return (-1);
        if (ch_flags & CH_NODATA)
                return (0);
        return (ch_fsize);
}

/*
 * Return the current position in the file.
 */
off_t
ch_tell(void)
{
        if (thisfile == NULL)
                return (-1);
        return ((ch_block * LBUFSIZE) + ch_offset);
}

/*
 * Get the current char and post-increment the read pointer.
 */
int
ch_forw_get(void)
{
        int c;

        if (thisfile == NULL)
                return (EOI);
        c = ch_get();
        if (c == EOI)
                return (EOI);
        if (ch_offset < LBUFSIZE-1) {
                ch_offset++;
        } else {
                ch_block ++;
                ch_offset = 0;
        }
        return (c);
}

/*
 * Pre-decrement the read pointer and get the new current char.
 */
int
ch_back_get(void)
{
        if (thisfile == NULL)
                return (EOI);
        if (ch_offset > 0) {
                ch_offset --;
        } else {
                if (ch_block <= 0)
                        return (EOI);
                if (!(ch_flags & CH_CANSEEK) && !buffered(ch_block-1))
                        return (EOI);
                ch_block--;
                ch_offset = LBUFSIZE-1;
        }
        return (ch_get());
}

/*
 * Set max amount of buffer space.
 * bufspace is in units of 1024 bytes.  -1 mean no limit.
 */
void
ch_setbufspace(int bufspace)
{
        if (bufspace < 0) {
                maxbufs = -1;
        } else {
                maxbufs = ((bufspace * 1024) + LBUFSIZE-1) / LBUFSIZE;
                if (maxbufs < 1)
                        maxbufs = 1;
        }
}

/*
 * Flush (discard) any saved file state, including buffer contents.
 */
void
ch_flush(void)
{
        struct bufnode *bn;

        if (thisfile == NULL)
                return;

        if (!(ch_flags & CH_CANSEEK)) {
                /*
                 * If input is a pipe, we don't flush buffer contents,
                 * since the contents can't be recovered.
                 */
                ch_fsize = -1;
                return;
        }

        /*
         * Initialize all the buffers.
         */
        FOR_BUFS(bn) {
                bufnode_buf(bn)->block = -1;
        }

        /*
         * Figure out the size of the file, if we can.
         */
        ch_fsize = filesize(ch_file);

        /*
         * Seek to a known position: the beginning of the file.
         */
        ch_fpos = 0;
        ch_block = 0; /* ch_fpos / LBUFSIZE; */
        ch_offset = 0; /* ch_fpos % LBUFSIZE; */

        if (lseek(ch_file, (off_t)0, SEEK_SET) == (off_t)-1) {
                /*
                 * Warning only; even if the seek fails for some reason,
                 * there's a good chance we're at the beginning anyway.
                 * {{ I think this is bogus reasoning. }}
                 */
                error("seek error to 0", NULL);
        }
}

/*
 * Allocate a new buffer.
 * The buffer is added to the tail of the buffer chain.
 */
static int
ch_addbuf(void)
{
        struct buf *bp;
        struct bufnode *bn;

        /*
         * Allocate and initialize a new buffer and link it
         * onto the tail of the buffer list.
         */
        bp = calloc(1, sizeof (struct buf));
        if (bp == NULL)
                return (1);
        ch_nbufs++;
        bp->block = -1;
        bn = &bp->node;

        BUF_INS_TAIL(bn);
        BUF_HASH_INS(bn, 0);
        return (0);
}

/*
 *
 */
static void
init_hashtbl(void)
{
        int h;

        for (h = 0; h < BUFHASH_SIZE; h++) {
                thisfile->hashtbl[h].hnext = END_OF_HCHAIN(h);
                thisfile->hashtbl[h].hprev = END_OF_HCHAIN(h);
        }
}

/*
 * Delete all buffers for this file.
 */
static void
ch_delbufs(void)
{
        struct bufnode *bn;

        while (ch_bufhead != END_OF_CHAIN) {
                bn = ch_bufhead;
                BUF_RM(bn);
                free(bufnode_buf(bn));
        }
        ch_nbufs = 0;
        init_hashtbl();
}

/*
 * Is it possible to seek on a file descriptor?
 */
int
seekable(int f)
{
        return (lseek(f, (off_t)1, SEEK_SET) != (off_t)-1);
}

/*
 * Force EOF to be at the current read position.
 * This is used after an ignore_eof read, during which the EOF may change.
 */
void
ch_set_eof(void)
{
        ch_fsize = ch_fpos;
}


/*
 * Initialize file state for a new file.
 */
void
ch_init(int f, int flags)
{
        /*
         * See if we already have a filestate for this file.
         */
        thisfile = get_filestate(curr_ifile);
        if (thisfile == NULL) {
                /*
                 * Allocate and initialize a new filestate.
                 */
                thisfile = calloc(1, sizeof (struct filestate));
                thisfile->buflist.next = thisfile->buflist.prev = END_OF_CHAIN;
                thisfile->nbufs = 0;
                thisfile->flags = 0;
                thisfile->fpos = 0;
                thisfile->block = 0;
                thisfile->offset = 0;
                thisfile->file = -1;
                thisfile->fsize = -1;
                ch_flags = flags;
                init_hashtbl();
                /*
                 * Try to seek; set CH_CANSEEK if it works.
                 */
                if ((flags & CH_CANSEEK) && !seekable(f))
                        ch_flags &= ~CH_CANSEEK;
                set_filestate(curr_ifile, (void *) thisfile);
        }
        if (thisfile->file == -1)
                thisfile->file = f;
        ch_flush();
}

/*
 * Close a filestate.
 */
void
ch_close(void)
{
        int keepstate = FALSE;

        if (thisfile == NULL)
                return;

        if (ch_flags & (CH_CANSEEK|CH_HELPFILE)) {
                /*
                 * We can seek or re-open, so we don't need to keep buffers.
                 */
                ch_delbufs();
        } else {
                keepstate = TRUE;
        }
        if (!(ch_flags & CH_KEEPOPEN)) {
                /*
                 * We don't need to keep the file descriptor open
                 * (because we can re-open it.)
                 */
                close(ch_file);
                ch_file = -1;
        } else {
                keepstate = TRUE;
        }
        if (!keepstate) {
                /*
                 * We don't even need to keep the filestate structure.
                 */
                free(thisfile);
                thisfile = NULL;
                set_filestate(curr_ifile, NULL);
        }
}

/*
 * Return ch_flags for the current file.
 */
int
ch_getflags(void)
{
        if (thisfile == NULL)
                return (0);
        return (ch_flags);
}