#include "line_proto.h"

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

/*
 * Our state
 */
struct line_proto {
    /* The sock_stream we read/write with */
    struct sock_stream *sock;

    /* Offset of trailing data in buf */
    size_t tail_offset;

    /* Length of trailing data in buf, if any */
    size_t tail_len;

    /* Last error */
    struct error_info err;
};

err_t line_proto_create (struct line_proto **lp_ptr, struct sock_stream *sock, struct error_info *err)
{
    struct line_proto *lp;

    // allocate
    if ((lp = calloc(1, sizeof(*lp))) == NULL)
        return SET_ERROR(err, ERR_CALLOC);

    // store
    lp->sock = sock;

    // return
    *lp_ptr = lp;

    return SUCCESS;
}

/*
 * This looks for a full '\r\n' terminated line at the beginning of the given buffer. If found, the \r\n will be
 * replaced with a '\0', and the offset to the beginning of the next line returned. If not found, zero is returned
 * (which is never a valid next-line offset).
 *
 * The given \a hint is an hint as to the offset at which to start scanning, used for incremental invocations of this
 * on the same buffer.
 *
 */
int _parse_line (char *buf, size_t len, size_t *hint) {
    int i;

    // empty buffer -> nothing
    if (len == 0)
        return 0;

    // look for terminating '\r\n' sequence
    for (i = *hint; i < len - 1; i++) {
        // match this + next char
        if (buf[i] == '\r' && buf[i + 1] == '\n')
            break;
    }

    // incomplete?
    if (i >= len - 1) {
        *hint = len - 1;
        return 0;
    }

    // mangle the newline off
    buf[i] = '\0';

    // return offset to next line
    return i + 2;
}

err_t line_proto_read (struct line_proto *lp, char *buf, size_t len)
{
    // offset to recv() new data into, offset to _parse_line hint, offset to next line from _parse_line
    size_t recv_offset = 0, peek_offset = 0, next_offset = 0;
    int ret;

    // adjust offset from previous data
    recv_offset = lp->tail_len;

    // move trailing data from previous line to front of buffer
    if (lp->tail_offset) {
        // move to front
        memmove(buf, buf + lp->tail_offset, lp->tail_len);

        // reset
        lp->tail_offset = 0;
        lp->tail_len = 0;
    }

    // readline loop
    do {
        // parse any line at the beginning of the buffer
        if ((next_offset = _parse_line(buf, recv_offset, &peek_offset)) > 0)
            break;

        // ensure there's enough space for it
        assert(recv_offset < len);
        
        // otherwise, read more data
        if ((ret = sock_stream_read(lp->sock, buf + recv_offset, len - recv_offset)) < 0)
            RETURN_SET_ERROR_INFO(&lp->err, sock_stream_error(lp->sock));

        // EOF?
        if (ret == 0)
            return SET_ERROR(&lp->err, ERR_READ_EOF);
        
        // update recv_offset
        recv_offset += ret;

    } while (1);

    // update state for next call
    lp->tail_offset = next_offset;
    lp->tail_len = recv_offset - next_offset;

    // ok
    return SUCCESS;
}

const struct error_info* line_proto_error (struct line_proto *lp)
{
    // return pointer
    return &lp->err;
}