src/history.c

/*
 * *****************************************************************************
 *
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2018-2021 Gavin D. Howard and contributors.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * *****************************************************************************
 *
 * Adapted from the following:
 *
 * linenoise.c -- guerrilla line editing library against the idea that a
 * line editing lib needs to be 20,000 lines of C code.
 *
 * You can find the original source code at:
 *   http://github.com/antirez/linenoise
 *
 * You can find the fork that this code is based on at:
 *   https://github.com/rain-1/linenoise-mob
 *
 * ------------------------------------------------------------------------
 *
 * This code is also under the following license:
 *
 * Copyright (c) 2010-2016, Salvatore Sanfilippo <antirez at gmail dot com>
 * Copyright (c) 2010-2013, Pieter Noordhuis <pcnoordhuis at gmail dot com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *  *  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *  *  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ------------------------------------------------------------------------
 *
 * Does a number of crazy assumptions that happen to be true in 99.9999% of
 * the 2010 UNIX computers around.
 *
 * References:
 * - http://invisible-island.net/xterm/ctlseqs/ctlseqs.html
 * - http://www.3waylabs.com/nw/WWW/products/wizcon/vt220.html
 *
 * Todo list:
 * - Filter bogus Ctrl+<char> combinations.
 * - Win32 support
 *
 * Bloat:
 * - History search like Ctrl+r in readline?
 *
 * List of escape sequences used by this program, we do everything just
 * with three sequences. In order to be so cheap we may have some
 * flickering effect with some slow terminal, but the lesser sequences
 * the more compatible.
 *
 * EL (Erase Line)
 *    Sequence: ESC [ n K
 *    Effect: if n is 0 or missing, clear from cursor to end of line
 *    Effect: if n is 1, clear from beginning of line to cursor
 *    Effect: if n is 2, clear entire line
 *
 * CUF (CUrsor Forward)
 *    Sequence: ESC [ n C
 *    Effect: moves cursor forward n chars
 *
 * CUB (CUrsor Backward)
 *    Sequence: ESC [ n D
 *    Effect: moves cursor backward n chars
 *
 * The following is used to get the terminal width if getting
 * the width with the TIOCGWINSZ ioctl fails
 *
 * DSR (Device Status Report)
 *    Sequence: ESC [ 6 n
 *    Effect: reports the current cusor position as ESC [ n ; m R
 *            where n is the row and m is the column
 *
 * When multi line mode is enabled, we also use two additional escape
 * sequences. However multi line editing is disabled by default.
 *
 * CUU (CUrsor Up)
 *    Sequence: ESC [ n A
 *    Effect: moves cursor up of n chars.
 *
 * CUD (CUrsor Down)
 *    Sequence: ESC [ n B
 *    Effect: moves cursor down of n chars.
 *
 * When bc_history_clearScreen() is called, two additional escape sequences
 * are used in order to clear the screen and position the cursor at home
 * position.
 *
 * CUP (CUrsor Position)
 *    Sequence: ESC [ H
 *    Effect: moves the cursor to upper left corner
 *
 * ED (Erase Display)
 *    Sequence: ESC [ 2 J
 *    Effect: clear the whole screen
 *
 * *****************************************************************************
 *
 * Code for line history.
 *
 */

#if BC_ENABLE_HISTORY

#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <strings.h>
#include <ctype.h>

#include <signal.h>

#include <termios.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/select.h>

#include <vector.h>
#include <history.h>
#include <read.h>
#include <file.h>
#include <vm.h>

static void bc_history_add(BcHistory *h, char *line);
static void bc_history_add_empty(BcHistory *h);

/**
 * Check if the code is a wide character.
 */
static bool bc_history_wchar(uint32_t cp) {

	size_t i;

	for (i = 0; i < bc_history_wchars_len; ++i) {

		// Ranges are listed in ascending order.  Therefore, once the
		// whole range is higher than the codepoint we're testing, the
		// codepoint won't be found in any remaining range => bail early.
		if (bc_history_wchars[i][0] > cp) return false;

		// Test this range.
		if (bc_history_wchars[i][0] <= cp && cp <= bc_history_wchars[i][1])
			return true;
	}

	return false;
}

/**
 * Check if the code is a combining character.
 */
static bool bc_history_comboChar(uint32_t cp) {

	size_t i;

	for (i = 0; i < bc_history_combo_chars_len; ++i) {

		// Combining chars are listed in ascending order, so once we pass
		// the codepoint of interest, we know it's not a combining char.
		if (bc_history_combo_chars[i] > cp) return false;
		if (bc_history_combo_chars[i] == cp) return true;
	}

	return false;
}

/**
 * Get length of previous UTF8 character.
 */
static size_t bc_history_prevCharLen(const char *buf, size_t pos) {
	size_t end = pos;
	for (pos -= 1; pos < end && (buf[pos] & 0xC0) == 0x80; --pos);
	return end - (pos >= end ? 0 : pos);
}

/**
 * Convert UTF-8 to Unicode code point.
 */
static size_t bc_history_codePoint(const char *s, size_t len, uint32_t *cp) {

	if (len) {

		uchar byte = (uchar) s[0];

		if ((byte & 0x80) == 0) {
			*cp = byte;
			return 1;
		}
		else if ((byte & 0xE0) == 0xC0) {

			if (len >= 2) {
				*cp = (((uint32_t) (s[0] & 0x1F)) << 6) |
					   ((uint32_t) (s[1] & 0x3F));
				return 2;
			}
		}
		else if ((byte & 0xF0) == 0xE0) {

			if (len >= 3) {
				*cp = (((uint32_t) (s[0] & 0x0F)) << 12) |
					  (((uint32_t) (s[1] & 0x3F)) << 6) |
					   ((uint32_t) (s[2] & 0x3F));
				return 3;
			}
		}
		else if ((byte & 0xF8) == 0xF0) {

			if (len >= 4) {
				*cp = (((uint32_t) (s[0] & 0x07)) << 18) |
					  (((uint32_t) (s[1] & 0x3F)) << 12) |
					  (((uint32_t) (s[2] & 0x3F)) << 6) |
					   ((uint32_t) (s[3] & 0x3F));
				return 4;
			}
		}
		else {
			*cp = 0xFFFD;
			return 1;
		}
	}

	*cp = 0;

	return 1;
}

/**
 * Get length of next grapheme.
 */
static size_t bc_history_nextLen(const char *buf, size_t buf_len,
                                 size_t pos, size_t *col_len)
{
	uint32_t cp;
	size_t beg = pos;
	size_t len = bc_history_codePoint(buf + pos, buf_len - pos, &cp);

	if (bc_history_comboChar(cp)) {
		// Currently unreachable?
		return 0;
	}

	if (col_len != NULL) *col_len = bc_history_wchar(cp) ? 2 : 1;

	pos += len;

	while (pos < buf_len) {

		len = bc_history_codePoint(buf + pos, buf_len - pos, &cp);

		if (!bc_history_comboChar(cp)) return pos - beg;

		pos += len;
	}

	return pos - beg;
}

/**
 * Get length of previous grapheme.
 */
static size_t bc_history_prevLen(const char *buf, size_t pos, size_t *col_len) {

	size_t end = pos;

	while (pos > 0) {

		uint32_t cp;
		size_t len = bc_history_prevCharLen(buf, pos);

		pos -= len;
		bc_history_codePoint(buf + pos, len, &cp);

		if (!bc_history_comboChar(cp)) {
			if (col_len != NULL) *col_len = 1 + (bc_history_wchar(cp) != 0);
			return end - pos;
		}
	}

	// Currently unreachable?
	return 0;
}

static ssize_t bc_history_read(char *buf, size_t n) {

	ssize_t ret;

	BC_SIG_LOCK;

	do {
		ret = read(STDIN_FILENO, buf, n);
	} while (ret == EINTR);

	BC_SIG_UNLOCK;

	return ret;
}

/**
 * Read a Unicode code point from a file.
 */
static BcStatus bc_history_readCode(char *buf, size_t buf_len,
                                    uint32_t *cp, size_t *nread)
{
	ssize_t n;

	assert(buf_len >= 1);

	n = bc_history_read(buf, 1);
	if (BC_ERR(n <= 0)) goto err;

	uchar byte = (uchar) buf[0];

	if ((byte & 0x80) != 0) {

		if ((byte & 0xE0) == 0xC0) {
			assert(buf_len >= 2);
			n = bc_history_read(buf + 1, 1);
			if (BC_ERR(n <= 0)) goto err;
		}
		else if ((byte & 0xF0) == 0xE0) {
			assert(buf_len >= 3);
			n = bc_history_read(buf + 1, 2);
			if (BC_ERR(n <= 0)) goto err;
		}
		else if ((byte & 0xF8) == 0xF0) {
			assert(buf_len >= 3);
			n = bc_history_read(buf + 1, 3);
			if (BC_ERR(n <= 0)) goto err;
		}
		else {
			n = -1;
			goto err;
		}
	}

	*nread = bc_history_codePoint(buf, buf_len, cp);

	return BC_STATUS_SUCCESS;

err:
	if (BC_ERR(n < 0)) bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);
	else *nread = (size_t) n;
	return BC_STATUS_EOF;
}

/**
 * Get column length from begining of buffer to current byte position.
 */
static size_t bc_history_colPos(const char *buf, size_t buf_len, size_t pos) {

	size_t ret = 0, off = 0;

	while (off < pos) {

		size_t col_len, len;

		len = bc_history_nextLen(buf, buf_len, off, &col_len);

		off += len;
		ret += col_len;
	}

	return ret;
}

/**
 * Return true if the terminal name is in the list of terminals we know are
 * not able to understand basic escape sequences.
 */
static inline bool bc_history_isBadTerm(void) {

	size_t i;
	char *term = getenv("TERM");

	if (term == NULL) return false;

	for (i = 0; bc_history_bad_terms[i]; ++i) {
		if (!strcasecmp(term, bc_history_bad_terms[i])) return true;
	}

	return false;
}

/**
 * Raw mode: 1960's black magic.
 */
static void bc_history_enableRaw(BcHistory *h) {

	struct termios raw;
	int err;

	assert(BC_TTYIN);

	if (h->rawMode) return;

	BC_SIG_LOCK;

	if (BC_ERR(tcgetattr(STDIN_FILENO, &h->orig_termios) == -1))
		bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);

	BC_SIG_UNLOCK;

	// Modify the original mode.
	raw = h->orig_termios;

	// Input modes: no break, no CR to NL, no parity check, no strip char,
	// no start/stop output control.
	raw.c_iflag &= (unsigned int) (~(BRKINT | ICRNL | INPCK | ISTRIP | IXON));

	// Control modes - set 8 bit chars.
	raw.c_cflag |= (CS8);

	// Local modes - choing off, canonical off, no extended functions,
	// no signal chars (^Z,^C).
	raw.c_lflag &= (unsigned int) (~(ECHO | ICANON | IEXTEN | ISIG));

	// Control chars - set return condition: min number of bytes and timer.
	// We want read to give every single byte, w/o timeout (1 byte, no timer).
	raw.c_cc[VMIN] = 1;
	raw.c_cc[VTIME] = 0;

	BC_SIG_LOCK;

	// Put terminal in raw mode after flushing.
	do {
		err = tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);
	} while (BC_ERR(err < 0) && errno == EINTR);

	BC_SIG_UNLOCK;

	if (BC_ERR(err < 0)) bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);

	h->rawMode = true;
}

static void bc_history_disableRaw(BcHistory *h) {

	sig_atomic_t lock;

	// Don't even check the return value as it's too late.
	if (!h->rawMode) return;

	BC_SIG_TRYLOCK(lock);

	if (BC_ERR(tcsetattr(STDIN_FILENO, TCSAFLUSH, &h->orig_termios) != -1))
		h->rawMode = false;

	BC_SIG_TRYUNLOCK(lock);
}

/**
 * Use the ESC [6n escape sequence to query the horizontal cursor position
 * and return it. On error -1 is returned, on success the position of the
 * cursor.
 */
static size_t bc_history_cursorPos(void) {

	char buf[BC_HIST_SEQ_SIZE];
	char *ptr, *ptr2;
	size_t cols, rows, i;

	// Report cursor location.
	bc_file_write(&vm.fout, bc_flush_none, "\x1b[6n", 4);
	bc_file_flush(&vm.fout, bc_flush_none);

	// Read the response: ESC [ rows ; cols R.
	for (i = 0; i < sizeof(buf) - 1; ++i) {
		if (bc_history_read(buf + i, 1) != 1 || buf[i] == 'R') break;
	}

	buf[i] = '\0';

	if (BC_ERR(buf[0] != BC_ACTION_ESC || buf[1] != '[')) return SIZE_MAX;

	// Parse it.
	ptr = buf + 2;
	rows = strtoul(ptr, &ptr2, 10);

	if (BC_ERR(!rows || ptr2[0] != ';')) return SIZE_MAX;

	ptr = ptr2 + 1;
	cols = strtoul(ptr, NULL, 10);

	if (BC_ERR(!cols)) return SIZE_MAX;

	return cols <= UINT16_MAX ? cols : 0;
}

/**
 * Try to get the number of columns in the current terminal, or assume 80
 * if it fails.
 */
static size_t bc_history_columns(void) {

	struct winsize ws;
	int ret;

	BC_SIG_LOCK;

	ret = ioctl(vm.fout.fd, TIOCGWINSZ, &ws);

	BC_SIG_UNLOCK;

	if (BC_ERR(ret == -1 || !ws.ws_col)) {

		// Calling ioctl() failed. Try to query the terminal itself.
		size_t start, cols;

		// Get the initial position so we can restore it later.
		start = bc_history_cursorPos();
		if (BC_ERR(start == SIZE_MAX)) return BC_HIST_DEF_COLS;

		// Go to right margin and get position.
		bc_file_write(&vm.fout, bc_flush_none, "\x1b[999C", 6);
		bc_file_flush(&vm.fout, bc_flush_none);
		cols = bc_history_cursorPos();
		if (BC_ERR(cols == SIZE_MAX)) return BC_HIST_DEF_COLS;

		// Restore position.
		if (cols > start) {
			bc_file_printf(&vm.fout, "\x1b[%zuD", cols - start);
			bc_file_flush(&vm.fout, bc_flush_none);
		}

		return cols;
	}

	return ws.ws_col;
}

#if BC_ENABLE_PROMPT
/**
 * Check if text is an ANSI escape sequence.
 */
static bool bc_history_ansiEscape(const char *buf, size_t buf_len, size_t *len)
{
	if (buf_len > 2 && !memcmp("\033[", buf, 2)) {

		size_t off = 2;

		while (off < buf_len) {

			char c = buf[off++];

			if ((c >= 'A' && c <= 'K' && c != 'I') ||
			    c == 'S' || c == 'T' || c == 'f' || c == 'm')
			{
				*len = off;
				return true;
			}
		}
	}

	return false;
}

/**
 * Get column length of prompt text.
 */
static size_t bc_history_promptColLen(const char *prompt, size_t plen) {

	char buf[BC_HIST_MAX_LINE + 1];
	size_t buf_len = 0, off = 0;

	while (off < plen) {

		size_t len;

		if (bc_history_ansiEscape(prompt + off, plen - off, &len)) {
			off += len;
			continue;
		}

		buf[buf_len++] = prompt[off++];
	}

	return bc_history_colPos(buf, buf_len, buf_len);
}
#endif // BC_ENABLE_PROMPT

/**
 * Rewrites the currently edited line accordingly to the buffer content,
 * cursor position, and number of columns of the terminal.
 */
static void bc_history_refresh(BcHistory *h) {

	char* buf = h->buf.v;
	size_t colpos, len = BC_HIST_BUF_LEN(h), pos = h->pos;

	bc_file_flush(&vm.fout, bc_flush_none);

	while(h->pcol + bc_history_colPos(buf, len, pos) >= h->cols) {

		size_t chlen = bc_history_nextLen(buf, len, 0, NULL);

		buf += chlen;
		len -= chlen;
		pos -= chlen;
	}

	while (h->pcol + bc_history_colPos(buf, len, len) > h->cols)
		len -= bc_history_prevLen(buf, len, NULL);

	// Cursor to left edge.
	bc_file_write(&vm.fout, bc_flush_none, "\r", 1);

	// Take the extra stuff into account.
	if (h->extras.len > 1) {
		len += h->extras.len - 1;
		pos += h->extras.len - 1;
		bc_file_write(&vm.fout, bc_flush_none, h->extras.v, h->extras.len - 1);
	}

	// Write the prompt, if desired.
#if BC_ENABLE_PROMPT
	if (BC_USE_PROMPT)
		bc_file_write(&vm.fout, bc_flush_none, h->prompt, h->plen);
#endif // BC_ENABLE_PROMPT

	bc_file_write(&vm.fout, bc_flush_none, buf, BC_HIST_BUF_LEN(h));

	// Erase to right.
	bc_file_write(&vm.fout, bc_flush_none, "\x1b[0K", 4);

	// Move cursor to original position.
	colpos = bc_history_colPos(buf, len, pos) + h->pcol;

	if (colpos) bc_file_printf(&vm.fout, "\r\x1b[%zuC", colpos);

	bc_file_flush(&vm.fout, bc_flush_none);
}

/**
 * Insert the character 'c' at cursor current position.
 */
static void bc_history_edit_insert(BcHistory *h, const char *cbuf, size_t clen)
{
	bc_vec_grow(&h->buf, clen);

	if (h->pos == BC_HIST_BUF_LEN(h)) {

		size_t colpos = 0, len;

		memcpy(bc_vec_item(&h->buf, h->pos), cbuf, clen);

		h->pos += clen;
		h->buf.len += clen - 1;
		bc_vec_pushByte(&h->buf, '\0');

		len = BC_HIST_BUF_LEN(h) + h->extras.len - 1;
#if BC_ENABLE_PROMPT
		colpos = bc_history_promptColLen(h->prompt, h->plen);
#endif // BC_ENABLE_PROMPT
		colpos += bc_history_colPos(h->buf.v, len, len);

		if (colpos < h->cols) {

			// Avoid a full update of the line in the trivial case.
			bc_file_write(&vm.fout, bc_flush_none, cbuf, clen);
			bc_file_flush(&vm.fout, bc_flush_none);
		}
		else bc_history_refresh(h);
	}
	else {

		size_t amt = BC_HIST_BUF_LEN(h) - h->pos;

		memmove(h->buf.v + h->pos + clen, h->buf.v + h->pos, amt);
		memcpy(h->buf.v + h->pos, cbuf, clen);

		h->pos += clen;
		h->buf.len += clen;
		h->buf.v[BC_HIST_BUF_LEN(h)] = '\0';

		bc_history_refresh(h);
	}
}

/**
 * Move cursor to the left.
 */
static void bc_history_edit_left(BcHistory *h) {

	if (h->pos <= 0) return;

	h->pos -= bc_history_prevLen(h->buf.v, h->pos, NULL);

	bc_history_refresh(h);
}

/**
 * Move cursor on the right.
*/
static void bc_history_edit_right(BcHistory *h) {

	if (h->pos == BC_HIST_BUF_LEN(h)) return;

	h->pos += bc_history_nextLen(h->buf.v, BC_HIST_BUF_LEN(h), h->pos, NULL);

	bc_history_refresh(h);
}

/**
 * Move cursor to the end of the current word.
 */
static void bc_history_edit_wordEnd(BcHistory *h) {

	size_t len = BC_HIST_BUF_LEN(h);

	if (!len || h->pos >= len) return;

	while (h->pos < len && isspace(h->buf.v[h->pos])) h->pos += 1;
	while (h->pos < len && !isspace(h->buf.v[h->pos])) h->pos += 1;

	bc_history_refresh(h);
}

/**
 * Move cursor to the start of the current word.
 */
static void bc_history_edit_wordStart(BcHistory *h) {

	size_t len = BC_HIST_BUF_LEN(h);

	if (!len) return;

	while (h->pos > 0 && isspace(h->buf.v[h->pos - 1])) h->pos -= 1;
	while (h->pos > 0 && !isspace(h->buf.v[h->pos - 1])) h->pos -= 1;

	bc_history_refresh(h);
}

/**
 * Move cursor to the start of the line.
 */
static void bc_history_edit_home(BcHistory *h) {

	if (!h->pos) return;

	h->pos = 0;

	bc_history_refresh(h);
}

/**
 * Move cursor to the end of the line.
 */
static void bc_history_edit_end(BcHistory *h) {

	if (h->pos == BC_HIST_BUF_LEN(h)) return;

	h->pos = BC_HIST_BUF_LEN(h);

	bc_history_refresh(h);
}

/**
 * Substitute the currently edited line with the next or previous history
 * entry as specified by 'dir' (direction).
 */
static void bc_history_edit_next(BcHistory *h, bool dir) {

	const char *dup, *str;

	if (h->history.len <= 1) return;

	BC_SIG_LOCK;

	if (h->buf.v[0]) dup = bc_vm_strdup(h->buf.v);
	else dup = "";

	// Update the current history entry before
	// overwriting it with the next one.
	bc_vec_replaceAt(&h->history, h->history.len - 1 - h->idx, &dup);

	BC_SIG_UNLOCK;

	// Show the new entry.
	h->idx += (dir == BC_HIST_PREV ? 1 : SIZE_MAX);

	if (h->idx == SIZE_MAX) {
		h->idx = 0;
		return;
	}
	else if (h->idx >= h->history.len) {
		h->idx = h->history.len - 1;
		return;
	}

	str = *((char**) bc_vec_item(&h->history, h->history.len - 1 - h->idx));
	bc_vec_string(&h->buf, strlen(str), str);
	assert(h->buf.len > 0);

	h->pos = BC_HIST_BUF_LEN(h);

	bc_history_refresh(h);
}

/**
 * Delete the character at the right of the cursor without altering the cursor
 * position. Basically this is what happens with the "Delete" keyboard key.
 */
static void bc_history_edit_delete(BcHistory *h) {

	size_t chlen, len = BC_HIST_BUF_LEN(h);

	if (!len || h->pos >= len) return;

	chlen = bc_history_nextLen(h->buf.v, len, h->pos, NULL);

	memmove(h->buf.v + h->pos, h->buf.v + h->pos + chlen, len - h->pos - chlen);

	h->buf.len -= chlen;
	h->buf.v[BC_HIST_BUF_LEN(h)] = '\0';

	bc_history_refresh(h);
}

static void bc_history_edit_backspace(BcHistory *h) {

	size_t chlen, len = BC_HIST_BUF_LEN(h);

	if (!h->pos || !len) return;

	chlen = bc_history_prevLen(h->buf.v, h->pos, NULL);

	memmove(h->buf.v + h->pos - chlen, h->buf.v + h->pos, len - h->pos);

	h->pos -= chlen;
	h->buf.len -= chlen;
	h->buf.v[BC_HIST_BUF_LEN(h)] = '\0';

	bc_history_refresh(h);
}

/**
 * Delete the previous word, maintaining the cursor at the start of the
 * current word.
 */
static void bc_history_edit_deletePrevWord(BcHistory *h) {

	size_t diff, old_pos = h->pos;

	while (h->pos > 0 && h->buf.v[h->pos - 1] == ' ') --h->pos;
	while (h->pos > 0 && h->buf.v[h->pos - 1] != ' ') --h->pos;

	diff = old_pos - h->pos;
	memmove(h->buf.v + h->pos, h->buf.v + old_pos,
	        BC_HIST_BUF_LEN(h) - old_pos + 1);
	h->buf.len -= diff;

	bc_history_refresh(h);
}

/**
 * Delete the next word, maintaining the cursor at the same position.
 */
static void bc_history_edit_deleteNextWord(BcHistory *h) {

	size_t next_end = h->pos, len = BC_HIST_BUF_LEN(h);

	while (next_end < len && h->buf.v[next_end] == ' ') ++next_end;
	while (next_end < len && h->buf.v[next_end] != ' ') ++next_end;

	memmove(h->buf.v + h->pos, h->buf.v + next_end, len - next_end);

	h->buf.len -= next_end - h->pos;

	bc_history_refresh(h);
}

static void bc_history_swap(BcHistory *h) {

	size_t pcl, ncl;
	char auxb[5];

	pcl = bc_history_prevLen(h->buf.v, h->pos, NULL);
	ncl = bc_history_nextLen(h->buf.v, BC_HIST_BUF_LEN(h), h->pos, NULL);

	// To perform a swap we need:
	// * nonzero char length to the left
	// * not at the end of the line
	if (pcl && h->pos != BC_HIST_BUF_LEN(h) && pcl < 5 && ncl < 5) {

		memcpy(auxb, h->buf.v + h->pos - pcl, pcl);
		memcpy(h->buf.v + h->pos - pcl, h->buf.v + h->pos, ncl);
		memcpy(h->buf.v + h->pos - pcl + ncl, auxb, pcl);

		h->pos += -pcl + ncl;

		bc_history_refresh(h);
	}
}

/**
 * Handle escape sequences.
 */
static void bc_history_escape(BcHistory *h) {

	char c, seq[3];

	if (BC_ERR(BC_HIST_READ(seq, 1))) return;

	c = seq[0];

	// ESC ? sequences.
	if (c != '[' && c != 'O') {
		if (c == 'f') bc_history_edit_wordEnd(h);
		else if (c == 'b') bc_history_edit_wordStart(h);
		else if (c == 'd') bc_history_edit_deleteNextWord(h);
	}
	else {

		if (BC_ERR(BC_HIST_READ(seq + 1, 1)))
			bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);

		// ESC [ sequences.
		if (c == '[') {

			c = seq[1];

			if (c >= '0' && c <= '9') {

				// Extended escape, read additional byte.
				if (BC_ERR(BC_HIST_READ(seq + 2, 1)))
					bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);

				if (seq[2] == '~' && c == '3') bc_history_edit_delete(h);
				else if(seq[2] == ';') {

					if (BC_ERR(BC_HIST_READ(seq, 2)))
						bc_vm_fatalError(BC_ERR_FATAL_IO_ERR);

					if (seq[0] != '5') return;
					else if (seq[1] == 'C') bc_history_edit_wordEnd(h);
					else if (seq[1] == 'D') bc_history_edit_wordStart(h);
				}
			}
			else {

				switch(c) {

					// Up.
					case 'A':
					{
						bc_history_edit_next(h, BC_HIST_PREV);
						break;
					}

					// Down.
					case 'B':
					{
						bc_history_edit_next(h, BC_HIST_NEXT);
						break;
					}

					// Right.
					case 'C':
					{
						bc_history_edit_right(h);
						break;
					}

					// Left.
					case 'D':
					{
						bc_history_edit_left(h);
						break;
					}

					// Home.
					case 'H':
					case '1':
					{
						bc_history_edit_home(h);
						break;
					}

					// End.
					case 'F':
					case '4':
					{
						bc_history_edit_end(h);
						break;
					}

					case 'd':
					{
						bc_history_edit_deleteNextWord(h);
						break;
					}
				}
			}
		}
		// ESC O sequences.
		else if (c == 'O') {

			switch (seq[1]) {

				case 'A':
				{
					bc_history_edit_next(h, BC_HIST_PREV);
					break;
				}

				case 'B':
				{
					bc_history_edit_next(h, BC_HIST_NEXT);
					break;
				}

				case 'C':
				{
					bc_history_edit_right(h);
					break;
				}

				case 'D':
				{
					bc_history_edit_left(h);
					break;
				}

				case 'F':
				{
					bc_history_edit_end(h);
					break;
				}

				case 'H':
				{
					bc_history_edit_home(h);
					break;
				}
			}
		}
	}
}

static void bc_history_reset(BcHistory *h) {

	h->oldcolpos = h->pos = h->idx = 0;
	h->cols = bc_history_columns();

	// The latest history entry is always our current buffer, that
	// initially is just an empty string.
	bc_history_add_empty(h);

	// Buffer starts empty.
	bc_vec_empty(&h->buf);
}

static void bc_history_printCtrl(BcHistory *h, unsigned int c) {

	char str[3] = "^A";
	const char newline[2] = "\n";

	str[1] = (char) (c + 'A' - BC_ACTION_CTRL_A);

	bc_vec_concat(&h->buf, str);

	bc_history_refresh(h);

	bc_vec_npop(&h->buf, sizeof(str));
	bc_vec_pushByte(&h->buf, '\0');

	if (c != BC_ACTION_CTRL_C && c != BC_ACTION_CTRL_D) {
		bc_file_write(&vm.fout, bc_flush_none, newline, sizeof(newline) - 1);
		bc_history_refresh(h);
	}
}

/**
 * This function is the core of the line editing capability of bc history.
 * It expects 'fd' to be already in "raw mode" so that every key pressed
 * will be returned ASAP to read().
 */
static BcStatus bc_history_edit(BcHistory *h, const char *prompt) {

	bc_history_reset(h);

	// Don't write the saved output the first time. This is because it has
	// already been written to output. In other words, don't uncomment the
	// line below or add anything like it.
	// bc_file_write(&vm.fout, bc_flush_none, h->extras.v, h->extras.len - 1);

#if BC_ENABLE_PROMPT
	if (BC_USE_PROMPT) {

		h->prompt = prompt;
		h->plen = strlen(prompt);
		h->pcol = bc_history_promptColLen(prompt, h->plen);

		bc_file_write(&vm.fout, bc_flush_none, prompt, h->plen);
		bc_file_flush(&vm.fout, bc_flush_none);
	}
#endif // BC_ENABLE_PROMPT

	for (;;) {

		BcStatus s;
		// Large enough for any encoding?
		char cbuf[32];
		unsigned int c = 0;
		size_t nread = 0;

		s = bc_history_readCode(cbuf, sizeof(cbuf), &c, &nread);
		if (BC_ERR(s)) return s;

		switch (c) {

			case BC_ACTION_LINE_FEED:
			case BC_ACTION_ENTER:
			{
				bc_vec_pop(&h->history);
				return s;
			}

			case BC_ACTION_TAB:
			{
				memcpy(cbuf, bc_history_tab, bc_history_tab_len + 1);
				bc_history_edit_insert(h, cbuf, bc_history_tab_len);
				break;
			}

			case BC_ACTION_CTRL_C:
			{
				bc_history_printCtrl(h, c);
				bc_file_write(&vm.fout, bc_flush_none, vm.sigmsg, vm.siglen);
				bc_file_write(&vm.fout, bc_flush_none, bc_program_ready_msg,
				              bc_program_ready_msg_len);
				bc_history_reset(h);
				bc_history_refresh(h);
				break;
			}

			case BC_ACTION_BACKSPACE:
			case BC_ACTION_CTRL_H:
			{
				bc_history_edit_backspace(h);
				break;
			}

			// Act as end-of-file.
			case BC_ACTION_CTRL_D:
			{
				bc_history_printCtrl(h, c);
				return BC_STATUS_EOF;
			}

			// Swaps current character with previous.
			case BC_ACTION_CTRL_T:
			{
				bc_history_swap(h);
				break;
			}

			case BC_ACTION_CTRL_B:
			{
				bc_history_edit_left(h);
				break;
			}

			case BC_ACTION_CTRL_F:
			{
				bc_history_edit_right(h);
				break;
			}

			case BC_ACTION_CTRL_P:
			{
				bc_history_edit_next(h, BC_HIST_PREV);
				break;
			}

			case BC_ACTION_CTRL_N:
			{
				bc_history_edit_next(h, BC_HIST_NEXT);
				break;
			}

			case BC_ACTION_ESC:
			{
				bc_history_escape(h);
				break;
			}

			// Delete the whole line.
			case BC_ACTION_CTRL_U:
			{
				bc_vec_string(&h->buf, 0, "");
				h->pos = 0;

				bc_history_refresh(h);

				break;
			}

			// Delete from current to end of line.
			case BC_ACTION_CTRL_K:
			{
				bc_vec_npop(&h->buf, h->buf.len - h->pos);
				bc_vec_pushByte(&h->buf, '\0');
				bc_history_refresh(h);
				break;
			}

			// Go to the start of the line.
			case BC_ACTION_CTRL_A:
			{
				bc_history_edit_home(h);
				break;
			}

			// Go to the end of the line.
			case BC_ACTION_CTRL_E:
			{
				bc_history_edit_end(h);
				break;
			}

			// Clear screen.
			case BC_ACTION_CTRL_L:
			{
				bc_file_write(&vm.fout, bc_flush_none, "\x1b[H\x1b[2J", 7);
				bc_history_refresh(h);
				break;
			}

			// Delete previous word.
			case BC_ACTION_CTRL_W:
			{
				bc_history_edit_deletePrevWord(h);
				break;
			}

			default:
			{
				if (c >= BC_ACTION_CTRL_A && c <= BC_ACTION_CTRL_Z)
					bc_history_printCtrl(h, c);
				else bc_history_edit_insert(h, cbuf, nread);
				break;
			}
		}
	}

	return BC_STATUS_SUCCESS;
}

static inline bool bc_history_stdinHasData(BcHistory *h) {
	int n;
	return pselect(1, &h->rdset, NULL, NULL, &h->ts, &h->sigmask) > 0 ||
	       (ioctl(STDIN_FILENO, FIONREAD, &n) >= 0 && n > 0);
}

/**
 * This function calls the line editing function bc_history_edit()
 * using the STDIN file descriptor set in raw mode.
 */
static BcStatus bc_history_raw(BcHistory *h, const char *prompt) {

	BcStatus s;

	assert(vm.fout.len == 0);

	bc_history_enableRaw(h);

	s = bc_history_edit(h, prompt);

	h->stdin_has_data = bc_history_stdinHasData(h);
	if (!h->stdin_has_data) bc_history_disableRaw(h);

	bc_file_write(&vm.fout, bc_flush_none, "\n", 1);
	bc_file_flush(&vm.fout, bc_flush_none);

	return s;
}

BcStatus bc_history_line(BcHistory *h, BcVec *vec, const char *prompt) {

	BcStatus s;
	char* line;

	s = bc_history_raw(h, prompt);
	assert(!s || s == BC_STATUS_EOF);

	bc_vec_string(vec, BC_HIST_BUF_LEN(h), h->buf.v);

	if (h->buf.v[0]) {

		BC_SIG_LOCK;

		line = bc_vm_strdup(h->buf.v);

		BC_SIG_UNLOCK;

		bc_history_add(h, line);
	}
	else bc_history_add_empty(h);

	bc_vec_concat(vec, "\n");

	return s;
}

static void bc_history_add(BcHistory *h, char *line) {

	if (h->history.len) {

		char *s = *((char**) bc_vec_item_rev(&h->history, 0));

		if (!strcmp(s, line)) {

			BC_SIG_LOCK;

			free(line);

			BC_SIG_UNLOCK;

			return;
		}
	}

	bc_vec_push(&h->history, &line);
}

static void bc_history_add_empty(BcHistory *h) {

	const char *line = "";

	if (h->history.len) {

		char *s = *((char**) bc_vec_item_rev(&h->history, 0));

		if (!s[0]) return;
	}

	bc_vec_push(&h->history, &line);
}

static void bc_history_string_free(void *str) {
	char *s = *((char**) str);
	BC_SIG_ASSERT_LOCKED;
	if (s[0]) free(s);
}

void bc_history_init(BcHistory *h) {

	BC_SIG_ASSERT_LOCKED;

	bc_vec_init(&h->buf, sizeof(char), NULL);
	bc_vec_init(&h->history, sizeof(char*), bc_history_string_free);
	bc_vec_init(&h->extras, sizeof(char), NULL);

	FD_ZERO(&h->rdset);
	FD_SET(STDIN_FILENO, &h->rdset);
	h->ts.tv_sec = 0;
	h->ts.tv_nsec = 0;

	sigemptyset(&h->sigmask);
	sigaddset(&h->sigmask, SIGINT);

	h->rawMode = h->stdin_has_data = false;
	h->badTerm = bc_history_isBadTerm();
}

void bc_history_free(BcHistory *h) {
	BC_SIG_ASSERT_LOCKED;
	bc_history_disableRaw(h);
#ifndef NDEBUG
	bc_vec_free(&h->buf);
	bc_vec_free(&h->history);
	bc_vec_free(&h->extras);
#endif // NDEBUG
}

/**
 * This special mode is used by bc history in order to print scan codes
 * on screen for debugging / development purposes.
 */
#if BC_DEBUG_CODE
void bc_history_printKeyCodes(BcHistory *h) {

	char quit[4];

	bc_vm_printf("Linenoise key codes debugging mode.\n"
	             "Press keys to see scan codes. "
	             "Type 'quit' at any time to exit.\n");

	bc_history_enableRaw(h);
	memset(quit, ' ', 4);

	while(true) {

		char c;
		ssize_t nread;

		nread = bc_history_read(&c, 1);
		if (nread <= 0) continue;

		// Shift string to left.
		memmove(quit, quit + 1, sizeof(quit) - 1);

		// Insert current char on the right.
		quit[sizeof(quit) - 1] = c;
		if (!memcmp(quit, "quit", sizeof(quit))) break;

		bc_vm_printf("'%c' %lu (type quit to exit)\n",
		             isprint(c) ? c : '?', (unsigned long) c);

		// Go left edge manually, we are in raw mode.
		bc_vm_putchar('\r', bc_flush_none);
		bc_file_flush(&vm.fout, bc_flush_none);
	}

	bc_history_disableRaw(h);
}
#endif // BC_DEBUG_CODE

#endif // BC_ENABLE_HISTORY