/* libfmt/quote.c - C-string quoting for pico-fmt
 *
 * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#include <string.h> /* for strnlen() */
#include <stdint.h> /* for uint{n}_t() */

#include <libfmt/fmt.h>

enum quote {
	QUOTE_NONE,   /* c */
	QUOTE_SIMPLE, /* \c */
	QUOTE_U4,     /* \uABCD */
	QUOTE_U8,     /* \UABCDABCD */
};

static inline enum quote needs_quote(uint32_t ch) {
	if (ch == '\a' ||
	    ch == '\b' ||
	    ch == '\f' ||
	    ch == '\n' ||
	    ch == '\r' ||
	    ch == '\t' ||
	    ch == '\v' ||
	    ch == '\\' ||
	    ch == '\'' ||
	    ch == '"' ||
	    ch == '?')
		return QUOTE_SIMPLE;
	else if (' ' <= ch && ch <= '~')
		return QUOTE_NONE;
	else if (ch < 0x10000)
		return QUOTE_U4;
	else
		return QUOTE_U8;
}

/**
 * Quote a string to ASCII-only C syntax.  Valid UTF-8 is quoted as
 * short C-escape characters, \uABCD or \UABCDABCD; invalid UTF-8 is
 * quoted as \xAB.
 */
static void libfmt_conv_quote(struct fmt_state *state) {
    uint32_t ch;
    uint8_t chlen;

    const char *in = va_arg(*state->args, char*);
    size_t in_len = strnlen(in, (state->flags & FMT_FLAG_PRECISION) ? state->precision : (size_t)-1);

    size_t out_len = 2;
    for (size_t pos = 0; pos < in_len;) {
	    if      ((in[pos] & 0b10000000) == 0b00000000) { ch = in[pos] & 0b01111111; chlen = 1; }
	    else if ((in[pos] & 0b11100000) == 0b11000000) { ch = in[pos] & 0b00011111; chlen = 2; }
	    else if ((in[pos] & 0b11110000) == 0b11100000) { ch = in[pos] & 0b00001111; chlen = 3; }
	    else if ((in[pos] & 0b11111000) == 0b11110000) { ch = in[pos] & 0b00000111; chlen = 4; }
	    else goto measure_invalid_utf8;
	    if ((ch == 0 && chlen != 1) || pos + chlen > in_len) goto measure_invalid_utf8;
	    for (uint8_t i = 1; i < chlen; i++) {
		    if ((in[pos+i] & 0b11000000) != 0b10000000) goto measure_invalid_utf8;
		    ch = (ch << 6) | (in[pos+i] & 0b00111111);
	    }
	    if (ch > 0x10FFFF) goto measure_invalid_utf8;
	    pos += chlen;

	    switch (needs_quote(ch)) {
	    case QUOTE_NONE   : out_len +=  1; break;
	    case QUOTE_SIMPLE : out_len +=  2; break;
	    case QUOTE_U4     : out_len +=  6; break;
	    case QUOTE_U8     : out_len += 10; break;
	    }
	    continue;
    measure_invalid_utf8:
	    pos++;
	    out_len += 4; /* \xAB */
    }

    if (!(state->flags & FMT_FLAG_LEFT)) {
	    for (size_t i = 0; i + out_len < state->width; i++) {
		    fmt_state_putchar(state, ' ');
	    }
    }

    fmt_state_putchar(state, '"');
    for (size_t pos = 0; pos < in_len;) {
	    if      ((in[pos] & 0b10000000) == 0b00000000) { ch = in[pos] & 0b01111111; chlen = 1; }
	    else if ((in[pos] & 0b11100000) == 0b11000000) { ch = in[pos] & 0b00011111; chlen = 2; }
	    else if ((in[pos] & 0b11110000) == 0b11100000) { ch = in[pos] & 0b00001111; chlen = 3; }
	    else if ((in[pos] & 0b11111000) == 0b11110000) { ch = in[pos] & 0b00000111; chlen = 4; }
	    else goto output_invalid_utf8;
	    if ((ch == 0 && chlen != 1) || pos + chlen > in_len) goto output_invalid_utf8;
	    for (uint8_t i = 1; i < chlen; i++) {
		    if ((in[pos+i] & 0b11000000) != 0b10000000) goto output_invalid_utf8;
		    ch = (ch << 6) | (in[pos+i] & 0b00111111);
	    }
	    if (ch > 0x10FFFF) goto output_invalid_utf8;
	    pos += chlen;

	    switch (needs_quote(ch)) {
	    case QUOTE_NONE:
		    fmt_state_putchar(state, ch);
		    break;
	    case QUOTE_SIMPLE:
		    fmt_state_putchar(state, '\\');
		    switch (ch) {
		    case '\a': fmt_state_putchar(state, 'a'); break;
		    case '\b': fmt_state_putchar(state, 'b'); break;
		    case '\f': fmt_state_putchar(state, 'f'); break;
		    case '\n': fmt_state_putchar(state, 'n'); break;
		    case '\r': fmt_state_putchar(state, 'r'); break;
		    case '\t': fmt_state_putchar(state, 't'); break;
		    case '\v': fmt_state_putchar(state, 'v'); break;
		    case '\\': fmt_state_putchar(state, '\\'); break;
		    case '\'': fmt_state_putchar(state, '\''); break;
		    case '"': fmt_state_putchar(state, '"'); break;
		    case '?': fmt_state_putchar(state, '?'); break;
		    }
		    break;
	    case QUOTE_U4:
		    fmt_state_putchar(state, '\\');
		    fmt_state_putchar(state, 'u');
		    fmt_state_putchar(state, (ch >> 12) & 0xF);
		    fmt_state_putchar(state, (ch >>  8) & 0xF);
		    fmt_state_putchar(state, (ch >>  4) & 0xF);
		    fmt_state_putchar(state, (ch >>  0) & 0xF);
		    break;
	    case QUOTE_U8:
		    fmt_state_putchar(state, '\\');
		    fmt_state_putchar(state, 'U');
		    fmt_state_putchar(state, (ch >> 28) & 0xF);
		    fmt_state_putchar(state, (ch >> 24) & 0xF);
		    fmt_state_putchar(state, (ch >> 20) & 0xF);
		    fmt_state_putchar(state, (ch >> 16) & 0xF);
		    fmt_state_putchar(state, (ch >> 12) & 0xF);
		    fmt_state_putchar(state, (ch >>  8) & 0xF);
		    fmt_state_putchar(state, (ch >>  4) & 0xF);
		    fmt_state_putchar(state, (ch >>  0) & 0xF);
		    break;
	    }
	    continue;
    output_invalid_utf8:
	    fmt_state_putchar(state, '\\');
	    fmt_state_putchar(state, 'x');
	    fmt_state_putchar(state, (in[pos] >> 4) & 0xF);
	    fmt_state_putchar(state, (in[pos] >> 0) & 0xF);
	    pos++;
    }
    fmt_state_putchar(state, '"');

    for (size_t i = 0; i + out_len < state->width; i++) {
	    fmt_state_putchar(state, ' ');
    }
}

[[gnu::constructor]]
static void libfmt_install_quote(void) {
	fmt_install('q', libfmt_conv_quote);
}