/* This file provides a termbox2-based backend for the Vis editor's terminal UI.
 * It is designed to be included from ui-terminal.c in place of ui-terminal-vt100.c
 * or ui-terminal-curses.c. Compile with termbox2 linked and define necessary
 * options like TB_OPT_ATTR_W=32 for truecolor support if desired.
 *
 * Focus is on portability, simplicity, and performance. We leverage termbox2's
 * double-buffering to eliminate flicker while keeping overhead low. Color
 * handling falls back gracefully from truecolor to 256 or 8 colors based on
 * terminal capabilities.
 *
 * Cells are inspected properly for content; empty data uses space. Colors map
 * from Vis CellColor (index or RGB) to termbox attrs, with approximation for
 * reduced palettes.
 */

#define TB_OPT_V1_COMPAT
#define TB_IMPL
#include "termbox2.h"
#define TB_OUTPUT_TRUECOLOR 1

#define CELL_COLOR_BLACK   { .index = 0 }
#define CELL_COLOR_RED     { .index = 1 }
#define CELL_COLOR_GREEN   { .index = 2 }
#define CELL_COLOR_YELLOW  { .index = 3 }
#define CELL_COLOR_BLUE    { .index = 4 }
#define CELL_COLOR_MAGENTA { .index = 5 }
#define CELL_COLOR_CYAN    { .index = 6 }
#define CELL_COLOR_WHITE   { .index = 7 }
#define CELL_COLOR_DEFAULT { .index = 9 }

#define CELL_ATTR_NORMAL    0
#define CELL_ATTR_UNDERLINE (1 << 0)
#define CELL_ATTR_REVERSE   (1 << 1)
#define CELL_ATTR_BLINK     (1 << 2)
#define CELL_ATTR_BOLD      (1 << 3)
#define CELL_ATTR_ITALIC    (1 << 4)
#define CELL_ATTR_DIM       (1 << 5)


#define UI_TERMKEY_FLAGS TERMKEY_FLAG_UTF8|TERMKEY_FLAG_NOTERMIOS

static int output_mode;

static const unsigned char color_256_to_16[256] = {
	 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
	 0,  4,  4,  4, 12, 12,  2,  6,  4,  4, 12, 12,  2,  2,  6,  4,
	12, 12,  2,  2,  2,  6, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10,
	10, 10, 10, 14,  1,  5,  4,  4, 12, 12,  3,  8,  4,  4, 12, 12,
	 2,  2,  6,  4, 12, 12,  2,  2,  2,  6, 12, 12, 10, 10, 10, 10,
	14, 12, 10, 10, 10, 10, 10, 14,  1,  1,  5,  4, 12, 12,  1,  1,
	 5,  4, 12, 12,  3,  3,  8,  4, 12, 12,  2,  2,  2,  6, 12, 12,
	10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14,  1,  1,  1,  5,
	12, 12,  1,  1,  1,  5, 12, 12,  1,  1,  1,  5, 12, 12,  3,  3,
	 3,  7, 12, 12, 10, 10, 10, 10, 14, 12, 10, 10, 10, 10, 10, 14,
	 9,  9,  9,  9, 13, 12,  9,  9,  9,  9, 13, 12,  9,  9,  9,  9,
	13, 12,  9,  9,  9,  9, 13, 12, 11, 11, 11, 11,  7, 12, 10, 10,
	10, 10, 10, 14,  9,  9,  9,  9,  9, 13,  9,  9,  9,  9,  9, 13,
	 9,  9,  9,  9,  9, 13,  9,  9,  9,  9,  9, 13,  9,  9,  9,  9,
	 9, 13, 11, 11, 11, 11, 11, 15,  0,  0,  0,  0,  0,  0,  8,  8,
	 8,  8,  8,  8,  7,  7,  7,  7,  7,  7, 15, 15, 15, 15, 15, 15
};

static void get_6cube_rgb(unsigned int n, int *r, int *g, int *b) {
	if (n < 16) {
		return;
	} else if (n < 232) {
		n -= 16;
		*r = (n / 36) ? (n / 36) * 40 + 55 : 0;
		*g = ((n / 6) % 6) ? ((n / 6) % 6) * 40 + 55 : 0;
		*b = (n % 6) ? (n % 6) * 40 + 55 : 0;
	} else if (n < 256) {
		n -= 232;
		*r = n * 10 + 8;
		*g = n * 10 + 8;
		*b = n * 10 + 8;
	}
}

static inline bool cell_color_equal(CellColor c1, CellColor c2) {
	if (c1.index != (uint8_t)-1 || c2.index != (uint8_t)-1)
		return c1.index == c2.index;
	return c1.r == c2.r && c1.g == c2.g && c1.b == c2.b;
}

static CellColor color_rgb(Ui *ui, uint8_t r, uint8_t g, uint8_t b) {
	return (CellColor){ .r = r, .g = g, .b = b, .index = (uint8_t)-1 };
}

static CellColor color_terminal(Ui *ui, uint8_t index) {
	return (CellColor){ .r = 0, .g = 0, .b = 0, .index = index };
}

static uintattr_t get_tb_attr(CellAttr a) {
	uintattr_t ret = 0;
	if (a & CELL_ATTR_BOLD) ret |= TB_BOLD;
	if (a & CELL_ATTR_UNDERLINE) ret |= TB_UNDERLINE;
	if (a & CELL_ATTR_REVERSE) ret |= TB_REVERSE;
	if (a & CELL_ATTR_BLINK) ret |= TB_BLINK;
	if (a & CELL_ATTR_ITALIC) ret |= TB_ITALIC;
	if (a & CELL_ATTR_DIM) ret |= TB_DIM;
	return ret;
}

static uintattr_t get_tb_color(CellColor c) {
	int mode = output_mode;
	int r, g, b;
	if (c.index != (uint8_t)-1) {
		if (c.index == 9) return TB_DEFAULT;
		static const int ansi_r[8] = {0, 128, 0, 128, 0, 128, 0, 192};
		static const int ansi_g[8] = {0, 0, 128, 128, 0, 0, 128, 192};
		static const int ansi_b[8] = {0, 0, 0, 0, 128, 128, 128, 192};
		r = ansi_r[c.index];
		g = ansi_g[c.index];
		b = ansi_b[c.index];
	} else {
		r = c.r; g = c.g; b = c.b;
	}

	if (mode == TB_OUTPUT_TRUECOLOR) {
		return (r << 16) | (g << 8) | b;
	}

	// Approximate to 256-color index
	int i = 0;
	if ((!r || (r - 55) % 40 == 0) &&
	    (!g || (g - 55) % 40 == 0) &&
	    (!b || (b - 55) % 40 == 0)) {
		i = 16;
		i += r ? ((r - 55) / 40) * 36 : 0;
		i += g ? ((g - 55) / 40) * 6 : 0;
		i += b ? ((b - 55) / 40) : 0;
	} else if (r == g && g == b && (r - 8) % 10 == 0 && r < 239) {
		i = 232 + ((r - 8) / 10);
	} else {
		unsigned lowest = UINT_MAX;
		for (int j = 16; j < 256; ++j) {
			int jr, jg, jb;
			get_6cube_rgb(j, &jr, &jg, &jb);
			int dr = jr - r, dg = jg - g, db = jb - b;
			unsigned distance = dr * dr + dg * dg + db * db;
			if (distance < lowest) {
				lowest = distance;
				i = j;
			}
		}
	}

	if (mode == TB_OUTPUT_256) {
		return i;
	} else { // TB_OUTPUT_NORMAL
		int idx16 = color_256_to_16[i];
		if (idx16 == 0) return TB_BLACK; // Treat as black for non-default
		if (idx16 < 8) return idx16 + 1;
		return (idx16 - 8 + 1) | TB_BRIGHT;
	}
}

static void ui_term_backend_blit(Ui *tui) {
	int w = tui->width, h = tui->height;
	Cell *cell = tui->cells;
	for (int y = 0; y < h; y++) {
		for (int x = 0; x < w; x++) {
			uint32_t ch = ' ';
			tb_utf8_char_to_unicode(&ch, cell->data);
			uintattr_t fg = get_tb_color(cell->style.fg) | get_tb_attr(cell->style.attr);
			uintattr_t bg = get_tb_color(cell->style.bg);
			tb_change_cell(x, y, ch, fg, bg);
			cell++;
		}
	}
	tb_present();
}

static void ui_term_backend_clear(Ui *tui) {
	tb_clear();
}

static bool ui_term_backend_resize(Ui *tui, int width, int height) {
	return true; // termbox2 handles resize internally
}

static void ui_term_backend_save(Ui *tui, bool fscr) {
	tb_shutdown();
}

static void ui_term_backend_restore(Ui *tui) {
	tb_init();
	tb_select_output_mode(output_mode);
	tb_hide_cursor();
	tb_clear();
}

int ui_terminal_colors(void) {
	switch (output_mode) {
	case TB_OUTPUT_TRUECOLOR: return 16777216;
	case TB_OUTPUT_256: return 256;
	default: return 16;
	}
}

static bool ui_term_backend_init(Ui *tui, char *term) {
	if (tb_init() < 0) return false;
	output_mode = tb_select_output_mode(TB_OUTPUT_TRUECOLOR);
	if (output_mode != TB_OUTPUT_TRUECOLOR)
		output_mode = tb_select_output_mode(TB_OUTPUT_256);
	if (output_mode != TB_OUTPUT_256)
		output_mode = TB_OUTPUT_NORMAL;
	tb_hide_cursor();
	return true;
}

static bool ui_backend_init(Ui *ui) {
	return true;
}

void ui_terminal_resume(Ui *term) { }

static void ui_term_backend_suspend(Ui *tui) { }

static void ui_term_backend_free(Ui *tui) {
	tb_shutdown();
}

static bool is_default_color(CellColor c) {
	return c.index == ((CellColor) CELL_COLOR_DEFAULT).index;
}