#pragma once

#include <stdint.h>

// The order in which display() flips the dots, and how it is spread over time.
// The numbers are part of the serial protocol (E command) and the ESP32 settings.
enum RefreshEffect : uint8_t
{
	EFFECT_INSTANT = 0, // column by column, left to right, as fast as possible
	EFFECT_SPARKLE = 1, // the changed dots one at a time, in a scrambled order
	EFFECT_WIPE = 2,    // column by column, left to right
	EFFECT_RAIN = 3,    // row by row, top to bottom
	EFFECT_CENTER = 4,  // column by column, from the middle outwards
	EFFECT_DIAGONAL = 5, // from the top left to the bottom right corner
	EFFECT_SPIRAL = 6,  // from the outside in, clockwise
	// The ones below are run by BROSE9323 itself (DotSequence uses column order for them)
	EFFECT_FLAP = 7,    // every dot to yellow (wipe), then the new image (wipe)
	EFFECT_PUSH = 8,    // the new image slides in from the right, pushing the old one out
	EFFECT_RANDOM = 9,  // one of the effects 1-8, chosen for each frame
	EFFECT_COUNT = 10,
};

// Flags for BROSE9323::setEffect()
const uint8_t EFFECT_FLAG_SMALL_ONLY = 1; // big changes (> 1/10 of the dots) are instant

// Visits every dot of a w x h display exactly once, in the order of an effect. Needs no
// buffer: the sparkle order comes from a maximal length LFSR (all states except 0, out
// of range values skipped), scrambled with a multiplication modulo the dot count.
class DotSequence
{
public:
	void begin(uint8_t effect, uint8_t w, uint8_t h, uint16_t seed)
	{
		_effect = effect < EFFECT_COUNT ? effect : EFFECT_INSTANT;
		_w = w;
		_h = h;
		_total = (uint16_t)w * h;
		_pos = 0;
		_diagonal = 0;
		_left = 0;
		_top = 0;
		_right = w - 1;
		_bottom = h - 1;
		_x = 0;
		_y = 0;
		_direction = 0;
		if (_effect != EFFECT_SPARKLE || _total == 0)
			return;

		uint8_t bits = 2;
		while (bits < 16 && ((1UL << bits) - 1) < _total)
			bits++;
		// Galois LFSR feedback masks with a maximal period, for 2..16 bits
		static const uint16_t masks[15] = {0x3, 0x6, 0xC, 0x14, 0x30, 0x60, 0xB8, 0x110,
										   0x240, 0x500, 0xE08, 0x1C80, 0x3802, 0x6000, 0xD008};
		_mask = masks[bits - 2];
		_period = (uint16_t)((1UL << bits) - 1);
		_lfsr = seed % _period + 1; // any state except 0

		// A multiplier without common factors with the total keeps the mapping 1:1
		_mult = 997 % _total;
		while (_mult == 0 || gcd(_mult, _total) != 1)
			_mult++;
	}

	// The next dot; false when every dot was visited
	bool next(uint8_t &x, uint8_t &y)
	{
		if (_effect == EFFECT_SPARKLE)
		{
			while (_pos < _period)
			{
				_pos++;
				uint16_t index = _lfsr - 1;
				_lfsr = (_lfsr & 1) ? (_lfsr >> 1) ^ _mask : _lfsr >> 1;
				if (index < _total)
				{
					uint16_t p = (uint32_t)index * _mult % _total;
					x = p % _w;
					y = p / _w;
					return true;
				}
			}
			return false;
		}

		if (_pos >= _total)
			return false;

		if (_effect == EFFECT_DIAGONAL)
		{
			// Diagonal d holds the dots with x + y = d, top to bottom
			while (true)
			{
				if (_y > (int16_t)_diagonal || _y >= _h)
				{
					_diagonal++;
					_y = 0;
					continue;
				}
				uint16_t dx = _diagonal - _y;
				uint8_t dy = _y++;
				if (dx < _w)
				{
					x = dx;
					y = dy;
					_pos++;
					return true;
				}
			}
		}

		if (_effect == EFFECT_SPIRAL)
		{
			x = _x;
			y = _y;
			_pos++;
			// Walk along the edge of the remaining rectangle, then make it smaller
			switch (_direction)
			{
			case 0: // right along the top
				if (_x < _right)
					_x++;
				else
				{
					_top++;
					_direction = 1;
					_y++;
				}
				break;
			case 1: // down the right side
				if (_y < _bottom)
					_y++;
				else
				{
					_right--;
					_direction = 2;
					_x--;
				}
				break;
			case 2: // left along the bottom
				if (_x > _left)
					_x--;
				else
				{
					_bottom--;
					_direction = 3;
					_y--;
				}
				break;
			default: // up the left side
				if (_y > _top)
					_y--;
				else
				{
					_left++;
					_direction = 0;
					_x++;
				}
				break;
			}
			return true;
		}

		uint16_t p = _pos++;
		if (_effect == EFFECT_RAIN)
		{
			x = p % _w;
			y = p / _w;
			return true;
		}
		uint8_t column = p / _h;
		y = p % _h;
		if (_effect == EFFECT_CENTER)
		{
			uint8_t middle = _w / 2;
			x = (column & 1) ? middle - (column + 1) / 2 : middle + column / 2;
		}
		else
			x = column;
		return true;
	}

	// Number of next() calls that return true
	uint16_t total() const { return _total; }

private:
	static uint16_t gcd(uint16_t a, uint16_t b)
	{
		while (b)
		{
			uint16_t t = a % b;
			a = b;
			b = t;
		}
		return a;
	}

	uint8_t _effect = EFFECT_INSTANT;
	uint8_t _w = 0, _h = 0;
	uint16_t _total = 0, _pos = 0;
	uint16_t _lfsr = 1, _mask = 0, _period = 0, _mult = 1;
	uint16_t _diagonal = 0;                                 // diagonal
	int16_t _left = 0, _top = 0, _right = 0, _bottom = 0;   // spiral
	int16_t _x = 0, _y = 0;                                 // spiral; _y also diagonal
	uint8_t _direction = 0;                                 // spiral
};