#include "action_list.h"

// ===================================================================
// Helper method declarations
// ===================================================================

#define DANGER_MIN(a,b) (((a)<(b))?(a):(b))

#define CLR_STONE NUM_MASK

static inline void
action_list_prepend(action_list_t *list, const enum A_TYPE type,
										const int8_t loc, const uint8_t data0,
										const uint8_t data1);

// ===================================================================
// Exported method implementations
// ===================================================================

void action_list_free(action_list_t *list) {
	if (list) {
		action_node_t *n = list->head, *nn;
		while (n) {
			nn = n->next;
			free(n);
			n = nn;
		}
		free(list);
	}
}

// Keep track of move offsets
static int8_t deltas[4];

void action_list_init(void) {
	deltas[0] = +board_size;
	deltas[1] = -board_size;
	deltas[2] = -1;
	deltas[3] = +1;
}

action_list_t *action_list_generate(void) {
	action_list_t *result = malloc(sizeof(struct action_list_s));
	// TODO: trap errno
	result->length = 0;
	result->head = NULL;

	const uint8_t black = (ply < 2) ? (ply==1) : (ply & 1),
		material = (black) ? black_count : white_count,
		flat = material & 0x7F,
		cap = (ply >= 2 && (material & 0x80)),
		standing = (ply >= 2 && flat);

	// Step across the board, reversed because we prepend to the list
	for (int8_t row = board_size - 1; row >= 0; row--) {
		for (int8_t col = board_size - 1; col >= 0; col--) {
			// We'll need these at various points: the location of this
			// square and the maximum number of stones we could pick up
			const int8_t loc = THE_COORDS(col, row);
			const uint8_t count = DANGER_MIN(COUNT_AT(loc), board_size);
			// Only try moves after CPS
			if (ply >= 2 && count && ((colours[loc] & 1) == current_colour)) {
				// There are stones, let's try moving them

				// Pre-compute end-stops and crushes
				uint8_t end_stops[4], crushes[4] = {0, 0, 0, 0};

				// These are upper bounds, not counting walls and such. UP DOWN LEFT RIGHT
				end_stops[0] = DANGER_MIN(board_size - row - 1, count);
				end_stops[1] = DANGER_MIN(row, count);
				end_stops[2] = DANGER_MIN(col, count);
				end_stops[3] = DANGER_MIN(board_size - col - 1, count);

				// Now we check for caps and walls
				const uint8_t cap_top = STONE_AT(loc) == STONE_CAPSTONE;
				for (uint8_t d = 0; d < 4; d++){
					const int8_t delta = deltas[d];
					const uint8_t stop = end_stops[d];
					end_stops[d] = 0;
					for (uint8_t k = 1; k <= stop; k++) {
						const enum STONE_VARIANT stone = STONE_AT(loc+k*delta);
						if (stone == STONE_STANDING) {
							if (cap_top) {
								crushes[d] = 0xFF;
								end_stops[d]++;
							}
							break;
						} else if (stone == STONE_CAPSTONE) {
							break;
						}
						end_stops[d]++;
					}
				}
				/*
				 * For each direction, generate all possible ordered integer
				 * partitions of 1 ≤ num ≤ count whose number of summands is
				 * exactly 1 ≤ summands ≤ min(end_stops[dir], num) -- we write
				 * summands as steps
				 */
				for (enum MOVE_DIRECTION dir = M_UP; dir <= M_RIGHT; dir++) {
					for (uint8_t num = 1; num <= count; num++) {
						for (uint8_t steps = 1;
								 steps <= end_stops[dir] && steps <= num;
								 steps++) {
							// TODO: Generalise to board_size!
							uint8_t gaps = 0x07 >> (board_size-steps-1);
							// 0b0000[0111] because 4-1=3 and 5-1=4
							do  {
								/*
								 * We skip the partition if it calls for multiple stones at
								 * the end with a crush.
								 */
								const uint8_t last_drop_check =
									(num > 1) ? (gaps & 1<<(num - 2)) : 1;
								if (crushes[dir] == 0 || last_drop_check) {
									// We have to record a crush!
									// THIS IS WHERE THE PROBLEM IS
									const uint8_t crush = (steps == end_stops[dir]) && crushes[dir];
									action_list_prepend(result, A_MOVE, loc,
																			(crush << 7) | gaps,
																			(dir<<4) | num);
								}
								/*
								 * With thanks to
								 * https://graphics.stanford.edu/~seander/bithacks.html#NextBitPermutation
								 * we have the following magic to generate the next
								 * permutation of steps-many set bits
								 */
								uint8_t t = (gaps | (gaps - 1));
								gaps = (t + 1) | (((~t & -~t) - 1) >> (__builtin_ctz(gaps) + 1));
							} while (gaps && (gaps + 1 <= (1<<(num-1))));
						}
					}
				}
			} else if (count == 0 && material) {
				// Empty square, generate placements
				if (flat) {
					action_list_prepend(result, A_PLACE, loc,
															STONE_FLAT, 0);
					if (standing)
						action_list_prepend(result, A_PLACE, loc,
																STONE_STANDING, 0);
				}
				if (cap)
					action_list_prepend(result, A_PLACE, loc,
															STONE_CAPSTONE, 0);
			}
		}
	}
	return result;
}

void action_take(action_node_t *action) {
	const int8_t loc = action->loc;
	if (action->type == A_PLACE) {
		const uint8_t black = (current_colour == C_BLACK);
		switch (action->data0) {
			case STONE_FLAT: {
				if (black) black_count--;
				else white_count--;
				colours[loc] = current_colour;
				celldat[loc] = NUM_INC | STONE_FLAT;
				break;
			}
			case STONE_STANDING:  {
				if (black) black_count--;
				else white_count--;
				colours[loc] = current_colour;
				celldat[loc] = NUM_INC | STONE_STANDING;
				break;
			}
			default: {
				if (black) black_count &= 0x7F;
				else white_count &= 0x7F;
				colours[loc] = current_colour;
				celldat[loc] = NUM_INC | STONE_CAPSTONE;
				break;
			}
		}
	} else {
		const uint8_t gaps = action->data0 & 0x7F, // not interested in
																							// whether we crushed,
																							// it will work out by
																							// anyway because we
																							// overwrite the top
																							// stone type. See (*)
																							// later for when we do
																							// need to know.
			num = action->data1 & 0x0F, // unpack
			dir = action->data1 >> 4;
		int8_t delta = deltas[dir];

		// Use the Kernighan method to count the set bits
		int8_t steps = 1;
		for (uint8_t _gaps = gaps; _gaps; steps++) _gaps &= _gaps - 1;

		// Move top stone type to destination
		celldat[loc+steps*delta] &= CLR_STONE; // necessary for crushing
		celldat[loc+steps*delta] |= STONE_AT(loc);
		celldat[loc] &= CLR_STONE;
		celldat[loc] |= STONE_FLAT; // should be optimised out

		uint8_t total = 1, gap_bit = 1 << (num - 2); // it's not important
																								 // what negative
																								 // shifts do here, we
																								 // don't use gap_bit
																								 // if num < 2
		// move stuff starting at destination
		for (uint8_t d = 1; d < num; d++, total++, gap_bit >>= 1) {
			// We took a step, move everything over so far
			if (gaps & gap_bit) {
				colours[loc+steps*delta] <<= total;
				colours[loc+steps*delta] |= colours[loc] & ((1 << total) - 1);
				colours[loc] >>= total;
				celldat[loc+steps*delta] += total*NUM_INC;
				celldat[loc] -= total*NUM_INC;
				// Reset for next step
				total = 0;
				steps--;
			}
		}
		// Move what remains (steps == 1 here always, so we simplify)
		colours[loc+delta] <<= total;
		colours[loc+delta] |= colours[loc] & ((1 << total) - 1);
		colours[loc] >>= total;
		celldat[loc+delta] += total*NUM_INC;
		celldat[loc] -= total*NUM_INC;
	}
	// Next ply
	ply++;
	if (ply == 2) {
		current_colour = C_WHITE;
	} else {
		if (current_colour == C_BLACK) current_colour = C_WHITE;
		else current_colour = C_BLACK;
	}
}

void action_undo(action_node_t *action) {
	// Previous ply
	if (ply>0) ply--;
	if (ply == 1) {
		current_colour = C_WHITE;
	} else {
		if (current_colour == C_BLACK) current_colour = C_WHITE;
		else current_colour = C_BLACK;
	}

	const int8_t loc = action->loc;
	if (action->type == A_PLACE) {
		const uint8_t black = (current_colour == C_BLACK);
		celldat[loc] = 0;
		if (action->data0 == STONE_CAPSTONE) {
			if (black) black_count |= 0x80;
			else white_count |= 0x80;
		} else {
			if (black) black_count++;
			else white_count++;
		}
	} else {
		// See action_take for comments, this is the time reversal, but
		// there is one caveat -- undoing a crush! (*)
		const uint8_t gaps = action->data0 & 0x7F,
			crush = action->data0 & 0x80,
			num = action->data1 & 0x0F,
			dir = action->data1 >> 4;
		const int8_t delta = deltas[dir];

		int8_t steps = 1;
		uint8_t gap_bit = 1, total = 1;
		for (int8_t d = 1; d < num; d++, total++, gap_bit <<= 1) {
			if (gaps & gap_bit) {
				colours[loc] <<= total;
				colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1);
				colours[loc+steps*delta] >>= total;
				celldat[loc] += total*NUM_INC;
				celldat[loc+steps*delta] -= total*NUM_INC;
				total = 0;
				steps++;
			}
		}
		colours[loc] <<= total;
		colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1);
		colours[loc+steps*delta] >>= total;

		celldat[loc] += total*NUM_INC;
		// celldat[loc] &= CLR_STONE; is not necessary, as STONE_FLAT == 0
		celldat[loc] |= STONE_AT(loc+steps*delta);
		celldat[loc+steps*delta] -= total*NUM_INC;
		celldat[loc+steps*delta] &= CLR_STONE;
		if (crush) {
			celldat[loc+steps*delta] |= STONE_STANDING;
		} else {
			celldat[loc+steps*delta] |= STONE_FLAT; // should be optimised out
		}
	}
}

void action_to_ptn(action_node_t* action, char* out_ptn) {
	const int8_t loc = action->loc;
	if (action->type == A_PLACE) {
		generate_place(loc, action->data0, out_ptn);
	} else {
		const uint8_t gaps = action->data0 & 0x7F,
			num = action->data1 & 0x0F, // unpack
			dir = action->data1 >> 4;

		uint8_t drops[board_size]; // we only ever need board_size-1 in
															 // drops actually, the last spot is to
															 // skip a bounds check at (**)
		uint8_t mask = 1, steps = 0;
		// Translate to a drop sequence
		drops[0] = 1; mask = 1;
		for (uint8_t d = 1; d < num; d++) {
			if (gaps & mask) {
				steps++;
				drops[steps] = 1; // (**) no bounds check
			} else {
				drops[steps] += 1;
			}
			mask <<= 1;
		}
		generate_move(loc, dir, steps+1, drops, out_ptn);
	}
}

// ===================================================================
// Helper method implementations
// ===================================================================

static inline void
action_list_prepend(action_list_t *list, const enum A_TYPE type,
										const int8_t loc, const uint8_t data0,
										const uint8_t data1) {
	action_node_t *new = malloc(sizeof(action_list_t));
	// TODO: trap errno
	list->length++;
	new->loc = loc;
	new->type = type;
	new->data0 = data0;
	new->data1 = data1;
	new->next = list->head;
	list->head = new;
}