package main

import (
	"errors"
	"math/rand"
	"time"
)

type Cell struct {
	x    uint
	y    uint
	live bool
}

func (c *Cell) NeighborCount(arr [][]Cell) uint {
	// Read grid dimensions
	width := uint(len(arr))
	height := uint(len(arr[0]))

	count := uint(0)
	// Iterate through 3x3 neighboring grid
	for i := -1; i <= 1; i++ {
		for j := -1; j <= 1; j++ {
			// Ignore own position
			if i == 0 && j == 0 {
				continue
			}
			// Get neighbor coordinates
			nx := uint(int(c.x+width)+i) % width
			ny := uint(int(c.y+height)+j) % height
			// Count if neighbor is alive
			if arr[nx][ny].live {
				count++
			}
		}
	}
	return count
}

func initGrid(width, height uint, parent ...[][]Cell) ([][]Cell, error) {
	exists := len(parent) == 1
	if exists && len(parent) > 1 {
		return nil, errors.New("Too many parents specified")
	}

	// Make first dimension
	cells := make([][]Cell, width)
	for i := uint(0); i < width; i++ {
		// Make second dimension
		cells[i] = make([]Cell, height)
		for j := uint(0); j < height; j++ {
			// Make cells
			cells[i][j].x = i
			cells[i][j].y = j
			// If specified, copy state from parent
			if exists {
				cells[i][j].live = parent[0][i][j].live
			} else {
				cells[i][j].live = rand.Intn(2) == 1
			}
		}
	}
	return cells, nil
}

func setup(callback func([][]Cell), scale, width, height uint, FPS time.Duration) chan bool {
	// Initialize grid at specified scale
	grid, _ := initGrid(width/scale, height/scale)

	// Prepare ticker and finishing flag
	ticker := time.NewTicker((1000 / FPS) * time.Millisecond)
	done := make(chan bool)

	// Run game loop
	go func() {
		for {
			select {
			case <-done:
				return
			case <-ticker.C:
				grid = draw(grid, callback)
			}
		}
	}()

	// Return flag to be stopped outside
	return done
}

func draw(grid [][]Cell, callback func([][]Cell)) [][]Cell {
	width := uint(len(grid))
	height := uint(len(grid[0]))
	generation, _ := initGrid(width, height, grid)

	// Iterate through grid
	for i := uint(0); i < width; i++ {
		for j := uint(0); j < height; j++ {
			// Count neighbors
			cout := grid[i][j].NeighborCount(grid)
			// Get state
			curr := grid[i][j].live
			// Apply rules
			died := curr && (cout < 2 || cout > 3)
			born := !curr && cout == 3
			next := curr && !died || born
			// Set state
			generation[i][j].live = next
			//   A * !(A * (B + C)) + !A * D
			// = A * !B * !C + !A * D
			// curr && cout >= 2 && cout <= 3 || !curr && cout == 3
		}
	}
	callback(generation)
	return generation
}