// uckf creates a deeply unsatisfying word search.

package main

import (
	"flag"
	"fmt"
	"log"
	"math/rand"
)

var edgeSize = flag.Int("n", 4, "Cells per side")

type scanState int
const (
	FuckIfIKnow scanState = iota
	Fucked
	NotFucked
)

type fuckness [3][3]scanState

func main() {
	flag.Parse()
	if (*edgeSize < 4) {
		log.Fatalf("can't fit a fuck into edge size %d", *edgeSize)
	}
	var board [][]byte
	for i := 0; i < *edgeSize; i++ {
		fuckingRow := make([]byte, *edgeSize)
		for j := 0; j < *edgeSize; j++ {
			fuckingRow[j] = byte((i+j)%4)
		}
		board=append(board, fuckingRow)
	}

	dump(board, "Starting position")

	var evals [][]fuckness
	for i := 0; i < *edgeSize; i++ {
		evals = append(evals, make([]fuckness, *edgeSize))
	}

	iterations := uint64(0)
	scream := uint64(1)
	for(isStillFucked(board, evals)) {
		fuckUp(board, evals)
		iterations++
		if iterations >= scream {
			dump(board, fmt.Sprint("Iteration", iterations))
			scream = iterations << 1
		}
	}

	dump(board, "Not a single fuck")
}

func onBoard(i, j int) bool {
	return i > 0 && j > 0 && i < *edgeSize && j < *edgeSize
}
func charAt(board [][]byte, i, j int) byte {
	if !onBoard(i, j) {
		return 5
	}
	return board[i][j]
}

func isStillFucked(board [][]byte, evals[][]fuckness) bool {
	isFucked := false
	for i, row := range board {
		for j, c := range row {
			for dr := -1; dr <= 1; dr++ {
				for dc := -1; dc <= 1; dc++ {
					if dr == 0 && dc == 0 {
						continue
					}
					if evals[i][j][dr+1][dc+1] == Fucked {
						isFucked = true
						continue
					}
					if evals[i][j][dr+1][dc+1] != FuckIfIKnow {
						continue
					}
					// find theoretical start of fuck
					fRow, fCol := i + int(c)*-dr, j + int(c)*-dc
					// evaluate fuckness
					locallyFucked := true
					for w := 0; w < 4; w++ {
						if charAt(board, fRow+w*dr, fCol+w*dc) != byte(w) {
							locallyFucked = false
							break
						}
					}
					if locallyFucked {
						// mark every letter involved as fucked
						isFucked = true
						for w := 0; w < 4; w++ {
							evals[i+w*dr][j+w*dc][dr+1][dc+1] = Fucked
						}
					} else {
						evals[i][j][dr+1][dc+1] = NotFucked
					}
				}
			}
		}
	}
	return isFucked
}

func isFucked(f fuckness) bool {
	for i := 0; i <3; i++ {
		for j := 0; j < 3; j++ {
			if i == 1 && j == 1 {
				continue
			}
			if f[i][j] == Fucked {
				return true
			}
		}
	}
	return false
}

func mightBeFucked(f fuckness) bool {
	for i := 0; i <3; i++ {
		for j := 0; j < 3; j++ {
			if i == 1 && j == 1 {
				continue
			}
			if f[i][j] == NotFucked {
				return true
			}
		}
	}
	return false
}

func fuckUp(board [][]byte, evals [][]fuckness) {
	var todo [][2]int
	for i, row := range evals {
		for j, e := range row {
			if isFucked(e) {
				todo = append(todo, [2]int{i, j})
			} else if mightBeFucked(e) {
				dump(board, "Oh fuck")
				log.Fatalf("unevaluated fuckness at %d, %d: %v", i, j, e)
			}
		}
	}

	rand.Shuffle(len(todo), func(i, j int) {
		todo[j], todo[i] = todo[i], todo[j]
	})

	// note: "head" moves frequently within this loop
	for head := 0; head < len(todo); head++ {
		item := todo[head]
		i, j := item[0], item[1]
		if(!isFucked(evals[i][j])) {
			continue
		}
		i2, j2 := -1, -1
		for head++; head < len(todo); head++ {
			item2 := todo[head]
			itmp, jtmp := item2[0], item2[1]
			if(isFucked(evals[itmp][jtmp])) {
				i2, j2 = itmp, jtmp
				break
			}
		}
		if i2 == -1 {
			// fuck it, swap randomly
			i2 = rand.Intn(*edgeSize)
			j2 = rand.Intn(*edgeSize)
		}
		if board[i][j] != board[i2][j2] {
			unevaluate(evals, i, j)
			unevaluate(evals, i2, j2)
			board[i][j], board[i2][j2] = board[i2][j2], board[i][j]
		}
	}
}

func unevaluate(evals [][]fuckness, i, j int) {
	for dr := -1; dr <= 1; dr++ {
		for dc := -1; dc <= 1; dc++ {
			for x := -3; x < 4; x++ {
				r := i + dr * x
				c := j + dc * x
				if onBoard(r, c) {
					evals[r][c][dr+1][dc+1] = FuckIfIKnow
				}
			}
		}
	}
}

func dump(board [][]byte, title string) {
	fmt.Println()
	for i := 0; i < *edgeSize; i++ {
		fmt.Print("--")
	}
	fmt.Println()
	fmt.Println(title)
	fmt.Println()
	for _, row := range board {
		for _, r := range row {
			fmt.Printf("%c ", "fuck"[r])
		}
		fmt.Println()
	}
}