# Minimal Global Functions for Puzzle8 Game
# Simple, fast, and focused on core gameplay

# Constants
SOLVED_STATE <- c(1, 2, 3, 4, 5, 6, 7, 8, 0)

# Utility functions
pos_to_coords <- function(pos) {
  list(row = (pos - 1) %/% 3 + 1, col = (pos - 1) %% 3 + 1)
}

coords_to_pos <- function(row, col) {
  (row - 1) * 3 + col
}

is_valid_position <- function(row, col) {
  row >= 1 && row <= 3 && col >= 1 && col <= 3
}

# Create a solvable puzzle using simple shuffling
create_solvable_puzzle <- function(moves = 100) {
  puzzle <- SOLVED_STATE
  blank_pos <- 9
  
  # Simple shuffling with valid moves
  for(i in 1:moves) {
    coords <- pos_to_coords(blank_pos)
    valid_moves <- c()
    
    # Check all four directions
    directions <- list(
      list(row = -1, col = 0),  # Up
      list(row = 1, col = 0),   # Down
      list(row = 0, col = -1),  # Left
      list(row = 0, col = 1)    # Right
    )
    
    for(dir in directions) {
      new_row <- coords$row + dir$row
      new_col <- coords$col + dir$col
      
      if(is_valid_position(new_row, new_col)) {
        valid_moves <- c(valid_moves, coords_to_pos(new_row, new_col))
      }
    }
    
    if(length(valid_moves) > 0) {
      move_pos <- sample(valid_moves, 1)
      
      # Swap tiles
      temp <- puzzle[blank_pos]
      puzzle[blank_pos] <- puzzle[move_pos]
      puzzle[move_pos] <- temp
      
      blank_pos <- move_pos
    }
  }
  
  # Ensure puzzle is not already solved
  if(identical(puzzle, SOLVED_STATE)) {
    return(create_solvable_puzzle(moves + 20))
  }
  
  return(puzzle)
}

# Check if puzzle is solved
is_solved <- function(puzzle) {
  identical(puzzle, SOLVED_STATE)
}

# Get blank position
get_blank_position <- function(puzzle) {
  which(puzzle == 0)[1]
}

# Get valid moves for current blank position
get_valid_moves <- function(blank_pos) {
  coords <- pos_to_coords(blank_pos)
  valid_moves <- c()
  
  directions <- list(
    list(row = -1, col = 0),  # Up
    list(row = 1, col = 0),   # Down
    list(row = 0, col = -1),  # Left
    list(row = 0, col = 1)    # Right
  )
  
  for(dir in directions) {
    new_row <- coords$row + dir$row
    new_col <- coords$col + dir$col
    
    if(is_valid_position(new_row, new_col)) {
      valid_moves <- c(valid_moves, coords_to_pos(new_row, new_col))
    }
  }
  
  return(valid_moves)
}

# Move tile with validation - core game mechanic
move_tile <- function(puzzle, tile_position) {
  blank_pos <- get_blank_position(puzzle)
  valid_moves <- get_valid_moves(blank_pos)
  
  if(tile_position %in% valid_moves) {
    # Create new puzzle state
    new_puzzle <- puzzle
    new_puzzle[blank_pos] <- puzzle[tile_position]
    new_puzzle[tile_position] <- 0
    
    return(list(puzzle = new_puzzle, moved = TRUE))
  }
  
  return(list(puzzle = puzzle, moved = FALSE))
}

# Check if puzzle is solvable using inversion count
is_solvable <- function(puzzle) {
  # Count inversions (excluding blank tile)
  tiles <- puzzle[puzzle != 0]
  inversions <- 0
  
  for(i in 1:(length(tiles) - 1)) {
    for(j in (i + 1):length(tiles)) {
      if(tiles[i] > tiles[j]) {
        inversions <- inversions + 1
      }
    }
  }
  
  # For 3x3 puzzle, solvable if inversions are even
  return(inversions %% 2 == 0)
}

# Validate puzzle state
validate_puzzle <- function(puzzle) {
  # Check length
  if(length(puzzle) != 9) {
    return(FALSE)
  }
  
  # Check if all numbers 0-8 are present exactly once
  expected_tiles <- 0:8
  if(!setequal(puzzle, expected_tiles)) {
    return(FALSE)
  }
  
  # Check if solvable
  if(!is_solvable(puzzle)) {
    return(FALSE)
  }
  
  return(TRUE)
}

# Generate test puzzles for development
generate_test_puzzles <- function(n = 5) {
  puzzles <- list()
  
  for(i in 1:n) {
    repeat {
      puzzle <- create_solvable_puzzle()
      if(validate_puzzle(puzzle) && !is_solved(puzzle)) {
        puzzles[[i]] <- puzzle
        break
      }
    }
  }
  
  return(puzzles)
}

# Simple puzzle statistics
get_puzzle_stats <- function(puzzle) {
  blank_pos <- get_blank_position(puzzle)
  valid_moves <- get_valid_moves(blank_pos)
  
  return(list(
    blank_position = blank_pos,
    valid_moves = valid_moves,
    num_valid_moves = length(valid_moves),
    is_solved = is_solved(puzzle),
    is_valid = validate_puzzle(puzzle)
  ))
}