package tetris

import "math/rand/v2"

const (
	boardRows = 20
	boardCols = 10
)

// cell represents a single board cell. Zero value is empty.
type cell struct {
	filled bool
	piece  pieceType // which piece type filled this cell (for color)
}

// gameState holds all mutable state for a Tetris game.
type gameState struct {
	board      [boardRows][boardCols]cell
	current    pieceType
	currentRot int
	currentRow int
	currentCol int
	next       pieceType
	score      int
	level      int
	lines      int
	gameOver   bool
}

// newGame creates a new game state, optionally starting at a given level.
func newGame(startLevel int) *gameState {
	g := &gameState{
		level: startLevel,
		next:  pieceType(rand.IntN(numPieceTypes)),
	}
	g.spawnPiece()
	return g
}

// spawnPiece pulls the next piece and generates a new next.
func (g *gameState) spawnPiece() {
	g.current = g.next
	g.next = pieceType(rand.IntN(numPieceTypes))
	g.currentRot = 0
	g.currentRow = 0
	g.currentCol = spawnCol(g.current, 0)

	if !g.canPlace(g.current, g.currentRot, g.currentRow, g.currentCol) {
		g.gameOver = true
	}
}

// canPlace checks whether the piece fits at the given position.
func (g *gameState) canPlace(pt pieceType, rot, row, col int) bool {
	shape := pieces[pt][rot]
	for _, off := range shape {
		r, c := row+off[0], col+off[1]
		if r < 0 || r >= boardRows || c < 0 || c >= boardCols {
			return false
		}
		if g.board[r][c].filled {
			return false
		}
	}
	return true
}

// moveLeft moves the current piece left if possible.
func (g *gameState) moveLeft() bool {
	if g.canPlace(g.current, g.currentRot, g.currentRow, g.currentCol-1) {
		g.currentCol--
		return true
	}
	return false
}

// moveRight moves the current piece right if possible.
func (g *gameState) moveRight() bool {
	if g.canPlace(g.current, g.currentRot, g.currentRow, g.currentCol+1) {
		g.currentCol++
		return true
	}
	return false
}

// moveDown moves the current piece down one row. Returns false if it cannot.
func (g *gameState) moveDown() bool {
	if g.canPlace(g.current, g.currentRot, g.currentRow+1, g.currentCol) {
		g.currentRow++
		return true
	}
	return false
}

// rotate rotates the current piece clockwise with wall kick attempts.
func (g *gameState) rotate() bool {
	newRot := (g.currentRot + 1) % 4

	// Try in-place first.
	if g.canPlace(g.current, newRot, g.currentRow, g.currentCol) {
		g.currentRot = newRot
		return true
	}

	// Wall kick: try +-1 column offset.
	for _, offset := range []int{-1, 1} {
		if g.canPlace(g.current, newRot, g.currentRow, g.currentCol+offset) {
			g.currentRot = newRot
			g.currentCol += offset
			return true
		}
	}

	// I piece: try +-2.
	if g.current == pieceI {
		for _, offset := range []int{-2, 2} {
			if g.canPlace(g.current, newRot, g.currentRow, g.currentCol+offset) {
				g.currentRot = newRot
				g.currentCol += offset
				return true
			}
		}
	}

	return false
}

// ghostRow returns the row where the piece would land.
func (g *gameState) ghostRow() int {
	row := g.currentRow
	for g.canPlace(g.current, g.currentRot, row+1, g.currentCol) {
		row++
	}
	return row
}

// hardDrop drops the piece to the bottom and returns the number of rows dropped.
func (g *gameState) hardDrop() int {
	ghost := g.ghostRow()
	dropped := ghost - g.currentRow
	g.currentRow = ghost
	return dropped
}

// lockPiece writes the current piece into the board.
func (g *gameState) lockPiece() {
	shape := pieces[g.current][g.currentRot]
	for _, off := range shape {
		r, c := g.currentRow+off[0], g.currentCol+off[1]
		if r >= 0 && r < boardRows && c >= 0 && c < boardCols {
			g.board[r][c] = cell{filled: true, piece: g.current}
		}
	}
}

// clearLines removes completed rows and returns how many were cleared.
func (g *gameState) clearLines() int {
	cleared := 0
	for r := boardRows - 1; r >= 0; r-- {
		full := true
		for c := range boardCols {
			if !g.board[r][c].filled {
				full = false
				break
			}
		}
		if full {
			cleared++
			// Shift everything above down.
			for rr := r; rr > 0; rr-- {
				g.board[rr] = g.board[rr-1]
			}
			g.board[0] = [boardCols]cell{}
			r++ // re-check this row since we shifted
		}
	}
	return cleared
}

// NES-style scoring multipliers per lines cleared.
var lineScoreMultipliers = [5]int{0, 40, 100, 300, 1200}

// addScore updates score, lines, and level after clearing rows.
func (g *gameState) addScore(linesCleared int) {
	if linesCleared > 0 && linesCleared <= 4 {
		g.score += lineScoreMultipliers[linesCleared] * (g.level + 1)
	}
	g.lines += linesCleared

	// Level up every 10 lines.
	newLevel := g.lines / 10
	if newLevel > g.level {
		g.level = newLevel
	}
}

// afterLock locks the piece, clears lines, scores, and spawns the next piece.
// Returns the number of lines cleared.
func (g *gameState) afterLock() int {
	g.lockPiece()
	cleared := g.clearLines()
	g.addScore(cleared)
	g.spawnPiece()
	return cleared
}

// tickInterval returns the gravity interval in milliseconds for the current level.
func tickInterval(level int) int {
	return max(800-level*60, 100)
}