package field

import (
	"fmt"
	"slices"
	"strconv"
	"strings"
)

type Properties struct {
	Rows            int
	Columns         int
	BlockRows       int
	BlockColumns    int
	BlockSizeRow    int
	BlockSizeColumn int
	Rating          float64
}

type Field struct {
	props   *Properties
	cells   [][]Cell
	changes []Change
}

type fieldSnapshot struct {
	numbers [][]int
	notes   [][][]int
	changes []Change
}

func New(props Properties, cells [][]Cell) (*Field, error) {
	if err := validateProperties(props); err != nil {
		return nil, err
	}
	if len(cells) != props.Rows {
		return nil, fmt.Errorf("%w: expected %d rows, got %d", ErrInvalidField, props.Rows, len(cells))
	}

	cloned := make([][]Cell, props.Rows)
	for row := 0; row < props.Rows; row++ {
		if len(cells[row]) != props.Columns {
			return nil, fmt.Errorf("%w: row %d has %d cells, expected %d", ErrInvalidField, row, len(cells[row]), props.Columns)
		}
		cloned[row] = make([]Cell, props.Columns)
		for column := 0; column < props.Columns; column++ {
			source := &cells[row][column]
			if source.pos == nil {
				return nil, fmt.Errorf("%w: cell %d/%d has no position", ErrInvalidField, row, column)
			}
			if !positionMatches(source.pos, props, row, column) {
				return nil, fmt.Errorf("%w: cell %d/%d has inconsistent position", ErrInvalidField, row, column)
			}
			if source.number < 0 || source.number > props.Rows {
				return nil, fmt.Errorf("%w: cell %d/%d contains %d", ErrInvalidField, row, column, source.number)
			}
			if source.notes == nil {
				return nil, fmt.Errorf("%w: cell %d/%d has no notes", ErrInvalidField, row, column)
			}
			notes, err := normalizeNotes(source.notes.numbers, props.Rows, source.number)
			if err != nil {
				return nil, fmt.Errorf("%w: cell %d/%d: %w", ErrInvalidField, row, column, err)
			}
			cloned[row][column] = Cell{
				number: source.number,
				notes:  &Notes{numbers: notes},
				pos:    NewPosition(row, column, row/props.BlockSizeRow, column/props.BlockSizeColumn, row%props.BlockSizeRow, column%props.BlockSizeColumn),
			}
		}
	}

	result := &Field{props: &props, cells: cloned}
	if !result.hasValidNumbers() || !result.hasValidNotes() {
		return nil, fmt.Errorf("%w: duplicate values or invalid candidates", ErrInvalidField)
	}
	return result, nil
}

func validateProperties(props Properties) error {
	if props.Rows <= 0 || props.Columns <= 0 || props.Rows != props.Columns {
		return fmt.Errorf("%w: rows and columns must be equal and positive", ErrInvalidField)
	}
	if props.BlockRows <= 0 || props.BlockColumns <= 0 || props.BlockSizeRow <= 0 || props.BlockSizeColumn <= 0 {
		return fmt.Errorf("%w: block dimensions must be positive", ErrInvalidField)
	}
	if props.BlockRows*props.BlockSizeRow != props.Rows || props.BlockColumns*props.BlockSizeColumn != props.Columns {
		return fmt.Errorf("%w: block dimensions do not cover the field", ErrInvalidField)
	}
	if props.BlockSizeRow*props.BlockSizeColumn != props.Rows {
		return fmt.Errorf("%w: each block must contain %d cells", ErrInvalidField, props.Rows)
	}
	return nil
}

func normalizeNotes(notes []int, max, cellNumber int) ([]int, error) {
	if cellNumber != 0 && len(notes) != 0 {
		return nil, fmt.Errorf("filled cells cannot contain notes")
	}
	result := slices.Clone(notes)
	slices.Sort(result)
	result = slices.Compact(result)
	for _, note := range result {
		if note < 1 || note > max {
			return nil, fmt.Errorf("note %d is out of range", note)
		}
	}
	return result, nil
}

func positionMatches(pos *Position, props Properties, row, column int) bool {
	return pos.row == row && pos.column == column &&
		pos.blockRow == row/props.BlockSizeRow && pos.blockColumn == column/props.BlockSizeColumn &&
		pos.inBlockRow == row%props.BlockSizeRow && pos.inBlockColumn == column%props.BlockSizeColumn
}

func (f *Field) GetRow(row int) (*Row, error) {
	if !f.hasStructure() || row < 0 || row >= f.props.Rows {
		return nil, ErrOutOfBounds
	}
	cells := make([]*Cell, f.props.Columns)
	for column := range f.cells[row] {
		cells[column] = &f.cells[row][column]
	}
	return &Row{Line: Line{cells: cells}}, nil
}

func (f *Field) GetColumn(column int) (*Column, error) {
	if !f.hasStructure() || column < 0 || column >= f.props.Columns {
		return nil, ErrOutOfBounds
	}
	cells := make([]*Cell, f.props.Rows)
	for row := range f.cells {
		cells[row] = &f.cells[row][column]
	}
	return &Column{Line: Line{cells: cells}}, nil
}

func (f *Field) GetBlock(row, column int) (*Block, error) {
	if !f.hasStructure() || row < 0 || row >= f.props.BlockRows || column < 0 || column >= f.props.BlockColumns {
		return nil, ErrOutOfBounds
	}
	startRow := row * f.props.BlockSizeRow
	startColumn := column * f.props.BlockSizeColumn
	cells := make([][]*Cell, f.props.BlockSizeRow)
	for blockRow := range cells {
		cells[blockRow] = make([]*Cell, f.props.BlockSizeColumn)
		for blockColumn := range cells[blockRow] {
			cells[blockRow][blockColumn] = &f.cells[startRow+blockRow][startColumn+blockColumn]
		}
	}
	return &Block{cells: cells}, nil
}

func (f *Field) GetEachPartAtPos(pos *Position) ([]Part, error) {
	if pos == nil {
		return nil, ErrOutOfBounds
	}
	row, err := f.GetRow(pos.row)
	if err != nil {
		return nil, err
	}
	column, err := f.GetColumn(pos.column)
	if err != nil {
		return nil, err
	}
	block, err := f.GetBlock(pos.blockRow, pos.blockColumn)
	if err != nil {
		return nil, err
	}
	return []Part{row, column, block}, nil
}

func (f *Field) GetCell(row, column int) (*Cell, error) {
	if !f.hasStructure() || row < 0 || row >= f.props.Rows || column < 0 || column >= f.props.Columns {
		return nil, ErrOutOfBounds
	}
	return &f.cells[row][column], nil
}

func (f *Field) GetProperties() (Properties, error) {
	if !f.hasStructure() {
		return Properties{}, ErrInvalidField
	}
	return *f.props, nil
}

func (f *Field) GetRating() float64 {
	if !f.hasStructure() {
		return 0
	}
	return f.props.Rating
}

func (f *Field) ForEachPart(fn func(Part)) {
	if !f.hasStructure() || fn == nil {
		return
	}
	f.ForEachRow(func(row *Row) { fn(row) })
	f.ForEachColumn(func(column *Column) { fn(column) })
	f.ForEachBlock(func(block *Block) { fn(block) })
}

func (f *Field) ForEachPartAtPos(pos *Position, fn func(Part)) error {
	if fn == nil {
		return nil
	}
	parts, err := f.GetEachPartAtPos(pos)
	if err != nil {
		return err
	}
	for _, part := range parts {
		fn(part)
	}
	return nil
}

func (f *Field) ForEachRow(fn func(*Row)) {
	if !f.hasStructure() || fn == nil {
		return
	}
	for row := 0; row < f.props.Rows; row++ {
		part, _ := f.GetRow(row)
		fn(part)
	}
}

func (f *Field) ForEachColumn(fn func(*Column)) {
	if !f.hasStructure() || fn == nil {
		return
	}
	for column := 0; column < f.props.Columns; column++ {
		part, _ := f.GetColumn(column)
		fn(part)
	}
}

func (f *Field) ForEachBlock(fn func(*Block)) {
	if !f.hasStructure() || fn == nil {
		return
	}
	for row := 0; row < f.props.BlockRows; row++ {
		for column := 0; column < f.props.BlockColumns; column++ {
			part, _ := f.GetBlock(row, column)
			fn(part)
		}
	}
}

func (f *Field) ForEachCell(fn func(*Cell)) {
	if !f.hasStructure() || fn == nil {
		return
	}
	for row := range f.cells {
		for column := range f.cells[row] {
			fn(&f.cells[row][column])
		}
	}
}

func (f *Field) SetRating(rating float64) {
	if f != nil && f.props != nil {
		f.props.Rating = rating
	}
}

func (f *Field) String() string {
	if !f.hasStructure() {
		return "<invalid field>"
	}
	var result strings.Builder
	for row := 0; row < f.props.Rows; row++ {
		if row > 0 && row%f.props.BlockSizeRow == 0 {
			result.WriteByte('\n')
		}
		for column := 0; column < f.props.Columns; column++ {
			if column > 0 {
				if column%f.props.BlockSizeColumn == 0 {
					result.WriteString(" | ")
				} else {
					result.WriteByte(' ')
				}
			}
			value := f.cells[row][column].number
			if value == 0 {
				result.WriteRune('·')
			} else {
				result.WriteString(strconv.Itoa(value))
			}
		}
		if row+1 < f.props.Rows {
			result.WriteByte('\n')
		}
	}
	return result.String()
}

func (f *Field) StringNotesForNumber(number int) string {
	if !f.hasStructure() || number < 1 || number > f.props.Rows {
		return ""
	}
	var result strings.Builder
	f.ForEachCell(func(cell *Cell) {
		if cell.notes.Has(number) {
			fmt.Fprintf(&result, "%d/%d\n", cell.pos.row, cell.pos.column)
		}
	})
	return strings.TrimSuffix(result.String(), "\n")
}

func (f *Field) StringNotes() string {
	if !f.hasStructure() {
		return "Notes:"
	}
	var result strings.Builder
	result.WriteString("Notes:\n")
	f.ForEachCell(func(cell *Cell) {
		fmt.Fprintf(&result, "Pos: %d/%d - Notes: %v\n", cell.pos.row, cell.pos.column, cell.notes.numbers)
	})
	return strings.TrimSuffix(result.String(), "\n")
}

func (f *Field) IsSolved() bool {
	if !f.IsValid() {
		return false
	}
	for row := range f.cells {
		for column := range f.cells[row] {
			if f.cells[row][column].number == 0 {
				return false
			}
		}
	}
	return true
}

func (f *Field) IsValid() bool {
	return f.hasStructure() && f.hasValidNumbers() && f.hasValidNotes()
}

func (f *Field) hasStructure() bool {
	if f == nil || f.props == nil || validateProperties(*f.props) != nil || len(f.cells) != f.props.Rows {
		return false
	}
	for row := range f.cells {
		if len(f.cells[row]) != f.props.Columns {
			return false
		}
		for column := range f.cells[row] {
			cell := &f.cells[row][column]
			if cell.notes == nil || cell.pos == nil || !positionMatches(cell.pos, *f.props, row, column) || cell.number < 0 || cell.number > f.props.Rows {
				return false
			}
		}
	}
	return true
}

func (f *Field) hasValidNumbers() bool {
	if !f.hasStructure() {
		return false
	}
	valid := true
	f.ForEachPart(func(part Part) {
		seen := make(map[int]struct{}, f.props.Rows)
		part.ForEachCell(func(cell *Cell) {
			if cell.number == 0 || !valid {
				return
			}
			if _, exists := seen[cell.number]; exists {
				valid = false
				return
			}
			seen[cell.number] = struct{}{}
		})
	})
	return valid
}

func (f *Field) hasValidNotes() bool {
	if !f.hasStructure() {
		return false
	}
	valid := true
	f.ForEachCell(func(cell *Cell) {
		if !valid {
			return
		}
		if cell.number != 0 && len(cell.notes.numbers) != 0 {
			valid = false
			return
		}
		previous := 0
		for _, note := range cell.notes.numbers {
			if note <= previous || note > f.props.Rows || f.hasPeerNumber(cell, note) {
				valid = false
				return
			}
			previous = note
		}
	})
	return valid
}

func (f *Field) ownsCell(cell *Cell) bool {
	if !f.hasStructure() || cell == nil || cell.pos == nil {
		return false
	}
	row, column := cell.pos.row, cell.pos.column
	return row >= 0 && row < f.props.Rows && column >= 0 && column < f.props.Columns && &f.cells[row][column] == cell
}

func (f *Field) hasPeerNumber(cell *Cell, number int) bool {
	if !f.ownsCell(cell) {
		return false
	}
	row, column := cell.pos.row, cell.pos.column
	for index := 0; index < f.props.Columns; index++ {
		if index != column && f.cells[row][index].number == number {
			return true
		}
	}
	for index := 0; index < f.props.Rows; index++ {
		if index != row && f.cells[index][column].number == number {
			return true
		}
	}
	startRow := cell.pos.blockRow * f.props.BlockSizeRow
	startColumn := cell.pos.blockColumn * f.props.BlockSizeColumn
	for blockRow := 0; blockRow < f.props.BlockSizeRow; blockRow++ {
		for blockColumn := 0; blockColumn < f.props.BlockSizeColumn; blockColumn++ {
			peer := &f.cells[startRow+blockRow][startColumn+blockColumn]
			if peer != cell && peer.number == number {
				return true
			}
		}
	}
	return false
}

func (f *Field) snapshot() fieldSnapshot {
	state := fieldSnapshot{numbers: make([][]int, len(f.cells)), notes: make([][][]int, len(f.cells)), changes: slices.Clone(f.changes)}
	for row := range f.cells {
		state.numbers[row] = make([]int, len(f.cells[row]))
		state.notes[row] = make([][]int, len(f.cells[row]))
		for column := range f.cells[row] {
			state.numbers[row][column] = f.cells[row][column].number
			state.notes[row][column] = slices.Clone(f.cells[row][column].notes.numbers)
		}
	}
	return state
}

func (f *Field) restore(state fieldSnapshot) {
	for row := range f.cells {
		for column := range f.cells[row] {
			f.cells[row][column].number = state.numbers[row][column]
			f.cells[row][column].notes.numbers = slices.Clone(state.notes[row][column])
		}
	}
	f.changes = slices.Clone(state.changes)
}