package sashimi

import (
	"context"
	"fmt"
	"reflect"
	"regexp"
	"strconv"
	"strings"
	"unicode"

	"zombiezen.com/go/sqlite"
	"zombiezen.com/go/sqlite/sqlitex"
)

// Stmt is a type alias for sqlite.Stmt to avoid zombiezen being a direct dependency
type Stmt = sqlite.Stmt

var placeholderRegex = regexp.MustCompile(`%[sd]`)

type DB struct {
	pool *sqlitex.Pool
}

// New creates a new database wrapper instance with connection pooling
func New(dbPath string) (*DB, error) {
	// Create connection pool with 10 connections max
	pool, err := sqlitex.NewPool(dbPath, sqlitex.PoolOptions{
		Flags:    sqlite.OpenReadWrite | sqlite.OpenCreate,
		PoolSize: 10,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to create connection pool: %w", err)
	}

	db := &DB{pool: pool}

	// Configure database using one connection from pool
	if err := db.configure(); err != nil {
		pool.Close()
		return nil, err
	}

	return db, nil
}

// configure sets up database pragmas
func (db *DB) configure() error {
	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection: %w", err)
	}
	defer db.pool.Put(conn)

	configs := []string{
		"PRAGMA journal_mode=WAL",
		"PRAGMA cache_size=-65536", // 64MB cache
		"PRAGMA foreign_keys=ON",
		"PRAGMA busy_timeout=5000", // 5 second timeout
	}

	for _, config := range configs {
		if err := sqlitex.Execute(conn, config, nil); err != nil {
			return fmt.Errorf("failed to configure database: %w", err)
		}
	}

	return nil
}

// Close closes the database connection pool
func (db *DB) Close() error {
	if db.pool != nil {
		return db.pool.Close()
	}
	return nil
}

// Pool returns the underlying connection pool
func (db *DB) Pool() *sqlitex.Pool {
	return db.pool
}

// Scan scans a SQLite statement result into a struct using field names
func (db *DB) Scan(stmt *PooledStmt, dest any) error {
	v := reflect.ValueOf(dest)
	if v.Kind() != reflect.Pointer || v.Elem().Kind() != reflect.Struct {
		return fmt.Errorf("dest must be a pointer to struct")
	}

	elem := v.Elem()
	typ := elem.Type()

	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		columnName := toSnakeCase(field.Name)

		fieldValue := elem.Field(i)
		if !fieldValue.CanSet() {
			continue
		}

		// Find column index by name
		colIndex := -1
		for j := 0; j < stmt.ColumnCount(); j++ {
			if stmt.ColumnName(j) == columnName {
				colIndex = j
				break
			}
		}

		if colIndex == -1 {
			continue // Column not found
		}

		switch fieldValue.Kind() {
		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
			fieldValue.SetInt(stmt.ColumnInt64(colIndex))
		case reflect.String:
			fieldValue.SetString(stmt.ColumnText(colIndex))
		case reflect.Float32, reflect.Float64:
			fieldValue.SetFloat(stmt.ColumnFloat(colIndex))
		case reflect.Bool:
			fieldValue.SetBool(stmt.ColumnInt(colIndex) != 0)
		}
	}

	return nil
}

// Query executes a query with fmt-style placeholders and automatically binds parameters
func (db *DB) Query(query string, args ...any) (*PooledStmt, error) {
	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return nil, fmt.Errorf("failed to get connection: %w", err)
	}

	convertedQuery, paramTypes := convertPlaceholders(query)

	stmt, err := conn.Prepare(convertedQuery)
	if err != nil {
		db.pool.Put(conn)
		return nil, err
	}

	// Bind parameters with correct types
	for i, arg := range args {
		if i >= len(paramTypes) {
			break
		}

		switch paramTypes[i] {
		case "s": // string
			if s, ok := arg.(string); ok {
				stmt.BindText(i+1, s)
			} else {
				stmt.BindText(i+1, fmt.Sprintf("%v", arg))
			}
		case "d": // integer
			switch v := arg.(type) {
			case int:
				stmt.BindInt64(i+1, int64(v))
			case int32:
				stmt.BindInt64(i+1, int64(v))
			case int64:
				stmt.BindInt64(i+1, v)
			case float64:
				stmt.BindInt64(i+1, int64(v))
			default:
				if i64, err := strconv.ParseInt(fmt.Sprintf("%v", arg), 10, 64); err == nil {
					stmt.BindInt64(i+1, i64)
				} else {
					stmt.BindInt64(i+1, 0)
				}
			}
		}
	}

	// Create a wrapped statement that releases the connection when finalized
	return &PooledStmt{Stmt: stmt, pool: db.pool, conn: conn}, nil
}

// PooledStmt wraps a statement to automatically release pool connections
type PooledStmt struct {
	*sqlite.Stmt
	pool      *sqlitex.Pool
	conn      *sqlite.Conn
	finalized bool
}

func (ps *PooledStmt) Finalize() error {
	if !ps.finalized {
		err := ps.Stmt.Finalize()
		ps.pool.Put(ps.conn)
		ps.finalized = true
		return err
	}
	return nil
}

// Get executes a query and returns the first row
func (db *DB) Get(dest any, query string, args ...any) error {
	stmt, err := db.Query(query, args...)
	if err != nil {
		return err
	}
	defer stmt.Finalize()

	hasRow, err := stmt.Step()
	if err != nil {
		return err
	}
	if !hasRow {
		return fmt.Errorf("no rows found")
	}

	return db.Scan(stmt, dest)
}

// Select executes a query and scans all rows into a slice
func (db *DB) Select(dest any, query string, args ...any) error {
	destValue := reflect.ValueOf(dest)
	if destValue.Kind() != reflect.Ptr || destValue.Elem().Kind() != reflect.Slice {
		return fmt.Errorf("dest must be a pointer to slice")
	}

	sliceValue := destValue.Elem()
	elemType := sliceValue.Type().Elem()

	// Ensure element type is a pointer to struct
	if elemType.Kind() != reflect.Ptr || elemType.Elem().Kind() != reflect.Struct {
		return fmt.Errorf("slice elements must be pointers to structs")
	}

	stmt, err := db.Query(query, args...)
	if err != nil {
		return err
	}
	defer stmt.Finalize()

	for {
		hasRow, err := stmt.Step()
		if err != nil {
			return err
		}
		if !hasRow {
			break
		}

		// Create new instance of the element type
		newElem := reflect.New(elemType.Elem())
		if err := db.Scan(stmt, newElem.Interface()); err != nil {
			return err
		}

		sliceValue.Set(reflect.Append(sliceValue, newElem))
	}

	return nil
}

// Exec executes a statement with fmt-style placeholders
func (db *DB) Exec(query string, args ...any) error {
	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection: %w", err)
	}
	defer db.pool.Put(conn)

	convertedQuery, paramTypes := convertPlaceholders(query)

	sqlArgs := make([]any, len(args))
	for i, arg := range args {
		if i < len(paramTypes) && paramTypes[i] == "d" {
			// Convert to int64 for integer parameters
			switch v := arg.(type) {
			case int:
				sqlArgs[i] = int64(v)
			case int32:
				sqlArgs[i] = int64(v)
			case int64:
				sqlArgs[i] = v
			default:
				sqlArgs[i] = arg
			}
		} else {
			sqlArgs[i] = arg
		}
	}

	return sqlitex.Execute(conn, convertedQuery, &sqlitex.ExecOptions{
		Args: sqlArgs,
	})
}

// Update updates specific fields in the database
func (db *DB) Update(tableName string, fields map[string]any, whereField string, whereValue any) error {
	if len(fields) == 0 {
		return nil // No changes
	}

	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection: %w", err)
	}
	defer db.pool.Put(conn)

	// Build UPDATE query
	setParts := make([]string, 0, len(fields))
	args := make([]any, 0, len(fields)+1)

	for field, value := range fields {
		setParts = append(setParts, field+" = ?")
		args = append(args, value)
	}

	args = append(args, whereValue)

	query := fmt.Sprintf("UPDATE %s SET %s WHERE %s = ?",
		tableName, strings.Join(setParts, ", "), whereField)

	return sqlitex.Execute(conn, query, &sqlitex.ExecOptions{
		Args: args,
	})
}

// Insert inserts a struct into the database
func (db *DB) Insert(tableName string, obj any, excludeFields ...string) (int64, error) {
	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return 0, fmt.Errorf("failed to get connection: %w", err)
	}
	defer db.pool.Put(conn)

	v := reflect.ValueOf(obj)
	if v.Kind() == reflect.Pointer {
		v = v.Elem()
	}
	t := v.Type()

	exclude := make(map[string]bool)
	for _, field := range excludeFields {
		exclude[toSnakeCase(field)] = true
	}

	var columns []string
	var placeholders []string
	var args []any

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		columnName := toSnakeCase(field.Name)
		if exclude[columnName] {
			continue
		}

		columns = append(columns, columnName)
		placeholders = append(placeholders, "?")
		args = append(args, v.Field(i).Interface())
	}

	query := fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s)",
		tableName, strings.Join(columns, ", "), strings.Join(placeholders, ", "))

	stmt, err := conn.Prepare(query)
	if err != nil {
		return 0, err
	}
	defer stmt.Finalize()

	// Bind parameters
	for i, arg := range args {
		switch v := arg.(type) {
		case string:
			stmt.BindText(i+1, v)
		case int, int32, int64:
			stmt.BindInt64(i+1, reflect.ValueOf(v).Int())
		case float32, float64:
			stmt.BindFloat(i+1, reflect.ValueOf(v).Float())
		default:
			stmt.BindText(i+1, fmt.Sprintf("%v", v))
		}
	}

	_, err = stmt.Step()
	if err != nil {
		return 0, err
	}

	return conn.LastInsertRowID(), nil
}

// Transaction executes multiple operations atomically
func (db *DB) Transaction(fn func() error) error {
	conn, err := db.pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection: %w", err)
	}
	defer db.pool.Put(conn)

	// Begin transaction
	if err := sqlitex.Execute(conn, "BEGIN", nil); err != nil {
		return err
	}

	// Execute operations
	err = fn()

	if err != nil {
		// Rollback on error
		sqlitex.Execute(conn, "ROLLBACK", nil)
		return err
	}

	// Commit on success
	return sqlitex.Execute(conn, "COMMIT", nil)
}

func convertPlaceholders(query string) (string, []string) {
	var paramTypes []string

	convertedQuery := placeholderRegex.ReplaceAllStringFunc(query, func(match string) string {
		paramTypes = append(paramTypes, match[1:]) // Remove % prefix
		return "?"
	})

	return convertedQuery, paramTypes
}

// toSnakeCase converts PascalCase to snake_case
func toSnakeCase(s string) string {
	var result strings.Builder
	runes := []rune(s)

	for i, r := range runes {
		if i > 0 {
			prev := runes[i-1]

			// Add underscore before digit if previous char was letter
			if unicode.IsDigit(r) && unicode.IsLetter(prev) {
				result.WriteByte('_')
			}
			// Add underscore before uppercase letter
			if unicode.IsUpper(r) {
				// Don't add if previous was also uppercase (unless end of acronym)
				if !unicode.IsUpper(prev) ||
					(i+1 < len(runes) && unicode.IsLower(runes[i+1])) {
					result.WriteByte('_')
				}
			}
		}
		result.WriteRune(unicode.ToLower(r))
	}
	return result.String()
}