package db

import (
	"fmt"
	"strings"
)

// Dialect 数据库方言接口
// 用于处理不同数据库之间的语法差异
type Dialect interface {
	// Quote 对表名/字段名添加引号
	// MySQL 使用反引号 `name`
	// PostgreSQL 使用双引号 "name"
	// SQLite 使用双引号或方括号 "name" 或 [name]
	Quote(name string) string

	// Placeholder 生成占位符
	// MySQL/SQLite 使用 ?
	// PostgreSQL 使用 $1, $2, $3...
	Placeholder(index int) string

	// Placeholders 生成多个占位符，用逗号分隔
	Placeholders(count int, startIndex int) string

	// SupportsLastInsertId 是否支持 LastInsertId
	// PostgreSQL 不支持，需要使用 RETURNING
	SupportsLastInsertId() bool

	// ReturningClause 生成 RETURNING 子句（用于 PostgreSQL）
	ReturningClause(column string) string

	// UpsertSQL 生成 Upsert 语句
	// MySQL: INSERT ... ON DUPLICATE KEY UPDATE ...
	// PostgreSQL: INSERT ... ON CONFLICT ... DO UPDATE SET ...
	// SQLite: INSERT OR REPLACE / INSERT ... ON CONFLICT ...
	UpsertSQL(table string, columns []string, uniqueKeys []string, updateColumns []string) string

	// GetName 获取方言名称
	GetName() string
}

// MySQLDialect MySQL 方言实现
type MySQLDialect struct{}

func (d *MySQLDialect) GetName() string {
	return "mysql"
}

func (d *MySQLDialect) Quote(name string) string {
	// 如果已经包含点号（表.字段）或空格（别名），不添加引号
	if strings.Contains(name, ".") || strings.Contains(name, " ") {
		return name
	}
	return "`" + name + "`"
}

func (d *MySQLDialect) Placeholder(index int) string {
	return "?"
}

func (d *MySQLDialect) Placeholders(count int, startIndex int) string {
	if count <= 0 {
		return ""
	}
	placeholders := make([]string, count)
	for i := 0; i < count; i++ {
		placeholders[i] = "?"
	}
	return strings.Join(placeholders, ",")
}

func (d *MySQLDialect) SupportsLastInsertId() bool {
	return true
}

func (d *MySQLDialect) ReturningClause(column string) string {
	return "" // MySQL 不支持 RETURNING
}

func (d *MySQLDialect) UpsertSQL(table string, columns []string, uniqueKeys []string, updateColumns []string) string {
	// INSERT INTO table (col1, col2) VALUES (?, ?)
	// ON DUPLICATE KEY UPDATE col1 = VALUES(col1), col2 = VALUES(col2)
	quotedCols := make([]string, len(columns))
	for i, col := range columns {
		quotedCols[i] = d.Quote(col)
	}

	placeholders := d.Placeholders(len(columns), 1)

	updateParts := make([]string, len(updateColumns))
	for i, col := range updateColumns {
		// 检查是否是 [#] 标记的直接 SQL
		if strings.HasSuffix(col, "[#]") {
			// 这种情况在调用处处理
			updateParts[i] = col
		} else {
			quotedCol := d.Quote(col)
			updateParts[i] = quotedCol + " = VALUES(" + quotedCol + ")"
		}
	}

	return fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s) ON DUPLICATE KEY UPDATE %s",
		d.Quote(table),
		strings.Join(quotedCols, ", "),
		placeholders,
		strings.Join(updateParts, ", "))
}

// PostgreSQLDialect PostgreSQL 方言实现
type PostgreSQLDialect struct{}

func (d *PostgreSQLDialect) GetName() string {
	return "postgres"
}

func (d *PostgreSQLDialect) Quote(name string) string {
	// 如果已经包含点号（表.字段）或空格（别名），不添加引号
	if strings.Contains(name, ".") || strings.Contains(name, " ") {
		return name
	}
	return "\"" + name + "\""
}

func (d *PostgreSQLDialect) Placeholder(index int) string {
	return fmt.Sprintf("$%d", index)
}

func (d *PostgreSQLDialect) Placeholders(count int, startIndex int) string {
	if count <= 0 {
		return ""
	}
	placeholders := make([]string, count)
	for i := 0; i < count; i++ {
		placeholders[i] = fmt.Sprintf("$%d", startIndex+i)
	}
	return strings.Join(placeholders, ",")
}

func (d *PostgreSQLDialect) SupportsLastInsertId() bool {
	return false // PostgreSQL 需要使用 RETURNING
}

func (d *PostgreSQLDialect) ReturningClause(column string) string {
	return " RETURNING " + d.Quote(column)
}

func (d *PostgreSQLDialect) UpsertSQL(table string, columns []string, uniqueKeys []string, updateColumns []string) string {
	// INSERT INTO table (col1, col2) VALUES ($1, $2)
	// ON CONFLICT (unique_key) DO UPDATE SET col1 = EXCLUDED.col1, col2 = EXCLUDED.col2
	quotedCols := make([]string, len(columns))
	for i, col := range columns {
		quotedCols[i] = d.Quote(col)
	}

	placeholders := d.Placeholders(len(columns), 1)

	quotedUniqueKeys := make([]string, len(uniqueKeys))
	for i, key := range uniqueKeys {
		quotedUniqueKeys[i] = d.Quote(key)
	}

	updateParts := make([]string, len(updateColumns))
	for i, col := range updateColumns {
		if strings.HasSuffix(col, "[#]") {
			updateParts[i] = col
		} else {
			quotedCol := d.Quote(col)
			updateParts[i] = quotedCol + " = EXCLUDED." + quotedCol
		}
	}

	return fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s) ON CONFLICT (%s) DO UPDATE SET %s",
		d.Quote(table),
		strings.Join(quotedCols, ", "),
		placeholders,
		strings.Join(quotedUniqueKeys, ", "),
		strings.Join(updateParts, ", "))
}

// SQLiteDialect SQLite 方言实现
type SQLiteDialect struct{}

func (d *SQLiteDialect) GetName() string {
	return "sqlite3"
}

func (d *SQLiteDialect) Quote(name string) string {
	// 如果已经包含点号（表.字段）或空格（别名），不添加引号
	if strings.Contains(name, ".") || strings.Contains(name, " ") {
		return name
	}
	return "\"" + name + "\""
}

func (d *SQLiteDialect) Placeholder(index int) string {
	return "?"
}

func (d *SQLiteDialect) Placeholders(count int, startIndex int) string {
	if count <= 0 {
		return ""
	}
	placeholders := make([]string, count)
	for i := 0; i < count; i++ {
		placeholders[i] = "?"
	}
	return strings.Join(placeholders, ",")
}

func (d *SQLiteDialect) SupportsLastInsertId() bool {
	return true
}

func (d *SQLiteDialect) ReturningClause(column string) string {
	return "" // SQLite 3.35+ 支持 RETURNING，但为兼容性暂不使用
}

func (d *SQLiteDialect) UpsertSQL(table string, columns []string, uniqueKeys []string, updateColumns []string) string {
	// INSERT INTO table (col1, col2) VALUES (?, ?)
	// ON CONFLICT (unique_key) DO UPDATE SET col1 = excluded.col1, col2 = excluded.col2
	quotedCols := make([]string, len(columns))
	for i, col := range columns {
		quotedCols[i] = d.Quote(col)
	}

	placeholders := d.Placeholders(len(columns), 1)

	quotedUniqueKeys := make([]string, len(uniqueKeys))
	for i, key := range uniqueKeys {
		quotedUniqueKeys[i] = d.Quote(key)
	}

	updateParts := make([]string, len(updateColumns))
	for i, col := range updateColumns {
		if strings.HasSuffix(col, "[#]") {
			updateParts[i] = col
		} else {
			quotedCol := d.Quote(col)
			updateParts[i] = quotedCol + " = excluded." + quotedCol
		}
	}

	return fmt.Sprintf("INSERT INTO %s (%s) VALUES (%s) ON CONFLICT (%s) DO UPDATE SET %s",
		d.Quote(table),
		strings.Join(quotedCols, ", "),
		placeholders,
		strings.Join(quotedUniqueKeys, ", "),
		strings.Join(updateParts, ", "))
}