package dm

import (
	"strconv"
	"strings"

	"mayfly-go/internal/db/dbm/sqlparser/base"
	"mayfly-go/internal/db/dbm/sqlparser/sqlstmt"
	"mayfly-go/internal/db/dbm/sqlparser/tokenizer"
)

// Parser 达梦方言 SQL 解析器
type Parser struct {
	*base.Lexer
}

// NewParser 创建达梦解析器
func NewParser(sql string) *Parser {
	return &Parser{
		Lexer: base.NewLexer(sql, tokenizer.DialectConfig{
			DoubleQuoteAsIdentifier: true,
		}),
	}
}

// Parse 解析单条 SQL 语句
func (p *Parser) Parse() (sqlstmt.Stmt, error) {
	p.SkipSemicolons()
	if p.Current().IsEOF() {
		return nil, nil
	}
	stmt := p.parseStatement()
	return stmt, nil
}

func (p *Parser) parseStatement() sqlstmt.Stmt {
	tok := p.Current()
	switch {
	case tok.IsKeyword("SELECT") || tok.Value == "(":
		return p.parseSelect()
	case tok.IsKeyword("INSERT"):
		return p.parseInsert()
	case tok.IsKeyword("UPDATE"):
		return p.parseUpdate()
	case tok.IsKeyword("DELETE"):
		return p.parseDelete()
	case tok.IsKeyword("CREATE"):
		return p.parseCreate()
	case tok.IsKeyword("DROP"):
		return p.parseDrop()
	case tok.IsKeyword("ALTER"):
		return p.parseAlter()
	case tok.IsKeyword("WITH"):
		return p.parseWith()
	case tok.IsKeyword("TRUNCATE"):
		return p.parseGenericDdl()
	default:
		return p.parseGenericStmt()
	}
}

// ---------- SELECT 解析 ----------

func (p *Parser) parseSelect() sqlstmt.Stmt {
	start := p.Pos
	var selectStmt *sqlstmt.SelectStmt

	if p.Current().Value == "(" {
		p.Consume()
		if p.Current().IsKeyword("SELECT") {
			selectStmt = p.parseSelectBody()
		} else {
			p.SkipParentheses()
			selectStmt = &sqlstmt.SelectStmt{}
		}
		p.ExpectValue(")")
	} else {
		selectStmt = p.parseSelectBody()
	}

	// UNION 解析
	selectStmt = p.parseUnions(selectStmt)

	// ORDER BY
	if len(selectStmt.OrderBy) == 0 && p.Current().IsKeyword("ORDER") {
		p.Consume()
		if p.Current().IsKeyword("BY") {
			p.Consume()
		}
		selectStmt.OrderBy = p.parseOrderBy()
	}

	// LIMIT（达梦支持 LIMIT offset, count 或 LIMIT count OFFSET offset）
	if p.Current().IsKeyword("LIMIT") {
		limit := &sqlstmt.Limit{}
		limitStart := p.Pos
		p.Consume()

		if p.Current().Type == tokenizer.TokenNumber {
			firstNum := p.Consume().Value
			firstVal, _ := strconv.Atoi(firstNum)

			// 检查是 LIMIT offset, count 还是 LIMIT count OFFSET offset
			if p.Current().Value == "," {
				// LIMIT offset, count 格式
				limit.Offset = firstVal
				p.Consume()
				if p.Current().Type == tokenizer.TokenNumber {
					countStr := p.Consume().Value
					limit.Count, _ = strconv.Atoi(countStr)
				}
			} else if p.Current().IsKeyword("OFFSET") {
				// LIMIT count OFFSET offset 格式
				limit.Count = firstVal
				p.Consume()
				if p.Current().Type == tokenizer.TokenNumber {
					offsetStr := p.Consume().Value
					limit.Offset, _ = strconv.Atoi(offsetStr)
				}
			} else {
				// 只有 LIMIT count
				limit.Count = firstVal
				limit.Offset = 0
			}
		}
		limit.Text = p.TextFrom(limitStart)
		selectStmt.Limit = limit
	}

	// FOR UPDATE
	if p.Current().IsKeyword("FOR") {
		p.Consume()
		if p.Current().IsKeyword("UPDATE") {
			p.Consume()
		}
	}

	// 更新完整文本
	selectStmt.Base = sqlstmt.Base{Text: p.TextFrom(start)}
	return selectStmt
}

func (p *Parser) parseSelectBody() *sqlstmt.SelectStmt {
	start := p.Pos

	distinct := false
	// 支持 SELECT TOP n（达梦特性）
	topCount := ""
	if p.Current().IsKeyword("SELECT") {
		p.Consume()
		if p.Current().IsKeyword("TOP") {
			p.Consume()
			if p.Current().Type == tokenizer.TokenNumber {
				topCount = p.Consume().Value
			}
		} else if p.Current().IsKeyword("DISTINCT") {
			p.Consume()
			distinct = true
		} else if p.Current().IsKeyword("ALL") {
			p.Consume()
		}
	}

	// SELECT 项
	var items []sqlstmt.SelectItem
	for !p.Current().IsEOF() && !p.IsSelectClauseEnd() {
		if p.Current().Value == "," {
			p.Consume()
			continue
		}
		itemStart := p.Pos
		p.SkipExpr()
		text := base.TrimTrailingComma(p.TextFromExclusive(itemStart))
		col, alias := p.ExtractColumnAndAlias(text)
		items = append(items, sqlstmt.SelectItem{
			Text:       text,
			ColumnName: col,
			Alias:      alias,
		})
	}

	selectStmt := &sqlstmt.SelectStmt{
		Base:     sqlstmt.Base{Text: p.TextFrom(start)},
		Distinct: distinct,
		Items:    items,
	}

	// FROM
	if p.Current().IsKeyword("FROM") {
		p.Consume()
		selectStmt.From = p.parseFromClause()
	}

	// JOIN
	for p.IsJoinStart() || p.Current().IsKeyword("JOIN") {
		if join := p.parseJoinClause(); join != nil {
			selectStmt.Joins = append(selectStmt.Joins, *join)
		}
	}

	// WHERE
	if p.Current().IsKeyword("WHERE") {
		p.Consume()
		whereStart := p.Pos
		p.SkipExpr()
		selectStmt.Where = &sqlstmt.Expr{Text: p.TextFromExclusive(whereStart)}
	}

	// GROUP BY
	if p.Current().IsKeyword("GROUP") {
		p.Consume()
		if p.Current().IsKeyword("BY") {
			p.Consume()
		}
		p.SkipGroupByExpr()
	}

	// HAVING
	if p.Current().IsKeyword("HAVING") {
		p.Consume()
		p.SkipExpr()
	}

	// ORDER BY
	if p.Current().IsKeyword("ORDER") {
		p.Consume()
		if p.Current().IsKeyword("BY") {
			p.Consume()
		}
		selectStmt.OrderBy = p.parseOrderBy()
	}

	// LIMIT 在 SELECT 子句中（如果有）
	if p.Current().IsKeyword("LIMIT") {
		limit := &sqlstmt.Limit{}
		limitStart := p.Pos
		p.Consume()

		if p.Current().Type == tokenizer.TokenNumber {
			firstNum := p.Consume().Value
			firstVal, _ := strconv.Atoi(firstNum)

			if p.Current().Value == "," {
				limit.Offset = firstVal
				p.Consume()
				if p.Current().Type == tokenizer.TokenNumber {
					countStr := p.Consume().Value
					limit.Count, _ = strconv.Atoi(countStr)
				}
			} else if p.Current().IsKeyword("OFFSET") {
				limit.Count = firstVal
				p.Consume()
				if p.Current().Type == tokenizer.TokenNumber {
					offsetStr := p.Consume().Value
					limit.Offset, _ = strconv.Atoi(offsetStr)
				}
			} else {
				limit.Count = firstVal
				limit.Offset = 0
			}
		}
		limit.Text = p.TextFrom(limitStart)
		selectStmt.Limit = limit
	}

	_ = topCount // 暂时未使用
	return selectStmt
}

func (p *Parser) parseUnions(selectStmt *sqlstmt.SelectStmt) *sqlstmt.SelectStmt {
	for p.Current().IsKeyword("UNION") {
		p.Consume()
		all := false
		if p.Current().IsKeyword("ALL") {
			p.Consume()
			all = true
		} else if p.Current().IsKeyword("DISTINCT") {
			p.Consume()
		}

		var nextSelect *sqlstmt.SelectStmt
		if p.Current().Value == "(" {
			p.Consume()
			if p.Current().IsKeyword("SELECT") {
				nextSelect = p.parseSelectBody()
			}
			p.ExpectValue(")")
		} else if p.Current().IsKeyword("SELECT") {
			nextSelect = p.parseSelectBody()
		}

		if nextSelect != nil {
			// 提取最后一个 unionSelect 的 ORDER BY 和 LIMIT 到外层
			if len(nextSelect.OrderBy) > 0 {
				selectStmt.OrderBy = nextSelect.OrderBy
				nextSelect.OrderBy = nil
			}
			if nextSelect.Limit != nil {
				selectStmt.Limit = nextSelect.Limit
				nextSelect.Limit = nil
			}
			selectStmt.Unions = append(selectStmt.Unions, sqlstmt.UnionClause{
				Select: nextSelect,
				All:    all,
			})
		}
	}
	return selectStmt
}

func (p *Parser) parseOrderBy() []sqlstmt.OrderByItem {
	var items []sqlstmt.OrderByItem
	for !p.Current().IsEOF() && !p.IsExprEnd() {
		if p.Current().Value == "," {
			p.Consume()
			continue
		}
		start := p.Pos
		p.SkipExpr()
		text := p.TextFromExclusive(start)

		desc := false
		upper := strings.ToUpper(text)
		if strings.HasSuffix(upper, " DESC") {
			desc = true
			text = strings.TrimSpace(text[:len(text)-5])
		} else if strings.HasSuffix(upper, " ASC") {
			text = strings.TrimSpace(text[:len(text)-4])
		}

		items = append(items, sqlstmt.OrderByItem{
			Text: text,
			Desc: desc,
		})
	}
	return items
}

// ---------- FROM 解析 ----------

func (p *Parser) parseFromClause() []sqlstmt.TableRef {
	var tables []sqlstmt.TableRef
	for !p.Current().IsEOF() && !p.IsFromClauseEnd() {
		if p.Current().Value == "," {
			p.Consume()
			continue
		}
		if p.IsJoinStart() || p.Current().IsKeyword("JOIN") {
			break
		}
		ref := p.parseTableRef()
		if ref.Name != "" {
			tables = append(tables, ref)
		}
	}
	return tables
}

func (p *Parser) parseTableRef() sqlstmt.TableRef {
	start := p.Pos

	// 子查询
	if p.Current().Value == "(" {
		p.Consume()
		if p.Current().IsKeyword("SELECT") {
			p.parseSelectBody()
		} else {
			p.SkipParentheses()
		}
		p.ExpectValue(")")

		var alias string
		if p.Current().IsKeyword("AS") {
			p.Consume()
		}
		if p.Current().Type == tokenizer.TokenIdentifier {
			alias = p.Unquote(p.Consume().Value)
		}
		return sqlstmt.TableRef{
			Name:  p.TextFrom(start),
			Alias: alias,
		}
	}

	if p.Current().Type != tokenizer.TokenIdentifier && p.Current().Type != tokenizer.TokenString {
		return sqlstmt.TableRef{}
	}

	ref := sqlstmt.TableRef{}
	part1 := p.Consume().Value

	if p.Current().Value == "." {
		p.Consume()
		if p.Current().Type == tokenizer.TokenIdentifier || p.Current().Type == tokenizer.TokenString {
			part2 := p.Consume().Value
			ref.Schema = p.Unquote(part1)
			ref.Name = p.Unquote(part2)
		} else {
			ref.Name = p.Unquote(part1)
		}
	} else {
		ref.Name = p.Unquote(part1)
	}

	if p.Current().IsKeyword("AS") {
		p.Consume()
	}
	if p.Current().Type == tokenizer.TokenIdentifier {
		ref.Alias = p.Unquote(p.Consume().Value)
	}

	return ref
}

func (p *Parser) parseJoinClause() *sqlstmt.JoinClause {
	start := p.Pos
	joinType := sqlstmt.JoinKindInner
	if p.Current().IsKeyword("LEFT") {
		p.Consume()
		if p.Current().IsKeyword("OUTER") {
			p.Consume()
		}
		joinType = sqlstmt.JoinKindLeft
	} else if p.Current().IsKeyword("RIGHT") {
		p.Consume()
		if p.Current().IsKeyword("OUTER") {
			p.Consume()
		}
		joinType = sqlstmt.JoinKindRight
	} else if p.Current().IsKeyword("FULL") {
		p.Consume()
		if p.Current().IsKeyword("OUTER") {
			p.Consume()
		}
		joinType = sqlstmt.JoinKindFull
	} else if p.Current().IsKeyword("CROSS") {
		p.Consume()
		joinType = sqlstmt.JoinKindCross
	} else if p.Current().IsKeyword("INNER") {
		p.Consume()
	}

	if !p.Current().IsKeyword("JOIN") {
		p.Pos = start
		return nil
	}
	p.Consume()

	tableRef := p.parseTableRef()
	if tableRef.Name == "" {
		p.Pos = start
		return nil
	}

	var onExpr *sqlstmt.Expr
	if p.Current().IsKeyword("ON") {
		p.Consume()
		onStart := p.Pos
		p.SkipExpr()
		onExpr = &sqlstmt.Expr{Text: p.TextFromExclusive(onStart)}
	} else if p.Current().IsKeyword("USING") {
		p.Consume()
		if p.Current().Value == "(" {
			p.SkipParentheses()
		}
	}

	return &sqlstmt.JoinClause{
		Kind:  joinType,
		Table: tableRef,
		On:    onExpr,
		Text:  p.TextFrom(start),
	}
}

// ---------- INSERT 解析 ----------

func (p *Parser) parseInsert() sqlstmt.Stmt {
	start := p.Pos
	p.Consume() // INSERT

	if p.Current().IsKeyword("INTO") {
		p.Consume()
	}

	tableRef := p.parseTableRef()

	// 解析列名列表
	columns := []string{}
	if p.Current().Value == "(" {
		p.Consume()
		for !p.Current().IsEOF() && p.Current().Value != ")" {
			if p.Current().Value == "," {
				p.Consume()
				continue
			}
			if p.Current().Type == tokenizer.TokenIdentifier {
				columns = append(columns, p.Unquote(p.Consume().Value))
			} else {
				p.Consume()
			}
		}
		if p.Current().Value == ")" {
			p.Consume()
		}
	}

	if p.Current().IsKeyword("VALUES") {
		p.Consume()
		for p.Current().Value == "(" {
			p.SkipParentheses()
			if p.Current().Value == "," {
				p.Consume()
			}
		}
	} else if p.Current().IsKeyword("SELECT") {
		p.parseSelect()
	}

	return &sqlstmt.InsertStmt{
		Base:    sqlstmt.Base{Text: p.TextFrom(start)},
		Table:   tableRef,
		Columns: columns,
	}
}

// ---------- UPDATE 解析 ----------

func (p *Parser) parseUpdate() sqlstmt.Stmt {
	start := p.Pos
	p.Consume() // UPDATE

	tableRef := p.parseTableRef()
	tables := []sqlstmt.TableRef{tableRef}

	// SET - 解析字段赋值
	assignments := make([]sqlstmt.Assignment, 0)
	if p.Current().IsKeyword("SET") {
		p.Consume()
		for !p.Current().IsEOF() {
			if p.Current().IsKeyword("WHERE") || p.Current().Value == ";" {
				break
			}
			assign := p.parseAssignment()
			if assign != nil {
				assignments = append(assignments, *assign)
			}
			if p.Current().Value == "," {
				p.Consume()
				continue
			}
			if p.Current().IsKeyword("WHERE") || p.Current().Value == ";" {
				break
			}
		}
	}

	var where *sqlstmt.Expr
	if p.Current().IsKeyword("WHERE") {
		p.Consume()
		whereStart := p.Pos
		p.SkipExpr()
		where = &sqlstmt.Expr{Text: p.TextFromExclusive(whereStart)}
	}

	return &sqlstmt.UpdateStmt{
		Base:   sqlstmt.Base{Text: p.TextFrom(start)},
		Tables: tables,
		Set:    assignments,
		Where:  where,
	}
}

// ---------- DELETE 解析 ----------

func (p *Parser) parseDelete() sqlstmt.Stmt {
	start := p.Pos
	p.Consume() // DELETE

	if p.Current().IsKeyword("FROM") {
		p.Consume()
	}

	// 使用 parseTableRef 正确解析表名
	tableRef := p.parseTableRef()
	tables := []sqlstmt.TableRef{tableRef}

	// WHERE
	var where *sqlstmt.Expr
	if p.Current().IsKeyword("WHERE") {
		p.Consume()
		whereStart := p.Pos
		p.SkipExpr()
		where = &sqlstmt.Expr{Text: p.TextFromExclusive(whereStart)}
	}

	return &sqlstmt.DeleteStmt{
		Base:   sqlstmt.Base{Text: p.TextFrom(start)},
		Tables: tables,
		Where:  where,
	}
}

// ---------- DDL 解析 ----------

func (p *Parser) parseCreate() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.DdlStmt{
		Base:    sqlstmt.Base{Text: p.TextFrom(start)},
		DdlKind: "CREATE",
	}
}

func (p *Parser) parseDrop() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.DdlStmt{
		Base:    sqlstmt.Base{Text: p.TextFrom(start)},
		DdlKind: "DROP",
	}
}

func (p *Parser) parseAlter() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.DdlStmt{
		Base:    sqlstmt.Base{Text: p.TextFrom(start)},
		DdlKind: "ALTER",
	}
}

func (p *Parser) parseGenericDdl() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.DdlStmt{
		Base:    sqlstmt.Base{Text: p.TextFrom(start)},
		DdlKind: "DDL",
	}
}

// ---------- WITH 解析 ----------

func (p *Parser) parseWith() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.WithStmt{
		Base: sqlstmt.Base{Text: p.TextFrom(start)},
	}
}

// ---------- 通用语句解析 ----------

func (p *Parser) parseGenericStmt() sqlstmt.Stmt {
	start := p.Pos
	p.SkipToNextStatement()
	return &sqlstmt.OtherStmt{
		Base: sqlstmt.Base{Text: p.TextFrom(start)},
	}
}

// parseAssignment 解析 SET 字段赋值：column = value
func (p *Parser) parseAssignment() *sqlstmt.Assignment {
	start := p.Pos
	colText := ""
	for !p.Current().IsEOF() && p.Current().Value != "=" && p.Current().Value != "," &&
		!p.Current().IsKeyword("WHERE") && p.Current().Value != ";" {
		colText += p.Consume().Value
	}
	if p.Current().Value != "=" {
		p.Pos = start
		return nil
	}
	p.Consume() // =

	valStart := p.Pos
	for !p.Current().IsEOF() && p.Current().Value != "," &&
		!p.Current().IsKeyword("WHERE") && p.Current().Value != ";" {
		if p.Current().Value == "(" {
			p.SkipParentheses()
			continue
		}
		p.Consume()
	}

	return &sqlstmt.Assignment{
		Column: p.Unquote(strings.TrimSpace(colText)),
		Value:  &sqlstmt.Expr{Text: p.TextFromExclusive(valStart)},
		Text:   p.TextFromExclusive(start),
	}
}