// Copyright 2015 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package executor

import (
	"github.com/juju/errors"
	"github.com/ngaut/log"
	"github.com/pingcap/tidb/ast"
	"github.com/pingcap/tidb/context"
	"github.com/pingcap/tidb/infoschema"
	"github.com/pingcap/tidb/plan"
)

// Compiler compiles an ast.StmtNode to a stmt.Statement.
type Compiler struct {
}

const (
	// IGNORE is a special label to identify the situations we want to ignore.
	IGNORE = "Ignore"
	// SimpleSelect represents SELECT statements like "select a from t" or "select 2".
	SimpleSelect = "Simple-Select"
	// ComplexSelect represents the other SELECT statements besides SIMPLE_SELECT.
	ComplexSelect = "Complex-Select"
	// AlterTable represents alter table statements.
	AlterTable = "AlterTable"
	// AnalyzeTable represents analyze table statements.
	AnalyzeTable = "AnalyzeTable"
	// Begin represents begin statements.
	Begin = "Begin"
	// Commit represents commit statements.
	Commit = "Commit"
	// CreateDatabase represents create database statements.
	CreateDatabase = "CreateDatabase"
	// CreateIndex represents create index statements.
	CreateIndex = "CreateIndex"
	// CreateTable represents create table statements.
	CreateTable = "CreateTable"
	// CreateUser represents create user statements.
	CreateUser = "CreateUser"
	// Delete represents delete statements.
	Delete = "Delete"
	// DropDatabase represents drop database statements.
	DropDatabase = "DropDatabase"
	// DropIndex represents drop index statements.
	DropIndex = "DropIndex"
	// DropTable represents drop table statements.
	DropTable = "DropTable"
	// Explain represents explain statements.
	Explain = "Explain"
	// Replace represents replace statements.
	Replace = "Replace"
	// Insert represents insert statements.
	Insert = "Insert"
	// LoadDataStmt represents load data statements.
	LoadDataStmt = "LoadData"
	// RollBack represents roll back statements.
	RollBack = "RollBack"
	// Set represents set statements.
	Set = "Set"
	// Show represents show statements.
	Show = "Show"
	// TruncateTable represents truncate table statements.
	TruncateTable = "TruncateTable"
	// Update represents update statements.
	Update = "Update"
)

func statementLabel(node ast.StmtNode) string {
	switch x := node.(type) {
	case *ast.AlterTableStmt:
		return AlterTable
	case *ast.AnalyzeTableStmt:
		return AnalyzeTable
	case *ast.BeginStmt:
		return Begin
	case *ast.CommitStmt:
		return Commit
	case *ast.CreateDatabaseStmt:
		return CreateDatabase
	case *ast.CreateIndexStmt:
		return CreateIndex
	case *ast.CreateTableStmt:
		return CreateTable
	case *ast.CreateUserStmt:
		return CreateUser
	case *ast.DeleteStmt:
		return Delete
	case *ast.DropDatabaseStmt:
		return DropDatabase
	case *ast.DropIndexStmt:
		return DropIndex
	case *ast.DropTableStmt:
		return DropTable
	case *ast.ExplainStmt:
		return Explain
	case *ast.InsertStmt:
		if x.IsReplace {
			return Replace
		}
		return Insert
	case *ast.LoadDataStmt:
		return LoadDataStmt
	case *ast.RollbackStmt:
		return RollBack
	case *ast.SelectStmt:
		return getSelectStmtLabel(x)
	case *ast.SetStmt, *ast.SetPwdStmt:
		return Set
	case *ast.ShowStmt:
		return Show
	case *ast.TruncateTableStmt:
		return TruncateTable
	case *ast.UpdateStmt:
		return Update
	case *ast.DeallocateStmt, *ast.ExecuteStmt, *ast.PrepareStmt, *ast.UseStmt:
		return IGNORE
	}
	return "other"
}

func getSelectStmtLabel(x *ast.SelectStmt) string {
	if x.From == nil {
		return SimpleSelect
	}
	tableRefs := x.From.TableRefs
	if tableRefs.Right == nil {
		switch ref := tableRefs.Left.(type) {
		case *ast.TableSource:
			switch ref.Source.(type) {
			case *ast.TableName:
				return SimpleSelect
			}
		}
	}
	return ComplexSelect
}

// Compile compiles an ast.StmtNode to an ast.Statement.
// After preprocessed and validated, it will be optimized to a plan,
// then wrappped to an adapter *statement as stmt.Statement.
func (c *Compiler) Compile(ctx context.Context, node ast.StmtNode) (ast.Statement, error) {
	stmtCount(node)
	is := GetInfoSchema(ctx)
	if err := plan.Preprocess(node, is, ctx); err != nil {
		return nil, errors.Trace(err)
	}
	// Validate should be after NameResolve.
	if err := plan.Validate(node, false); err != nil {
		return nil, errors.Trace(err)
	}
	p, err := plan.Optimize(ctx, node, is)
	if err != nil {
		return nil, errors.Trace(err)
	}
	_, isDDL := node.(ast.DDLNode)
	sa := &statement{
		is:    is,
		plan:  p,
		text:  node.Text(),
		isDDL: isDDL,
	}
	return sa, nil
}

// GetInfoSchema gets TxnCtx InfoSchema if snapshot schema is not set,
// Otherwise, snapshot schema is returned.
func GetInfoSchema(ctx context.Context) infoschema.InfoSchema {
	sessVar := ctx.GetSessionVars()
	var is infoschema.InfoSchema
	if snap := sessVar.SnapshotInfoschema; snap != nil {
		is = snap.(infoschema.InfoSchema)
		log.Infof("[%d] use snapshot schema %d", sessVar.ConnectionID, is.SchemaMetaVersion())
	} else {
		is = sessVar.TxnCtx.InfoSchema.(infoschema.InfoSchema)
	}
	return is
}