package exporter

import (
	"fmt"
	"reflect"
	"strings"
)

// Options to control the generation done by GenerateSQL.
type Options int

const (
	SchemaOnly Options = iota
	SchemaAndColumnNames
)

// GenerateSQL takes in a "table type", that is a table whose fields are slices.
// Each field will be interpreted as a table. The sql struct tags will be used
// to generate the SQL schema. A package name is taken in to be included in the
// returned string. If a malformed type is passed in, this function will panic.
func GenerateSQL(inputType interface{}, pkg string, opt Options) string {
	header := fmt.Sprintf("package %s\n\n// Generated by //go/sql/exporter/\n// DO NOT EDIT\n\nconst Schema = `", pkg)

	body := strings.Builder{}
	t := reflect.TypeOf(inputType)
	for i := 0; i < t.NumField(); i++ {
		table := t.Field(i) // Fields of the outer type are expected to be tables.
		if table.Type.Kind() != reflect.Slice {
			panic(`Expected table should be a slice: ` + table.Name)
		}
		body.WriteString("CREATE TABLE IF NOT EXISTS ")
		body.WriteString(table.Name)
		body.WriteString(" (")
		row := table.Type.Elem()
		wasFirst := true
		for j := 0; j < row.NumField(); j++ {
			col := row.Field(j)
			sqlText, ok := col.Tag.Lookup("sql")
			if !ok {
				panic(`Field missing "sql" tag:` + table.Name + "." + row.Name())
			}
			if !wasFirst {
				body.WriteString(",")
			}
			wasFirst = false
			body.WriteString("\n  ")
			body.WriteString(strings.TrimSpace(sqlText))
		}
		body.WriteString("\n);\n")
	}
	body.WriteString("`\n")
	cols := ""
	if opt == SchemaAndColumnNames {
		cols += columnNames(inputType)
	}
	return header + body.String() + cols
}

// columnNames takes in a "table type", that is a table whose fields are slices.
// Each field will be interpreted as a table. The sql struct tags will be used
// to generate a variable for each table that contains the column names in the
// order they appear in the struct. If a malformed type is passed in, this
// function will panic.
//
// Indexes and computed columns are ignored.
func columnNames(inputType interface{}) string {
	body := strings.Builder{}

	t := reflect.TypeOf(inputType)
	for i := 0; i < t.NumField(); i++ {
		body.WriteString("\n")
		table := t.Field(i) // Fields of the outer type are expected to be tables.
		if table.Type.Kind() != reflect.Slice {
			panic(`Expected table should be a slice: ` + table.Name)
		}
		body.WriteString(`var `)
		body.WriteString(table.Name)
		body.WriteString(" = []string{")
		row := table.Type.Elem()
		for j := 0; j < row.NumField(); j++ {
			col := row.Field(j)
			sqlText, ok := col.Tag.Lookup("sql")
			if !ok {
				panic(`Field missing "sql" tag:` + table.Name + "." + row.Name())
			}
			sqlText = strings.TrimSpace(sqlText)
			if strings.Contains(sqlText, "STORED") || strings.HasPrefix(sqlText, "INDEX") || strings.HasPrefix(sqlText, "PRIMARY") || strings.HasPrefix(sqlText, "INVERTED") {
				continue
			}
			body.WriteString("\n")
			colName := strings.SplitN(sqlText, " ", 2)[0]
			body.WriteString("\t\"")
			body.WriteString(colName)
			body.WriteString(`",`)
		}
		body.WriteString("\n}\n")
	}
	return body.String()
}