package sqlx

import (
	"bytes"
	"errors"
	"reflect"
	"strconv"
	"strings"

	"github.com/jmoiron/sqlx/reflectx"
)

// Bindvar types supported by Rebind, BindMap and BindStruct.
const (
	UNKNOWN = iota
	QUESTION
	DOLLAR
	NAMED
)

// BindType returns the bindtype for a given database given a drivername.
func BindType(driverName string) int {
	switch driverName {
	case "postgres", "pgx":
		return DOLLAR
	case "mysql":
		return QUESTION
	case "sqlite3":
		return QUESTION
	case "oci8":
		return NAMED
	}
	return UNKNOWN
}

// FIXME: this should be able to be tolerant of escaped ?'s in queries without
// losing much speed, and should be to avoid confusion.

// Rebind a query from the default bindtype (QUESTION) to the target bindtype.
func Rebind(bindType int, query string) string {
	switch bindType {
	case QUESTION, UNKNOWN:
		return query
	}

	qb := []byte(query)
	// Add space enough for 10 params before we have to allocate
	rqb := make([]byte, 0, len(qb)+10)
	j := 1
	for _, b := range qb {
		if b == '?' {
			switch bindType {
			case DOLLAR:
				rqb = append(rqb, '$')
			case NAMED:
				rqb = append(rqb, ':', 'a', 'r', 'g')
			}
			for _, b := range strconv.Itoa(j) {
				rqb = append(rqb, byte(b))
			}
			j++
		} else {
			rqb = append(rqb, b)
		}
	}
	return string(rqb)
}

// Experimental implementation of Rebind which uses a bytes.Buffer.  The code is
// much simpler and should be more resistant to odd unicode, but it is twice as
// slow.  Kept here for benchmarking purposes and to possibly replace Rebind if
// problems arise with its somewhat naive handling of unicode.
func rebindBuff(bindType int, query string) string {
	if bindType != DOLLAR {
		return query
	}

	b := make([]byte, 0, len(query))
	rqb := bytes.NewBuffer(b)
	j := 1
	for _, r := range query {
		if r == '?' {
			rqb.WriteRune('$')
			rqb.WriteString(strconv.Itoa(j))
			j++
		} else {
			rqb.WriteRune(r)
		}
	}

	return rqb.String()
}

// In expands slice values in args, returning the modified query string
// and a new arg list that can be executed by a database. The `query` should
// use the `?` bindVar.  The return value uses the `?` bindVar.
func In(query string, args ...interface{}) (string, []interface{}, error) {
	// argMeta stores reflect.Value and length for slices and
	// the value itself for non-slice arguments
	type argMeta struct {
		v      reflect.Value
		i      interface{}
		length int
	}

	var flatArgsCount int
	var anySlices bool

	meta := make([]argMeta, len(args))

	for i, arg := range args {
		v := reflect.ValueOf(arg)
		t := reflectx.Deref(v.Type())

		if t.Kind() == reflect.Slice {
			meta[i].length = v.Len()
			meta[i].v = v

			anySlices = true
			flatArgsCount += meta[i].length

			if meta[i].length == 0 {
				return "", nil, errors.New("empty slice passed to 'in' query")
			}
		} else {
			meta[i].i = arg
			flatArgsCount++
		}
	}

	// don't do any parsing if there aren't any slices;  note that this means
	// some errors that we might have caught below will not be returned.
	if !anySlices {
		return query, args, nil
	}

	newArgs := make([]interface{}, 0, flatArgsCount)

	var arg, offset int
	var buf bytes.Buffer

	for i := strings.IndexByte(query[offset:], '?'); i != -1; i = strings.IndexByte(query[offset:], '?') {
		if arg >= len(meta) {
			// if an argument wasn't passed, lets return an error;  this is
			// not actually how database/sql Exec/Query works, but since we are
			// creating an argument list programmatically, we want to be able
			// to catch these programmer errors earlier.
			return "", nil, errors.New("number of bindVars exceeds arguments")
		}

		argMeta := meta[arg]
		arg++

		// not a slice, continue.
		// our questionmark will either be written before the next expansion
		// of a slice or after the loop when writing the rest of the query
		if argMeta.length == 0 {
			offset = offset + i + 1
			newArgs = append(newArgs, argMeta.i)
			continue
		}

		// write everything up to and including our ? character
		buf.WriteString(query[:offset+i+1])

		newArgs = append(newArgs, argMeta.v.Index(0).Interface())

		for si := 1; si < argMeta.length; si++ {
			buf.WriteString(", ?")
			newArgs = append(newArgs, argMeta.v.Index(si).Interface())
		}

		// slice the query and reset the offset. this avoids some bookkeeping for
		// the write after the loop
		query = query[offset+i+1:]
		offset = 0
	}

	buf.WriteString(query)

	if arg < len(meta) {
		return "", nil, errors.New("number of bindVars less than number arguments")
	}

	return buf.String(), newArgs, nil
}