// Copyright 2024 Dolthub, 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cast

import (
	"fmt"
	"strings"
	"unicode/utf8"

	cerrors "github.com/cockroachdb/errors"
	"gopkg.in/src-d/go-errors.v1"

	pgtypes "github.com/dolthub/doltgresql/server/types"
)

// errOutOfRange is returned when a value is out of range for a given type.
var errOutOfRange = errors.NewKind("%s out of range")

// handleStringCast handles casts to the string types that may have length restrictions. Returns an error if other types
// are passed in. Will always return the correct string, even on error, as some contexts may ignore the error.
func handleStringCast(input string, targetType *pgtypes.DoltgresType) (string, error) {
	tm := targetType.GetAttTypMod()
	switch targetType.ID {
	case pgtypes.BpChar.ID:
		if tm == -1 {
			return input, nil
		}
		maxChars, err := pgtypes.GetTypModFromCharLength("char", tm)
		if err != nil {
			return "", err
		}
		length := uint32(maxChars)
		str, runeLength := truncateString(input, length)
		if runeLength > length {
			return input, cerrors.Wrap(pgtypes.ErrCastOutOfRange, fmt.Sprintf("value too long for type %s", targetType.String()))
		} else if runeLength < length {
			return str + strings.Repeat(" ", int(length-runeLength)), nil
		} else {
			return str, nil
		}
	case pgtypes.InternalChar.ID:
		str, _ := truncateString(input, pgtypes.InternalCharLength)
		return str, nil
	case pgtypes.Name.ID:
		// Name seems to never throw an error, regardless of the context or how long the input is
		str, _ := truncateString(input, uint32(targetType.TypLength))
		return str, nil
	case pgtypes.VarChar.ID:
		if tm == -1 {
			return input, nil
		}
		length := uint32(pgtypes.GetCharLengthFromTypmod(tm))
		str, runeLength := truncateString(input, length)
		if runeLength > length {
			return input, cerrors.Wrap(pgtypes.ErrCastOutOfRange, fmt.Sprintf("value too long for type %s", targetType.String()))
		} else {
			return str, nil
		}
	default:
		return "", cerrors.Errorf("internal cast called to handle non-string type")
	}
}

// truncateString returns a string that has been truncated to the given length. Uses the rune count rather than the
// byte count. Returns the input string if it's smaller than the length. Also returns the rune count of the string.
func truncateString(val string, runeLimit uint32) (string, uint32) {
	runeLength := uint32(utf8.RuneCountInString(val))
	if runeLength > runeLimit {
		// TODO: figure out if there's a faster way to truncate based on rune count
		startString := val
		for i := uint32(0); i < runeLimit; i++ {
			_, size := utf8.DecodeRuneInString(val)
			val = val[size:]
		}
		return startString[:len(startString)-len(val)], runeLength
	}
	return val, runeLength
}