// Copyright 2024 Kelvin Clement Mwinuka
//
// 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 str

import (
	"errors"
	"fmt"
	"github.com/echovault/echovault/internal"
	"github.com/echovault/echovault/internal/constants"
)

func handleSetRange(params internal.HandlerFuncParams) ([]byte, error) {
	keys, err := setRangeKeyFunc(params.Command)
	if err != nil {
		return nil, err
	}

	key := keys.WriteKeys[0]

	offset, ok := internal.AdaptType(params.Command[2]).(int)
	if !ok {
		return nil, errors.New("offset must be an integer")
	}

	newStr := params.Command[3]

	if !params.KeyExists(params.Context, key) {
		if _, err = params.CreateKeyAndLock(params.Context, key); err != nil {
			return nil, err
		}
		if err = params.SetValue(params.Context, key, newStr); err != nil {
			return nil, err
		}
		params.KeyUnlock(params.Context, key)
		return []byte(fmt.Sprintf(":%d\r\n", len(newStr))), nil
	}

	if _, err := params.KeyLock(params.Context, key); err != nil {
		return nil, err
	}
	defer params.KeyUnlock(params.Context, key)

	str, ok := params.GetValue(params.Context, key).(string)
	if !ok {
		return nil, fmt.Errorf("value at key %s is not a string", key)
	}

	// If the offset  >= length of the string, append the new string to the old one.
	if offset >= len(str) {
		newStr = str + newStr
		if err = params.SetValue(params.Context, key, newStr); err != nil {
			return nil, err
		}
		return []byte(fmt.Sprintf(":%d\r\n", len(newStr))), nil
	}

	// If the offset is < 0, prepend the new string to the old one.
	if offset < 0 {
		newStr = newStr + str
		if err = params.SetValue(params.Context, key, newStr); err != nil {
			return nil, err
		}
		return []byte(fmt.Sprintf(":%d\r\n", len(newStr))), nil
	}

	strRunes := []rune(str)

	for i := 0; i < len(newStr); i++ {
		// If we're still withing the length of the original string, replace the rune in strRunes
		if offset < len(str) {
			strRunes[offset] = rune(newStr[i])
			offset += 1
			continue
		}
		// We are past the length of the original string, append the remainder of newStr to strRunes
		strRunes = append(strRunes, []rune(newStr)[i:]...)
		break
	}

	if err = params.SetValue(params.Context, key, string(strRunes)); err != nil {
		return nil, err
	}

	return []byte(fmt.Sprintf(":%d\r\n", len(strRunes))), nil
}

func handleStrLen(params internal.HandlerFuncParams) ([]byte, error) {
	keys, err := strLenKeyFunc(params.Command)
	if err != nil {
		return nil, err
	}

	key := keys.ReadKeys[0]

	if !params.KeyExists(params.Context, key) {
		return []byte(":0\r\n"), nil
	}

	if _, err := params.KeyRLock(params.Context, key); err != nil {
		return nil, err
	}
	defer params.KeyRUnlock(params.Context, key)

	value, ok := params.GetValue(params.Context, key).(string)

	if !ok {
		return nil, fmt.Errorf("value at key %s is not a string", key)
	}

	return []byte(fmt.Sprintf(":%d\r\n", len(value))), nil
}

func handleSubStr(params internal.HandlerFuncParams) ([]byte, error) {
	keys, err := subStrKeyFunc(params.Command)
	if err != nil {
		return nil, err
	}

	key := keys.ReadKeys[0]

	start, startOk := internal.AdaptType(params.Command[2]).(int)
	end, endOk := internal.AdaptType(params.Command[3]).(int)
	reversed := false

	if !startOk || !endOk {
		return nil, errors.New("start and end indices must be integers")
	}

	if !params.KeyExists(params.Context, key) {
		return nil, fmt.Errorf("key %s does not exist", key)
	}

	if _, err = params.KeyRLock(params.Context, key); err != nil {
		return nil, err
	}
	defer params.KeyRUnlock(params.Context, key)

	value, ok := params.GetValue(params.Context, key).(string)
	if !ok {
		return nil, fmt.Errorf("value at key %s is not a string", key)
	}

	if start < 0 {
		start = len(value) - internal.AbsInt(start)
	}
	if end < 0 {
		end = len(value) - internal.AbsInt(end)
	}

	if end >= 0 && end >= start {
		end += 1
	}

	if end > len(value) {
		end = len(value)
	}

	if start > end {
		reversed = true
		start, end = end, start
	}

	str := value[start:end]

	if reversed {
		res := ""
		for i := len(str) - 1; i >= 0; i-- {
			res = res + string(str[i])
		}
		str = res
	}

	return []byte(fmt.Sprintf("$%d\r\n%s\r\n", len(str), str)), nil
}

func Commands() []internal.Command {
	return []internal.Command{
		{
			Command:    "setrange",
			Module:     constants.StringModule,
			Categories: []string{constants.StringCategory, constants.WriteCategory, constants.SlowCategory},
			Description: `(SETRANGE key offset value) 
Overwrites part of a string value with another by offset. Creates the key if it doesn't exist.`,
			Sync:              true,
			KeyExtractionFunc: setRangeKeyFunc,
			HandlerFunc:       handleSetRange,
		},
		{
			Command:           "strlen",
			Module:            constants.StringModule,
			Categories:        []string{constants.StringCategory, constants.ReadCategory, constants.FastCategory},
			Description:       "(STRLEN key) Returns length of the key's value if it's a string.",
			Sync:              false,
			KeyExtractionFunc: strLenKeyFunc,
			HandlerFunc:       handleStrLen,
		},
		{
			Command:           "substr",
			Module:            constants.StringModule,
			Categories:        []string{constants.StringCategory, constants.ReadCategory, constants.SlowCategory},
			Description:       "(SUBSTR key start end) Returns a substring from the string value.",
			Sync:              false,
			KeyExtractionFunc: subStrKeyFunc,
			HandlerFunc:       handleSubStr,
		},
		{
			Command:           "getrange",
			Module:            constants.StringModule,
			Categories:        []string{constants.StringCategory, constants.ReadCategory, constants.SlowCategory},
			Description:       "(GETRANGE key start end) Returns a substring from the string value.",
			Sync:              false,
			KeyExtractionFunc: subStrKeyFunc,
			HandlerFunc:       handleSubStr,
		},
	}
}