// 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 raft

import (
	"context"
	"encoding/json"
	"fmt"
	"github.com/echovault/echovault/internal"
	"github.com/echovault/echovault/internal/config"
	"github.com/hashicorp/raft"
	"io"
	"log"
	"net"
	"strings"
	"time"
)

type FSMOpts struct {
	Config                config.Config
	GetState              func() map[string]internal.KeyData
	GetCommand            func(command string) (internal.Command, error)
	CreateKeyAndLock      func(ctx context.Context, key string) (bool, error)
	SetValue              func(ctx context.Context, key string, value interface{}) error
	SetExpiry             func(ctx context.Context, key string, expire time.Time, touch bool)
	KeyUnlock             func(ctx context.Context, key string)
	DeleteKey             func(ctx context.Context, key string) error
	StartSnapshot         func()
	FinishSnapshot        func()
	SetLatestSnapshotTime func(msec int64)
	GetHandlerFuncParams  func(ctx context.Context, cmd []string, conn *net.Conn) internal.HandlerFuncParams
}

type FSM struct {
	options FSMOpts
}

func NewFSM(opts FSMOpts) raft.FSM {
	return raft.FSM(&FSM{
		options: opts,
	})
}

// Apply Implements raft.FSM interface
func (fsm *FSM) Apply(log *raft.Log) interface{} {
	switch log.Type {
	default:
		// No-Op
	case raft.LogCommand:
		var request internal.ApplyRequest

		if err := json.Unmarshal(log.Data, &request); err != nil {
			return internal.ApplyResponse{
				Error:    err,
				Response: nil,
			}
		}

		ctx := context.WithValue(context.Background(), internal.ContextServerID("ServerID"), request.ServerID)
		ctx = context.WithValue(ctx, internal.ContextConnID("ConnectionID"), request.ConnectionID)

		switch strings.ToLower(request.Type) {
		default:
			return internal.ApplyResponse{
				Error:    fmt.Errorf("unsupported raft command type %s", request.Type),
				Response: nil,
			}

		case "delete-key":
			if err := fsm.options.DeleteKey(ctx, request.Key); err != nil {
				return internal.ApplyResponse{
					Error:    err,
					Response: nil,
				}
			}
			return internal.ApplyResponse{
				Error:    nil,
				Response: []byte("OK"),
			}

		case "command":
			// Handle command
			command, err := fsm.options.GetCommand(request.CMD[0])
			if err != nil {
				return internal.ApplyResponse{
					Error:    err,
					Response: nil,
				}
			}

			handler := command.HandlerFunc

			subCommand, ok := internal.GetSubCommand(command, request.CMD).(internal.SubCommand)
			if ok {
				handler = subCommand.HandlerFunc
			}

			if res, err := handler(fsm.options.GetHandlerFuncParams(ctx, request.CMD, nil)); err != nil {
				return internal.ApplyResponse{
					Error:    err,
					Response: nil,
				}
			} else {
				return internal.ApplyResponse{
					Error:    nil,
					Response: res,
				}
			}
		}
	}

	return nil
}

// Snapshot implements raft.FSM interface
func (fsm *FSM) Snapshot() (raft.FSMSnapshot, error) {
	return NewFSMSnapshot(SnapshotOpts{
		config:                fsm.options.Config,
		startSnapshot:         fsm.options.StartSnapshot,
		finishSnapshot:        fsm.options.FinishSnapshot,
		setLatestSnapshotTime: fsm.options.SetLatestSnapshotTime,
		data:                  fsm.options.GetState(),
	}), nil
}

// Restore implements raft.FSM interface
func (fsm *FSM) Restore(snapshot io.ReadCloser) error {
	b, err := io.ReadAll(snapshot)

	if err != nil {
		log.Fatal(err)
		return err
	}

	data := internal.SnapshotObject{
		State:                      make(map[string]internal.KeyData),
		LatestSnapshotMilliseconds: 0,
	}

	if err = json.Unmarshal(b, &data); err != nil {
		log.Fatal(err)
		return err
	}

	// Set state
	ctx := context.Background()
	for k, v := range internal.FilterExpiredKeys(data.State) {
		if _, err = fsm.options.CreateKeyAndLock(ctx, k); err != nil {
			log.Fatal(err)
		}
		if err = fsm.options.SetValue(ctx, k, v.Value); err != nil {
			log.Fatal(err)
		}
		fsm.options.SetExpiry(ctx, k, v.ExpireAt, false)
		fsm.options.KeyUnlock(ctx, k)
	}
	// Set latest snapshot milliseconds
	fsm.options.SetLatestSnapshotTime(data.LatestSnapshotMilliseconds)

	return nil
}