/*
 * Copyright 2018-present Open Networking Foundation

 * 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 adaptercore

import (
    "reflect"
    "runtime"

    "github.com/opencord/voltha-go/common/log"
)

// DeviceState OLT Device state
type DeviceState int

const (
    // deviceStateNull OLT is not instantiated
    deviceStateNull DeviceState = iota
    // deviceStateInit OLT is instantiated
    deviceStateInit
    // deviceStateConnected Grpc session established with OLT
    deviceStateConnected
    // deviceStateUp Admin state of OLT is UP
    deviceStateUp
    // deviceStateDown Admin state of OLT is down
    deviceStateDown
)

// Trigger for changing the state
type Trigger int

const (
    // DeviceInit Go to Device init state
    DeviceInit Trigger = iota
    // GrpcConnected Go to connected state
    GrpcConnected
    // DeviceUpInd Go to Device up state
    DeviceUpInd
    // DeviceDownInd Go to Device down state
    DeviceDownInd
    // GrpcDisconnected Go to Device init state
    GrpcDisconnected
)

// TransitionHandler function type for handling transition
type TransitionHandler func() error

// Transition to store state machine
type Transition struct {
    previousState []DeviceState
    currentState  DeviceState
    before        []TransitionHandler
    after         []TransitionHandler
}

// TransitionMap to store all the states and current device state
type TransitionMap struct {
    transitions        map[Trigger]Transition
    currentDeviceState DeviceState
}

//    OpenoltDevice state machine:
//
//        null ----> init ------> connected -----> up -----> down
//                   ^ ^             |             ^         | |
//                   | |             |             |         | |
//                   | +-------------+             +---------+ |
//                   |                                         |
//                   +-----------------------------------------+

// NewTransitionMap create a new state machine with all the transitions
func NewTransitionMap(dh *DeviceHandler) *TransitionMap {
    var transitionMap TransitionMap
    transitionMap.currentDeviceState = deviceStateNull
    transitionMap.transitions = make(map[Trigger]Transition)
    // In doInit establish the grpc session
    transitionMap.transitions[DeviceInit] =
        Transition{
            previousState: []DeviceState{deviceStateNull},
            currentState:  deviceStateInit,
            before:        []TransitionHandler{dh.doStateInit},
            after:         []TransitionHandler{dh.postInit}}
    // If gRpc session fails, re-establish the grpc session
    transitionMap.transitions[GrpcDisconnected] =
        Transition{
            previousState: []DeviceState{deviceStateConnected, deviceStateDown},
            currentState:  deviceStateInit,
            before:        []TransitionHandler{dh.doStateInit},
            after:         []TransitionHandler{dh.postInit}}
    // in doConnected, create logical device and read the indications
    transitionMap.transitions[GrpcConnected] =
        Transition{
            previousState: []DeviceState{deviceStateInit},
            currentState:  deviceStateConnected,
            before:        []TransitionHandler{dh.doStateConnected}}

    // Once the olt UP is indication received, then do state up
    transitionMap.transitions[DeviceUpInd] =
        Transition{
            previousState: []DeviceState{deviceStateConnected, deviceStateDown},
            currentState:  deviceStateUp,
            before:        []TransitionHandler{dh.doStateUp}}
    // If olt DOWN indication comes then do sate down
    transitionMap.transitions[DeviceDownInd] =
        Transition{
            previousState: []DeviceState{deviceStateUp},
            currentState:  deviceStateDown,
            before:        []TransitionHandler{dh.doStateDown}}

    return &transitionMap
}

// funcName gets the handler function name
func funcName(f interface{}) string {
    p := reflect.ValueOf(f).Pointer()
    rf := runtime.FuncForPC(p)
    return rf.Name()
}

// isValidTransition checks for the new state transition is valid from current state
func (tMap *TransitionMap) isValidTransition(trigger Trigger) bool {
    // Validate the state transition
    for _, state := range tMap.transitions[trigger].previousState {
        if tMap.currentDeviceState == state {
            return true
        }
    }
    return false
}

// Handle moves the state machine to next state based on the trigger and invokes the before and
//         after handlers
func (tMap *TransitionMap) Handle(trigger Trigger) {

    // Check whether the transtion is valid from current state
    if !tMap.isValidTransition(trigger) {
        log.Errorw("Invalid transition triggered ", log.Fields{"CurrentState": tMap.currentDeviceState, "Trigger": trigger})
        return
    }

    // Invoke the before handlers
    beforeHandlers := tMap.transitions[trigger].before
    if beforeHandlers != nil {
        for _, handler := range beforeHandlers {
            log.Debugw("running-before-handler", log.Fields{"handler": funcName(handler)})
            if err := handler(); err != nil {
                // TODO handle error
                return
            }
        }
    } else {
        log.Debugw("No handlers for before", log.Fields{"trigger": trigger})
    }

    // Update the state
    tMap.currentDeviceState = tMap.transitions[trigger].currentState
    log.Debugw("Updated device state ", log.Fields{"CurrentDeviceState": tMap.currentDeviceState})

    // Invoke the after handlers
    afterHandlers := tMap.transitions[trigger].after
    if afterHandlers != nil {
        for _, handler := range afterHandlers {
            log.Debugw("running-after-handler", log.Fields{"handler": funcName(handler)})
            if err := handler(); err != nil {
                // TODO handle error
                return
            }
        }
    } else {
        log.Debugw("No handlers for after", log.Fields{"trigger": trigger})
    }
}