/*
Copyright 2016 The Kubernetes Authors All rights reserved.

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 eviction

import (
	"fmt"
	"strings"
	"time"

	"k8s.io/kubernetes/pkg/api"
	"k8s.io/kubernetes/pkg/api/resource"
	"k8s.io/kubernetes/pkg/util/sets"
)

const (
	unsupportedEvictionSignal = "unsupported eviction signal %v"
)

// signalToResource maps a Signal to its associated Resource.
var signalToResource = map[Signal]api.ResourceName{
	SignalMemoryAvailable: api.ResourceMemory,
}

// validSignal returns true if the signal is supported.
func validSignal(signal Signal) bool {
	_, found := signalToResource[signal]
	return found
}

// ParseThresholdConfig parses the flags for thresholds.
func ParseThresholdConfig(evictionHard, evictionSoft, evictionSoftGracePeriod string) ([]Threshold, error) {
	results := []Threshold{}

	hardThresholds, err := parseThresholdStatements(evictionHard)
	if err != nil {
		return nil, err
	}
	results = append(results, hardThresholds...)

	softThresholds, err := parseThresholdStatements(evictionSoft)
	if err != nil {
		return nil, err
	}
	gracePeriods, err := parseGracePeriods(evictionSoftGracePeriod)
	if err != nil {
		return nil, err
	}
	for i := range softThresholds {
		signal := softThresholds[i].Signal
		period, found := gracePeriods[signal]
		if !found {
			return nil, fmt.Errorf("grace period must be specified for the soft eviction threshold %v", signal)
		}
		softThresholds[i].GracePeriod = period
	}
	results = append(results, softThresholds...)
	return results, nil
}

// parseThresholdStatements parses the input statements into a list of Threshold objects.
func parseThresholdStatements(expr string) ([]Threshold, error) {
	if len(expr) == 0 {
		return nil, nil
	}
	results := []Threshold{}
	statements := strings.Split(expr, ",")
	signalsFound := sets.NewString()
	for _, statement := range statements {
		result, err := parseThresholdStatement(statement)
		if err != nil {
			return nil, err
		}
		if signalsFound.Has(string(result.Signal)) {
			return nil, fmt.Errorf("found duplicate eviction threshold for signal %v", result.Signal)
		}
		signalsFound.Insert(string(result.Signal))
		results = append(results, result)
	}
	return results, nil
}

// parseThresholdStatement parses a threshold statement.
func parseThresholdStatement(statement string) (Threshold, error) {
	tokens2Operator := map[string]ThresholdOperator{
		"<": OpLessThan,
	}
	var (
		operator ThresholdOperator
		parts    []string
	)
	for token := range tokens2Operator {
		parts = strings.Split(statement, token)
		// if we got a token, we know this was the operator...
		if len(parts) > 1 {
			operator = tokens2Operator[token]
			break
		}
	}
	if len(operator) == 0 || len(parts) != 2 {
		return Threshold{}, fmt.Errorf("invalid eviction threshold syntax %v, expected <signal><operator><value>", statement)
	}
	signal := Signal(parts[0])
	if !validSignal(signal) {
		return Threshold{}, fmt.Errorf(unsupportedEvictionSignal, signal)
	}

	quantity, err := resource.ParseQuantity(parts[1])
	if err != nil {
		return Threshold{}, err
	}
	return Threshold{
		Signal:   signal,
		Operator: operator,
		Value:    *quantity,
	}, nil
}

// parseGracePeriods parses the grace period statements
func parseGracePeriods(expr string) (map[Signal]time.Duration, error) {
	if len(expr) == 0 {
		return nil, nil
	}
	results := map[Signal]time.Duration{}
	statements := strings.Split(expr, ",")
	for _, statement := range statements {
		parts := strings.Split(statement, "=")
		if len(parts) != 2 {
			return nil, fmt.Errorf("invalid eviction grace period syntax %v, expected <signal>=<duration>", statement)
		}
		signal := Signal(parts[0])
		if !validSignal(signal) {
			return nil, fmt.Errorf(unsupportedEvictionSignal, signal)
		}

		gracePeriod, err := time.ParseDuration(parts[1])
		if err != nil {
			return nil, err
		}
		if gracePeriod < 0 {
			return nil, fmt.Errorf("invalid eviction grace period specified: %v, must be a positive value", parts[1])
		}

		// check against duplicate statements
		if _, found := results[signal]; found {
			return nil, fmt.Errorf("duplicate eviction grace period specified for %v", signal)
		}
		results[signal] = gracePeriod
	}
	return results, nil
}