/*
 * Minio Cloud Storage, (C) 2016, 2017 Minio, 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 cmd

import "time"

// commonTime returns a maximally occurring time from a list of time.
func commonTime(modTimes []time.Time) (modTime time.Time, count int) {
	var maxima int // Counter for remembering max occurrence of elements.
	timeOccurenceMap := make(map[time.Time]int)
	// Ignore the uuid sentinel and count the rest.
	for _, time := range modTimes {
		if time == timeSentinel {
			continue
		}
		timeOccurenceMap[time]++
	}
	// Find the common cardinality from previously collected
	// occurrences of elements.
	for time, count := range timeOccurenceMap {
		if count == maxima && time.After(modTime) {
			maxima = count
			modTime = time

		} else if count > maxima {
			maxima = count
			modTime = time
		}
	}
	// Return the collected common uuid.
	return modTime, maxima
}

// Beginning of unix time is treated as sentinel value here.
var timeSentinel = time.Unix(0, 0).UTC()

// Boot modTimes up to disk count, setting the value to time sentinel.
func bootModtimes(diskCount int) []time.Time {
	modTimes := make([]time.Time, diskCount)
	// Boots up all the modtimes.
	for i := range modTimes {
		modTimes[i] = timeSentinel
	}
	return modTimes
}

// Extracts list of times from xlMetaV1 slice and returns, skips
// slice elements which have errors. As a special error
// errFileNotFound is treated as a initial good condition.
func listObjectModtimes(partsMetadata []xlMetaV1, errs []error) (modTimes []time.Time) {
	modTimes = bootModtimes(len(partsMetadata))
	// Set a new time value, specifically set when
	// error == errFileNotFound (this is needed when this is a
	// fresh PutObject).
	timeNow := time.Now().UTC()
	for index, metadata := range partsMetadata {
		if errs[index] == nil {
			// Once the file is found, save the uuid saved on disk.
			modTimes[index] = metadata.Stat.ModTime
		} else if errs[index] == errFileNotFound {
			// Once the file is not found then the epoch is current time.
			modTimes[index] = timeNow
		}
	}
	return modTimes
}

// Returns slice of online disks needed.
// - slice returing readable disks.
// - modTime of the Object
func listOnlineDisks(disks []StorageAPI, partsMetadata []xlMetaV1, errs []error) (onlineDisks []StorageAPI, modTime time.Time) {
	onlineDisks = make([]StorageAPI, len(disks))

	// List all the file commit ids from parts metadata.
	modTimes := listObjectModtimes(partsMetadata, errs)

	// Reduce list of UUIDs to a single common value.
	modTime, _ = commonTime(modTimes)

	// Create a new online disks slice, which have common uuid.
	for index, t := range modTimes {
		if t == modTime {
			onlineDisks[index] = disks[index]
		} else {
			onlineDisks[index] = nil
		}
	}
	return onlineDisks, modTime
}

// Return disks with the outdated or missing object.
func outDatedDisks(disks []StorageAPI, partsMetadata []xlMetaV1, errs []error) (outDatedDisks []StorageAPI) {
	outDatedDisks = make([]StorageAPI, len(disks))
	latestDisks, _ := listOnlineDisks(disks, partsMetadata, errs)
	for index, disk := range latestDisks {
		if errorCause(errs[index]) == errFileNotFound {
			outDatedDisks[index] = disks[index]
			continue
		}
		if errs[index] != nil {
			continue
		}
		if disk == nil {
			outDatedDisks[index] = disks[index]
		}
	}
	return outDatedDisks
}

// Returns if the object should be healed.
func xlShouldHeal(partsMetadata []xlMetaV1, errs []error) bool {
	modTime, _ := commonTime(listObjectModtimes(partsMetadata, errs))
	for index := range partsMetadata {
		if errs[index] == errDiskNotFound {
			continue
		}
		if errs[index] != nil {
			return true
		}
		if modTime != partsMetadata[index].Stat.ModTime {
			return true
		}
	}
	return false
}

// xlHealStat - returns a structure which describes how many data,
// parity erasure blocks are missing and if it is possible to heal
// with the blocks present.
func xlHealStat(xl xlObjects, partsMetadata []xlMetaV1, errs []error) HealObjectInfo {
	// Less than quorum erasure coded blocks of the object have the same create time.
	// This object can't be healed with the information we have.
	modTime, count := commonTime(listObjectModtimes(partsMetadata, errs))
	if count < xl.readQuorum {
		return HealObjectInfo{
			Status:              quorumUnavailable,
			MissingDataCount:    0,
			MissingPartityCount: 0,
		}
	}

	// If there isn't a valid xlMeta then we can't heal the object.
	xlMeta, err := pickValidXLMeta(partsMetadata, modTime)
	if err != nil {
		return HealObjectInfo{
			Status:              corrupted,
			MissingDataCount:    0,
			MissingPartityCount: 0,
		}
	}

	// Compute heal statistics like bytes to be healed, missing
	// data and missing parity count.
	missingDataCount := 0
	missingParityCount := 0

	for i, err := range errs {
		// xl.json is not found, which implies the erasure
		// coded blocks are unavailable in the corresponding disk.
		// First half of the disks are data and the rest are parity.
		if realErr := errorCause(err); realErr == errFileNotFound || realErr == errDiskNotFound {
			if xlMeta.Erasure.Distribution[i]-1 < xl.dataBlocks {
				missingDataCount++
			} else {
				missingParityCount++
			}
		}
	}

	// This object can be healed. We have enough object metadata
	// to reconstruct missing erasure coded blocks.
	return HealObjectInfo{
		Status:              canHeal,
		MissingDataCount:    missingDataCount,
		MissingPartityCount: missingParityCount,
	}
}