// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"io/ioutil"
	"net/http"
	"runtime"
	"strconv"
	"sync"
	"time"

	"github.com/shirou/gopsutil/v3/mem"

	"github.com/minio/minio/internal/config/api"
	xioutil "github.com/minio/minio/internal/ioutil"
	"github.com/minio/minio/internal/logger"
)

type apiConfig struct {
	mu sync.RWMutex

	requestsDeadline time.Duration
	requestsPool     chan struct{}
	clusterDeadline  time.Duration
	listQuorum       int
	corsAllowOrigins []string
	// total drives per erasure set across pools.
	totalDriveCount          int
	replicationWorkers       int
	replicationFailedWorkers int
	transitionWorkers        int

	staleUploadsExpiry          time.Duration
	staleUploadsCleanupInterval time.Duration
	deleteCleanupInterval       time.Duration
}

const cgroupLimitFile = "/sys/fs/cgroup/memory/memory.limit_in_bytes"

func cgroupLimit(limitFile string) (limit uint64) {
	buf, err := ioutil.ReadFile(limitFile)
	if err != nil {
		return 9223372036854771712
	}
	limit, err = strconv.ParseUint(string(buf), 10, 64)
	if err != nil {
		return 9223372036854771712
	}
	return limit
}

func availableMemory() (available uint64) {
	available = 8 << 30 // Default to 8 GiB when we can't find the limits.

	if runtime.GOOS == "linux" {
		available = cgroupLimit(cgroupLimitFile)

		// No limit set, It's the highest positive signed 64-bit
		// integer (2^63-1), rounded down to multiples of 4096 (2^12),
		// the most common page size on x86 systems - for cgroup_limits.
		if available != 9223372036854771712 {
			// This means cgroup memory limit is configured.
			return
		} // no-limit set proceed to set the limits based on virtual memory.

	} // for all other platforms limits are based on virtual memory.

	memStats, err := mem.VirtualMemory()
	if err != nil {
		return
	}

	available = memStats.Available / 2
	return
}

func (t *apiConfig) init(cfg api.Config, setDriveCounts []int) {
	t.mu.Lock()
	defer t.mu.Unlock()

	t.clusterDeadline = cfg.ClusterDeadline
	t.corsAllowOrigins = cfg.CorsAllowOrigin
	maxSetDrives := 0
	for _, setDriveCount := range setDriveCounts {
		t.totalDriveCount += setDriveCount
		if setDriveCount > maxSetDrives {
			maxSetDrives = setDriveCount
		}
	}

	var apiRequestsMaxPerNode int
	if cfg.RequestsMax <= 0 {
		maxMem := availableMemory()

		// max requests per node is calculated as
		// total_ram / ram_per_request
		// ram_per_request is (2MiB+128KiB) * driveCount \
		//    + 2 * 10MiB (default erasure block size v1) + 2 * 1MiB (default erasure block size v2)
		blockSize := xioutil.BlockSizeLarge + xioutil.BlockSizeSmall
		apiRequestsMaxPerNode = int(maxMem / uint64(maxSetDrives*blockSize+int(blockSizeV1*2+blockSizeV2*2)))

		if globalIsErasure {
			logger.Info("Automatically configured API requests per node based on available memory on the system: %d", apiRequestsMaxPerNode)
		}
	} else {
		apiRequestsMaxPerNode = cfg.RequestsMax
		if len(globalEndpoints.Hostnames()) > 0 {
			apiRequestsMaxPerNode /= len(globalEndpoints.Hostnames())
		}
	}

	if cap(t.requestsPool) < apiRequestsMaxPerNode {
		// Only replace if needed.
		// Existing requests will use the previous limit,
		// but new requests will use the new limit.
		// There will be a short overlap window,
		// but this shouldn't last long.
		t.requestsPool = make(chan struct{}, apiRequestsMaxPerNode)
	}
	t.requestsDeadline = cfg.RequestsDeadline
	t.listQuorum = cfg.GetListQuorum()
	if globalReplicationPool != nil &&
		cfg.ReplicationWorkers != t.replicationWorkers {
		globalReplicationPool.ResizeFailedWorkers(cfg.ReplicationFailedWorkers)
		globalReplicationPool.ResizeWorkers(cfg.ReplicationWorkers)
	}
	t.replicationFailedWorkers = cfg.ReplicationFailedWorkers
	t.replicationWorkers = cfg.ReplicationWorkers
	if globalTransitionState != nil && cfg.TransitionWorkers != t.transitionWorkers {
		globalTransitionState.UpdateWorkers(cfg.TransitionWorkers)
	}
	t.transitionWorkers = cfg.TransitionWorkers

	t.staleUploadsExpiry = cfg.StaleUploadsExpiry
	t.staleUploadsCleanupInterval = cfg.StaleUploadsCleanupInterval
	t.deleteCleanupInterval = cfg.DeleteCleanupInterval
}

func (t *apiConfig) getListQuorum() int {
	t.mu.RLock()
	defer t.mu.RUnlock()

	return t.listQuorum
}

func (t *apiConfig) getCorsAllowOrigins() []string {
	t.mu.RLock()
	defer t.mu.RUnlock()

	corsAllowOrigins := make([]string, len(t.corsAllowOrigins))
	copy(corsAllowOrigins, t.corsAllowOrigins)
	return corsAllowOrigins
}

func (t *apiConfig) getStaleUploadsCleanupInterval() time.Duration {
	t.mu.RLock()
	defer t.mu.RUnlock()

	if t.staleUploadsCleanupInterval == 0 {
		return 6 * time.Hour // default 6 hours
	}

	return t.staleUploadsCleanupInterval
}

func (t *apiConfig) getStaleUploadsExpiry() time.Duration {
	t.mu.RLock()
	defer t.mu.RUnlock()

	if t.staleUploadsExpiry == 0 {
		return 24 * time.Hour // default 24 hours
	}

	return t.staleUploadsExpiry
}

func (t *apiConfig) getDeleteCleanupInterval() time.Duration {
	t.mu.RLock()
	defer t.mu.RUnlock()

	if t.deleteCleanupInterval == 0 {
		return 5 * time.Minute // every 5 minutes
	}

	return t.deleteCleanupInterval
}

func (t *apiConfig) getClusterDeadline() time.Duration {
	t.mu.RLock()
	defer t.mu.RUnlock()

	if t.clusterDeadline == 0 {
		return 10 * time.Second
	}

	return t.clusterDeadline
}

func (t *apiConfig) getRequestsPool() (chan struct{}, time.Duration) {
	t.mu.RLock()
	defer t.mu.RUnlock()

	if t.requestsPool == nil {
		return nil, time.Duration(0)
	}

	return t.requestsPool, t.requestsDeadline
}

// maxClients throttles the S3 API calls
func maxClients(f http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if val := globalServiceFreeze.Load(); val != nil {
			if unlock, ok := val.(chan struct{}); ok && unlock != nil {
				// Wait until unfrozen.
				<-unlock
			}
		}

		pool, deadline := globalAPIConfig.getRequestsPool()
		if pool == nil {
			f.ServeHTTP(w, r)
			return
		}

		globalHTTPStats.addRequestsInQueue(1)

		deadlineTimer := time.NewTimer(deadline)
		defer deadlineTimer.Stop()

		select {
		case pool <- struct{}{}:
			defer func() { <-pool }()
			globalHTTPStats.addRequestsInQueue(-1)
			f.ServeHTTP(w, r)
		case <-deadlineTimer.C:
			// Send a http timeout message
			writeErrorResponse(r.Context(), w,
				errorCodes.ToAPIErr(ErrOperationMaxedOut),
				r.URL)
			globalHTTPStats.addRequestsInQueue(-1)
			return
		case <-r.Context().Done():
			globalHTTPStats.addRequestsInQueue(-1)
			return
		}
	}
}

func (t *apiConfig) getReplicationFailedWorkers() int {
	t.mu.RLock()
	defer t.mu.RUnlock()

	return t.replicationFailedWorkers
}

func (t *apiConfig) getReplicationWorkers() int {
	t.mu.RLock()
	defer t.mu.RUnlock()

	return t.replicationWorkers
}

func (t *apiConfig) getTransitionWorkers() int {
	t.mu.RLock()
	defer t.mu.RUnlock()

	return t.transitionWorkers
}
