// Copyright (C) The Arvados Authors. All rights reserved.
//
// SPDX-License-Identifier: AGPL-3.0

package dispatchcloud

import (
	"errors"
	"log"
	"os/exec"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.curoverse.com/arvados.git/sdk/go/arvados"
)

var (
	ErrInstanceTypesNotConfigured = errors.New("site configuration does not list any instance types")
	discountConfiguredRAMPercent  = 5
)

// ConstraintsNotSatisfiableError includes a list of available instance types
// to be reported back to the user.
type ConstraintsNotSatisfiableError struct {
	error
	AvailableTypes []arvados.InstanceType
}

var pdhRegexp = regexp.MustCompile(`^[0-9a-f]{32}\+(\d+)$`)

// estimateDockerImageSize estimates how much disk space will be used
// by a Docker image, given the PDH of a collection containing a
// Docker image that was created by "arv-keepdocker".  Returns
// estimated number of bytes of disk space that should be reserved.
func estimateDockerImageSize(collectionPDH string) int64 {
	m := pdhRegexp.FindStringSubmatch(collectionPDH)
	if m == nil {
		log.Printf("estimateDockerImageSize: '%v' did not match pdhRegexp, returning 0", collectionPDH)
		return 0
	}
	n, err := strconv.ParseInt(m[1], 10, 64)
	if err != nil || n < 122 {
		log.Printf("estimateDockerImageSize: short manifest %v or error (%v), returning 0", n, err)
		return 0
	}
	// To avoid having to fetch the collection, take advantage of
	// the fact that the manifest storing a container image
	// uploaded by arv-keepdocker has a predictable format, which
	// allows us to estimate the size of the image based on just
	// the size of the manifest.
	//
	// Use the following heuristic:
	// - Start with the length of the mainfest (n)
	// - Subtract 80 characters for the filename and file segment
	// - Divide by 42 to get the number of block identifiers ('hash\+size\ ' is 32+1+8+1)
	// - Assume each block is full, multiply by 64 MiB
	return ((n - 80) / 42) * (64 * 1024 * 1024)
}

// EstimateScratchSpace estimates how much available disk space (in
// bytes) is needed to run the container by summing the capacity
// requested by 'tmp' mounts plus disk space required to load the
// Docker image.
func EstimateScratchSpace(ctr *arvados.Container) (needScratch int64) {
	for _, m := range ctr.Mounts {
		if m.Kind == "tmp" {
			needScratch += m.Capacity
		}
	}

	// Account for disk space usage by Docker, assumes the following behavior:
	// - Layer tarballs are buffered to disk during "docker load".
	// - Individual layer tarballs are extracted from buffered
	// copy to the filesystem
	dockerImageSize := estimateDockerImageSize(ctr.ContainerImage)

	// The buffer is only needed during image load, so make sure
	// the baseline scratch space at least covers dockerImageSize,
	// and assume it will be released to the job afterwards.
	if needScratch < dockerImageSize {
		needScratch = dockerImageSize
	}

	// Now reserve space for the extracted image on disk.
	needScratch += dockerImageSize

	return
}

// ChooseInstanceType returns the cheapest available
// arvados.InstanceType big enough to run ctr.
func ChooseInstanceType(cc *arvados.Cluster, ctr *arvados.Container) (best arvados.InstanceType, err error) {
	if len(cc.InstanceTypes) == 0 {
		err = ErrInstanceTypesNotConfigured
		return
	}

	needScratch := EstimateScratchSpace(ctr)

	needVCPUs := ctr.RuntimeConstraints.VCPUs

	needRAM := ctr.RuntimeConstraints.RAM + ctr.RuntimeConstraints.KeepCacheRAM
	needRAM = (needRAM * 100) / int64(100-discountConfiguredRAMPercent)

	ok := false
	for _, it := range cc.InstanceTypes {
		switch {
		case ok && it.Price > best.Price:
		case int64(it.Scratch) < needScratch:
		case int64(it.RAM) < needRAM:
		case it.VCPUs < needVCPUs:
		case it.Preemptible != ctr.SchedulingParameters.Preemptible:
		case it.Price == best.Price && (it.RAM < best.RAM || it.VCPUs < best.VCPUs):
			// Equal price, but worse specs
		default:
			// Lower price || (same price && better specs)
			best = it
			ok = true
		}
	}
	if !ok {
		availableTypes := make([]arvados.InstanceType, 0, len(cc.InstanceTypes))
		for _, t := range cc.InstanceTypes {
			availableTypes = append(availableTypes, t)
		}
		sort.Slice(availableTypes, func(a, b int) bool {
			return availableTypes[a].Price < availableTypes[b].Price
		})
		err = ConstraintsNotSatisfiableError{
			errors.New("constraints not satisfiable by any configured instance type"),
			availableTypes,
		}
		return
	}
	return
}

// SlurmNodeTypeFeatureKludge ensures SLURM accepts every instance
// type name as a valid feature name, even if no instances of that
// type have appeared yet.
//
// It takes advantage of some SLURM peculiarities:
//
// (1) A feature is valid after it has been offered by a node, even if
// it is no longer offered by any node. So, to make a feature name
// valid, we can add it to a dummy node ("compute0"), then remove it.
//
// (2) To test whether a set of feature names are valid without
// actually submitting a job, we can call srun --test-only with the
// desired features.
//
// SlurmNodeTypeFeatureKludge does a test-and-fix operation
// immediately, and then periodically, in case slurm restarts and
// forgets the list of valid features. It never returns (unless there
// are no node types configured, in which case it returns
// immediately), so it should generally be invoked with "go".
func SlurmNodeTypeFeatureKludge(cc *arvados.Cluster) {
	if len(cc.InstanceTypes) == 0 {
		return
	}
	var features []string
	for _, it := range cc.InstanceTypes {
		features = append(features, "instancetype="+it.Name)
	}
	for {
		slurmKludge(features)
		time.Sleep(2 * time.Second)
	}
}

const slurmDummyNode = "compute0"

func slurmKludge(features []string) {
	allFeatures := strings.Join(features, ",")

	cmd := exec.Command("sinfo", "--nodes="+slurmDummyNode, "--format=%f", "--noheader")
	out, err := cmd.CombinedOutput()
	if err != nil {
		log.Printf("running %q %q: %s (output was %q)", cmd.Path, cmd.Args, err, out)
		return
	}
	if string(out) == allFeatures+"\n" {
		// Already configured correctly, nothing to do.
		return
	}

	log.Printf("configuring node %q with all node type features", slurmDummyNode)
	cmd = exec.Command("scontrol", "update", "NodeName="+slurmDummyNode, "Features="+allFeatures)
	log.Printf("running: %q %q", cmd.Path, cmd.Args)
	out, err = cmd.CombinedOutput()
	if err != nil {
		log.Printf("error: scontrol: %s (output was %q)", err, out)
	}
}