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

package dispatchcloud

import (
	"errors"
	"regexp"
	"sort"
	"strconv"

	"git.arvados.org/arvados.git/sdk/go/arvados"
)

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

var 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 {
		return 0
	}
	n, err := strconv.ParseInt(m[1], 10, 64)
	if err != nil || n < 122 {
		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 manifest (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 += int64(cc.Containers.ReserveExtraRAM)
	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
}