package netmap

import (
	"cmp"
	"fmt"
	"slices"

	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/api/netmap"
	"git.frostfs.info/TrueCloudLab/hrw"
)

// processSelectors processes selectors and returns error is any of them is invalid.
func (c *context) processSelectors(p PlacementPolicy) error {
	for i := range p.selectors {
		fName := p.selectors[i].GetFilter()
		if fName != mainFilterName {
			_, ok := c.processedFilters[p.selectors[i].GetFilter()]
			if !ok {
				return fmt.Errorf("%w: SELECT FROM '%s'", errFilterNotFound, fName)
			}
		}

		sName := p.selectors[i].GetName()

		c.processedSelectors[sName] = &p.selectors[i]

		result, err := c.getSelection(p.selectors[i])
		if err != nil {
			return err
		}

		c.selections[sName] = result
	}

	return nil
}

// calcNodesCount returns number of buckets and minimum number of nodes in every bucket
// for the given selector.
func calcNodesCount(s netmap.Selector) (int, int) {
	switch s.GetClause() {
	case netmap.Same:
		return 1, int(s.GetCount())
	default:
		return int(s.GetCount()), 1
	}
}

// calcBucketWeight computes weight for a node bucket.
func calcBucketWeight(ns nodes, a aggregator, wf weightFunc) float64 {
	for i := range ns {
		a.Add(wf(ns[i]))
	}

	return a.Compute()
}

// getSelection returns nodes grouped by s.attribute.
// Last argument specifies if more buckets can be used to fulfill CBF.
func (c *context) getSelection(s netmap.Selector) ([]nodes, error) {
	bucketCount, nodesInBucket := calcNodesCount(s)
	buckets := c.getSelectionBase(s)

	if c.strict && len(buckets) < bucketCount {
		return nil, fmt.Errorf("%w: '%s'", errNotEnoughNodes, s.GetName())
	}

	// We need deterministic output in case there is no pivot.
	// If pivot is set, buckets are sorted by HRW.
	// However, because initial order influences HRW order for buckets with equal weights,
	// we also need to have deterministic input to HRW sorting routine.
	if len(c.hrwSeed) == 0 {
		if s.GetAttribute() == "" {
			slices.SortFunc(buckets, func(b1, b2 nodeAttrPair) int {
				return cmp.Compare(b1.nodes[0].Hash(), b2.nodes[0].Hash())
			})
		} else {
			slices.SortFunc(buckets, func(b1, b2 nodeAttrPair) int {
				return cmp.Compare(b1.attr, b2.attr)
			})
		}
	}

	maxNodesInBucket := nodesInBucket * int(c.cbf)
	res := make([]nodes, 0, len(buckets))
	fallback := make([]nodes, 0, len(buckets))

	for i := range buckets {
		ns := buckets[i].nodes
		if len(ns) >= maxNodesInBucket {
			res = append(res, ns[:maxNodesInBucket])
		} else if len(ns) >= nodesInBucket {
			fallback = append(fallback, ns)
		}
	}

	if len(res) < bucketCount {
		// Fallback to using minimum allowed backup factor (1).
		res = append(res, fallback...)
		if c.strict && len(res) < bucketCount {
			return nil, fmt.Errorf("%w: '%s'", errNotEnoughNodes, s.GetName())
		}
	}

	if len(c.hrwSeed) != 0 {
		weights := make([]float64, len(res))
		a := new(meanIQRAgg)
		for i := range res {
			a.clear()
			weights[i] = calcBucketWeight(res[i], a, c.weightFunc)
		}

		hrw.SortHasherSliceByWeightValue(res, weights, c.hrwSeedHash)
	}

	if len(res) < bucketCount {
		if len(res) == 0 {
			return nil, errNotEnoughNodes
		}
		bucketCount = len(res)
	}

	if s.GetAttribute() == "" {
		res, fallback = res[:bucketCount], res[bucketCount:]
		for i := range fallback {
			index := i % bucketCount
			if len(res[index]) >= maxNodesInBucket {
				break
			}
			res[index] = append(res[index], fallback[i]...)
		}
	}

	return res[:bucketCount], nil
}

type nodeAttrPair struct {
	attr  string
	nodes nodes
}

// getSelectionBase returns nodes grouped by selector attribute.
// It it guaranteed that each pair will contain at least one node.
func (c *context) getSelectionBase(s netmap.Selector) []nodeAttrPair {
	fName := s.GetFilter()
	f := c.processedFilters[fName]
	isMain := fName == mainFilterName
	result := []nodeAttrPair{}
	nodeMap := map[string][]NodeInfo{}
	attr := s.GetAttribute()

	for i := range c.netMap.nodes {
		if c.usedNodes[c.netMap.nodes[i].hash] {
			continue
		}
		if isMain || c.match(f, c.netMap.nodes[i]) {
			if attr == "" {
				// Default attribute is transparent identifier which is different for every node.
				result = append(result, nodeAttrPair{attr: "", nodes: nodes{c.netMap.nodes[i]}})
			} else {
				v := c.netMap.nodes[i].Attribute(attr)
				nodeMap[v] = append(nodeMap[v], c.netMap.nodes[i])
			}
		}
	}

	if attr != "" {
		for k, ns := range nodeMap {
			result = append(result, nodeAttrPair{attr: k, nodes: ns})
		}
	}

	if len(c.hrwSeed) != 0 {
		var ws []float64
		for i := range result {
			ws = result[i].nodes.appendWeightsTo(c.weightFunc, ws[:0])
			hrw.SortHasherSliceByWeightValue(result[i].nodes, ws, c.hrwSeedHash)
		}
	}

	return result
}