af83/edwig

package model

type IndexableExtractor func(ModelInstance) ModelId

type Index struct {
    extractor    IndexableExtractor
    byIndexable  map[ModelId][]ModelId
    byIdentifier map[ModelId]ModelId
}

func NewIndex(extractor IndexableExtractor) *Index {
    return &Index{
        extractor:    extractor,
        byIndexable:  make(map[ModelId][]ModelId),
        byIdentifier: make(map[ModelId]ModelId),
    }
}

func (index *Index) Index(model ModelInstance) {
    modelId := model.modelId()
    indexable := index.extractor(model)

    currentIndexable, ok := index.byIdentifier[modelId]
    if ok {
        if currentIndexable != indexable {
            index.removeFromIndexable(currentIndexable, modelId)
        } else {
            return
        }
    }

    index.byIndexable[indexable] = append(index.byIndexable[indexable], modelId)
    index.byIdentifier[modelId] = indexable
}

func (index *Index) Find(indexable ModelId) ([]ModelId, bool) {
    modelIds, ok := index.byIndexable[indexable]
    return modelIds, ok
}

func (index *Index) Delete(modelId ModelId) {
    currentIndexable, ok := index.byIdentifier[modelId]
    if !ok {
        return
    }

    index.removeFromIndexable(currentIndexable, modelId)
    delete(index.byIdentifier, modelId)
}

func (index *Index) IndexableLength(indexable ModelId) int {
    return len(index.byIndexable[indexable])
}

func (index *Index) removeFromIndexable(indexable, modelId ModelId) {
    if len(index.byIndexable[indexable]) == 0 {
        return
    }
    for i, indexedModelId := range index.byIndexable[indexable] {
        if indexedModelId == modelId {
            index.byIndexable[indexable] = append(index.byIndexable[indexable][:i], index.byIndexable[indexable][i+1:]...)
            if len(index.byIndexable[indexable]) == 0 {
                delete(index.byIndexable, indexable)
            }
            return
        }
    }
}