// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file

package catapult

import (
	"errors"
)

// HistogramSet is a collection of Histograms and related Diagnostics.
type HistogramSet struct {
	histograms  []Histogram
	diagnostics []Diagnostic
}

// AddHistogram adds a histogram to this HistogramSet.
//
// If this HistogramSet already contains a Diagnostic, the addition fails and
// an error is returned.
//
// TODO(kharland): This API does not allow adding a Histogram after Diagnostics
// have been added because it is not clear if the caller intended for the new
// Histogram to contain the same references to the shared Diagnostics in this
// HistogramSet as the existing Histograms. Allow adding Histograms after
// Diagnostics when Fuchsia needs this functionality.
func (h *HistogramSet) AddHistogram(histogram Histogram) error {
	if len(h.diagnostics) > 0 {
		return errors.New("can't add Histogram after adding Diagnostics")
	}
	h.histograms = append(h.histograms, histogram)
	return nil
}

// AddSharedDiagnostic adds a diagnostic to this HistogramSet.
//
// A shared Diagnostic is a diagnostic that exists in the HistogramSet, so
// that it may be referenced by Histograms within the set. A reference to the
// Diagnostic is automatically added to each Histogram in the set when calling
// this method. name is used as the key for this reference.
func (h *HistogramSet) AddSharedDiagnostic(name string, diagnostic Diagnostic) {
	h.diagnostics = append(h.diagnostics, diagnostic)

	guid := diagnostic.GetGUID()

	// Reference the diagnostic's GUID in each Histogram in this set.
	//
	// Use the loop index instead of the loop variable since this directly
	// mutates the histogram.
	for i := range h.histograms {
		h.histograms[i].AddDiagnostic(name, guid)
	}
}

// ToJSON returns a JSON-serializable representation of this HistogramSet.
func (h *HistogramSet) ToJSON() []interface{} {
	jsonObject := []interface{}{}
	// Diagnostics must come first in the HistogramSet or Catapult will reject
	// the upload request.
	for _, entry := range h.diagnostics {
		jsonObject = append(jsonObject, entry)
	}
	for _, entry := range h.histograms {
		jsonObject = append(jsonObject, entry)
	}
	return jsonObject
}