// Copyright 2017 The Go 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 benchstat

import (
	"fmt"

	"golang.org/x/perf/internal/stats"
)

// A Table is a table for display in the benchstat output.
type Table struct {
	Metric      string
	OldNewDelta bool // is this an old-new-delta table?
	Configs     []string
	Groups      []string
	Rows        []*Row
}

// A Row is a table row for display in the benchstat output.
type Row struct {
	Benchmark string     // benchmark name
	Group     string     // group name
	Scaler    Scaler     // formatter for stats means
	Metrics   []*Metrics // columns of statistics
	Delta     string     // formatted percent change
	Note      string     // additional information
	Change    int        // +1 better, -1 worse, 0 unchanged
}

// Tables returns tables comparing the benchmarks in the collection.
func (c *Collection) Tables() []*Table {
	deltaTest := c.DeltaTest
	if deltaTest == nil {
		deltaTest = UTest
	}
	alpha := c.Alpha
	if alpha == 0 {
		alpha = 0.05
	}

	// Update statistics.
	for _, m := range c.Metrics {
		m.computeStats()
	}

	var tables []*Table
	key := Key{}
	for _, key.Unit = range c.Units {
		table := new(Table)
		table.Configs = c.Configs
		table.Groups = c.Groups
		table.Metric = metricOf(key.Unit)
		table.OldNewDelta = len(c.Configs) == 2
		for _, key.Group = range c.Groups {
			for _, key.Benchmark = range c.Benchmarks[key.Group] {
				row := &Row{Benchmark: key.Benchmark}
				if len(c.Groups) > 1 {
					// Show group headers if there is more than one group.
					row.Group = key.Group
				}

				for _, key.Config = range c.Configs {
					m := c.Metrics[key]
					if m == nil {
						row.Metrics = append(row.Metrics, new(Metrics))
						continue
					}
					row.Metrics = append(row.Metrics, m)
					if row.Scaler == nil {
						row.Scaler = NewScaler(m.Mean, m.Unit)
					}
				}

				// If there are only two configs being compared, add stats.
				if table.OldNewDelta {
					k0 := key
					k0.Config = c.Configs[0]
					k1 := key
					k1.Config = c.Configs[1]
					old := c.Metrics[k0]
					new := c.Metrics[k1]
					// If one is missing, omit row entirely.
					// TODO: Control this better.
					if old == nil || new == nil {
						continue
					}
					pval, testerr := deltaTest(old, new)
					row.Delta = "~"
					if testerr == stats.ErrZeroVariance {
						row.Note = "(zero variance)"
					} else if testerr == stats.ErrSampleSize {
						row.Note = "(too few samples)"
					} else if testerr == stats.ErrSamplesEqual {
						row.Note = "(all equal)"
					} else if testerr != nil {
						row.Note = fmt.Sprintf("(%s)", testerr)
					} else if pval < alpha {
						pct := ((new.Mean / old.Mean) - 1.0) * 100.0
						row.Delta = fmt.Sprintf("%+.2f%%", pct)
						if pct < 0 == (table.Metric != "speed") { // smaller is better, except speeds
							row.Change = +1
						} else {
							row.Change = -1
						}
					}
					if row.Note == "" && pval != -1 {
						row.Note = fmt.Sprintf("(p=%0.3f n=%d+%d)", pval, len(old.RValues), len(new.RValues))
					}
				}

				table.Rows = append(table.Rows, row)
			}
		}

		if len(table.Rows) > 0 {
			if c.AddGeoMean {
				addGeomean(c, table, key.Unit, table.OldNewDelta)
			}
			tables = append(tables, table)
		}
	}

	return tables
}

// metricOf returns the name of the metric with the given unit.
func metricOf(unit string) string {
	switch unit {
	case "ns/op":
		return "time/op"
	case "B/op":
		return "alloc/op"
	case "MB/s":
		return "speed"
	default:
		return unit
	}
}

// addGeomean adds a "geomean" row to the table,
// showing the geometric mean of all the benchmarks.
func addGeomean(c *Collection, t *Table, unit string, delta bool) {
	row := &Row{Benchmark: "[Geo mean]"}
	key := Key{Unit: unit}
	geomeans := []float64{}
	maxCount := 0
	for _, key.Config = range c.Configs {
		var means []float64
		for _, key.Group = range c.Groups {
			for _, key.Benchmark = range c.Benchmarks[key.Group] {
				m := c.Metrics[key]
				// Omit 0 values from the geomean calculation,
				// as these either make the geomean undefined
				// or zero (depending on who you ask). This
				// typically comes up with things like
				// allocation counts, where it's fine to just
				// ignore the benchmark.
				if m != nil && m.Mean != 0 {
					means = append(means, m.Mean)
				}
			}
		}
		if len(means) > maxCount {
			maxCount = len(means)
		}
		if len(means) == 0 {
			row.Metrics = append(row.Metrics, new(Metrics))
			delta = false
		} else {
			geomean := stats.GeoMean(means)
			geomeans = append(geomeans, geomean)
			if row.Scaler == nil {
				row.Scaler = NewScaler(geomean, unit)
			}
			row.Metrics = append(row.Metrics, &Metrics{
				Unit: unit,
				Mean: geomean,
			})
		}
	}
	if maxCount <= 1 {
		// Only one benchmark contributed to this geomean.
		// Since the geomean is the same as the benchmark
		// result, don't bother outputting it.
		return
	}
	if delta {
		row.Delta = fmt.Sprintf("%+.2f%%", ((geomeans[1]/geomeans[0])-1.0)*100.0)
	}
	t.Rows = append(t.Rows, row)
}