web-tuner/density.go

package main

import (
	"fmt"
	"sort"
	"sync"
)

type DensityChord struct {
	Chord   string   `json:"chord"`
	Root    string   `json:"root"`
	Quality string   `json:"quality"`
	Frets   []int    `json:"frets"`
	Fingers int      `json:"fingers"`
	Notes   []string `json:"notes"`
}

type DensityCandidate struct {
	Tuning      []string       `json:"tuning"`
	TuningMIDI  []int          `json:"tuning_midi"`
	Root        string         `json:"root"`
	Chord       string         `json:"chord"`
	Chords      []DensityChord `json:"chords"`
	ValidChords int            `json:"valid_chords"`
	MajMinCount int            `json:"maj_min_count"`
	HighCompat  bool           `json:"high_compat"`
	AvgFingers  float64        `json:"avg_fingers"`
}

func findDensityTunings(query ShapeQuery, maxFret, maxFingers int) ([]DensityCandidate, error) {
	tunings, err := findCandidateTunings(query)
	if err != nil {
		return nil, err
	}

	nStrings := len(query.Shape.Frets)
	results := make([]DensityCandidate, len(tunings))

	var wg sync.WaitGroup
	for idx, ct := range tunings {
		wg.Add(1)
		go func(i int, t candidateTuning) {
			defer wg.Done()

			chords := scoreTuningDensity(t.tuningMIDI, maxFret, maxFingers)

			tuningNames := make([]string, nStrings)
			for s := 0; s < nStrings; s++ {
				tuningNames[s] = midiToNoteName(t.tuningMIDI[s])
			}

			majMin := 0
			totalFingers := 0
			for _, c := range chords {
				if c.Quality == "major" || c.Quality == "minor" {
					majMin++
				}
				totalFingers += c.Fingers
			}

			avg := 0.0
			if len(chords) > 0 {
				avg = float64(totalFingers) / float64(len(chords))
			}

			results[i] = DensityCandidate{
				Tuning:      tuningNames,
				TuningMIDI:  t.tuningMIDI,
				Root:        SemitoneToNote[t.root],
				Chord:       SemitoneToNote[t.root] + " " + query.TargetQuality,
				Chords:      chords,
				ValidChords: len(chords),
				MajMinCount: majMin,
				HighCompat:  majMin > 5,
				AvgFingers:  avg,
			}
		}(idx, ct)
	}
	wg.Wait()

	sort.Slice(results, func(i, j int) bool {
		if results[i].ValidChords != results[j].ValidChords {
			return results[i].ValidChords > results[j].ValidChords
		}
		return results[i].AvgFingers < results[j].AvgFingers
	})

	return results, nil
}

func scoreTuningDensity(tuningMIDI []int, maxFret, maxFingers int) []DensityChord {
	nStrings := len(tuningMIDI)
	defs := GetChordDefinitions()

	type chordDef struct {
		quality   string
		intervals []int
	}
	var allDefs []chordDef
	for _, cat := range defs {
		for name, ivs := range cat {
			allDefs = append(allDefs, chordDef{name, ivs})
		}
	}

	type chordKey struct {
		root    int
		quality string
	}
	best := make(map[chordKey]DensityChord)

	optCount := maxFret + 2
	totalCombinations := 1
	for i := 0; i < nStrings; i++ {
		totalCombinations *= optCount
	}

	fingering := make([]string, nStrings)
	for combo := 0; combo < totalCombinations; combo++ {
		tmp := combo
		for s := nStrings - 1; s >= 0; s-- {
			val := tmp % optCount
			tmp /= optCount
			if val == maxFret+1 {
				fingering[s] = "x"
			} else {
				fingering[s] = fmt.Sprintf("%d", val)
			}
		}

		if !isValidMuteConfig(fingering) {
			continue
		}
		fingers := countEffectiveFingers(fingering, nStrings)
		if fingers > maxFingers {
			continue
		}

		var soundedPCs []int
		frets := make([]int, nStrings)
		notes := make([]string, nStrings)
		for s := 0; s < nStrings; s++ {
			if fingering[s] == "x" {
				frets[s] = -1
				notes[s] = "x"
				continue
			}
			fn := atoi(fingering[s])
			frets[s] = fn
			midi := tuningMIDI[s] + fn
			pc := midi % 12
			soundedPCs = append(soundedPCs, pc)
			notes[s] = midiToNoteName(midi)
		}

		if len(soundedPCs) < 2 {
			continue
		}

		uniquePCs := uniqueInts(soundedPCs)

		// try each unique PC as root, match against chord dictionary
		type candidate struct {
			root    int
			quality string
			size    int
			bassIdx int
		}
		var candidates []candidate
		for ri, root := range uniquePCs {
			ivSet := make(map[int]bool)
			for _, pc := range soundedPCs {
				ivSet[(pc-root+12)%12] = true
			}
			for _, cd := range allDefs {
				if len(ivSet) != len(cd.intervals) {
					continue
				}
				ok := true
				for _, iv := range cd.intervals {
					if !ivSet[iv] {
						ok = false
						break
					}
				}
				if ok {
					candidates = append(candidates, candidate{root, cd.quality, len(cd.intervals), ri})
				}
			}
		}

		if len(candidates) == 0 {
			continue
		}

		// pick simplest: fewest intervals, bass preference
		pick := candidates[0]
		for _, c := range candidates[1:] {
			if c.size < pick.size || (c.size == pick.size && c.bassIdx < pick.bassIdx) {
				pick = c
			}
		}

		ck := chordKey{pick.root, pick.quality}
		existing, exists := best[ck]
		if !exists || fingers < existing.Fingers {
			fretsCopy := make([]int, nStrings)
			copy(fretsCopy, frets)
			notesCopy := make([]string, nStrings)
			copy(notesCopy, notes)

			best[ck] = DensityChord{
				Chord:   SemitoneToNote[pick.root] + " " + pick.quality,
				Root:    SemitoneToNote[pick.root],
				Quality: pick.quality,
				Frets:   fretsCopy,
				Fingers: fingers,
				Notes:   notesCopy,
			}
		}
	}

	result := make([]DensityChord, 0, len(best))
	for _, dc := range best {
		result = append(result, dc)
	}

	sort.Slice(result, func(i, j int) bool {
		ri := qualityRank(result[i].Quality)
		rj := qualityRank(result[j].Quality)
		if ri != rj {
			return ri < rj
		}
		return result[i].Fingers < result[j].Fingers
	})

	return result
}

func qualityRank(q string) int {
	switch q {
	case "major":
		return 0
	case "minor":
		return 1
	default:
		return 2
	}
}