web-tuner/fingerings.go

package main

import (
	"fmt"
	"strings"
	"sync"
)

type ChordResult struct {
	Chord        string     `json:"chord"`
	Root         string     `json:"root"`
	Quality      string     `json:"quality"`
	Category     string     `json:"category"`
	Fingering    []string   `json:"fingering"`
	Alternatives [][]string `json:"alternatives"`
}

type chordSpec struct {
	fullName  string
	quality   string
	category  string
	intervals []int
}

func findChordFingerings(cfg Config) []ChordResult {
	tuning := cfg.Tuning
	numStrings := len(tuning)
	maxFret := cfg.Frets
	maxFingers := cfg.MaxFingers

	defs := GetChordDefinitions()

	var specs []chordSpec
	for category, group := range defs {
		for name, intervals := range group {
			label := titleCase(category)
			if len(label) > 1 {
				label = label[:len(label)-1]
			}
			full := fmt.Sprintf("%s %s", titleCase(name), label)
			specs = append(specs, chordSpec{
				fullName:  full,
				quality:   name,
				category:  category,
				intervals: intervals,
			})
		}
	}

	optCount := maxFret + 2 // 0..maxFret + "x"
	totalCombinations := 1
	for i := 0; i < numStrings; i++ {
		totalCombinations *= optCount
	}

	type intermediateResult struct {
		chord       string
		root        string
		quality     string
		category    string
		fingering   []string
		intervalSet map[int]bool
	}

	var mu sync.Mutex
	var allResults []intermediateResult
	generatedFingerings := make(map[string]bool)

	var wg sync.WaitGroup
	for _, spec := range specs {
		wg.Add(1)
		go func(sp chordSpec) {
			defer wg.Done()

			intervalSet := make(map[int]bool, len(sp.intervals))
			for _, iv := range sp.intervals {
				intervalSet[iv] = true
			}

			var localResults []intermediateResult

			fingering := make([]string, numStrings)
			for combo := 0; combo < totalCombinations; combo++ {
				tmp := combo
				for s := numStrings - 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
				}
				if countEffectiveFingers(fingering, numStrings) > maxFingers {
					continue
				}

				frettedSemitones := make([]int, 0, numStrings)
				for i, f := range fingering {
					if f == "x" {
						continue
					}
					fretNum := atoi(f)
					sem := (NoteToSemitone[strings.TrimSpace(tuning[i])] + fretNum) % 12
					frettedSemitones = append(frettedSemitones, sem)
				}

				uniqueNotes := uniqueInts(frettedSemitones)
				if len(uniqueNotes) < len(sp.intervals) {
					continue
				}

				for _, root := range uniqueNotes {
					match := true
					intervalsFound := make(map[int]bool, len(frettedSemitones))
					for _, sem := range frettedSemitones {
						intervalsFound[(sem-root+12)%12] = true
					}
					if len(intervalsFound) != len(intervalSet) {
						match = false
					} else {
						for iv := range intervalSet {
							if !intervalsFound[iv] {
								match = false
								break
							}
						}
					}
					if !match {
						continue
					}

					key := fingeringKey(fingering)
					mu.Lock()
					if generatedFingerings[key] {
						mu.Unlock()
						continue
					}
					generatedFingerings[key] = true
					mu.Unlock()

					rootName := SemitoneToNote[root]
					fCopy := make([]string, numStrings)
					copy(fCopy, fingering)

					localResults = append(localResults, intermediateResult{
						chord:       fmt.Sprintf("%s %s", rootName, sp.fullName),
						root:        rootName,
						quality:     sp.quality,
						category:    sp.category,
						fingering:   fCopy,
						intervalSet: intervalSet,
					})
					break
				}
			}

			mu.Lock()
			allResults = append(allResults, localResults...)
			mu.Unlock()
		}(spec)
	}
	wg.Wait()

	// Group by chord name
	grouped := make(map[string][]intermediateResult)
	for _, r := range allResults {
		key := r.chord
		grouped[key] = append(grouped[key], r)
	}

	var finalResults []ChordResult
	for chordName, fingerings := range grouped {
		first := fingerings[0]
		checked := make(map[string]bool)
		var primary []string
		var alternatives [][]string
		hasFrettedPrimary := false

		for _, r := range fingerings {
			key := fingeringKey(r.fingering)
			if checked[key] {
				continue
			}
			checked[key] = true

			isOpen := isOpenChord(r.fingering)
			isFretted := !isOpen
			isExact := isSameChord(r.fingering, tuning, r.intervalSet)

			if isExact {
				if isFretted {
					if !hasFrettedPrimary {
						primary = r.fingering
						hasFrettedPrimary = true
					} else {
						alternatives = append(alternatives, r.fingering)
					}
				} else if !hasFrettedPrimary {
					if primary == nil {
						primary = r.fingering
					} else {
						alternatives = append(alternatives, r.fingering)
					}
				} else {
					alternatives = append(alternatives, r.fingering)
				}
			} else {
				if primary != nil {
					alternatives = append(alternatives, r.fingering)
				} else if primary == nil && len(alternatives) == 0 {
					primary = r.fingering
				} else {
					alternatives = append(alternatives, r.fingering)
				}
			}

			// Generate muted variations of primary
			if primary != nil && fingeringKey(r.fingering) == fingeringKey(primary) {
				muteAlts := generateMutedVariations(primary, tuning, r.intervalSet, maxFingers)
				alternatives = append(alternatives, muteAlts...)
			}
		}

		if primary == nil && len(alternatives) > 0 {
			primary = alternatives[0]
			alternatives = alternatives[1:]
		}

		if primary == nil {
			continue
		}

		cleanName := chordName
		for _, suffix := range []string{" Triad", " Sixth", " Seventh", " Ninth", " Eleventh", " Thirteenth"} {
			cleanName = strings.ReplaceAll(cleanName, suffix, "")
		}

		// Deduplicate alternatives
		seen := make(map[string]bool)
		seen[fingeringKey(primary)] = true
		var dedupAlts [][]string
		for _, alt := range alternatives {
			k := fingeringKey(alt)
			if seen[k] {
				continue
			}
			if countFingers(alt) > maxFingers {
				continue
			}
			seen[k] = true
			dedupAlts = append(dedupAlts, alt)
		}

		finalResults = append(finalResults, ChordResult{
			Chord:        cleanName,
			Root:         first.root,
			Quality:      first.quality,
			Category:     first.category,
			Fingering:    primary,
			Alternatives: dedupAlts,
		})
	}

	return finalResults
}

func isValidMuteConfig(fingering []string) bool {
	for i, f := range fingering {
		if f == "x" && i != 0 && i != len(fingering)-1 {
			return false
		}
	}
	return true
}

func countEffectiveFingers(fingering []string, numStrings int) int {
	type fretInfo struct {
		fret    int
		strings []int
	}

	frets := make(map[int][]int)
	for i, f := range fingering {
		if f == "x" || f == "0" {
			continue
		}
		fv := atoi(f)
		frets[fv] = append(frets[fv], i)
	}

	if len(frets) == 0 {
		return 0
	}

	type fingerKey struct {
		fret  int
		barre bool
	}
	used := make(map[fingerKey]bool)

	for fret, strings := range frets {
		if len(strings) >= 2 {
			start := strings[0]
			end := strings[len(strings)-1]
			for _, s := range strings {
				if s < start {
					start = s
				}
				if s > end {
					end = s
				}
			}
			if end-start <= 4 {
				valid := true
				for i := start; i <= end; i++ {
					if fingering[i] == "x" {
						continue
					}
					fv := atoi(fingering[i])
					if fv < fret {
						valid = false
						break
					}
				}
				if valid {
					used[fingerKey{fret, true}] = true
				}
			}
		}
	}

	for fret := range frets {
		found := false
		for k := range used {
			if k.fret == fret {
				found = true
				break
			}
		}
		if !found {
			used[fingerKey{fret, false}] = true
		}
	}

	count := 0
	for k := range used {
		if k.barre {
			count += 2
		} else {
			count++
		}
	}
	return count
}

func detectBarres(fingering []string, numStrings int) []map[string]interface{} {
	frets := make(map[int][]int)
	for i, f := range fingering {
		if f == "x" || f == "0" {
			continue
		}
		frets[atoi(f)] = append(frets[atoi(f)], i)
	}

	var barres []map[string]interface{}
	for fret, strings := range frets {
		if len(strings) < 2 {
			continue
		}
		valid := true
		for i := 0; i < numStrings; i++ {
			if fingering[i] == "x" {
				continue
			}
			fv := atoi(fingering[i])
			if fv < fret {
				valid = false
				break
			}
		}
		if valid {
			barres = append(barres, map[string]interface{}{
				"fret":    fret,
				"strings": strings,
			})
		}
	}
	return barres
}

func isSameChord(fingering []string, tuning []string, intervals map[int]bool) bool {
	var fretted []int
	for i, f := range fingering {
		if f == "x" {
			continue
		}
		note := (NoteToSemitone[strings.TrimSpace(tuning[i])] + atoi(f)) % 12
		fretted = append(fretted, note)
	}

	roots := uniqueInts(fretted)
	for _, root := range roots {
		iSet := make(map[int]bool)
		for _, note := range fretted {
			iSet[(note-root+12)%12] = true
		}
		if len(iSet) == len(intervals) {
			match := true
			for iv := range intervals {
				if !iSet[iv] {
					match = false
					break
				}
			}
			if match {
				return true
			}
		}
	}
	return false
}

func generateMutedVariations(primary []string, tuning []string, intervals map[int]bool, maxFingers int) [][]string {
	n := len(primary)
	var results [][]string

	for numMute := 1; numMute < n; numMute++ {
		combinations(n, numMute, func(idxs []int) {
			test := make([]string, n)
			copy(test, primary)
			for _, i := range idxs {
				test[i] = "x"
			}
			if !isValidMuteConfig(test) {
				return
			}
			if countFingers(test) > maxFingers {
				return
			}
			if isSameChord(test, tuning, intervals) {
				cp := make([]string, n)
				copy(cp, test)
				results = append(results, cp)
			}
		})
	}
	return results
}

func combinations(n, k int, fn func([]int)) {
	idxs := make([]int, k)
	for i := range idxs {
		idxs[i] = i
	}

	for {
		cp := make([]int, k)
		copy(cp, idxs)
		fn(cp)

		i := k - 1
		for i >= 0 && idxs[i] == i+n-k {
			i--
		}
		if i < 0 {
			break
		}
		idxs[i]++
		for j := i + 1; j < k; j++ {
			idxs[j] = idxs[j-1] + 1
		}
	}
}

func isOpenChord(fingering []string) bool {
	for _, f := range fingering {
		if f != "0" && f != "x" {
			return false
		}
	}
	return true
}

func countFingers(fingering []string) int {
	count := 0
	for _, f := range fingering {
		if f != "x" && f != "0" {
			count++
		}
	}
	return count
}

func fingeringKey(f []string) string {
	return strings.Join(f, ",")
}

func uniqueInts(s []int) []int {
	seen := make(map[int]bool, len(s))
	var result []int
	for _, v := range s {
		if !seen[v] {
			seen[v] = true
			result = append(result, v)
		}
	}
	return result
}

func atoi(s string) int {
	n := 0
	for _, c := range s {
		n = n*10 + int(c-'0')
	}
	return n
}

func titleCase(s string) string {
	if len(s) == 0 {
		return s
	}
	b := []byte(s)
	if b[0] >= 'a' && b[0] <= 'z' {
		b[0] -= 32
	}
	return string(b)
}