Source File
	buffers.go

Belonging Package
	github.com/reeflective/readline/internal/editor

package editor

import (
	"fmt"
	"sort"
	"strconv"
	"strings"
	"sync"
	"unicode"

	"github.com/reeflective/readline/internal/color"
	"github.com/reeflective/readline/internal/completion"
)

var (
	// validRegisterKeys - All valid register IDs (keys) for read/write Vim registers.
	// validRegisterKeys = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-\"".

	numRegisters   = 10
	alphaRegisters = 52
)

// Buffers is a list of registers in which to put yanked/cut contents.
// These buffers technically are Vim registers with full functionality.
type Buffers struct {
	num      map[int][]rune  // numbered registers (0-9)
	alpha    map[rune][]rune // lettered registers ( a-z )
	ro       map[rune][]rune // read-only registers ( . % : )
	waiting  bool            // The user wants to use a still unidentified register
	selected bool            // We have identified the register, and acting on it.
	active   rune            // Any of the read/write registers ("/num/alpha)
	mutex    *sync.Mutex
}

// NewBuffers is a required constructor to set up all the buffers/registers
// for the shell, because it contains maps that must be correctly initialized.
func NewBuffers() *Buffers {
	return &Buffers{
		num:   make(map[int][]rune, numRegisters),
		alpha: make(map[rune][]rune, alphaRegisters),
		ro:    map[rune][]rune{},
		mutex: &sync.Mutex{},
	}
}

// SetActive sets the currently active register/buffer.
// Valid values are letters (lower/upper), digits (1-9),
// or read-only buffers ( . % : ).
func (reg *Buffers) SetActive(register rune) {
	defer func() {
		// We now have an active, identified register
		reg.waiting = false
		reg.selected = true
	}()

	// Numbered
	num, err := strconv.Atoi(string(register))
	if err == nil && num < 10 {
		reg.active = register
		return
	}
	// Read-only
	if _, found := reg.ro[register]; found {
		reg.active = register

		return
	}

	// Else, lettered
	reg.active = register
}

// Get returns the contents of a given register.
// If the rune is nil (rune(0)), it returns the value of the kill buffer (the " Vim register).
// If the rune is an alphanumeric comprised in the valid register IDs, their content is returned.
// If the register name is invalid, the function returns an empty rune slice.
func (reg *Buffers) Get(register rune) []rune {
	if register == 0 {
		return reg.GetKill()
	}

	num, err := strconv.Atoi(string(register))
	if err == nil {
		return reg.num[num]
	}

	if buf, found := reg.alpha[register]; found {
		return buf
	}

	if buf, found := reg.ro[register]; found {
		return buf
	}

	return nil
}

// Active returns the contents of the active buffer/register (or the kill
// buffer if no active register is active), and resets the active register.
func (reg *Buffers) Active() []rune {
	defer reg.Reset()

	if !reg.waiting && !reg.selected {
		return reg.GetKill()
	}

	return reg.Get(reg.active)
}

// Pop rotates the kill ring and returns the new top.
func (reg *Buffers) Pop() []rune {
	if len(reg.num) == 0 {
		return nil
	}

	// Reassign the kill buffer and
	// pop the first numbered register.
	buf := string(reg.num[0])
	delete(reg.num, 0)

	for i := 0; i < len(reg.num); i++ {
		reg.num[i] = []rune(string(reg.num[i+1]))
		delete(reg.num, i+1)
	}

	return []rune(buf)
}

// GetKill returns the contents of the kill buffer.
func (reg *Buffers) GetKill() []rune {
	if len(reg.num) == 0 {
		return nil
	}

	return reg.num[0]
}

// Write writes a slice to the currently active buffer, and/or to the kill one.
// After the operation, the buffers are reset, eg. none is considered active.
func (reg *Buffers) Write(content ...rune) {
	buf := string(content)

	defer reg.Reset()

	if len(content) == 0 || buf == "" {
		return
	}

	// Either write to the active register, or add to numbered ones.
	if reg.selected {
		reg.WriteTo(reg.active, []rune(buf)...)
	} else {
		reg.writeNum(-1, []rune(buf))
	}
}

// WriteTo writes a slice directly to a target register.
// If the register name is invalid, nothing is written anywhere.
func (reg *Buffers) WriteTo(register rune, content ...rune) {
	buf := string(content)

	if len(content) == 0 || buf == "" {
		return
	}

	if register == 0 {
		reg.writeNum(0, []rune(buf))
		return
	}

	// If number register.
	num, err := strconv.Atoi(string(register))
	if num > 0 && num < 10 && err != nil {
		reg.writeNum(num, []rune(buf))
		return
	}

	// If lettered register.
	if unicode.IsLetter(register) {
		reg.writeAlpha(register, []rune(buf))
		return
	}
}

// IsSelected returns the name of the selected register, and
// true if one is indeed selected, or the default one and false.
func (reg *Buffers) IsSelected() (name string, selected bool) {
	return string(reg.active), reg.selected
}

// Reset forgets any active/pending buffer/register, but does not delete its contents.
func (reg *Buffers) Reset() {
	reg.active = 0
	reg.waiting = false
	reg.selected = false
}

// Complete returns the contents of all buffers as a structured list of completions.
func (reg *Buffers) Complete() completion.Values {
	vals := make([]completion.Candidate, 0)

	// Alpha and numbered registers
	vals = append(vals, reg.completeNumRegs()...)
	vals = append(vals, reg.completeAlphaRegs()...)

	// Disable sorting, force list long and add hint.
	comps := completion.AddRaw(vals)
	if comps.NoSort == nil {
		comps.NoSort = make(map[string]bool)
	}

	comps.NoSort["*"] = true

	if comps.ListLong == nil {
		comps.ListLong = make(map[string]bool)
	}

	comps.ListLong["*"] = true

	// Registers Hint
	hint := color.Bold + color.FgBlue + "(registers)"

	if len(vals) == 0 {
		hint += " - empty -"
	}

	comps.Messages.Add(hint)

	return comps
}

func (reg *Buffers) writeNum(register int, buf []rune) {
	// No numbered register above 10
	if register > numRegisters-1 {
		return
	}

	// Add to the stack with the specified register
	if register > 0 {
		reg.num[register] = buf

		return
	}

	// No push to the stack if we are already using 9
	for i := len(reg.num); i > 0; i-- {
		if i == numRegisters {
			i--
		}

		reg.num[i] = append([]rune{}, reg.num[i-1]...)
	}

	reg.num[0] = append([]rune{}, buf...)
}

func (reg *Buffers) writeAlpha(register rune, buf []rune) {
	appendRegs := "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	appended := false

	for _, char := range appendRegs {
		if char == register {
			register = unicode.ToLower(reg.active)
			_, exists := reg.alpha[register]

			if exists {
				reg.alpha[register] = append(reg.alpha[register], buf...)
			} else {
				reg.alpha[register] = buf
			}

			appended = true
		}
	}

	if !appended {
		reg.alpha[register] = buf
	}
}

func (reg *Buffers) completeNumRegs() []completion.Candidate {
	regs := make([]completion.Candidate, 0)
	tag := color.Dim + "num ([0-9])" + color.Reset

	var nums []int
	for reg := range reg.num {
		nums = append(nums, reg)
	}

	sort.Ints(nums)

	for _, num := range nums {
		buf := reg.num[num]
		display := strings.ReplaceAll(string(buf), "\n", ` `)

		comp := completion.Candidate{
			Tag:     tag,
			Value:   string(buf),
			Display: fmt.Sprintf("%s\"%d%s %s", color.Dim, num, color.DimReset, display),
		}

		regs = append(regs, comp)
	}

	return regs
}

func (reg *Buffers) completeAlphaRegs() []completion.Candidate {
	regs := make([]completion.Candidate, 0)
	tag := color.Dim + "alpha ([a-z], [A-Z])" + color.Reset

	var lett []rune
	for slot := range reg.alpha {
		lett = append(lett, slot)
	}

	sort.Slice(lett, func(i, j int) bool { return i < j })

	for _, letter := range lett {
		buf := reg.alpha[letter]
		display := strings.ReplaceAll(string(buf), "\n", ` `)

		comp := completion.Candidate{
			Tag:     tag,
			Value:   string(buf),
			Display: fmt.Sprintf("%s\"%s%s %s", color.Dim, string(letter), color.DimReset, display),
		}

		regs = append(regs, comp)
	}

	return regs
}

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