flabk/pkg/asld/walker.go

package asld

import (
	"bytes"
	"fmt"
)

// Walker.... texas ranger.
// Except he's a cringe conservative.
//
// This is also cringe but not for cringe reasons.

type symbol byte

const (
	symbolOpenParen symbol = iota
	symbolClosedParen
	symbolOpenArray
	symbolClosedArray
	symbolString
	symbolColon
	symbolNullStart
	symbolEOB // End-Of-Buffer
)

const (
	statusOK status = iota
	statusError
	statusWalkerNotAffected
)

var (
	stoppable = []SymbolInfo{
		symbolOpenParen: {
			self:   '{',
			closer: '}',
		},
		symbolClosedParen: {
			self: '}',
		},
		symbolOpenArray: {
			self:   '[',
			closer: ']',
		},
		symbolClosedArray: {
			self: ']',
		},
		symbolString: {
			self:   '"',
			closer: '"',
		},
		symbolColon: {
			self: ':',
		},
	}
)

type status int
type walkerStatus struct {
	walker
	status
}

func (w walker) Reset() walker {
	w.position = 0
	return w
}

func (w walker) Debug() {
	for index, b := range w.content {
		out := string(b)
		if w.position == index {
			out = "<[_" + out + "_]>"
		}
		print(out)
	}
	print("\n")
	print("globPos", w.globPos)
	print("\n")
}

func (w walker) SliceInner() (walker, bool) {
	// the !ok scenario here is only if the code is bad
	s, ok := stoppableByByte[w.Current()]
	// Debug
	if !ok {
		panic(w)
	}
	var height uint
	for pos := w.position + 1; pos < w.len; pos++ {
		curr := w.content[pos]
		if curr == s.self && s.self != s.closer {
			height++
			continue
		}
		if curr == s.closer {
			if height == 0 {
				return w.Between(w.position+1, pos), ok
			}
			height--
		}
	}
	return w, false
}

type walker struct {
	content  []byte
	len      int
	position int
	globPos  int
}

func newWalker(data []byte) walker {
	return walker{
		content: data,
		len:     len(data),
	}
}

func (w walker) Between(lower, upper int) walker {
	// As lower, and upper, are offsets from the beginning
	// of this walker's buffer, we can diff lower and w.position
	// for an offset to set global position at
	w.content = w.content[lower:upper]
	offset := lower - w.position
	w.position = 0
	w.globPos += offset
	return w
}

// Sub returns a subwalker from the current position
func (w walker) Sub() walker {
	w.content = w.content[w.position:]
	w.len = len(w.content)
	w.position = 0
	return w
}

// Until returns a subwalker from position 0 to the current position
func (w walker) Until() walker {
	w.content = w.content[:w.position]
	w.len = len(w.content)
	return w
}

func (w walker) Pos(v int) walker {
	offset := v - w.position
	w.position = v
	w.globPos += offset
	return w
}

// ToOrStay will stay at where the walker is if b is the
// same as the current walker position.
//
// Otherwise, calls To
func (w walker) ToOrStay(b byte) (walker, bool) {
	if w.Current() == b {
		return w, true
	}
	return w.To(b)
}

func (w walker) To(b byte) (walker, bool) {
	for pos := w.position + 1; pos < w.len; pos++ {
		if w.content[pos] == b {
			return w.Pos(pos), true
		}
	}
	return w, false
}

func (w walker) WalkThroughSpaces() walker {
	for pos := w.position; pos < w.len; pos++ {
		b := w.content[pos]
		if _, ok := stoppableByByte[b]; ok || (b >= '0' && b <= '9') || b == '-' || w.IsNullAt(pos) {
			return w.Pos(pos)
		}
	}
	return w
}

func (w walker) StayOrNext() (walker, symbol) {
	if sym, ok := stoppableByByte[w.content[w.position]]; ok {
		return w, sym.enum
	}

	return w.Next()
}

func (w walker) Next() (walker, symbol) {
	w, s := w.ToNext()
	return w.Sub(), s
}

func (w walker) IsNullAt(pos int) bool {
	return w.content[pos] == 'n' && w.len-pos >= 4 && bytes.Equal(w.content[pos:pos+4], null)
}

func (w walker) ToNext() (walker, symbol) {
	for pos := w.position + 1; pos < w.len; pos++ {
		if w.IsNullAt(pos) {
			return w.Pos(pos), symbolNullStart
		}
		if s, ok := stoppableByByte[w.content[pos]]; ok {
			return w.Pos(pos), s.enum
		}
	}
	return w, symbolEOB
}

// CommaOrEnd walks to the next comma, or, if none
// is present in the current walker scope, returns
// itself with status statusWalkerNotAffected.
func (w walker) CommaOrEnd() (walkerStatus, error) {
	if w.Current() == ',' {
		w = w.Pos(w.position + 1)
	}
	for pos := w.position; pos < w.len; pos++ {
		if in(openRaw, w.content[pos]) {
			sb, ok := stoppableByByte[w.content[pos]]
			if !ok {
				panic("ok someone fucked up somewhere")
			}
			w, ok = w.To(sb.closer)
			if !ok {
				return walkerStatus{
					status: statusError,
					walker: w,
				}, fmt.Errorf("%w %s", ErrNoMatching, string(sb.closer))
			}
			pos = w.position
			continue
		}
		if w.content[pos] == ',' {
			return walkerStatus{
				status: statusOK,
				walker: w.Pos(pos),
			}, nil
		}
	}

	return walkerStatus{
		status: statusWalkerNotAffected,
		walker: w,
	}, nil
}

func (w walker) Current() byte {
	return w.content[w.position]
}

func (w walker) CurrentSymbol() (SymbolInfo, bool) {
	b, ok := stoppableByByte[w.Current()]
	return b, ok
}

func (w walker) String() string {
	if w.Current() == '"' {
		w, _ = w.SliceInner()
	}
	return string(w.content)
}