super-graph/json/strip.go

package json

import (
	"bytes"
)

func Strip(b []byte, path []string) []byte {
	s := 0
	state := expectKey

	kb := make([][]byte, 0, len(path))
	for _, k := range path {
		kb = append(kb, []byte(k))
	}

	s, e, d := 0, 0, 0
	ki := 0
	pm := false

	for i := 0; i < len(b); i++ {
		if state == expectObjClose || state == expectListClose {
			switch b[i] {
			case '{', '[':
				d++
			case '}', ']':
				d--
			}
		}

		switch {
		case state == expectKey && b[i] == '"':
			state = expectKeyClose
			s = i

		case state == expectKeyClose && b[i] == '"':
			state = expectColon
			if ki == len(kb) {
				ki = 0
			}
			pm = bytes.Equal(b[(s+1):i], kb[ki])
			if pm {
				ki++
			}

		case state == expectColon && b[i] == ':':
			state = expectValue

		case state == expectValue && b[i] == '"':
			state = expectString
			s = i

		case state == expectString && b[i] == '"':
			e = i

		case state == expectValue && b[i] == '[':
			state = expectListClose
			s = i
			d++

		case state == expectListClose && d == 0 && b[i] == ']':
			e = i

		case state == expectValue && b[i] == '{':
			state = expectObjClose
			s = i
			d++

		case state == expectObjClose && d == 0 && b[i] == '}':
			e = i

		case state == expectValue && (b[i] >= '0' && b[i] <= '9'):
			state = expectNumClose
			s = i

		case state == expectNumClose &&
			((b[i] < '0' || b[i] > '9') &&
				(b[i] != '.' && b[i] != 'e' && b[i] != 'E' && b[i] != '+' && b[i] != '-')):
			i--
			e = i

		case state == expectValue &&
			(b[i] == 'f' || b[i] == 'F' || b[i] == 't' || b[i] == 'T'):
			state = expectBoolClose
			s = i

		case state == expectBoolClose && (b[i] == 'e' || b[i] == 'E'):
			e = i
		}

		if e != 0 {
			if pm && (b[s] == '[' || b[s] == '{') {
				b = b[s:(e + 1)]
				i = 0

				if ki == len(kb) {
					return b
				}
			}

			state = expectKey
			e = 0
		}
	}

	return nil
}