package filter

import (
	"smesh.lol/pkg/lol/errorf"
)

func skipJSONValue(b []byte) (val []byte, r []byte, err error) {
	if len(b) == 0 {
		err = errorf.E([]byte("empty input"))
		return
	}
	start := 0
	end := 0
	switch b[0] {
	case '{':
		end, err = findMatchingBrace(b, '{', '}')
	case '[':
		end, err = findMatchingBrace(b, '[', ']')
	case '"':
		end, err = findClosingQuote(b)
	case 't':
		if len(b) >= 4 && string(b[:4]) == "true" {
			end = 4
		} else {
			err = errorf.E([]byte("invalid JSON value starting with 't'"))
		}
	case 'f':
		if len(b) >= 5 && string(b[:5]) == "false" {
			end = 5
		} else {
			err = errorf.E([]byte("invalid JSON value starting with 'f'"))
		}
	case 'n':
		if len(b) >= 4 && string(b[:4]) == "null" {
			end = 4
		} else {
			err = errorf.E([]byte("invalid JSON value starting with 'n'"))
		}
	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
		end = scanNumber(b)
	default:
		err = errorf.E([]byte("invalid JSON value starting with '%c'"), b[0])
	}
	if err != nil {
		return
	}
	val = b[start:end]
	r = b[end:]
	return
}

func findMatchingBrace(b []byte, open, close byte) (end int, err error) {
	if len(b) == 0 || b[0] != open {
		err = errorf.E([]byte("expected '%c'"), open)
		return
	}
	depth := 0
	inString := false
	escaped := false
	for i := 0; i < len(b); i++ {
		c := b[i]
		if escaped {
			escaped = false
			continue
		}
		if c == '\\' && inString {
			escaped = true
			continue
		}
		if c == '"' {
			inString = !inString
			continue
		}
		if inString {
			continue
		}
		if c == open {
			depth++
		} else if c == close {
			depth--
			if depth == 0 {
				end = i + 1
				return
			}
		}
	}
	err = errorf.E([]byte("unmatched '%c'"), open)
	return
}

func findClosingQuote(b []byte) (end int, err error) {
	if len(b) == 0 || b[0] != '"' {
		err = errorf.E([]byte("expected '\"'"))
		return
	}
	escaped := false
	for i := 1; i < len(b); i++ {
		c := b[i]
		if escaped {
			escaped = false
			continue
		}
		if c == '\\' {
			escaped = true
			continue
		}
		if c == '"' {
			end = i + 1
			return
		}
	}
	err = errorf.E([]byte("unclosed string"))
	return
}

func scanNumber(b []byte) (end int) {
	for i := 0; i < len(b); i++ {
		c := b[i]
		if (c >= '0' && c <= '9') || c == '-' || c == '+' || c == '.' || c == 'e' || c == 'E' {
			continue
		}
		end = i
		return
	}
	end = len(b)
	return
}