remote-darkness/internal/css/parser.go

package css

import (
	"fmt"

	"github.com/gorilla/css/scanner"
)

type CSSParser struct {
	*scanner.Scanner
}

func (parser *CSSParser) tolerantRead(extraTokens []*CSSToken) (token *scanner.Token) {
tokenLoop:
	for {
		token = parser.Scanner.Next()
		switch {
		case isNativeNonMachineContent(token):
			if extraTokens != nil {
				extraTokens = append(extraTokens, &CSSToken{Type: TokenType_Native, NativeToken: token})
			}
		default:
			break tokenLoop
		}
	}
	return
}

func (parser *CSSParser) readPropertyValue() (result *CSSToken, token *scanner.Token, err error) {
	result = &CSSToken{Type: TokenType_PropertyValue, SubTokens: []*CSSToken{}}
propValueLoop:
	for {
		token = parser.tolerantRead(result.SubTokens)
		switch {
		case token.Type == scanner.TokenChar && token.Value == "}" || token.Value == ";": // closure or prop end
			break propValueLoop
		case token.Type == scanner.TokenEOF || token.Type == scanner.TokenError:
			err = fmt.Errorf("expected continuation of property value but got %s", token.String())
		default:
			result.SubTokens = append(result.SubTokens, &CSSToken{Type: TokenType_Native, NativeToken: token})
		}
	}
	return
}

// ",selector,selector,...selector{"
func (parser *CSSParser) readSelectors(currentToken *scanner.Token) (result []*CSSToken, token *scanner.Token, err error) {
	result = []*CSSToken{}
	currentSelector := &CSSToken{Type: TokenType_Selector, SubTokens: []*CSSToken{}}
	token = currentToken
selectorsLoop:
	for {
		switch {
		case token.Type == scanner.TokenChar && token.Value == "{": // closure begin
			result = append(result,
				currentSelector)
			break selectorsLoop
		case token.Type == scanner.TokenChar && token.Value == ",": // new selector upcoming
			result = append(result,
				currentSelector,
				&CSSToken{Type: TokenType_Native, NativeToken: token})
			currentSelector = &CSSToken{Type: TokenType_Selector, SubTokens: []*CSSToken{}}
		case token.Type == scanner.TokenS && len(currentSelector.SubTokens) <= 0: // space, current selector still empty
			result = append(result,
				&CSSToken{Type: TokenType_Native, NativeToken: token})
		case token.Type == scanner.TokenEOF || token.Type == scanner.TokenError:
			err = fmt.Errorf("expected selector but got %s", token.String())
			return
		default:
			currentSelector.SubTokens = append(currentSelector.SubTokens, &CSSToken{Type: TokenType_Native, NativeToken: token})
		}
		token = parser.tolerantRead(result)
	}
	return
}

// "prop;prop;...prop}"
func (parser *CSSParser) readRuleClosure() (result []*CSSToken, token *scanner.Token, err error) {
	result = []*CSSToken{}
closureLoop:
	for {
		token = parser.tolerantRead(result)
		switch {
		case token.Type == scanner.TokenChar && token.Value == "}": // closure end
			break closureLoop
		case token.Type == scanner.TokenEOF || token.Type == scanner.TokenError:
			err = fmt.Errorf("expected continuation of rule but got %s", token.String())
			return
		case token.Type == scanner.TokenChar,
			token.Type == scanner.TokenIdent: // property name
			property := &CSSToken{Type: TokenType_Property, SubTokens: []*CSSToken{}}
			propName := &CSSToken{Type: TokenType_PropertyName, SubTokens: []*CSSToken{}}
		propNameLoop:
			for {
				switch {
				case token.Type == scanner.TokenChar && token.Value == ":": // end of prop name
					property.SubTokens = append(property.SubTokens, propName,
						&CSSToken{Type: TokenType_Native, NativeToken: token})
					break propNameLoop
				default:
					propName.SubTokens = append(propName.SubTokens,
						&CSSToken{Type: TokenType_Native, NativeToken: token})
				}
				token = parser.tolerantRead(result)
			}

			// prop value
			var intermediate *CSSToken
			intermediate, token, err = parser.readPropertyValue()
			if err != nil {
				break closureLoop
			}
			property.SubTokens = append(property.SubTokens, intermediate)

			result = append(result, property)
			if token.Value == ";" {
				result = append(result, &CSSToken{Type: TokenType_Native, NativeToken: token})
			}
			if token.Value == "}" {
				break closureLoop
			}
		default:
			result = append(result, &CSSToken{Type: TokenType_Native, NativeToken: token})
		}
	}
	return
}