package parser

import "git.tebibyte.media/arf/arf/lexer"

// operatorTokens lists all symbolic tokens that can act as a command to a
// phrase.
var operatorTokens = []lexer.TokenKind {
        lexer.TokenKindColon,
        lexer.TokenKindPlus,
        lexer.TokenKindMinus,
        lexer.TokenKindIncrement,
        lexer.TokenKindDecrement,
        lexer.TokenKindAsterisk,
        lexer.TokenKindSlash,
        lexer.TokenKindExclamation,
        lexer.TokenKindPercent,
        lexer.TokenKindPercentAssignment,
        lexer.TokenKindTilde,
        lexer.TokenKindTildeAssignment,
        lexer.TokenKindAssignment,
        lexer.TokenKindEqualTo,
        lexer.TokenKindNotEqualTo,
        lexer.TokenKindLessThanEqualTo,
        lexer.TokenKindLessThan,
        lexer.TokenKindLShift,
        lexer.TokenKindLShiftAssignment,
        lexer.TokenKindGreaterThan,
        lexer.TokenKindGreaterThanEqualTo,
        lexer.TokenKindRShift,
        lexer.TokenKindRShiftAssignment,
        lexer.TokenKindBinaryOr,
        lexer.TokenKindBinaryOrAssignment,
        lexer.TokenKindLogicalOr,
        lexer.TokenKindBinaryAnd,
        lexer.TokenKindBinaryAndAssignment,
        lexer.TokenKindLogicalAnd,
        lexer.TokenKindBinaryXor,
        lexer.TokenKindBinaryXorAssignment,
}

// isTokenOperator returns whether or not the token is an operator token.
func isTokenOperator (token lexer.Token) (isOperator bool) {
	for _, kind := range operatorTokens {
		if token.Is(kind) {
			isOperator = true
			return
		}
	}

	return
}

// validPhraseStartTokens lists all tokens that are expected when parsing the
// first part of a phrase.
var validPhraseStartTokens = append (
	operatorTokens,
	lexer.TokenKindLBracket,
	lexer.TokenKindName,
	lexer.TokenKindString)
	
// validBlockLevelPhraseTokens lists all tokens that are expected when parsing
// a block level phrase.
var validBlockLevelPhraseTokens = append (
	validArgumentStartTokens,
	lexer.TokenKindNewline,
	lexer.TokenKindReturnDirection)
	
// validDelimitedPhraseTokens is like validBlockLevelPhraseTokens, but it also
// includes a right brace token.
var validDelimitedPhraseTokens = append (
	validArgumentStartTokens,
	lexer.TokenKindNewline,
	lexer.TokenKindIndent,
	lexer.TokenKindRBracket,
	lexer.TokenKindReturnDirection)

// controlFlowKinds contains a list of all phrase kinds that must have a block
// underneath them.
var controlFlowKinds = []PhraseKind {
	PhraseKindIf,
	PhraseKindElse,
	PhraseKindElseIf,
	PhraseKindFor,
	PhraseKindWhile,
	PhraseKindDefer,
	PhraseKindCase,
}

// parseBlock parses an indented block of phrases
func (parser *parsingOperation) parseBlock (
	indent int,
) (
	block Block,
	err error,
) {
	for {
		// if we've left the block, stop parsing
		if !parser.token.Is(lexer.TokenKindIndent) { return }
		if parser.token.Value().(int) != indent    { return }

		var phrase Phrase
		phrase, err = parser.parseBlockLevelPhrase(indent)
		block = append(block, phrase)
		if err != nil { return }
	}
}

// parseBlockLevelPhrase parses a phrase that is not being used as an argument
// to something else. This method is allowed to do things like parse return
// directions, and indented blocks beneath the phrase.
func (parser *parsingOperation) parseBlockLevelPhrase (
	indent int,
) (
	phrase Phrase,
	err error,
) {
	if !parser.token.Is(lexer.TokenKindIndent) { return }
	if parser.token.Value().(int) != indent    { return }
	err = parser.nextToken(validPhraseStartTokens...)
	if err != nil { return }

	expectRightBracket := false
	if parser.token.Is(lexer.TokenKindLBracket) {
		expectRightBracket = true
		err = parser.nextToken()
		if err != nil { return }
	}

	// get command
	err = parser.expect(validPhraseStartTokens...)
	if err != nil { return }
	phrase.command,
	phrase.kind,
	phrase.operator,
	err = parser.parsePhraseCommand()
	if err != nil { return }

	for {
		if expectRightBracket {
			// delimited
			// [someFunc arg1 arg2 arg3] -> someVariable
			err = parser.expect(validDelimitedPhraseTokens...)
			if err != nil { return }

			// we are delimited so we can safely skip whitespace
			err = parser.skipWhitespace()
			if err != nil { return }

			if parser.token.Is(lexer.TokenKindRBracket) {
				// this is an ending delimiter
				err = parser.nextToken()
				if err != nil { return }
				break
				
			}
		} else {
			// not delimited
			// someFunc arg1 arg2 arg3 -> someVariable
			err = parser.expect(validBlockLevelPhraseTokens...)
			if err != nil { return }

			if parser.token.Is(lexer.TokenKindReturnDirection) {
				// we've reached a return direction, so that
				// means this is the end of the phrase
				break
			} else if parser.token.Is(lexer.TokenKindNewline) {
				// we've reached the end of the line, so that
				// means this is the end of the phrase.
				break
			}
		}

		// if we've got this far, we are parsing an argument
		var argument Argument
		argument, err = parser.parseArgument()
		phrase.arguments = append(phrase.arguments, argument)
	}

	// expect newline or return direction
	err = parser.expect (
		lexer.TokenKindNewline,
		lexer.TokenKindReturnDirection)
	if err != nil { return }
	expectReturnDirection := parser.token.Is(lexer.TokenKindReturnDirection)

	// if we have hit a return direction, parse it...
	if expectReturnDirection {
		err = parser.nextToken()
		if err != nil { return }
		
		for {
			err = parser.expect (
				lexer.TokenKindNewline,
				lexer.TokenKindName)
			if err != nil { return }
			// ...until we hit a newline
			if parser.token.Is(lexer.TokenKindNewline) { break }

			var returnee Argument
			returnee, err = parser.parseArgument()
			if err != nil { return }

			phrase.returnees = append(phrase.returnees, returnee)
		}
	}
	
	err = parser.nextToken()
	if err != nil { return }

	// if this is a control flow phrase, parse block under it
	isControlFlow := false
	for _, kind := range controlFlowKinds {
		if phrase.kind == kind {
			isControlFlow = true
			break
		}
	}

	if isControlFlow {
		phrase.block, err = parser.parseBlock(indent + 1)
	}

	return
}

// parseArgumentLevelPhrase parses a phrase that is being used as an argument to
// something. It is forbidden from using return direction, and it must be
// delimited by brackets.
func (parser *parsingOperation) parseArgumentLevelPhrase () (
	phrase Phrase,
	err error,
) {
	err = parser.expect(lexer.TokenKindLBracket)
	if err != nil { return }

	// get command
	err = parser.nextToken(validPhraseStartTokens...)
	if err != nil { return }
	phrase.command,
	phrase.kind,
	phrase.operator,
	err = parser.parsePhraseCommand()
	if err != nil { return }

	for {
		// delimited
		// [someFunc arg1 arg2 arg3] -> someVariable
		err = parser.expect(validDelimitedPhraseTokens...)
		if err != nil { return }

		if parser.token.Is(lexer.TokenKindRBracket) {
			// this is an ending delimiter
			err = parser.nextToken()
			if err != nil { return }
			return
			
		} else if parser.token.Is(lexer.TokenKindNewline) {
			// we are delimited, so we can safely skip
			// newlines
			err = parser.nextToken()
			if err != nil { return }
			continue
			
		} else if parser.token.Is(lexer.TokenKindIndent) {
			// we are delimited, so we can safely skip
			// indents
			err = parser.nextToken()
			if err != nil { return }
			continue
		}
			
		// this is an argument
		var argument Argument
		argument, err = parser.parseArgument()
		phrase.arguments = append(phrase.arguments, argument)
	}
}

// parsePhraseCommand parses the command argument of a phrase.
func (parser *parsingOperation) parsePhraseCommand () (
	command  Argument,
	kind     PhraseKind,
	operator lexer.TokenKind,
	err      error,
) {
	if isTokenOperator(parser.token) {
		err = parser.expect(operatorTokens...)
		if err != nil { return }

		if parser.token.Is(lexer.TokenKindColon) {
			kind = PhraseKindCase
		} else if parser.token.Is(lexer.TokenKindAssignment) {
			kind = PhraseKindAssign
		} else {
			kind = PhraseKindOperator
			operator = parser.token.Kind()
		}
		
		err = parser.nextToken()
		return
	}

	// phrase command is not an operator, it is just a normal argument
	command, err = parser.parseArgument()
	if err != nil { return }

	// determine semantic role of phrase
	if command.kind == ArgumentKindString {
		kind = PhraseKindCallExternal
		
	} else if command.kind == ArgumentKindIdentifier {
		identifier := command.value.(Identifier)
		if len(identifier.trail) == 1 {
			switch identifier.trail[0] {
			case "loc":
				kind = PhraseKindReference
			case "cast":
				kind = PhraseKindCast
			case "defer":
				kind = PhraseKindDefer
			case "if":
				kind = PhraseKindIf
			case "elseif":
				kind = PhraseKindElseIf
			case "else":
				kind = PhraseKindElse
			case "switch":
				kind = PhraseKindSwitch
			case "while":
				kind = PhraseKindWhile
			case "for":
				kind = PhraseKindFor
			}
		}
	}
	
	return
}