package subex

import (
	"main/walk"
)

func expectBracket(l *RuneReader, ifLeft walk.Datum, ifRight walk.Datum) walk.Datum {
	switch l.next() {
		case '(':
			return ifLeft
		case ')':
			return ifRight
		default:
			panic("Expected ( or )")
	}
}

// Having just read termType, read in a bracket and return the corresponding walk.Datum
func parseTerminatorDatumLiteral(termType rune, l *RuneReader) walk.Datum {
	switch termType {
		case '@':
			return expectBracket(l, walk.ArrayBegin, walk.ArrayEnd)
		case '~':
			return expectBracket(l, walk.StartString{}, walk.EndString{})
		case '#':
			return expectBracket(l, walk.MapBegin, walk.MapEnd)
		default:
			return nil
	}
}

func parseReplacement(l *RuneReader) (output []TransducerOutput) {
	// TODO escaping
	loop: for {
		r := l.next()
		switch r {
			case eof:
				panic("Missing closing \"")
			case '"':
				break loop
			case '$':
				slot := l.next()
				if slot == eof {
					panic("Missing slot character")
				}
				output = append(output, TransducerReplacementLoad{datum: slot})
			case '@', '~', '#':
				output = append(output, TransducerReplacementRune{datum: parseTerminatorDatumLiteral(r, l)})
			default:
				output = append(output, TransducerReplacementRune{datum: r})
		}
	}
	return output
}

// Parse the contents of a range subex [] into a map
func parseRangeSubex(l *RuneReader) map[walk.Datum]walk.Datum {
	// TODO escaping
	parts := make(map[walk.Datum]walk.Datum)
	var froms []walk.Datum
	var hasTo bool
	for {
		fromsStart := l.next()
		if fromsStart == ']' {
			hasTo = false
			break
		} else if fromsStart == '=' {
			hasTo = true
			break
		} else {
			datum := parseTerminatorDatumLiteral(fromsStart, l)
			if datum != nil {
				froms = append(froms, datum)
				continue
			}
		}
		if l.accept("-") {
			fromsEnd := l.next()
			if fromsEnd == ']' || fromsEnd == '=' {
				l.rewind()
				fromsEnd = fromsStart
			}
			for i := fromsStart; i <= fromsEnd; i += 1 {
				froms = append(froms, i)
			}
		} else {
			froms = append(froms, fromsStart)
		}
	}
	if len(froms) == 0 {
		panic("Missing from part of range expression")
	}

	var tos []walk.Datum
	if hasTo {
		for {
			tosStart := l.next()
			if tosStart == ']' {
				break
			} else {
				datum := parseTerminatorDatumLiteral(tosStart, l)
				if datum != nil {
					tos = append(tos, datum)
					continue
				}
			}
			if l.accept("-") {
				tosEnd := l.next()
				if tosEnd == ']' {
					l.rewind()
					tosEnd = tosStart
				}
				for i := tosStart; i <= tosEnd; i += 1 {
					tos = append(tos, i)
				}
			} else {
				tos = append(tos, tosStart)
			}
		}
	} else {
		tos = froms
	}
	if len(tos) == 0 {
		panic("Missing to part of range expression")
	}
	
	for i, from := range froms {
		parts[from] = tos[i % len(tos)]
	}
	return parts
}

func parseSubex(l *RuneReader, minPower int) SubexAST {
	var lhs SubexAST
	r := l.next()
	switch r {
		case eof:
			return nil
		case '(':
			lhs = parseSubex(l, 0)
			if !l.accept(")") {
				panic("Missing matching )")
			}
		case '[':
			rangeParts := parseRangeSubex(l)
			lhs = SubexASTRange {rangeParts}
		case ')', '*', '-', '|', '!', '?', ';':
			l.rewind()
			return nil
		case '$':
			slot := l.next()
			if slot == eof {
				panic("Missing slot character")
			}
			match := parseSubex(l, 100)
			if match == nil {
				panic("Missing regex for store")
			}
			lhs = SubexASTStore{
				match: match,
				slot: slot,
			}
		case '"':
			replacement := parseReplacement(l)
			lhs = SubexASTOutput{replacement}
		case '.':
			lhs = SubexASTCopyAny{}
		case '@', '#', '~':
			lhs = SubexASTCopyRune{datum: parseTerminatorDatumLiteral(r, l)}
		default:
			lhs = SubexASTCopyRune{datum: r}
	}
	loop: for {
		if minPower <= 0 {
			next := parseSubex(l, 1)
			if next != nil {
				lhs = SubexASTConcat{lhs, next}
				continue loop
			}
		}
		r := l.next()
		switch {
			case r == '*' && minPower <= 8:
				lhs = SubexASTMaximise{lhs}
			case r == '-' && minPower <= 8:
				lhs = SubexASTMinimise{lhs}
			case r == '!' && minPower <= 8:
				lhs = SubexASTTry{lhs}
			case r == '?' && minPower <= 8:
				lhs = SubexASTMaybe{lhs}
			case r == '|' && minPower <= 4:
				rhs := parseSubex(l, 5)
				if rhs == nil {
					panic("Missing subex after |")
				}
				lhs = SubexASTOr{lhs, rhs}
			case r == ';' && minPower <= 2:
				rhs := parseSubex(l, 3)
				if rhs == nil {
					panic("Missing subex after ;")
				}
				lhs = SubexASTJoin{
					content: lhs,
					delimiter: rhs,
				}
			default:
				l.rewind()
				break loop
		}
	}
	return lhs
}

func Parse(input string) SubexAST {
	l := RuneReader {
		input: input,
		pos: 0,
		width: 0,
	}
	return parseSubex(&l, 0)
}