package subex

import (
	"main/walk"
	"strconv"
	"strings"
)

type RuneReader interface {
	Next() rune
	Rewind()
}

func accept(l RuneReader, chars string) bool {
	r := l.Next()
	for _, char := range chars {
		if char == r {
			return true
		}
	}
	l.Rewind()
	return false
}

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

func isNumericRune(r rune) bool {
	return '0' <= r && r <= '9' || r == '.'
}

// Having just parsed a `, read until the next ` and parse the contents into a list of non-string atoms
func parseNonStringLiteral(l RuneReader) (literals []walk.Atom) {
	for {
		r := l.Next()
		if isNumericRune(r) {
			var builder strings.Builder
			builder.WriteRune(r)
			for {
				r := l.Next()
				if !isNumericRune(r) {
					l.Rewind()
					break
				}
				builder.WriteRune(r)
			}
			numberString := builder.String()
			number, err := strconv.ParseFloat(numberString, 64)
			if err != nil {
				panic("Invalid number literal")
			}
			literals = append(literals, walk.ValueNumber(number))
			continue
		}
		switch r {
			case '`', '~':
				return literals
			case ' ', '\t':
				continue
			case 'n':
				if accept(l, "u") && accept(l, "l") && accept(l, "l") {
					literals = append(literals, walk.ValueNull{})
				} else {
					panic("Invalid literal")
				}
			case 't':
				if accept(l, "r") && accept(l, "u") && accept(l, "e") {
					literals = append(literals, walk.ValueBool(true))
				} else {
					panic("Invalid literal")
				}
			case 'f':
				if accept(l, "a") && accept(l, "l") && accept(l, "s") && accept(l, "e") {
					literals = append(literals, walk.ValueBool(false))
				} else {
					panic("Invalid literal")
				}
			case '{':
				literals = append(literals, walk.MapBegin)
			case '}':
				literals = append(literals, walk.MapEnd)
			case '[':
				literals = append(literals, walk.ArrayBegin)
			case ']':
				literals = append(literals, walk.ArrayEnd)
			default:
				panic("Invalid literal")
		}
	}
}

func charIsDigit(c rune) bool {
	return '0' <= c && c <= '9'
}

// Parse a positive integer, reads digits 0-9 and stops at the first non-digit
func parseInt(l RuneReader) (output int) {
	for {
		char := l.Next()
		if charIsDigit(char) {
			output = output * 10 + int(char - '0')
		} else {
			break
		}
	}
	l.Rewind()
	return output
}

// Having just read {, read in and parse the range contents
func parseRepeatRange(l RuneReader) (output []ConvexRange) {
	loop: for {
		var start, end int
		char := l.Next()
		l.Rewind()
		if char == '-' {
			start = -1
		} else {
			start = parseInt(l)
		}
		switch l.Next() {
			case ',':
				output = append(output, ConvexRange{start, start})
				continue loop
			case '-':
				char := l.Next()
				if charIsDigit(char) {
					l.Rewind()
					end = parseInt(l)
				} else {
					l.Rewind()
					end = -1
				}
			case '}':
				output = append(output, ConvexRange{start, start})
				break loop
			default:
				panic("Invalid character in repeat specifier")
		}
		switch l.Next() {
			case ',':
				output = append(output, ConvexRange{start, end})
				continue loop
			case '}':
				output = append(output, ConvexRange{start, end})
				break loop
			default:
				panic("Invalid character in repeat specifier")
		}
	}
	return output
}

func parseReplacement(l RuneReader) (output []OutputContent) {
	// 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, OutputLoad{slot: slot})
			case '`':
				literals := parseNonStringLiteral(l)
				for _, literal := range literals {
					output = append(output, OutputAtomLiteral {literal})
				}
			case '"':
				output = append(output, OutputAtomLiteral {walk.StringTerminal{}})
			default:
				output = append(output, OutputAtomLiteral{atom: walk.StringAtom(r)})
		}
	}
	return output
}

// Parse the contents of a range subex [] into a map
func parseRangeSubex(l RuneReader) map[walk.Atom]walk.Atom {
	// TODO escaping
	parts := make(map[walk.Atom]walk.Atom)
	var froms []walk.Atom
	var hasTo bool
	for {
		fromsStart := l.Next()
		if fromsStart == ']' {
			hasTo = false
			break
		} else if fromsStart == '=' {
			hasTo = true
			break
		} else if fromsStart == '`' {
			literals := parseNonStringLiteral(l)
			froms = append(froms, literals...)
			continue
		} else if fromsStart == '"' {
			froms = append(froms, walk.StringTerminal{})
			continue
		}
		if accept(l, "-") {
			fromsEnd := l.Next()
			if fromsEnd == ']' || fromsEnd == '=' {
				l.Rewind()
				fromsEnd = fromsStart
			}
			for i := fromsStart; i <= fromsEnd; i += 1 {
				froms = append(froms, walk.StringAtom(i))
			}
		} else {
			froms = append(froms, walk.StringAtom(fromsStart))
		}
	}
	if len(froms) == 0 {
		panic("Missing from part of range expression")
	}

	var tos []walk.Atom
	if hasTo {
		for {
			tosStart := l.Next()
			if tosStart == ']' {
				break
			} else if tosStart == '`' {
				literals := parseNonStringLiteral(l)
				tos = append(tos, literals...)
				continue
			} else if tosStart == '"' {
				tos = append(tos, walk.StringTerminal{})
				continue
			}
			if accept(l, "-") {
				tosEnd := l.Next()
				if tosEnd == ']' {
					l.Rewind()
					tosEnd = tosStart
				}
				for i := tosStart; i <= tosEnd; i += 1 {
					tos = append(tos, walk.StringAtom(i))
				}
			} else {
				tos = append(tos, walk.StringAtom(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 !accept(l, ")") {
				panic("Missing matching )")
			}
		case '[':
			rangeParts := parseRangeSubex(l)
			lhs = SubexASTRange {rangeParts}
		case ')', '|', ';', '{', '+', '-', '*', '/', '!', '$':
			l.Rewind()
			return nil
		case '=':
			replacement := parseReplacement(l)
			lhs = SubexASTOutput{replacement}
		case '.':
			lhs = SubexASTCopyAny{}
		case '?':
			lhs = SubexASTCopyBool{}
		case '%':
			lhs = SubexASTCopyNumber{}
		case '_':
			lhs = SubexASTCopyStringAtom{}
		case '#':
			lhs = SubexASTCopyString{}
		case ',':
			lhs = SubexASTCopyValue{}
		case '"':
			lhs = SubexASTCopyAtom {walk.StringTerminal{}}
		case '`':
			literals := parseNonStringLiteral(l)
			lhs = SubexASTEmpty{}
			for _, literal := range literals {
				lhs = SubexASTConcat {lhs, SubexASTCopyAtom {literal}}
			}
		case '~':
			literals := parseNonStringLiteral(l)
			var replacement []OutputContent
			for _, literal := range literals {
				replacement = append(replacement, OutputAtomLiteral {literal})
			}
			lhs = SubexASTOutput {replacement}
		default:
			lhs = SubexASTCopyAtom{Atom: walk.StringAtom(r)}
	}
	loop: for {
		if minPower <= 0 {
			next := parseSubex(l, 1)
			if next != nil {
				lhs = SubexASTConcat{lhs, next}
				continue loop
			}
		}
		r := l.Next()
		switch {
			case r == '{' && minPower <= 8:
				lhs = SubexASTRepeat {
					Content: lhs,
					Acceptable: parseRepeatRange(l),
				}
			case r == '+' && minPower <= 8:
				lhs = SubexASTSum {lhs}
			case r == '*' && minPower <= 8:
				lhs = SubexASTProduct {lhs}
			case r == '-' && minPower <= 8:
				lhs = SubexASTNegate {lhs}
			case r == '/' && minPower <= 8:
				lhs = SubexASTReciprocal {lhs}
			case r == '!' && minPower <= 8:
				lhs = SubexASTNot {lhs}
			case r == '$' && minPower <= 8:
				slot := l.Next()
				if slot == eof {
					panic("Missing slot character")
				}
				lhs = SubexASTStore{
					Match: lhs,
					Slot: slot,
				}
			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(l RuneReader) SubexAST {
	ast := parseSubex(l, 0)
	if ast == nil {
		return SubexASTEmpty{}
	}
	return ast
}