package subex

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

type Type int
const (
	AnyType Type = iota
	ValueType
	RuneType
)

func resolveTypes(t1 Type, t2 Type) Type {
	if t1 == AnyType {
		return t2
	}

	if t2 == AnyType {
		return t1
	}

	if t1 == t2 {
		return t1
	}

	panic("Types don't match in parser")
}

type Structure int
const (
	NoneStructure Structure = iota
	StringStructure
	ArrayStructure
	ArrayValuesStructure
	MapStructure
)
func (s Structure) String() string {
	switch s {
	case NoneStructure:
		return "-"
	case StringStructure:
		return "~"
	case ArrayStructure:
		return "@"
	case ArrayValuesStructure:
		return ":"
	case MapStructure:
		return "#"
	default:
		panic("Invalid structure")
	}
}

type DestructureMethod int
const (
	Normal DestructureMethod = iota
	Iterate
)

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 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 parseScalarLiteral(l RuneReader) (walk.Scalar, bool) {
	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")
		}
		return walk.NumberValue(number), true
	}
	switch r {
		case 'n':
			if accept(l, "u") && accept(l, "l") && accept(l, "l") {
				return walk.NullValue{}, true
			} else {
				panic("Invalid literal")
			}
		case 't':
			if accept(l, "r") && accept(l, "u") && accept(l, "e") {
				return walk.BoolValue(true), true
			} else {
				panic("Invalid literal")
			}
		case 'f':
			if accept(l, "a") && accept(l, "l") && accept(l, "s") && accept(l, "e") {
				return walk.BoolValue(false), true
			} else {
				panic("Invalid literal")
			}
		default:
			fmt.Printf("%c\n", r)
			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 parseValueReplacement(l RuneReader, end rune) (output SubexAST) {
	output = SubexASTEmpty{}
	// TODO escaping
	// TODO add arrays, maps and strings
	loop: for {
		r := l.Next()
		switch r {
		case eof:
			panic("Missing closing `")
		case ' ':
		case end:
			break loop
		case '$':
			slot := l.Next()
			if slot == eof {
				panic("Missing slot character")
			}
			output = SubexASTConcat {
				First: output,
				Second: SubexASTOutputValueLoad {
					slot: slot,
				},
			}
		// TODO: destructures
		case '#':
			if !accept(l, "(") {
				panic("Missing ( after #")
			}
			output = SubexASTConcat {
				First: output,
				Second: SubexASTDestructure {
					Destructure: NoneStructure,
					Structure: MapStructure,
					Content: parseValueReplacement(l, ')'),
				},
			}
			if !accept(l, "#") {
				panic("Missing # after )")
			}
		case '"':
			output = SubexASTConcat {
				First: output,
				Second: SubexASTDestructure {
					Destructure: NoneStructure,
					Structure: StringStructure,
					Content: parseRuneReplacement(l, '"'),
				},
			}
		default:
			l.Rewind()
			scalar, ok := parseScalarLiteral(l)
			if !ok {
				panic("Invalid scalar literal")
			}
			output = SubexASTConcat {
				First: output,
				Second: SubexASTOutputValueLiteral {
					literal: scalar,
				},
			}
		}
	}
	return output
}

func parseRuneReplacement(l RuneReader, end rune) (output SubexAST) {
	output = SubexASTEmpty{}
	// TODO escaping
	loop: for {
		r := l.Next()
		switch r {
		case eof:
			panic("Missing closing `")
		case end:
			break loop
		case '$':
			slot := l.Next()
			if slot == eof {
				panic("Missing slot character")
			}
			output = SubexASTConcat {
				First: output,
				Second: SubexASTOutputRuneLoad {
					slot: slot,
				},
			}
		default:
			output = SubexASTConcat {
				First: output,
				Second: SubexASTOutputRuneLiteral {
					literal: r,
				},
			}
		}
	}
	return output
}

// Parse the contents of a range subex [] into a map
// func parseRangeSubex(l RuneReader) map[walk.AtomOLD]walk.AtomOLD {
// 	// TODO escaping
// 	parts := make(map[walk.AtomOLD]walk.AtomOLD)
// 	var froms []walk.AtomOLD
// 	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.NewAtomStringTerminal())
// 			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.NewAtomStringRune(i))
// 			}
// 		} else {
// 			froms = append(froms, walk.NewAtomStringRune(fromsStart))
// 		}
// 	}
// 	if len(froms) == 0 {
// 		panic("Missing from part of range expression")
// 	}

// 	var tos []walk.AtomOLD
// 	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.NewAtomStringTerminal())
// 				continue
// 			}
// 			if accept(l, "-") {
// 				tosEnd := l.Next()
// 				if tosEnd == ']' {
// 					l.Rewind()
// 					tosEnd = tosStart
// 				}
// 				for i := tosStart; i <= tosEnd; i += 1 {
// 					tos = append(tos, walk.NewAtomStringRune(i))
// 				}
// 			} else {
// 				tos = append(tos, walk.NewAtomStringRune(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 parseDestructure(l RuneReader, destructure Structure, inType Type) (lhs SubexAST, outType Type) {
	var method rune
	switch l.Next() {
	case '(':
		method = ')'
	case '[':
		method = ']'
	default:
		panic("Missing ( or [ after destructure start")
	}

	var innerInType Type
	var expectedInType Type
	switch destructure {
	case NoneStructure:
		innerInType = inType
		expectedInType = inType
	case StringStructure:
		innerInType = RuneType
		expectedInType = ValueType
	case ArrayStructure:
		innerInType = ValueType
		expectedInType = ValueType
	case ArrayValuesStructure:
		innerInType = ValueType
		expectedInType = ValueType
	case MapStructure:
		innerInType = ValueType
		expectedInType = ValueType
	default:
		panic("Invalid structure")
	}

	resolveTypes(inType, expectedInType)

	lhs, innerOutType := parseSubex(l, 0, innerInType)
	if !accept(l, string(method)) {
		panic("Missing matching ) or ]")
	}

	switch method {
	case ')':
	case ']':
		lhs = SubexASTRepeat {
			Content: lhs,
			Acceptable: []ConvexRange{{
				Start: -1,
				End: 0,
			}},
		}
	default:
		panic("Invalid method")
	}

	var structure Structure
	var expectedInnerOutType Type
	r := l.Next()
	switch r {
	case '-':
		structure = NoneStructure
		expectedInnerOutType = innerOutType
	case '~':
		structure = StringStructure
		expectedInnerOutType = RuneType
	case '@':
		structure = ArrayStructure
		expectedInnerOutType = ValueType
	case ':':
		structure = ArrayValuesStructure
		expectedInnerOutType = ValueType
	case '#':
		structure = MapStructure
		expectedInnerOutType = ValueType
	default:
		panic("Missing matching destructure")
	}

	innerOutType = resolveTypes(innerOutType, expectedInnerOutType)

	switch structure {
	case NoneStructure:
		outType = innerOutType
	case StringStructure:
		outType = ValueType
	case ArrayStructure:
		outType = ValueType
	case ArrayValuesStructure:
		outType = ValueType
	case MapStructure:
		outType = ValueType
	}

	lhs = SubexASTDestructure {
		Destructure: destructure,
		Structure: structure,
		Content: lhs,
	}

	return lhs, outType
}

func parseSubex(l RuneReader, minPower int, inType Type) (lhs SubexAST, outType Type) {
	start:
	r := l.Next()
	switch r {
		case eof:
			return nil, inType
		case '(':
			lhs, outType = parseSubex(l, 0, inType)
			if !accept(l, ")") {
				panic("Missing matching )")
			}
		case '-':
			lhs, outType = parseDestructure(l, NoneStructure, inType)
		case '~':
			lhs, outType = parseDestructure(l, StringStructure, inType)
		case '@':
			lhs, outType = parseDestructure(l, ArrayStructure, inType)
		case ':':
			lhs, outType = parseDestructure(l, ArrayValuesStructure, inType)
		case '#':
			lhs, outType = parseDestructure(l, MapStructure, inType)
		case '"':
			if inType == ValueType {
				var innerOutType Type
				lhs, innerOutType = parseSubex(l, 0, RuneType)
				if !accept(l, "\"") {
					panic("Missing matching \"")
				}
				resolveTypes(innerOutType, RuneType)
				lhs = SubexASTDestructure {
					Destructure: StringStructure,
					Structure: StringStructure,
					Content: lhs,
				}
				outType = ValueType
			} else {
				l.Rewind()
				return SubexASTEmpty{}, inType
			}
		// TODO
		// case '[':
		// 	rangeParts := parseRangeSubex(l)
		// 	lhs = SubexASTRange {rangeParts}
		case ')', ']', '|', ';', '{', '+', '*', '/', '!', '=', '$':
			l.Rewind()
			return SubexASTEmpty{}, inType
		case '.':
			outType = inType
			if inType == RuneType {
				lhs = SubexASTCopyAnyRune{}
			} else {
				lhs = SubexASTCopyAnyValue{}
			}
		case ',':
			switch inType {
			case ValueType:
				outType = inType
				lhs = SubexASTCopyAnySimpleValue{}
			case RuneType:
				outType = inType
				lhs = SubexASTCopyRune{','}
			default:
				panic("Invalid inType")
			}
		case '?':
			outType = inType
			lhs = SubexASTCopyBool{}
		case '%':
			outType = inType
			lhs = SubexASTCopyNumber{}
		case '`':
			outType = inType
			switch inType {
			case ValueType:
				lhs = parseValueReplacement(l, '`')
			case RuneType:
				lhs = parseRuneReplacement(l, '`')
			default:
				panic("Invalid inType")
			}
		case ' ':
			if inType == RuneType {
				outType = RuneType
				lhs = SubexASTCopyRune {' '}
			} else {
				goto start
			}
		default:
			outType = inType
			if inType == RuneType {
				lhs = SubexASTCopyRune {r}
			} else {
				l.Rewind()
				scalar, ok := parseScalarLiteral(l)
				if !ok {
					panic("Invalid subex")
				}
				lhs = SubexASTCopyScalar {scalar}
			}
	}
	loop: for {
		if minPower <= 20 {
			next, outType2 := parseSubex(l, 21, inType)
			// TODO: next might legitimately be SubexASTEmpty, e.g. ``
			if next != nil && (next != SubexASTEmpty{}) {
				outType = resolveTypes(outType, outType2)
				lhs = SubexASTConcat{lhs, next}
				continue loop
			}
		}
		r := l.Next()
		switch {
			case r == '{' && minPower <= 4:
				lhs = SubexASTRepeat {
					Content: lhs,
					Acceptable: parseRepeatRange(l),
				}
			case r == '+' && minPower <= 4:
				lhs = SubexASTSum {lhs}
				resolveTypes(inType, ValueType)
				outType = resolveTypes(outType, ValueType)
			case r == '*' && minPower <= 4:
				lhs = SubexASTProduct {lhs}
				resolveTypes(inType, ValueType)
				outType = resolveTypes(outType, ValueType)
			case r == '!' && minPower <= 4:
				lhs = SubexASTNot {lhs}
				resolveTypes(inType, ValueType)
				outType = resolveTypes(outType, ValueType)
			case r == '$' && minPower <= 4:
				slot := l.Next()
				if slot == eof {
					panic("Missing slot character")
				}
				if slot == '_' {
					lhs = SubexASTDiscard {
						Content: lhs,
						InnerOutType: outType,
					}
				} else {
					if inType == ValueType {
						lhs = SubexASTStoreValues {
							Match: lhs,
							Slot: slot,
						}
					} else {
						lhs = SubexASTStoreRunes {
							Match: lhs,
							Slot: slot,
						}
					}
				}
				outType = AnyType
			case r == '|' && minPower <= 8:
				rhs, outType2 := parseSubex(l, 9, inType)
				outType = resolveTypes(outType, outType2)
				if rhs == nil {
					panic("Missing subex after |")
				}
				lhs = SubexASTOr{lhs, rhs}
			default:
				l.Rewind()
				break loop
		}
	}
	return lhs, outType
}

func Parse(l RuneReader) SubexAST {
	ast, outType := parseSubex(l, 0, ValueType)
	outType = resolveTypes(outType, ValueType)
	if ast == nil {
		return SubexASTEmpty{}
	}
	return ast
}