package odin_tokenizer

import "core:fmt"
import "core:unicode"
import "core:unicode/utf8"

Error_Handler :: #type proc(pos: Pos, fmt: string, args: ..any)

Flag :: enum {
	Insert_Semicolon,
}
Flags :: distinct bit_set[Flag; u32]

Tokenizer :: struct {
	// Immutable data
	path: string,
	src:  string,
	err:  Error_Handler,

	flags: Flags,

	// Tokenizing state
	ch:          rune,
	offset:      int,
	read_offset: int,
	line_offset: int,
	line_count:  int,
	insert_semicolon: bool,

	// Mutable data
	error_count: int,
}

init :: proc(t: ^Tokenizer, src: string, path: string, err: Error_Handler = default_error_handler) {
	t.src = src
	t.err = err
	t.ch = ' '
	t.offset = 0
	t.read_offset = 0
	t.line_offset = 0
	t.line_count = len(src) > 0 ? 1 : 0
	t.error_count = 0
	t.path = path

	advance_rune(t)
	if t.ch == utf8.RUNE_BOM {
		advance_rune(t)
	}
}

@(private)
offset_to_pos :: proc(t: ^Tokenizer, offset: int) -> Pos {
	line := t.line_count
	column := offset - t.line_offset + 1

	return Pos {
		file = t.path,
		offset = offset,
		line = line,
		column = column,
	}
}

default_error_handler :: proc(pos: Pos, msg: string, args: ..any) {
	fmt.eprintf("%s(%d:%d) ", pos.file, pos.line, pos.column)
	fmt.eprintf(msg, ..args)
	fmt.eprintf("\n")
}

error :: proc(t: ^Tokenizer, offset: int, msg: string, args: ..any) {
	pos := offset_to_pos(t, offset)
	if t.err != nil {
		t.err(pos, msg, ..args)
	}
	t.error_count += 1
}

advance_rune :: proc(using t: ^Tokenizer) {
	if read_offset < len(src) {
		offset = read_offset
		if ch == '\n' {
			line_offset = offset
			line_count += 1
		}
		r, w := rune(src[read_offset]), 1
		switch {
		case r == 0:
			error(t, t.offset, "illegal character NUL")
		case r >= utf8.RUNE_SELF:
			r, w = utf8.decode_rune_in_string(src[read_offset:])
			if r == utf8.RUNE_ERROR && w == 1 {
				error(t, t.offset, "illegal UTF-8 encoding")
			} else if r == utf8.RUNE_BOM && offset > 0 {
				error(t, t.offset, "illegal byte order mark")
			}
		}
		read_offset += w
		ch = r
	} else {
		offset = len(src)
		if ch == '\n' {
			line_offset = offset
			line_count += 1
		}
		ch = -1
	}
}

peek_byte :: proc(t: ^Tokenizer, offset := 0) -> byte {
	if t.read_offset+offset < len(t.src) {
		return t.src[t.read_offset+offset]
	}
	return 0
}

skip_whitespace :: proc(t: ^Tokenizer) {
	if t.insert_semicolon {
		for {
			switch t.ch {
			case ' ', '\t', '\r':
				advance_rune(t)
			case:
				return
			}
		}
	} else {
		for {
			switch t.ch {
			case ' ', '\t', '\r', '\n':
				advance_rune(t)
			case:
				return
			}
		}
	}
}

is_letter :: proc(r: rune) -> bool {
	if r < utf8.RUNE_SELF {
		switch r {
		case '_':
			return true
		case 'A'..='Z', 'a'..='z':
			return true
		}
	}
	return unicode.is_letter(r)
}
is_digit :: proc(r: rune) -> bool {
	if '0' <= r && r <= '9' {
		return true
	}
	return unicode.is_digit(r)
}


scan_comment :: proc(t: ^Tokenizer) -> string {
	offset := t.offset-1
	next := -1
	general: {
		if t.ch == '/' || t.ch == '!' { // // #! comments
			advance_rune(t)
			for t.ch != '\n' && t.ch >= 0 {
				advance_rune(t)
			}

			next = t.offset
			if t.ch == '\n' {
				next += 1
			}
			break general
		}

		/* style comment */
		advance_rune(t)
		nest := 1
		for t.ch >= 0 && nest > 0 {
			ch := t.ch
			advance_rune(t)
			if ch == '/' && t.ch == '*' {
				nest += 1
			}

			if ch == '*' && t.ch == '/' {
				nest -= 1
				advance_rune(t)
				next = t.offset
				if nest == 0 {
					break general
				}
			}
		}

		error(t, offset, "comment not terminated")
	}

	lit := t.src[offset : t.offset]

	// NOTE(bill): Strip CR for line comments
	for len(lit) > 2 && lit[1] == '/' && lit[len(lit)-1] == '\r' {
		lit = lit[:len(lit)-1]
	}


	return string(lit)
}

scan_identifier :: proc(t: ^Tokenizer) -> string {
	offset := t.offset

	for is_letter(t.ch) || is_digit(t.ch) {
		advance_rune(t)
	}

	return string(t.src[offset : t.offset])
}

scan_string :: proc(t: ^Tokenizer) -> string {
	offset := t.offset-1

	for {
		ch := t.ch
		if ch == '\n' || ch < 0 {
			error(t, offset, "string literal was not terminated")
			break
		}
		advance_rune(t)
		if ch == '"' {
			break
		}
		if ch == '\\' {
			scan_escape(t)
		}
	}

	return string(t.src[offset : t.offset])
}

scan_raw_string :: proc(t: ^Tokenizer) -> string {
	offset := t.offset-1

	for {
		ch := t.ch
		if ch == utf8.RUNE_EOF {
			error(t, offset, "raw string literal was not terminated")
			break
		}
		advance_rune(t)
		if ch == '`' {
			break
		}
	}

	return string(t.src[offset : t.offset])
}

digit_val :: proc(r: rune) -> int {
	switch r {
	case '0'..='9':
		return int(r-'0')
	case 'A'..='F':
		return int(r-'A' + 10)
	case 'a'..='f':
		return int(r-'a' + 10)
	}
	return 16
}

scan_escape :: proc(t: ^Tokenizer) -> bool {
	offset := t.offset

	n: int
	base, max: u32
	switch t.ch {
	case 'a', 'b', 'e', 'f', 'n', 't', 'v', 'r', '\\', '\'', '\"':
		advance_rune(t)
		return true

	case '0'..='7':
		n, base, max = 3, 8, 255
	case 'x':
		advance_rune(t)
		n, base, max = 2, 16, 255
	case 'u':
		advance_rune(t)
		n, base, max = 4, 16, utf8.MAX_RUNE
	case 'U':
		advance_rune(t)
		n, base, max = 8, 16, utf8.MAX_RUNE
	case:
		if t.ch < 0 {
			error(t, offset, "escape sequence was not terminated")
		} else {
			error(t, offset, "unknown escape sequence")
		}
		return false
	}

	x: u32
	for n > 0 {
		d := u32(digit_val(t.ch))
		for d >= base {
			if t.ch < 0 {
				error(t, t.offset, "escape sequence was not terminated")
			} else {
				error(t, t.offset, "illegal character %d in escape sequence", t.ch)
			}
			return false
		}

		x = x*base + d
		advance_rune(t)
		n -= 1
	}

	if x > max || 0xd800 <= x && x <= 0xe000 {
		error(t, offset, "escape sequence is an invalid Unicode code point")
		return false
	}
	return true
}

scan_rune :: proc(t: ^Tokenizer) -> string {
	offset := t.offset-1
	valid := true
	n := 0
	for {
		ch := t.ch
		if ch == '\n' || ch < 0 {
			if valid {
				error(t, offset, "rune literal not terminated")
				valid = false
			}
			break
		}
		advance_rune(t)
		if ch == '\'' {
			break
		}
		n += 1
		if ch == '\\' {
			if !scan_escape(t)  {
				valid = false
			}
		}
	}

	if valid && n != 1 {
		error(t, offset, "illegal rune literal")
	}

	return string(t.src[offset : t.offset])
}

scan_number :: proc(t: ^Tokenizer, seen_decimal_point: bool) -> (Token_Kind, string) {
	scan_mantissa :: proc(t: ^Tokenizer, base: int) {
		for digit_val(t.ch) < base || t.ch == '_' {
			advance_rune(t)
		}
	}
	scan_exponent :: proc(t: ^Tokenizer, kind: ^Token_Kind) {
		if t.ch == 'e' || t.ch == 'E' {
			kind^ = .Float
			advance_rune(t)
			if t.ch == '-' || t.ch == '+' {
				advance_rune(t)
			}
			if digit_val(t.ch) < 10 {
				scan_mantissa(t, 10)
			} else {
				error(t, t.offset, "illegal floating-point exponent")
			}
		}

		// NOTE(bill): This needs to be here for sanity's sake
		switch t.ch {
		case 'i', 'j', 'k':
			kind^ = .Imag
			advance_rune(t)
		}
	}
	scan_fraction :: proc(t: ^Tokenizer, kind: ^Token_Kind) -> (early_exit: bool) {
		if t.ch == '.' && peek_byte(t) == '.' {
			return true
		}
		if t.ch == '.' {
			kind^ = .Float
			advance_rune(t)
			scan_mantissa(t, 10)
		}
		return false
	}


	offset := t.offset
	kind := Token_Kind.Integer
	seen_point := seen_decimal_point

	if seen_point {
		offset -= 1
		kind = .Float
		scan_mantissa(t, 10)
		scan_exponent(t, &kind)
	} else {
		if t.ch == '0' {
			int_base :: proc(t: ^Tokenizer, kind: ^Token_Kind, base: int, msg: string) {
				prev := t.offset
				advance_rune(t)
				scan_mantissa(t, base)
				if t.offset - prev <= 1 {
					kind^ = .Invalid
					error(t, t.offset, msg)
				}
			}

			advance_rune(t)
			switch t.ch {
			case 'b': int_base(t, &kind,  2, "illegal binary integer")
			case 'o': int_base(t, &kind,  8, "illegal octal integer")
			case 'd': int_base(t, &kind, 10, "illegal decimal integer")
			case 'z': int_base(t, &kind, 12, "illegal dozenal integer")
			case 'x': int_base(t, &kind, 16, "illegal hexadecimal integer")
			case 'h':
				prev := t.offset
				advance_rune(t)
				scan_mantissa(t, 16)
				if t.offset - prev <= 1 {
					kind = .Invalid
					error(t, t.offset, "illegal hexadecimal floating-point number")
				} else {
					sub := t.src[prev+1 : t.offset]
					digit_count := 0
					for d in sub {
						if d != '_' {
							digit_count += 1
						}
					}

					switch digit_count {
					case 4, 8, 16: break
					case:
						error(t, t.offset, "invalid hexadecimal floating-point number, expected 4, 8, or 16 digits, got %d", digit_count)
					}
				}

			case:
				seen_point = false
				scan_mantissa(t, 10)
				if t.ch == '.' {
					seen_point = true
					if scan_fraction(t, &kind) {
						return kind, string(t.src[offset : t.offset])
					}
				}
				scan_exponent(t, &kind)
				return kind, string(t.src[offset : t.offset])
			}
		}
	}

	scan_mantissa(t, 10)

	if scan_fraction(t, &kind) {
		return kind, string(t.src[offset : t.offset])
	}

	scan_exponent(t, &kind)

	return kind, string(t.src[offset : t.offset])
}


scan :: proc(t: ^Tokenizer) -> Token {
	skip_whitespace(t)

	offset := t.offset

	kind: Token_Kind
	lit: string
	pos := offset_to_pos(t, offset)

	switch ch := t.ch; true {
	case is_letter(ch):
		lit = scan_identifier(t)
		kind = .Ident
		check_keyword: if len(lit) > 1 {
			// TODO(bill): Maybe have a hash table lookup rather than this linear search
			for i in Token_Kind.B_Keyword_Begin ..= Token_Kind.B_Keyword_End {
				if lit == tokens[i] {
					kind = Token_Kind(i)
					break check_keyword
				}
			}
			for keyword, i in custom_keyword_tokens {
				if lit == keyword {
					kind = Token_Kind(i+1) + .B_Custom_Keyword_Begin
					break check_keyword
				}
			}
			break check_keyword
		}
	case '0' <= ch && ch <= '9':
		kind, lit = scan_number(t, false)
	case:
		advance_rune(t)
		switch ch {
		case -1:
			kind = .EOF
			if t.insert_semicolon {
				t.insert_semicolon = false
				kind = .Semicolon
				lit = "\n"
				return Token{kind, lit, pos}
			}
		case '\n':
			t.insert_semicolon = false
			kind = .Semicolon
			lit = "\n"
		case '\\':
			if .Insert_Semicolon in t.flags {
				t.insert_semicolon = false
			}
			token := scan(t)
			if token.pos.line == pos.line {
				error(t, token.pos.offset, "expected a newline after \\")
			}
			return token

		case '\'':
			kind = .Rune
			lit = scan_rune(t)
		case '"':
			kind = .String
			lit = scan_string(t)
		case '`':
			kind = .String
			lit = scan_raw_string(t)
		case '.':
			kind = .Period
			switch t.ch {
			case '0'..='9':
				kind, lit = scan_number(t, true)
			case '.':
				advance_rune(t)
				kind = .Ellipsis
				switch t.ch {
				case '<':
					advance_rune(t)
					kind = .Range_Half
				case '=':
					advance_rune(t)
					kind = .Range_Full
				}
			}
		case '@': kind = .At
		case '$': kind = .Dollar
		case '?': kind = .Question
		case '^': kind = .Pointer
		case ';': kind = .Semicolon
		case ',': kind = .Comma
		case ':': kind = .Colon
		case '(': kind = .Open_Paren
		case ')': kind = .Close_Paren
		case '[': kind = .Open_Bracket
		case ']': kind = .Close_Bracket
		case '{': kind = .Open_Brace
		case '}': kind = .Close_Brace
		case '%':
			kind = .Mod
			switch t.ch {
			case '=':
				advance_rune(t)
				kind = .Mod_Eq
			case '%':
				advance_rune(t)
				kind = .Mod_Mod
				if t.ch == '=' {
					advance_rune(t)
					kind = .Mod_Mod_Eq
				}
			}
		case '*':
			kind = .Mul
			if t.ch == '=' {
				advance_rune(t)
				kind = .Mul_Eq
			}
		case '=':
			kind = .Eq
			if t.ch == '=' {
				advance_rune(t)
				kind = .Cmp_Eq
			}
		case '~':
			kind = .Xor
			if t.ch == '=' {
				advance_rune(t)
				kind = .Xor_Eq
			}
		case '!':
			kind = .Not
			if t.ch == '=' {
				advance_rune(t)
				kind = .Not_Eq
			}
		case '+':
			kind = .Add
			switch t.ch {
			case '=':
				advance_rune(t)
				kind = .Add_Eq
			case '+':
				advance_rune(t)
				kind = .Increment
			}
		case '-':
			kind = .Sub
			switch t.ch {
			case '-':
				advance_rune(t)
				kind = .Decrement
				if t.ch == '-' {
					advance_rune(t)
					kind = .Undef
				}
			case '>':
				advance_rune(t)
				kind = .Arrow_Right
			case '=':
				advance_rune(t)
				kind = .Sub_Eq
			}
		case '#':
			kind = .Hash
			if t.ch == '!' {
				kind = .Comment
				lit = scan_comment(t)
			}
		case '/':
			kind = .Quo
			switch t.ch {
			case '/', '*':
				kind = .Comment
				lit = scan_comment(t)
			case '=':
				advance_rune(t)
				kind = .Quo_Eq
			}
		case '<':
			kind = .Lt
			switch t.ch {
			case '=':
				advance_rune(t)
				kind = .Lt_Eq
			case '<':
				advance_rune(t)
				kind = .Shl
				if t.ch == '=' {
					advance_rune(t)
					kind = .Shl_Eq
				}
			}
		case '>':
			kind = .Gt
			switch t.ch {
			case '=':
				advance_rune(t)
				kind = .Gt_Eq
			case '>':
				advance_rune(t)
				kind = .Shr
				if t.ch == '=' {
					advance_rune(t)
					kind = .Shr_Eq
				}
			}
		case '&':
			kind = .And
			switch t.ch {
			case '~':
				advance_rune(t)
				kind = .And_Not
				if t.ch == '=' {
					advance_rune(t)
					kind = .And_Not_Eq
				}
			case '=':
				advance_rune(t)
				kind = .And_Eq
			case '&':
				advance_rune(t)
				kind = .Cmp_And
				if t.ch == '=' {
					advance_rune(t)
					kind = .Cmp_And_Eq
				}
			}
		case '|':
			kind = .Or
			switch t.ch {
			case '=':
				advance_rune(t)
				kind = .Or_Eq
			case '|':
				advance_rune(t)
				kind = .Cmp_Or
				if t.ch == '=' {
					advance_rune(t)
					kind = .Cmp_Or_Eq
				}
			}
		case:
			if ch != utf8.RUNE_BOM {
				error(t, t.offset, "illegal character '%r': %d", ch, ch)
			}
			kind = .Invalid
		}
	}

	if .Insert_Semicolon in t.flags {
		#partial switch kind {
		case .Invalid, .Comment:
			// Preserve insert_semicolon info
		case .Ident, .Context, .Typeid, .Break, .Continue, .Fallthrough, .Return,
		     .Integer, .Float, .Imag, .Rune, .String, .Undef,
		     .Question, .Pointer, .Close_Paren, .Close_Bracket, .Close_Brace,
		     .Increment, .Decrement, .Or_Return:
			/*fallthrough*/
			t.insert_semicolon = true
		case:
			t.insert_semicolon = false
			break
		}
	}

	if lit == "" {
		lit = string(t.src[offset : t.offset])
	}
	return Token{kind, lit, pos}
}
