// Copyright (c) 2020-2024 Joe Conigliaro. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module scanner

import v2.token
import v2.pref

@[flag]
pub enum Mode {
	normal
	scan_comments
	skip_interpolation
}

pub struct Scanner {
	pref               &pref.Preferences
	mode               Mode
	skip_interpolation bool
mut:
	file        &token.File = &token.File{}
	src         string
	insert_semi bool
pub mut:
	offset int // current char offset
	pos    int // token offset (start of current token)
	lit    string
	// strings literals & interpolation
	in_str_incomplete   bool
	in_str_inter        bool
	str_inter_cbr_depth int
	str_quote           u8
}

pub fn new_scanner(prefs &pref.Preferences, mode Mode) &Scanner {
	unsafe {
		return &Scanner{
			pref:               prefs
			mode:               mode
			skip_interpolation: mode.has(.skip_interpolation)
		}
	}
}

pub fn (mut s Scanner) init(file &token.File, src string) {
	// reset since scanner instance may be reused
	s.offset = 0
	s.pos = 0
	s.lit = ''
	// s.in_str_incomplete = false
	// s.in_str_inter = false
	// s.str_inter_cbr_depth = 0
	// init
	s.file = unsafe { file }
	s.src = src
}

@[direct_array_access]
pub fn (mut s Scanner) scan() token.Token {
	// before whitespace call to keep whitespaces in string
	// NOTE: before start: simply for a little more efficiency
	// if !s.skip_interpolation && s.in_str_incomplete {
	if s.in_str_incomplete {
		s.in_str_incomplete = false
		s.pos = s.offset
		s.string_literal(false, s.str_quote)
		s.lit = s.src[s.pos..s.offset]
		return .string
	}
	start:
	s.whitespace()
	if s.offset == s.src.len {
		s.lit = ''
		if s.insert_semi {
			s.insert_semi = false
			return .semicolon
		}
		s.file.add_line(s.offset)
		return .eof
	}
	c := s.src[s.offset]
	s.pos = s.offset
	preserve_insert_semi := s.insert_semi
	s.insert_semi = false
	if c == `\n` {
		s.lit = ''
		return .semicolon
	}
	// comment | `/=` | `/`
	else if c == `/` {
		c2 := s.src[s.offset + 1]
		// comment
		if c2 in [`/`, `*`] {
			if preserve_insert_semi {
				s.insert_semi = true
			}
			s.comment()
			if !s.mode.has(.scan_comments) {
				unsafe {
					goto start
				}
			}
			s.lit = s.src[s.pos..s.offset]
			return .comment
		}
		// `/=`
		else if c2 == `=` {
			s.offset += 2
			return .div_assign
		}
		s.offset++
		// `/`
		return .div
	}
	// number
	else if c >= `0` && c <= `9` {
		s.number()
		s.lit = s.src[s.pos..s.offset]
		s.insert_semi = true
		return .number
	}
	// keyword | name
	else if (c >= `a` && c <= `z`) || (c >= `A` && c <= `Z`) || c in [`_`, `@`] {
		s.offset++
		// NOTE: I have made `@[` a token instead of using `@` and `[` because `@`
		// is not currently used as a token, and it is also easier to parse this way.
		// if/when `@` becomes used as a token of its own, then I may change this.
		if c == `@` && s.src[s.offset] == `[` {
			s.offset++
			return .attribute
		}
		for s.offset < s.src.len {
			c3 := s.src[s.offset]
			if c3.is_alnum() || c3 == `_` {
				s.offset++
				continue
			}
			break
		}
		s.lit = s.src[s.pos..s.offset]
		tok := token.Token.from_string_tinyv(s.lit)
		if tok in [.key_break, .key_continue, .key_none, .key_return, .key_false, .key_true, .name] {
			s.insert_semi = true
		}
		return tok
	}
	// string
	else if c in [`'`, `"`] {
		s.offset++
		if !s.in_str_inter {
			s.str_quote = c
		}
		// TODO: I would prefer a better way to handle raw
		s.string_literal(s.in_str_inter || s.src[s.offset - 2] == `r`, c)
		s.lit = s.src[s.pos..s.offset]
		s.insert_semi = true
		return .string
	}
	// byte (char) `a`
	else if c == `\`` {
		s.offset++
		// NOTE: if there is more than one char still scan it
		// we can error at a later stage. should we error now?
		for {
			c2 := s.src[s.offset]
			if c2 == c {
				break
			} else if c2 == `\\` {
				s.offset += 2
				continue
			}
			s.offset++
		}
		s.offset++
		s.lit = s.src[s.pos + 1..s.offset - 1]
		s.insert_semi = true
		return .char
	}
	// s.lit not set, as tokens below get converted directly to string
	// s.lit = c
	s.lit = ''
	s.offset++
	match c {
		`.` {
			c2 := s.src[s.offset]
			if c2 >= `0` && c2 <= `9` {
				// TODO: only really need decimal
				s.number()
				s.lit = s.src[s.pos..s.offset]
				return .number
			} else if c2 == `.` {
				s.offset++
				if s.src[s.offset] == `.` {
					s.offset++
					return .ellipsis
				}
				return .dotdot
			}
			return .dot
		}
		`:` {
			if s.src[s.offset] == `=` {
				s.offset++
				return .decl_assign
			}
			return .colon
		}
		`!` {
			c2 := s.src[s.offset]
			if c2 == `=` {
				s.offset++
				return .ne
			} else if c2 == `i` {
				c3 := s.src[s.offset + 1]
				c4_is_space := s.src[s.offset + 2] in [` `, `\t`]
				if c3 == `n` && c4_is_space {
					s.offset += 2
					return .not_in
				} else if c3 == `s` && c4_is_space {
					s.offset += 2
					return .not_is
				}
			}
			s.insert_semi = true
			return .not
		}
		`=` {
			c2 := s.src[s.offset]
			if c2 == `=` {
				s.offset++
				return .eq
			}
			return .assign
		}
		`+` {
			c2 := s.src[s.offset]
			if c2 == `+` {
				s.offset++
				return .inc
			} else if c2 == `=` {
				s.offset++
				return .plus_assign
			}
			return .plus
		}
		`-` {
			c2 := s.src[s.offset]
			if c2 == `-` {
				s.offset++
				return .dec
			} else if c2 == `=` {
				s.offset++
				return .minus_assign
			}
			return .minus
		}
		`%` {
			if s.src[s.offset] == `=` {
				s.offset++
				return .mod_assign
			}
			return .mod
		}
		`*` {
			if s.src[s.offset] == `=` {
				s.offset++
				return .mul_assign
			}
			return .mul
		}
		`^` {
			if s.src[s.offset] == `=` {
				s.offset++
				return .xor_assign
			}
			return .xor
		}
		`&` {
			c2 := s.src[s.offset]
			if c2 == `&` {
				// so that we parse &&Type as two .amp instead of .and
				// but this requires there is a space. we could check
				// for capital or some other way, this is simplest for now.
				if s.offset + 1 <= s.src.len && s.src[s.offset + 1] in [` `, `\t`] {
					s.offset++
					return .and
				}
			} else if c2 == `=` {
				s.offset++
				return .and_assign
			}
			return .amp
		}
		`|` {
			c2 := s.src[s.offset]
			if c2 == `|` {
				s.offset++
				return .logical_or
			} else if c2 == `=` {
				s.offset++
				return .or_assign
			}
			return .pipe
		}
		`<` {
			c2 := s.src[s.offset]
			if c2 == `<` {
				s.offset++
				if s.src[s.offset] == `=` {
					s.offset++
					return .left_shift_assign
				}
				return .left_shift
			} else if c2 == `=` {
				s.offset++
				return .le
			} else if c2 == `-` {
				s.offset++
				return .arrow
			}
			return .lt
		}
		`>` {
			c2 := s.src[s.offset]
			if c2 == `>` {
				s.offset++
				c3 := s.src[s.offset]
				if c3 == `>` {
					s.offset++
					if s.src[s.offset] == `=` {
						s.offset++
						return .right_shift_unsigned_assign
					}
					return .right_shift_unsigned
				} else if c3 == `=` {
					s.offset++
					return .right_shift_assign
				}
				return .right_shift
			} else if c2 == `=` {
				s.offset++
				return .ge
			}
			return .gt
		}
		`#` {
			// if we choose to scan whole line
			// s.line()
			return .hash
		}
		// `@` { return .at }
		`~` {
			return .bit_not
		}
		`,` {
			return .comma
		}
		`$` {
			if s.in_str_inter {
				return .str_dollar
			}
			return .dollar
		}
		`{` {
			if s.in_str_inter {
				s.str_inter_cbr_depth++
			}
			return .lcbr
		}
		`}` {
			if s.in_str_inter {
				s.str_inter_cbr_depth--
				if s.str_inter_cbr_depth == 0 {
					s.in_str_incomplete = true
					s.in_str_inter = false
				}
			}
			s.insert_semi = true
			return .rcbr
		}
		`(` {
			return .lpar
		}
		`)` {
			s.insert_semi = true
			return .rpar
		}
		`[` {
			s.insert_semi = true
			return .lsbr
		}
		`]` {
			s.insert_semi = true
			return .rsbr
		}
		`;` {
			return .semicolon
		}
		`?` {
			s.insert_semi = true
			return .question
		}
		else {
			return .unknown
		}
	}
}

// skip whitespace
@[direct_array_access]
fn (mut s Scanner) whitespace() {
	for s.offset < s.src.len {
		c := s.src[s.offset]
		if c in [` `, `\t`, `\r`] {
			s.offset++
			continue
		} else if c == `\n` {
			if s.insert_semi {
				return
			}
			s.offset++
			s.file.add_line(s.offset)
			continue
		}
		break
	}
	// s.insert_semi = false
}

@[direct_array_access]
fn (mut s Scanner) line() {
	// a newline reached here will get recorded by next whitespace call
	// we could add them manually here, but whitespace is called anyway
	for s.offset < s.src.len {
		if s.src[s.offset] == `\n` {
			break
		}
		s.offset++
	}
}

@[direct_array_access]
fn (mut s Scanner) comment() {
	s.offset++
	c := s.src[s.offset]
	// single line
	if c == `/` {
		s.line()
	}
	// multi line
	else if c == `*` {
		s.offset++
		mut ml_comment_depth := 1
		for s.offset < s.src.len {
			c2 := s.src[s.offset]
			c3 := s.src[s.offset + 1]
			if c2 == `\n` {
				s.offset++
				s.file.add_line(s.offset)
			} else if c2 == `/` && c3 == `*` {
				s.offset += 2
				ml_comment_depth++
			} else if c2 == `*` && c3 == `/` {
				s.offset += 2
				ml_comment_depth--
				if ml_comment_depth == 0 {
					break
				}
			} else {
				s.offset++
			}
		}
	}
}

@[direct_array_access]
fn (mut s Scanner) string_literal(scan_as_raw bool, c_quote u8) {
	// shortcut, scan whole string
	if scan_as_raw {
		for s.offset < s.src.len && s.src[s.offset] != c_quote {
			s.offset++
		}
		s.offset++
		return
	}
	// normal strings
	for s.offset < s.src.len {
		c := s.src[s.offset]
		// escape `\\n` | `\'`
		if c == `\\` {
			s.offset += 2
			continue
		} else if c == `\n` {
			s.offset++
			s.file.add_line(s.offset)
			continue
		} else if c == `$` && s.src[s.offset + 1] == `{` {
			s.in_str_inter = true
			if s.skip_interpolation {
				s.str_inter_cbr_depth++
				s.offset += 2
				continue
			} else {
				return
			}
		} else if s.skip_interpolation && s.in_str_inter {
			if c == `{` {
				s.str_inter_cbr_depth++
			} else if c == `}` {
				s.str_inter_cbr_depth--
				if s.str_inter_cbr_depth == 0 {
					s.in_str_inter = false
				}
			}
		} else if c == c_quote && !s.in_str_inter {
			s.offset++
			break
		}
		s.offset++
	}
}

@[direct_array_access]
fn (mut s Scanner) number() {
	if s.src[s.offset] == `0` {
		s.offset++
		c := s.src[s.offset]
		// TODO: impl proper underscore support
		// 0b (binary)
		if c in [`b`, `B`] {
			s.offset++
			for {
				c2 := s.src[s.offset]
				if c2 in [`0`, `1`] || c2 == `_` {
					s.offset++
					continue
				}
				return
			}
		}
		// 0x (hex)
		else if c in [`x`, `X`] {
			s.offset++
			for {
				c2 := s.src[s.offset]
				if (c2 >= `0` && c2 <= `9`) || (c2 >= `a` && c2 <= `f`)
					|| (c2 >= `A` && c2 <= `F`) || c2 == `_` {
					s.offset++
					continue
				}
				return
			}
		}
		// 0o (octal)
		else if c in [`o`, `O`] {
			s.offset++
			for {
				c2 := s.src[s.offset]
				if c2 >= `0` && c2 <= `7` {
					s.offset++
					continue
				}
				return
			}
		}
	}
	mut has_decimal := false
	mut has_exponent := false
	// TODO: proper impl of fraction / exponent
	// continue decimal (and also completion of bin/octal)
	for s.offset < s.src.len {
		c := s.src[s.offset]
		if (c >= `0` && c <= `9`) || c == `_` {
			s.offset++
			continue
		}
		// fraction
		else if !has_decimal && c == `.` && s.src[s.offset + 1] != `.` {
			has_decimal = true
			s.offset++
			continue
		}
		// exponent
		else if !has_exponent && c in [`e`, `E`] {
			has_exponent = true
			s.offset++
			continue
		}
		break
	}
}