# lex.ludic — source text -> a token slice. Tokens carry their kind, their
# text (identifiers, strings, operators), an integer value (numbers, char
# literals) and a line for diagnostics.

const TK_ID:  int = 0
const TK_INT: int = 1
const TK_STR: int = 2
const TK_OP:  int = 3
const TK_NL:  int = 4
const TK_EOF: int = 5
const TK_FLOAT: int = 6
const TK_INTERP: int = 7      # `text {expr} text` — raw content, split by the parser

property Tok { kind: int = 0, text: pointer = null, ival: int = 0, line: int = 0 }

var toks: []Tok

function tok_push(kind: int, text: pointer, ival: int, line: int) -> void {
  let t = new Tok
  t.kind = kind;  t.text = text;  t.ival = ival;  t.line = line
  push(toks, t)
}

# does src match the 2-char operator op at position i?
function two_at(src: pointer, i: int, a: int, b: int) -> bool {
  return src[i] == a and src[i + 1] == b
}

function is_op1(c: int) -> bool {
  # + - * / % < > = ( ) { } [ ] , : . ! @
  if c == '+' or c == '-' or c == '*' or c == '/' or c == '%' { return true }
  if c == '<' or c == '>' or c == '=' { return true }
  if c == '(' or c == ')' or c == '{' or c == '}' { return true }
  if c == '[' or c == ']' or c == ',' or c == ':' or c == '.' { return true }
  if c == '!' or c == '@' { return true }
  if c == '&' or c == '|' or c == '^' or c == '~' { return true }   # & | ^ ~
  return false
}

# The two bytes that delimit escapes, spelled numerically on purpose: this file
# is what teaches the compiler to read `'\''` and `'\\'`, and the seed that
# bootstraps it must lex it without already knowing those spellings.
const CH_SQUOTE: int = 39      # '
const CH_BACKSLASH: int = 92   # \

# the byte an escape sequence `\e` stands for, shared by "strings" and 'chars':
# \n \r \t \0 are the named ones; anything else (\\ \' \" \`) is itself.
function unescape(e: int) -> int {
  if e == 'n' { return 10 }
  if e == 'r' { return 13 }
  if e == 't' { return 9 }
  if e == '0' { return 0 }
  return e
}

# a character the language has no use for is an error, never silently dropped:
# `x = 5 $ 3` must not compile as `x = 5 3`.
function lex_error(line: int, c: int) -> void {
  let ch = bytes(2);  ch[0] = c;  ch[1] = 0
  lex_fail(line, `unexpected character '{ch}' (byte {c})`)
}

# the closing backtick of the template literal that opens at s[i]: a hole's `{...}` is code, so a
# string, a char or another template inside it is skipped whole - `a {f(`b {c}`)} d` is one literal
function tmpl_end(s: pointer, i0: int, n: int) -> int {
  var i = i0 + 1
  while i < n and s[i] != '`' {
    if s[i] == CH_BACKSLASH { i += 2;  continue }
    if s[i] == '{' and i + 1 < n and s[i + 1] == '{' { i += 2;  continue }
    if s[i] == '{' {
      i = hole_end(s, i + 1, n)
    }
    i += 1
  }
  return i
}
# the `}` that closes a hole whose code starts at s[i]; n when there is none
function hole_end(s: pointer, i0: int, n: int) -> int {
  var i = i0
  var depth = 1
  while i < n {
    let d = s[i]
    if d == '"' or d == CH_SQUOTE {
      i += 1
      while i < n and s[i] != d { if s[i] == CH_BACKSLASH { i += 1 };  i += 1 }
    }
    else if d == '`' { i = tmpl_end(s, i, n) }
    else if d == '{' { depth += 1 }
    else if d == '}' {
      depth -= 1
      if depth == 0 { return i }
    }
    i += 1
  }
  return n
}

# report a lexical error in the standard `file:line: error: msg` shape and stop
function lex_fail(line: int, msg: pointer) -> void {
  let m = `{g_parse_file}:{line}: error: {msg}\n`
  file_write(file_stderr(), m, len(m))
  exit(1)
}

function lex(src: pointer) -> void { lex_at(src, 1) }

# lex `src` with its first line numbered `first_line` (an interpolation hole is
# re-lexed on its own, and keeps the line of the string it sits in)
function lex_at(src: pointer, first_line: int) -> void {
  toks = new []Tok
  var i = 0
  var line = first_line
  let n = len(src)
  while i < n {
    let c = src[i]
    if c == '\n' { tok_push(TK_NL, null, 0, line); line += 1; i += 1; continue }
    if c == ' ' or c == '\t' or c == '\r' { i += 1; continue }
    if c == '#' {                                   # '#' comment to end of line
      while i < n and src[i] != '\n' { i += 1 }
      continue
    }
    if c == '"' {                                   # "string"
      i += 1
      let start = i
      let out = bytes(n)
      var j = 0
      while i < n and src[i] != '"' {
        if src[i] == CH_BACKSLASH {              # backslash escape
          out[j] = unescape(src[i + 1]);  j += 1;  i += 2
        } else { out[j] = src[i]; j += 1; i += 1 }
      }
      i += 1
      out[j] = 0
      tok_push(TK_STR, out, 0, line)
      continue
    }
    if c == '`' {                                   # `interpolated string` — captured raw
      let e = tmpl_end(src, i, n)
      let out = bytes(n)
      var j = 0
      i += 1
      while i < e {
        out[j] = src[i]
        j += 1
        i += 1
      }
      i = e + 1
      out[j] = 0
      tok_push(TK_INTERP, out, 0, line)
      continue
    }
    if c == CH_SQUOTE {                              # 'c' char literal -> int
      i += 1
      var v = 0
      if src[i] == CH_BACKSLASH { v = unescape(src[i + 1]);  i += 2 }
      else { v = src[i];  i += 1 }
      if src[i] != CH_SQUOTE { lex_fail(line, "unterminated character literal (expected closing ')") }
      i += 1
      tok_push(TK_INT, null, v, line)
      continue
    }
    if char_is_digit(c) {
      if c == '0' and src[i + 1] == 'x' {     # 0x hex
        var v = 0
        var lv: long = 0
        var digits = 0
        i += 2
        while i < n {
          let h = src[i]
          var d = 0
          if char_is_digit(h) { d = h - 48 }
          else { if h >= 'a' and h <= 'f' { d = h - 87 }
                 else { if h >= 'A' and h <= 'F' { d = h - 55 } else { break } } }
          v = v * 16 + d
          lv = lv * long(16) + long(d)
          if digits > 0 or d > 0 { digits += 1 }
          i += 1
        }
        # up to 8 hex digits is a 32-bit pattern (0xFFFFFFFF is -1, as it always was); more is a long
        var big: pointer = null
        if digits > 8 { big = string(lv) }
        tok_push(TK_INT, big, v, line)
        continue
      }
      var v = 0
      var lv: long = 0
      let nstart = i
      while i < n and char_is_digit(src[i]) {
        v = v * 10 + (src[i] - 48)
        lv = lv * long(10) + long(src[i] - 48)
        i += 1
      }
      # a fractional part makes it a Q16.16 fixed literal (its text is kept: in a
      # float context the literal is exactly that decimal instead)
      if i < n and src[i] == '.' and char_is_digit(src[i + 1]) {
        i += 1
        # Accumulate only the first 4 fractional digits: `fnum << 16` must stay
        # in i32 (5+ digits overflow), and Q16.16 resolves ~4-5 decimals anyway.
        # Extra digits are still consumed so they don't become a stray token.
        var fnum = 0;  var fden = 1
        while i < n and char_is_digit(src[i]) {
          if fden < 10000 { fnum = fnum * 10 + (src[i] - 48);  fden *= 10 }
          i += 1
        }
        let bits = (v << 16) + ((fnum << 16) + (fden >> 1)) / fden
        tok_push(TK_FLOAT, src[nstart..i], bits, line)
        continue
      }
      # a decimal past 2^31 - 1 does not fit an int: it is a long, and keeps its value as text
      var big: pointer = null
      if lv > long(2147483647) { big = string(lv) }
      tok_push(TK_INT, big, v, line)
      continue
    }
    if char_is_alpha(c) {
      let start = i
      while i < n and char_is_alnum(src[i]) { i += 1 }
      tok_push(TK_ID, src[start..i], 0, line)
      continue
    }
    if c == ';' { tok_push(TK_NL, null, 0, line); i += 1; continue }   # ';'
    # two-character operators
    if two_at(src, i, 45, 62) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # ->
    if two_at(src, i, 61, 62) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # =>
    if two_at(src, i, 61, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # ==
    if two_at(src, i, 33, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # !=
    if two_at(src, i, 60, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # <=
    if two_at(src, i, 62, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # >=
    if two_at(src, i, 43, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # +=
    if two_at(src, i, 45, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # -=
    if two_at(src, i, 42, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # *=
    if two_at(src, i, 47, 61) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # /=
    if two_at(src, i, 46, 46) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # ..
    if two_at(src, i, 60, 60) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # <<
    if two_at(src, i, 62, 62) { tok_push(TK_OP, src[i..i + 2], 0, line); i += 2; continue }  # >>
    if is_op1(c) { tok_push(TK_OP, src[i..i + 1], 0, line); i += 1; continue }
    lex_error(line, c)
  }
  tok_push(TK_EOF, null, 0, line)
}