#ifndef INCLUDE_lexerlexer
#define INCLUDE_lexerlexer

#include "token.h"
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
  const char *buf;
  int pos;
  int line;
  int col;
} _LX;

/* Error reporting with line/column info */
static void perror_at(_LX *lx, const char *msg) {
  fprintf(stderr, "[LEXER] Error at line %d, column %d: %s\n", lx->line, lx->col, msg);
  exit(1);
}

#define sic static inline char
#define sii static inline int
#define siv static inline void
#define sit static inline _T

sic lxpeek(_LX *lx) { return lx->buf[lx->pos]; }

sic lxget(_LX *lx) { return lx->buf[lx->pos++]; }

static inline char *lx_strdup_checked(_LX *lx, const char *s) {
  char *p = strdup(s);
  if (!p) {
    perror_at(lx, "out of memory");
  }
  return p;
}

siv lxskipws(_LX *lx) {
  while (lxpeek(lx) == ' ' || lxpeek(lx) == '\t') {
    if (lxpeek(lx) == '\t') lx->col += 8; else lx->col++;
    lxget(lx);
  }
}

sit lxnext(_LX *lx) {
  lxskipws(lx);
  char c = lxpeek(lx);
  if (c == 0)
    return (_T){TK_EOF, 0, NULL};
  
  // Track newlines
  if (c == '\n') {
    lx->line++;
    lx->col = 0;
    lxget(lx);
    return lxnext(lx); // recurse to get next token
  }

  if (isalpha(c) || c == '_') {
    int start = lx->pos;
    while (isalnum(lxpeek(lx)) || lxpeek(lx) == '_')
      lxget(lx);
    int len = lx->pos - start;
    char *text = strndup(lx->buf + start, len);
    if (!text) {
      perror_at(lx, "out of memory");
    }
    return (_T){checkkw(text), 0, text};
  }
  if (isdigit(c)) {
    int start = lx->pos;
    while (isdigit(lxpeek(lx)))
      lxget(lx);
    int len = lx->pos - start;
    char *text = strndup(lx->buf + start, len);
    if (!text) {
      perror_at(lx, "out of memory");
    }
    return (_T){TK_NUMBER, atoi(text), text};
  }

  lxget(lx);
  lx->col++;
  // handle multi-char tokens
  if (c == '=') {
    if (lxpeek(lx) == '=') { lxget(lx); lx->col++; return (_T){TK_EQ,0,lx_strdup_checked(lx,"==")}; }
    return (_T){TK_ASSIGN, 0, lx_strdup_checked(lx,"=")};
  }
  if (c == '!') {
    if (lxpeek(lx) == '=') { lxget(lx); lx->col++; return (_T){TK_NE,0,lx_strdup_checked(lx,"!=")}; }
    return (_T){TK_BANG,0,lx_strdup_checked(lx,"!")};
  }
  if (c == '<') {
    if (lxpeek(lx) == '=') { lxget(lx); lx->col++; return (_T){TK_LE,0,lx_strdup_checked(lx,"<=")}; }
    if (lxpeek(lx) == '<') { lxget(lx); lx->col++; return (_T){TK_SHL,0,lx_strdup_checked(lx,"<<")}; }
    return (_T){TK_LT,0,lx_strdup_checked(lx,"<")};
  }
  if (c == '>') {
    if (lxpeek(lx) == '=') { lxget(lx); lx->col++; return (_T){TK_GE,0,lx_strdup_checked(lx,">=")}; }
    if (lxpeek(lx) == '>') { lxget(lx); lx->col++; return (_T){TK_SHR,0,lx_strdup_checked(lx,">>")}; }
    return (_T){TK_GT,0,lx_strdup_checked(lx,">")};
  }
  if (c == '&') {
    if (lxpeek(lx) == '&') { lxget(lx); lx->col++; return (_T){TK_AND,0,lx_strdup_checked(lx,"&&")}; }
  }
  if (c == '|') {
    if (lxpeek(lx) == '|') { lxget(lx); lx->col++; return (_T){TK_OR,0,lx_strdup_checked(lx,"||")}; }
  }
  if (c == '"') {
    // String literal
    int start = lx->pos; // pos is already after the opening quote
    while (lxpeek(lx) != '"' && lxpeek(lx) != 0) {
      if (lxpeek(lx) == '\\') {
        lxget(lx); // consume backslash
        if (lxpeek(lx) != 0) lxget(lx); // consume escaped char
      } else {
        lxget(lx);
      }
    }
    if (lxpeek(lx) == '"') {
      int len = lx->pos - start; // length of content
      lxget(lx); // consume closing quote
      char *text = strndup(lx->buf + start, len); // start at content
      if (!text) {
        perror_at(lx, "out of memory");
      }
      return (_T){TK_STRING, 0, text};
    } else {
      perror_at(lx, "unterminated string literal");
    }
  }
  switch (c) {
  case '(':
    return (_T){TK_LPAREN, 0, lx_strdup_checked(lx,"(")};
  case ')':
    return (_T){TK_RPAREN, 0, lx_strdup_checked(lx,")")};
  case '{':
    return (_T){TK_LBRACE, 0, lx_strdup_checked(lx,"{")};
  case '}':
    return (_T){TK_RBRACE, 0, lx_strdup_checked(lx,"}")};
  case ';':
    return (_T){TK_SEMI, 0, lx_strdup_checked(lx,";")};
  case '+':
    return (_T){TK_PLUS, 0, lx_strdup_checked(lx,"+")};
  case '-':
    return (_T){TK_MINUS, 0, lx_strdup_checked(lx,"-")};
  case '*':
    return (_T){TK_STAR, 0, lx_strdup_checked(lx,"*")};
  case '/':
    return (_T){TK_SLASH, 0, lx_strdup_checked(lx,"/")};
  case '&':
    return (_T){TK_AMP, 0, lx_strdup_checked(lx,"&")};
  case '|':
    return (_T){TK_BAR, 0, lx_strdup_checked(lx,"|")};
  case '^':
    return (_T){TK_CARET, 0, lx_strdup_checked(lx,"^")};
  case '%':
    return (_T){TK_PERCENT, 0, lx_strdup_checked(lx,"%")};
  case ',':
    return (_T){TK_COMMA, 0, lx_strdup_checked(lx,",")};
  case '\'':
    return (_T){TK_SQUOTE, 0, lx_strdup_checked(lx,"'")};
  case '"':
    return (_T){TK_DQUOTE, 0, lx_strdup_checked(lx,"\"")};
  case '[':
    return (_T){TK_LBRACKET, 0, lx_strdup_checked(lx,"[")};
  case ']':
    return (_T){TK_RBRACKET, 0, lx_strdup_checked(lx,"]")};
  default:
    return (_T){TK_INVALID, 0, NULL};
  }
}

#undef sic
#undef sii
#undef siv
#undef sit

#endif