#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "lexer.h"

static char peekChar(Lexer* l);
static void readChar(Lexer* l);
static char* readIdentifier(Lexer* l);
static char* readNumber(Lexer* l);
static int isLetter(char c);
static int isDigit(char c);

static Token* newTickToken(Lexer* l);
static Token* newToken(Lexer* l, TokenType tt);
static Token* newIdentToken(Lexer* l, char* literal, TokenType tt);
static Token* newWhitespaceToken(Lexer* l);

Lexer*
NewLexer(const char* filename)
{
    FILE* fp;
    fp = fopen(filename, "r");

    if (fp == NULL)
    {
        printf("Can't open the file for some reason\n");
        return NULL;
    }

    fseek(fp, 0, SEEK_END);
    int fileSize = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    printf("fileSize: %d\n", fileSize);

    Lexer* state = malloc(sizeof(Lexer));
    state->rawFile = malloc((sizeof(char) * fileSize) + 1);
    state->rawLen = fileSize;
    state->readPosition = 0;

    size_t read = fread(state->rawFile, sizeof(char), fileSize, fp);
    fclose(fp);

    if (read != fileSize)
    {
        printf("something borked.  only read %d bytes of %d\n", (int)read, fileSize);

        free(state->rawFile);
        free(state);

        return NULL;
    }

    state->rawFile[fileSize] = '\0';
    state->line = 1;
    state->column = 0;

    readChar(state);
    return state;
}

void
FreeLexer(Lexer* l)
{
    free(l->rawFile);
    free(l);
}

Token*
NextToken(Lexer* l)
{
    Token* tok;
    switch (l->ch) {
        case '#':
            tok = newToken(l, TT_HASH);
            break;
        case '*':
            tok = newToken(l, TT_ASTERISK);
            break;
        case '_':
            tok = newToken(l, TT_UNDERSCORE);
            break;
        case '-':
            tok = newToken(l, TT_DASH);
            break;
        case '.':
            tok = newToken(l, TT_PERIOD);
            break;
        case '>':
            tok = newToken(l, TT_GT);
            break;
        case '`':
            tok = newTickToken(l);
            break;
        case '\0':
            tok = newToken(l, TT_EOF);
            break;
        case '\n':
            tok = newToken(l, TT_NEWLINE);
            l->line++;
            l->column = 0;
            break;
        case ' ':
        case '\t':
            tok = newWhitespaceToken(l);
            break;
        case '\r':
            readChar(l);
            return NextToken(l); // lets GOOOOO
        default:
            if (isLetter(l->ch))
            {
                int start = l->column;
                char* literal = readIdentifier(l);
                tok = newIdentToken(l, literal, TT_WORD);
                tok->column = start;
                return tok;
            }
            else if (isDigit(l->ch))
            {
                int start = l->column;
                char* literal = readNumber(l);
                tok = newIdentToken(l, literal, TT_NUMBER);
                tok->column = start;
                return tok;
            }
            else
            {
                tok = newToken(l, TT_ILLEGAL);
            }
            //printf("Invalid token: %X\n", l->ch);
            //return NULL;
    }

    readChar(l);
    return tok;
}

static
Token*
newWhitespaceToken(Lexer* l)
{
    Token* tok = malloc(sizeof(Token));
    tok->line = l->line;
    tok->column = l->column;
    tok->type = TT_WHITESPACE;

    int position = l->position;
    // grab the char so we can use this funciton for both
    // spaces and tabs.
    char ch = l->ch;
    while (peekChar(l) == ch){
        readChar(l);
    }

    int count = l->position - position+1;
    tok->literal = malloc(sizeof(char)*count+1);
    for (int i = 0; i < count; i++) {
        tok->literal[i] = ch;
    }
    tok->literal[count] = '\0';
    tok->length = count;
    tok->next = NULL;
    return tok;
}

static
char*
readNumber(Lexer* l)
{
    int position = l->position;
    while (isDigit(l->ch))
    {
        readChar(l);
    }

    int len = (l->position - position);
    char* out = malloc(sizeof(char) * len + 1);
    memcpy(out, &l->rawFile[position], len);
    out[len] = '\0';
    return out;
}

static
char*
readIdentifier(Lexer* l)
{
    int position = l->position;
    while (isLetter(l->ch))
    {
        readChar(l);
    }

    int len = (l->position - position);
    char* out = malloc(sizeof(char) * len + 1);
    memcpy(out, &l->rawFile[position], len);
    out[len] = '\0';
    return out;
}

static
char
peekChar(Lexer* l)
{

    if (l->readPosition >= l->rawLen) {
        return '\0';
    }

    return l->rawFile[l->readPosition];
}

static
void
readChar(Lexer* l)
{
    l->column++;
    if (l->readPosition >= l->rawLen)
    {
        l->ch = 0;
    }
    else
    {
        l->ch = l->rawFile[l->readPosition];
    }

    l->position = l->readPosition;
    l->readPosition++;
}

int
isLetter(char ch)
{
    return (('a' <= ch && ch <= 'z') || ('A' <= ch && ch <= 'Z') || ch == '_');
}

int
isDigit(char ch)
{
    return ('0' <= ch && ch <= '9');
}

void
FreeToken(Token* t)
{
    free(t->literal);
    free(t);
}

static
Token*
newTickToken(Lexer* l)
{

    if (l->position+3 > l->rawLen) {
        printf("premature EOF parsing ticks\n");
        return newToken(l, TT_BACKTICK);
    }

    // peek up to two more characters
    int i;
    for(i = 0; i < 3; i++) {
        if (l->rawFile[l->position+i] != '`') {
            return newToken(l, TT_BACKTICK);
        }
    }

    Token* tok = malloc(sizeof(Token));
    tok->line = l->line;
    tok->column = l->column;
    tok->literal = "```";
    tok->type = TT_TRIPLEBACKTICK;
    tok->length = 3;
    tok->next = NULL;
    readChar(l);
    readChar(l);
    return tok;
}

static
Token*
newToken(Lexer* l,
         TokenType tt)
{
    Token* tok = malloc(sizeof(Token));
    char* nc = malloc(sizeof(char)+1);
    *nc = l->ch;
    nc[1] = '\0';
    tok->type = tt;
    tok->literal = nc;
    tok->line = l->line;
    tok->column = l->column;
    tok->length = 1;
    tok->next = NULL;
    return tok;
}

static
Token*
newIdentToken(Lexer* l,
              char* literal,
              TokenType tt)
{
    Token* tok = malloc(sizeof(Token));
    tok->type = tt;
    tok->literal = literal;
    tok->line = l->line;
    tok->column = l->column;
    tok->length = strlen(literal);
    tok->next = NULL;
    return tok;
}