#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <ctype.h>
#include <assert.h>
#include <stdbool.h>

#include "os.h"
#include "s8slice.h"

typedef struct Parser {
	S8Slice file;
	int64_t cursor; 
} Parser;

typedef struct Token {
	enum {
		TOKEN_UNDEFINED,
		TOKEN_INT,
		TOKEN_IDENTIFIER,
		TOKEN_STRING,
		TOKEN_SYNTAX_ERROR,
		TOKEN_EOF,
	} kind;
	union {
		S8Slice identifier;
		S8Slice string;
		int     integer;
	};
} Token;

Parser parser_attach(S8Slice file)
{
	return (Parser){.file = file, .cursor = 0};
}

static int parser_peek(Parser* p)
{
	const int ch = p->cursor >= p->file.len
		? EOF
		: (int)p->file.data[p->cursor];
	return ch;
}

static int parser_getch(Parser* p)
{
	const int ch = p->cursor >= p->file.len
		? EOF
		: (int)p->file.data[p->cursor];
	p->cursor += 1;
	if (ch == '\n' && parser_peek(p) == '\r') {
		p->cursor += 1;
	}
	return ch;
}

static void parser_ungetch(Parser* p)
{
	if (p->cursor > 0) {
		p->cursor -= 1;
	}
}

static void parser_discard(Parser* p, int (*f) (int))
{
	int ch;
	while (ch = parser_getch(p), f(ch))
		/* noop */;
	if (ch != EOF)
		parser_ungetch(p);
}

static Token read_integer(Parser* p)
{
	/* FIXME: add support for 0x prefixes */

	/* the first char should be guaranteed to be isdigit */
	assert(isdigit(parser_peek(p)));

	int ch = EOF;
	int n = 0;
	while (ch = parser_getch(p), isdigit(ch)) {
		n *= 10;
		n += ch - '0';
	}
	parser_ungetch(p);

	Token t = {.kind = TOKEN_INT, .integer = n};

	return t;
}

static Token read_identifier(Parser* p)
{
	int ch = EOF;

	/* the first char should be guaranteed to be isalpha */
	assert(isalpha(parser_peek(p)));

	int64_t begin = p->cursor;
	while (ch = parser_getch(p), isalnum(ch))
		/* NOOP */;
	parser_ungetch(p);
	int64_t end = p->cursor;

	Token t = {
		.kind = TOKEN_IDENTIFIER,
		.identifier = s8slice(&p->file, begin, end)
	};

	return t;
}

static Token read_string(Parser* p)
{
	int ch = EOF;

	/* the first char should be guaranteed to be '"' */
	assert(parser_peek(p) == '"');

	(void)parser_getch(p); /* skip quote */
	int64_t begin = p->cursor;
	while (ch = parser_getch(p), ch != '"' && ch != '\n' && ch != EOF)
		/* NOOP */;
	if (ch != '"') {
		fprintf(stderr, "syntax error: expected \", found %c\n", ch);
		exit(EXIT_FAILURE);
	}
	int64_t end = p->cursor - 1; /* subtract one to ignore end quote */

	Token t = {
		.kind = TOKEN_STRING,
		.identifier = s8slice(&p->file, begin, end)
	};

	return t;
}

static Token read_token(Parser* p)
{
	int ch = parser_peek(p);

	Token t;

	if (ch == EOF) {
		t.kind = TOKEN_EOF;
	} else if (isalpha(ch)) {
		t = read_identifier(p);
	} else if (isdigit(ch)) {
		t = read_integer(p);
	} else if (ch == '"') {
		t = read_string(p);
	}

	return t;
}

int main(int argc, char** argv)
{
	if (argc != 2) {
		fprintf(stderr, "Usage: %s <file>\n", argv[0] ? argv[0] : "program");
		exit(EXIT_FAILURE);
	}

	S8Slice path = s8slice_from_cstr(argv[1]);
	const S8Slice f = os_open_file(path, OS_READ);

	if (f.len == -1) {
		fprintf(stderr, "could not open file %s: %s\n", path.data, strerror(errno));
		exit(EXIT_FAILURE);
	}

	Parser p = parser_attach(f);
	Token t = {0};
	while (true) {
		parser_discard(&p, isspace);
		Token t = read_token(&p);
		if (t.kind == TOKEN_IDENTIFIER) {
			S8Slice s = t.identifier;
			printf("{.len = %lld, .data = %.*s}\n", s.len, (int)s.len, s.data);
		} else if (t.kind == TOKEN_INT) {
			printf("%d\n", t.integer);
		} else if (t.kind == TOKEN_STRING) {
			S8Slice s = t.identifier;
			printf("{.len = %lld, .data = %.*s}\n", s.len, (int)s.len, s.data);
		} else if (t.kind == TOKEN_EOF) {
			break;
		}
	}

	return EXIT_SUCCESS;
}