#include <time.h>

#include <glib.h>
#include <glib/gstdio.h>
#include <gio/gio.h>
#include <libxml/tree.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>

#include "currency.h"
#include "mp.h"

typedef struct {
	char* short_name;
	MPNumber value;
} currency;

static currency* currencies = NULL;
static int currency_count = 0;

static gboolean downloading_rates = FALSE;
static gboolean loaded_rates = FALSE;

static char* get_rate_filepath()
{
	return g_build_filename(g_get_user_cache_dir(), "mate-calc", "eurofxref-daily.xml", NULL);
}

static int currency_get_index(const char *short_name)
{
	int i;

	for (i = 0; i < currency_count; i++)
	{
		if (!strcmp(short_name, currencies[i].short_name))
		{
			if (mp_is_negative(&currencies[i].value) || mp_is_zero(&currencies[i].value))
			{
				return -1;
			}
			else
			{
				return i;
			}
		}
	}

	return -1;
}

/* A file needs to be redownloaded if it doesn't exist, or every 7 days.
 * When an error occur, it probably won't hurt to try to download again.
 */
static int currency_rates_needs_update()
{
	gchar* filename = get_rate_filepath();
	struct stat buf;

	if (!g_file_test(filename, G_FILE_TEST_IS_REGULAR))
	{
		g_free(filename);
		return 1;
	}

	if (g_stat(filename, &buf) == -1)
	{
		g_free(filename);
		return 1;
	}

	g_free(filename);

	if (difftime(time(NULL), buf.st_mtime) > (60 * 60 * 24 * 7))
	{
		return 1;
	}

	return 0;
}


static void download_cb(GObject* object, GAsyncResult* result, gpointer user_data)
{
	GError* error = NULL;

	if (g_file_copy_finish(G_FILE(object), result, &error))
	{
		g_debug("Rates updated");
	}
	else
	{
		g_warning("Couldn't download currency file: %s", error->message);
	}

	g_clear_error(&error);
	downloading_rates = FALSE;
}


static void currency_download_rates()
{
	gchar* filename;
	gchar* directory;
	GFile* source;
	GFile* dest;

	downloading_rates = TRUE;
	g_debug("Downloading rates...");

	filename = get_rate_filepath();
	directory = g_path_get_dirname(filename);
	g_mkdir_with_parents(directory, 0755);
	g_free(directory);

	/* HACK: It is safe? */
	source = g_file_new_for_uri("http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");
	dest = g_file_new_for_path(filename);
	g_free(filename);

	g_file_copy_async(source, dest, G_FILE_COPY_OVERWRITE, G_PRIORITY_DEFAULT, NULL, NULL, NULL, download_cb, NULL);
	g_object_unref(source);
	g_object_unref(dest);
}


static void set_rate(xmlNodePtr node, currency* cur)
{
	xmlAttrPtr attribute;

	for (attribute = node->properties; attribute; attribute = attribute->next)
	{
		if (strcmp((char*) attribute->name, "currency") == 0)
		{
			cur->short_name = (char*) xmlNodeGetContent((xmlNodePtr) attribute);
		}
		else if (strcmp ((char*) attribute->name, "rate") == 0)
		{
			char* val = (char*) xmlNodeGetContent((xmlNodePtr) attribute);
			mp_set_from_string(val, 10, &(cur->value));
			xmlFree(val);
		}
	}
}

static void currency_load_rates()
{
	char* filename = get_rate_filepath();
	xmlDocPtr document;
	xmlXPathContextPtr xpath_ctx;
	xmlXPathObjectPtr xpath_obj;
	int i;
	int len;

	g_return_if_fail(g_file_test(filename, G_FILE_TEST_IS_REGULAR));

	xmlInitParser();
	document = xmlReadFile(filename, NULL, 0);
	g_free (filename);

	if (document == NULL)
	{
		fprintf(stderr, "Couldn't parse data file\n");
		return;
	}

	xpath_ctx = xmlXPathNewContext(document);

	if (xpath_ctx == NULL)
	{
		xmlFreeDoc(document);
		fprintf(stderr, "Couldn't create XPath context\n");
		return;
	}

	xmlXPathRegisterNs(xpath_ctx, BAD_CAST("xref"), BAD_CAST("http://www.ecb.int/vocabulary/2002-08-01/eurofxref"));
	xpath_obj = xmlXPathEvalExpression(BAD_CAST("//xref:Cube[@currency][@rate]"), xpath_ctx);

	if (xpath_obj == NULL)
	{
		xmlXPathFreeContext(xpath_ctx);
		xmlFreeDoc(document);
		fprintf(stderr, "Couldn't create XPath object\n");
		return;
	}

	len = (xpath_obj->nodesetval) ? xpath_obj->nodesetval->nodeNr : 0;
	currency_count = len + 1;
	currencies = g_slice_alloc0(sizeof(currency) * currency_count);

	for (i = 0; i < len; i++)
	{
		if (xpath_obj->nodesetval->nodeTab[i]->type == XML_ELEMENT_NODE)
		{
			set_rate(xpath_obj->nodesetval->nodeTab[i], &currencies[i]);
		}

		// Avoid accessing removed elements
		if (xpath_obj->nodesetval->nodeTab[i]->type != XML_NAMESPACE_DECL)
		{
			xpath_obj->nodesetval->nodeTab[i] = NULL;
		}
	}

	currencies[len].short_name = g_strdup("EUR");
	MPNumber foo;
	mp_set_from_integer(1, &foo);
	currencies[len].value = foo;

	xmlXPathFreeObject(xpath_obj);
	xmlXPathFreeContext(xpath_ctx);
	xmlFreeDoc(document);
	xmlCleanupParser();

	g_debug("Rates loaded");
	loaded_rates = TRUE;
}


gboolean currency_convert(const MPNumber* from_amount, const char* source_currency, const char* target_currency, MPNumber* to_amount)
{
	int from_index, to_index;

	if (downloading_rates)
	{
		return FALSE;
	}

	/* Update currency if necessary */
	if (currency_rates_needs_update())
	{
		currency_download_rates();
		return FALSE;
	}

	if (!loaded_rates)
	{
		currency_load_rates();
	}

	from_index = currency_get_index(source_currency);
	to_index = currency_get_index(target_currency);

	if (from_index < 0 || to_index < 0)
	{
		return FALSE;
	}

	if (mp_is_zero(&currencies[from_index].value) || mp_is_zero(&currencies[to_index].value))
	{
		mp_set_from_integer(0, to_amount);
		return FALSE;
	}

	mp_divide(from_amount, &currencies[from_index].value, to_amount);
	mp_multiply(to_amount, &currencies[to_index].value, to_amount);

	return TRUE;
}

void currency_free_resources()
{
	int i;

	for (i = 0; i < currency_count; i++)
	{
		if (currencies[i].short_name != NULL)
		{
			xmlFree(currencies[i].short_name);
		}
	}

	g_slice_free1(currency_count * sizeof(currency), currencies);

	currencies = NULL;
	currency_count = 0;
}