#include <thread>
#include <windows.h>
#include <wininet.h>
#include <libxml/HTMLparser.h>
#include <libxml/HTMLtree.h>
#include <libxml/xpath.h>

#include "resource.h"
#include "data.h"
#include "episodelistview.h"
#include "util.h"
#include "win.h"

static Unique<HINTERNET, InternetCloseHandle> s_hi =
	InternetOpenW(L"Episode Browser", INTERNET_OPEN_TYPE_DIRECT, nullptr, nullptr, 0);

/* ParsedDoc downloads and parses an HTML document. */
struct ParsedDoc
{
	Unique<HINTERNET, InternetCloseHandle> hiUrl;
	Unique<htmlParserCtxtPtr, xmlFreeParserCtxt> ctxt;
	char bufI[1024];
	char bufX[1024];

	ParsedDoc(const wchar_t* wszUrl, const char* szUrl)
	{
		if (!s_hi.Bad(0))
			throw Win32Error();

		hiUrl = InternetOpenUrlW(s_hi.v, wszUrl, nullptr, 0, INTERNET_FLAG_NO_UI, 0);
		if (!hiUrl.Bad(0))
			throw InternetError();

		ctxt = htmlCreatePushParserCtxt(nullptr, nullptr, bufX, sizeof(bufX), szUrl, XML_CHAR_ENCODING_UTF8);
		if (!ctxt.Bad(0))
			throw XmlError();

		htmlCtxtUseOptions(ctxt.v, HTML_PARSE_RECOVER|HTML_PARSE_NOERROR|HTML_PARSE_NOWARNING);

		BOOL r;
		DWORD cbRead;
		while (r = InternetReadFile(hiUrl.v, bufI, sizeof(bufI), &cbRead), cbRead) {
			if (!r)
				throw InternetError();
			if (!htmlParseChunk(ctxt.v, bufI, cbRead, 0))
				throw XmlError();
		}
		htmlParseChunk(ctxt.v, bufI, 0, 1); /* Stop parsing. */
	}

	operator htmlDocPtr() { return ctxt.v->myDoc; }
};

static inline void XmlFree(void* p) { xmlFree(p); }

template <size_t N>
bool WcharsFromXmlchars(wchar_t (&dst)[N], xmlChar* utf8_)
{
	Unique<xmlChar*, XmlFree> utf8 = utf8_;
	if (!utf8.Bad(0))
		throw XmlError();

	/* Truncate if source is larger than destination. */
	int lenUtf8 = xmlStrlen(utf8.v);
	utf8.v[Min(N, static_cast<size_t>(lenUtf8))] = 0;

	/* Convert internal representation from UTF-8 to Latin-1,
	 * which seems to actually convert the string to proper UTF-8
	 * (???). */
	unsigned char lat1[N];
	int lenLat1 = N-1;
	if (UTF8Toisolat1(lat1, &lenLat1, utf8.v, &lenUtf8) <= 0)
		return false;
	lat1[lenLat1] = 0;

	/* Write wide string to destination, if it fits. */
	char* const src = reinterpret_cast<char*>(lat1);
	const int cchNarrow = lenLat1+1;
	const int cchWide = MultiByteToWideChar(CP_UTF8, 0, src, cchNarrow, nullptr, 0);
	if (static_cast<size_t>(cchWide) > N)
		return false;
	return MultiByteToWideChar(CP_UTF8, 0, src, cchNarrow, dst, cchWide);
}

/* The Fetch* functions are run in a separate thread via WaitFor. The
 * main thread and the fetch thread communicate by setting flags on a
 * shared byte. At any given time, only a single fetch thread may be
 * performing work. */

enum Signal
{
	READY = 1<<0,	/* Main -> fetch: start working! */
	DONE = 1<<1,	/* Fetch -> main: work is done. */
	ABORT = 1<<2	/* Main -> fetch: exit prematurely! */
};

void WaitFor(void (*f)(unsigned char*))
{
	extern HWND g_hWnd;
	static unsigned char sig = READY;
	static UINT_PTR iTimer = 0;

	static auto procTimer = [](HWND, UINT, UINT_PTR, DWORD) -> void
	{
		static int i = 0;

		if (sig & DONE) {
			extern EpisodeListView* g_elv;
			KillTimer(nullptr, iTimer);
			i = 0;
			sig = READY; /* Reset signals. */
			g_elv->Update(); /* Reset status bar. */
			EnableMenuItem(GetMenu(g_hWnd), IDM_FILE_FETCH_CANCEL, MF_GRAYED);
		} else {
			/* Animate ellipsis in status bar. */
			static const wchar_t* text[] = {L".", L"..", L"...", L""};
			i = (i+1)%(sizeof(text)/sizeof(*text));
			Status(text[i], 1);
		}
	};

	static auto procThread = [](void (*f)(unsigned char*)) noexcept -> void
	{
		SET_TERMINATE;
		while (!(sig & READY))
			Sleep(100);
		sig = 0;
		EnableMenuItem(GetMenu(g_hWnd), IDM_FILE_FETCH_CANCEL, MF_ENABLED);
		try {
			f(&sig);
			sig |= DONE;
		} catch (...) {
			sig |= DONE;
			ShowException(L"Remote data could not be fetched due to an error: %s",
			    L"Error", MB_ICONWARNING);
		}
	};

	/* Null indicates that any active task should be cancelled. */
	if (!f) {
		sig |= ABORT;
		EnableMenuItem(GetMenu(g_hWnd), IDM_FILE_FETCH_CANCEL, MF_GRAYED);
		return;
	}

	/* Ensure that only a single thread is waited on. */
	if (!(sig & READY)) {
		if (EBMessageBox(L"Another task is active. "
		    L"Do you want to cancel the existing task and start a new one?",
		    L"Error", MB_YESNO|MB_ICONWARNING) == IDYES)
			sig |= ABORT;
		else
			return;
	}

	std::thread(procThread, f).detach();
	Status(L".", 1);
	Prefer(iTimer = SetTimer(nullptr, iTimer, 500, procTimer));
}

void FetchData(unsigned char* sig)
{
	/* The remote data is retrieved using WinINet from the
	 * Detective Conan World wiki. Using libxml2's "push parser",
	 * the HTML is parsed piece by piece as it is retrieved. The
	 * episode data are contained in table rows matching a (very!)
	 * specific XPath query. This is fragile theoretically, but
	 * unlikely to break practically. */

	ParsedDoc doc(L"https://www.detectiveconanworld.com/wiki/Anime",
	    "https://www.detectiveconanworld.com/wiki/Anime");

	Unique<xmlXPathContextPtr, xmlXPathFreeContext> xpathCtx = xmlXPathNewContext(doc);
	if (!xpathCtx.Bad(0))
		throw XmlError();

	Unique<xmlXPathObjectPtr, xmlXPathFreeObject> xpathObj = xmlXPathEvalExpression(
	    reinterpret_cast<const xmlChar*>("//tr[./td[1] != '' and ./td[3][@style='background:#f2fde9;']]"),
	    xpathCtx.v);
	if (!xpathObj.Bad(0))
		throw XmlError();

	xmlNodeSetPtr nodes = xpathObj.v->nodesetval;

	if (!nodes || !nodes->nodeNr)
		throw std::runtime_error("could not find remote episode information");

	for (int i = 0; i < nodes->nodeNr; i++) {
		extern FileView<ElvDataA> g_fvElv;
		extern FileView<DlvDataA> g_fvDlv;

		if (*sig & ABORT)
			return;

		const xmlNodePtr node = nodes->nodeTab[i];
		if (xmlChildElementCount(node) != 8)
			throw std::runtime_error("unexpected remote data format");

		ElvDataA& e = g_fvElv.At(i);
		DlvDataA& d = g_fvDlv.At(i);

		/* Each datum is contained within a specific cell in
		 * the row. The child element count above ensures that
		 * none of the following nodes are null. */
		const xmlNodePtr nodeEp = xmlFirstElementChild(node);
		const xmlNodePtr nodeTitle = xmlNextElementSibling(xmlNextElementSibling(nodeEp));
		const xmlNodePtr nodeDate = xmlNextElementSibling(nodeTitle);
		const xmlNodePtr nodeSource = xmlNextElementSibling(
		    xmlNextElementSibling(xmlNextElementSibling(nodeDate)));
		const xmlNodePtr nodeHint = xmlNextElementSibling(nodeSource);

		WcharsFromXmlchars(d.date, xmlNodeGetContent(nodeDate));
		WcharsFromXmlchars(d.source, xmlNodeGetContent(nodeSource));
		WcharsFromXmlchars(d.hint, xmlNodeGetContent(nodeHint));
		e.bTVOriginal = wcsncmp(d.source, L"TV", 2) == 0? 1: 0;
		WcharsFromXmlchars(e.siEp, xmlNodeGetContent(nodeEp));
		e.siEp[wcscspn(e.siEp, L"W")] = 0; /* Remove potential "WPS" suffix. */
		WcharsFromXmlchars(e.title, xmlNodeGetContent(nodeTitle));

		/* Retrieve the link to the episode's wiki entry,
		 * which should be the first (and only) child element
		 * of the title node. */
		const xmlNodePtr nodeLink = xmlFirstElementChild(nodeTitle);
		if (nodeLink)
			WcharsFromXmlchars(d.wiki,
			    xmlGetProp(nodeLink, reinterpret_cast<const xmlChar*>("href")));
	}
}

void FetchScreenwriters(unsigned char* sig)
{
	extern FileView<DlvDataA> g_fvDlv;
	extern CfgA& g_cfg;

	/* Screenwriters are expensive to fetch, so we try to avoid
	 * fetching screenwriters for episodes that already have a
	 * screenwriter. Additionally, in the same session, we don't
	 * try to fetch screenwriters for episodes for which we have
	 * already tried to fetch screenwriters. We keep track of
	 * these states using the iLast variable. */
	static int iLast = -1;
	int iMax = g_cfg.cEp-1;

	/* Find the last episode that has a screenwriter. */
	if (iLast == -1)
		for (size_t i = 0; i < g_fvDlv.c; i++)
			if (const DlvDataA& d = g_fvDlv[i]; !d.date[0]) {
				iMax = i-1;
				break;
			} else if (d.screenwriter[0])
				iLast = i;

	FINALLY { Status(L""); };

	/* Fetch screenwriters for the rest of the episodes. */
	const wchar_t prefix[] = L"https://www.detectiveconanworld.com";
	wchar_t url[256];
	Wcscpy(url, prefix);
	for (iLast++; iLast < iMax; iLast++) {
		if (*sig & ABORT)
			return;

		wchar_t msg[48];
		Swprintf(msg, L"Fetching screenwriter for episode %d...", iLast+1);
		Status(msg);

		/* Retrieve URL for episode's wiki page. */
		DlvDataA& d = g_fvDlv[iLast];
		Wcscpy(Buf(url)+Len(prefix), d.wiki);

		/* Retrieve screenwriter from HTML. */
		ParsedDoc doc(url, nullptr);
		Unique<xmlXPathContextPtr, xmlXPathFreeContext> xpathCtx = xmlXPathNewContext(doc);
		if (!xpathCtx.Bad(0))
			throw XmlError();

		Unique<xmlXPathObjectPtr, xmlXPathFreeObject> xpathObj =
			xmlXPathEvalExpression(reinterpret_cast<const xmlChar*>(
			    "//th[contains(text(), 'Screenplay:')]/following-sibling::td"),
			    xpathCtx.v);
		if (!xpathObj.Bad(0))
			throw XmlError();

		xmlNodeSetPtr nodes = xpathObj.v->nodesetval;
		if (nodes && nodes->nodeNr)
			WcharsFromXmlchars(d.screenwriter, xmlNodeGetContent(nodes->nodeTab[0]));
	}
}