// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_M_VM_H

/// Matrix Virtual Machine
///
namespace ircd::m::vm
{
	struct error; // custom exception
	struct init;
	struct opts;
	struct copts;
	struct eval;
	enum fault :uint;
	enum phase :uint;
	using fault_t = std::underlying_type<fault>::type;

	extern const opts default_opts;
	extern const copts default_copts;
	extern log::log log;
	extern ctx::dock dock;
	extern bool ready;

	string_view reflect(const fault &);
	string_view reflect(const phase &);
	http::code http_code(const fault &);
	string_view loghead(const mutable_buffer &, const eval &);
	string_view loghead(const eval &);    // single tls buffer

	fault execute(eval &, const event &);
	size_t execute(eval &, const vector_view<const event> &);
	fault inject(eval &, json::iov &, const json::iov &);
}

namespace ircd::m::vm::sequence
{
	extern ctx::dock dock;
	extern uint64_t retired;      // already written; always monotonic
	extern uint64_t committed;    // pending write; usually monotonic
	extern uint64_t uncommitted;  // evaluating; not monotonic
	static size_t pending;

	const uint64_t &get(const eval &);
	uint64_t get(id::event::buf &); // [GET]
	uint64_t max();
	uint64_t min();
};

struct ircd::m::vm::init
{
	init(), ~init() noexcept;
};

/// Event Evaluation Device
///
/// This object conducts the evaluation of an event or a tape of multiple
/// events. An event is evaluated in an attempt to execute it. Events which
/// fail during evaluation won't be executed; such is the case for events which
/// have already been executed, or events which are invalid or lead to invalid
/// transitions or actions of the machine etc.
///
struct ircd::m::vm::eval
:instance_list<eval>
{
	static uint64_t id_ctr;
	static uint executing;
	static uint injecting;

	const vm::opts *opts {&default_opts};
	const vm::copts *copts {nullptr};
	ctx::ctx *ctx {ctx::current};
	vm::eval *parent {nullptr};
	vm::eval *child {nullptr};
	uint64_t id {++id_ctr};
	uint64_t sequence {0};
	std::shared_ptr<db::txn> txn;
	unique_mutable_buffer buf;

	vector_view<const m::event> pdus;
	const json::iov *issue {nullptr};
	const event *event_ {nullptr};
	string_view room_id;
	event::id::buf event_id;
	event::conforms report;
	string_view room_version;
	hook::base *hook {nullptr};
	vm::phase phase {vm::phase(0)};
	bool room_internal {false};

	void mfetch_keys() const;

  public:
	operator const event::id::buf &() const
	{
		return event_id;
	}

	eval(const vm::opts &);
	eval(const vm::copts &);
	eval(const event &, const vm::opts & = default_opts);
	eval(const vector_view<m::event> &, const vm::opts & = default_opts);
	eval(const json::array &event, const vm::opts & = default_opts);
	eval(json::iov &event, const json::iov &content, const vm::copts & = default_copts);
	eval() = default;
	eval(eval &&) = delete;
	eval(const eval &) = delete;
	eval &operator=(eval &&) = delete;
	eval &operator=(const eval &) = delete;
	~eval() noexcept;

	static bool for_each(const ctx::ctx *const &, const std::function<bool (eval &)> &);
	static eval *find_parent(const eval &, const ctx::ctx & = ctx::cur());
	static eval *find_root(const eval &, const ctx::ctx & = ctx::cur());
	static size_t count(const ctx::ctx *const &);

	static bool for_each(const std::function<bool (eval &)> &);
	static bool for_each_pdu(const std::function<bool (const event &)> &);
	static const event *find_pdu(const eval &, const event::id &);
	static const event *find_pdu(const event::id &);
	static size_t count(const event::id &);
	static eval *find(const event::id &);
	static eval &get(const event::id &);

	static bool sequnique(const uint64_t &seq);
	static eval *seqnext(const uint64_t &seq);
	static eval *seqmax();
	static eval *seqmin();
	static void seqsort();
};

/// Evaluation faults. These are reasons which evaluation has halted but may
/// continue after the user defaults the fault. They are basically types of
/// interrupts and traps, which are supposed to be recoverable. Only the
/// GENERAL protection fault (#gp) is an abort and is not supposed to be
/// recoverable. The fault codes have the form of bitflags so they can be
/// used in masks; outside of that case only one fault is dealt with at
/// a time so they can be switched as they appear in the enum.
///
enum ircd::m::vm::fault
:uint
{
	ACCEPT        = 0x00,  ///< No fault.
	EXISTS        = 0x01,  ///< Replaying existing event. (#ex)
	GENERAL       = 0x02,  ///< General protection fault. (#gp)
	INVALID       = 0x04,  ///< Non-conforming event format. (#ud)
	AUTH          = 0x08,  ///< Auth rules violation. (#av)
	STATE         = 0x10,  ///< Required state is missing (#st)
	EVENT         = 0x20,  ///< Eval requires addl events in the ef register (#ef)
};

/// Evaluation phases
enum ircd::m::vm::phase
:uint
{
	NONE,                  ///< No phase; not entered.
	DUPCHK,                ///< Duplicate check & hold.
	EXECUTE,               ///< Execution entered.
	ISSUE,                 ///< Issue phase.
	CONFORM,               ///< Conformity check phase.
	ACCESS,                ///< Access control phase.
	VERIFY,                ///< Signature verification.
	FETCH_AUTH,            ///< Authentication events fetch phase.
	AUTH_STATIC,           ///< Static authentication phase.
	FETCH_PREV,            ///< Previous events fetch phase.
	FETCH_STATE,           ///< State events fetch phase.
	PRECOMMIT,             ///< Precommit sequence.
	AUTH_RELA,             ///< Relative authentication phase.
	COMMIT,                ///< Commit sequence.
	AUTH_PRES,             ///< Authentication phase.
	EVALUATE,              ///< Evaluation phase.
	INDEX,                 ///< Indexing & transaction building phase.
	POST,                  ///< Transaction-included effects phase.
	WRITE,                 ///< Write transaction.
	RETIRE,                ///< Retire phase
	NOTIFY,                ///< Notifications phase.
	EFFECTS,               ///< Effects phase.
	_NUM_
};

/// Evaluation Options
struct ircd::m::vm::opts
{
	/// The remote server name which is conducting this eval.
	string_view node_id;

	/// The mxid of the user which is conducting this eval.
	string_view user_id;

	/// The txnid from the node conducting the eval.
	string_view txn_id;

	/// Enabled phases of evaluation.
	std::bitset<num_of<vm::phase>()> phase {-1UL};

	/// Custom write_opts to use during write.
	dbs::write_opts wopts;

	/// Broadcast to local clients (/sync stream).
	bool notify_clients {true};

	/// Broadcast to federation servers (/federation/send/).
	bool notify_servers {true};

	/// False to allow a dirty conforms report (not recommended).
	bool conforming {true};

	/// False to bypass all auth phases.
	bool auth {true};

	/// False to bypass all fetch phases.
	bool fetch {true};

	/// Mask of conformity failures to allow without considering dirty.
	event::conforms non_conform;

	/// If the event was already checked before the eval, set this to true
	/// and include the report (see below).
	bool conformed {false};

	/// When conformed=true, this report will be included instead of generating
	/// one during the eval. This is useful if a conformity check was already
	/// done before eval.
	event::conforms report;

	/// True hints that the event is known to be redacted. False hints that
	/// the event is not redacted. -1 is automatic, which may make a query.
	int8_t redacted {-1};

	/// When true, the event is expected to have its content; hash mismatch
	/// is not permitted. When false, hash mismatch is permitted when the
	/// event is known to be redacted (see above).
	bool require_content {false};

	/// Supply the room version; overrides/avoids any internal query.
	string_view room_version;

	/// Toggles whether event may be considered a "present event" and may
	/// update the optimized present state table of the room if it is proper.
	bool present {true};

	/// Evaluate in EDU mode. Input must not have event_id and none will be
	/// generated for it.
	bool edu {false};

	/// Bypass check for event having already been evaluated so it can be
	/// replayed through the system (not recommended).
	bool replays {false};

	/// Bypass check for another evaluation of the same event_id already
	/// occurring. If this is false (not recommended) two duplicate events
	/// being evaluated may race through the core.
	bool unique {true};

	/// When true, events in array inputs are evaluated as they are provided
	/// without any reordering before eval.
	bool ordered {false};

	/// If the input event has a reference to already-strung json we can use
	/// that directly when writing to the DB. When this is false we will
	/// re-stringify the event internally either from a referenced source or
	/// the tuple if no source is referenced. This should only be set to true
	/// if the evaluator already performed this and the json source is good.
	bool json_source {false};

	/// Whether to gather all unknown keys from an input vector of events and
	/// perform a parallel/mass fetch before proceeding with the evals.
	bool mfetch_keys {true};

	/// Throws fault::EVENT if *all* of the prev_events do not exist locally.
	/// This is used to enforce that at least one path is traversable. This
	/// test is conducted after waiting if fetch_prev and fetch_prev_wait.
	bool fetch_prev_any {false};

	/// Throws fault::EVENT if *any* of the prev_events do not exist locally.
	/// This is used to enforce that all references have been acquired; other
	/// corollary conditions are similar to fetch_prev_any.
	bool fetch_prev_all {false};

	/// The number of iterations of the wait cycle which checks for missing
	/// prev_events will iterate before issuing remote fetches for them.
	/// The default is 0 which bypasses the functionality, and is recommended
	/// when the evaluator is confident missing prev_events won't arrive
	/// elsehow. Setting to -1 enables it with an auto/conf value.
	size_t fetch_prev_wait_count {0};

	/// Base time to wait for missing prev_events to arrive at the server by
	/// some other means before issuing remote fetches for them. The waiting
	/// occurs in a loop where prev_events satisfaction is checked at each
	/// iteration. This value is multiplied by the number of iterations for
	/// multiplicative backoff. The default of -1 is auto / conf.
	milliseconds fetch_prev_wait_time {-1};

	/// The limit on the number of events to backfill if any of the prev_events
	/// are missing. -1 is auto / conf.
	size_t fetch_prev_limit = -1;

	/// Considers any missing prev_event as an indication of possible missing
	/// state from a history we don't have; allowing a state acquisition. This
	/// is not practical to apply by default as internal decisions are better.
	bool fetch_state_any {false};

	/// This option affects the behavior for a case where we are missing the
	/// (depth - 1) prev_events reference, thus other resolved references
	/// are not adjacent. Yet at the claimed depth there is no apparent gap
	/// in the timeline. If true, we assume possible missing state in this
	/// case, but by default that is far too unrealistic in practice.
	bool fetch_state_shallow {false};

	/// Evaluators can set this value to optimize the creation of the database
	/// transaction where the event will be stored. This value should be set
	/// to the amount of space the event consumes; the JSON-serialized size is
	/// a good value here. Default of -1 will automatically use serialized().
	size_t reserve_bytes = -1;

	/// This value is added to reserve_bytes to account for indexing overhead
	/// in the database transaction allocation. Most evaluators have little
	/// reason to ever adjust this.
	size_t reserve_index {1024};

	/// Coarse limit for array evals. The counter is incremented for every
	/// event; both accepted and faulted.
	size_t limit = -1;

	/// Mask of faults that are not thrown as exceptions out of eval(). If
	/// masked, the fault is returned from eval(). By default, the EXISTS
	/// fault is masked which means existing events won't kill eval loops.
	fault_t nothrows
	{
		EXISTS
	};

	/// Mask of faults that are logged to the error facility in vm::log.
	fault_t errorlog
	{
		~(EXISTS)
	};

	/// Mask of faults that are logged to the warning facility in vm::log
	fault_t warnlog
	{
		EXISTS
	};

	/// Whether to log a debug message on successful eval.
	bool debuglog_accept {false};

	/// Whether to log an info message on successful eval.
	bool infolog_accept {false};

	opts() noexcept;
};

/// Extension structure to vm::opts which includes additional options for
/// commissioning events originating from this server which are then passed
/// through eval (this process is also known as issuing).
struct ircd::m::vm::copts
:opts
{
	/// A matrix-spec opaque token from a client identifying this eval.
	string_view client_txnid;

	/// This bitmask covers all of the top-level properties of m::event
	/// which will be generated internally during injection unless they
	/// already exist. Clearing any of these bits will prevent the internal
	/// generation of these properties (i.e. for EDU's).
	event::keys::selection prop_mask
	{
		event::keys::include
		{
			"auth_events",
			"depth",
			"event_id",
			"hashes",
			"origin",
			"origin_server_ts",
			"prev_events",
			"prev_state",
			"signatures",
		}
	};

	/// Call the issue hook or bypass
	bool issue {true};

	/// Whether to log a debug message before commit
	bool debuglog_precommit {false};

	/// Whether to log an info message after commit accepted
	bool infolog_postcommit {false};

	copts() noexcept;
};

struct ircd::m::vm::error
:m::error
{
	vm::fault code;

	template<class... args> error(const http::code &, const fault &, const string_view &fmt, args&&... a);
	template<class... args> error(const fault &, const string_view &fmt, args&&... a);
	template<class... args> error(const string_view &fmt, args&&... a);
};

template<class... args>
ircd::m::vm::error::error(const string_view &fmt,
                          args&&... a)
:error
{
	http::INTERNAL_SERVER_ERROR, fault::GENERAL, fmt, std::forward<args>(a)...
}
{}

template<class... args>
ircd::m::vm::error::error(const fault &code,
                          const string_view &fmt,
                          args&&... a)
:error
{
	http_code(code), code, fmt, std::forward<args>(a)...
}
{}

template<class... args>
ircd::m::vm::error::error(const http::code &httpcode,
                          const fault &code,
                          const string_view &fmt,
                          args&&... a)
:m::error
{
	child, httpcode, reflect(code), fmt, std::forward<args>(a)...
}
,code
{
	code
}
{}