// The Construct
//
// Copyright (C) The Construct Developers, Authors & Contributors
// Copyright (C) 2016-2020 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_ACQUIRE_H

namespace ircd::m
{
	struct acquire;
}

struct ircd::m::acquire
:instance_list<ircd::m::acquire>
{
	struct opts;
	struct result;

	static log::log log;
	static conf::item<size_t> fetch_max;
	static conf::item<size_t> submit_max;
	static conf::item<size_t> attempt_max;
	static uint64_t ids;

	const uint64_t id {++ids};
	const struct opts &opts;
	vm::opts head_vmopts;
	vm::opts history_vmopts;
	vm::opts state_vmopts;
	std::list<result> fetching;
	uint32_t fetches {0};
	uint32_t evals {0};
	uint32_t acquires {0};

  private:
	bool full() const noexcept;
	string_view loghead() const;

	bool handle(result &);
	bool handle();

	bool started(const event::id &) const;
	bool start(const event::id &, const string_view &, const bool &, const size_t &, const vm::opts *const &);
	bool submit(const event::id &, const string_view &, const bool &, const size_t &, const vm::opts *const &);

	bool fetch_head(const m::event &, const int64_t &);
	void acquire_head();

	bool fetch_history(event::idx &);
	void acquire_history();

	bool fetch_timeline(event::idx &);
	void acquire_timeline();

	bool fetch_state(const m::event::id &, const string_view &);
	void acquire_state();

  public:
	acquire(const struct opts &);
	acquire(const acquire &) = delete;
	acquire &operator=(const acquire &) = delete;
	~acquire() noexcept;
};

template<>
decltype(ircd::m::acquire::list)
ircd::instance_list<ircd::m::acquire>::list;

struct ircd::m::acquire::opts
{
	/// Room apropos; note that the event_id in this structure may have some
	/// effect on the result after deducing other options instead of defaults.
	m::room room;

	/// Optional remote host first considered as the target for operations in
	/// case caller has better information for what will most likely succeed.
	string_view hint;

	/// For diagnostic and special use; forces remote operations through the
	/// hint, and fails them if the hint is insufficient.
	bool hint_only {false};

	/// Perform head acquisition. Setting to false will disable the ability
	/// to reconnoiter the latest events from remote servers. Note that setting
	/// a depth ceiling effectively makes this false.
	bool head {true};

	/// Perform history acquisition. Setting this to false disables depthwise
	/// operations which fill in timeline gaps below the head.
	bool history {true};

	/// Perform timeline acquisition. Setting this to false disables
	/// breadthwise operations which fill in timeline gaps below the head.
	bool timeline {true};

	/// Perform state acquisition. Setting this to false may result in an
	/// acquisition that is missing state events and subject to inconsistency
	/// from the ABA problem etc.
	bool state {true};

	/// Provide a viewport size; generally obtained from the eponymous conf
	/// item and used for initial backfill
	size_t viewport_size {0};

	/// Depthwise window of acquisition; concentrate on specific depth window
	pair<int64_t> depth {0, 0};

	/// Won't fetch missing of ref outside this range.
	pair<event::idx> ref {0, -1UL};

	/// Avoids filling gaps with a depth sounding outside of the range
	pair<size_t> gap {0, -1UL};

	/// The number of rounds the algorithm runs for.
	size_t rounds {-1UL};

	/// Total event limit over all operations.
	size_t fetch_max {acquire::fetch_max};

	/// Limit the number of requests in flight at any given time.
	size_t submit_max {acquire::submit_max};

	/// Fetch attempt cap passed to m::fetch, because the default there is
	/// unlimited and that's usually a waste of time in practice.
	size_t attempt_max {acquire::attempt_max};

	/// Limit on the depth of leafs pursued by the timeline acquisition.
	size_t leaf_depth {0};

	/// Default vm::opts to be used during eval; some options are
	/// unconditionally overriden to perform some evals. Use caution, setting
	/// options may cause results not expected from this interface.
	vm::opts vmopts;
};

struct ircd::m::acquire::result
{
	event::id::buf event_id;
	const m::vm::opts *vmopts {nullptr};
	ctx::future<fetch::result> future;

	result(const vm::opts *, const event::id &, ctx::future<fetch::result> &&);
	result() = default;
};