package sim

import (
	"halcyon/config"
	"halcyon/fixed"
	"halcyon/world"
)

// Ore travels in containers. A ship has no hold of its own: it tows containers
// behind it, and every kilogram of them (the container and the ore in it) adds
// to the mass its engine has to push. Containers belong to no one: any ship can
// tow any container that is adrift near it.
const (
	ContainerMassKg        = 500  // an empty container
	ContainerCapKg         = 2000 // ore one container holds
	ContainerRangeKm       = 10   // "near the ship": how close a container must be to be attached
	MaxOrder               = 10   // empty containers the station delivers per request
	MaxContainersPerPlayer = 50   // the station will not deliver past this many of a player's ordered containers
	ContainerLifeDays      = 10   // a container adrift this long vanishes, so lost ones cannot pile up
)

// Container is a free-floating body. It has no owner.
type Container struct {
	ID int64
	// OrderedBy is the player who had the station deliver it. It is bookkeeping for
	// the ordering allowance only (MaxContainersPerPlayer): it gives no right to the
	// container, which anyone may tow, and a sale ends it.
	OrderedBy int64
	Pos       fixed.Vec
	Vel       fixed.Vec
	Ore       [world.NumOre]int64 // kg of each ore inside
	Towed     int64               // the ship towing it, or 0 while it drifts on its own
	// Dropped is the ship that last let it go: when the container is sold, that ship
	// and its player are paid.
	Dropped int64
	// ExpiresAt is when a container that stays adrift vanishes (seconds since the
	// world began); 0 while it is in tow.
	ExpiresAt int64
}

func (c *Container) OreTotal() int64 {
	var t int64
	for _, v := range c.Ore {
		t += v
	}
	return t
}

// Mass is the container plus the ore in it, in kg.
func (c *Container) Mass() int64 { return ContainerMassKg + c.OreTotal() }

// Room is how much more ore fits, in kg.
func (c *Container) Room() int64 { return ContainerCapKg - c.OreTotal() }

// Tow summarises the containers a ship is towing.
type Tow struct {
	Count    int
	Ore      [world.NumOre]int64
	OreTotal int64
	Room     int64
	Mass     int64
}

func (s *State) towOf(shipID int64) Tow {
	var t Tow
	for _, c := range s.Containers {
		if c.Towed != shipID {
			continue
		}
		t.Count++
		for o, kg := range c.Ore {
			t.Ore[o] += kg
		}
		t.OreTotal += c.OreTotal()
		t.Room += c.Room()
		t.Mass += c.Mass()
	}
	return t
}

// shipMass is everything the engine pushes: hull, fuel and towed containers.
func (s *State) shipMass(sh *Ship) fixed.F {
	return sh.baseMass() + fixed.FromInt(s.towOf(sh.ID).Mass)
}

func (s *State) newContainer(orderedBy int64, pos, vel fixed.Vec) *Container {
	s.NextContainer++
	c := &Container{ID: s.NextContainer, OrderedBy: orderedBy, Pos: pos, Vel: vel}
	s.Containers = append(s.Containers, c) // IDs only grow, so the slice stays sorted
	return c
}

// canAttach reports whether container c is adrift and near enough to take in tow.
func (s *State) canAttach(sh *Ship, c *Container) bool {
	return c.Towed == 0 && s.canReach(sh, c.Pos, c.Vel, ContainerRangeKm)
}

// nearbyFree counts the drifting containers the ship could attach now.
func (s *State) nearbyFree(sh *Ship) int {
	n := 0
	for _, c := range s.Containers {
		if s.canAttach(sh, c) {
			n++
		}
	}
	return n
}

// attach takes every drifting container near the ship in tow.
func (s *State) attach(sh *Ship, tc *tickCtx) {
	n := 0
	for _, c := range s.Containers {
		if s.canAttach(sh, c) {
			c.Towed, c.Pos, c.Vel, c.ExpiresAt = sh.ID, sh.Pos, sh.Vel, 0
			n++
		}
	}
	if n > 0 {
		tc.res.Events = append(tc.res.Events, Event{tc.tick, sh.ID, "attach", itoa(int64(n)) + " containers"})
	}
}

// detach lets go of everything the ship is towing. The containers keep drifting
// with the ship's velocity.
func (s *State) detach(sh *Ship, tc *tickCtx) {
	n := 0
	for _, c := range s.Containers {
		if c.Towed == sh.ID {
			s.letGo(c, sh.ID, tc.now)
			n++
		}
	}
	if n > 0 {
		tc.res.Events = append(tc.res.Events, Event{tc.tick, sh.ID, "detach", itoa(int64(n)) + " containers"})
	}
}

// order has the station deliver up to n empty containers to the ship's position,
// provided the ship is close to the station. It returns how many were delivered.
func (s *State) order(sh *Ship, n int, tc *tickCtx) int {
	if n > MaxOrder {
		n = MaxOrder
	}
	if n <= 0 || sh.Pos.Sub(tc.stPos).Len() > fixed.FromInt(DockRangeKm) {
		return 0
	}
	owned := 0
	for _, c := range s.Containers {
		if c.OrderedBy == sh.Owner {
			owned++
		}
	}
	n = min(n, MaxContainersPerPlayer-owned)
	for i := 0; i < n; i++ {
		c := s.newContainer(sh.Owner, sh.Pos, sh.Vel)
		c.ExpiresAt = tc.now + ContainerLifeDays*config.SecondsPerDay // delivered adrift
	}
	if n > 0 {
		tc.res.Events = append(tc.res.Events, Event{tc.tick, sh.ID, "delivery", itoa(int64(n)) + " containers"})
	}
	return n
}

// fillTow pours mined ore into the ship's containers, first come first filled.
// The caller has checked that it all fits.
func (s *State) fillTow(shipID int64, taken [world.NumOre]int64) {
	for o, kg := range taken {
		for _, c := range s.Containers {
			if kg == 0 {
				break
			}
			if c.Towed != shipID {
				continue
			}
			put := min(kg, c.Room())
			c.Ore[o] += put
			kg -= put
		}
	}
}

// syncTow keeps a ship's containers where the ship is.
func (s *State) syncTow(sh *Ship) {
	for _, c := range s.Containers {
		if c.Towed == sh.ID {
			c.Pos, c.Vel = sh.Pos, sh.Vel
		}
	}
}

// releaseTow sets a lost ship's containers adrift.
func (s *State) releaseTow(sh *Ship, now int64) {
	for _, c := range s.Containers {
		if c.Towed == sh.ID {
			s.letGo(c, sh.ID, now)
		}
	}
}

// letGo sets a towed container adrift and starts its ten days.
func (s *State) letGo(c *Container, ship, now int64) {
	c.Towed, c.Dropped = 0, ship
	c.ExpiresAt = now + ContainerLifeDays*config.SecondsPerDay
}

// expireContainers removes containers that have been adrift for their ten days,
// with whatever ore they hold. A container adrift with no timer at all (from a
// snapshot made before there was one) is given a full ten days from now.
func (s *State) expireContainers(tc *tickCtx) {
	kept := s.Containers[:0]
	for _, c := range s.Containers {
		if c.Towed == 0 {
			if c.ExpiresAt == 0 {
				c.ExpiresAt = tc.now + ContainerLifeDays*config.SecondsPerDay
			} else if tc.now >= c.ExpiresAt {
				tc.res.Events = append(tc.res.Events, Event{tc.tick, c.Dropped, "expired", "container " + itoa(c.ID) + " adrift for " + itoa(ContainerLifeDays) + " days"})
				continue
			}
		}
		kept = append(kept, c)
	}
	s.Containers = kept
}

// sellNearStation buys every drifting container that has ore in it and is close
// to the station, at the tick's positions. The station takes the container along
// with the ore, so a sold container is gone. The ship that last let it go, and its
// player, are paid. Empty containers are not bought.
func (s *State) sellNearStation(tc *tickCtx) {
	kept := s.Containers[:0]
	for _, c := range s.Containers {
		payee := s.ship(c.Dropped)
		if c.Towed != 0 || c.OreTotal() == 0 || payee == nil || c.Pos.Sub(tc.stPos).Len() > fixed.FromInt(DockRangeKm) {
			kept = append(kept, c)
			continue
		}
		value := s.Market.Value(c.Ore)
		s.Credits[payee.Owner] += value
		payee.Earned += value
		for o, kg := range c.Ore {
			tc.sold[o] += kg
		}
		tc.res.Events = append(tc.res.Events, Event{tc.tick, payee.ID, "sold", itoa(value) + " credits (container " + itoa(c.ID) + " taken)"})
	}
	s.Containers = kept
}

// driftContainers moves the containers nobody is towing. The star pulls them
// exactly as it pulls ships; one that falls in is lost with its ore.
func (s *State) driftContainers(orbitSpeed fixed.F, dt int64, tick int, res *DayResult) {
	dtF := fixed.FromInt(dt)
	kept := s.Containers[:0]
	for _, c := range s.Containers {
		if c.Towed == 0 {
			r := c.Pos.Len()
			if r < fixed.FromInt(StarRadiusKm) {
				res.Events = append(res.Events, Event{tick, c.Dropped, "lost", "container " + itoa(c.ID) + " fell into the star"})
				continue
			}
			g := orbitSpeed.Mul(orbitSpeed).Mul(dtF).Div(r)
			c.Vel = c.Vel.Sub(c.Pos.Unit().Scale(g))
			c.Pos = c.Pos.Add(c.Vel.Scale(dtF))
		}
		kept = append(kept, c)
	}
	s.Containers = kept
}

// migrateLegacyCargo turns ore that a ship still carries in the cargo hold of
// the earlier design into towed containers, so nothing is lost across the change.
func (s *State) migrateLegacyCargo() {
	for _, sh := range s.Ships {
		var left int64
		for _, kg := range sh.Cargo {
			left += kg
		}
		for left > 0 {
			c := s.newContainer(0, sh.Pos, sh.Vel) // not counted against anyone's ordering allowance
			c.Towed = sh.ID
			for o := range sh.Cargo {
				put := min(sh.Cargo[o], c.Room())
				c.Ore[o] += put
				sh.Cargo[o] -= put
				left -= put
			}
		}
		sh.Cargo = [world.NumOre]int64{}
	}
}