package sim

import (
	"crypto/sha256"
	"encoding/binary"
	"sort"
)

// Hash returns a digest of the complete simulation state. Two runs from the
// same seed and inputs must produce identical hashes.
func (s *State) Hash() [32]byte {
	h := sha256.New()
	w := func(vs ...int64) {
		var b [8]byte
		for _, v := range vs {
			binary.LittleEndian.PutUint64(b[:], uint64(v))
			h.Write(b[:])
		}
	}
	w(s.Day, int64(len(s.Asteroids)))
	for i := range s.Asteroids {
		a := &s.Asteroids[i]
		w(a.ID)
		for _, o := range a.Ore {
			w(o)
		}
	}
	w(int64(len(s.Ships)))
	for _, sh := range s.Ships {
		alive := int64(0)
		if sh.Alive {
			alive = 1
		}
		w(sh.ID, sh.Owner, alive, int64(sh.Pos.X), int64(sh.Pos.Y), int64(sh.Pos.Z),
			int64(sh.Vel.X), int64(sh.Vel.Y), int64(sh.Vel.Z),
			int64(sh.Fuel), sh.Earned, int64(sh.Throttle), int64(sh.Azimuth), int64(sh.Pitch), sh.Target)
		for _, c := range sh.Cargo {
			w(c)
		}
		h.Write(sh.CPU.MarshalState())
	}
	owners := make([]int64, 0, len(s.Credits))
	for o := range s.Credits {
		owners = append(owners, o)
	}
	sort.Slice(owners, func(i, j int) bool { return owners[i] < owners[j] })
	for _, o := range owners {
		w(o, s.Credits[o])
	}
	for _, v := range s.Market.Supply {
		w(v)
	}
	var out [32]byte
	copy(out[:], h.Sum(nil))
	return out
}