package hexagram

import (
	"git.mleku.dev/mleku/dendrite/pkg/permutation"
	"git.mleku.dev/mleku/dendrite/pkg/state"
)

// variantTables holds 6 lookup tables, one per S_3 permutation.
// variantTables[Identity] is identical to the canonical table.
//
// To look up a rule for hexagram h under permutation p: the hexagram
// bits encode state in p's frame, so we apply p^-1 to map back to the
// canonical frame, then look up the canonical rule.
var variantTables [permutation.Count][64]Rule

func init() {
	for _, p := range permutation.All() {
		inv := p.Inverse()
		for h := range uint8(64) {
			canonical := inv.ApplyHexagram(state.Hexagram(h))
			variantTables[p][h] = table[uint8(canonical)]
		}
	}
}

// LookupVariant returns the rule for hexagram h under permutation p.
// When p is Identity, this is equivalent to Lookup(h).
func LookupVariant(h state.Hexagram, p permutation.Perm) Rule {
	return variantTables[p][uint8(h)]
}

// keyToPerm maps a 3-bit projection key (0-7) to an S_3 permutation.
// Keys 6 and 7 are collapse points that alias to existing permutations.
var keyToPerm = [8]permutation.Perm{
	permutation.Identity, // 000: face XY
	permutation.Swap12,   // 001: face XZ
	permutation.Swap02,   // 010: face YZ
	permutation.Swap01,   // 011: edge bias
	permutation.Cycle012, // 100: vertex A
	permutation.Cycle021, // 101: vertex B
	permutation.Identity, // 110: collapse → Identity
	permutation.Swap12,   // 111: collapse → Swap12
}

// LookupProjected returns the rule for hexagram h given a 3-bit projection
// key. The key determines the S_3 permutation applied to the hexagram
// before rule lookup. Collapse keys (6, 7) reduce to their parent
// permutations, which is the geometric meaning of projection collapse:
// the rule table simplifies.
func LookupProjected(h state.Hexagram, projKey uint8) Rule {
	p := keyToPerm[projKey&0b111]
	return variantTables[p][uint8(h)]
}

// LookupFull returns the rule for a hexagram given the full 6-bit
// projection encoding (vertex in low 3 bits, key in high 3 bits).
// The vertex contributes to the hexagram's inner trigram (it IS the
// inner trigram). The key determines the projection permutation.
func LookupFull(h state.Hexagram, proj6bit uint8) Rule {
	key := (proj6bit >> 3) & 0b111
	return LookupProjected(h, key)
}