// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

package hbrt

import (
	"encoding/binary"
	"math"
)

// hashKey returns a canonical string key for use in HbHash.Index.
// Two Values that compare equal via valueEqual MUST produce the same
// string and the ok flag must be true. Pointer-identity key types
// (array, object, hash, block, pointer) return ok=false so the caller
// falls back to a linear scan using valueEqual.
//
// Numeric normalization: doubles that represent an exact int64 fold
// into the same slot as the corresponding integer, so h[1] and h[1.0]
// address the same bucket (matches valueEqual's cross-type numeric
// compare). -0.0 is normalized to +0.0 for the same reason.
//
// The single-byte type prefix prevents cross-type collisions
// (e.g., the string "N" must not collide with a Nil key).
func hashKey(v Value) (string, bool) {
	switch {
	case v.IsNil():
		return "N", true
	case v.IsString():
		return "S" + v.AsString(), true
	case v.IsNumeric():
		var buf [9]byte
		if v.IsNumInt() {
			buf[0] = 'I'
			binary.LittleEndian.PutUint64(buf[1:], uint64(v.AsNumInt()))
			return string(buf[:]), true
		}
		d := v.AsDouble()
		if d == 0 {
			d = 0 // collapse -0.0 into +0.0
		}
		if !math.IsNaN(d) && !math.IsInf(d, 0) {
			if f, fr := math.Modf(d); fr == 0 && f >= -9.2233720368547758e18 && f <= 9.2233720368547758e18 {
				buf[0] = 'I'
				binary.LittleEndian.PutUint64(buf[1:], uint64(int64(f)))
				return string(buf[:]), true
			}
		}
		buf[0] = 'F'
		binary.LittleEndian.PutUint64(buf[1:], math.Float64bits(d))
		return string(buf[:]), true
	case v.IsLogical():
		if v.AsBool() {
			return "L1", true
		}
		return "L0", true
	case v.IsDate():
		var buf [9]byte
		buf[0] = 'D'
		binary.LittleEndian.PutUint64(buf[1:], uint64(v.AsJulian()))
		return string(buf[:]), true
	case v.IsTimestamp():
		var buf [13]byte
		buf[0] = 'T'
		binary.LittleEndian.PutUint64(buf[1:9], uint64(v.AsJulian()))
		binary.LittleEndian.PutUint32(buf[9:], uint32(v.AsTimeMs()))
		return string(buf[:]), true
	}
	return "", false
}

// ensureIndex builds or rebuilds HbHash.Index if it looks stale
// (nil, or its size differs from the count of currently indexable
// keys in Keys). Callers should invoke it before any Index read when
// the hash may have been mutated via direct slice access.
func (h *HbHash) ensureIndex() {
	// Fast path: Index exists and mirrors every indexable key.
	if h.Index != nil {
		want := 0
		for _, k := range h.Keys {
			if _, ok := hashKey(k); ok {
				want++
			}
		}
		if want == len(h.Index) {
			return
		}
	}
	h.Index = make(map[string]int, len(h.Keys))
	for i, k := range h.Keys {
		if kk, ok := hashKey(k); ok {
			h.Index[kk] = i
		}
	}
}

// Lookup returns the slot index of key in Keys/Values, or -1 if absent.
// Runs in O(1) for indexable key types; falls back to O(N) linear scan
// (matching valuesEqual) for non-indexable types.
func (h *HbHash) Lookup(key Value) int {
	if kk, ok := hashKey(key); ok {
		h.ensureIndex()
		if i, found := h.Index[kk]; found {
			return i
		}
		return -1
	}
	for i, k := range h.Keys {
		if valueEqual(k, key) {
			return i
		}
	}
	return -1
}

// Has reports whether key exists in the hash.
func (h *HbHash) Has(key Value) bool {
	return h.Lookup(key) >= 0
}

// HashGet returns the value bound to key, or NIL if absent.
// (Named HashGet to avoid clashing with method-tables named Get.)
func (h *HbHash) HashGet(key Value) Value {
	if i := h.Lookup(key); i >= 0 {
		return h.Values[i]
	}
	return MakeNil()
}

// Set binds key → val, overwriting if key exists. Returns true if the
// key was newly added (false if it updated an existing slot).
func (h *HbHash) Set(key, val Value) bool {
	if i := h.Lookup(key); i >= 0 {
		h.Values[i] = val
		return false
	}
	h.appendPair(key, val)
	return true
}

// Append adds key → val without checking for existence. Caller must
// guarantee the key is not already present (e.g., bulk loaders).
func (h *HbHash) Append(key, val Value) {
	h.appendPair(key, val)
}

func (h *HbHash) appendPair(key, val Value) {
	i := len(h.Keys)
	h.Keys = append(h.Keys, key)
	h.Values = append(h.Values, val)
	if kk, ok := hashKey(key); ok {
		if h.Index == nil {
			h.Index = make(map[string]int, 8)
		}
		h.Index[kk] = i
	}
}

// Delete removes key. Returns true if the key was present.
// The remaining keys keep their insertion order (Harbour KEEPORDER
// semantic). Index is rebuilt because every slot after the removed
// one shifts down by one.
func (h *HbHash) Delete(key Value) bool {
	i := h.Lookup(key)
	if i < 0 {
		return false
	}
	h.Keys = append(h.Keys[:i], h.Keys[i+1:]...)
	h.Values = append(h.Values[:i], h.Values[i+1:]...)
	h.Index = nil
	return true
}

// HashFromPairs builds an HbHash from alternating key/value Values
// (as produced by HB_HASH literal / hb_Hash()). Uses Append for each
// pair after stripping duplicates to match HB_HASH semantics where
// repeated keys keep the last-assigned value.
func HashFromPairs(pairs []Value) *HbHash {
	h := &HbHash{}
	for i := 0; i+1 < len(pairs); i += 2 {
		h.Set(pairs[i], pairs[i+1])
	}
	return h
}