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

// Five pcode interpreter — executes pcode bytecode on a Thread.
// Each opcode directly calls the corresponding Thread method,
// so pcode execution is semantically identical to gengo-compiled code.

package hbrt

import (
	"encoding/binary"
	"fmt"
	"math"
)

// ExecPcode runs a pcode function on the given thread.
func ExecPcode(t *Thread, fn *PcodeFunc, mod *PcodeModule) {
	code := fn.Code
	pc := 0 // program counter

	t.Frame(fn.Params, fn.Locals)
	defer t.EndProc()

	for pc < len(code) {
		op := code[pc]
		pc++

		switch op {
		case PcOpNop:
			// do nothing

		// --- Stack ---
		case PcOpPushNil:
			t.PushNil()
		case PcOpPushTrue:
			t.PushBool(true)
		case PcOpPushFalse:
			t.PushBool(false)
		case PcOpPushInt:
			v := int64(binary.LittleEndian.Uint64(code[pc:]))
			pc += 8
			t.PushLong(v)
		case PcOpPushDouble:
			bits := binary.LittleEndian.Uint64(code[pc:])
			pc += 8
			t.PushDouble(math.Float64frombits(bits), 0, 0)
		case PcOpPushString:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.PushString(string(code[pc : pc+slen]))
			pc += slen
		case PcOpPushBool:
			t.PushBool(code[pc] != 0)
			pc++
		case PcOpPushLocal:
			idx := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.PushLocal(idx)
		case PcOpPopLocal:
			idx := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.PopLocal(idx)
		case PcOpPop:
			t.Pop()
		case PcOpDup:
			t.Dup()

		// --- Arithmetic ---
		case PcOpPlus:
			t.Plus()
		case PcOpMinus:
			t.Minus()
		case PcOpMult:
			t.Mult()
		case PcOpDivide:
			t.Divide()
		case PcOpMod:
			t.Modulus()
		case PcOpPower:
			t.Power()
		case PcOpNegate:
			t.Negate()

		// --- Comparison ---
		case PcOpEqual:
			t.Equal()
		case PcOpNotEqual:
			t.NotEqual()
		case PcOpLess:
			t.Less()
		case PcOpGreater:
			t.Greater()
		case PcOpLessEq:
			t.LessEqual()
		case PcOpGreaterEq:
			t.GreaterEqual()
		case PcOpInString:
			t.InString()

		// --- Logical ---
		case PcOpAnd:
			t.And()
		case PcOpOr:
			t.Or()
		case PcOpNot:
			t.Not()

		// --- Flow control ---
		case PcOpJump:
			offset := int32(binary.LittleEndian.Uint32(code[pc:]))
			pc += 4
			pc += int(offset)
		case PcOpJumpFalse:
			offset := int32(binary.LittleEndian.Uint32(code[pc:]))
			pc += 4
			if !t.PopLogical() {
				pc += int(offset)
			}
		case PcOpJumpTrue:
			offset := int32(binary.LittleEndian.Uint32(code[pc:]))
			pc += 4
			if t.PopLogical() {
				pc += int(offset)
			}
		case PcOpReturn:
			return
		case PcOpRetValue:
			t.RetValue()
			return

		// --- Frame ---
		case PcOpFrame:
			// Already called at function entry; skip if re-encountered
			pc += 4 // params + locals
		case PcOpEndProc:
			return

		// --- Function calls ---
		case PcOpPushSymbol:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			name := string(code[pc : pc+slen])
			pc += slen
			sym := t.VM().FindSymbol(name)
			t.PushSymbol(sym)
		case PcOpPushNilArg:
			t.PushNil()
		case PcOpFunction:
			nArgs := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.Function(nArgs)
		case PcOpDo:
			nArgs := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.Do(nArgs)

		// --- Self / OOP ---
		case PcOpPushSelf:
			t.PushSelf()
		case PcOpPushSelfField:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			name := string(code[pc : pc+slen])
			pc += slen
			t.PushSelfField(name)
		case PcOpSetSelfField:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			name := string(code[pc : pc+slen])
			pc += slen
			t.SetSelfField(name)
		case PcOpSend:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			name := string(code[pc : pc+slen])
			pc += slen
			nArgs := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.Send(name, nArgs)

		// --- Array ---
		case PcOpArrayGen:
			count := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.ArrayGen(count)
		case PcOpArrayPush:
			t.ArrayPush()
		case PcOpArrayPop:
			t.ArrayPop()

		// --- Block ---
		case PcOpPushBlock:
			codeLen := int(binary.LittleEndian.Uint32(code[pc:]))
			pc += 4
			blockCode := make([]byte, codeLen)
			copy(blockCode, code[pc:pc+codeLen])
			pc += codeLen
			nDetached := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2

			// Create a Go function that interprets the block's pcode
			blockFn := &PcodeFunc{Code: blockCode}
			modCopy := mod
			t.PushBlock(func(t2 *Thread) {
				ExecPcode(t2, blockFn, modCopy)
			}, nDetached)

		// --- Local ops ---
		case PcOpLocalAddInt:
			idx := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			val := int32(binary.LittleEndian.Uint32(code[pc:]))
			pc += 4
			t.LocalAddInt(idx, int64(val))
		case PcOpInc:
			t.Inc()
		case PcOpDec:
			t.Dec()

		case PcOpPopLogical:
			t.PopLogical()

		case PcOpLine:
			pc += 2 // skip line number (for debugging)

		case PcOpHalt:
			return

		default:
			panic(fmt.Sprintf("unknown pcode opcode: 0x%02X at pc=%d", op, pc-1))
		}
	}
}