// 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.
// Full variant — installs a defer/recover so panics from inside the
// pcode body (HbError, BreakValue, user Break) are re-panicked with
// proper frame unwinding. Used for general-purpose pcode evaluation.
func ExecPcode(t *Thread, fn *PcodeFunc, mod *PcodeModule) {
	t.Frame(fn.Params, fn.Locals)
	defer t.EndProc()
	execPcodeBody(t, fn, mod)
}

// ExecPcodeFast is a hot-path variant for short, pure expressions
// (FiveSql2 WHERE predicates, inline lambdas) where the caller has
// already guaranteed that the body will not panic with HbError /
// BreakValue. Skips the defer+recover dance in EndProc, saving ~15ns
// per call × tens of thousands of rows in scan loops.
//
// Contract: caller is responsible for panic discipline. If the pcode
// body panics, the frame stack is still cleaned up (EndProcFast) but
// no diagnostic is logged and SEQUENCE/RECOVER will not see the panic.
func ExecPcodeFast(t *Thread, fn *PcodeFunc, mod *PcodeModule) {
	t.Frame(fn.Params, fn.Locals)
	execPcodeBody(t, fn, mod)
	t.EndProcFast()
}

// execPcodeBody is the shared opcode dispatch loop.
func execPcodeBody(t *Thread, fn *PcodeFunc, mod *PcodeModule) {
	code := fn.Code
	pc := 0 // program counter

	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 PcOpPushMemvar:
			slen := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			name := string(code[pc : pc+slen])
			pc += slen
			// Resolve through Memvars (PRIVATE shadows PUBLIC).
			// Unknown names push NIL — matches Harbour behavior for
			// undeclared memvars inside `&(expr)`.
			if t.Memvars != nil {
				if v, ok := t.Memvars.Get(name); ok {
					t.push(v)
					continue
				}
			}
			t.PushNil()
		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

		// --- Workarea field access (peephole for FieldGet(literal)) ---
		case PcOpFieldGet:
			fIdx := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			// Hot path — SqlScan plugs a direct field getter closure into
			// t.FastFieldGetter before running the predicate, so we skip
			// PushSymbol + Function dispatch + FieldGet RTL's own Frame.
			if fg := t.FastFieldGetter; fg != nil {
				t.PushValue(fg(fIdx))
			} else {
				// Generic fallback: resolve through RTL symbol table
				t.PushSymbol(t.VM().FindSymbol("FIELDGET"))
				t.PushNil()
				t.PushLong(int64(fIdx))
				t.Function(1)
			}

		// --- AllTrim(FieldGet(n)) fused peephole ---
		case PcOpFieldTrim:
			fIdx := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			// Fast path: use direct field getter, trim inline.
			var v Value
			if fg := t.FastFieldGetter; fg != nil {
				v = fg(fIdx)
			} else {
				// Fallback: resolve via FIELDGET RTL
				t.PushSymbol(t.VM().FindSymbol("FIELDGET"))
				t.PushNil()
				t.PushLong(int64(fIdx))
				t.Function(1)
				v = t.Pop2()
			}
			if v.IsString() {
				s := v.AsString()
				// ASCII-space trim — DBF CHAR fields pad with 0x20 only
				lo, hi := 0, len(s)
				for lo < hi && s[lo] == ' ' {
					lo++
				}
				for hi > lo && s[hi-1] == ' ' {
					hi--
				}
				if lo == 0 && hi == len(s) {
					t.PushValue(v)
				} else {
					t.PushString(s[lo:hi])
				}
			} else {
				t.PushValue(v)
			}

		// --- 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()

		// --- Hash --- (PcOpHashGen has been declared since the
		// initial pcode design but its dispatch case was missing,
		// so any pcode body that built a hash literal panicked
		// with "unknown pcode opcode: 0x51".)
		case PcOpHashGen:
			count := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			t.HashGen(count)

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

			// Snapshot closure-captured locals from the *current*
			// frame into the new block's Detached slice. The body
			// reads/writes them via PcOpPushDetached / PcOpPopDetached
			// at the indices the compiler reserved. Without this,
			// `{|x| x + outer }` saw `outer` as NIL because the
			// block fn ran with its own frame and the body's lookup
			// for `outer` fell through to the memvar table.
			captured := make([]Value, nDetached)
			for i := 0; i < nDetached; i++ {
				srcIdx := int(binary.LittleEndian.Uint16(code[pc:]))
				pc += 2
				captured[i] = t.Local(srcIdx)
			}

			// Create a Go function that interprets the block's pcode.
			// Params count must be threaded through so ExecPcode's
			// Frame() pulls Eval()'s args off the stack into the
			// block's locals — without it, `{|x| x*x }` saw x=NIL
			// and `x * x` panicked on the multiplication.
			blockFn := &PcodeFunc{Code: blockCode, Params: nParams}
			modCopy := mod
			blockVal := MakeBlock(nil, nDetached) // Fn patched below
			bb := (*HbBlock)(blockVal.ptr)
			if nDetached > 0 {
				copy(bb.Detached, captured)
			}
			bb.Fn = func(t2 *Thread) {
				// Install this block as the currently-executing
				// block so PcOpPushDetached / PcOpPopDetached can
				// resolve their slots. Restore the previous one on
				// exit so nested-block evaluation (`{|| eval(b2) }`)
				// pops back to the outer block.
				prev := t2.CurBlock()
				t2.SetCurBlock(bb)
				defer t2.SetCurBlock(prev)
				ExecPcode(t2, blockFn, modCopy)
			}
			t.PushValue(blockVal)

		case PcOpPushDetached:
			slot := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			bb := t.CurBlock()
			if bb != nil && slot < len(bb.Detached) {
				t.PushValue(bb.Detached[slot])
			} else {
				t.PushNil()
			}

		case PcOpPopDetached:
			slot := int(binary.LittleEndian.Uint16(code[pc:]))
			pc += 2
			val := t.pop()
			bb := t.CurBlock()
			if bb != nil && slot < len(bb.Detached) {
				bb.Detached[slot] = val
			}

		// --- 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))
		}
	}
}