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

// genpc — Five pcode generator. Compiles AST to bytecode for FRB interpreter mode.
// Mirrors gengo's logic but emits bytecode opcodes instead of Go source code.

package genpc

import (
	"encoding/binary"
	"five/compiler/ast"
	"five/compiler/token"
	"five/hbrt"
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"
)

// Generate compiles an AST file to a PcodeModule.
func Generate(file *ast.File) *hbrt.PcodeModule {
	g := &generator{
		mod: &hbrt.PcodeModule{
			Name:  file.Name,
			Funcs: make(map[string]*hbrt.PcodeFunc),
		},
	}

	for _, d := range file.Decls {
		switch decl := d.(type) {
		case *ast.FuncDecl:
			g.emitFunc(decl)
		default:
			// ClassDecl, MethodDecl, top-level VarDecl, etc. are not
			// expressible in pcode form today — record the kind so the
			// caller can surface a clear "rebuild without --pcode"
			// diagnostic instead of silently dropping the declaration.
			g.noteUnsupported(fmt.Sprintf("%T", decl))
		}
	}

	g.mod.Warnings = g.Warnings()
	return g.mod
}

// CompileExpr compiles a single expression AST to a standalone PcodeFunc
// that, when executed, leaves the expression's value on the stack as a
// return value. Used by FiveSql2 for prepared-statement-style caching:
// compile WHERE / SELECT expressions once per query, execute per row.
//
// The returned function takes zero parameters and zero locals.
// Caller provides field access context via the current workarea.
func CompileExpr(expr ast.Expr) *hbrt.PcodeFunc {
	g := &generator{
		mod:    &hbrt.PcodeModule{Funcs: make(map[string]*hbrt.PcodeFunc)},
		locals: make(map[string]int),
	}
	// Note: ExecPcode emits its own Frame/EndProc around this code.
	// We just emit the expression evaluation + RetValue.
	g.emitExpr(expr)
	g.emit(hbrt.PcOpRetValue)

	return &hbrt.PcodeFunc{
		Name:   "_EXPR",
		Code:   g.code,
		Params: 0,
		Locals: 0,
	}
}

type generator struct {
	mod  *hbrt.PcodeModule
	code []byte
	locals map[string]int
	// detached, when non-nil, intercepts IdentExpr/AssignExpr lookups
	// inside a block body. Names found in the *enclosing* locals are
	// auto-promoted to capture slots in declaration order so the body
	// emits PcOpPushDetached / PcOpPopDetached against the slot index
	// rather than falling through to the runtime memvar table.
	detached *detachedMap
	// Unsupported AST node kinds encountered during emit, recorded
	// once per kind. Exposed via Module().Warnings so the build
	// pipeline can surface a clear "node X not supported in pcode
	// mode" diagnostic instead of silently emitting PushNil/no-op
	// (the previous behavior, which masked bugs as wrong results).
	unsupported map[string]bool
}

// noteUnsupported records that an AST node kind was hit by the
// silent-fallback path. Caller emits PushNil/Pop to keep the stack
// shape valid; the diagnostic itself is collected and reported once
// per kind at module-level after Generate completes.
func (g *generator) noteUnsupported(kind string) {
	if g.unsupported == nil {
		g.unsupported = map[string]bool{}
	}
	g.unsupported[kind] = true
}

// Warnings returns the accumulated unsupported-node diagnostics in
// stable (sorted) order so build output is deterministic.
func (g *generator) Warnings() []string {
	if len(g.unsupported) == 0 {
		return nil
	}
	out := make([]string, 0, len(g.unsupported))
	for k := range g.unsupported {
		out = append(out, "pcode: AST node not supported in --pcode/FRB-pcode mode: "+k+
			" (emitted as no-op; rebuild without --pcode to keep this construct)")
	}
	sort.Strings(out)
	return out
}

// detachedMap accumulates the closure captures requested by a block
// body in encounter order. The enclosing scope's locals map is read
// to translate a free-variable name into the source-local index that
// the PushBlock op must snapshot.
type detachedMap struct {
	enclosing map[string]int // outer scope's local name -> 1-based local index
	slot      map[string]int // captured name -> 0-based detached slot
	srcOrder  []int          // 0-based slot -> source local index (1-based)
}

func newDetachedMap(enclosing map[string]int) *detachedMap {
	return &detachedMap{
		enclosing: enclosing,
		slot:      map[string]int{},
	}
}

// resolve returns (slot, true) if `name` resolves through the
// enclosing scope and reserves a capture slot for it on first use.
// Returns (0, false) for names not in the enclosing scope — caller
// falls back to the memvar lookup or another resolution path.
func (d *detachedMap) resolve(name string) (int, bool) {
	if d == nil {
		return 0, false
	}
	if s, ok := d.slot[name]; ok {
		return s, true
	}
	src, ok := d.enclosing[name]
	if !ok {
		return 0, false
	}
	s := len(d.srcOrder)
	d.slot[name] = s
	d.srcOrder = append(d.srcOrder, src)
	return s, true
}

func (d *detachedMap) sources() []int {
	if d == nil {
		return nil
	}
	return d.srcOrder
}

func (g *generator) emit(b ...byte) {
	g.code = append(g.code, b...)
}

func (g *generator) emitU16(v uint16) {
	var buf [2]byte
	binary.LittleEndian.PutUint16(buf[:], v)
	g.code = append(g.code, buf[:]...)
}

func (g *generator) emitI32(v int32) {
	var buf [4]byte
	binary.LittleEndian.PutUint32(buf[:], uint32(v))
	g.code = append(g.code, buf[:]...)
}

func (g *generator) emitI64(v int64) {
	var buf [8]byte
	binary.LittleEndian.PutUint64(buf[:], uint64(v))
	g.code = append(g.code, buf[:]...)
}

func (g *generator) emitF64(v float64) {
	var buf [8]byte
	binary.LittleEndian.PutUint64(buf[:], math.Float64bits(v))
	g.code = append(g.code, buf[:]...)
}

func (g *generator) emitString(op byte, s string) {
	g.emit(op)
	g.emitU16(uint16(len(s)))
	g.code = append(g.code, []byte(s)...)
}

func (g *generator) pc() int {
	return len(g.code)
}

// placeholder for jump offset, returns position to patch
func (g *generator) emitJumpPlaceholder(op byte) int {
	g.emit(op)
	pos := g.pc()
	g.emitI32(0) // placeholder
	return pos
}

func (g *generator) patchJump(pos int) {
	offset := int32(g.pc() - pos - 4) // relative to after the offset bytes
	binary.LittleEndian.PutUint32(g.code[pos:], uint32(offset))
}

// --- Function ---

func (g *generator) emitFunc(fn *ast.FuncDecl) {
	g.code = nil
	g.locals = make(map[string]int)

	// Build local map. PRG is case-insensitive so all keys are
	// uppercased here; every lookup site below must mirror this.
	idx := 1
	for _, p := range fn.Params {
		g.locals[strings.ToUpper(p.Name)] = idx
		idx++
	}
	for _, d := range fn.Decls {
		if vd, ok := d.(*ast.VarDecl); ok && vd.Scope == ast.ScopeLocal {
			for _, v := range vd.Vars {
				g.locals[strings.ToUpper(v.Name)] = idx
				idx++
			}
		}
	}
	for _, s := range fn.Body {
		if vd, ok := s.(*ast.VarDecl); ok && vd.Scope == ast.ScopeLocal {
			for _, v := range vd.Vars {
				g.locals[strings.ToUpper(v.Name)] = idx
				idx++
			}
		}
	}

	nLocals := idx - 1 - len(fn.Params)

	// Emit LOCAL initializers
	localIdx := len(fn.Params) + 1
	for _, d := range fn.Decls {
		vd, ok := d.(*ast.VarDecl)
		if !ok || vd.Scope != ast.ScopeLocal {
			continue
		}
		for _, v := range vd.Vars {
			if v.Init != nil {
				g.emitExpr(v.Init)
				g.emit(hbrt.PcOpPopLocal)
				g.emitU16(uint16(localIdx))
			}
			localIdx++
		}
	}

	// Emit body
	for _, s := range fn.Body {
		g.emitStmt(s)
	}

	// Implicit return NIL
	g.emit(hbrt.PcOpPushNil)
	g.emit(hbrt.PcOpRetValue)

	pf := &hbrt.PcodeFunc{
		Name:   fn.Name,
		Code:   make([]byte, len(g.code)),
		Params: len(fn.Params),
		Locals: nLocals,
	}
	copy(pf.Code, g.code)
	g.mod.Funcs[strings.ToUpper(fn.Name)] = pf
}

// --- Statements ---

func (g *generator) emitStmt(stmt ast.Stmt) {
	switch s := stmt.(type) {
	case *ast.ReturnStmt:
		if s.Value != nil {
			g.emitExpr(s.Value)
			g.emit(hbrt.PcOpRetValue)
		} else {
			g.emit(hbrt.PcOpPushNil)
			g.emit(hbrt.PcOpRetValue)
		}

	case *ast.ExprStmt:
		if assign, ok := s.X.(*ast.AssignExpr); ok {
			g.emitAssign(assign)
		} else if call, ok := s.X.(*ast.CallExpr); ok {
			g.emitCallStmt(call)
		} else {
			g.emitExpr(s.X)
			g.emit(hbrt.PcOpPop)
		}

	case *ast.IfStmt:
		g.emitIf(s)

	case *ast.DoWhileStmt:
		g.emitDoWhile(s)

	case *ast.ForStmt:
		g.emitFor(s)

	case *ast.ExitStmt:
		// handled by loop
		g.emit(hbrt.PcOpHalt) // placeholder

	case *ast.QOutStmt:
		g.emitQOut(s)

	case *ast.VarDecl:
		// Mid-function LOCAL
		for _, v := range s.Vars {
			if v.Init != nil {
				g.emitExpr(v.Init)
				if idx, ok := g.locals[strings.ToUpper(v.Name)]; ok {
					g.emit(hbrt.PcOpPopLocal)
					g.emitU16(uint16(idx))
				} else {
					g.emit(hbrt.PcOpPop)
				}
			}
		}

	default:
		// Unsupported statement — record once per kind so the build
		// pipeline can surface a clear "AST node not supported in
		// pcode mode" warning instead of silently dropping the stmt.
		g.noteUnsupported(fmt.Sprintf("stmt %T", stmt))
	}
}

func (g *generator) emitIf(s *ast.IfStmt) {
	g.emitExpr(s.Cond)
	jumpFalse := g.emitJumpPlaceholder(hbrt.PcOpJumpFalse)

	for _, stmt := range s.Body {
		g.emitStmt(stmt)
	}

	if len(s.ElseIfs) > 0 || len(s.ElseBody) > 0 {
		// `jumpEnds` collects every "branch-taken → skip rest of IF"
		// jump that has to be patched once the entire IF chain ends.
		// Original code only stashed each ELSEIF's terminator in `_ =
		// jumpEnd2` and never patched it, so the offset stayed 0 and
		// the runtime kept walking into the next ELSEIF's
		// PcOpJumpFalse opcode as if it were data — silent bytecode
		// corruption in pcode mode.
		jumpEnds := []int{g.emitJumpPlaceholder(hbrt.PcOpJump)}
		g.patchJump(jumpFalse)

		for _, elif := range s.ElseIfs {
			g.emitExpr(elif.Cond)
			nextJump := g.emitJumpPlaceholder(hbrt.PcOpJumpFalse)
			for _, stmt := range elif.Body {
				g.emitStmt(stmt)
			}
			jumpEnds = append(jumpEnds, g.emitJumpPlaceholder(hbrt.PcOpJump))
			g.patchJump(nextJump)
		}

		for _, stmt := range s.ElseBody {
			g.emitStmt(stmt)
		}
		for _, j := range jumpEnds {
			g.patchJump(j)
		}
	} else {
		g.patchJump(jumpFalse)
	}
}

func (g *generator) emitDoWhile(s *ast.DoWhileStmt) {
	loopStart := g.pc()
	for _, stmt := range s.Body {
		g.emitStmt(stmt)
	}
	g.emitExpr(s.Cond)
	// Jump back if true
	g.emit(hbrt.PcOpJumpTrue)
	offset := int32(loopStart - g.pc() - 4)
	g.emitI32(offset)
}

func (g *generator) emitFor(s *ast.ForStmt) {
	idx, ok := g.locals[strings.ToUpper(s.Var)]
	if !ok {
		return
	}
	// Init: var := start
	g.emitExpr(s.Start)
	g.emit(hbrt.PcOpPopLocal)
	g.emitU16(uint16(idx))

	// Detect step direction statically (matches gengo's emitFor):
	//   * no Step      → +1, ascending
	//   * literal -N   → descending
	//   * unary MINUS  → descending
	// Anything else (variable, expression) defaults to ascending.
	// Without this we always emitted `var <= to`, which made `FOR
	// 5 TO 1 STEP -1` exit on the first iteration; and we always
	// stepped by hardcoded +1, which made `FOR i := 1 TO 10 STEP
	// 2` summed 1+2+...+10 (55) instead of 1+3+5+7+9 (25).
	negStep := false
	if s.Step != nil {
		if lit, ok := s.Step.(*ast.LiteralExpr); ok {
			if lit.Kind == token.INT && len(lit.Value) > 0 && lit.Value[0] == '-' {
				negStep = true
			}
		}
		if un, ok := s.Step.(*ast.UnaryExpr); ok && un.Op == token.MINUS {
			negStep = true
		}
	}

	loopStart := g.pc()
	// Comparison: ascending → var <= to; descending → var >= to.
	g.emit(hbrt.PcOpPushLocal)
	g.emitU16(uint16(idx))
	g.emitExpr(s.To)
	if negStep {
		g.emit(hbrt.PcOpGreaterEq)
	} else {
		g.emit(hbrt.PcOpLessEq)
	}
	jumpOut := g.emitJumpPlaceholder(hbrt.PcOpJumpFalse)

	// Body
	for _, stmt := range s.Body {
		g.emitStmt(stmt)
	}

	// Increment: var := var + step (re-evaluating step per iter is
	// fine; constant-folding can hoist it later). Push var, push
	// step, add, store back.
	g.emit(hbrt.PcOpPushLocal)
	g.emitU16(uint16(idx))
	if s.Step != nil {
		g.emitExpr(s.Step)
	} else {
		g.emit(hbrt.PcOpPushInt)
		g.emitI64(1)
	}
	g.emit(hbrt.PcOpPlus)
	g.emit(hbrt.PcOpPopLocal)
	g.emitU16(uint16(idx))

	// Jump back to comparison
	g.emit(hbrt.PcOpJump)
	g.emitI32(int32(loopStart - g.pc() - 4))

	g.patchJump(jumpOut)
}

func (g *generator) emitQOut(s *ast.QOutStmt) {
	sym := "QOUT"
	if s.IsQQ {
		sym = "QQOUT"
	}
	g.emitString(hbrt.PcOpPushSymbol, sym)
	g.emit(hbrt.PcOpPushNil)
	for _, expr := range s.Exprs {
		g.emitExpr(expr)
	}
	g.emit(hbrt.PcOpFunction)
	g.emitU16(uint16(len(s.Exprs)))
}

// --- Expressions ---

func (g *generator) emitExpr(expr ast.Expr) {
	switch e := expr.(type) {
	case *ast.LiteralExpr:
		switch e.Kind {
		case token.INT:
			g.emit(hbrt.PcOpPushInt)
			v := parseInt64(e.Value)
			g.emitI64(v)
		case token.DOUBLE:
			g.emit(hbrt.PcOpPushDouble)
			v := parseFloat64(e.Value)
			g.emitF64(v)
		case token.STRING:
			g.emitString(hbrt.PcOpPushString, e.Value)
		case token.TRUE:
			g.emit(hbrt.PcOpPushTrue)
		case token.FALSE:
			g.emit(hbrt.PcOpPushFalse)
		case token.NIL_LIT:
			g.emit(hbrt.PcOpPushNil)
		}

	case *ast.IdentExpr:
		upper := strings.ToUpper(e.Name)
		if upper == "SELF" {
			g.emit(hbrt.PcOpPushSelf)
			return
		}
		// Locals are keyed case-insensitively. Look up via uppercase
		// (also covers blocks: their params are stored ToUpper). The
		// previous raw `e.Name` lookup missed any caller that wrote
		// the identifier in different case from the declaration —
		// `{|x| x * x }` invoked via Eval(b, 7) silently saw x=NIL.
		if idx, ok := g.locals[upper]; ok {
			g.emit(hbrt.PcOpPushLocal)
			g.emitU16(uint16(idx))
		} else if slot, ok := g.detached.resolve(upper); ok {
			// Free variable that resolves to an enclosing-frame
			// local — promote to a closure capture slot and read it
			// from this block's Detached at runtime.
			g.emit(hbrt.PcOpPushDetached)
			g.emitU16(uint16(slot))
		} else {
			// Unknown at compile time → runtime memvar lookup. This
			// makes `&(expr)` and the debugger's `p` see PRIVATEs
			// (including the frame-local injection the debugger does).
			g.emitString(hbrt.PcOpPushMemvar, upper)
		}

	case *ast.BinaryExpr:
		g.emitExpr(e.Left)
		g.emitExpr(e.Right)
		g.emitBinaryOp(e.Op)

	case *ast.UnaryExpr:
		g.emitExpr(e.X)
		switch e.Op {
		case token.MINUS:
			g.emit(hbrt.PcOpNegate)
		case token.NOT:
			g.emit(hbrt.PcOpNot)
		}

	case *ast.CallExpr:
		g.emitCall(e)

	case *ast.IIfExpr:
		g.emitExpr(e.Cond)
		jumpFalse := g.emitJumpPlaceholder(hbrt.PcOpJumpFalse)
		g.emitExpr(e.True)
		jumpEnd := g.emitJumpPlaceholder(hbrt.PcOpJump)
		g.patchJump(jumpFalse)
		g.emitExpr(e.False)
		g.patchJump(jumpEnd)

	case *ast.SelfExpr:
		g.emit(hbrt.PcOpPushSelf)

	case *ast.SendExpr:
		g.emitExpr(e.Object)
		if e.HasParens {
			for _, arg := range e.Args {
				g.emitExpr(arg)
			}
			g.emitString(hbrt.PcOpSend, strings.ToUpper(e.Method))
			g.emitU16(uint16(len(e.Args)))
		} else {
			if _, isSelf := e.Object.(*ast.SelfExpr); isSelf {
				// Replace with PushSelfField (pop the self we pushed)
				g.code = g.code[:len(g.code)] // keep self on stack... actually use dedicated op
				g.emit(hbrt.PcOpPop) // remove self
				g.emitString(hbrt.PcOpPushSelfField, strings.ToUpper(e.Method))
			}
		}

	case *ast.ArrayLitExpr:
		for _, item := range e.Items {
			g.emitExpr(item)
		}
		g.emit(hbrt.PcOpArrayGen)
		g.emitU16(uint16(len(e.Items)))

	case *ast.BlockExpr:
		// `{|p| body }` — compile body to its own pcode buffer with
		// the block's params occupying locals 1..len(Params). Free
		// variables in the body that resolve to an enclosing-frame
		// local are routed through Detached[i]: PcOpPushDetached /
		// PcOpPopDetached. The block creator (PcOpPushBlock) records
		// each captured slot's source-local index so the interpreter
		// snapshots the enclosing value into Detached[i] at block
		// construction time.
		//
		// Without this, every closure that referenced a caller local
		// fell through to the runtime memvar lookup and silently
		// returned NIL — silently breaking AEval/Eval/SqlScan
		// predicates in --pcode / FRB-pcode mode.
		savedCode := g.code
		savedLocals := g.locals
		savedDet := g.detached
		g.code = nil
		g.locals = make(map[string]int, len(e.Params))
		g.detached = newDetachedMap(savedLocals) // capture-on-demand
		for i, p := range e.Params {
			g.locals[strings.ToUpper(p)] = i + 1
		}
		g.emitExpr(e.Body)
		g.emit(hbrt.PcOpRetValue)
		body := g.code
		captureIdx := g.detached.sources() // src indices in capture order
		g.code = savedCode
		g.locals = savedLocals
		g.detached = savedDet

		g.emit(hbrt.PcOpPushBlock)
		g.emitI32(int32(len(body)))
		g.code = append(g.code, body...)
		g.emitU16(uint16(len(e.Params)))     // nParams
		g.emitU16(uint16(len(captureIdx)))   // nDetached
		for _, srcIdx := range captureIdx {
			g.emitU16(uint16(srcIdx))
		}

	case *ast.SeqExpr:
		// Comma-separated expression list inside a code block:
		// `{|| e1, e2, e3 }`. Evaluate each in order, pop intermediate
		// results so only the last value remains. Same semantics as
		// gengo's SeqExpr handler.
		for i, item := range e.Items {
			g.emitExpr(item)
			if i < len(e.Items)-1 {
				g.emit(hbrt.PcOpPop)
			}
		}

	case *ast.HashLitExpr:
		// `{ "k" => 1, ... }` — push each key+value pair, HashGen
		// builds the hash from the top-N stack pairs. Without this
		// case, the hash literal silently fell through to PushNil
		// and any subsequent `h[key]` panicked at ArrayPush with
		// "argument error (op: [])".
		for i, k := range e.Keys {
			g.emitExpr(k)
			g.emitExpr(e.Values[i])
		}
		g.emit(hbrt.PcOpHashGen)
		g.emitU16(uint16(len(e.Keys)))

	case *ast.IndexExpr:
		// arr[idx] — push array, push index, ArrayPush reads element.
		// (ArrayPush is the "get" op; ArrayPop is the "set" op — names
		// kept to match the Harbour stack-machine convention.)
		// Without this case, indexed reads in pcode silently emitted
		// PushNil via the default fallback, so `arr[i]` always
		// returned NIL and `n + arr[i]` panicked at the +.
		g.emitExpr(e.X)
		g.emitExpr(e.Index)
		g.emit(hbrt.PcOpArrayPush)

	case *ast.PostfixExpr:
		// `x++` / `x--` — read current value (becomes the expression
		// result), apply Inc/Dec to the LOCAL slot, leave the
		// pre-modification value on the stack so it round-trips
		// correctly when used as an expression. As a statement the
		// caller does Pop afterward.
		// Without this case, postfix on pcode-mode silently emitted
		// PushNil → `n++` was a no-op, breaking DO WHILE / FOR
		// patterns that mutate the loop counter.
		if id, isIdent := e.X.(*ast.IdentExpr); isIdent {
			if idx, found := g.locals[strings.ToUpper(id.Name)]; found {
				g.emit(hbrt.PcOpPushLocal)
				g.emitU16(uint16(idx))
				delta := int64(1)
				if e.Op == token.DEC {
					delta = -1
				}
				g.emit(hbrt.PcOpLocalAddInt)
				g.emitU16(uint16(idx))
				g.emitI32(int32(delta))
				return
			}
		}
		// Anything else (memvar, alias->field, arr[i]) — emit the
		// expression as a no-op for now and document the gap.
		g.emitExpr(e.X)

	case *ast.AliasExpr:
		// Pcode mode: only the M-> / MEMVAR-> namespace (memvar
		// access) is wired up. The general workarea-alias form
		// (`FOO->bar`, `(expr)->(body)`) needs new opcodes for
		// alias dispatch + workarea context save/restore — until
		// then it falls through to the generic NIL fallback so
		// callers see "missing data" rather than crash.
		if aliasIdent, ok1 := e.Alias.(*ast.IdentExpr); ok1 {
			if fieldIdent, ok2 := e.Field.(*ast.IdentExpr); ok2 {
				upper := strings.ToUpper(aliasIdent.Name)
				if upper == "M" || upper == "MEMVAR" {
					g.emitString(hbrt.PcOpPushMemvar, fieldIdent.Name)
					return
				}
			}
		}
		g.emit(hbrt.PcOpPushNil)

	case *ast.AssignExpr:
		// Assignment as an expression — perform the store and leave
		// the assigned value on the eval stack so a containing
		// expression (e.g. SeqExpr inside `{|| acc += v, acc }`) can
		// consume it. emitAssign by itself is statement-shaped and
		// pops the value; we route through it then push the final
		// value with a load matching the destination.
		g.emitAssignAsExpr(e)

	default:
		// Record the unsupported kind and emit PushNil so the stack
		// shape stays valid — callers can keep compiling but the
		// build pipeline raises a clear pcode-mode-incompat warning.
		g.noteUnsupported(fmt.Sprintf("expr %T", expr))
		g.emit(hbrt.PcOpPushNil)
	}
}

// emitAssignAsExpr emits an assignment whose value remains on the
// eval stack (expression context). Mirrors emitAssign's storage
// paths but appends a value-producing load so callers — typically
// SeqExpr items inside a code block body — can chain.
func (g *generator) emitAssignAsExpr(a *ast.AssignExpr) {
	// Local / detached compound op.
	if a.Op != token.ASSIGN {
		if op, ok := compoundBinOp(a.Op); ok {
			if ident, isIdent := a.Left.(*ast.IdentExpr); isIdent {
				up := strings.ToUpper(ident.Name)
				if idx, found := g.locals[up]; found {
					g.emit(hbrt.PcOpPushLocal)
					g.emitU16(uint16(idx))
					g.emitExpr(a.Right)
					g.emit(op)
					g.emit(hbrt.PcOpDup) // keep value as expression result
					g.emit(hbrt.PcOpPopLocal)
					g.emitU16(uint16(idx))
					return
				}
				if slot, ok := g.detached.resolve(up); ok {
					g.emit(hbrt.PcOpPushDetached)
					g.emitU16(uint16(slot))
					g.emitExpr(a.Right)
					g.emit(op)
					g.emit(hbrt.PcOpDup)
					g.emit(hbrt.PcOpPopDetached)
					g.emitU16(uint16(slot))
					return
				}
			}
		}
	}
	// Plain assignment.
	if ident, ok := a.Left.(*ast.IdentExpr); ok {
		up := strings.ToUpper(ident.Name)
		if idx, found := g.locals[up]; found {
			g.emitExpr(a.Right)
			g.emit(hbrt.PcOpDup)
			g.emit(hbrt.PcOpPopLocal)
			g.emitU16(uint16(idx))
			return
		}
		if slot, ok := g.detached.resolve(up); ok {
			g.emitExpr(a.Right)
			g.emit(hbrt.PcOpDup)
			g.emit(hbrt.PcOpPopDetached)
			g.emitU16(uint16(slot))
			return
		}
	}
	// Self field setter — :=. PcOpSetSelfField consumes the value
	// and pushes nothing; re-emit Right after to leave the value.
	if send, ok := a.Left.(*ast.SendExpr); ok {
		if _, isSelf := send.Object.(*ast.SelfExpr); isSelf {
			g.emitExpr(a.Right)
			g.emit(hbrt.PcOpDup)
			g.emitString(hbrt.PcOpSetSelfField, strings.ToUpper(send.Method))
			return
		}
	}
	// Fallback: evaluate Right and leave it as the expression value
	// (no destination wired). Mirrors the statement-form fallback
	// minus the trailing Pop.
	g.emitExpr(a.Right)
}

func (g *generator) emitBinaryOp(op token.Kind) {
	switch op {
	case token.PLUS:
		g.emit(hbrt.PcOpPlus)
	case token.MINUS:
		g.emit(hbrt.PcOpMinus)
	case token.STAR:
		g.emit(hbrt.PcOpMult)
	case token.SLASH:
		g.emit(hbrt.PcOpDivide)
	case token.PERCENT:
		g.emit(hbrt.PcOpMod)
	case token.POWER:
		g.emit(hbrt.PcOpPower)
	case token.EQ, token.EXEQ:
		g.emit(hbrt.PcOpEqual)
	case token.NEQ:
		g.emit(hbrt.PcOpNotEqual)
	case token.LT:
		g.emit(hbrt.PcOpLess)
	case token.GT:
		g.emit(hbrt.PcOpGreater)
	case token.LTE:
		g.emit(hbrt.PcOpLessEq)
	case token.GTE:
		g.emit(hbrt.PcOpGreaterEq)
	case token.AND:
		g.emit(hbrt.PcOpAnd)
	case token.OR:
		g.emit(hbrt.PcOpOr)
	case token.DOLLAR:
		g.emit(hbrt.PcOpInString)
	}
}

func (g *generator) emitCall(e *ast.CallExpr) {
	if ident, ok := e.Func.(*ast.IdentExpr); ok {
		// Peephole: FieldGet(<int literal>) → PcOpFieldGet <idx>.
		// Skips the entire PushSymbol + Function + Frame + RTL path in
		// favor of a direct workarea field access. Huge win for WHERE
		// predicates on scan loops where this is the per-row hot op.
		if strings.EqualFold(ident.Name, "FieldGet") && len(e.Args) == 1 {
			if lit, ok := e.Args[0].(*ast.LiteralExpr); ok && lit.Kind == token.INT {
				if n, err := strconv.Atoi(lit.Value); err == nil && n > 0 && n <= 0xFFFF {
					g.emit(hbrt.PcOpFieldGet)
					g.emitU16(uint16(n))
					return
				}
			}
		}
		// Peephole: AllTrim(FieldGet(<int literal>)) → PcOpFieldTrim <idx>.
		// Fuses the character-field CHAR-trim normalization that
		// SqlExprToPrg auto-wraps into one opcode, saving one Function
		// dispatch + one intermediate string allocation per row.
		if strings.EqualFold(ident.Name, "AllTrim") && len(e.Args) == 1 {
			if inner, ok := e.Args[0].(*ast.CallExpr); ok {
				if innerIdent, ok := inner.Func.(*ast.IdentExpr); ok &&
					strings.EqualFold(innerIdent.Name, "FieldGet") &&
					len(inner.Args) == 1 {
					if lit, ok := inner.Args[0].(*ast.LiteralExpr); ok && lit.Kind == token.INT {
						if n, err := strconv.Atoi(lit.Value); err == nil && n > 0 && n <= 0xFFFF {
							g.emit(hbrt.PcOpFieldTrim)
							g.emitU16(uint16(n))
							return
						}
					}
				}
			}
		}
		g.emitString(hbrt.PcOpPushSymbol, strings.ToUpper(ident.Name))
		g.emit(hbrt.PcOpPushNil)
		for _, arg := range e.Args {
			g.emitExpr(arg)
		}
		g.emit(hbrt.PcOpFunction)
		g.emitU16(uint16(len(e.Args)))
	} else {
		g.emitExpr(e.Func)
		for _, arg := range e.Args {
			g.emitExpr(arg)
		}
		g.emit(hbrt.PcOpDo)
		g.emitU16(uint16(len(e.Args)))
	}
}

func (g *generator) emitCallStmt(e *ast.CallExpr) {
	if ident, ok := e.Func.(*ast.IdentExpr); ok {
		g.emitString(hbrt.PcOpPushSymbol, strings.ToUpper(ident.Name))
		g.emit(hbrt.PcOpPushNil)
		for _, arg := range e.Args {
			g.emitExpr(arg)
		}
		g.emit(hbrt.PcOpDo)
		g.emitU16(uint16(len(e.Args)))
	} else {
		g.emitExpr(e.Func)
		for _, arg := range e.Args {
			g.emitExpr(arg)
		}
		g.emit(hbrt.PcOpDo)
		g.emitU16(uint16(len(e.Args)))
	}
}

func (g *generator) emitAssign(a *ast.AssignExpr) {
	// Compound operators (+=, -=, *=, /=, %=, ^=) need to fold the
	// existing left-hand value with the right. Without this they got
	// emitted as plain `:=`, dropping the accumulator: `n += i`
	// behaved as `n := i`. So the FOR loop reduce idiom (e.g.
	// `n := 0 ; FOR i := 1 TO 10 ; n += i ; NEXT`) returned only
	// the LAST iteration's increment.
	if a.Op != token.ASSIGN {
		op, ok := compoundBinOp(a.Op)
		if ok {
			if ident, isIdent := a.Left.(*ast.IdentExpr); isIdent {
				up := strings.ToUpper(ident.Name)
				if idx, found := g.locals[up]; found {
					g.emit(hbrt.PcOpPushLocal)
					g.emitU16(uint16(idx))
					g.emitExpr(a.Right)
					g.emit(op)
					g.emit(hbrt.PcOpPopLocal)
					g.emitU16(uint16(idx))
					return
				}
				if slot, ok := g.detached.resolve(up); ok {
					// Compound on a captured outer local — read/
					// write through Detached so the closure mutates
					// the captured snapshot.
					g.emit(hbrt.PcOpPushDetached)
					g.emitU16(uint16(slot))
					g.emitExpr(a.Right)
					g.emit(op)
					g.emit(hbrt.PcOpPopDetached)
					g.emitU16(uint16(slot))
					return
				}
			}
		}
	}
	if ident, ok := a.Left.(*ast.IdentExpr); ok {
		up := strings.ToUpper(ident.Name)
		if idx, found := g.locals[up]; found {
			g.emitExpr(a.Right)
			g.emit(hbrt.PcOpPopLocal)
			g.emitU16(uint16(idx))
			return
		}
		if slot, ok := g.detached.resolve(up); ok {
			g.emitExpr(a.Right)
			g.emit(hbrt.PcOpPopDetached)
			g.emitU16(uint16(slot))
			return
		}
	}
	// Self field assignment
	if send, ok := a.Left.(*ast.SendExpr); ok {
		if _, isSelf := send.Object.(*ast.SelfExpr); isSelf {
			g.emitExpr(a.Right)
			g.emitString(hbrt.PcOpSetSelfField, strings.ToUpper(send.Method))
			return
		}
	}
	g.emitExpr(a.Right)
	g.emit(hbrt.PcOpPop)
}

// compoundBinOp maps an `<op>=` token to the binary opcode it
// produces against the left-hand value. Returns false for ASSIGN
// (the caller should take the plain-store path).
func compoundBinOp(k token.Kind) (byte, bool) {
	switch k {
	case token.PLUSEQ:
		return hbrt.PcOpPlus, true
	case token.MINUSEQ:
		return hbrt.PcOpMinus, true
	case token.STAREQ:
		return hbrt.PcOpMult, true
	case token.SLASHEQ:
		return hbrt.PcOpDivide, true
	case token.PERCENTEQ:
		return hbrt.PcOpMod, true
	case token.POWEREQ:
		return hbrt.PcOpPower, true
	}
	return 0, false
}

func parseInt64(s string) int64 {
	var v int64
	for _, c := range s {
		if c >= '0' && c <= '9' {
			v = v*10 + int64(c-'0')
		}
	}
	if len(s) > 0 && s[0] == '-' {
		v = -v
	}
	return v
}

func parseFloat64(s string) float64 {
	var v float64
	var dec float64
	inDec := false
	for _, c := range s {
		if c == '.' {
			inDec = true
			dec = 0.1
			continue
		}
		if c >= '0' && c <= '9' {
			if inDec {
				v += float64(c-'0') * dec
				dec *= 0.1
			} else {
				v = v*10 + float64(c-'0')
			}
		}
	}
	if len(s) > 0 && s[0] == '-' {
		v = -v
	}
	return v
}