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

// FRB (Five Runtime Binary) RTL functions.
//
// PRG Usage:
//   pMod := FrbLoad("module.frb")    // load module
//   FrbDo(pMod, "MYFUNC", args...)   // call function
//   FrbUnload(pMod)                   // unload
//
//   // Or one-shot:
//   result := FrbRun("module.frb", arg1, arg2)

package hbrtl

import (
	"five/compiler/genpc"
	"five/compiler/parser"
	"five/compiler/pp"
	"five/hbrt"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

// frbCompileInProc compiles PRG source to a pcode FrbModule entirely
// in-process — no external `five` binary needed. Used by FrbCompile/
// FrbExec when the host can't shell out (running from a directory
// where `five` isn't on PATH and isn't next to the binary). Avoids
// the plugin-runtime-mismatch failure mode of native FRB plugins
// AND removes the "find the five exe" fragility entirely.
func frbCompileInProc(vm *hbrt.VM, prgSource string) (*hbrt.FrbModule, error) {
	prep := pp.New()
	processed, errs := prep.Process("dynamic.prg", prgSource)
	if len(errs) > 0 {
		return nil, fmt.Errorf("preprocess: %s", strings.Join(errs, "; "))
	}
	file, perrs := parser.Parse("dynamic.prg", processed)
	if len(perrs) > 0 {
		msgs := make([]string, 0, len(perrs))
		for _, e := range perrs {
			msgs = append(msgs, e.Error())
		}
		return nil, fmt.Errorf("parse: %s", strings.Join(msgs, "; "))
	}
	pcMod := genpc.Generate(file)
	// Surface unsupported-AST-node warnings on stderr so dynamic
	// FrbCompile callers see "pcode: AST node X not supported …"
	// instead of getting a silently-broken module back.
	for _, w := range pcMod.Warnings {
		fmt.Fprintln(os.Stderr, w)
	}

	// Build a FrbModule from the pcode functions. Mirrors what
	// hbrt/frb.go's frbLoadPcode does, but without the disk hop.
	frbMod := &hbrt.FrbModule{
		Name:      "dynamic",
		LocalSyms: make(map[string]*hbrt.Symbol),
		OldSyms:   make(map[string]*hbrt.Symbol),
		BindMode:  hbrt.FrbBindDefault,
		VM:        vm,
	}
	for name, fn := range pcMod.Funcs {
		pcFn := fn
		pcModRef := pcMod
		goFunc := func(t *hbrt.Thread) {
			hbrt.ExecPcode(t, pcFn, pcModRef)
		}
		frbMod.LocalSyms[name] = &hbrt.Symbol{
			Name:  name,
			Scope: hbrt.FsPublic | hbrt.FsLocal,
			Func:  goFunc,
		}
	}
	// Register non-Main symbols globally (Main stays module-local).
	for name, sym := range frbMod.LocalSyms {
		if name == "MAIN" {
			continue
		}
		old := vm.FindSymbol(name)
		if old != nil {
			frbMod.OldSyms[name] = old
			continue
		}
		vm.RegisterSymbol(sym)
		frbMod.Registered = append(frbMod.Registered, name)
	}
	return frbMod, nil
}

// findFiveExe locates the 'five' compiler binary
func findFiveExe() string {
	// 1. Check same directory as running executable
	if exe, err := os.Executable(); err == nil {
		dir := filepath.Dir(exe)
		fiveExe := filepath.Join(dir, "five")
		if _, err := os.Stat(fiveExe); err == nil {
			return fiveExe
		}
	}
	// 2. Check PATH
	if p, err := exec.LookPath("five"); err == nil {
		return p
	}
	// 3. Check current directory
	if _, err := os.Stat("./five"); err == nil {
		abs, _ := filepath.Abs("./five")
		return abs
	}
	return "five" // hope it's in PATH
}

// FRBLOAD(cFileName) → pModule
func FrbLoadFunc(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	filename := t.Local(1).AsString()
	mod, err := hbrt.FrbLoad(t.VM(), filename)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FrbLoad error: %v\n", err)
		t.RetNil()
		return
	}
	t.RetPointer(mod)
}

// FRBDO(pModule, cFuncName [, args...]) → xResult
func FrbDoFunc(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	modVal := t.Local(1)
	funcName := strings.ToUpper(t.Local(2).AsString())

	// Look up function: module-local scope first, then VM global
	var fn func(*hbrt.Thread)
	if modVal.IsPointer() {
		if mod, ok := modVal.AsPointer().(*hbrt.FrbModule); ok {
			fn = mod.FindFunc(funcName)
		}
	}
	if fn == nil {
		sym := t.VM().FindSymbol(funcName)
		if sym != nil {
			fn = sym.Func
		}
	}
	if fn == nil {
		t.RetNil()
		return
	}

	// Snapshot SP *before* pushing args. After the inner call,
	// Frame()/PcOpRetValue should have left SP back at this baseline,
	// but pcode-mode bodies can occasionally leak intermediate stack
	// values (e.g. FOR-loop control vestiges). Reseating SP to the
	// snapshot before reading retVal stops those leaks from polluting
	// the caller's argument frame — which is what made
	// `? "label", FrbDo(...), "tail"` show "1" or "2" in place of the
	// label string when the inner function had a loop.
	savedSP := t.SP()

	// Push args for the function
	for i := 3; i <= nParams; i++ {
		t.PushValue(t.Local(i))
	}
	t.PendingParams2(nParams - 2)
	fn(t)

	t.SetSP(savedSP)
	t.PushValue(t.GetRetValue())
	t.RetValue()
}

// FRBUNLOAD(pModule) → NIL
func FrbUnloadFunc(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	v := t.Local(1)
	if !v.IsNil() && v.IsPointer() {
		if mod, ok := v.AsPointer().(*hbrt.FrbModule); ok {
			hbrt.FrbUnload(mod)
		}
	}
	t.RetNil()
}

// FRBCOMPILE(cPrgSource) → pModule
// Compile PRG source string to FRB module in memory. In-process pcode
// compilation is the default — no external `five` binary or `go`
// toolchain needed at runtime. The legacy native-plugin path is still
// reachable via hbrt.FrbCompileSource for callers that want it, but
// that path is fragile (Go plugins require byte-identical runtime).
func FrbCompileFunc(t *hbrt.Thread) {
	t.Frame(1, 0)
	defer t.EndProc()

	source := t.Local(1).AsString()
	mod, err := frbCompileInProc(t.VM(), source)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FrbCompile error: %v\n", err)
		t.RetNil()
		return
	}
	t.RetPointer(mod)
}

// FRBEXEC(cPrgSource [, args...]) → xResult
// Compile PRG source, run Main(), unload — all in one call.
func FrbExecFunc(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	source := t.Local(1).AsString()
	mod, err := frbCompileInProc(t.VM(), source)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FrbExec error: %v\n", err)
		t.RetNil()
		return
	}
	defer hbrt.FrbUnload(mod)

	// Look up MAIN inside the freshly-compiled module first, NOT
	// via t.VM().FindSymbol — Main is intentionally kept module-local
	// (frbLoadPcode skips it during VM registration), so a global
	// lookup would resolve to the *caller's* Main and recurse forever.
	fn := mod.FindFunc("MAIN")
	if fn == nil {
		t.RetNil()
		return
	}

	savedSP := t.SP()
	for i := 2; i <= nParams; i++ {
		t.PushValue(t.Local(i))
	}
	t.PendingParams2(nParams - 1)
	fn(t)
	t.SetSP(savedSP)

	t.PushValue(t.GetRetValue())
	t.RetValue()
}

// FRBRUN(cFileName [, args...]) → xResult
// Load, execute startup function, unload — all in one call.
func FrbRunFunc(t *hbrt.Thread) {
	nParams := t.ParamCount()
	t.Frame(nParams, 0)
	defer t.EndProc()

	filename := t.Local(1).AsString()
	mod, err := hbrt.FrbLoad(t.VM(), filename)
	if err != nil {
		t.RetNil()
		return
	}
	defer hbrt.FrbUnload(mod)

	// Same module-local Main lookup as FrbExec — see comment there
	// for why a t.VM().FindSymbol("MAIN") would recurse into the
	// outer (caller's) Main.
	fn := mod.FindFunc("MAIN")
	if fn == nil {
		t.RetNil()
		return
	}

	savedSP := t.SP()
	for i := 2; i <= nParams; i++ {
		t.PushValue(t.Local(i))
	}
	t.PendingParams2(nParams - 1)
	fn(t)
	t.SetSP(savedSP)

	t.PushValue(t.GetRetValue())
	t.RetValue()
}