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

// FRB in-memory compilation — compile PRG source at runtime and execute.
// This is Five's equivalent of Harbour's hb_compileFromBuf() + hb_hrbRun().
//
// Usage from PRG:
//   pMod := FrbCompile(cPrgSource)        // compile PRG string → FRB in memory
//   result := FrbDo(pMod, "MYFUNC", args) // call compiled function
//   FrbUnload(pMod)
//
//   // Or one-shot:
//   result := FrbExec(cPrgSource)          // compile + run Main() + unload

package hbrt

import (
	"encoding/binary"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"plugin"
)

// FrbCompileSource compiles PRG source code to an FRB module in memory.
// Strategy:
//   1. If Go isn't installed, go straight to pcode mode.
//   2. Try the native Go-plugin path first (faster, native speed).
//   3. If the plugin build fails, OR if loading the resulting plugin
//      fails (the most common failure: "plugin was built with a
//      different version of package runtime", which fires whenever
//      the host binary and the plugin weren't compiled byte-for-byte
//      against the same Go runtime — happens routinely after `go
//      build` rebuilds), fall back to pcode mode. Pcode is a few x
//      slower but always works.
func FrbCompileSource(vm *VM, prgSource string, fiveExe string) (*FrbModule, error) {
	if !isGoAvailable() {
		return frbCompilePcode(vm, prgSource, fiveExe)
	}

	mod, err := frbCompilePlugin(vm, prgSource, fiveExe)
	if err == nil {
		return mod, nil
	}
	// Plugin path failed — try pcode. Don't surface the plugin
	// error: pcode either works (return its module) or doesn't
	// (return its error).
	return frbCompilePcode(vm, prgSource, fiveExe)
}

// frbCompilePlugin is the original native-plugin path, factored out
// of FrbCompileSource so the latter can pick a fallback on failure.
func frbCompilePlugin(vm *VM, prgSource string, fiveExe string) (*FrbModule, error) {
	tmpDir, err := os.MkdirTemp("", "frb-mem-*")
	if err != nil {
		return nil, err
	}

	// Write PRG source to temp file with unique name
	prgFile := filepath.Join(tmpDir, fmt.Sprintf("dynamic_%d.prg", frbSeq))
	frbSeq++
	if err := os.WriteFile(prgFile, []byte(prgSource), 0644); err != nil {
		os.RemoveAll(tmpDir)
		return nil, err
	}

	// Find five executable
	if fiveExe == "" {
		fiveExe, _ = os.Executable()
	}

	// Compile PRG → FRB using five frb command
	frbFile := filepath.Join(tmpDir, "dynamic.frb")
	cmd := exec.Command(fiveExe, "frb", prgFile, "-o", frbFile)
	if output, err := cmd.CombinedOutput(); err != nil {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("compile failed: %s\n%w", string(output), err)
	}

	// Load FRB
	mod, err := FrbLoad(vm, frbFile)
	if err != nil {
		os.RemoveAll(tmpDir)
		return nil, err
	}
	// Override TempDir to clean up everything
	mod.TempDir = tmpDir

	return mod, nil
}

// FrbCompileDirect compiles PRG source directly to a Go plugin without
// going through the five CLI. Uses the compiler packages directly.
// This is faster than FrbCompileSource for hot compilation.
func FrbCompileDirect(vm *VM, prgSource string) (*FrbModule, error) {
	tmpDir, err := os.MkdirTemp("", "frb-direct-*")
	if err != nil {
		return nil, err
	}

	// We need the Five project root for go.mod replace directive
	fiveRoot := findFiveRoot()
	if fiveRoot == "" {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("cannot find Five project root (go.mod)")
	}

	// Write Go source — import compiler packages inline
	// This uses exec to run a helper that does the compilation
	helperSrc := fmt.Sprintf(`package main
import (
	"five/compiler/gengo"
	"five/compiler/parser"
	"five/compiler/pp"
	"fmt"
	"os"
)
func main() {
	source := %q
	pre := pp.New()
	processed, _ := pre.Process("dynamic.prg", source)
	file, errs := parser.Parse("dynamic.prg", processed)
	if len(errs) > 0 {
		for _, e := range errs { fmt.Fprintln(os.Stderr, e) }
		os.Exit(1)
	}
	goSrc := gengo.GenerateLibrary(file)
	fmt.Print(goSrc)
}
`, prgSource)

	helperFile := filepath.Join(tmpDir, "helper.go")
	os.WriteFile(helperFile, []byte(helperSrc), 0644)

	// Write go.mod for helper
	goMod := fmt.Sprintf("module frbhelper\n\ngo 1.21\n\nrequire five v0.0.0\nreplace five => %s\n", fiveRoot)
	os.WriteFile(filepath.Join(tmpDir, "go.mod"), []byte(goMod), 0644)

	// Run go mod tidy + generate
	tidyCmd := exec.Command("go", "mod", "tidy")
	tidyCmd.Dir = tmpDir
	tidyCmd.CombinedOutput()

	genCmd := exec.Command("go", "run", "helper.go")
	genCmd.Dir = tmpDir
	goSrcBytes, err := genCmd.Output()
	if err != nil {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("codegen failed: %w", err)
	}

	// Write generated module.go
	os.WriteFile(filepath.Join(tmpDir, "module.go"), goSrcBytes, 0644)
	os.Remove(helperFile) // remove helper, keep module.go

	// Build plugin
	soFile := filepath.Join(tmpDir, "module.so")
	buildCmd := exec.Command("go", "build", "-buildmode=plugin", "-o", soFile, "module.go")
	buildCmd.Dir = tmpDir
	if output, err := buildCmd.CombinedOutput(); err != nil {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("plugin build failed: %s\n%w", string(output), err)
	}

	// Load plugin
	p, err := plugin.Open(soFile)
	if err != nil {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("plugin load failed: %w", err)
	}

	vm.RegisterLibModules()

	return &FrbModule{
		Name:    "<dynamic>",
		Plugin:  p,
		TempDir: tmpDir,
	}, nil
}

// findFiveRoot locates the Five project root by searching for go.mod
func findFiveRoot() string {
	// Try executable location first
	if exe, err := os.Executable(); err == nil {
		dir := filepath.Dir(exe)
		for d := dir; ; d = filepath.Dir(d) {
			if _, err := os.Stat(filepath.Join(d, "go.mod")); err == nil {
				return d
			}
			if d == filepath.Dir(d) {
				break
			}
		}
	}
	// Try current directory
	if cwd, err := os.Getwd(); err == nil {
		for d := cwd; ; d = filepath.Dir(d) {
			if _, err := os.Stat(filepath.Join(d, "go.mod")); err == nil {
				return d
			}
			if d == filepath.Dir(d) {
				break
			}
		}
	}
	return ""
}

var frbSeq int // sequence number for unique module names

// isGoAvailable checks if the Go compiler is installed.
func isGoAvailable() bool {
	for _, p := range []string{"go", "/usr/local/go/bin/go", "/usr/bin/go"} {
		if _, err := exec.LookPath(p); err == nil {
			return true
		}
		if _, err := os.Stat(p); err == nil {
			return true
		}
	}
	return false
}

// frbCompilePcode compiles PRG source to pcode FRB (no Go needed).
func frbCompilePcode(vm *VM, prgSource string, fiveExe string) (*FrbModule, error) {
	tmpDir, err := os.MkdirTemp("", "frb-pcode-*")
	if err != nil {
		return nil, err
	}

	prgFile := filepath.Join(tmpDir, fmt.Sprintf("dynamic_%d.prg", frbSeq))
	frbSeq++
	os.WriteFile(prgFile, []byte(prgSource), 0644)

	frbFile := filepath.Join(tmpDir, "dynamic.frb")
	cmd := exec.Command(fiveExe, "frb", prgFile, "-o", frbFile, "--pcode")
	if output, err := cmd.CombinedOutput(); err != nil {
		os.RemoveAll(tmpDir)
		return nil, fmt.Errorf("pcode compile failed: %s\n%w", string(output), err)
	}

	mod, err := FrbLoad(vm, frbFile)
	if err != nil {
		os.RemoveAll(tmpDir)
		return nil, err
	}
	mod.TempDir = tmpDir
	return mod, nil
}

var _ = binary.LittleEndian // keep import