package main

import (
	"flag"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"

	"gotlin/internal/lang"
)

func main() {
	if len(os.Args) < 2 {
		usage()
	}

	switch os.Args[1] {
	case "build":
		runBuild(os.Args[2:])
	case "run":
		runRun(os.Args[2:])
	default:
		runBuild(os.Args[1:])
	}
}

func runBuild(args []string) {
	fs := flag.NewFlagSet("build", flag.ExitOnError)
	srcOnly := fs.Bool("src", false, "emit Go source instead of building an executable")
	outPath := fs.String("o", "", "output file path")
	fs.Usage = func() {
		fmt.Fprintln(os.Stderr, "usage: gotlinc build [-src] [-o output] <input.gt>")
	}
	normalizedArgs, err := normalizeBuildArgs(args)
	if err != nil {
		fail(err)
	}
	if err := fs.Parse(normalizedArgs); err != nil {
		fail(err)
	}
	if fs.NArg() != 1 {
		fs.Usage()
		os.Exit(2)
	}

	inputPath := fs.Arg(0)
	goSrc := compileFile(inputPath, !*srcOnly)

	if *srcOnly {
		if *outPath == "" {
			_, _ = os.Stdout.WriteString(goSrc)
			return
		}
		if err := os.WriteFile(*outPath, []byte(goSrc), 0o644); err != nil {
			fail(err)
		}
		return
	}

	outputPath := *outPath
	if outputPath == "" {
		outputPath = defaultExecutablePath(inputPath)
	}

	if err := buildExecutable(goSrc, outputPath); err != nil {
		fail(err)
	}
}

func runRun(args []string) {
	fs := flag.NewFlagSet("run", flag.ExitOnError)
	fs.Usage = func() {
		fmt.Fprintln(os.Stderr, "usage: gotlinc run <input.gt> [program args...]")
	}
	if err := fs.Parse(args); err != nil {
		fail(err)
	}
	if fs.NArg() < 1 {
		fs.Usage()
		os.Exit(2)
	}

	inputPath := fs.Arg(0)
	goSrc := compileFile(inputPath, true)

	tmpFile, err := os.CreateTemp("", "gotlinc-*.go")
	if err != nil {
		fail(err)
	}
	tmpPath := tmpFile.Name()
	defer os.Remove(tmpPath)

	if _, err := tmpFile.WriteString(goSrc); err != nil {
		_ = tmpFile.Close()
		fail(err)
	}
	if err := tmpFile.Close(); err != nil {
		fail(err)
	}

	cmdArgs := append([]string{"run", tmpPath}, fs.Args()[1:]...)
	cmd := exec.Command("go", cmdArgs...)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Stdin = os.Stdin
	if err := cmd.Run(); err != nil {
		fail(err)
	}
}

func compileFile(inputPath string, forceMain bool) string {
	src, err := os.ReadFile(inputPath)
	if err != nil {
		fail(err)
	}

	program, err := lang.Parse(string(src))
	if err != nil {
		fail(err)
	}

	var goSrc []byte
	if forceMain {
		goSrc, err = lang.GenerateGoMain(program)
	} else {
		goSrc, err = lang.GenerateGo(program)
	}
	if err != nil {
		fail(err)
	}
	if forceMain {
		return addBestEffortLineDirectives(string(goSrc), inputPath, string(src))
	}
	return string(goSrc)
}

func buildExecutable(goSrc string, outputPath string) error {
	tmpFile, err := os.CreateTemp("", "gotlinc-build-*.go")
	if err != nil {
		return err
	}
	tmpPath := tmpFile.Name()
	defer os.Remove(tmpPath)

	if _, err := tmpFile.WriteString(goSrc); err != nil {
		_ = tmpFile.Close()
		return err
	}
	if err := tmpFile.Close(); err != nil {
		return err
	}

	cmd := exec.Command("go", "build", "-o", outputPath, tmpPath)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Stdin = os.Stdin
	return cmd.Run()
}

func defaultExecutablePath(inputPath string) string {
	base := strings.TrimSuffix(filepath.Base(inputPath), filepath.Ext(inputPath))
	if runtime.GOOS == "windows" && filepath.Ext(base) != ".exe" {
		base += ".exe"
	}
	return base
}

func normalizeBuildArgs(args []string) ([]string, error) {
	var flags []string
	var positional []string

	for i := 0; i < len(args); i++ {
		arg := args[i]
		switch {
		case arg == "-src":
			flags = append(flags, arg)
		case arg == "-o":
			if i+1 >= len(args) {
				return nil, fmt.Errorf("missing value for -o")
			}
			flags = append(flags, arg, args[i+1])
			i++
		case strings.HasPrefix(arg, "-o="):
			flags = append(flags, arg)
		case strings.HasPrefix(arg, "-"):
			flags = append(flags, arg)
		default:
			positional = append(positional, arg)
		}
	}

	return append(flags, positional...), nil
}

func usage() {
	fmt.Fprintln(os.Stderr, "usage:")
	fmt.Fprintln(os.Stderr, "  gotlinc build [-src] [-o output] <input.gt>")
	fmt.Fprintln(os.Stderr, "  gotlinc run <input.gt> [program args...]")
	fmt.Fprintln(os.Stderr, "")
	fmt.Fprintln(os.Stderr, "default command: build")
	os.Exit(2)
}

func fail(err error) {
	fmt.Fprintln(os.Stderr, err)
	os.Exit(1)
}

func addBestEffortLineDirectives(goSrc string, inputPath string, gtSrc string) string {
	fnLines := sourceFunctionLines(gtSrc)
	if len(fnLines) == 0 {
		return goSrc
	}

	pattern := regexp.MustCompile(`^\s*func\s+(?:\(\s*[^)]*\)\s+)?([A-Za-z_][A-Za-z0-9_]*)\s*\(`)
	lines := strings.Split(goSrc, "\n")
	out := make([]string, 0, len(lines)+len(fnLines))
	for _, line := range lines {
		m := pattern.FindStringSubmatch(line)
		if len(m) == 2 {
			if gtLine, ok := fnLines[m[1]]; ok {
				out = append(out, fmt.Sprintf("//line %s:%d", inputPath, gtLine))
			}
		}
		out = append(out, line)
	}
	return strings.Join(out, "\n")
}

func sourceFunctionLines(src string) map[string]int {
	out := map[string]int{}
	pattern := regexp.MustCompile(`^\s*fun\s+([A-Za-z_][A-Za-z0-9_]*)\s*\(`)
	lines := strings.Split(src, "\n")
	for i, line := range lines {
		m := pattern.FindStringSubmatch(line)
		if len(m) == 2 {
			if _, exists := out[m[1]]; !exists {
				out[m[1]] = i + 1
			}
		}
	}
	return out
}