package printer

import (
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	"github.com/mmcloughlin/avo"
)

type Printer interface {
	Print(*avo.File) ([]byte, error)
}

type Builder func(Config) Printer

type Config struct {
	Name string
	Argv []string
	Pkg  string
}

func NewDefaultConfig() Config {
	return Config{
		Name: "avo",
		Pkg:  pkg(),
	}
}

func NewArgvConfig() Config {
	return Config{
		Argv: os.Args,
		Pkg:  pkg(),
	}
}

// NewGoRunConfig produces a Config for a generator that's expected to be
// executed via "go run ...".
func NewGoRunConfig() Config {
	path := mainfile()
	if path == "" {
		return NewDefaultConfig()
	}
	argv := []string{"go", "run", filepath.Base(path)}
	if len(os.Args) > 1 {
		argv = append(argv, os.Args[1:]...)
	}
	return Config{
		Argv: argv,
		Pkg:  pkg(),
	}
}

func (c Config) GeneratedBy() string {
	if c.Argv == nil {
		return c.Name
	}
	return fmt.Sprintf("command: %s", strings.Join(c.Argv, " "))
}

func (c Config) GeneratedWarning() string {
	return fmt.Sprintf("Code generated by %s. DO NOT EDIT.", c.GeneratedBy())
}

// mainfile attempts to determine the file path of the main function by
// inspecting the stack. Returns empty string on failure.
func mainfile() string {
	pc := make([]uintptr, 10)
	n := runtime.Callers(0, pc)
	if n == 0 {
		return ""
	}
	pc = pc[:n]
	frames := runtime.CallersFrames(pc)
	for {
		frame, more := frames.Next()
		if frame.Function == "main.main" {
			return frame.File
		}
		if !more {
			break
		}
	}
	return ""
}

// pkg guesses the name of the package from the working directory.
func pkg() string {
	if cwd, err := os.Getwd(); err == nil {
		return filepath.Base(cwd)
	}
	return ""
}