package main

// see `man 5 githooks` for details

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

func main() {
	log.SetFlags(0)

	defer log.Println("Exiting craft")
	log.Println("Starting craft")

	hookType := getHookType()
	log.Printf("Git hook type: %s\n", hookType)

	repo := getRepositoryPath()
	log.Printf("Git repository: %s\n", repo)

	for {
		eof, update := getUpdate()
		if eof {
			break
		}
		log.Printf("Git ref update: %s\n", update)
		commit := update.updated
		workbench := prepareWorkbench(repo, commit)
		defer os.RemoveAll(workbench)
		craft(workbench)
	}
}

func runCommand(dir string, name string, args ...string) {
	log.Printf("%s %s\n", name, strings.Join(args, " "))
	command := exec.Command(name, args...)
	command.Dir = dir
	command.Stderr = os.Stderr
	command.Stdout = os.Stdout
	err := command.Run()
	if err != nil {
		log.Fatal(err)
	}
}

func craft(workbench string) {
	script := `#!/bin/sh

source craft.sh
build
`

	cmd := exec.Command("busybox", "ash")
	cmd.Dir = workbench
	cmd.Stdin = bytes.NewBufferString(script)
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	err := cmd.Run()
	if err != nil {
		log.Fatal(err)
	}
}

func prepareWorkbench(repo string, commit string) string {
	workbench, err := os.MkdirTemp("", "*-craft")
	if err != nil {
		log.Fatal(err)
	}

	runCommand(
		workbench,
		"git",
		"clone",
		repo,
		workbench,
	)

	runCommand(
		workbench,
		"git",
		"--git-dir",
		filepath.Join(workbench, ".git"),
		"--work-tree",
		workbench,
		"checkout",
		commit,
	)

	runCommand(
		workbench,
		"git",
		"--git-dir",
		filepath.Join(workbench, ".git"),
		"--work-tree",
		workbench,
		"submodule",
		"update",
		"--depth=1",
		"--init",
		"--recursive",
	)

	return workbench
}

func getHookType() string {
	args := len(os.Args)
	if args != 1 {
		log.Fatalf("Expected zero arguments but %d were given", args-1)
	}
	prefix := `hooks/`
	path := os.Args[0]
	hookType := strings.TrimPrefix(path, prefix)
	if path == hookType {
		log.Fatalf("Hook path '%s' has no '%s' prefix", path, prefix)
	}
	validateHookType(hookType)
	return hookType
}

func validateHookType(hookType string) {
	validTypes := [...]string{
		`post-receive`,
	}
	for _, currentType := range validTypes {
		if hookType == currentType {
			return
		}
	}
	log.Fatalf("Not supported Git hook type '%s'\n", hookType)
}

func getRepositoryPath() string {
	cwd, err := os.Getwd()
	if err != nil {
		log.Fatal(err)
	}
	return cwd
}

type update struct {
	old, updated, ref string
}

func (u update) String() string {
	ret := fmt.Sprintf("'%s' from '%s' to '%s'", u.ref, u.old, u.updated)
	return ret
}

func getUpdate() (bool, update) {
	var u update
	_, err := fmt.Scanf("%s %s %s\n", &u.old, &u.updated, &u.ref)
	if err != nil {
		if errors.Is(err, io.EOF) {
			return true, u
		} else {
			log.Fatal(err)
		}
	}
	return false, u
}