// Copyright (C) 2024  Umorpha Systems
// SPDX-License-Identifier: AGPL-3.0-or-later

package gitcache

import (
	"errors"
	"os"
	"os/exec"
	"path/filepath"
	"sync"
	"time"
	"io"
	"fmt"
)

const tsDir = "x-gitcache-ts"

type Cache struct {
	Dir       string
	MinPeriod time.Duration

	initOnce sync.Once
	initErr  error
}

// "ll" stands for "low level" /////////////////////////////////////////////////

func (cache *Cache) llInit(stderr io.Writer) error {
	fmt.Fprintf(stderr, "[gitcache] Initializing cache...\n")
	cmd := exec.Command("git", "init", "--bare", cache.Dir)
	cmd.Stderr = stderr
	if err := cmd.Run(); err != nil {
		return err
	}
	if err := os.Mkdir(filepath.Join(cache.Dir, tsDir), 0o777); err != nil && !errors.Is(err, os.ErrExist) {
		return err
	}
	return nil
}

func (cache *Cache) llFetch(stderr io.Writer, namespace, url string) error {
	fmt.Fprintf(stderr, "[gitcache] Fetching %q...\n", url)
	cmd := exec.Command("git",
		"fetch",
		"--no-write-fetch-head",
		"--no-recurse-submodules",
		"--no-tags",
		"--prune",
		"--",
		url, "*:refs/namespaces/"+namespace+"/*")
	cmd.Dir = cache.Dir
	cmd.Stderr = stderr
	return cmd.Run()
}

////////////////////////////////////////////////////////////////////////////////

func (cache *Cache) init(stderr io.Writer) error {
	cache.initOnce.Do(func() {
		cache.initErr = cache.llInit(stderr)
	})
	return cache.initErr
}

func (cache *Cache) Fetch(stderr io.Writer, url string) error {
	if err := cache.init(stderr); err != nil {
		return err
	}
	id := url2id(url)
	tsFile := filepath.Join(cache.Dir, tsDir, id)
	if cache.MinPeriod != 0 {
		ts, err := mtime(tsFile)
		if err == nil && ts.Add(cache.MinPeriod).After(time.Now()) {
			return nil
		}
	}
	if err := cache.llFetch(stderr, id, url); err != nil {
		return err
	}
	return touch(tsFile)
}

func (cache *Cache) Clone(stderr io.Writer, url, dir string, flags ...string) error {
	if err := cache.Fetch(stderr, url); err != nil {
		return err
	}

	cacheDir, err := filepath.Abs(cache.Dir)
	if err != nil {
		return err
	}
	cacheURL := "ext::git --namespace " + url2id(url) + " %s " + cacheDir

	fmt.Fprintf(stderr, "[gitcache] Cloning %q to %q...\n", url, dir)
	cmd := exec.Command("git", append(append([]string{
		"-c", "protocol.ext.allow=user",
		"-c", "url." + cacheURL + ".insteadOf=" + url,
		"clone",
	}, flags...), "--", url, dir)...)
	cmd.Stderr = stderr
	if err := cmd.Run(); err != nil {
		return err
	}

	return nil
}

func (cache *Cache) RevParse(stderr io.Writer, url, rev string) (string, error) {
	if err := cache.Fetch(stderr, url); err != nil {
		return "", err
	}

	// `git rev-parse` doesn't obey `--namespace`, so we have to
	// create a temporary clone to do this :(
	tmpdir, err := os.MkdirTemp("", "gitcache-revparse")
	if err != nil {
		return "", err
	}
	defer os.RemoveAll(tmpdir)
	gitdir := filepath.Join(tmpdir, "clone.git")
	if err := cache.Clone(stderr, url, gitdir, "--mirror"); err != nil {
		return "", err
	}

	cmd := exec.Command("git", "rev-parse", "--verify", rev)
	cmd.Dir = gitdir
	cmd.Stderr = stderr
	out, err := cmd.Output()
	if err != nil {
		return "", err
	}
	return string(out[:len(out)-1]), nil
}