package upstream

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"reflect"
	"time"
)

func CacheDir(root string) string { return filepath.Join(root, "build", "upstream") }

func ReadLock(root string) (Lock, error) {
	var lock Lock
	b, err := os.ReadFile(filepath.Join(root, "gitea.lock.json"))
	if err != nil {
		return lock, err
	}
	if err = json.Unmarshal(b, &lock); err != nil {
		return lock, err
	}
	return lock, lock.validateIdentity()
}

func LoadPinned(root string) (*Snapshot, error) {
	lock, err := ReadLock(root)
	if err != nil {
		return nil, err
	}
	s, err := Load(CacheDir(root))
	if err != nil {
		return nil, err
	}
	if !reflect.DeepEqual(lock, s.Lock) {
		return nil, fmt.Errorf("upstream cache differs from gitea.lock.json; run upstream prepare after reviewing the lock")
	}
	return s, nil
}

// Prepare fetches immutable commit files only if the cache is absent. A corrupt
// cache is an error, not permission to silently replace local evidence.
func Prepare(ctx context.Context, root string) (*Snapshot, error) {
	return prepareFrom(ctx, root, "https://raw.githubusercontent.com/go-gitea/gitea/")
}

func prepareFrom(ctx context.Context, root, rawBase string) (*Snapshot, error) {
	lock, err := ReadLock(root)
	if err != nil {
		return nil, err
	}
	if _, err = os.Stat(filepath.Join(CacheDir(root), "lock.json")); err == nil {
		return LoadPinned(root)
	} else if !os.IsNotExist(err) {
		return nil, err
	}
	client := &http.Client{Timeout: 45 * time.Second}
	s := &Snapshot{Lock: lock, Files: map[string][]byte{}}
	for name, hash := range lock.Files {
		if !SafePath(name) {
			return nil, fmt.Errorf("unsafe locked path %q", name)
		}
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, rawBase+lock.Commit+"/"+name, nil)
		if err != nil {
			return nil, err
		}
		req.Header.Set("User-Agent", "GiteaMailTemplates-locked-cache")
		resp, err := client.Do(req)
		if err != nil {
			return nil, err
		}
		b, readErr := io.ReadAll(io.LimitReader(resp.Body, 16<<20))
		resp.Body.Close()
		if readErr != nil {
			return nil, readErr
		}
		if resp.StatusCode != http.StatusOK {
			return nil, fmt.Errorf("%s: HTTP %d", name, resp.StatusCode)
		}
		if Digest(b) != hash {
			return nil, fmt.Errorf("download checksum mismatch: %s", name)
		}
		s.Files[name] = b
	}
	if err = s.validate(); err != nil {
		return nil, err
	}
	dir := CacheDir(root)
	if err = os.MkdirAll(filepath.Dir(dir), 0755); err != nil {
		return nil, err
	}
	stage, err := os.MkdirTemp(filepath.Dir(dir), ".upstream-cache-")
	if err != nil {
		return nil, err
	}
	defer os.RemoveAll(stage)
	for name, b := range s.Files {
		target := filepath.Join(stage, filepath.FromSlash(name))
		if err = os.MkdirAll(filepath.Dir(target), 0755); err != nil {
			return nil, err
		}
		if err = os.WriteFile(target, b, 0644); err != nil {
			return nil, err
		}
	}
	b, _ := json.MarshalIndent(lock, "", "  ")
	if err = os.WriteFile(filepath.Join(stage, "lock.json"), append(b, '\n'), 0644); err != nil {
		return nil, err
	}
	if _, err = os.Stat(dir); err == nil {
		return nil, fmt.Errorf("incomplete upstream cache exists at %s; inspect it before removing it", dir)
	}
	if err = os.Rename(stage, dir); err != nil {
		return nil, err
	}
	fmt.Printf("[PASS] Downloaded locked Gitea %s (%s) to build cache\n", lock.Tag, lock.Commit)
	return LoadPinned(root)
}

func SyncRoot(ctx context.Context, tag, root string) error {
	if err := os.MkdirAll(filepath.Join(root, "build"), 0755); err != nil {
		return err
	}
	if err := Sync(ctx, tag, CacheDir(root)); err != nil {
		return err
	}
	s, err := Load(CacheDir(root))
	if err != nil {
		return err
	}
	b, err := json.MarshalIndent(s.Lock, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(filepath.Join(root, "gitea.lock.json"), append(b, '\n'), 0644)
}