// Package upstream loads and explicitly synchronizes the reviewed Gitea snapshot.
package upstream

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
)

type Lock struct {
	Schema     int               `json:"schema"`
	Repository string            `json:"repository"`
	Tag        string            `json:"tag"`
	Commit     string            `json:"commit"`
	Files      map[string]string `json:"files"`
}

type Snapshot struct {
	Lock      Lock
	Files     map[string][]byte
	Templates map[string][]byte // mail/... paths, including shared partials
	Locales   map[string]map[string]string
}

// AdapterSources also binds the preview's formatting and rendering semantics to
// the upstream implementation reviewed during this migration. A changed source
// requires reviewing the adapter before accepting another snapshot.
var AdapterSources = map[string]string{
	"modules/translation/translation.go":      "4217cbd9beb79c0e1be52dd9a7d7705b9ff4becc2d9515d49236db126da0f7ee",
	"modules/translation/i18n/localestore.go": "e55a7832d01753622a7d47e904de95e5aed7ad3535c59bf6ac3fec4346e40e9d",
	"modules/translation/i18n/format.go":      "f440236eaf1f73fe0a9aa36a2c036a4b34c6ab28c9e4cf971bef7fceee701cb4",
	"modules/templates/mail.go":               "fb8204b79f700f88c7c3f0da16e50c3d678a2216e62e98f712805ed1d42ab3a9",
}

func Digest(data []byte) string {
	h := sha256.Sum256(data)
	return hex.EncodeToString(h[:])
}

func SafePath(p string) bool {
	return p != "." && fs.ValidPath(p) && !strings.ContainsAny(p, "\\:")
}

func Load(dir string) (*Snapshot, error) {
	s, err := loadFiles(dir)
	if err != nil {
		return nil, err
	}
	return s, s.validate()
}

// Ownership/checksum validation is separate so explicitly syncing after an
// adapter review can replace an older, still intact snapshot.
func loadFiles(dir string) (*Snapshot, error) {
	data, err := os.ReadFile(filepath.Join(dir, "lock.json"))
	if err != nil {
		return nil, fmt.Errorf("snapshot lock: %w (run upstream sync explicitly)", err)
	}
	s := &Snapshot{Files: map[string][]byte{}}
	if err := json.Unmarshal(data, &s.Lock); err != nil {
		return nil, err
	}
	if err := s.Lock.validateIdentity(); err != nil {
		return nil, err
	}
	for p, expected := range s.Lock.Files {
		if !SafePath(p) {
			return nil, fmt.Errorf("unsafe snapshot path %q", p)
		}
		b, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(p)))
		if err != nil {
			return nil, err
		}
		if Digest(b) != expected {
			return nil, fmt.Errorf("snapshot checksum mismatch: %s", p)
		}
		s.Files[p] = b
	}
	// Unlocked files must not silently become input to a build.
	err = filepath.WalkDir(dir, func(p string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.Type()&os.ModeSymlink != 0 {
			return fmt.Errorf("snapshot symlinks are unsupported: %s", p)
		}
		if d.IsDir() {
			return nil
		}
		rel, _ := filepath.Rel(dir, p)
		rel = filepath.ToSlash(rel)
		if rel != "lock.json" {
			if _, ok := s.Files[rel]; !ok {
				return fmt.Errorf("unlocked snapshot file: %s", rel)
			}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	return s, nil
}

func (lock Lock) validateIdentity() error {
	if lock.Schema != 1 || lock.Repository != "https://github.com/go-gitea/gitea" || !validTag(lock.Tag) || len(lock.Commit) != 40 || len(lock.Files) == 0 {
		return fmt.Errorf("invalid snapshot identity or unsupported version")
	}
	if _, err := hex.DecodeString(lock.Commit); err != nil {
		return fmt.Errorf("invalid snapshot commit: %w", err)
	}
	return nil
}

func (s *Snapshot) validate() error {
	if err := s.Lock.validateIdentity(); err != nil {
		return err
	}
	for p, hash := range AdapterSources {
		if Digest(s.Files[p]) != hash {
			return fmt.Errorf("upstream adapter changed: %s; review preview semantics before syncing", p)
		}
	}
	if len(s.Files["LICENSE"]) == 0 {
		return fmt.Errorf("missing upstream license")
	}
	s.Templates = map[string][]byte{}
	s.Locales = map[string]map[string]string{}
	for p, b := range s.Files {
		switch {
		case p == "public/assets/img/favicon.png":
			if len(b) == 0 {
				return fmt.Errorf("missing preview favicon")
			}
		case strings.HasPrefix(p, "templates/mail/") && strings.HasSuffix(p, ".tmpl"):
			s.Templates[strings.TrimPrefix(p, "templates/")] = b
		case strings.HasPrefix(p, "options/locale/locale_") && strings.HasSuffix(p, ".json"):
			locale := strings.TrimSuffix(strings.TrimPrefix(p, "options/locale/locale_"), ".json")
			values, err := DecodeLocale(b)
			if err != nil {
				return fmt.Errorf("%s: %w", p, err)
			}
			s.Locales[locale] = values
		default:
			if p != "LICENSE" {
				if _, ok := AdapterSources[p]; !ok {
					return fmt.Errorf("unsupported snapshot file: %s", p)
				}
			}
		}
	}
	if len(s.Entrypoints()) == 0 || len(s.Templates["mail/base/head.tmpl"]) == 0 || len(s.Templates["mail/base/footer.tmpl"]) == 0 || len(s.Locales["en-US"]) == 0 {
		return fmt.Errorf("snapshot is missing entrypoints, shared partials, or English translations")
	}
	return ValidateKeys(s)
}

// DecodeLocale mirrors Gitea's flat or one-level nested JSON catalog layout.
func DecodeLocale(data []byte) (map[string]string, error) {
	var raw map[string]any
	if err := json.Unmarshal(data, &raw); err != nil {
		return nil, err
	}
	result := map[string]string{}
	for k, v := range raw {
		switch v := v.(type) {
		case string:
			result[k] = v
		case map[string]any:
			for inner, value := range v {
				str, ok := value.(string)
				if !ok {
					return nil, fmt.Errorf("unsupported translation value: %s.%s", k, inner)
				}
				result[k+"."+inner] = str
			}
		default:
			return nil, fmt.Errorf("unsupported translation value: %s", k)
		}
	}
	return result, nil
}

func (s *Snapshot) Entrypoints() []string {
	var result []string
	for p := range s.Templates {
		if !strings.HasPrefix(p, "mail/base/") {
			result = append(result, p)
		}
	}
	sort.Strings(result)
	return result
}

func (s *Snapshot) Languages() []string {
	var langs []string
	for l := range s.Locales {
		langs = append(langs, l)
	}
	sort.Strings(langs)
	return langs
}

func TemplateID(p string) string { return strings.TrimSuffix(path.Base(p), ".tmpl") }