package synthetic

import (
	"encoding/json"
	"fmt"
	"hash/fnv"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"
	"unicode"

	"github.com/uopi/uopi/internal/datasource"
)

// VersionMeta describes a single persisted revision of a synthetic signal,
// mirroring storage.VersionMeta so the frontend treats every versioned document
// type uniformly.
type VersionMeta struct {
	Version int       `json:"version"`
	Name    string    `json:"name"`
	Tag     string    `json:"tag,omitempty"`
	Current bool      `json:"current"`
	SavedAt time.Time `json:"savedAt"`
}

func (s *Synthetic) versionsDir() string {
	return filepath.Join(s.storePath, "synthetic_versions")
}

// slugForFile maps an arbitrary signal name to a filesystem-safe stem. A short
// hash of the full name is appended so distinct names that sanitise to the same
// stem (e.g. "A:B" and "A_B") never share backup files.
func slugForFile(name string) string {
	var b strings.Builder
	for _, r := range name {
		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '-' || r == '_' {
			b.WriteRune(r)
		} else {
			b.WriteByte('_')
		}
	}
	h := fnv.New32a()
	_, _ = h.Write([]byte(name))
	return fmt.Sprintf("%s-%08x", b.String(), h.Sum32())
}

func (s *Synthetic) versionPath(name string, version int) string {
	return filepath.Join(s.versionsDir(), fmt.Sprintf("%s.v%d.json", slugForFile(name), version))
}

// backupVersion writes a single signal revision to the versions directory.
func (s *Synthetic) backupVersion(def SignalDef) error {
	if err := os.MkdirAll(s.versionsDir(), 0o755); err != nil {
		return err
	}
	data, err := json.MarshalIndent(def, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(s.versionPath(def.Name, def.Version), data, 0o644)
}

// Versions returns metadata for every persisted revision of the named signal,
// newest first. The live revision is flagged Current.
func (s *Synthetic) Versions(name string) ([]VersionMeta, error) {
	cur, err := s.GetSignal(name)
	if err != nil {
		return nil, err
	}
	curV := cur.Version
	if curV < 1 {
		curV = 1
	}

	var savedAt time.Time
	if info, err := os.Stat(s.defsFilePath()); err == nil {
		savedAt = info.ModTime()
	}
	out := []VersionMeta{{Version: curV, Name: cur.Name, Tag: cur.Tag, Current: true, SavedAt: savedAt}}

	entries, err := os.ReadDir(s.versionsDir())
	if err != nil && !os.IsNotExist(err) {
		return nil, err
	}
	prefix := slugForFile(name) + ".v"
	for _, e := range entries {
		fn := e.Name()
		if e.IsDir() || !strings.HasPrefix(fn, prefix) || !strings.HasSuffix(fn, ".json") {
			continue
		}
		vStr := strings.TrimSuffix(strings.TrimPrefix(fn, prefix), ".json")
		v, err := strconv.Atoi(vStr)
		if err != nil {
			continue
		}
		def, err := s.readVersion(name, v)
		if err != nil {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}
		out = append(out, VersionMeta{Version: v, Name: def.Name, Tag: def.Tag, SavedAt: info.ModTime()})
	}

	sort.Slice(out, func(i, j int) bool { return out[i].Version > out[j].Version })
	return out, nil
}

// GetVersion returns a specific revision of the named signal. The current
// revision comes from the live store; older revisions from their backup file.
func (s *Synthetic) GetVersion(name string, version int) (SignalDef, error) {
	cur, err := s.GetSignal(name)
	if err != nil {
		return SignalDef{}, err
	}
	curV := cur.Version
	if curV < 1 {
		curV = 1
	}
	if version == curV {
		return cur, nil
	}
	return s.readVersion(name, version)
}

func (s *Synthetic) readVersion(name string, version int) (SignalDef, error) {
	data, err := os.ReadFile(s.versionPath(name, version))
	if os.IsNotExist(err) {
		return SignalDef{}, datasource.ErrNotFound
	}
	if err != nil {
		return SignalDef{}, err
	}
	var def SignalDef
	if err := json.Unmarshal(data, &def); err != nil {
		return SignalDef{}, fmt.Errorf("parse revision: %w", err)
	}
	return def, nil
}

// PromoteVersion makes a past revision current by re-saving it on top of
// history (non-destructive). Returns the resulting current definition.
func (s *Synthetic) PromoteVersion(name string, version int) (SignalDef, error) {
	def, err := s.GetVersion(name, version)
	if err != nil {
		return SignalDef{}, err
	}
	def.Tag = fmt.Sprintf("restored from v%d", version)
	if err := s.UpdateSignal(def); err != nil {
		return SignalDef{}, err
	}
	return s.GetSignal(name)
}

// ForkVersion creates a brand-new synthetic signal from a specific revision,
// assigning a fresh unique name and resetting its version to 1.
func (s *Synthetic) ForkVersion(name string, version int) (SignalDef, error) {
	def, err := s.GetVersion(name, version)
	if err != nil {
		return SignalDef{}, err
	}
	def.Name = fmt.Sprintf("%s_fork_%d", name, time.Now().UnixMilli())
	def.Version = 1
	def.Tag = ""
	if err := s.AddSignal(def); err != nil {
		return SignalDef{}, err
	}
	return def, nil
}