package session

import (
	"encoding/json"
	"os"
	"path/filepath"
	"strings"
	"time"
)

// FileEntry represents a single file in the workspace manifest.
type FileEntry struct {
	Path  string    `json:"path"`
	Size  int64     `json:"size"`
	Mtime time.Time `json:"mtime"`
}

// Manifest represents a point-in-time snapshot of workspace files.
type Manifest struct {
	CapturedAt time.Time   `json:"captured_at"`
	Files      []FileEntry `json:"files"`
}

// ignoredPaths returns true for paths that should be excluded from manifest diffing.
func ignoredPath(relPath string) bool {
	// Ignore .ctask/ directory contents
	if strings.HasPrefix(relPath, ".ctask/") || strings.HasPrefix(relPath, ".ctask\\") {
		return true
	}
	// Ignore task.yaml (ctask updates this itself)
	if relPath == "task.yaml" {
		return true
	}
	// Ignore sessions.log (ctask's own logging)
	if relPath == "logs/sessions.log" || relPath == "logs\\sessions.log" {
		return true
	}
	return false
}

// CaptureManifest walks the workspace directory and captures file metadata.
func CaptureManifest(wsDir string) (*Manifest, error) {
	m := &Manifest{
		CapturedAt: time.Now().UTC().Truncate(time.Second),
	}

	err := filepath.Walk(wsDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return nil // skip files we can't stat
		}
		if info.IsDir() {
			// Skip .ctask directory entirely
			rel, _ := filepath.Rel(wsDir, path)
			if rel == ".ctask" {
				return filepath.SkipDir
			}
			return nil
		}

		rel, err := filepath.Rel(wsDir, path)
		if err != nil {
			return nil
		}
		// Normalize to forward slashes for consistency
		rel = filepath.ToSlash(rel)

		m.Files = append(m.Files, FileEntry{
			Path:  rel,
			Size:  info.Size(),
			Mtime: info.ModTime().UTC().Truncate(time.Second),
		})
		return nil
	})
	if err != nil {
		return nil, err
	}

	return m, nil
}

// WriteManifest writes a manifest to a JSON file.
func WriteManifest(path string, m *Manifest) error {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}
	data, err := json.MarshalIndent(m, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0644)
}

// ReadManifest reads a manifest from a JSON file.
func ReadManifest(path string) (*Manifest, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	var m Manifest
	if err := json.Unmarshal(data, &m); err != nil {
		return nil, err
	}
	return &m, nil
}

// ManifestDiff represents the differences between two manifests.
type ManifestDiff struct {
	Added    []string // files only in end manifest
	Modified []string // files in both, but size or mtime differ
	Deleted  []string // files only in start manifest
}

// DiffManifests compares start and end manifests, applying ignore rules.
func DiffManifests(start, end *Manifest) *ManifestDiff {
	diff := &ManifestDiff{}

	startMap := make(map[string]FileEntry)
	for _, f := range start.Files {
		if !ignoredPath(f.Path) {
			startMap[f.Path] = f
		}
	}

	endMap := make(map[string]FileEntry)
	for _, f := range end.Files {
		if !ignoredPath(f.Path) {
			endMap[f.Path] = f
		}
	}

	// Added: in end but not start
	for path := range endMap {
		if _, ok := startMap[path]; !ok {
			diff.Added = append(diff.Added, path)
		}
	}

	// Modified: in both but different size or mtime
	for path, endEntry := range endMap {
		if startEntry, ok := startMap[path]; ok {
			if endEntry.Size != startEntry.Size || !endEntry.Mtime.Equal(startEntry.Mtime) {
				diff.Modified = append(diff.Modified, path)
			}
		}
	}

	// Deleted: in start but not end
	for path := range startMap {
		if _, ok := endMap[path]; !ok {
			diff.Deleted = append(diff.Deleted, path)
		}
	}

	return diff
}

// NotesUpdated checks if notes.md was modified between manifests.
func NotesUpdated(diff *ManifestDiff) bool {
	for _, f := range diff.Modified {
		if f == "notes.md" {
			return true
		}
	}
	for _, f := range diff.Added {
		if f == "notes.md" {
			return true
		}
	}
	return false
}