// Package trust implements SPEC §7's per-project command-preset trust
// gating. Command presets are not trusted by default; the first time
// an agent attempts to spawn / start / restart a process tied to one,
// the MCP tool returns a `needs_trust` error and patterm surfaces a UI
// confirmation. The user's acceptance is persisted to disk so the
// confirmation isn't repeated every run.
//
// Trust is keyed by `(project, preset name)` in v1. Freeform-argv
// command spawns bypass entirely (the agent had to compose the argv,
// so the trust decision is already implicit).
package trust

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"sync"
)

// Store is one project's trust file. Safe for concurrent use.
type Store struct {
	path string

	mu      sync.RWMutex
	granted map[string]bool
}

// Open loads (or creates) the trust file for projectKey. The file is
// stored at $XDG_DATA_HOME/patterm/projects/<projectKey>/trust.json
// (SPEC §3). Missing-file is not an error — it simply means no presets
// are trusted yet.
func Open(projectKey string) (*Store, error) {
	if projectKey == "" {
		return nil, errors.New("trust.Open: empty project key")
	}
	base, err := dataDir()
	if err != nil {
		return nil, err
	}
	dir := filepath.Join(base, "projects", projectKey)
	if err := os.MkdirAll(dir, 0o700); err != nil {
		return nil, fmt.Errorf("trust: mkdir %s: %w", dir, err)
	}
	path := filepath.Join(dir, "trust.json")
	s := &Store{path: path, granted: make(map[string]bool)}
	if err := s.loadLocked(); err != nil {
		return nil, err
	}
	return s, nil
}

func dataDir() (string, error) {
	if h := os.Getenv("XDG_DATA_HOME"); h != "" {
		return filepath.Join(h, "patterm"), nil
	}
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(home, ".local", "share", "patterm"), nil
}

// IsTrusted reports whether preset is granted.
func (s *Store) IsTrusted(preset string) bool {
	if preset == "" {
		return false
	}
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.granted[preset]
}

// Grant records that preset is trusted and persists the file.
func (s *Store) Grant(preset string) error {
	if preset == "" {
		return errors.New("trust.Grant: empty preset")
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.granted[preset] {
		return nil
	}
	s.granted[preset] = true
	return s.saveLocked()
}

// Revoke removes a trust grant. Not used by the SPEC v1 flow but
// useful for tests and future "untrust this" UI.
func (s *Store) Revoke(preset string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if !s.granted[preset] {
		return nil
	}
	delete(s.granted, preset)
	return s.saveLocked()
}

// List returns the trusted presets in sorted order. For UI debugging.
func (s *Store) List() []string {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]string, 0, len(s.granted))
	for k := range s.granted {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// Path returns the trust file path. Used by tests / diagnostics.
func (s *Store) Path() string { return s.path }

type fileShape struct {
	// Presets is the JSON shape on disk: a list of granted preset names.
	// Using a list (not a map) keeps the file diff-friendly and ordering
	// stable across re-saves.
	Presets []string `json:"presets"`
}

func (s *Store) loadLocked() error {
	b, err := os.ReadFile(s.path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return fmt.Errorf("trust: read %s: %w", s.path, err)
	}
	if len(b) == 0 {
		return nil
	}
	var f fileShape
	if err := json.Unmarshal(b, &f); err != nil {
		return fmt.Errorf("trust: parse %s: %w", s.path, err)
	}
	for _, p := range f.Presets {
		s.granted[p] = true
	}
	return nil
}

func (s *Store) saveLocked() error {
	out := make([]string, 0, len(s.granted))
	for k := range s.granted {
		out = append(out, k)
	}
	sort.Strings(out)
	body, err := json.MarshalIndent(fileShape{Presets: out}, "", "  ")
	if err != nil {
		return err
	}
	body = append(body, '\n')
	tmp := s.path + ".tmp"
	if err := os.WriteFile(tmp, body, 0o600); err != nil {
		return fmt.Errorf("trust: write %s: %w", tmp, err)
	}
	if err := os.Rename(tmp, s.path); err != nil {
		return fmt.Errorf("trust: rename %s: %w", s.path, err)
	}
	return nil
}