package skill

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"sync"
)

const (
	// DefaultSkillsDir is the default directory for user-installed skills.
	DefaultSkillsDir = "~/.agents/skills"

	// SkillManifestFile is the name of the skill manifest file.
	SkillManifestFile = "SKILL.md"
)

// Manager is a thread-safe registry for loading, storing, and querying Skills.
//
// Skills are loaded from a directory tree where each subdirectory containing
// a SKILL.md file is treated as a skill. The Manager automatically discovers
// skills on initialization and provides methods for finding skills by trigger
// keywords or by name.
type Manager struct {
	mu        sync.RWMutex
	skillsDir string
	skills    map[string]*Skill
}

// NewManager creates a new Skill manager that scans the given directory for skills.
// If skillsDir is empty, DefaultSkillsDir is used.
func NewManager(skillsDir string) *Manager {
	if skillsDir == "" {
		skillsDir = DefaultSkillsDir
	}
	// Expand ~ to home directory
	skillsDir = expandHome(skillsDir)

	return &Manager{
		skillsDir: skillsDir,
		skills:    make(map[string]*Skill),
	}
}

// LoadAll scans the skills directory and loads all skills found.
// It returns the number of skills loaded and any errors encountered.
func (m *Manager) LoadAll() (int, error) {
	m.mu.Lock()
	defer m.mu.Unlock()

	// Clear existing skills
	m.skills = make(map[string]*Skill)

	// Check if skills directory exists
	info, err := os.Stat(m.skillsDir)
	if err != nil {
		if os.IsNotExist(err) {
			return 0, nil // No skills directory yet — not an error
		}
		return 0, fmt.Errorf("skill: cannot access skills directory %q: %w", m.skillsDir, err)
	}
	if !info.IsDir() {
		return 0, fmt.Errorf("skill: %q is not a directory", m.skillsDir)
	}

	// Read all entries in the skills directory
	entries, err := os.ReadDir(m.skillsDir)
	if err != nil {
		return 0, fmt.Errorf("skill: failed to read skills directory %q: %w", m.skillsDir, err)
	}

	var loadErrors []string
	loaded := 0

	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}

		skillDir := filepath.Join(m.skillsDir, entry.Name())
		skillPath := filepath.Join(skillDir, SkillManifestFile)

		if _, err := os.Stat(skillPath); os.IsNotExist(err) {
			continue // No SKILL.md in this directory — skip
		}

		skill, err := ParseSkillFile(skillPath)
		if err != nil {
			loadErrors = append(loadErrors, fmt.Sprintf("%s: %v", entry.Name(), err))
			continue
		}

		m.skills[skill.Name] = skill
		loaded++
	}

	if len(loadErrors) > 0 {
		return loaded, fmt.Errorf("skill: loaded %d skills with %d errors: %s",
			loaded, len(loadErrors), joinStrings(loadErrors, "; "))
	}

	return loaded, nil
}

// GetSkill retrieves a skill by its name. Returns false if not found.
func (m *Manager) GetSkill(name string) (*Skill, bool) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	skill, ok := m.skills[name]
	return skill, ok
}

// ListSkills returns all loaded skills sorted by name.
func (m *Manager) ListSkills() []*Skill {
	m.mu.RLock()
	defer m.mu.RUnlock()

	result := make([]*Skill, 0, len(m.skills))
	for _, skill := range m.skills {
		result = append(result, skill)
	}

	sort.Slice(result, func(i, j int) bool {
		return result[i].Name < result[j].Name
	})
	return result
}

// FindSkill finds skills whose triggers match the given query string.
// Returns all matching skills sorted by relevance (more trigger matches first).
func (m *Manager) FindSkill(query string) []*Skill {
	m.mu.RLock()
	defer m.mu.RUnlock()

	var matches []*Skill
	for _, skill := range m.skills {
		if skill.MatchTrigger(query) {
			matches = append(matches, skill)
		}
	}

	// Sort by number of matching triggers (descending)
	sort.Slice(matches, func(i, j int) bool {
		return countMatches(matches[i], query) > countMatches(matches[j], query)
	})

	return matches
}

// SkillsDir returns the directory being scanned for skills.
func (m *Manager) SkillsDir() string {
	return m.skillsDir
}

// Reload refreshes all skills from disk.
func (m *Manager) Reload() (int, error) {
	return m.LoadAll()
}

// countMatches counts how many of the skill's triggers match the query.
func countMatches(skill *Skill, query string) int {
	count := 0
	queryLower := strings.ToLower(query)
	for _, trigger := range skill.Triggers {
		if strings.Contains(queryLower, strings.ToLower(trigger)) {
			count++
		}
	}
	return count
}

// expandHome replaces "~" with the user's home directory.
func expandHome(path string) string {
	if len(path) > 0 && path[0] == '~' {
		home, err := os.UserHomeDir()
		if err != nil {
			return path
		}
		return filepath.Join(home, path[1:])
	}
	return path
}

// joinStrings joins a slice of strings with a separator.
func joinStrings(parts []string, sep string) string {
	if len(parts) == 0 {
		return ""
	}
	result := parts[0]
	for _, p := range parts[1:] {
		result += sep + p
	}
	return result
}