// Package skills parses skill metadata from SKILL.md front-matter and
// provides an in-memory registry for skill discovery and session-level loading.
package skills

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

// SkillsPath returns the directory to search for skill modules.
// Resolved from OLLIE_SKILLS_PATH, then ~/.config/ollie/skills.
func SkillsPath() string {
	if p := os.Getenv("OLLIE_SKILLS_PATH"); p != "" {
		return p
	}
	home, _ := os.UserHomeDir()
	return home + "/.config/ollie/skills"
}

// SkillInfo describes an available skill module.
type SkillInfo struct {
	Name        string
	Description string
	Dir         string // directory containing SKILL.md
}

// Registry discovers and loads skills from the filesystem.
// Tracks which skills are loaded per session.
type Registry struct {
	mu       sync.RWMutex
	sessions map[string]map[string]bool // sessionID → skill name → loaded
}

func NewRegistry() *Registry {
	return &Registry{
		sessions: make(map[string]map[string]bool),
	}
}

// Discover validates that the skills directory is readable.
// Retained for backward compatibility; discovery is now dynamic.
func (r *Registry) Discover() error {
	dir := SkillsPath()
	if _, err := os.ReadDir(dir); err != nil {
		return fmt.Errorf("read skills dir %s: %w", dir, err)
	}
	return nil
}

// discover scans the skills directory and returns all found skills.
func (r *Registry) discover() map[string]SkillInfo {
	dir := SkillsPath()
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil
	}
	skills := make(map[string]SkillInfo)
	for _, e := range entries {
		if !e.IsDir() {
			continue
		}
		name := e.Name()
		skillDir := filepath.Join(dir, name)
		skillFile := filepath.Join(skillDir, "SKILL.md")
		f, err := os.Open(skillFile)
		if err != nil {
			continue
		}
		meta, err := ParseFrontMatter(f, name, skillDir)
		f.Close()
		if err != nil {
			continue
		}
		skills[name] = SkillInfo{
			Name:        meta.Name,
			Description: meta.Description,
			Dir:         skillDir,
		}
	}
	return skills
}

// Summaries returns all discovered skills.
func (r *Registry) Summaries() []SkillInfo {
	skills := r.discover()
	out := make([]SkillInfo, 0, len(skills))
	for _, info := range skills {
		out = append(out, info)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out
}

// Load marks a skill as loaded for the given session.
func (r *Registry) Load(sessionID, name string) error {
	skills := r.discover()
	if _, exists := skills[name]; !exists {
		return fmt.Errorf("skill not found: %s", name)
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	if r.sessions[sessionID] == nil {
		r.sessions[sessionID] = make(map[string]bool)
	}
	r.sessions[sessionID][name] = true
	return nil
}

// Unload removes a skill from the session's loaded set.
func (r *Registry) Unload(sessionID, name string) error {
	r.mu.Lock()
	defer r.mu.Unlock()
	if _, ok := r.sessions[sessionID]; ok {
		delete(r.sessions[sessionID], name)
		if len(r.sessions[sessionID]) == 0 {
			delete(r.sessions, sessionID)
		}
	}
	return nil
}

// Loaded returns skills currently loaded for a session.
func (r *Registry) Loaded(sessionID string) []SkillInfo {
	r.mu.RLock()
	names, ok := r.sessions[sessionID]
	r.mu.RUnlock()
	if !ok {
		return nil
	}
	skills := r.discover()
	out := make([]SkillInfo, 0, len(names))
	for name := range names {
		if info, exists := skills[name]; exists {
			out = append(out, info)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
	return out
}

// SkillContent reads and returns the full content of a skill's SKILL.md file,
// with front-matter stripped. Returns (content, error).
func (r *Registry) SkillContent(name string) (string, error) {
	skills := r.discover()
	info, exists := skills[name]
	if !exists {
		return "", fmt.Errorf("skill not found: %s", name)
	}
	data, err := os.ReadFile(filepath.Join(info.Dir, "SKILL.md"))
	if err != nil {
		return "", fmt.Errorf("read skill %s: %w", name, err)
	}
	return StripFrontMatter(string(data)), nil
}

// IsLoaded checks if a skill is loaded for the given session.
func (r *Registry) IsLoaded(sessionID, name string) bool {
	r.mu.RLock()
	defer r.mu.RUnlock()
	names, ok := r.sessions[sessionID]
	if !ok {
		return false
	}
	return names[name]
}

// StripFrontMatter removes YAML front-matter from a markdown string,
// returning everything after the closing ---.
func StripFrontMatter(content string) string {
	lines := strings.Split(content, "\n")
	if len(lines) < 2 || strings.TrimSpace(lines[0]) != "---" {
		return content
	}
	inFM := false
	bodyStart := 0
	for i, line := range lines {
		if strings.TrimSpace(line) == "---" {
			if !inFM {
				inFM = true
			} else {
				bodyStart = i + 1
				break
			}
		}
	}
	if bodyStart == 0 {
		return content
	}
	return strings.Join(lines[bodyStart:], "\n")
}