package skill

import (
	"bytes"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"gopkg.in/yaml.v3"
)

type Meta struct {
	Name        string `yaml:"name"`
	Description string `yaml:"description"`
	Path        string `yaml:"-"`
}

type Skill struct {
	Meta
	Body string // full SKILL.md body (instructions)
}

// Discover scans skillsDir and returns metadata for all valid skills.
func Discover(skillsDir string) ([]Meta, error) {
	entries, err := os.ReadDir(skillsDir)
	if err != nil {
		return nil, err
	}
	var metas []Meta
	for _, e := range entries {
		if !e.IsDir() {
			continue
		}
		path := filepath.Join(skillsDir, e.Name(), "SKILL.md")
		data, err := os.ReadFile(path)
		if err != nil {
			continue
		}
		meta, err := parseMeta(data)
		if err != nil {
			continue
		}
		meta.Path = filepath.Join(skillsDir, e.Name())
		metas = append(metas, meta)
	}
	return metas, nil
}

// Load returns a fully loaded skill including body.
func Load(skillDir string) (*Skill, error) {
	data, err := os.ReadFile(filepath.Join(skillDir, "SKILL.md"))
	if err != nil {
		return nil, err
	}
	meta, err := parseMeta(data)
	if err != nil {
		return nil, err
	}
	meta.Path = skillDir
	body := extractBody(data)
	return &Skill{Meta: meta, Body: body}, nil
}

// ToXML generates <available_skills> XML for agent system prompts.
func ToXML(metas []Meta) string {
	var sb strings.Builder
	sb.WriteString("<available_skills>\n")
	for _, m := range metas {
		fmt.Fprintf(&sb, "  <skill>\n    <name>%s</name>\n    <description>%s</description>\n    <location>%s/SKILL.md</location>\n  </skill>\n",
			m.Name, m.Description, m.Path)
	}
	sb.WriteString("</available_skills>")
	return sb.String()
}

func parseMeta(data []byte) (Meta, error) {
	var meta Meta
	if !bytes.HasPrefix(data, []byte("---")) {
		return meta, fmt.Errorf("missing frontmatter")
	}
	parts := bytes.SplitN(data, []byte("---"), 3)
	if len(parts) < 3 {
		return meta, fmt.Errorf("invalid frontmatter")
	}
	return meta, yaml.Unmarshal(parts[1], &meta)
}

func extractBody(data []byte) string {
	parts := bytes.SplitN(data, []byte("---"), 3)
	if len(parts) < 3 {
		return string(data)
	}
	return strings.TrimSpace(string(parts[2]))
}