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 递归扫描 skillsDir，返回所有包含 SKILL.md 的目录的元数据。
func Discover(skillsDir string) ([]Meta, error) {
	var metas []Meta
	filepath.Walk(skillsDir, func(path string, info os.FileInfo, err error) error {
		if err != nil || info.IsDir() || info.Name() != "SKILL.md" {
			return nil
		}
		data, err := os.ReadFile(path)
		if err != nil {
			return nil
		}
		meta, err := parseMeta(data)
		if err != nil {
			return nil
		}
		meta.Path = filepath.Dir(path)
		metas = append(metas, meta)
		return nil
	})
	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.
// 如果 skill 有完整内容，会注入到 prompt 中。
func ToXML(metas []Meta) string {
	var sb strings.Builder
	sb.WriteString("<available_skills>\n")
	for _, m := range metas {
		// 尝试加载完整 skill 内容
		s, err := Load(m.Path)
		if err == nil && s.Body != "" {
			fmt.Fprintf(&sb, "  <skill name=\"%s\">\n    <description>%s</description>\n    <instructions>\n%s\n    </instructions>\n  </skill>\n",
				m.Name, m.Description, s.Body)
		} else {
			fmt.Fprintf(&sb, "  <skill name=\"%s\">\n    <description>%s</description>\n  </skill>\n",
				m.Name, m.Description)
		}
	}
	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]))
}