// Package prompt enriches a raw user prompt before it reaches a backend. The
// only enrichment today is style-preset suffixes; future passes can add
// negative-prompt resolution, safety filters, etc.
package prompt

import (
	_ "embed"
	"fmt"
	"sort"
	"strings"

	"gopkg.in/yaml.v3"
)

//go:embed styles.yaml
var stylesYAML []byte

type stylesFile struct {
	Styles map[string]string `yaml:"styles"`
}

var defaultStyles map[string]string

func init() {
	var f stylesFile
	if err := yaml.Unmarshal(stylesYAML, &f); err != nil {
		panic(fmt.Sprintf("prompt: parse embedded styles.yaml: %v", err))
	}
	defaultStyles = f.Styles
}

// Styles returns the names of registered style presets, sorted.
func Styles() []string {
	out := make([]string, 0, len(defaultStyles))
	for k := range defaultStyles {
		out = append(out, k)
	}
	sort.Strings(out)
	return out
}

// HasStyle reports whether name is a known preset.
func HasStyle(name string) bool {
	_, ok := defaultStyles[name]
	return ok
}

// Apply returns the prompt with the named style preset appended. Unknown
// styles return an error rather than silently passing the prompt through —
// surprising the caller with missing style is worse than a hard error.
func Apply(prompt, style string) (string, error) {
	if style == "" {
		return prompt, nil
	}
	suffix, ok := defaultStyles[style]
	if !ok {
		return "", fmt.Errorf("unknown style %q, available: %v", style, Styles())
	}
	if strings.TrimSpace(prompt) == "" {
		return suffix, nil
	}
	return prompt + ", " + suffix, nil
}