package review

import (
	"embed"
	"encoding/json"
	"fmt"
	"os"
	"strings"
	"unicode/utf8"

	"github.com/goccy/go-yaml"
)

//go:embed personas/*.yaml
var embeddedPersonas embed.FS

// Persona defines a specialized review role with focused expertise.
type Persona struct {
	Name         string   `json:"name" yaml:"name"`
	DisplayName  string   `json:"display_name" yaml:"display_name"`
	ModelPref    string   `json:"model_preference,omitempty" yaml:"model_preference,omitempty"`
	Identity     string   `json:"identity" yaml:"identity"`
	Focus        []string `json:"focus" yaml:"focus"`
	Ignore       []string `json:"ignore" yaml:"ignore"`
	Severity     Severity `json:"severity" yaml:"severity"`
	OutputFormat string   `json:"output_format,omitempty" yaml:"output_format,omitempty"`
}

// Severity defines what constitutes each severity level for this persona.
// These are prompt guidance for the LLM, not output format changes.
type Severity struct {
	Major string `json:"major" yaml:"major"`
	Minor string `json:"minor" yaml:"minor"`
	Nit   string `json:"nit" yaml:"nit"`
}

// LoadPersona loads a persona from a JSON or YAML file path.
// Format is detected by file extension: .yaml/.yml for YAML, .json or other for JSON.
func LoadPersona(path string) (*Persona, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read persona file %s: %w", path, err)
	}
	return parsePersona(data, path)
}

// LoadBuiltinPersona loads a built-in persona by name.
// Returns an error if the persona doesn't exist.
// Built-in personas are stored in YAML format.
func LoadBuiltinPersona(name string) (*Persona, error) {
	// Try YAML first (preferred format)
	yamlFile := name + ".yaml"
	data, err := embeddedPersonas.ReadFile("personas/" + yamlFile)
	if err == nil {
		return parsePersona(data, "builtin:"+yamlFile)
	}

	// Fall back to JSON for backwards compatibility
	jsonFile := name + ".json"
	data, err = embeddedPersonas.ReadFile("personas/" + jsonFile)
	if err != nil {
		available := ListBuiltinPersonas()
		return nil, fmt.Errorf("unknown built-in persona %q (available: %s)", name, strings.Join(available, ", "))
	}
	return parsePersona(data, "builtin:"+jsonFile)
}

// ListBuiltinPersonas returns the names of all built-in personas.
// Returns an empty slice if the embedded directory cannot be read.
func ListBuiltinPersonas() []string {
	entries, err := embeddedPersonas.ReadDir("personas")
	if err != nil {
		return []string{}
	}
	seen := make(map[string]bool)
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		// Strip extension to get persona name
		var personaName string
		switch {
		case strings.HasSuffix(name, ".yaml"):
			personaName = strings.TrimSuffix(name, ".yaml")
		case strings.HasSuffix(name, ".yml"):
			personaName = strings.TrimSuffix(name, ".yml")
		case strings.HasSuffix(name, ".json"):
			personaName = strings.TrimSuffix(name, ".json")
		default:
			continue
		}
		if !seen[personaName] {
			seen[personaName] = true
		}
	}
	var names []string
	for name := range seen {
		names = append(names, name)
	}
	return names
}

// parsePersona parses persona data from JSON or YAML format.
// Format is detected by the source file extension.
func parsePersona(data []byte, source string) (*Persona, error) {
	lowerSource := strings.ToLower(source)
	isYAML := strings.HasSuffix(lowerSource, ".yaml") || strings.HasSuffix(lowerSource, ".yml")

	var p Persona
	var err error
	if isYAML {
		// go-yaml v1.16.0+ has built-in protection against deeply nested structures
		err = yaml.Unmarshal(data, &p)
	} else {
		err = json.Unmarshal(data, &p)
	}
	if err != nil {
		return nil, fmt.Errorf("parse persona %s: %w", source, err)
	}
	if err := validatePersona(&p, source); err != nil {
		return nil, err
	}
	return &p, nil
}

func validatePersona(p *Persona, source string) error {
	if p.Name == "" {
		return fmt.Errorf("persona %s: name is required", source)
	}
	if p.Identity == "" {
		return fmt.Errorf("persona %s: identity is required", source)
	}
	// DisplayName defaults to Name if not set
	if p.DisplayName == "" {
		p.DisplayName = p.Name
	}
	return nil
}

// CapitalizeFirst capitalizes the first rune of a string in a Unicode-safe way.
// Returns the original string if it's empty.
func CapitalizeFirst(s string) string {
	if s == "" {
		return s
	}
	r, size := utf8.DecodeRuneInString(s)
	if r == utf8.RuneError {
		return s
	}
	return strings.ToUpper(string(r)) + s[size:]
}