package majordomo

import (
	"context"
	"encoding/json"
	"fmt"
	"reflect"
	"strings"

	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
)

// SchemaFor re-exports llm.SchemaFor: a JSON Schema derived from a Go type,
// suitable for WithSchema and tool parameters.
func SchemaFor[T any]() (json.RawMessage, error) { return llm.SchemaFor[T]() }

// Generate performs a structured-output request and unmarshals the result
// into T: the schema is derived from T (llm.SchemaFor), injected via the
// provider's native structured-output mechanism, and the response text is
// decoded into a T value.
//
//	type Verdict struct {
//	    Guilty bool   `json:"guilty"`
//	    Why    string `json:"why" description:"one-sentence rationale"`
//	}
//	v, err := majordomo.Generate[Verdict](ctx, m, req)
func Generate[T any](ctx context.Context, m Model, req Request, opts ...Option) (T, error) {
	var zero T
	schema, err := llm.SchemaFor[T]()
	if err != nil {
		return zero, err
	}

	name := "response"
	if t := reflect.TypeFor[T](); t.Name() != "" {
		name = strings.ToLower(t.Name())
	}

	resp, err := m.Generate(ctx, req, append(opts, llm.WithSchema(schema, name))...)
	if err != nil {
		return zero, err
	}

	text := strings.TrimSpace(resp.Text())
	if text == "" {
		return zero, fmt.Errorf("majordomo: structured response from %s is empty (finish: %s)", resp.Model, resp.FinishReason)
	}
	// Defensive: some models wrap JSON in a markdown fence despite the
	// schema constraint.
	text = stripFence(text)

	var out T
	if err := json.Unmarshal([]byte(text), &out); err != nil {
		return zero, fmt.Errorf("majordomo: decode structured response from %s: %w (text: %.200s)", resp.Model, err, text)
	}
	return out, nil
}

// stripFence removes a surrounding markdown code fence, if present.
func stripFence(s string) string {
	if !strings.HasPrefix(s, "```") {
		return s
	}
	s = strings.TrimPrefix(s, "```")
	// Drop an optional language tag on the opening fence line.
	if i := strings.IndexByte(s, '\n'); i >= 0 {
		s = s[i+1:]
	}
	s = strings.TrimSuffix(strings.TrimSpace(s), "```")
	return strings.TrimSpace(s)
}