package prompt

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"gitea.maximumdirect.net/eric/scriptorium/internal/domain"
	"text/template"
)

var (
	ErrMissingRequiredInput = errors.New("missing required input artifact")
	ErrUnknownInput         = errors.New("referenced unknown input artifact")
	ErrInvalidTemplate      = errors.New("invalid prompt template")
	ErrRenderFailure        = errors.New("prompt render failure")
	ErrInvalidMessageRole   = errors.New("invalid or empty message role")
)

type goRenderer struct{}

func NewGoRenderer() Renderer {
	return &goRenderer{}
}

func (r *goRenderer) Render(ctx context.Context, profile *domain.PromptProfile, inputs map[string]*domain.Artifact, vars map[string]string) (*domain.RenderedPrompt, error) {
	if profile == nil {
		return nil, fmt.Errorf("%w: nil profile", ErrRenderFailure)
	}

	// 1. Verify required inputs
	for _, req := range profile.ExpectedInputs {
		art, ok := inputs[req]
		if !ok || art == nil {
			return nil, fmt.Errorf("%w: %s", ErrMissingRequiredInput, req)
		}
	}

	// 2. Setup template functions
	funcs := template.FuncMap{
		"input": func(name string) (string, error) {
			art, ok := inputs[name]
			if !ok {
				return "", fmt.Errorf("%w: %s", ErrUnknownInput, name)
			}
			return string(art.Body), nil
		},
	}

	var renderedMessages []domain.RenderedMessage

	for i, tmplMsg := range profile.Templates {
		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		default:
		}

		if tmplMsg.Role == "" {
			return nil, fmt.Errorf("%w: message %d", ErrInvalidMessageRole, i)
		}

		// Parse and execute template
		tmpl, err := template.New(fmt.Sprintf("msg_%d", i)).Funcs(funcs).Option("missingkey=error").Parse(tmplMsg.Content)
		if err != nil {
			return nil, fmt.Errorf("%w: message %d: %v", ErrInvalidTemplate, i, err)
		}

		var buf bytes.Buffer
		if err := tmpl.Execute(&buf, vars); err != nil {
			return nil, fmt.Errorf("%w: message %d: %w", ErrRenderFailure, i, err)
		}

		renderedMessages = append(renderedMessages, domain.RenderedMessage{
			Role:    tmplMsg.Role,
			Content: buf.String(),
		})
	}

	return &domain.RenderedPrompt{
		Messages: renderedMessages,
	}, nil
}