package fa

import (
	"context"
	"fmt"
	"net/url"
	"strings"

	"github.com/PuerkitoBio/goquery"

	"git.anthrove.art/public/go-fa-api/internal/urls"
)

// SendNote sends a new private message (note) to a user. Requires login.
//
// FA's note form posts to /msg/send/ with a per-form CSRF key that must
// be scraped from the notes inbox (or any page that renders the send
// form). This method does the scrape + post in one call.
//
// Returns nil on success. ErrUnauthorized when not logged in.
// *SystemMessageError when FA rejects the send (recipient blocked, rate
// limited, etc.).
func (c *Client) SendNote(ctx context.Context, to string, subject string, body string, opts ...Option) error {
	to = strings.TrimSpace(to)
	if to == "" {
		return fmt.Errorf("fa: SendNote: empty recipient")
	}
	if subject == "" {
		return fmt.Errorf("fa: SendNote: empty subject")
	}
	if body == "" {
		return fmt.Errorf("fa: SendNote: empty body")
	}

	// Scrape the form key from /msg/pms/. The notes inbox renders the same
	// CSRF key in any note-related form on the page; we don't actually need
	// to be replying to anything to harvest it.
	var key string
	err := c.fetch(ctx, urls.MsgPMs(), func(doc *goquery.Document) error {
		key = findNoteKey(doc)
		if key == "" {
			return fmt.Errorf("%w: SendNote: could not locate form key on /msg/pms/", ErrUnauthorized)
		}
		return nil
	}, opts...)
	if err != nil {
		return err
	}

	v := url.Values{}
	v.Set("key", key)
	v.Set("to", to)
	v.Set("subject", subject)
	v.Set("message", body)
	v.Set("send", "Send Note")
	_, err = c.postForm(ctx, urls.Host+"/msg/send/", v, opts...)
	return err
}

// findNoteKey looks for a hidden input named "key" inside any form that
// targets the notes subsystem (/msg/send/ or /msg/pms/). FA reuses the
// same key value across these forms within a session.
func findNoteKey(doc *goquery.Document) string {
	var key string
	doc.Find("form[action='/msg/send/'] input[name='key'], form[action='/msg/pms/'] input[name='key'], form[action^='/msg/'] input[name='key']").EachWithBreak(func(_ int, sel *goquery.Selection) bool {
		if v := strings.TrimSpace(trimAttr(sel, "value")); v != "" {
			key = v
			return false
		}
		return true
	})
	return key
}