package fa

import (
	"strings"

	"github.com/PuerkitoBio/goquery"
)

// classifySystemMessage looks at a fetched document and, when it is one of
// FA's gate/error templates rather than a real content page, maps it to the
// most specific sentinel error. Returns nil for normal content pages so
// parsing continues.
//
// FA emits at least two distinct gate templates:
//
//   - <title>System Error</title> generic "not found / no permission /
//     rate limited" page with the human message in a section-body.
//   - <title>Login Required …</title> auth-gated content (some submissions
//     are not viewable anonymously). Always maps to ErrUnauthorized.
//
// We classify by <title> first to pick a template, then by message text
// within the section-body when needed. Anything else is left for the
// downstream parser to handle.
func classifySystemMessage(doc *goquery.Document) error {
	pageTitle := strings.ToLower(strings.TrimSpace(doc.Find("title").First().Text()))

	switch {
	case strings.HasPrefix(pageTitle, "login required"):
		return ErrUnauthorized
	case pageTitle == "system error",
		strings.HasPrefix(pageTitle, "system error"):
		// fall through to body classification below
	default:
		return nil
	}

	headerTitle := trimText(doc.Find("section .section-header h2").First())
	if headerTitle == "" {
		headerTitle = trimText(doc.Find("h2").First())
	}
	body := strings.TrimSpace(doc.Find("section .section-body").First().Text())
	if body == "" {
		body = strings.TrimSpace(doc.Find(".section-body").First().Text())
	}

	low := strings.ToLower(headerTitle + " " + body)
	switch {
	case strings.Contains(low, "not in our database"),
		strings.Contains(low, "submission not found"),
		strings.Contains(low, "user not found"),
		strings.Contains(low, "journal not found"),
		strings.Contains(low, "page not found"),
		strings.Contains(low, "no such"):
		return ErrNotFound
	case strings.Contains(low, "you must be logged in"),
		strings.Contains(low, "log in to view"),
		strings.Contains(low, "permission to view"),
		strings.Contains(low, "permission to access"):
		return ErrUnauthorized
	case strings.Contains(low, "rate limit"),
		strings.Contains(low, "too many requests"):
		return ErrRateLimited
	}
	return &SystemMessageError{Title: headerTitle, Body: body}
}