package feed

import (
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"

	"golang.org/x/net/html"
)

type FeedBuilder interface {
    GenerateFeed() string
}

type FeedInfo struct {
    SiteName    string   
    SiteUrl     string
    SiteDesc    string
    PageUrls    []string
    errors      map[string]error
} 

type FeedItem struct {
    Url         string
    Title       string
    Author      string
    EscapedText string
    PubTime     time.Time
    RawText     string
}

func fetchPage(url string) (string, error) {
    resp, err := http.Get(url)
    if err != nil {
        return "", fmt.Errorf("Error sending Get request: %w", err)
    }
    defer resp.Body.Close()
    body, err := io.ReadAll(resp.Body)

    return string(body), nil
}

func parseTime(timestr string) (time.Time, error) {
    var formats = []string {
        time.ANSIC,
        time.UnixDate,
        time.RubyDate,
        time.RFC822,
        time.RFC822Z,
        time.RFC850,
        time.RFC1123,
        time.RFC1123Z,
        "2006-01-02 15:04:05 -0700 -0700",
        time.RFC3339,
        time.RFC3339Nano,
        time.DateTime,
        time.DateOnly,
    }
    var pagetime time.Time
    var err error
    for _, f := range formats {
        pagetime, err = time.Parse(f, timestr)
        if err == nil {
            return pagetime, err
        }
    }
    return pagetime, fmt.Errorf("Error parsing time: invalid format")
}

func getHtmlElement(doc *html.Node, tag string) (*html.Node, error) {
    var f func(*html.Node, string)
    var element *html.Node
    f = func(n *html.Node, s string) {
        if n.Type == html.ElementNode && n.Data == s{
            element = n
            return
        }
        for c := n.FirstChild; c != nil; c = c.NextSibling {
            f(c, tag)
        }
    }
    f(doc, tag)
    if element == nil {
        return nil, fmt.Errorf("no <%s> element found", tag)
    }
    return element, nil
}

func (f *FeedItem) ParseContent(content string) error {
    doc, err := html.Parse(strings.NewReader(content))
    if err != nil {
        return fmt.Errorf("Error parsing HTML: %w", err)
    }
    earticle, err := getHtmlElement(doc, "article")
    if err != nil {
        return err
    }
    var builder strings.Builder
    html.Render(&builder, earticle)
    f.RawText = builder.String()

    etime, err := getHtmlElement(earticle, "time")
    if err != nil {
        return err
    }
    var pubTime time.Time
    for _, d := range etime.Attr {
        if d.Key == "datetime" {
            pubTime, err = parseTime(d.Val)
        }
        if err != nil {
            return  fmt.Errorf("Error parsing time: %w", err)
        }
        f.PubTime = pubTime
    }
    return nil 
}

func NewFeedItem(url string) (*FeedItem, error) {
    rawhtml, err := fetchPage(url)
    if err != nil {
        return nil, fmt.Errorf("Could not fetch page '%s': %w", url, err)
    }
    item := FeedItem{
        Url: url,
    }
    item.ParseContent(rawhtml);
    if err != nil {
        return nil, fmt.Errorf("Could not parse feed item: %w", err)
    }
    return &item, nil
}

// parseArticle returns an error if it could not parse the HTML or if it could not parse a time
// if a time could not be parsed, the parsed html article will still be returned
func parseArticle(content string) (string, *time.Time, error) {
    doc, err := html.Parse(strings.NewReader(content))
    if err != nil {
        return "", nil, fmt.Errorf("Error parsing HTML: %w", err)
    }
    var f func(*html.Node, string)
    var element *html.Node
    var pagetime time.Time
    f = func(n *html.Node, tag string) {
        if n.Type == html.ElementNode && n.Data == tag {
            element = n
            return
        }
        for c := n.FirstChild; c != nil; c = c.NextSibling {
            f(c, tag)
        }
    }

    f(doc, "article")
    var builder strings.Builder
    html.Render(&builder, element)

    f(element, "time")
    for _, d := range element.Attr {
        if d.Key == "datetime" {
            pagetime, err = parseTime(d.Val)
        }
    }

    return builder.String(), &pagetime, nil 
}