package proxy

import (
	"bytes"
	"encoding/json"
	"encoding/xml"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"
)

// RequestRecord holds the raw request we sent.
type RequestRecord struct {
	Method  string      `json:"method"`
	URL     string      `json:"url"`
	Headers http.Header `json:"headers"`
}

// ResponseRecord holds raw response for the details panel.
type ResponseRecord struct {
	Status     int         `json:"status"`
	StatusText string      `json:"statusText"`
	Headers    http.Header `json:"headers"`
	Body       string      `json:"body"`
}

// FetchResult is returned by Fetch: parsed feed plus raw request/response.
type FetchResult struct {
	Request  RequestRecord  `json:"request"`
	Response ResponseRecord `json:"response"`
	Feed     *Feed          `json:"feed,omitempty"`
	IsImage  bool           `json:"isImage,omitempty"` // true when response is image/* (no feed parse)
	Error    string         `json:"error,omitempty"`
}

// Feed represents a generic OPDS 1.x/2.x feed for navigation.
type Feed struct {
	Kind          string    `json:"kind"`          // "navigation" | "acquisition" | "unknown"
	Title         string    `json:"title,omitempty"`
	ID            string    `json:"id,omitempty"`
	Links         []Link    `json:"links"`
	Publications  []Pub     `json:"publications,omitempty"`
	Navigation    []Link    `json:"navigation,omitempty"`
	Entries       []Entry   `json:"entries,omitempty"`       // OPDS 1.x
	Metadata      *Metadata `json:"metadata,omitempty"`
}

type Metadata struct {
	Title   string `json:"title,omitempty"`
	ID      string `json:"id,omitempty"`
	Updated string `json:"updated,omitempty"`
}

type Link struct {
	Href   string `json:"href"`
	Type   string `json:"type,omitempty"`
	Rel    string `json:"rel,omitempty"`
	Title  string `json:"title,omitempty"`
	Length int64  `json:"length,omitempty"`
	// OPDS-PS (p5) extension: stream/page info
	Count        string `json:"p5:count,omitempty"`        // total pages
	LastRead     string `json:"p5:lastRead,omitempty"`    // last read page
	LastReadDate string `json:"p5:lastReadDate,omitempty"` // when last read
}

type Pub struct {
	Metadata *Metadata `json:"metadata,omitempty"`
	Links    []Link    `json:"links,omitempty"`
	Title    string    `json:"title,omitempty"`
}

type Entry struct {
	Title  string `json:"title,omitempty"`
	ID     string `json:"id,omitempty"`
	Links  []Link `json:"links,omitempty"`
}

// Client performs HTTP requests and records request/response.
type Client struct {
	httpClient *http.Client
}

func NewClient() *Client {
	return &Client{
		httpClient: &http.Client{
			Timeout:   30 * time.Second,
			Transport: &http.Transport{},
		},
	}
}

// Fetch fetches targetURL (GET or POST with optional body), records request/response, and parses OPDS feed.
func (c *Client) Fetch(method, targetURL string, headers http.Header, body []byte) (*FetchResult, error) {
	u, err := url.Parse(targetURL)
	if err != nil {
		return &FetchResult{Error: "invalid URL: " + err.Error()}, nil
	}
	if u.Scheme == "" {
		u.Scheme = "https"
	}
	targetURL = u.String()

	var bodyReader io.Reader
	if len(body) > 0 && (method == "POST" || method == "PUT") {
		bodyReader = bytes.NewReader(body)
	}

	req, err := http.NewRequest(method, targetURL, bodyReader)
	if err != nil {
		return &FetchResult{Error: err.Error()}, nil
	}

	// Default Accept for OPDS
	req.Header.Set("Accept", "application/opds+json, application/opds+xml, application/json, application/xml, text/xml, */*")
	req.Header.Set("User-Agent", "OPDS-PS-Explorer/1.0")
	for k, v := range headers {
		if strings.EqualFold(k, "Host") {
			continue
		}
		for _, vv := range v {
			req.Header.Add(k, vv)
		}
	}

	reqRecord := RequestRecord{
		Method:  req.Method,
		URL:     req.URL.String(),
		Headers: cloneHeader(req.Header),
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return &FetchResult{
			Request: reqRecord,
			Error:   "request failed: " + err.Error(),
		}, nil
	}
	defer resp.Body.Close()

	respBody, _ := io.ReadAll(resp.Body)
	respRecord := ResponseRecord{
		Status:     resp.StatusCode,
		StatusText: resp.Status,
		Headers:    cloneHeader(resp.Header),
		Body:       string(respBody),
	}

	result := &FetchResult{
		Request:  reqRecord,
		Response: respRecord,
	}

	ct := resp.Header.Get("Content-Type")
	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
		if strings.HasPrefix(ct, "image/") {
			result.IsImage = true
			// Do not parse image response as feed; leave body as-is in response for debugging
		} else {
			result.Feed = parseFeed(respBody, ct)
		}
	}

	return result, nil
}

// ProxyStream fetches targetURL and streams the response to w (for images/binary). Caller must not write to w before calling.
func (c *Client) ProxyStream(targetURL string, w http.ResponseWriter) (int, error) {
	u, err := url.Parse(targetURL)
	if err != nil {
		return 0, err
	}
	if u.Scheme == "" {
		u.Scheme = "https"
	}
	targetURL = u.String()

	req, err := http.NewRequest(http.MethodGet, targetURL, nil)
	if err != nil {
		return 0, err
	}
	req.Header.Set("User-Agent", "OPDS-PS-Explorer/1.0")
	req.Header.Set("Accept", "*/*")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return 0, err
	}
	defer resp.Body.Close()

	for k, v := range resp.Header {
		for _, vv := range v {
			w.Header().Add(k, vv)
		}
	}
	w.WriteHeader(resp.StatusCode)
	n, err := io.Copy(w, resp.Body)
	return int(n), err
}

func linkFromXML(href, typ, rel, title, count, lastRead, lastReadDate string) Link {
	return Link{
		Href:         href,
		Type:         typ,
		Rel:          rel,
		Title:        title,
		Count:        count,
		LastRead:     lastRead,
		LastReadDate: lastReadDate,
	}
}

func cloneHeader(h http.Header) http.Header {
	h2 := make(http.Header)
	for k, v := range h {
		h2[k] = append([]string(nil), v...)
	}
	return h2
}

func parseFeed(body []byte, contentType string) *Feed {
	feed := &Feed{}

	switch {
	case strings.Contains(contentType, "json"):
		// OPDS 2.0 or JSON feed
		var opds2 struct {
			Metadata    *Metadata `json:"metadata"`
			Links       []Link    `json:"links"`
			Publications []struct {
				Metadata *Metadata `json:"metadata"`
				Links    []Link    `json:"links"`
			} `json:"publications"`
			Navigation []Link `json:"navigation"`
		}
		if err := json.Unmarshal(body, &opds2); err != nil {
			feed.Kind = "unknown"
			feed.Links = []Link{}
			return feed
		}
		feed.Kind = "acquisition"
		if len(opds2.Navigation) > 0 {
			feed.Kind = "navigation"
		}
		if opds2.Metadata != nil {
			feed.Metadata = opds2.Metadata
			feed.Title = opds2.Metadata.Title
			feed.ID = opds2.Metadata.ID
		}
		feed.Links = opds2.Links
		feed.Navigation = opds2.Navigation
		for _, p := range opds2.Publications {
			title := ""
			if p.Metadata != nil {
				title = p.Metadata.Title
			}
			feed.Publications = append(feed.Publications, Pub{
				Metadata: p.Metadata,
				Links:    p.Links,
				Title:    title,
			})
		}
		return feed

	case strings.Contains(contentType, "xml"):
		// OPDS 1.x
		var opds1 struct {
			XMLName xml.Name `xml:"feed"`
			Title   string   `xml:"title"`
			ID      string   `xml:"id"`
			Updated string   `xml:"updated"`
			Link    []struct {
				Href          string `xml:"href,attr"`
				Type          string `xml:"type,attr"`
				Rel           string `xml:"rel,attr"`
				Title         string `xml:"title,attr"`
				P5Count       string `xml:"http://vaemendis.net/opds-pse/ns count,attr"`
				P5LastRead    string `xml:"http://vaemendis.net/opds-pse/ns lastRead,attr"`
				P5LastReadDate string `xml:"http://vaemendis.net/opds-pse/ns lastReadDate,attr"`
			} `xml:"link"`
			Entry []struct {
				Title string `xml:"title"`
				ID    string `xml:"id"`
				Link  []struct {
					Href           string `xml:"href,attr"`
					Type           string `xml:"type,attr"`
					Rel            string `xml:"rel,attr"`
					Title          string `xml:"title,attr"`
					P5Count        string `xml:"http://vaemendis.net/opds-pse/ns count,attr"`
					P5LastRead     string `xml:"http://vaemendis.net/opds-pse/ns lastRead,attr"`
					P5LastReadDate string `xml:"http://vaemendis.net/opds-pse/ns lastReadDate,attr"`
				} `xml:"link"`
			} `xml:"entry"`
		}
		if err := xml.Unmarshal(body, &opds1); err != nil {
			feed.Kind = "unknown"
			return feed
		}
		feed.Kind = "acquisition"
		feed.Title = opds1.Title
		feed.ID = opds1.ID
		feed.Metadata = &Metadata{Title: opds1.Title, ID: opds1.ID, Updated: opds1.Updated}
		for _, l := range opds1.Link {
			feed.Links = append(feed.Links, linkFromXML(l.Href, l.Type, l.Rel, l.Title, l.P5Count, l.P5LastRead, l.P5LastReadDate))
			if l.Rel == "subsection" || l.Rel == "start" || l.Rel == "self" {
				feed.Navigation = append(feed.Navigation, linkFromXML(l.Href, l.Type, l.Rel, l.Title, l.P5Count, l.P5LastRead, l.P5LastReadDate))
			}
		}
		for _, e := range opds1.Entry {
			entry := Entry{Title: e.Title, ID: e.ID}
			for _, l := range e.Link {
				entry.Links = append(entry.Links, linkFromXML(l.Href, l.Type, l.Rel, l.Title, l.P5Count, l.P5LastRead, l.P5LastReadDate))
			}
			feed.Entries = append(feed.Entries, entry)
		}
		return feed
	}

	feed.Kind = "unknown"
	return feed
}

// FormatHeaders returns headers as a string for display.
func FormatHeaders(h http.Header) string {
	var b strings.Builder
	for k, v := range h {
		for _, vv := range v {
			fmt.Fprintf(&b, "%s: %s\n", k, vv)
		}
	}
	return b.String()
}