package pub

import (
	"encoding/json"
	"fmt"
	"github.com/go-fed/activity/streams"
	"github.com/go-fed/activity/vocab"
	"io/ioutil"
	"net/http"
	"net/url"
	"strings"
	"time"
)

const (
	postContentTypeHeader = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\""
	getAcceptHeader       = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\""
	contentTypeHeader     = "Content-Type"
	acceptHeader          = "Accept"
	publicActivityPub     = "https://www.w3.org/ns/activitystreams#Public"
	publicJsonLD          = "Public"
	publicJsonLDAS        = "as:Public"
)

var alternatives = []string{"application/activity+json"}

func trimAll(s []string) []string {
	var r []string
	for _, e := range s {
		r = append(r, strings.Trim(e, " "))
	}
	return r
}

func headerEqualsOneOf(header string, acceptable []string) bool {
	sanitizedHeader := strings.Join(trimAll(strings.Split(header, ";")), ";")
	for _, v := range acceptable {
		// Remove any number of whitespace after ;'s
		sanitizedV := strings.Join(trimAll(strings.Split(v, ";")), ";")
		if sanitizedHeader == sanitizedV {
			return true
		}
	}
	return false
}

func isActivityPubPost(r *http.Request) bool {
	return r.Method == "POST" && headerEqualsOneOf(r.Header.Get(contentTypeHeader), []string{postContentTypeHeader, contentTypeHeader})
}

func isActivityPubGet(r *http.Request) bool {
	return r.Method == "GET" && headerEqualsOneOf(r.Header.Get(acceptHeader), []string{getAcceptHeader, contentTypeHeader})
}

// isPublic determines if a target is the Public collection as defined in the
// spec, including JSON-LD compliant collections.
func isPublic(s string) bool {
	return s == publicActivityPub || s == publicJsonLD || s == publicJsonLDAS
}

// dereference makes an HTTP GET request to an IRI in order to obtain the
// ActivityStream representation.
func dereference(c *http.Client, u url.URL, agent string) ([]byte, error) {
	// TODO: (section 7.1) The server MUST dereference the collection (with the user's credentials)
	req, err := http.NewRequest("GET", u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Add(acceptHeader, getAcceptHeader)
	req.Header.Add("Accept-Charset", "utf-8")
	req.Header.Add("Date", time.Now().UTC().Format("Mon, 02 Jan 2006 15:04:05")+" GMT")
	req.Header.Add("User-Agent", fmt.Sprintf("%s (go-fed ActivityPub)", agent))
	resp, err := c.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("Request to %s failed (%d): %s", u.String(), resp.StatusCode, resp.Status)
	}
	return ioutil.ReadAll(resp.Body)
}

// TODO: (Section 7) HTTP caching mechanisms [RFC7234] SHOULD be respected when appropriate, both when receiving responses from other servers as well as sending responses to other servers.

// prepare takes a DeliverableObject and returns a list of the proper recipient
// target URIs. Additionally, the DeliverableObject will have any hidden
// hidden recipients ("bto" and "bcc") stripped from it.
func (c *Client) prepare(o DeliverableObject) ([]url.URL, error) {
	// Get inboxes of recipients
	var r []url.URL
	r = append(r, getToIRIs(o)...)
	r = append(r, getBToIRIs(o)...)
	r = append(r, getCcIRIs(o)...)
	r = append(r, getBccIRIs(o)...)
	r = append(r, getAudienceIRIs(o)...)
	// TODO: Handle public collection
	receiverActors, err := c.resolveInboxes(r, 0, c.MaxDepth)
	if err != nil {
		return nil, err
	}
	targets := getInboxes(receiverActors)
	// Get inboxes of sender(s)
	senderActors, err := c.resolveInboxes(getActorsAttributedToURI(o), 0, c.MaxDepth)
	if err != nil {
		return nil, err
	}
	ignore := getInboxes(senderActors)
	// Post-processing
	r = dedupeIRIs(targets, ignore)
	stripHiddenRecipients(o)
	return r, nil
}

// resolveInboxes takes a list of Actor id URIs and returns them as concrete
// instances of ActorObject. It applies recursively when it encounters a target
// that is a Collection or OrderedCollection.
func (c *Client) resolveInboxes(r []url.URL, depth int, max int) ([]ActorObject, error) {
	if depth >= max {
		return nil, nil
	}
	a := make([]ActorObject, 0, len(r))
	for _, u := range r {
		// Do not retry here -- if a dereference fails, then fail the
		// entire delivery.
		resp, err := dereference(c.Client, u, c.Agent)
		if err != nil {
			return nil, err
		}
		var m map[string]interface{}
		if err = json.Unmarshal(resp, &m); err != nil {
			return nil, err
		}
		var actor ActorObject
		var co *streams.Collection
		var oc *streams.OrderedCollection
		var cp *streams.CollectionPage
		var ocp *streams.OrderedCollectionPage
		// Set AT MOST one of: co, oc, cp, ocp
		// If none of these are set, attempt to use actor
		if err = toActorCollectionResolver(&actor, &co, &oc, &cp, &ocp).Deserialize(m); err != nil {
			return nil, err
		}
		// If a recipient is a Collection or OrderedCollection, then the
		// server MUST dereference the collection. Note that this also
		// applies to CollectionPage and OrderedCollectionPage.
		var uris []url.URL
		if co != nil {
			uris := getURIsInItemer(co.Raw())
			actors, err := c.resolveInboxes(uris, depth+1, max)
			if err != nil {
				return nil, err
			}
			a = append(a, actors...)
		} else if oc != nil {
			uris := getURIsInOrderedItemer(oc.Raw())
			actors, err := c.resolveInboxes(uris, depth+1, max)
			if err != nil {
				return nil, err
			}
			a = append(a, actors...)
		} else if cp != nil {
			cb := func(c vocab.CollectionPageType) error {
				uris = getURIsInItemer(c)
				return nil
			}
			err := doForCollectionPage(c.Client, c.Agent, cb, cp.Raw())
			if err != nil {
				return nil, err
			}
			actors, err := c.resolveInboxes(uris, depth+1, max)
			if err != nil {
				return nil, err
			}
			a = append(a, actors...)
		} else if ocp != nil {
			cb := func(c vocab.OrderedCollectionPageType) error {
				uris = getURIsInOrderedItemer(c)
				return nil
			}
			err := doForOrderedCollectionPage(c.Client, c.Agent, cb, ocp.Raw())
			if err != nil {
				return nil, err
			}
			actors, err := c.resolveInboxes(uris, depth+1, max)
			if err != nil {
				return nil, err
			}
			a = append(a, actors...)
		} else if actor != nil {
			a = append(a, actor)
		}
	}
	return a, nil
}

// getInboxes extracts the 'inbox' IRIs from actors.
func getInboxes(a []ActorObject) []url.URL {
	var u []url.URL
	for _, actor := range a {
		if actor.HasInbox() {
			u = append(u, actor.GetInbox())
		}
	}
	return u
}

// getActorAttributedToURI attempts to find the URIs for the "actor" and
// "attributedTo" originators on the object.
func getActorsAttributedToURI(a ActorObject) []url.URL {
	var u []url.URL
	for i := 0; i < a.AttributedToLen(); i++ {
		if a.IsAttributedToObject(i) {
			obj := a.GetAttributedToObject(i)
			if obj.HasId() {
				u = append(u, obj.GetId())
			}
		} else if a.IsAttributedToLink(i) {
			l := a.GetAttributedToLink(i)
			if l.HasHref() {
				u = append(u, l.GetHref())
			}
		} else if a.IsAttributedToIRI(i) {
			u = append(u, a.GetAttributedToIRI(i))
		}
	}
	for i := 0; i < a.ActorLen(); i++ {
		if a.IsActorObject(i) {
			obj := a.GetActorObject(i)
			if obj.HasId() {
				u = append(u, obj.GetId())
			}
		} else if a.IsActorLink(i) {
			l := a.GetActorLink(i)
			if l.HasHref() {
				u = append(u, l.GetHref())
			}
		} else if a.IsActorIRI(i) {
			u = append(u, a.GetActorIRI(i))
		}
	}
	return u
}

// stripHiddenRecipients removes "bto" and "bcc" from the DeliverableObject.
// Note that this requirement of the specification is under "Section 6: Client
// to Server Interactions", the Social API, and not the Federative API.
func stripHiddenRecipients(o DeliverableObject) {
	for o.BtoLen() > 0 {
		if o.IsBtoObject(0) {
			o.RemoveBtoObject(0)
		} else if o.IsBtoLink(0) {
			o.RemoveBtoLink(0)
		} else if o.IsBtoIRI(0) {
			o.RemoveBtoIRI(0)
		}
	}
	for o.BccLen() > 0 {
		if o.IsBccObject(0) {
			o.RemoveBccObject(0)
		} else if o.IsBccLink(0) {
			o.RemoveBccLink(0)
		} else if o.IsBtoIRI(0) {
			o.RemoveBccIRI(0)
		}
	}
}

// dedupeIRIs will deduplicate final inbox IRIs. The ignore list is applied to
// the final list
func dedupeIRIs(recipients, ignored []url.URL) (out []url.URL) {
	ignoredMap := make(map[url.URL]bool, len(ignored))
	for _, elem := range ignored {
		ignoredMap[elem] = true
	}
	outMap := make(map[url.URL]bool, len(recipients))
	for k, _ := range outMap {
		if !ignoredMap[k] {
			out = append(out, k)
		}
	}
	return
}

func getToIRIs(o DeliverableObject) []url.URL {
	var r []url.URL
	for i := 0; i < o.ToLen(); i++ {
		if o.IsToObject(i) {
			obj := o.GetToObject(i)
			if obj.HasId() {
				r = append(r, obj.GetId())
			}
		} else if o.IsToLink(i) {
			l := o.GetToLink(i)
			if l.HasHref() {
				r = append(r, l.GetHref())
			}
		} else if o.IsToIRI(i) {
			r = append(r, o.GetToIRI(i))
		}
	}
	return r
}

func getBToIRIs(o DeliverableObject) []url.URL {
	var r []url.URL
	for i := 0; i < o.BtoLen(); i++ {
		if o.IsBtoObject(i) {
			obj := o.GetBtoObject(i)
			if obj.HasId() {
				r = append(r, obj.GetId())
			}
		} else if o.IsBtoLink(i) {
			l := o.GetBtoLink(i)
			if l.HasHref() {
				r = append(r, l.GetHref())
			}
		} else if o.IsBtoIRI(i) {
			r = append(r, o.GetBtoIRI(i))
		}
	}
	return r
}

func getCcIRIs(o DeliverableObject) []url.URL {
	var r []url.URL
	for i := 0; i < o.CcLen(); i++ {
		if o.IsCcObject(i) {
			obj := o.GetCcObject(i)
			if obj.HasId() {
				r = append(r, obj.GetId())
			}
		} else if o.IsCcLink(i) {
			l := o.GetCcLink(i)
			if l.HasHref() {
				r = append(r, l.GetHref())
			}
		} else if o.IsCcIRI(i) {
			r = append(r, o.GetCcIRI(i))
		}
	}
	return r
}

func getBccIRIs(o DeliverableObject) []url.URL {
	var r []url.URL
	for i := 0; i < o.BccLen(); i++ {
		if o.IsBccObject(i) {
			obj := o.GetBccObject(i)
			if obj.HasId() {
				r = append(r, obj.GetId())
			}
		} else if o.IsBccLink(i) {
			l := o.GetBccLink(i)
			if l.HasHref() {
				r = append(r, l.GetHref())
			}
		} else if o.IsBccIRI(i) {
			r = append(r, o.GetBccIRI(i))
		}
	}
	return r
}

func getAudienceIRIs(o DeliverableObject) []url.URL {
	var r []url.URL
	for i := 0; i < o.AudienceLen(); i++ {
		if o.IsAudienceObject(i) {
			obj := o.GetAudienceObject(i)
			if obj.HasId() {
				r = append(r, obj.GetId())
			}
		} else if o.IsAudienceLink(i) {
			l := o.GetAudienceLink(i)
			if l.HasHref() {
				r = append(r, l.GetHref())
			}
		} else if o.IsAudienceIRI(i) {
			r = append(r, o.GetAudienceIRI(i))
		}
	}
	return r
}

// doForCollectionPage applies a function over a collection and its subsequent
// pages recursively. It returns the first non-nil error it encounters.
func doForCollectionPage(h *http.Client, agent string, cb func(c vocab.CollectionPageType) error, c vocab.CollectionPageType) error {
	err := cb(c)
	if err != nil {
		return err
	}
	if c.IsNextCollectionPage() {
		// Handle this one weird trick that other peers HATE federating
		// with.
		return doForCollectionPage(h, agent, cb, c.GetNextCollectionPage())
	} else if c.IsNextLink() {
		l := c.GetNextLink()
		if l.HasHref() {
			u := l.GetHref()
			resp, err := dereference(h, u, agent)
			if err != nil {
				return err
			}
			var m map[string]interface{}
			err = json.Unmarshal(resp, &m)
			if err != nil {
				return err
			}
			next, err := toCollectionPage(m)
			if err != nil {
				return err
			}
			if next != nil {
				return doForCollectionPage(h, agent, cb, next.Raw())
			}
		}
	} else if c.IsNextIRI() {
		u := c.GetNextIRI()
		resp, err := dereference(h, u, agent)
		if err != nil {
			return err
		}
		var m map[string]interface{}
		err = json.Unmarshal(resp, &m)
		if err != nil {
			return err
		}
		next, err := toCollectionPage(m)
		if err != nil {
			return err
		}
		if next != nil {
			return doForCollectionPage(h, agent, cb, next.Raw())
		}
	}
	return nil
}

// doForOrderedCollectionPage applies a function over a collection and its
// subsequent pages recursively. It returns the first non-nil error it
// encounters.
func doForOrderedCollectionPage(h *http.Client, agent string, cb func(c vocab.OrderedCollectionPageType) error, c vocab.OrderedCollectionPageType) error {
	err := cb(c)
	if err != nil {
		return err
	}
	if c.IsNextOrderedCollectionPage() {
		// Handle this one weird trick that other peers HATE federating
		// with.
		return doForOrderedCollectionPage(h, agent, cb, c.GetNextOrderedCollectionPage())
	} else if c.IsNextLink() {
		l := c.GetNextLink()
		if l.HasHref() {
			u := l.GetHref()
			resp, err := dereference(h, u, agent)
			if err != nil {
				return err
			}
			var m map[string]interface{}
			err = json.Unmarshal(resp, &m)
			if err != nil {
				return err
			}
			next, err := toOrderedCollectionPage(m)
			if err != nil {
				return err
			}
			if next != nil {
				return doForOrderedCollectionPage(h, agent, cb, next.Raw())
			}
		}
	} else if c.IsNextIRI() {
		u := c.GetNextIRI()
		resp, err := dereference(h, u, agent)
		if err != nil {
			return err
		}
		var m map[string]interface{}
		err = json.Unmarshal(resp, &m)
		if err != nil {
			return err
		}
		next, err := toOrderedCollectionPage(m)
		if err != nil {
			return err
		}
		if next != nil {
			return doForOrderedCollectionPage(h, agent, cb, next.Raw())
		}
	}
	return nil
}

type itemer interface {
	ItemsLen() (l int)
	IsItemsObject(index int) (ok bool)
	GetItemsObject(index int) (v vocab.ObjectType)
	IsItemsLink(index int) (ok bool)
	GetItemsLink(index int) (v vocab.LinkType)
	IsItemsIRI(index int) (ok bool)
	GetItemsIRI(index int) (v url.URL)
}

// getURIsInItemer will extract 'items' from the provided Collection or
// CollectionPage.
func getURIsInItemer(i itemer) []url.URL {
	var u []url.URL
	for j := 0; j < i.ItemsLen(); j++ {
		if i.IsItemsObject(j) {
			obj := i.GetItemsObject(j)
			if obj.HasId() {
				u = append(u, obj.GetId())
			}
		} else if i.IsItemsLink(j) {
			l := i.GetItemsLink(j)
			if l.HasHref() {
				u = append(u, l.GetHref())
			}
		} else if i.IsItemsIRI(j) {
			u = append(u, i.GetItemsIRI(j))
		}
	}
	return u
}

type orderedItemer interface {
	OrderedItemsLen() (l int)
	IsOrderedItemsObject(index int) (ok bool)
	GetOrderedItemsObject(index int) (v vocab.ObjectType)
	IsOrderedItemsLink(index int) (ok bool)
	GetOrderedItemsLink(index int) (v vocab.LinkType)
	IsOrderedItemsIRI(index int) (ok bool)
	GetOrderedItemsIRI(index int) (v url.URL)
}

// getURIsInOrderedItemer will extract 'items' from the provided
// OrderedCollection or OrderedCollectionPage.
func getURIsInOrderedItemer(i orderedItemer) []url.URL {
	var u []url.URL
	for j := 0; j < i.OrderedItemsLen(); j++ {
		if i.IsOrderedItemsObject(j) {
			obj := i.GetOrderedItemsObject(j)
			if obj.HasId() {
				u = append(u, obj.GetId())
			}
		} else if i.IsOrderedItemsLink(j) {
			l := i.GetOrderedItemsLink(j)
			if l.HasHref() {
				u = append(u, l.GetHref())
			}
		} else if i.IsOrderedItemsIRI(j) {
			u = append(u, i.GetOrderedItemsIRI(j))
		}
	}
	return u
}