// Package jmap implements a subset of JMAP Core (RFC 8620) and JMAP Mail
// (RFC 8621) — enough for a real JMAP client to discover the session,
// list mailboxes, and query/fetch messages. Scoped deliberately: Email/set
// (flag changes, delete), Email/import (send), and push (EventSource) are
// deferred, along with Sieve/ManageSieve entirely (RFC 5804, not started
// this phase — noted here, not silently skipped, since ManageSieve was
// originally paired with this phase in the plan).
//
// This exists alongside — not instead of — Phase 8's direct REST API,
// which the webmail SPA still uses. JMAP here is independently testable
// and available for third-party JMAP clients per the plan's config toggle
// (jmap.external_enabled); a later pass can migrate the SPA's internals to
// call this instead without changing its own REST contract.
package jmap

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"

	"gomail/internal/accounts"
	"gomail/internal/auth"
	"gomail/internal/db"
	"gomail/internal/mailstore"
)

const (
	coreCapability = "urn:ietf:params:jmap:core"
	mailCapability = "urn:ietf:params:jmap:mail"
)

type Handler struct {
	database *db.DB
	store    *mailstore.Store
	hostname string
}

func NewHandler(database *db.DB, store *mailstore.Store, hostname string) *Handler {
	return &Handler{database: database, store: store, hostname: hostname}
}

func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
	mux.HandleFunc("/.well-known/jmap", h.session)
	mux.HandleFunc("/jmap/api", h.api)
}

// ── Session resource (RFC 8620 §2) ─────────────────────────────────────────────

func (h *Handler) session(w http.ResponseWriter, r *http.Request) {
	user, ok := h.authenticate(r)
	if !ok {
		w.Header().Set("WWW-Authenticate", `Basic realm="GoMail JMAP"`)
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}

	resp := map[string]any{
		"capabilities": map[string]any{
			coreCapability: map[string]any{
				"maxSizeUpload":         50 * 1024 * 1024,
				"maxConcurrentUpload":   4,
				"maxSizeRequest":        10 * 1024 * 1024,
				"maxConcurrentRequests": 4,
				"maxCallsInRequest":     16,
				"maxObjectsInGet":       500,
				"maxObjectsInSet":       500,
			},
			mailCapability: map[string]any{
				"maxMailboxesPerEmail":       10,
				"maxMailboxDepth":            1,
				"maxSizeMailboxName":         255,
				"maxSizeAttachmentsPerEmail": 50 * 1024 * 1024,
				"emailQuerySortOptions":      []string{"receivedAt"},
				"mayCreateTopLevelMailbox":   false,
			},
		},
		"accounts": map[string]any{
			user.ID: map[string]any{
				"name":                   user.Email,
				"isPersonal":             true,
				"isReadOnly":             false,
				"accountCapabilities":    map[string]any{mailCapability: map[string]any{}},
			},
		},
		"primaryAccounts": map[string]string{mailCapability: user.ID},
		"username":        user.Email,
		"apiUrl":          "/jmap/api",
		"downloadUrl":     "/jmap/download/{accountId}/{blobId}/{name}",
		"uploadUrl":       "/jmap/upload/{accountId}",
		"eventSourceUrl":  "/jmap/events",
		"state":           "1",
	}
	writeJSON(w, http.StatusOK, resp)
}

func (h *Handler) authenticate(r *http.Request) (*db.User, bool) {
	username, password, ok := r.BasicAuth()
	if !ok {
		return nil, false
	}
	return auth.Authenticate(h.database, username, password, auth.ScopeIMAP)
}

// ── API endpoint (RFC 8620 §3) ──────────────────────────────────────────────────

type request struct {
	Using       []string        `json:"using"`
	MethodCalls [][3]any        `json:"methodCalls"`
}

type response struct {
	MethodResponses [][3]any `json:"methodResponses"`
	SessionState    string   `json:"sessionState"`
}

func (h *Handler) api(w http.ResponseWriter, r *http.Request) {
	user, ok := h.authenticate(r)
	if !ok {
		w.Header().Set("WWW-Authenticate", `Basic realm="GoMail JMAP"`)
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}
	if r.Method != http.MethodPost {
		w.WriteHeader(http.StatusMethodNotAllowed)
		return
	}

	var req request
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, "invalid JMAP request: "+err.Error(), http.StatusBadRequest)
		return
	}

	resp := response{SessionState: "1"}
	provider := accounts.NewGoMailProvider(h.database, h.store, user)

	for _, call := range req.MethodCalls {
		methodName, _ := call[0].(string)
		args, _ := call[1].(map[string]any)
		callID, _ := call[2].(string)

		result := h.dispatch(r.Context(), provider, user, methodName, args)
		resp.MethodResponses = append(resp.MethodResponses, [3]any{result.name, result.args, callID})
	}

	writeJSON(w, http.StatusOK, resp)
}

type methodResult struct {
	name string
	args map[string]any
}

func (h *Handler) dispatch(ctx context.Context, provider *accounts.GoMailProvider, user *db.User, method string, args map[string]any) methodResult {
	switch method {
	case "Core/echo":
		return methodResult{name: "Core/echo", args: args}

	case "Mailbox/get":
		return h.mailboxGet(ctx, provider, user)

	case "Email/query":
		return h.emailQuery(ctx, provider, args)

	case "Email/get":
		return h.emailGet(ctx, provider, args)

	default:
		return methodResult{name: "error", args: map[string]any{"type": "unknownMethod", "description": fmt.Sprintf("method %q not implemented", method)}}
	}
}

// ── Mailbox/get ───────────────────────────────────────────────────────────────

func (h *Handler) mailboxGet(ctx context.Context, provider *accounts.GoMailProvider, user *db.User) methodResult {
	folders, err := provider.ListFolders(ctx)
	if err != nil {
		return methodResult{name: "error", args: map[string]any{"type": "serverFail", "description": err.Error()}}
	}

	var list []map[string]any
	for _, f := range folders {
		list = append(list, map[string]any{
			"id":            f.ID,
			"name":          f.DisplayName,
			"role":          jmapRole(f.Type),
			"totalEmails":   f.TotalCount,
			"unreadEmails":  f.UnreadCount,
			"parentId":      nil,
			"sortOrder":     0,
			"isSubscribed":  true,
		})
	}

	return methodResult{name: "Mailbox/get", args: map[string]any{
		"accountId": user.ID, "state": "1", "list": list, "notFound": []string{},
	}}
}

func jmapRole(folderType string) any {
	switch folderType {
	case "inbox":
		return "inbox"
	case "sent":
		return "sent"
	case "drafts":
		return "drafts"
	case "trash":
		return "trash"
	case "junk":
		return "junk"
	default:
		return nil
	}
}

// ── Email/query ───────────────────────────────────────────────────────────────

func (h *Handler) emailQuery(ctx context.Context, provider *accounts.GoMailProvider, args map[string]any) methodResult {
	filter, _ := args["filter"].(map[string]any)
	mailboxID := "INBOX"
	if filter != nil {
		if m, ok := filter["inMailbox"].(string); ok && m != "" {
			mailboxID = m
		}
	}

	headers, err := provider.ListMessages(ctx, mailboxID, accounts.ListOpts{})
	if err != nil {
		return methodResult{name: "error", args: map[string]any{"type": "serverFail", "description": err.Error()}}
	}

	ids := make([]string, len(headers))
	for i, hdr := range headers {
		ids[i] = mailboxID + ":" + hdr.ID // composite ID since JMAP IDs are global, ours are per-folder
	}

	return methodResult{name: "Email/query", args: map[string]any{
		"ids": ids, "queryState": "1", "canCalculateChanges": false,
		"position": 0, "total": len(ids),
	}}
}

// ── Email/get ─────────────────────────────────────────────────────────────────

func (h *Handler) emailGet(ctx context.Context, provider *accounts.GoMailProvider, args map[string]any) methodResult {
	rawIDs, _ := args["ids"].([]any)

	var list []map[string]any
	var notFound []string
	for _, raw := range rawIDs {
		compositeID, _ := raw.(string)
		mailboxID, messageID, ok := splitCompositeID(compositeID)
		if !ok {
			notFound = append(notFound, compositeID)
			continue
		}
		full, err := provider.GetMessage(ctx, mailboxID, messageID)
		if err != nil {
			notFound = append(notFound, compositeID)
			continue
		}
		list = append(list, map[string]any{
			"id":         compositeID,
			"mailboxIds": map[string]bool{mailboxID: true},
			"from":       []map[string]string{{"email": full.From}},
			"to":         []map[string]string{{"email": full.To}},
			"subject":    full.Subject,
			"receivedAt": full.Date,
			"size":       full.SizeBytes,
			"preview":    truncatePreview(string(full.Raw)),
		})
	}

	return methodResult{name: "Email/get", args: map[string]any{
		"state": "1", "list": list, "notFound": notFound,
	}}
}

func splitCompositeID(id string) (mailboxID, messageID string, ok bool) {
	idx := strings.LastIndex(id, ":")
	if idx == -1 {
		return "", "", false
	}
	return id[:idx], id[idx+1:], true
}

func truncatePreview(raw string) string {
	sep := "\r\n\r\n"
	body := raw
	if idx := strings.Index(raw, sep); idx >= 0 {
		body = raw[idx+len(sep):]
	}
	if len(body) > 200 {
		body = body[:200]
	}
	return body
}

func writeJSON(w http.ResponseWriter, code int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	json.NewEncoder(w).Encode(v)
}