package api

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"strconv"
	"strings"

	"github.com/go-chi/chi/v5"
	"github.com/jackc/pgx/v5/pgconn"

	"github.com/karti-ai/openmail/internal/core"
	"github.com/karti-ai/openmail/internal/mail"
)

const maxIngestBytes = 30 << 20 // 30 MiB raw message cap

func (s *Server) createInbox(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	var body struct {
		Address     string  `json:"address"`
		DisplayName *string `json:"display_name"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil || body.Address == "" {
		writeErr(w, http.StatusBadRequest, "invalid_request", "address is required")
		return
	}
	ib, err := s.core.CreateInbox(r.Context(), s.podID, body.Address, body.DisplayName)
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusCreated, ib)
}

func (s *Server) listInboxes(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	list, err := s.core.ListInboxes(r.Context(), s.podID)
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"inboxes": list})
}

func (s *Server) getInbox(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	ib, err := s.core.GetInbox(r.Context(), chi.URLParam(r, "id"))
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, ib)
}

// ingest accepts a raw RFC 5322 message body and stores it in the inbox — the
// milestone-1 seed path, and the same path a MailBackend uses for real inbound.
func (s *Server) ingest(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	inboxID := chi.URLParam(r, "id")
	if _, err := s.core.GetInbox(r.Context(), inboxID); handleErr(w, err) {
		return
	}
	raw, err := io.ReadAll(io.LimitReader(r.Body, maxIngestBytes))
	if err != nil || len(raw) == 0 {
		writeErr(w, http.StatusBadRequest, "invalid_request", "raw message body required")
		return
	}
	msg, err := s.core.IngestRaw(r.Context(), inboxID, raw)
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusCreated, msg)
}

func (s *Server) listMessages(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
	list, err := s.core.ListMessages(r.Context(), chi.URLParam(r, "id"), limit)
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"messages": list})
}

func (s *Server) getMessage(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	m, err := s.core.GetMessage(r.Context(), chi.URLParam(r, "id"), chi.URLParam(r, "msgID"))
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, m)
}

func (s *Server) listThreads(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	list, err := s.core.ListThreads(r.Context(), chi.URLParam(r, "id"))
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"threads": list})
}

func (s *Server) getThread(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	inboxID := chi.URLParam(r, "id")
	threadID := chi.URLParam(r, "threadID")
	t, err := s.core.GetThread(r.Context(), inboxID, threadID)
	if handleErr(w, err) {
		return
	}
	msgs, err := s.core.GetThreadMessages(r.Context(), inboxID, threadID)
	if handleErr(w, err) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"thread": t, "messages": msgs})
}

func (s *Server) sendMessage(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	inboxID := chi.URLParam(r, "id")
	ib, err := s.core.GetInbox(r.Context(), inboxID)
	if handleErr(w, err) {
		return
	}
	var body struct {
		To      []string `json:"to"`
		Cc      []string `json:"cc"`
		Bcc     []string `json:"bcc"`
		Subject string   `json:"subject"`
		Text    string   `json:"text"`
		HTML    string   `json:"html"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil || len(body.To) == 0 {
		writeErr(w, http.StatusBadRequest, "invalid_request", "at least one 'to' recipient is required")
		return
	}
	s.dispatch(w, r, &mail.OutgoingMessage{
		InboxID: inboxID, From: ib.Address,
		To: body.To, Cc: body.Cc, Bcc: body.Bcc,
		Subject: body.Subject, Text: body.Text, HTML: body.HTML,
	})
}

func (s *Server) replyMessage(w http.ResponseWriter, r *http.Request) {
	if !s.requireCore(w) {
		return
	}
	inboxID := chi.URLParam(r, "id")
	ib, err := s.core.GetInbox(r.Context(), inboxID)
	if handleErr(w, err) {
		return
	}
	orig, err := s.core.GetMessage(r.Context(), inboxID, chi.URLParam(r, "msgID"))
	if handleErr(w, err) {
		return
	}
	var body struct {
		Text string `json:"text"`
		HTML string `json:"html"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeErr(w, http.StatusBadRequest, "invalid_request", "invalid body")
		return
	}
	out := &mail.OutgoingMessage{
		InboxID: inboxID, From: ib.Address,
		Subject: replySubject(orig.Subject),
		Text:    body.Text, HTML: body.HTML,
		References: append(append([]string{}, orig.References...), strPtr(orig.MessageIDHdr)...),
	}
	if orig.MessageIDHdr != nil {
		out.InReplyTo = *orig.MessageIDHdr
	}
	if orig.FromAddr != nil {
		out.To = []string{*orig.FromAddr}
	}
	s.dispatch(w, r, out)
}

// dispatch hands an outgoing message to the active backend, translating the
// NullBackend's ErrNotSupported into a clear 503 (no send path configured yet).
func (s *Server) dispatch(w http.ResponseWriter, r *http.Request, out *mail.OutgoingMessage) {
	res, err := s.backend.Send(r.Context(), out)
	if errors.Is(err, mail.ErrNotSupported) {
		writeErr(w, http.StatusServiceUnavailable, "send_unavailable",
			"no send-capable mail backend configured (relay/imap_smtp/embedded land in later milestones)")
		return
	}
	if err != nil {
		writeErr(w, http.StatusBadGateway, "send_failed", err.Error())
		return
	}
	writeJSON(w, http.StatusAccepted, res)
}

func handleErr(w http.ResponseWriter, err error) bool {
	var pgErr *pgconn.PgError
	switch {
	case err == nil:
		return false
	case errors.Is(err, core.ErrNotFound):
		writeErr(w, http.StatusNotFound, "not_found", "resource not found")
	case errors.As(err, &pgErr) && pgErr.Code == "22P02":
		// invalid_text_representation, e.g. a malformed UUID in the path — treat
		// as not found rather than a 500 that echoes the driver error.
		writeErr(w, http.StatusNotFound, "not_found", "resource not found")
	case errors.As(err, &pgErr) && pgErr.Code == "23505":
		// unique_violation, e.g. an inbox address that already exists.
		writeErr(w, http.StatusConflict, "conflict", "resource already exists")
	default:
		writeErr(w, http.StatusInternalServerError, "internal_error", "internal error")
	}
	return true
}

func replySubject(s *string) string {
	if s == nil || strings.TrimSpace(*s) == "" {
		return "Re:"
	}
	trimmed := strings.TrimSpace(*s)
	if strings.HasPrefix(strings.ToLower(trimmed), "re:") {
		return trimmed
	}
	return "Re: " + trimmed
}

func strPtr(s *string) []string {
	if s == nil || *s == "" {
		return nil
	}
	return []string{*s}
}