// Package api holds the student-facing JSON handlers of the jz.bm plugin,
// served under /_bm/api/v1 behind the golem15.user jwt.auth guard.
//
// Every response is built field by field and wrapped in {"data": ...}; a
// paginated list adds {"meta": ...}. Timestamps are RFC 3339 in
// Europe/Warsaw, dates are YYYY-MM-DD.
package api

import (
	"net/http"
	"sort"
	"time"

	"git.golem15.com/golem15/summercms/modules/bouncer"
	"git.golem15.com/golem15/summercms/modules/phrasebook"
	"git.golem15.com/golem15/summercms/modules/wire"
	"gorm.io/gorm"
)

// Handlers serves the API. The plugin builds it in Routes; tests build it
// with their own database and clock.
type Handlers struct {
	// DB returns the application database, or nil while none is published.
	// It is resolved per request: the binary boots plugins before serve
	// publishes the database.
	DB func() *gorm.DB
	// Translator returns the application translator for validation
	// messages; nil gives English.
	Translator func() *phrasebook.Translator
	// Now is the clock; nil means time.Now.
	Now func() time.Time
	// PerPage is the default page size of /materials.
	PerPage int
	// DashboardLimit is the number of sessions and deadlines on /dashboard.
	DashboardLimit int
	// PublicURL is the absolute base URL of the application
	// (jz.bm.public_url), used for the calendar feed URL and the links in
	// it. Empty means the scheme and Host of the request.
	PublicURL string
}

func (h *Handlers) now() time.Time {
	if h.Now != nil {
		return h.Now()
	}
	return time.Now()
}

func (h *Handlers) perPage() int {
	if h.PerPage > 0 {
		return min(h.PerPage, maxPerPage)
	}
	return defaultPerPage
}

func (h *Handlers) dashboardLimit() int {
	if h.DashboardLimit > 0 {
		return h.DashboardLimit
	}
	return 5
}

func (h *Handlers) translator() *phrasebook.Translator {
	if h.Translator == nil {
		return nil
	}
	return h.Translator()
}

const (
	defaultPerPage = 20
	maxPerPage     = 100
)

// caller returns the signed-in user's ID. It answers 401 itself and returns
// false when there is none (the jwt.auth guard normally answers first).
func (h *Handlers) caller(w http.ResponseWriter, r *http.Request) (uint, bool) {
	user, ok := bouncer.User(r.Context())
	if !ok || user == nil || user.ID == 0 {
		wire.WriteJSON(w, http.StatusUnauthorized, map[string]any{"error": true, "message": "Unauthenticated."})
		return 0, false
	}
	return user.ID, true
}

// db returns the database bound to the request context. It answers 503
// itself and returns false while no database is published.
func (h *Handlers) db(w http.ResponseWriter, r *http.Request) (*gorm.DB, bool) {
	var db *gorm.DB
	if h.DB != nil {
		db = h.DB()
	}
	if db == nil {
		wire.WriteJSON(w, http.StatusServiceUnavailable, map[string]any{"error": true, "message": "Database unavailable."})
		return nil, false
	}
	return db.WithContext(r.Context()), true
}

func writeData(w http.ResponseWriter, v any) {
	wire.WriteJSON(w, http.StatusOK, map[string]any{"data": v})
}

func writeNotFound(w http.ResponseWriter) {
	wire.WriteJSON(w, http.StatusNotFound, map[string]any{"error": true, "message": "Not found."})
}

// writeValidation answers 422 with Laravel's validation body: the first
// message and the errors object from lagoon.ValidateRequest.
func writeValidation(w http.ResponseWriter, errs map[string][]string) {
	keys := make([]string, 0, len(errs))
	for k := range errs {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	message := "The given data was invalid."
	if len(keys) > 0 && len(errs[keys[0]]) > 0 {
		message = errs[keys[0]][0]
	}
	wire.WriteJSON(w, http.StatusUnprocessableEntity, map[string]any{"message": message, "errors": errs})
}

func writeOpaque500(w http.ResponseWriter) { wire.WriteOpaque500(w) }

// writeJSONPage writes a lagoon.Page as it is: {data, meta}.
func writeJSONPage(w http.ResponseWriter, page any) { wire.WriteJSON(w, http.StatusOK, page) }