package api

import (
	"fmt"
	"net/http"
	"time"
)

// Buckets a report may be cut into. A whitelist rather than passing the string
// through: date_trunc takes a text argument, so an unchecked value is either a
// database error surfaced to a shop floor or, in a query built by
// concatenation, something much worse.
var buckets = map[string]bool{
	"hour": true, "day": true, "week": true, "month": true,
}

// maxWindow bounds a report at two years. Not for safety - for honesty: an
// open-ended range on a 2 vCPU box times out at the proxy and the user sees a
// blank screen with no explanation.
const maxWindow = 2 * 366 * 24 * time.Hour

func (s *Server) reportQuery(r *http.Request) (ReportQuery, error) {
	p := PrincipalFrom(r.Context())
	q := r.URL.Query()

	// The tenant comes from the session. A client_id parameter would be a
	// cross-tenant read waiting for somebody to try it.
	out := ReportQuery{ClientID: p.ClientID}

	// A shop may be named by uuid or by its slug. Resolved here, where an
	// unknown one is a 400 the caller can read, rather than in Postgres where
	// a malformed uuid is a cast error and surfaces as a 500.
	if raw := siteParam(r); raw != "" {
		id, err := s.siteIDFor(r.Context(), p.ClientID, raw)
		if err != nil {
			return out, fmt.Errorf("could not look up that shop: %w", err)
		}
		if id == "" {
			return out, fmt.Errorf("no shop called %q", raw)
		}
		out.SiteID = id
	}

	now := s.now()
	from, err := parseDay(q.Get("from"), now.AddDate(0, 0, -29))
	if err != nil {
		return out, fmt.Errorf("`from` is not a date: %w", err)
	}
	to, err := parseDay(q.Get("to"), now)
	if err != nil {
		return out, fmt.Errorf("`to` is not a date: %w", err)
	}
	// `to` is inclusive to the user ("1st to the 7th" includes the 7th) and
	// exclusive in SQL. Doing that conversion in one place is the difference
	// between a report that quietly misses its own last day and one that does
	// not.
	if len(trim(q.Get("to"))) == 10 {
		to = to.AddDate(0, 0, 1)
	}
	if !to.After(from) {
		return out, fmt.Errorf("`to` must be after `from`")
	}
	if to.Sub(from) > maxWindow {
		return out, fmt.Errorf("that range is longer than two years - " +
			"please narrow it")
	}
	out.From, out.To = from, to

	out.Bucket = trim(q.Get("bucket"))
	if out.Bucket == "" {
		out.Bucket = "day"
	}
	if !buckets[out.Bucket] {
		return out, fmt.Errorf("bucket must be hour, day, week or month")
	}

	out.Timezone = trim(q.Get("tz"))
	if out.Timezone == "" {
		out.Timezone = "UTC"
	}
	// Validated here, where a bad name is a 400 the user can fix, rather than
	// in Postgres where it is a 500.
	if _, err := time.LoadLocation(out.Timezone); err != nil {
		return out, fmt.Errorf("unknown timezone %q", out.Timezone)
	}
	return out, nil
}

// parseDay accepts a plain date or a full RFC3339 timestamp. Shop staff type
// dates; the desktop app sends timestamps.
func parseDay(s string, def time.Time) (time.Time, error) {
	s = trim(s)
	if s == "" {
		return def.UTC(), nil
	}
	if len(s) == 10 {
		return time.Parse("2006-01-02", s)
	}
	t, err := time.Parse(time.RFC3339, s)
	return t.UTC(), err
}

func (s *Server) handleFootfall(w http.ResponseWriter, r *http.Request) {
	q, err := s.reportQuery(r)
	if err != nil {
		badRequest(w, err.Error())
		return
	}
	points, totals, err := s.Store.Footfall(r.Context(), q)
	if err != nil {
		s.serverError(w, "footfall", err)
		return
	}
	writeJSON(w, http.StatusOK, FootfallReport{
		From:              q.From.Format(time.RFC3339),
		To:                q.To.Format(time.RFC3339),
		Bucket:            q.Bucket,
		TZ:                q.Timezone,
		Points:            points,
		Total:             totals.UniqueVisitors,
		Visits:            totals.Visits,
		FractionBelowGate: totals.FractionBelowGate,
		WorstSite:         totals.WorstSite,
	})
}

func (s *Server) handleConversion(w http.ResponseWriter, r *http.Request) {
	q, err := s.reportQuery(r)
	if err != nil {
		badRequest(w, err.Error())
		return
	}
	rep, err := s.Store.Conversion(r.Context(), q)
	if err != nil {
		s.serverError(w, "conversion", err)
		return
	}
	writeJSON(w, http.StatusOK, rep)
}

func (s *Server) handleSites(w http.ResponseWriter, r *http.Request) {
	p := PrincipalFrom(r.Context())
	sites, err := s.Store.SiteHealth(r.Context(), p.ClientID)
	if err != nil {
		s.serverError(w, "site health", err)
		return
	}
	if sites == nil {
		// A JSON null would make every caller handle two empty cases.
		sites = []SiteHealth{}
	}
	writeJSON(w, http.StatusOK, sites)
}