// PUT /api/me/timezone — accept the client's IANA timezone and store
// it on the user row. The system-playlist scheduler (#392 Half B)
// reads this column to fire each user's daily 03:00 build in their
// local time.
//
// Scheduler.Refresh(ctx, userID) is invoked in a later commit (Task 3)
// so a timezone change takes effect synchronously rather than waiting
// for the hourly reconciliation pass.

package api

import (
	"encoding/json"
	"net/http"
	"time"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// putTimezoneBody is the JSON body for PUT /api/me/timezone.
type putTimezoneBody struct {
	Timezone string `json:"timezone"`
}

func (h *handlers) handlePutTimezone(w http.ResponseWriter, r *http.Request) {
	user, ok := auth.UserFromContext(r.Context())
	if !ok {
		writeErr(w, apierror.Unauthorized("unauthorized", "authentication required"))
		return
	}

	var body putTimezoneBody
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeErr(w, apierror.BadRequest("bad_body", "invalid JSON body"))
		return
	}
	if body.Timezone == "" {
		writeErr(w, apierror.BadRequest("bad_body", "timezone is required"))
		return
	}
	if _, err := time.LoadLocation(body.Timezone); err != nil {
		writeErr(w, apierror.BadRequest("invalid_timezone",
			"timezone must be a valid IANA name (e.g. America/New_York)"))
		return
	}

	q := dbq.New(h.pool)
	if err := q.UpdateUserTimezone(r.Context(), dbq.UpdateUserTimezoneParams{
		ID:       user.ID,
		Timezone: body.Timezone,
	}); err != nil {
		h.logger.Error("api: update timezone", "err", err)
		writeErr(w, apierror.InternalMsg("update failed", err))
		return
	}

	// Reschedule the user's daily build at their new timezone. Failure
	// here doesn't undo the DB write — the hourly reconciliation pass
	// would pick up the new tz within an hour at worst.
	if h.playlistScheduler != nil {
		if err := h.playlistScheduler.Refresh(r.Context(), user.ID); err != nil {
			h.logger.Warn("api: scheduler refresh after timezone update",
				"user_id", uuidToString(user.ID), "err", err)
		}
	}

	w.WriteHeader(http.StatusNoContent)
}