package api

import (
	"context"
	"database/sql"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/yeniklas/terdut-server/internal/models"
)

func handleCreateSchedule(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var req struct {
			UserID int64    `json:"user_id"`
			Dates  []string `json:"dates"`
		}
		if err := decodeJSON(r, &req); err != nil {
			respond(w, http.StatusBadRequest, errResp("invalid request body"))
			return
		}
		if req.UserID == 0 {
			respond(w, http.StatusBadRequest, errResp("user_id is required"))
			return
		}
		if len(req.Dates) == 0 {
			respond(w, http.StatusBadRequest, errResp("dates must not be empty"))
			return
		}
		for _, d := range req.Dates {
			if _, err := time.Parse("2006-01-02", d); err != nil {
				respond(w, http.StatusBadRequest, errResp("invalid date: "+d+" (expected YYYY-MM-DD)"))
				return
			}
		}

		// Verify the user exists.
		var exists int
		if err := db.QueryRowContext(r.Context(), "SELECT 1 FROM users WHERE id = ?", req.UserID).Scan(&exists); err != nil {
			respond(w, http.StatusNotFound, errResp("user not found"))
			return
		}

		// All-or-nothing: if any date already has an assignment, reject the whole request.
		tx, err := db.BeginTx(r.Context(), nil)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		defer tx.Rollback()

		for _, d := range req.Dates {
			if _, err := tx.ExecContext(r.Context(),
				"INSERT INTO schedule_entries (user_id, date) VALUES (?, ?)", req.UserID, d); err != nil {
				if strings.Contains(err.Error(), "UNIQUE constraint failed") {
					respond(w, http.StatusConflict, errResp("date already assigned: "+d))
					return
				}
				respond(w, http.StatusInternalServerError, errResp("internal error"))
				return
			}
		}
		if err := tx.Commit(); err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}

		// Return the newly created entries.
		dateSet := make(map[string]bool, len(req.Dates))
		for _, d := range req.Dates {
			dateSet[d] = true
		}
		all, err := scheduleRange(r.Context(), db, req.Dates[0], req.Dates[len(req.Dates)-1])
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		created := []models.ScheduleEntry{}
		for _, e := range all {
			if dateSet[e.Date] {
				created = append(created, e)
			}
		}
		respond(w, http.StatusCreated, created)
	}
}

func handleListSchedule(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		q := r.URL.Query()
		from, to := q.Get("from"), q.Get("to")

		if from != "" {
			if _, err := time.Parse("2006-01-02", from); err != nil {
				respond(w, http.StatusBadRequest, errResp("invalid from date (expected YYYY-MM-DD)"))
				return
			}
		}
		if to != "" {
			if _, err := time.Parse("2006-01-02", to); err != nil {
				respond(w, http.StatusBadRequest, errResp("invalid to date (expected YYYY-MM-DD)"))
				return
			}
		}

		entries, err := scheduleRange(r.Context(), db, from, to)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		respond(w, http.StatusOK, entries)
	}
}

func handleDeleteSchedule(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		id, err := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
		if err != nil {
			respond(w, http.StatusBadRequest, errResp("invalid schedule id"))
			return
		}
		res, err := db.ExecContext(r.Context(), "DELETE FROM schedule_entries WHERE id = ?", id)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		if n, _ := res.RowsAffected(); n == 0 {
			respond(w, http.StatusNotFound, errResp("schedule entry not found"))
			return
		}
		w.WriteHeader(http.StatusNoContent)
	}
}

func handleCurrentSchedule(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		today := time.Now().UTC().Format("2006-01-02")

		var e models.ScheduleEntry
		var ts int64
		err := db.QueryRowContext(r.Context(), `
			SELECT s.id, s.user_id, u.username, s.date, s.created_at
			FROM   schedule_entries s
			JOIN   users u ON u.id = s.user_id
			WHERE  s.date = ?`, today).Scan(&e.ID, &e.UserID, &e.Username, &e.Date, &ts)
		if err == sql.ErrNoRows {
			respond(w, http.StatusNotFound, errResp("no one is on call today"))
			return
		}
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		e.CreatedAt = time.Unix(ts, 0).UTC()
		respond(w, http.StatusOK, e)
	}
}

// scheduleRange returns schedule entries ordered by date.
// from and to are YYYY-MM-DD strings; an empty string means unbounded on that side.
func scheduleRange(ctx context.Context, db *sql.DB, from, to string) ([]models.ScheduleEntry, error) {
	where := []string{}
	args := []any{}
	if from != "" {
		where = append(where, "s.date >= ?")
		args = append(args, from)
	}
	if to != "" {
		where = append(where, "s.date <= ?")
		args = append(args, to)
	}

	clause := "1=1"
	if len(where) > 0 {
		clause = strings.Join(where, " AND ")
	}

	rows, err := db.QueryContext(ctx, `
		SELECT s.id, s.user_id, u.username, s.date, s.created_at
		FROM   schedule_entries s
		JOIN   users u ON u.id = s.user_id
		WHERE  `+clause+`
		ORDER  BY s.date ASC`, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	entries := []models.ScheduleEntry{}
	for rows.Next() {
		var e models.ScheduleEntry
		var ts int64
		if err := rows.Scan(&e.ID, &e.UserID, &e.Username, &e.Date, &ts); err != nil {
			return nil, err
		}
		e.CreatedAt = time.Unix(ts, 0).UTC()
		entries = append(entries, e)
	}
	return entries, rows.Err()
}