package api

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

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

// alertSelectFrom is the shared SELECT … FROM … clause used by all alert queries.
// It LEFT JOINs users so acknowledged_by username is always available.
const alertSelectFrom = `
	SELECT a.id, a.fingerprint, a.name, a.status,
	       a.labels, a.annotations,
	       a.starts_at, a.ends_at, a.generator_url, a.received_at,
	       a.acknowledged_by, a.acknowledged_at, u.username,
	       a.archived_at
	FROM   alerts a
	LEFT   JOIN users u ON u.id = a.acknowledged_by`

func handleListAlerts(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		q := r.URL.Query()

		where := []string{}
		args := []any{}

		if status := q.Get("status"); status != "" {
			where = append(where, "a.status = ?")
			args = append(args, status)
		}
		if name := q.Get("name"); name != "" {
			where = append(where, "a.name = ?")
			args = append(args, name)
		}
		if archived := q.Get("archived"); archived == "true" {
			where = append(where, "a.archived_at IS NOT NULL")
		} else {
			where = append(where, "a.archived_at IS NULL")
		}

		if from := q.Get("from"); from != "" {
			if t, err := time.Parse("2006-01-02", from); err == nil {
				where = append(where, "a.received_at >= ?")
				args = append(args, t.UTC().Unix())
			}
		}
		if to := q.Get("to"); to != "" {
			if t, err := time.Parse("2006-01-02", to); err == nil {
				where = append(where, "a.received_at < ?")
				args = append(args, t.UTC().AddDate(0, 0, 1).Unix())
			}
		}

		limit := 50
		if l := q.Get("limit"); l != "" {
			if n, err := strconv.Atoi(l); err == nil && n > 0 && n <= 500 {
				limit = n
			}
		}

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

		rows, err := db.QueryContext(r.Context(),
			fmt.Sprintf("%s WHERE %s ORDER BY a.received_at DESC LIMIT ?", alertSelectFrom, clause),
			args...)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		defer rows.Close()

		alerts := []models.Alert{}
		for rows.Next() {
			a, err := scanAlert(rows)
			if err != nil {
				respond(w, http.StatusInternalServerError, errResp("internal error"))
				return
			}
			alerts = append(alerts, a)
		}
		respond(w, http.StatusOK, alerts)
	}
}

func handleGetAlert(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 alert id"))
			return
		}
		a, err := fetchAlert(r.Context(), db, id)
		if err == sql.ErrNoRows {
			respond(w, http.StatusNotFound, errResp("alert not found"))
			return
		}
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		respond(w, http.StatusOK, a)
	}
}

func handleAcknowledge(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 alert id"))
			return
		}
		user, _ := userFromContext(r.Context())

		res, err := db.ExecContext(r.Context(),
			"UPDATE alerts SET acknowledged_by = ?, acknowledged_at = ? WHERE id = ?",
			user.ID, time.Now().Unix(), id)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		if n, _ := res.RowsAffected(); n == 0 {
			respond(w, http.StatusNotFound, errResp("alert not found"))
			return
		}

		a, _ := fetchAlert(r.Context(), db, id)
		respond(w, http.StatusOK, a)
	}
}

func handleUnacknowledge(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 alert id"))
			return
		}

		res, err := db.ExecContext(r.Context(),
			"UPDATE alerts SET acknowledged_by = NULL, acknowledged_at = NULL 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("alert not found"))
			return
		}
		w.WriteHeader(http.StatusNoContent)
	}
}

// fetchAlert loads a single alert by ID using the shared JOIN query.
func fetchAlert(ctx context.Context, db *sql.DB, id int64) (models.Alert, error) {
	return scanAlert(db.QueryRowContext(ctx, alertSelectFrom+" WHERE a.id = ?", id))
}

// scanner is satisfied by both *sql.Row and *sql.Rows.
type scanner interface {
	Scan(dest ...any) error
}

func scanAlert(s scanner) (models.Alert, error) {
	var a models.Alert
	var labelsJSON, annotationsJSON string
	var startsAtUnix, receivedAtUnix int64
	var endsAtUnix, ackAtUnix, archivedAtUnix *int64
	var ackByID *int64
	var ackByUser *string

	if err := s.Scan(
		&a.ID, &a.Fingerprint, &a.Name, &a.Status,
		&labelsJSON, &annotationsJSON,
		&startsAtUnix, &endsAtUnix,
		&a.GeneratorURL, &receivedAtUnix,
		&ackByID, &ackAtUnix, &ackByUser,
		&archivedAtUnix,
	); err != nil {
		return a, err
	}

	json.Unmarshal([]byte(labelsJSON), &a.Labels)          //nolint:errcheck
	json.Unmarshal([]byte(annotationsJSON), &a.Annotations) //nolint:errcheck
	a.StartsAt = time.Unix(startsAtUnix, 0).UTC()
	a.ReceivedAt = time.Unix(receivedAtUnix, 0).UTC()
	if endsAtUnix != nil {
		t := time.Unix(*endsAtUnix, 0).UTC()
		a.EndsAt = &t
	}
	if ackByID != nil {
		t := time.Unix(*ackAtUnix, 0).UTC()
		a.AcknowledgedByID = ackByID
		a.AcknowledgedByUser = ackByUser
		a.AcknowledgedAt = &t
	}
	if archivedAtUnix != nil {
		t := time.Unix(*archivedAtUnix, 0).UTC()
		a.ArchivedAt = &t
	}
	return a, nil
}

func handleArchive(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 alert id"))
			return
		}
		res, err := db.ExecContext(r.Context(),
			"UPDATE alerts SET archived_at = unixepoch() 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("alert not found"))
			return
		}
		a, _ := fetchAlert(r.Context(), db, id)
		respond(w, http.StatusOK, a)
	}
}

func handleUnarchive(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 alert id"))
			return
		}
		res, err := db.ExecContext(r.Context(),
			"UPDATE alerts SET archived_at = NULL 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("alert not found"))
			return
		}
		w.WriteHeader(http.StatusNoContent)
	}
}