package api

import (
	"database/sql"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"
)

func handleStatsAlerts(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		where, args := statsFilter(r.URL.Query(), "received_at")

		// COALESCE because SUM over zero rows is NULL, not 0, and a count of
		// nothing is 0 — without it an empty window is a 500 rather than a
		// legitimately empty report.
		var total, firing, resolved int64
		err := db.QueryRowContext(r.Context(), fmt.Sprintf(`
			SELECT COUNT(*),
			       COALESCE(SUM(CASE WHEN status = 'firing'   THEN 1 ELSE 0 END), 0),
			       COALESCE(SUM(CASE WHEN status = 'resolved' THEN 1 ELSE 0 END), 0)
			FROM alerts WHERE %s`, where), args.all()...,
		).Scan(&total, &firing, &resolved)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		respond(w, http.StatusOK, map[string]int64{
			"total":    total,
			"firing":   firing,
			"resolved": resolved,
		})
	}
}

func handleStatsTop(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		where, args := statsFilter(r.URL.Query(), "received_at")

		limit := 10
		if l := r.URL.Query().Get("limit"); l != "" {
			var n int
			fmt.Sscanf(l, "%d", &n)
			if n > 0 && n <= 100 {
				limit = n
			}
		}
		rows, err := db.QueryContext(r.Context(), fmt.Sprintf(`
			SELECT name, COUNT(*) AS cnt
			FROM   alerts
			WHERE  %s
			GROUP  BY name
			ORDER  BY cnt DESC
			LIMIT  %s`, where, args.add(limit)), args.all()...)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		defer rows.Close()

		type entry struct {
			Name  string `json:"name"`
			Count int64  `json:"count"`
		}
		result := []entry{}
		for rows.Next() {
			var e entry
			if err := rows.Scan(&e.Name, &e.Count); err != nil {
				respond(w, http.StatusInternalServerError, errResp("internal error"))
				return
			}
			result = append(result, e)
		}
		respond(w, http.StatusOK, result)
	}
}

func handleStatsByHour(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		where, args := statsFilter(r.URL.Query(), "received_at")

		rows, err := db.QueryContext(r.Context(), fmt.Sprintf(`
			SELECT EXTRACT(HOUR FROM to_timestamp(received_at) AT TIME ZONE 'UTC')::int AS hr,
			       COUNT(*) AS cnt
			FROM   alerts
			WHERE  %s
			GROUP  BY hr
			ORDER  BY hr ASC`, where), args.all()...)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		defer rows.Close()

		counts := make(map[int]int64, 24)
		for rows.Next() {
			var hr int
			var cnt int64
			if err := rows.Scan(&hr, &cnt); err != nil {
				respond(w, http.StatusInternalServerError, errResp("internal error"))
				return
			}
			counts[hr] = cnt
		}

		type entry struct {
			Hour  int   `json:"hour"`
			Count int64 `json:"count"`
		}
		result := make([]entry, 24)
		for h := range result {
			result[h] = entry{Hour: h, Count: counts[h]}
		}
		respond(w, http.StatusOK, result)
	}
}

func handleStatsByDay(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		where, args := statsFilter(r.URL.Query(), "received_at")

		// Postgres EXTRACT(DOW …) → 0=Sunday … 6=Saturday, the same numbering
		// SQLite's strftime('%w') returned, so the frontend needs no change.
		rows, err := db.QueryContext(r.Context(), fmt.Sprintf(`
			SELECT EXTRACT(DOW FROM to_timestamp(received_at) AT TIME ZONE 'UTC')::int AS dow,
			       COUNT(*) AS cnt
			FROM   alerts
			WHERE  %s
			GROUP  BY dow
			ORDER  BY dow ASC`, where), args.all()...)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}
		defer rows.Close()

		counts := make(map[int]int64, 7)
		for rows.Next() {
			var dow int
			var cnt int64
			if err := rows.Scan(&dow, &cnt); err != nil {
				respond(w, http.StatusInternalServerError, errResp("internal error"))
				return
			}
			counts[dow] = cnt
		}

		dayNames := [7]string{"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
		type entry struct {
			Day     int    `json:"day"`
			DayName string `json:"day_name"`
			Count   int64  `json:"count"`
		}
		result := make([]entry, 7)
		for d := range result {
			result[d] = entry{Day: d, DayName: dayNames[d], Count: counts[d]}
		}
		respond(w, http.StatusOK, result)
	}
}

// handleStatsIncidents reports the queue and the two numbers a rota actually
// cares about: how long it takes someone to pick work up, and how long it takes
// to finish. Neither was computable before incidents existed — alert rows are
// mutated in place and carry no acknowledgement or closure time.
func handleStatsIncidents(db *sql.DB) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		where, args := statsFilter(r.URL.Query(), "triggered_at")

		// The counts are COALESCEd because SUM over zero rows is NULL, not 0.
		// The averages are not: mtta and mttr stay null on purpose, since zero
		// would read as "instant" rather than "nothing to measure yet".
		var total, triggered, acknowledged, resolved int64
		var mtta, mttr *float64
		err := db.QueryRowContext(r.Context(), fmt.Sprintf(`
			SELECT COUNT(*),
			       COALESCE(SUM(CASE WHEN status = 'triggered'    THEN 1 ELSE 0 END), 0),
			       COALESCE(SUM(CASE WHEN status = 'acknowledged' THEN 1 ELSE 0 END), 0),
			       COALESCE(SUM(CASE WHEN status = 'resolved'     THEN 1 ELSE 0 END), 0),
			       AVG(CASE WHEN acknowledged_at IS NOT NULL
			                THEN acknowledged_at - triggered_at END),
			       AVG(CASE WHEN resolved_at IS NOT NULL
			                THEN resolved_at - triggered_at END)
			FROM incidents WHERE %s`, where), args.all()...,
		).Scan(&total, &triggered, &acknowledged, &resolved, &mtta, &mttr)
		if err != nil {
			respond(w, http.StatusInternalServerError, errResp("internal error"))
			return
		}

		respond(w, http.StatusOK, map[string]any{
			"total":        total,
			"triggered":    triggered,
			"acknowledged": acknowledged,
			"resolved":     resolved,
			// Null until something has actually been acknowledged or resolved —
			// zero would read as "instant", which is a different claim.
			"mtta_seconds": mtta,
			"mttr_seconds": mttr,
		})
	}
}

// statsFilter builds a WHERE clause and args from optional ?from and ?to query
// params, filtering on timeCol. Archived rows are always excluded, matching the
// default list views.
func statsFilter(q url.Values, timeCol string) (where string, args *sqlArgs) {
	args = &sqlArgs{}
	clauses := []string{"archived_at IS NULL"}
	if from := q.Get("from"); from != "" {
		if t, err := time.Parse("2006-01-02", from); err == nil {
			clauses = append(clauses, timeCol+" >= "+args.add(t.UTC().Unix()))
		}
	}
	if to := q.Get("to"); to != "" {
		if t, err := time.Parse("2006-01-02", to); err == nil {
			clauses = append(clauses, timeCol+" < "+args.add(t.UTC().AddDate(0, 0, 1).Unix()))
		}
	}
	return strings.Join(clauses, " AND "), args
}