package api

import (
	"context"
	"fmt"
	"sort"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"
)

type EnergyBar struct {
	Time    time.Time `json:"time"`
	Buy     float64   `json:"buy"`
	Sell    float64   `json:"sell"`
	Produce float64   `json:"produce"`
	Consume float64   `json:"consume"`
}

type PowerPoint struct {
	Time  time.Time `json:"time"`
	PV    float64   `json:"pv"`
	Barn  float64   `json:"barn"`
	House float64   `json:"house"`
}

type BatteryPoint struct {
	Time  time.Time `json:"time"`
	Level float64   `json:"level"`
}

var periodDefaults = map[string]int{
	"day":   30,
	"week":  12,
	"month": 12,
}

// viewForRange picks the right continuous aggregate views for the given time range.
func viewForRange(timeRange string) (invView, meterView, interval string) {
	switch timeRange {
	case "1h":
		return "inverter_10m", "power_meter_10m", "1 hour"
	case "6h":
		return "inverter_10m", "power_meter_10m", "6 hours"
	case "7d":
		return "inverter_1h", "power_meter_1h", "7 days"
	default: // "24h" and anything else
		return "inverter_10m", "power_meter_10m", "24 hours"
	}
}

func sortedUnion(maps ...map[time.Time]float64) []time.Time {
	seen := make(map[time.Time]bool)
	for _, m := range maps {
		for t := range m {
			seen[t] = true
		}
	}
	times := make([]time.Time, 0, len(seen))
	for t := range seen {
		times = append(times, t)
	}
	sort.Slice(times, func(i, j int) bool { return times[i].Before(times[j]) })
	return times
}

func getPower(ctx context.Context, pool *pgxpool.Pool, timeRange string) ([]PowerPoint, error) {
	invView, meterView, interval := viewForRange(timeRange)

	type colRow struct {
		bucket time.Time
		value  float64
	}
	queryCol := func(sql string) (map[time.Time]float64, error) {
		rows, err := pool.Query(ctx, sql)
		if err != nil {
			return nil, err
		}
		defer rows.Close()
		m := make(map[time.Time]float64)
		for rows.Next() {
			var r colRow
			if err := rows.Scan(&r.bucket, &r.value); err != nil {
				return nil, err
			}
			m[r.bucket] = r.value
		}
		return m, rows.Err()
	}

	pvSQL := fmt.Sprintf(
		`SELECT bucket, COALESCE(pv_power, 0) FROM %s WHERE bucket >= NOW() - '%s'::interval ORDER BY bucket`,
		invView, interval)
	houseSQL := fmt.Sprintf(
		`SELECT bucket, COALESCE(total_power, 0) FROM %s WHERE device = 'house' AND bucket >= NOW() - '%s'::interval ORDER BY bucket`,
		meterView, interval)
	barnSQL := fmt.Sprintf(
		`SELECT bucket, COALESCE(total_power, 0) FROM %s WHERE device = 'barn' AND bucket >= NOW() - '%s'::interval ORDER BY bucket`,
		meterView, interval)

	type result struct {
		m   map[time.Time]float64
		err error
	}
	pvCh := make(chan result, 1)
	houseCh := make(chan result, 1)
	barnCh := make(chan result, 1)

	go func() { m, e := queryCol(pvSQL); pvCh <- result{m, e} }()
	go func() { m, e := queryCol(houseSQL); houseCh <- result{m, e} }()
	go func() { m, e := queryCol(barnSQL); barnCh <- result{m, e} }()

	pvRes := <-pvCh
	houseRes := <-houseCh
	barnRes := <-barnCh

	if pvRes.err != nil {
		return nil, pvRes.err
	}
	if houseRes.err != nil {
		return nil, houseRes.err
	}
	if barnRes.err != nil {
		return nil, barnRes.err
	}

	times := sortedUnion(pvRes.m, houseRes.m, barnRes.m)
	pts := make([]PowerPoint, 0, len(times))
	for _, t := range times {
		pts = append(pts, PowerPoint{
			Time:  t,
			PV:    pvRes.m[t],
			House: houseRes.m[t],
			Barn:  barnRes.m[t],
		})
	}
	return pts, nil
}

func getBattery(ctx context.Context, pool *pgxpool.Pool, timeRange string) ([]BatteryPoint, error) {
	invView, _, interval := viewForRange(timeRange)

	sql := fmt.Sprintf(
		`SELECT bucket, COALESCE(battery_soc, 0) FROM %s WHERE bucket >= NOW() - '%s'::interval ORDER BY bucket`,
		invView, interval)

	rows, err := pool.Query(ctx, sql)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var pts []BatteryPoint
	for rows.Next() {
		var p BatteryPoint
		if err := rows.Scan(&p.Time, &p.Level); err != nil {
			return nil, err
		}
		pts = append(pts, p)
	}
	return pts, rows.Err()
}

func getBars(ctx context.Context, pool *pgxpool.Pool, period string, count int) ([]EnergyBar, error) {
	var periodTrunc, rangeInterval string
	switch period {
	case "day":
		periodTrunc = "day"
		rangeInterval = fmt.Sprintf("%d days", count+1)
	case "week":
		periodTrunc = "week"
		rangeInterval = fmt.Sprintf("%d weeks", count+1)
	case "month":
		periodTrunc = "month"
		rangeInterval = fmt.Sprintf("%d months", count+1)
	default:
		return nil, fmt.Errorf("unknown period %q", period)
	}

	// DISTINCT ON picks the last-written daily row for each period bucket,
	// then LAG() computes the delta (energy consumed/produced/traded) over
	// that period. Fetching count+1 rows ensures LAG has a previous value
	// for the first bar; we trim to count at the end.
	sql := fmt.Sprintf(`
WITH inv_last AS (
  SELECT DISTINCT ON (date_trunc('%[1]s', bucket))
         date_trunc('%[1]s', bucket) AS period,
         grid_import_kwh, grid_export_kwh, pv_energy_kwh
  FROM inverter_daily
  WHERE bucket >= NOW() - '%[2]s'::interval
  ORDER BY date_trunc('%[1]s', bucket), bucket DESC
),
house_last AS (
  SELECT DISTINCT ON (date_trunc('%[1]s', bucket))
         date_trunc('%[1]s', bucket) AS period,
         import_kwh
  FROM power_meter_daily
  WHERE device = 'house' AND bucket >= NOW() - '%[2]s'::interval
  ORDER BY date_trunc('%[1]s', bucket), bucket DESC
),
barn_last AS (
  SELECT DISTINCT ON (date_trunc('%[1]s', bucket))
         date_trunc('%[1]s', bucket) AS period,
         import_kwh
  FROM power_meter_daily
  WHERE device = 'barn' AND bucket >= NOW() - '%[2]s'::interval
  ORDER BY date_trunc('%[1]s', bucket), bucket DESC
),
joined AS (
  SELECT
    i.period,
    i.grid_import_kwh,
    LAG(i.grid_import_kwh) OVER (ORDER BY i.period) AS prev_import,
    i.grid_export_kwh,
    LAG(i.grid_export_kwh) OVER (ORDER BY i.period) AS prev_export,
    i.pv_energy_kwh,
    LAG(i.pv_energy_kwh)   OVER (ORDER BY i.period) AS prev_pv,
    h.import_kwh                                        AS house_kwh,
    LAG(h.import_kwh) OVER (ORDER BY i.period)         AS prev_house,
    b.import_kwh                                        AS barn_kwh,
    LAG(b.import_kwh) OVER (ORDER BY i.period)         AS prev_barn
  FROM inv_last i
  LEFT JOIN house_last h ON h.period = i.period
  LEFT JOIN barn_last  b ON b.period = i.period
)
SELECT
  period,
  GREATEST(0, grid_import_kwh - prev_import)                                           AS buy,
  GREATEST(0, grid_export_kwh - prev_export)                                           AS sell,
  GREATEST(0, pv_energy_kwh   - prev_pv)                                               AS produce,
  GREATEST(0, COALESCE(house_kwh - prev_house, 0) + COALESCE(barn_kwh - prev_barn, 0)) AS consume
FROM joined
WHERE prev_import IS NOT NULL
ORDER BY period
`, periodTrunc, rangeInterval)

	rows, err := pool.Query(ctx, sql)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var bars []EnergyBar
	for rows.Next() {
		var b EnergyBar
		if err := rows.Scan(&b.Time, &b.Buy, &b.Sell, &b.Produce, &b.Consume); err != nil {
			return nil, err
		}
		bars = append(bars, b)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	// Trim to the requested count (the LAG window requires one extra row)
	if len(bars) > count {
		bars = bars[len(bars)-count:]
	}
	return bars, nil
}