package store

import (
	"bytes"
	"context"
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/gob"
	"encoding/hex"
	"errors"
	"fmt"

	"wh/sim"
)

// Ship statuses.
const (
	StatusInventory = "inventory" // built, can be programmed
	StatusLaunching = "launching" // enters the belt on the next run
	StatusActive    = "active"    // in the belt
	StatusDestroyed = "destroyed"
)

var (
	ErrNotFound = errors.New("not found")
	ErrState    = errors.New("ship is not in the right state for that")
	ErrTaken    = errors.New("name already taken")
)

type Player struct {
	ID      int64
	Name    string
	Credits int64
}

type Ship struct {
	ID          int64
	OwnerID     int64
	Status      string
	ProgramSize int
	DownlinkDay int64 // -1 if none yet
}

func HashKey(key string) string {
	h := sha256.Sum256([]byte(key))
	return hex.EncodeToString(h[:])
}

// Register creates a player with one command ship in inventory and returns
// the player's API key (shown once; only its hash is stored).
func (s *Store) Register(ctx context.Context, name string) (Player, string, int64, error) {
	var (
		p      Player
		shipID int64
		key    string
	)
	b := make([]byte, 24)
	if _, err := rand.Read(b); err != nil {
		return p, "", 0, err
	}
	key = hex.EncodeToString(b)
	err := s.WithTx(ctx, func(q *Q) error {
		var n int
		if err := q.row(ctx, `SELECT COUNT(*) FROM players WHERE name = ?`, name).Scan(&n); err != nil {
			return err
		}
		if n > 0 {
			return ErrTaken
		}
		if err := q.row(ctx, `INSERT INTO players (name, key_hash) VALUES (?, ?) RETURNING id`,
			name, HashKey(key)).Scan(&p.ID); err != nil {
			return err
		}
		p.Name = name
		return q.row(ctx, `INSERT INTO ships (owner_id, status) VALUES (?, ?) RETURNING id`,
			p.ID, StatusInventory).Scan(&shipID)
	})
	return p, key, shipID, err
}

func (q *Q) PlayerByKey(ctx context.Context, key string) (Player, error) {
	var p Player
	err := q.row(ctx, `SELECT id, name, credits FROM players WHERE key_hash = ?`, HashKey(key)).
		Scan(&p.ID, &p.Name, &p.Credits)
	if err == sql.ErrNoRows {
		return p, ErrNotFound
	}
	return p, err
}

func (q *Q) PlayerShips(ctx context.Context, owner int64) ([]Ship, error) {
	rows, err := q.query(ctx, `SELECT id, owner_id, status, COALESCE(LENGTH(program), 0), downlink_day
		FROM ships WHERE owner_id = ? ORDER BY id`, owner)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []Ship
	for rows.Next() {
		var sh Ship
		if err := rows.Scan(&sh.ID, &sh.OwnerID, &sh.Status, &sh.ProgramSize, &sh.DownlinkDay); err != nil {
			return nil, err
		}
		out = append(out, sh)
	}
	return out, rows.Err()
}

// ownedStatus returns the ship's status if owner owns it.
func (q *Q) ownedStatus(ctx context.Context, owner, ship int64) (string, error) {
	var st string
	err := q.row(ctx, `SELECT status FROM ships WHERE id = ? AND owner_id = ?`, ship, owner).Scan(&st)
	if err == sql.ErrNoRows {
		return "", ErrNotFound
	}
	return st, err
}

func (q *Q) requireOneRow(res sql.Result, err error) error {
	if err != nil {
		return err
	}
	if n, _ := res.RowsAffected(); n == 0 {
		return ErrState
	}
	return nil
}

// SetProgram replaces the program of a ship that is still in inventory.
func (q *Q) SetProgram(ctx context.Context, owner, ship int64, prog []byte) error {
	if _, err := q.ownedStatus(ctx, owner, ship); err != nil {
		return err
	}
	res, err := q.exec(ctx, `UPDATE ships SET program = ? WHERE id = ? AND owner_id = ? AND status = ?`,
		prog, ship, owner, StatusInventory)
	return q.requireOneRow(res, err)
}

// Launch queues an inventory ship (which must have a program) to enter the
// belt on the next daily run.
func (q *Q) Launch(ctx context.Context, owner, ship int64) error {
	if _, err := q.ownedStatus(ctx, owner, ship); err != nil {
		return err
	}
	res, err := q.exec(ctx, `UPDATE ships SET status = ? WHERE id = ? AND owner_id = ? AND status = ?
		AND program IS NOT NULL`, StatusLaunching, ship, owner, StatusInventory)
	return q.requireOneRow(res, err)
}

// SetUplink stores the message delivered on the next run, replacing any
// message already queued.
func (q *Q) SetUplink(ctx context.Context, owner, ship int64, data []byte) error {
	if _, err := q.ownedStatus(ctx, owner, ship); err != nil {
		return err
	}
	res, err := q.exec(ctx, `UPDATE ships SET uplink = ? WHERE id = ? AND owner_id = ? AND status IN (?, ?)`,
		data, ship, owner, StatusActive, StatusLaunching)
	return q.requireOneRow(res, err)
}

// Downlink returns the latest downlink and the day it was produced.
func (q *Q) Downlink(ctx context.Context, owner, ship int64) ([]byte, int64, error) {
	var (
		data []byte
		day  int64
	)
	err := q.row(ctx, `SELECT downlink, downlink_day FROM ships WHERE id = ? AND owner_id = ?`, ship, owner).
		Scan(&data, &day)
	if err == sql.ErrNoRows {
		return nil, 0, ErrNotFound
	}
	return data, day, err
}

// PendingLaunches returns ships due to launch, ordered by id.
func (q *Q) PendingLaunches(ctx context.Context) ([]sim.Launch, error) {
	rows, err := q.query(ctx, `SELECT id, owner_id, program FROM ships WHERE status = ? ORDER BY id`, StatusLaunching)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []sim.Launch
	for rows.Next() {
		var l sim.Launch
		if err := rows.Scan(&l.ShipID, &l.Owner, &l.Program); err != nil {
			return nil, err
		}
		out = append(out, l)
	}
	return out, rows.Err()
}

// PendingUplinks returns queued uplinks, ordered by ship id.
func (q *Q) PendingUplinks(ctx context.Context) ([]sim.Uplink, error) {
	rows, err := q.query(ctx, `SELECT id, uplink FROM ships WHERE uplink IS NOT NULL ORDER BY id`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []sim.Uplink
	for rows.Next() {
		var u sim.Uplink
		if err := rows.Scan(&u.ShipID, &u.Data); err != nil {
			return nil, err
		}
		out = append(out, u)
	}
	return out, rows.Err()
}

// LoadState returns the most recent world snapshot, or nil if none exists.
func (q *Q) LoadState(ctx context.Context) (*sim.State, error) {
	var data []byte
	err := q.row(ctx, `SELECT data FROM snapshots ORDER BY day DESC LIMIT 1`).Scan(&data)
	if err == sql.ErrNoRows {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	var st sim.State
	if err := gob.NewDecoder(bytes.NewReader(data)).Decode(&st); err != nil {
		return nil, fmt.Errorf("decode snapshot: %w", err)
	}
	return &st, nil
}

func (q *Q) SaveState(ctx context.Context, st *sim.State) error {
	var buf bytes.Buffer
	if err := gob.NewEncoder(&buf).Encode(st); err != nil {
		return err
	}
	h := st.Hash()
	_, err := q.exec(ctx, `INSERT INTO snapshots (day, hash, data) VALUES (?, ?, ?)`,
		st.Day, hex.EncodeToString(h[:]), buf.Bytes())
	return err
}

// RecordRun writes the outputs of a completed day.
func (q *Q) RecordRun(ctx context.Context, res sim.DayResult, ranAt string) error {
	h := res.Hash
	if _, err := q.exec(ctx, `INSERT INTO day_runs (day, hash, ran_at) VALUES (?, ?, ?)`,
		res.Day, hex.EncodeToString(h[:]), ranAt); err != nil {
		return err
	}
	for _, e := range res.Events {
		if _, err := q.exec(ctx, `INSERT INTO events (day, tick, ship_id, kind, detail) VALUES (?, ?, ?, ?, ?)`,
			res.Day, e.Tick, e.ShipID, e.Kind, e.Detail); err != nil {
			return err
		}
	}
	for _, d := range res.Downlinks {
		if _, err := q.exec(ctx, `UPDATE ships SET downlink = ?, downlink_day = ? WHERE id = ?`,
			d.Data, res.Day, d.ShipID); err != nil {
			return err
		}
	}
	return nil
}

// AfterRun clears delivered uplinks, activates launched ships, marks
// destroyed ones and updates player balances.
func (q *Q) AfterRun(ctx context.Context, st *sim.State) error {
	if _, err := q.exec(ctx, `UPDATE ships SET uplink = NULL WHERE uplink IS NOT NULL`); err != nil {
		return err
	}
	if _, err := q.exec(ctx, `UPDATE ships SET status = ? WHERE status = ?`, StatusActive, StatusLaunching); err != nil {
		return err
	}
	for _, sh := range st.Ships {
		if !sh.Alive {
			if _, err := q.exec(ctx, `UPDATE ships SET status = ? WHERE id = ?`, StatusDestroyed, sh.ID); err != nil {
				return err
			}
		}
	}
	for owner, credits := range st.Credits {
		if _, err := q.exec(ctx, `UPDATE players SET credits = ? WHERE id = ?`, credits, owner); err != nil {
			return err
		}
	}
	return nil
}