package lagoon

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"git.golem15.com/golem15/summercms/modules/lagoon/attach"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// DeferredFileType is the slave_type of a deferred binding that points at a
// system_files row: the table name, never a PHP class string.
const DeferredFileType = "system_files"

// DeferredBinding is one row of WinterCMS's deferred_bindings table: a
// pending bind (IsBind true) or unbind of the slave SlaveType/SlaveID to the
// MasterField relation of a MasterType record that one admin's form session
// (SessionKey, BackendUserID) has not saved yet. PivotData holds the
// DeferredEnvelope JSON or is nil.
type DeferredBinding struct {
	ID            uint      `gorm:"column:id;primaryKey"`
	MasterType    string    `gorm:"column:master_type"`
	MasterField   string    `gorm:"column:master_field"`
	SlaveType     string    `gorm:"column:slave_type"`
	SlaveID       string    `gorm:"column:slave_id"`
	PivotData     *string   `gorm:"column:pivot_data"`
	SessionKey    string    `gorm:"column:session_key"`
	IsBind        bool      `gorm:"column:is_bind"`
	BackendUserID uint      `gorm:"column:backend_user_id"`
	CreatedAt     time.Time `gorm:"column:created_at"`
	UpdatedAt     time.Time `gorm:"column:updated_at"`
}

// TableName is deferred_bindings.
func (DeferredBinding) TableName() string { return "deferred_bindings" }

// DeferredKey identifies one admin's pending work on one master type: the
// form's session key, the backend admin who owns it and the master record's
// morph type (MorphType). Every deferred-binding operation is scoped by all
// three, so a session key used by another admin, or against another model,
// matches nothing.
type DeferredKey struct {
	SessionKey string
	AdminID    uint
	MasterType string
}

func (k DeferredKey) validate() error {
	if strings.TrimSpace(k.SessionKey) == "" {
		return fmt.Errorf("lagoon: deferred binding session key is empty")
	}
	if k.AdminID == 0 {
		return fmt.Errorf("lagoon: deferred binding admin id is zero")
	}
	if strings.TrimSpace(k.MasterType) == "" {
		return fmt.Errorf("lagoon: deferred binding master type is empty")
	}
	return nil
}

// DeferredEnvelope is the framework's pivot_data shape,
// {"created":true,"pivot":{...}}. Created marks a slave row that was created
// under deferral, which PurgeDeferred deletes with an expired binding; Pivot
// holds the pivot values of a deferred belongsToMany link. A binding without
// the envelope (nil pivot_data, or JSON without these keys) is a plain link.
type DeferredEnvelope struct {
	Created bool           `json:"created,omitempty"`
	Pivot   map[string]any `json:"pivot,omitempty"`
}

// Envelope decodes the binding's pivot_data. Nil or empty pivot_data is the
// zero envelope (a plain link); invalid JSON is an error.
func (b DeferredBinding) Envelope() (DeferredEnvelope, error) {
	var env DeferredEnvelope
	if b.PivotData == nil || strings.TrimSpace(*b.PivotData) == "" {
		return env, nil
	}
	if err := json.Unmarshal([]byte(*b.PivotData), &env); err != nil {
		return DeferredEnvelope{}, fmt.Errorf("lagoon: deferred binding %d pivot_data: %w", b.ID, err)
	}
	return env, nil
}

// MorphType is the master_type or slave_type string of model: its
// attach.Owner MorphName when it implements attach.Owner, else its GORM table
// name under db's naming strategy. An empty result is an error.
func MorphType(db *gorm.DB, model any) (string, error) {
	if model == nil {
		return "", fmt.Errorf("lagoon: morph type of a nil model")
	}
	if owner, ok := model.(attach.Owner); ok {
		if name := strings.TrimSpace(owner.MorphName()); name != "" {
			return name, nil
		}
		return "", fmt.Errorf("lagoon: morph type of %T is empty", model)
	}
	if db == nil {
		return "", fmt.Errorf("lagoon: gorm db is nil")
	}
	stmt := &gorm.Statement{DB: db}
	if err := stmt.Parse(model); err != nil {
		return "", fmt.Errorf("lagoon: morph type of %T: %w", model, err)
	}
	if stmt.Schema == nil || strings.TrimSpace(stmt.Schema.Table) == "" {
		return "", fmt.Errorf("lagoon: morph type of %T is empty", model)
	}
	return stmt.Schema.Table, nil
}

func deferredSession(ctx context.Context, tx *gorm.DB) *gorm.DB {
	if ctx == nil {
		ctx = context.Background()
	}
	return tx.Session(&gorm.Session{NewDB: true, Context: ctx})
}

func checkDeferredArgs(tx *gorm.DB, key DeferredKey, field, slaveType, slaveID string) error {
	if tx == nil {
		return fmt.Errorf("lagoon: gorm db is nil")
	}
	if err := key.validate(); err != nil {
		return err
	}
	if strings.TrimSpace(field) == "" {
		return fmt.Errorf("lagoon: deferred binding field is empty")
	}
	if strings.TrimSpace(slaveType) == "" {
		return fmt.Errorf("lagoon: deferred binding slave type is empty")
	}
	if strings.TrimSpace(slaveID) == "" {
		return fmt.Errorf("lagoon: deferred binding slave id is empty")
	}
	return nil
}

// findBinding is WinterCMS's DeferredBinding::findBindingRecord, scoped to
// the owning admin and locked for the rest of the transaction.
func findBinding(ctx context.Context, tx *gorm.DB, key DeferredKey, field, slaveType, slaveID string) (*DeferredBinding, error) {
	var row DeferredBinding
	err := deferredSession(ctx, tx).
		Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("master_type = ? AND master_field = ? AND slave_type = ? AND slave_id = ? AND session_key = ? AND backend_user_id = ?",
			key.MasterType, field, slaveType, slaveID, key.SessionKey, key.AdminID).
		Order("id").
		Take(&row).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("lagoon: find deferred binding: %w", err)
	}
	return &row, nil
}

func insertBinding(ctx context.Context, tx *gorm.DB, key DeferredKey, field, slaveType, slaveID string, bind bool, env *DeferredEnvelope) error {
	row := DeferredBinding{
		MasterType:    key.MasterType,
		MasterField:   field,
		SlaveType:     slaveType,
		SlaveID:       slaveID,
		SessionKey:    key.SessionKey,
		IsBind:        bind,
		BackendUserID: key.AdminID,
	}
	if env != nil && (env.Created || len(env.Pivot) > 0) {
		raw, err := json.Marshal(env)
		if err != nil {
			return fmt.Errorf("lagoon: deferred binding envelope: %w", err)
		}
		s := string(raw)
		row.PivotData = &s
	}
	if err := deferredSession(ctx, tx).Create(&row).Error; err != nil {
		return fmt.Errorf("lagoon: insert deferred binding: %w", err)
	}
	return nil
}

func deleteBinding(ctx context.Context, tx *gorm.DB, id uint) error {
	if err := deferredSession(ctx, tx).Where("id = ?", id).Delete(&DeferredBinding{}).Error; err != nil {
		return fmt.Errorf("lagoon: delete deferred binding: %w", err)
	}
	return nil
}

// DeferredBind records that slaveType/slaveID is to be bound to the field
// relation of key's unsaved master, with env (nil for a plain link) as its
// pivot_data. It ports WinterCMS's DeferredBinding::beforeCreate: a second
// bind of the same slave in the same session writes nothing, and a bind
// that meets a pending unbind of the same slave cancels it (the unbind row
// is deleted and no bind row is written). An empty session key, a zero
// AdminID or an empty MasterType is an error.
func DeferredBind(ctx context.Context, tx *gorm.DB, key DeferredKey, field, slaveType, slaveID string, env *DeferredEnvelope) error {
	if err := checkDeferredArgs(tx, key, field, slaveType, slaveID); err != nil {
		return err
	}
	existing, err := findBinding(ctx, tx, key, field, slaveType, slaveID)
	if err != nil {
		return err
	}
	if existing != nil {
		if existing.IsBind {
			return nil
		}
		return deleteBinding(ctx, tx, existing.ID)
	}
	return insertBinding(ctx, tx, key, field, slaveType, slaveID, true, env)
}

// DeferredUnbind records that slaveType/slaveID is to be unbound from the
// field relation of key's master. A second unbind writes nothing. An unbind
// that meets a pending bind of the same slave cancels the pair: the bind
// row is deleted, no unbind row is written, and the cancelled bind is
// returned so the caller can remove the slave it created (a pending upload
// or a child created under deferral). Otherwise it returns nil.
func DeferredUnbind(ctx context.Context, tx *gorm.DB, key DeferredKey, field, slaveType, slaveID string) (*DeferredBinding, error) {
	if err := checkDeferredArgs(tx, key, field, slaveType, slaveID); err != nil {
		return nil, err
	}
	existing, err := findBinding(ctx, tx, key, field, slaveType, slaveID)
	if err != nil {
		return nil, err
	}
	if existing != nil {
		if !existing.IsBind {
			return nil, nil
		}
		if err := deleteBinding(ctx, tx, existing.ID); err != nil {
			return nil, err
		}
		return existing, nil
	}
	return nil, insertBinding(ctx, tx, key, field, slaveType, slaveID, false, nil)
}

// DeferredBindings returns key's bindings whose master_field is one of
// fields, in id order, locked FOR UPDATE so two saves with the same session
// key are serialized. No fields means no bindings.
func DeferredBindings(ctx context.Context, tx *gorm.DB, key DeferredKey, fields []string) ([]DeferredBinding, error) {
	if tx == nil {
		return nil, fmt.Errorf("lagoon: gorm db is nil")
	}
	if err := key.validate(); err != nil {
		return nil, err
	}
	if len(fields) == 0 {
		return nil, nil
	}
	var rows []DeferredBinding
	err := deferredSession(ctx, tx).
		Clauses(clause.Locking{Strength: "UPDATE"}).
		Where("session_key = ? AND backend_user_id = ? AND master_type = ? AND master_field IN ?",
			key.SessionKey, key.AdminID, key.MasterType, fields).
		Order("id").
		Find(&rows).Error
	if err != nil {
		return nil, fmt.Errorf("lagoon: deferred bindings: %w", err)
	}
	return rows, nil
}

// DeferredForget deletes exactly the bindings with the given ids, after
// their work has been applied. The caller passes only ids it read for its
// own key through DeferredBindings.
func DeferredForget(ctx context.Context, tx *gorm.DB, ids []uint) error {
	if tx == nil {
		return fmt.Errorf("lagoon: gorm db is nil")
	}
	if len(ids) == 0 {
		return nil
	}
	if err := deferredSession(ctx, tx).Where("id IN ?", ids).Delete(&DeferredBinding{}).Error; err != nil {
		return fmt.Errorf("lagoon: forget deferred bindings: %w", err)
	}
	return nil
}

// DeferredSlaves returns a subquery selecting the slave_id values of key's
// bindings for field and slaveType in one direction (bind true for pending
// binds, false for pending unbinds), for use as CAST(pk AS TEXT) IN (?) in
// a list query (WinterCMS's withDeferred). slave_id is a text column, so the
// primary key must be cast to text for the comparison.
func DeferredSlaves(tx *gorm.DB, key DeferredKey, field, slaveType string, bind bool) *gorm.DB {
	return tx.Session(&gorm.Session{NewDB: true}).
		Model(&DeferredBinding{}).
		Select("slave_id").
		Where("session_key = ? AND backend_user_id = ? AND master_type = ? AND master_field = ? AND slave_type = ? AND is_bind = ?",
			key.SessionKey, key.AdminID, key.MasterType, field, slaveType, bind)
}