package postgres

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"

	"knowledge-governance/internal/governance"
)

var ErrInvalidUISettings = errors.New("invalid UI settings")

const uiSettingsColumns = `id,state,document_refresh_seconds,resource_refresh_seconds,stalled_after_seconds,finalizing_after_seconds,ingestion_concurrency,test_weknora_base_url,production_weknora_base_url,production_tenant_id,production_knowledge_base_id,updated_by,created_at,activated_at,retired_at,error_code`

const getActiveUISettingsSQL = `
SELECT ` + uiSettingsColumns + `
FROM ui_setting_revisions
WHERE state = 'active'
`

const createUISettingsCandidateSQL = `
INSERT INTO ui_setting_revisions(
    id,state,document_refresh_seconds,resource_refresh_seconds,
    stalled_after_seconds,finalizing_after_seconds,ingestion_concurrency,
    test_weknora_base_url,production_weknora_base_url,production_tenant_id,
    production_knowledge_base_id,updated_by,created_at
) VALUES($1,'validated',$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12)
RETURNING ` + uiSettingsColumns + `
`

const getUISettingsRevisionSQL = `
SELECT ` + uiSettingsColumns + `
FROM ui_setting_revisions
WHERE id=$1
`

const lockUISettingsRevisionSQL = `
SELECT ` + uiSettingsColumns + `
FROM ui_setting_revisions
WHERE id=$1
FOR UPDATE
`

const retireActiveUISettingsSQL = `
UPDATE ui_setting_revisions
SET state='retired',retired_at=$2
WHERE state='active' AND id<>$1
`

const activateUISettingsSQL = `
UPDATE ui_setting_revisions
SET state='active',activated_at=$2,retired_at=NULL,error_code=''
WHERE id=$1 AND state='validated'
RETURNING ` + uiSettingsColumns + `
`

func (s *Store) GetActiveUISettings(ctx context.Context) (governance.UISettings, error) {
	return scanUISettings(s.db.QueryRow(ctx, getActiveUISettingsSQL))
}

func (s *Store) CreateUISettingsCandidate(ctx context.Context, request governance.CreateUISettingsCandidateRequest) (governance.UISettings, error) {
	if !request.Valid() {
		return governance.UISettings{}, ErrInvalidUISettings
	}
	id, err := newOpaqueID("uis-")
	if err != nil {
		return governance.UISettings{}, fmt.Errorf("create UI settings id: %w", err)
	}
	return scanUISettings(s.db.QueryRow(ctx, createUISettingsCandidateSQL,
		id, request.DocumentRefreshSeconds, request.ResourceRefreshSeconds,
		request.StalledAfterSeconds, request.FinalizingAfterSeconds, request.IngestionConcurrency,
		request.TestWeKnoraBaseURL, request.ProductionWeKnoraBaseURL,
		request.ProductionTenantID, request.ProductionKnowledgeBaseID,
		request.UpdatedBy, request.Now.UTC()))
}

// GetUISettingsRevision reads one revision in any state. Activation uses it to
// compare the incoming endpoint against the active one before letting an
// engineer apply a change only an admin may author.
func (s *Store) GetUISettingsRevision(ctx context.Context, revisionID string) (governance.UISettings, error) {
	if !validShortID(revisionID) {
		return governance.UISettings{}, ErrInvalidUISettings
	}
	return scanUISettings(s.db.QueryRow(ctx, getUISettingsRevisionSQL, revisionID))
}

func (s *Store) ActivateUISettings(ctx context.Context, revisionID string, now time.Time) (governance.UISettings, error) {
	if !validShortID(revisionID) || now.IsZero() {
		return governance.UISettings{}, ErrInvalidUISettings
	}
	var tx pgx.Tx
	var err error
	ownsTransaction := false
	if existing, ok := s.db.(pgx.Tx); ok {
		tx = existing
	} else {
		beginner, ok := s.db.(interface {
			Begin(context.Context) (pgx.Tx, error)
		})
		if !ok {
			return governance.UISettings{}, errors.New("store does not support transactions")
		}
		tx, err = beginner.Begin(ctx)
		if err != nil {
			return governance.UISettings{}, fmt.Errorf("begin UI settings activation: %w", err)
		}
		ownsTransaction = true
		defer func() { _ = tx.Rollback(ctx) }()
	}
	candidate, err := scanUISettings(tx.QueryRow(ctx, lockUISettingsRevisionSQL, revisionID))
	if err != nil {
		return governance.UISettings{}, err
	}
	if candidate.State == "active" {
		if ownsTransaction {
			if err := tx.Commit(ctx); err != nil {
				return governance.UISettings{}, fmt.Errorf("commit UI settings activation: %w", err)
			}
		}
		return candidate, nil
	}
	if candidate.State != "validated" {
		return governance.UISettings{}, ErrInvalidUISettings
	}
	activatedAt := now.UTC()
	if _, err := tx.Exec(ctx, retireActiveUISettingsSQL, revisionID, activatedAt); err != nil {
		return governance.UISettings{}, fmt.Errorf("retire active UI settings: %w", err)
	}
	active, err := scanUISettings(tx.QueryRow(ctx, activateUISettingsSQL, revisionID, activatedAt))
	if err != nil {
		return governance.UISettings{}, err
	}
	if ownsTransaction {
		if err := tx.Commit(ctx); err != nil {
			return governance.UISettings{}, fmt.Errorf("commit UI settings activation: %w", err)
		}
	}
	return active, nil
}

func scanUISettings(row interface{ Scan(...any) error }) (governance.UISettings, error) {
	var settings governance.UISettings
	if err := row.Scan(&settings.ID, &settings.State, &settings.DocumentRefreshSeconds,
		&settings.ResourceRefreshSeconds, &settings.StalledAfterSeconds, &settings.FinalizingAfterSeconds,
		&settings.IngestionConcurrency, &settings.TestWeKnoraBaseURL, &settings.ProductionWeKnoraBaseURL,
		&settings.ProductionTenantID, &settings.ProductionKnowledgeBaseID,
		&settings.UpdatedBy, &settings.CreatedAt, &settings.ActivatedAt, &settings.RetiredAt, &settings.ErrorCode); err != nil {
		return governance.UISettings{}, fmt.Errorf("scan UI settings: %w", err)
	}
	if settings.State != "validated" && settings.State != "active" && settings.State != "retired" && settings.State != "failed" {
		return governance.UISettings{}, errors.New("invalid UI settings state")
	}
	return settings, nil
}