package store

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"time"

	"github.com/iceBear67/simplepages/internal/cas"
)

// State is where a deployment sits in its lifecycle. The values mirror the
// CHECK constraint in the schema; api carries the same set for the wire and
// TestStateConstantsMatchTheWire asserts the two never drift.
type State string

const (
	// StatePending: the row exists and nothing else does.
	StatePending State = "pending"
	// StateUploading: a manifest has been accepted, so every blob it names is
	// already refcounted and safe from GC while its content is still arriving.
	StateUploading State = "uploading"
	// StateReady: every blob is present and the directory tree is assembled.
	// Only a ready deployment may be activated.
	StateReady State = "ready"
	// StateFailed: abandoned. Its manifest rows get dropped so refcounts fall
	// and GC can reclaim whatever only it referenced.
	StateFailed State = "failed"
	// StateDeleting: GC has claimed it and is removing its tree.
	StateDeleting State = "deleting"
)

// Deployment is a row of the deployments table.
//
// ID is internal and never leaves the server; PublicID is what the API and the
// CLI use. Keeping them separate means a URL cannot be walked to a neighbouring
// project's deployment by incrementing an integer.
type Deployment struct {
	ID        int64
	PublicID  string
	ProjectID int64
	State     State
	Active    bool

	FileCount  int
	TotalBytes int64
	// CreatedByKey is empty once that key has been deleted; the schema sets it
	// to NULL rather than losing the deployment.
	CreatedByKey string
	Meta         map[string]string
	Error        string

	CreatedAt     time.Time
	FinalizedAt   *time.Time
	ActivatedAt   *time.Time
	DeactivatedAt *time.Time
}

// FileRow is one manifest entry as stored.
//
// There is deliberately no mode: a client-supplied permission bit must never
// reach the filesystem, which is why the schema has no column for one either.
// The encoding column is likewise not represented — v1 only ever writes ” —
// but it stays in the primary key so pre-compressed variants can be added later
// without a painful migration.
type FileRow struct {
	Path   string
	Digest cas.Digest
	Size   int64
}

const deploymentColumns = `id, public_id, project_id, state, active, file_count, total_bytes,
	created_by_key, meta, error, created_at, finalized_at, activated_at, deactivated_at`

func scanDeployment(row rowScanner) (*Deployment, error) {
	var d Deployment
	var createdBy, meta, errText sql.NullString
	var created int64
	var finalized, activated, deactivated sql.NullInt64
	err := row.Scan(&d.ID, &d.PublicID, &d.ProjectID, &d.State, &d.Active, &d.FileCount,
		&d.TotalBytes, &createdBy, &meta, &errText, &created, &finalized, &activated, &deactivated)
	if err != nil {
		return nil, mapErr(err)
	}
	d.CreatedByKey = createdBy.String
	d.Error = errText.String
	d.CreatedAt = time.Unix(created, 0).UTC()
	d.FinalizedAt = timePtr(finalized)
	d.ActivatedAt = timePtr(activated)
	d.DeactivatedAt = timePtr(deactivated)
	if meta.String != "" && meta.String != "{}" {
		// Metadata is whatever the CI job attached. A row that will not parse is
		// not worth failing a rollback over, so it is dropped rather than
		// returned as an error.
		_ = json.Unmarshal([]byte(meta.String), &d.Meta)
	}
	return &d, nil
}

// NewDeploymentID mints a deployment's public identifier.
//
// 64 bits from crypto/rand, which is not a capability and is not treated as
// one: every endpoint taking a deployment id sits behind RequireProject, and
// DeploymentByPublicID is always scoped by project, so knowing an id grants
// nothing. The randomness is here so two concurrent CI jobs never collide and
// so ids carry no information about how many deployments the server has seen.
func NewDeploymentID() (string, error) {
	var buf [8]byte
	if _, err := rand.Read(buf[:]); err != nil {
		return "", err
	}
	return "dpl_" + hex.EncodeToString(buf[:]), nil
}

// CreateDeployment inserts a pending deployment and fills in its ID, PublicID
// and CreatedAt. Nothing touches the filesystem until a manifest arrives.
func (d *DB) CreateDeployment(ctx context.Context, dep *Deployment) error {
	if dep.PublicID == "" {
		id, err := NewDeploymentID()
		if err != nil {
			return err
		}
		dep.PublicID = id
	}
	meta := "{}"
	if len(dep.Meta) > 0 {
		b, err := json.Marshal(dep.Meta)
		if err != nil {
			return err
		}
		meta = string(b)
	}
	now := unixNow()
	return d.Tx(ctx, func(tx *sql.Tx) error {
		res, err := tx.ExecContext(ctx, `
			INSERT INTO deployments (public_id, project_id, state, created_by_key, meta, created_at)
			VALUES (?, ?, ?, ?, ?, ?)`,
			dep.PublicID, dep.ProjectID, StatePending, nullString(dep.CreatedByKey), meta, now)
		if err != nil {
			return mapErr(err)
		}
		id, err := res.LastInsertId()
		if err != nil {
			return err
		}
		dep.ID = id
		dep.State = StatePending
		dep.CreatedAt = time.Unix(now, 0).UTC()
		return nil
	})
}

// DeploymentByPublicID looks up one deployment within one project.
//
// The project is part of the lookup rather than something to check afterwards.
// A handler holding a project-scoped identity therefore cannot name another
// project's deployment at all: the wrong project simply yields ErrNotFound,
// which is also the right answer to give — it reveals nothing about whether the
// id exists elsewhere.
func (d *DB) DeploymentByPublicID(ctx context.Context, projectID int64, publicID string) (*Deployment, error) {
	return scanDeployment(d.r.QueryRowContext(ctx,
		`SELECT `+deploymentColumns+` FROM deployments WHERE project_id = ? AND public_id = ?`,
		projectID, publicID))
}

// ActiveDeployment returns the deployment a project is currently serving, or
// ErrNotFound when it has never activated one. The partial unique index makes
// "at most one" a property of the database rather than of this query.
func (d *DB) ActiveDeployment(ctx context.Context, projectID int64) (*Deployment, error) {
	return scanDeployment(d.r.QueryRowContext(ctx,
		`SELECT `+deploymentColumns+` FROM deployments WHERE project_id = ? AND active = 1`,
		projectID))
}

// ListDeployments pages one project's deployments, newest first.
//
// The cursor is the public id of the last row of the previous page. An id that
// no longer exists — GC ran between pages — yields an empty page rather than an
// error, which is the behaviour a paging client can actually handle.
func (d *DB) ListDeployments(ctx context.Context, projectID int64, state State, limit int, cursor string) (deployments []*Deployment, next string, err error) {
	if limit <= 0 || limit > 500 {
		limit = 100
	}
	rows, err := d.r.QueryContext(ctx, `
		SELECT `+deploymentColumns+` FROM deployments
		WHERE project_id = ?
		  AND (? = '' OR state = ?)
		  AND (? = '' OR id < (SELECT id FROM deployments WHERE public_id = ?))
		ORDER BY id DESC LIMIT ?`,
		projectID, string(state), string(state), cursor, cursor, limit+1)
	if err != nil {
		return nil, "", err
	}
	defer rows.Close()
	for rows.Next() {
		dep, err := scanDeployment(rows)
		if err != nil {
			return nil, "", err
		}
		deployments = append(deployments, dep)
	}
	if err := rows.Err(); err != nil {
		return nil, "", err
	}
	if len(deployments) > limit {
		deployments = deployments[:limit]
		next = deployments[len(deployments)-1].PublicID
	}
	return deployments, next, nil
}

// SetManifest replaces a deployment's file list and reports which blobs the
// server does not have content for yet.
//
// The ordering here is the point of the whole upload protocol. The manifest
// rows land *before* any blob is uploaded, and the insert triggers bump each
// blob's refcount as they do, so from this transaction's commit onwards every
// blob the deployment needs is protected from GC. That closes the race the
// obvious design has: "the server told me it already had this blob, then
// deleted it while I was uploading the others".
//
// Re-sending a manifest is allowed while the deployment is pending or
// uploading, because a CLI that lost its connection mid-negotiation should be
// able to start over without creating a second deployment.
func (d *DB) SetManifest(ctx context.Context, deploymentID int64, files []FileRow) (missing []cas.Digest, missingBytes int64, err error) {
	// One entry per distinct digest, in first-appearance order, so the missing
	// list — and therefore the client's upload order — is deterministic.
	type need struct {
		digest cas.Digest
		size   int64
	}
	var needs []need
	seen := make(map[cas.Digest]int64, len(files))
	var totalBytes int64
	for _, f := range files {
		totalBytes += f.Size
		if prev, ok := seen[f.Digest]; ok {
			if prev != f.Size {
				return nil, 0, fmt.Errorf("%w: the manifest gives digest %s both %d and %d bytes",
					cas.ErrSizeMismatch, f.Digest, prev, f.Size)
			}
			continue
		}
		seen[f.Digest] = f.Size
		needs = append(needs, need{f.Digest, f.Size})
	}

	now := unixNow()
	err = d.Tx(ctx, func(tx *sql.Tx) error {
		// Tx re-runs this function on SQLITE_BUSY, so the results are rebuilt
		// from scratch each attempt rather than appended to.
		missing, missingBytes = nil, 0

		var state State
		if err := tx.QueryRowContext(ctx,
			`SELECT state FROM deployments WHERE id = ?`, deploymentID).Scan(&state); err != nil {
			return mapErr(err)
		}
		if state != StatePending && state != StateUploading {
			return fmt.Errorf("%w: deployment is %s; a manifest may only be set while pending or uploading",
				ErrConflict, state)
		}

		// Discard any earlier attempt. A refcount that goes 1 -> 0 -> 1 inside
		// this transaction is safe because GC needs the same single write
		// connection and so can never observe the zero.
		if _, err := tx.ExecContext(ctx,
			`DELETE FROM deployment_files WHERE deployment_id = ?`, deploymentID); err != nil {
			return err
		}

		// Prepared statements rather than batched multi-row VALUES: a 50,000
		// file manifest is a few hundred milliseconds of Exec either way, and
		// this version has no chunk arithmetic to get wrong and no bound on how
		// many parameters one statement may carry.
		insertBlob, err := tx.PrepareContext(ctx, `
			INSERT INTO blobs (digest, size, present, created_at, last_ref_at)
			VALUES (?, ?, 0, ?, ?) ON CONFLICT(digest) DO NOTHING`)
		if err != nil {
			return err
		}
		defer insertBlob.Close()
		readBlob, err := tx.PrepareContext(ctx, `SELECT size, present FROM blobs WHERE digest = ?`)
		if err != nil {
			return err
		}
		defer readBlob.Close()

		for _, n := range needs {
			if _, err := insertBlob.ExecContext(ctx, n.digest.Bytes(), n.size, now, now); err != nil {
				return err
			}
			var have int64
			var present bool
			if err := readBlob.QueryRowContext(ctx, n.digest.Bytes()).Scan(&have, &present); err != nil {
				return mapErr(err)
			}
			if have != n.size {
				// A digest fixes its content and therefore its length, so this
				// is a client that computed one of the two wrong. Surfacing it
				// here beats accepting a manifest whose byte totals are fiction.
				return fmt.Errorf("%w: digest %s is %d bytes on this server, the manifest declares %d",
					cas.ErrSizeMismatch, n.digest, have, n.size)
			}
			if !present {
				missing = append(missing, n.digest)
				missingBytes += n.size
			}
		}

		insertFile, err := tx.PrepareContext(ctx, `
			INSERT INTO deployment_files (deployment_id, path, digest, size) VALUES (?, ?, ?, ?)`)
		if err != nil {
			return err
		}
		defer insertFile.Close()
		for _, f := range files {
			if _, err := insertFile.ExecContext(ctx, deploymentID, f.Path, f.Digest.Bytes(), f.Size); err != nil {
				return mapErr(err)
			}
		}

		_, err = tx.ExecContext(ctx,
			`UPDATE deployments SET state = ?, file_count = ?, total_bytes = ? WHERE id = ?`,
			StateUploading, len(files), totalBytes, deploymentID)
		return err
	})
	if err != nil {
		return nil, 0, err
	}
	return missing, missingBytes, nil
}

// DeploymentFiles returns the manifest, ordered by path so assembly creates
// each directory once and in a predictable order.
func (d *DB) DeploymentFiles(ctx context.Context, deploymentID int64) ([]FileRow, error) {
	rows, err := d.r.QueryContext(ctx,
		`SELECT path, digest, size FROM deployment_files WHERE deployment_id = ? ORDER BY path`,
		deploymentID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var files []FileRow
	for rows.Next() {
		var f FileRow
		var raw []byte
		if err := rows.Scan(&f.Path, &raw, &f.Size); err != nil {
			return nil, err
		}
		if f.Digest, err = cas.FromBytes(raw); err != nil {
			return nil, err
		}
		files = append(files, f)
	}
	return files, rows.Err()
}

// MarkDeploymentReady records that assembly succeeded.
//
// Idempotent, and deliberately so: the CLI retries finalize after re-uploading
// blobs that went missing, and a retry must not turn a good deployment into an
// error. finalized_at keeps its original value so the timestamp reflects the
// first success rather than the last attempt.
func (d *DB) MarkDeploymentReady(ctx context.Context, id int64) error {
	now := unixNow()
	return d.Tx(ctx, func(tx *sql.Tx) error {
		res, err := tx.ExecContext(ctx, `
			UPDATE deployments SET state = ?, finalized_at = COALESCE(finalized_at, ?), error = NULL
			WHERE id = ? AND state IN (?, ?)`,
			StateReady, now, id, StateUploading, StateReady)
		if err != nil {
			return err
		}
		return requireOneRow(ctx, tx, res, id, "finalize")
	})
}

// ActivateDeployment makes one ready deployment the project's active one and
// demotes whatever held that role before.
//
// Demotion comes first because deployments_one_active is a partial unique index,
// checked per statement: promoting before demoting would collide with the row
// still holding active = 1. The demotion deliberately excludes the target, so
// re-activating the deployment that is already active is a no-op that refreshes
// its timestamp rather than a transaction that briefly leaves the project with
// nothing active.
//
// The caller is expected to hold the project lock and to have already built
// whatever in-memory snapshot it means to publish: once this commits, SQLite is
// the truth and a crash before the pointer store is recovered from here.
func (d *DB) ActivateDeployment(ctx context.Context, projectID, deploymentID int64) error {
	now := unixNow()
	return d.Tx(ctx, func(tx *sql.Tx) error {
		if _, err := tx.ExecContext(ctx, `
			UPDATE deployments SET active = 0, deactivated_at = ?
			WHERE project_id = ? AND active = 1 AND id <> ?`,
			now, projectID, deploymentID); err != nil {
			return err
		}
		res, err := tx.ExecContext(ctx, `
			UPDATE deployments SET active = 1, activated_at = ?, deactivated_at = NULL
			WHERE id = ? AND project_id = ? AND state = ?`,
			now, deploymentID, projectID, StateReady)
		if err != nil {
			return mapErr(err)
		}
		return requireOneRow(ctx, tx, res, deploymentID, "activate")
	})
}

// MarkDeploymentFailed records why a deployment was abandoned. The manifest
// rows stay for now; GC drops them, which is what lets its blobs be reclaimed.
func (d *DB) MarkDeploymentFailed(ctx context.Context, id int64, reason string) error {
	return d.Tx(ctx, func(tx *sql.Tx) error {
		res, err := tx.ExecContext(ctx, `
			UPDATE deployments SET state = ?, error = ? WHERE id = ? AND state IN (?, ?, ?)`,
			StateFailed, truncate(reason, 1024), id, StatePending, StateUploading, StateFailed)
		if err != nil {
			return err
		}
		return requireOneRow(ctx, tx, res, id, "fail")
	})
}

// requireOneRow turns "the UPDATE matched nothing" into the reason it matched
// nothing, which is either a deployment that is gone or one in a state the
// operation does not apply to.
func requireOneRow(ctx context.Context, tx *sql.Tx, res sql.Result, id int64, op string) error {
	n, err := res.RowsAffected()
	if err != nil {
		return err
	}
	if n > 0 {
		return nil
	}
	var state State
	if err := tx.QueryRowContext(ctx, `SELECT state FROM deployments WHERE id = ?`, id).Scan(&state); err != nil {
		return mapErr(err)
	}
	return fmt.Errorf("%w: cannot %s a deployment that is %s", ErrConflict, op, state)
}

func truncate(s string, max int) string {
	if len(s) <= max {
		return s
	}
	return s[:max] + "…"
}