package artifacts

import (
	"bytes"
	"context"
	"fmt"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
)

const (
	// MaxCurrentCommitPointerBytes bounds the mutable commit-selection record.
	MaxCurrentCommitPointerBytes int64 = 64 << 10
	// MaxRemoteCommitManifestBytes bounds an immutable commit manifest.
	MaxRemoteCommitManifestBytes int64 = 4 << 20
	// MaxRemoteSessionManifestBytes bounds the selected session manifest.
	MaxRemoteSessionManifestBytes int64 = 8 << 20
)

func loadCommittedCurrentState(
	ctx context.Context,
	store storage.ObjectStore,
	sessionPrefix string,
	pointerKey string,
	validation CurrentStateValidation,
) (*CurrentState, error) {
	_, pointerData, err := readCurrentStateControlObject(ctx, store, pointerKey, "current commit pointer", MaxCurrentCommitPointerBytes)
	if err != nil {
		return nil, err
	}
	pointer, err := DecodeCurrentCommitPointer(pointerData)
	if err != nil {
		return nil, err
	}
	if err := pointer.ValidateForSessionPrefix(sessionPrefix); err != nil {
		return nil, err
	}

	commitData, err := readVerifiedRemoteObject(ctx, store, pointer.CommitKey, pointer.CommitSHA256, pointer.CommitSize, pointer.CommitGeneration, "remote commit manifest", MaxRemoteCommitManifestBytes)
	if err != nil {
		return nil, fmt.Errorf("read selected remote commit %q: %w", pointer.CommitKey, err)
	}
	commit, err := DecodeRemoteCommitManifest(commitData)
	if err != nil {
		return nil, err
	}
	if err := commit.ValidateForSessionPrefix(sessionPrefix); err != nil {
		return nil, err
	}
	if err := validatePointerCommitIdentity(pointer, commit); err != nil {
		return nil, err
	}

	sessionManifest, ok := commit.Artifact(RemoteArtifactTypeSessionManifest)
	if !ok {
		return nil, fmt.Errorf("remote commit must declare exactly one session manifest artifact")
	}
	manifestData, err := readVerifiedRemoteObject(ctx, store, sessionManifest.DestinationKey, sessionManifest.SHA256, sessionManifest.Size, sessionManifest.Generation, "committed session manifest", MaxRemoteSessionManifestBytes)
	if err != nil {
		return nil, fmt.Errorf("read committed session manifest %q: %w", sessionManifest.DestinationKey, err)
	}
	m, err := decodeCommittedManifest(ctx, manifestData)
	if err != nil {
		return nil, err
	}
	if err := validateCommitManifestIdentity(commit, m); err != nil {
		return nil, err
	}

	state := &CurrentState{
		SessionPrefix:      sessionPrefix,
		CurrentRunIDKey:    pointerKey,
		CurrentPointerKey:  pointerKey,
		CurrentManifestKey: sessionManifest.DestinationKey,
		RunID:              commit.RunID,
		Manifest:           m,
		ManifestData:       append([]byte(nil), manifestData...),
		Commit:             commit,
		Pointer:            pointer,
	}
	if err := ValidateCurrentStateIdentity(state, validation); err != nil {
		return nil, err
	}
	return state, nil
}

func validatePointerCommitIdentity(pointer *CurrentCommitPointer, commit *RemoteCommitManifest) error {
	if pointer == nil || commit == nil {
		return fmt.Errorf("current commit pointer and remote commit are required")
	}
	if pointer.Campaign != commit.Campaign || pointer.SessionID != commit.SessionID || pointer.RunID != commit.RunID {
		return fmt.Errorf("current commit pointer identity does not match selected remote commit")
	}
	return nil
}

func validateCommitManifestIdentity(commit *RemoteCommitManifest, m *manifest.Manifest) error {
	if commit == nil || m == nil {
		return fmt.Errorf("remote commit and committed session manifest are required")
	}
	if commit.Campaign != strings.TrimSpace(m.Campaign) ||
		commit.SessionID != strings.TrimSpace(m.SessionID) ||
		commit.RunID != strings.TrimSpace(m.RunID) {
		return fmt.Errorf("selected remote commit identity does not match committed session manifest")
	}
	return nil
}

func readVerifiedRemoteObject(
	ctx context.Context,
	store storage.ObjectStore,
	key string,
	wantSHA256 string,
	wantSize int64,
	wantGeneration string,
	category string,
	maxBytes int64,
) ([]byte, error) {
	info, data, err := readCurrentStateControlObject(ctx, store, key, category, maxBytes)
	if err != nil {
		return nil, err
	}
	if int64(len(data)) != wantSize {
		return nil, fmt.Errorf("size mismatch: got %d, want %d", len(data), wantSize)
	}
	if checksum := remoteObjectSHA256(data); checksum != wantSHA256 {
		return nil, fmt.Errorf("checksum mismatch: got %s, want %s", checksum, wantSHA256)
	}
	if info.Size > 0 && info.Size != wantSize {
		return nil, fmt.Errorf("storage size mismatch: got %d, want %d", info.Size, wantSize)
	}
	if strings.TrimSpace(info.ETag) != wantGeneration {
		return nil, fmt.Errorf("generation mismatch: got %q, want %q", info.ETag, wantGeneration)
	}
	return data, nil
}

func readCurrentStateControlObject(ctx context.Context, store storage.ObjectStore, key, category string, maxBytes int64) (storage.ObjectInfo, []byte, error) {
	info, data, err := storage.ReadObjectBounded(ctx, store, key, maxBytes)
	if err != nil {
		return storage.ObjectInfo{}, nil, fmt.Errorf("read %s control object %q with %d-byte limit: %w", category, key, maxBytes, err)
	}
	return info, data, nil
}

func decodeCommittedManifest(ctx context.Context, data []byte) (*manifest.Manifest, error) {
	m, err := (&manifest.LocalStore{}).LoadReader(ctx, bytes.NewReader(data))
	if err != nil {
		return nil, fmt.Errorf("committed session manifest decode failed: %w", err)
	}
	return m, nil
}