// Package engine assembles Promptkit's internal execution components.
package engine

import (
	"context"
	"fmt"
	"io/fs"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	openrouter "gitea.maximumdirect.net/eric/promptkit-backend-openrouter"
	rakestrawhome "gitea.maximumdirect.net/eric/promptkit-backend-rakestrawhome"
	"gitea.maximumdirect.net/eric/promptkit/internal/artifact"
	"gitea.maximumdirect.net/eric/promptkit/internal/backend"
	"gitea.maximumdirect.net/eric/promptkit/internal/capacity"
	"gitea.maximumdirect.net/eric/promptkit/internal/catalog"
	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
	"gitea.maximumdirect.net/eric/promptkit/internal/llm"
	"gitea.maximumdirect.net/eric/promptkit/internal/profile"
	"gitea.maximumdirect.net/eric/promptkit/internal/prompt"
	"gitea.maximumdirect.net/eric/promptkit/internal/promptdef"
	"gitea.maximumdirect.net/eric/promptkit/internal/usecase"
	"gitea.maximumdirect.net/eric/promptkit/internal/validate"
)

// Config carries construction settings selected by the public facade.
type Config struct {
	PromptDir  string
	ProfileDir string
	SchemaDir  string
	Timeout    time.Duration
	HTTPClient *http.Client
}

// Options collects construction choices from the public facade.
type Options struct {
	llmClient             llm.Client
	artifactReader        artifact.Reader
	promptDefinitions     promptdef.Repository
	profiles              profile.Repository
	fallbackProfiles      profile.Repository
	memoryProfiles        profile.Repository
	backends              []domain.Backend
	validator             validate.Validator
	promptSource          bool
	profileSource         bool
	fallbackProfileSource bool
	memorySource          bool
	validatorSource       bool
	artifactSource        bool
}

// SetLLMClient selects the client collaborator for one engine.
func (o *Options) SetLLMClient(client llm.Client) { o.llmClient = client }

// SetArtifactReader selects the artifact collaborator for one engine.
func (o *Options) SetArtifactReader(reader artifact.Reader) {
	o.artifactReader = reader
	o.artifactSource = true
}

// SetPromptFS selects a prompt source rooted in fsys.
func (o *Options) SetPromptFS(fsys fs.FS, root string) error {
	if err := validateSourceFS(fsys, root); err != nil {
		return err
	}
	o.promptDefinitions = promptdef.NewFSRepository(fsys, root)
	o.promptSource = true
	return nil
}

// SetPromptFile selects a single prompt file.
func (o *Options) SetPromptFile(path string) error {
	fsys, root, directory, err := fileSource(path)
	if err != nil {
		return err
	}
	o.promptDefinitions = promptdef.NewFileRepository(fsys, root, directory)
	o.promptSource = true
	return nil
}

// SetProfileFS selects an ordinary profile source rooted in fsys.
func (o *Options) SetProfileFS(fsys fs.FS, root string) error {
	if err := validateSourceFS(fsys, root); err != nil {
		return err
	}
	o.profiles = profile.NewFSRepository(fsys, root)
	o.profileSource = true
	return nil
}

// SetProfileFile selects a single ordinary profile file.
func (o *Options) SetProfileFile(path string) error {
	fsys, root, _, err := fileSource(path)
	if err != nil {
		return err
	}
	o.profiles = profile.NewFSRepository(fsys, root)
	o.profileSource = true
	return nil
}

// SetFallbackProfileFS selects a fallback profile source rooted in fsys.
func (o *Options) SetFallbackProfileFS(fsys fs.FS, root string) error {
	if err := validateSourceFS(fsys, root); err != nil {
		return err
	}
	o.fallbackProfiles = profile.NewFSRepository(fsys, root)
	o.fallbackProfileSource = true
	return nil
}

// SetMemoryProfiles validates and stores application-owned profile definitions.
func (o *Options) SetMemoryProfiles(definitions []domain.ExecutionProfile) error {
	repository, err := profile.NewMemoryRepository(definitions)
	if err != nil {
		return err
	}
	o.memoryProfiles = repository
	o.memorySource = true
	return nil
}

// AddBackend appends one backend registration.
func (o *Options) AddBackend(backend domain.Backend) { o.backends = append(o.backends, backend) }

// SetSchemaFS selects a schema source rooted in fsys.
func (o *Options) SetSchemaFS(fsys fs.FS, root string) error {
	if err := validateSourceFS(fsys, root); err != nil {
		return err
	}
	o.validator = validate.NewFSValidator(fsys, root)
	o.validatorSource = true
	return nil
}

// SetSchemaFile selects a single schema file.
func (o *Options) SetSchemaFile(path string) error {
	fsys, root, _, err := fileSource(path)
	if err != nil {
		return err
	}
	o.validator = validate.NewFSValidator(fsys, root)
	o.validatorSource = true
	return nil
}

// Engine forwards domain operations to the single assembled use-case runner.
type Engine struct {
	runner *usecase.Runner
}

// New assembles an engine from facade-selected configuration and collaborators.
func New(cfg Config, options Options) (*Engine, error) {
	promptDefinitions := options.promptDefinitions
	if !options.promptSource {
		if strings.TrimSpace(cfg.PromptDir) == "" {
			return nil, fmt.Errorf("prompt directory is required")
		}
		promptDefinitions = promptdef.NewFilesystemRepository(cfg.PromptDir)
	}

	maintained, err := catalog.Load(
		catalog.Source{Name: "OpenRouter", ExpectedBackendID: backend.OpenRouterID, FS: openrouter.FS(), Root: openrouter.Root},
		catalog.Source{Name: "Rakestrawhome", ExpectedBackendID: backend.RakestrawHomeID, FS: rakestrawhome.FS(), Root: rakestrawhome.Root},
	)
	if err != nil {
		return nil, fmt.Errorf("failed to load maintained catalogs: %w", err)
	}

	maintainedProfiles, err := newMaintainedProfileRepository(maintained.Profiles, maintained.Backends)
	if err != nil {
		return nil, fmt.Errorf("failed to construct Promptkit-maintained profiles: %w", err)
	}

	profiles := newProfileRepository(cfg.ProfileDir, options, maintainedProfiles)
	registry, err := backend.NewRegistry(maintained.Backends, options.backends)
	if err != nil {
		return nil, fmt.Errorf("failed to construct backend registry: %w", err)
	}
	manager, err := capacity.NewManager(registry.CapacityPolicies())
	if err != nil {
		return nil, fmt.Errorf("failed to construct backend capacity manager: %w", err)
	}

	validator := options.validator
	if !options.validatorSource {
		schemaDir := cfg.SchemaDir
		if strings.TrimSpace(schemaDir) == "" {
			schemaDir = defaults.SchemaDirDefault
		}
		validator = validate.NewStandardValidator(schemaDir)
	}
	client := options.llmClient
	if client == nil {
		client, err = llm.NewOpenAICompatibleClient(llm.OpenAICompatibleConfig{Timeout: cfg.Timeout, HTTPClient: cfg.HTTPClient})
		if err != nil {
			return nil, err
		}
	}
	client = capacity.NewClient(manager, client)
	reader := options.artifactReader
	if !options.artifactSource {
		reader = artifact.NewCompositeReader()
	}

	return &Engine{runner: usecase.NewRunnerWithRepairer(promptDefinitions, profiles, registry, reader, prompt.NewGoRenderer(), client, validator, usecase.NewDefaultOutputRepairer(client), manager)}, nil
}

func newProfileRepository(profileDir string, options Options, maintained profile.Repository) profile.Repository {
	repository := maintained
	if options.fallbackProfileSource {
		repository = profile.NewOverlayRepository(options.fallbackProfiles, repository)
	}
	if options.profileSource {
		repository = profile.NewOverlayRepository(options.profiles, repository)
	} else if strings.TrimSpace(profileDir) != "" {
		repository = profile.NewOverlayRepository(profile.NewFilesystemRepository(profileDir), repository)
	}
	if options.memorySource {
		repository = profile.NewOverlayRepository(options.memoryProfiles, repository)
	}
	return profile.NewResolvingRepository(repository)
}

func validateSourceFS(fsys fs.FS, root string) error {
	if fsys == nil {
		return fmt.Errorf("source filesystem is nil")
	}
	if strings.TrimSpace(root) == "" {
		return fmt.Errorf("source root is required")
	}
	return nil
}

func fileSource(name string) (fs.FS, string, string, error) {
	if strings.TrimSpace(name) == "" {
		return nil, "", "", fmt.Errorf("source path is required")
	}
	directory := filepath.Dir(name)
	base := filepath.Base(name)
	if base == "." || base == string(filepath.Separator) {
		return nil, "", "", fmt.Errorf("source path must name a file")
	}
	info, err := os.Stat(name)
	if err != nil {
		return nil, "", "", fmt.Errorf("failed to access source file %q: %w", name, err)
	}
	if info.IsDir() {
		return nil, "", "", fmt.Errorf("source path %q must be a file", name)
	}
	return os.DirFS(directory), filepath.ToSlash(base), directory, nil
}

func (e *Engine) InspectPrompt(ctx context.Context, id, version string) (*domain.PromptInspection, error) {
	return e.runner.InspectPrompt(ctx, id, version)
}
func (e *Engine) InspectProfile(ctx context.Context, id string) (*domain.ProfileInspection, error) {
	return e.runner.InspectProfile(ctx, id)
}
func (e *Engine) Prepare(ctx context.Context, request domain.RunRequest) (*domain.PreparedRun, error) {
	return e.runner.Prepare(ctx, request)
}
func (e *Engine) PrepareExecution(ctx context.Context, request domain.RunRequest) (*usecase.PreparedExecution, error) {
	return e.runner.PrepareExecution(ctx, request)
}
func (e *Engine) Run(ctx context.Context, request domain.RunRequest) (*domain.RunResult, error) {
	return e.runner.Run(ctx, request)
}
func (e *Engine) RunPrepared(ctx context.Context, prepared *usecase.PreparedExecution) (*domain.RunResult, error) {
	return e.runner.RunPrepared(ctx, prepared)
}