// Package modelmigration creates a reviewable v2 installation candidate from legacy model files.
package modelmigration

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/aritmolab/thothii/tools/tht/internal/config"
	"github.com/compose-spec/compose-go/v2/dotenv"
	"gopkg.in/yaml.v3"
)

const maxMigrationInputBytes = 1 << 20

// Request contains the facts that do not exist unambiguously in the three legacy model sources.
type Request struct {
	InstallationPath    string
	OutputPath          string
	SessionDefault      string
	EmbeddingID         string
	EmbeddingDimensions int
}

type legacyDescriptor struct {
	SchemaVersion       int                      `yaml:"schemaVersion,omitempty"`
	Profile             string                   `yaml:"profile"`
	ProjectDirectory    string                   `yaml:"projectDirectory"`
	EnvFile             string                   `yaml:"envFile"`
	WorkspaceRepository workspaceRepository      `yaml:"workspaceRepository"`
	Authentication      authenticationDescriptor `yaml:"authentication"`
	MetadataGeneration  legacyMetadataCatalog    `yaml:"metadataGeneration"`
	Overrides           []string                 `yaml:"overrides,omitempty"`
}

type workspaceRepository struct {
	Remote string `yaml:"remote"`
	Branch string `yaml:"branch"`
	Access string `yaml:"access"`
}

type authenticationDescriptor struct {
	ConfigDirectory   string             `yaml:"configDirectory"`
	RuntimeProjection *runtimeProjection `yaml:"runtimeProjection,omitempty"`
}

type runtimeProjection struct {
	Directory string `yaml:"directory"`
	UID       uint32 `yaml:"uid"`
	GID       uint32 `yaml:"gid"`
}

type legacyMetadataCatalog struct {
	Default string                `yaml:"default"`
	Models  []legacyMetadataModel `yaml:"models"`
}

type legacyMetadataModel struct {
	ID        string        `yaml:"id"`
	Label     string        `yaml:"label"`
	LiteLLM   legacyLiteLLM `yaml:"litellm"`
	APIKeyEnv string        `yaml:"apiKeyEnv"`
}

type legacyLiteLLM struct {
	Provider        string                `yaml:"provider"`
	Model           string                `yaml:"model"`
	DisableThinking bool                  `yaml:"disableThinking"`
	Endpoint        *config.ModelEndpoint `yaml:"endpoint"`
}

type piCatalog struct {
	Providers map[string]piProvider `json:"providers"`
}

type piProvider struct {
	BaseURL string    `json:"baseUrl"`
	API     string    `json:"api"`
	APIKey  string    `json:"apiKey"`
	Models  []piModel `json:"models"`
}

type piModel struct {
	ID            string                     `json:"id"`
	Name          string                     `json:"name"`
	Reasoning     bool                       `json:"reasoning"`
	Input         []string                   `json:"input,omitempty"`
	Cost          *config.ModelCost          `json:"cost,omitempty"`
	ContextWindow int                        `json:"contextWindow"`
	MaxTokens     int                        `json:"maxTokens"`
	Compat        *config.ModelCompatibility `json:"compat,omitempty"`
}

type piSettings struct {
	DefaultProjectTrust string   `json:"defaultProjectTrust"`
	EnabledModels       []string `json:"enabledModels"`
}

type candidateDescriptor struct {
	SchemaVersion       int                      `yaml:"schemaVersion"`
	Profile             string                   `yaml:"profile"`
	ProjectDirectory    string                   `yaml:"projectDirectory"`
	EnvFile             string                   `yaml:"envFile"`
	WorkspaceRepository workspaceRepository      `yaml:"workspaceRepository"`
	ModelCatalog        config.ModelCatalog      `yaml:"modelCatalog"`
	Authentication      authenticationDescriptor `yaml:"authentication"`
	Overrides           []string                 `yaml:"overrides,omitempty"`
}

// Run reads every legacy source, reports ambiguity without publishing, and otherwise writes one
// new candidate. It never modifies or removes the legacy files.
func Run(request Request) error {
	if !filepath.IsAbs(request.InstallationPath) || filepath.Base(request.InstallationPath) != "thothii-installation.yaml" {
		return errors.New("installation migration requires an absolute thothii-installation.yaml path")
	}
	outputExtension := strings.ToLower(filepath.Ext(request.OutputPath))
	if !filepath.IsAbs(request.OutputPath) || outputExtension != ".yaml" && outputExtension != ".yml" ||
		filepath.Clean(request.OutputPath) == filepath.Clean(request.InstallationPath) {
		return errors.New("installation migration output must be a different absolute YAML path")
	}
	if request.SessionDefault == "" || request.EmbeddingID == "" || request.EmbeddingDimensions <= 0 {
		return errors.New("installation migration requires session default, embedding id, and positive embedding dimensions")
	}
	if _, err := os.Lstat(request.OutputPath); err == nil {
		return errors.New("installation migration output already exists")
	} else if !os.IsNotExist(err) {
		return errors.New("installation migration output is unavailable")
	}

	var legacy legacyDescriptor
	if err := decodeYAML(request.InstallationPath, &legacy); err != nil {
		return fmt.Errorf("legacy installation: %w", err)
	}
	if legacy.SchemaVersion != 0 {
		return errors.New("legacy installation: schemaVersion must be absent")
	}
	var piModels piCatalog
	if err := decodeJSON(filepath.Join(legacy.ProjectDirectory, "deploy", "pi", "models.json"), &piModels); err != nil {
		return fmt.Errorf("deploy/pi/models.json: %w", err)
	}
	var settings piSettings
	if err := decodeJSON(filepath.Join(legacy.ProjectDirectory, "deploy", "pi", "settings.json"), &settings); err != nil {
		return fmt.Errorf("deploy/pi/settings.json: %w", err)
	}

	catalog, err := reconcileCatalog(legacy, piModels, settings, request)
	if err != nil {
		return err
	}
	environment, err := parseEnvironment(legacy.EnvFile)
	if err != nil {
		return errors.New("legacy installation envFile is unavailable or invalid")
	}
	if err := catalog.Validate(environment); err != nil {
		return fmt.Errorf("modelCatalog candidate: %w", err)
	}
	candidate := candidateDescriptor{
		SchemaVersion: 2, Profile: legacy.Profile, ProjectDirectory: legacy.ProjectDirectory,
		EnvFile: legacy.EnvFile, WorkspaceRepository: legacy.WorkspaceRepository,
		ModelCatalog: catalog, Authentication: legacy.Authentication, Overrides: legacy.Overrides,
	}
	contents, err := yaml.Marshal(candidate)
	if err != nil {
		return errors.New("installation migration candidate could not be encoded")
	}
	return publishCandidate(request.OutputPath, contents)
}

func reconcileCatalog(legacy legacyDescriptor, piModels piCatalog, settings piSettings, request Request) (config.ModelCatalog, error) {
	catalog := config.ModelCatalog{
		Defaults:  config.ModelCatalogDefaults{Session: request.SessionDefault},
		Embedding: config.ModelCatalogEmbedding{ID: request.EmbeddingID, Dimensions: request.EmbeddingDimensions},
		Providers: make(map[string]config.ModelProvider),
	}
	enabled := make(map[string]struct{}, len(settings.EnabledModels))
	for index, canonical := range settings.EnabledModels {
		providerID, modelID, ok := splitCanonical(canonical)
		if !ok {
			return catalog, fmt.Errorf("deploy/pi/settings.json enabledModels[%d]: canonical provider/model identity is required", index)
		}
		if _, duplicate := enabled[canonical]; duplicate {
			return catalog, fmt.Errorf("deploy/pi/settings.json enabledModels[%d]: duplicate identity %q", index, canonical)
		}
		enabled[canonical] = struct{}{}
		piProvider, custom := piModels.Providers[providerID]
		if !custom {
			provider := catalog.Providers[providerID]
			if len(provider.Models) == 0 {
				provider = config.ModelProvider{
					Authentication: config.ModelAuthentication{Mode: "pi_auth"},
					Session:        &config.ModelSessionAdapter{Mode: "pi_builtin"},
					Models:         make(map[string]config.CatalogModel),
				}
			}
			provider.Models[modelID] = config.CatalogModel{Session: &config.SessionModel{}}
			catalog.Providers[providerID] = provider
			continue
		}
		model, found := findPiModel(piProvider.Models, modelID)
		if !found {
			return catalog, fmt.Errorf("deploy/pi/settings.json enabledModels[%d]: %q is missing from deploy/pi/models.json", index, canonical)
		}
		provider, exists := catalog.Providers[providerID]
		if !exists {
			auth, authErr := migratePiAuthentication(providerID, piProvider)
			if authErr != nil {
				return catalog, authErr
			}
			provider = config.ModelProvider{
				Endpoint: &config.ModelEndpoint{BaseURL: piProvider.BaseURL}, Authentication: auth,
				Session: &config.ModelSessionAdapter{Mode: "openai_compatible"},
				Models:  make(map[string]config.CatalogModel),
			}
		}
		provider.Models[modelID] = config.CatalogModel{
			Label: model.Name,
			Session: &config.SessionModel{
				Reasoning: model.Reasoning, Input: model.Input, Cost: model.Cost,
				ContextWindow: model.ContextWindow, MaxTokens: model.MaxTokens,
				Compatibility: model.Compat,
			},
		}
		catalog.Providers[providerID] = provider
	}
	if _, ok := enabled[request.SessionDefault]; !ok {
		return catalog, fmt.Errorf("session default %q is not enabled by deploy/pi/settings.json", request.SessionDefault)
	}

	metadataIDs := make(map[string]string, len(legacy.MetadataGeneration.Models))
	for index, old := range legacy.MetadataGeneration.Models {
		canonical, mergeErr := mergeMetadataModel(&catalog, old)
		if mergeErr != nil {
			return catalog, fmt.Errorf("metadataGeneration.models[%d]: %w", index, mergeErr)
		}
		if old.ID == "" {
			return catalog, fmt.Errorf("metadataGeneration.models[%d]: id is required", index)
		}
		if _, duplicate := metadataIDs[old.ID]; duplicate {
			return catalog, fmt.Errorf("metadataGeneration.models[%d]: duplicate legacy id %q", index, old.ID)
		}
		metadataIDs[old.ID] = canonical
	}
	if len(metadataIDs) > 0 {
		mapped, ok := metadataIDs[legacy.MetadataGeneration.Default]
		if !ok {
			return catalog, errors.New("metadataGeneration.default does not identify one legacy model")
		}
		catalog.Defaults.MetadataGeneration = mapped
	} else if legacy.MetadataGeneration.Default != "" {
		return catalog, errors.New("metadataGeneration.default is set without models")
	}
	return catalog, nil
}

func mergeMetadataModel(catalog *config.ModelCatalog, old legacyMetadataModel) (string, error) {
	if old.LiteLLM.Provider == "" || old.LiteLLM.Model == "" {
		return "", errors.New("litellm.provider and litellm.model are required")
	}
	type match struct{ provider, model string }
	matches := make([]match, 0, 1)
	for providerID, provider := range catalog.Providers {
		if old.LiteLLM.Endpoint != nil && !sameEndpoint(provider.Endpoint, old.LiteLLM.Endpoint) {
			continue
		}
		for modelID, model := range provider.Models {
			upstream := model.UpstreamModel
			if upstream == "" {
				upstream = modelID
			}
			if upstream == old.LiteLLM.Model && (old.LiteLLM.Endpoint != nil || providerID == old.LiteLLM.Provider) {
				matches = append(matches, match{providerID, modelID})
			}
		}
	}
	if len(matches) > 1 {
		return "", errors.New("model identity matches more than one Pi provider")
	}
	providerID, modelID := old.LiteLLM.Provider, old.LiteLLM.Model
	if len(matches) == 1 {
		providerID, modelID = matches[0].provider, matches[0].model
	}
	provider, exists := catalog.Providers[providerID]
	desiredAuth := config.ModelAuthentication{Mode: "none"}
	if old.APIKeyEnv != "" {
		desiredAuth = config.ModelAuthentication{Mode: "secret_env", APIKeyEnv: old.APIKeyEnv}
	}
	if !exists {
		provider = config.ModelProvider{
			Endpoint: old.LiteLLM.Endpoint, Authentication: desiredAuth,
			MetadataGeneration: &config.ModelMetadataAdapter{LiteLLMProvider: old.LiteLLM.Provider},
			Models:             make(map[string]config.CatalogModel),
		}
	} else {
		if provider.Authentication != desiredAuth {
			return "", fmt.Errorf("provider %q authentication conflicts between Pi and metadata generation", providerID)
		}
		if old.LiteLLM.Endpoint != nil && !sameEndpoint(provider.Endpoint, old.LiteLLM.Endpoint) {
			return "", fmt.Errorf("provider %q endpoint conflicts between Pi and metadata generation", providerID)
		}
		if provider.MetadataGeneration != nil && provider.MetadataGeneration.LiteLLMProvider != old.LiteLLM.Provider {
			return "", fmt.Errorf("provider %q LiteLLM adapter is ambiguous", providerID)
		}
		provider.MetadataGeneration = &config.ModelMetadataAdapter{LiteLLMProvider: old.LiteLLM.Provider}
	}
	model := provider.Models[modelID]
	if model.MetadataGeneration != nil {
		return "", fmt.Errorf("canonical identity %q is claimed by more than one legacy metadata model", providerID+"/"+modelID)
	}
	if model.Label == "" {
		model.Label = old.Label
	}
	if modelID != old.LiteLLM.Model {
		model.UpstreamModel = old.LiteLLM.Model
	}
	model.MetadataGeneration = &config.MetadataGenerationModel{DisableThinking: old.LiteLLM.DisableThinking}
	provider.Models[modelID] = model
	catalog.Providers[providerID] = provider
	return providerID + "/" + modelID, nil
}

func migratePiAuthentication(providerID string, provider piProvider) (config.ModelAuthentication, error) {
	if provider.BaseURL == "" || provider.API != "openai-completions" {
		return config.ModelAuthentication{}, fmt.Errorf("deploy/pi/models.json provider %q: only explicit openai-completions endpoints can migrate", providerID)
	}
	if strings.HasPrefix(provider.APIKey, "$") && len(provider.APIKey) > 1 {
		return config.ModelAuthentication{Mode: "secret_env", APIKeyEnv: provider.APIKey[1:]}, nil
	}
	if provider.APIKey == "local" {
		return config.ModelAuthentication{Mode: "none"}, nil
	}
	return config.ModelAuthentication{}, fmt.Errorf("deploy/pi/models.json provider %q: API key cannot be reconciled without guessing", providerID)
}

func findPiModel(models []piModel, id string) (piModel, bool) {
	var found piModel
	count := 0
	for _, model := range models {
		if model.ID == id {
			found, count = model, count+1
		}
	}
	return found, count == 1
}

func splitCanonical(value string) (string, string, bool) {
	parts := strings.Split(value, "/")
	return first(parts), second(parts), len(parts) == 2 && parts[0] != "" && parts[1] != ""
}

func first(parts []string) string {
	if len(parts) > 0 {
		return parts[0]
	}
	return ""
}
func second(parts []string) string {
	if len(parts) > 1 {
		return parts[1]
	}
	return ""
}

func sameEndpoint(left, right *config.ModelEndpoint) bool {
	if left == nil || right == nil {
		return left == nil && right == nil
	}
	return left.BaseURL == right.BaseURL && left.APIVersion == right.APIVersion
}

func decodeYAML(path string, target any) error {
	source, err := readBounded(path)
	if err != nil {
		return err
	}
	decoder := yaml.NewDecoder(bytes.NewReader(source))
	decoder.KnownFields(true)
	if err := decoder.Decode(target); err != nil {
		return errors.New("invalid or unsupported YAML")
	}
	var trailing any
	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
		return errors.New("multiple YAML documents are not supported")
	}
	return nil
}

func decodeJSON(path string, target any) error {
	source, err := readBounded(path)
	if err != nil {
		return err
	}
	decoder := json.NewDecoder(bytes.NewReader(source))
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(target); err != nil {
		return errors.New("invalid or unsupported JSON")
	}
	var trailing any
	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
		return errors.New("trailing JSON is not supported")
	}
	return nil
}

func readBounded(path string) ([]byte, error) {
	info, err := os.Lstat(path)
	if err != nil || !info.Mode().IsRegular() || info.Mode()&os.ModeSymlink != 0 || info.Size() < 1 || info.Size() > maxMigrationInputBytes {
		return nil, errors.New("source is unavailable or unsafe")
	}
	return os.ReadFile(path)
}

func parseEnvironment(path string) (map[string]string, error) {
	source, err := readBounded(path)
	if err != nil {
		return nil, err
	}
	return dotenv.ParseWithLookup(bytes.NewReader(source), os.LookupEnv)
}

func publishCandidate(path string, contents []byte) error {
	directory := filepath.Dir(path)
	if err := os.MkdirAll(directory, 0o700); err != nil {
		return errors.New("create migration output directory")
	}
	temporary, err := os.CreateTemp(directory, ".installation-v2-*")
	if err != nil {
		return errors.New("create installation migration candidate")
	}
	name := temporary.Name()
	published := false
	defer func() {
		if !published {
			_ = os.Remove(name)
		}
	}()
	if err := temporary.Chmod(0o600); err == nil {
		_, err = temporary.Write(contents)
	}
	if closeErr := temporary.Close(); err == nil {
		err = closeErr
	}
	if err != nil {
		return errors.New("write installation migration candidate")
	}
	if err := os.Link(name, path); err != nil {
		if os.IsExist(err) {
			return errors.New("installation migration output already exists")
		}
		return errors.New("publish installation migration candidate")
	}
	published = true
	_ = os.Remove(name)
	return nil
}

// ParseDimensions is shared by the host command without accepting floats or signs.
func ParseDimensions(value string) (int, error) {
	dimensions, err := strconv.Atoi(value)
	if err != nil || dimensions <= 0 {
		return 0, errors.New("embedding dimensions must be a positive integer")
	}
	return dimensions, nil
}