package state

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/weatherreporter/internal/adapters/scriptorium"
	"gitea.maximumdirect.net/eric/weatherreporter/internal/briefing"
	"gitea.maximumdirect.net/eric/weatherreporter/internal/config"
	"gitea.maximumdirect.net/eric/weatherreporter/internal/promptinput"
	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
)

type FilesystemStore struct {
	root            string
	snapshotsDir    string
	reportsDir      string
	dataPackagesDir string
	preflightDir    string
}

type ArtifactPaths struct {
	Briefing       string `json:"briefing"`
	Metadata       string `json:"metadata"`
	DataPackage    string `json:"dataPackage"`
	Preflight      string `json:"preflight"`
	RenderedReport string `json:"renderedReport,omitempty"`
}

func NewFilesystemStore(cfg config.WorkspaceConfig) (*FilesystemStore, error) {
	if cfg.Root == "" {
		return nil, fmt.Errorf("workspace root is required")
	}
	for name, value := range map[string]string{
		"snapshots_dir":     cfg.SnapshotsDir,
		"reports_dir":       cfg.ReportsDir,
		"data_packages_dir": cfg.DataPackagesDir,
		"preflight_dir":     cfg.PreflightDir,
	} {
		if err := validateRelativeDir(name, value); err != nil {
			return nil, err
		}
	}
	return &FilesystemStore{
		root:            filepath.Clean(cfg.Root),
		snapshotsDir:    filepath.Clean(cfg.SnapshotsDir),
		reportsDir:      filepath.Clean(cfg.ReportsDir),
		dataPackagesDir: filepath.Clean(cfg.DataPackagesDir),
		preflightDir:    filepath.Clean(cfg.PreflightDir),
	}, nil
}

func (s *FilesystemStore) Paths(resolved report.Resolved) (ArtifactPaths, error) {
	if s == nil {
		return ArtifactPaths{}, fmt.Errorf("state store is required")
	}
	metadata := resolved.Metadata()
	if metadata.RunID == "" {
		return ArtifactPaths{}, fmt.Errorf("run id is required")
	}
	group, err := reportGroup(resolved.Definition.ID)
	if err != nil {
		return ArtifactPaths{}, err
	}
	validDate := resolved.ValidPeriod.Start.Format("2006-01-02")
	filenameBase := metadata.RunID
	return ArtifactPaths{
		Briefing:       s.join(s.snapshotsDir, group, validDate, filenameBase+".briefing.json"),
		Metadata:       s.join(s.snapshotsDir, group, validDate, filenameBase+".metadata.json"),
		DataPackage:    s.join(s.dataPackagesDir, group, validDate, filenameBase+".data_package.json"),
		Preflight:      s.join(s.preflightDir, group, validDate, filenameBase+".render.json"),
		RenderedReport: s.join(s.reportsDir, group, filenameBase+".md"),
	}, nil
}

func (s *FilesystemStore) SaveBriefing(_ context.Context, resolved report.Resolved, pkg briefing.Package) (string, error) {
	paths, err := s.Paths(resolved)
	if err != nil {
		return "", err
	}
	if err := writeJSONAtomic(paths.Briefing, pkg); err != nil {
		return "", err
	}
	return paths.Briefing, nil
}

func (s *FilesystemStore) SaveDataPackage(_ context.Context, resolved report.Resolved, pkg promptinput.Package) (string, error) {
	paths, err := s.Paths(resolved)
	if err != nil {
		return "", err
	}
	if err := promptinput.Validate(pkg); err != nil {
		return "", err
	}
	if err := writeJSONAtomic(paths.DataPackage, pkg); err != nil {
		return "", err
	}
	return paths.DataPackage, nil
}

func (s *FilesystemStore) SavePreflight(_ context.Context, resolved report.Resolved, result *scriptorium.RenderResult) (string, error) {
	if result == nil {
		return "", fmt.Errorf("render result is required")
	}
	paths, err := s.Paths(resolved)
	if err != nil {
		return "", err
	}
	if err := writeJSONAtomic(paths.Preflight, result); err != nil {
		return "", err
	}
	return paths.Preflight, nil
}

func (s *FilesystemStore) PrepareRenderedReport(_ context.Context, resolved report.Resolved) (string, error) {
	paths, err := s.Paths(resolved)
	if err != nil {
		return "", err
	}
	if err := os.MkdirAll(filepath.Dir(paths.RenderedReport), 0o755); err != nil {
		return "", fmt.Errorf("create rendered report directory %q: %w", filepath.Dir(paths.RenderedReport), err)
	}
	return paths.RenderedReport, nil
}

func (s *FilesystemStore) SaveMetadata(_ context.Context, metadata Metadata) (string, error) {
	if metadata.RunID == "" {
		return "", fmt.Errorf("metadata run id is required")
	}
	if metadata.BriefingPath == "" {
		return "", fmt.Errorf("metadata briefing path is required")
	}
	if metadata.DataPackagePath == "" {
		return "", fmt.Errorf("metadata data package path is required")
	}
	if metadata.PreflightPath == "" {
		return "", fmt.Errorf("metadata preflight path is required")
	}
	path := metadataPathFromStored(metadata)
	if path == "" {
		return "", fmt.Errorf("metadata path cannot be resolved")
	}
	if err := writeJSONAtomic(path, metadata); err != nil {
		return "", err
	}
	return path, nil
}

func (s *FilesystemStore) FindPriorDailySnapshot(ctx context.Context, resolved report.Resolved) (*PriorSnapshot, error) {
	return s.FindPriorSnapshot(ctx, resolved)
}

func (s *FilesystemStore) FindPriorSnapshot(_ context.Context, resolved report.Resolved) (*PriorSnapshot, error) {
	if resolved.Definition.ComparisonStrategy != report.CompareSameValidDate && resolved.Definition.ComparisonStrategy != report.CompareWeekendWindow {
		return nil, nil
	}
	group, err := reportGroup(resolved.Definition.ID)
	if err != nil {
		return nil, err
	}
	dirs, err := s.metadataDirectories(resolved, group)
	if err != nil {
		return nil, err
	}

	var candidates []Metadata
	for _, dir := range dirs {
		entries, err := os.ReadDir(dir)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return nil, fmt.Errorf("read snapshot metadata directory %q: %w", dir, err)
		}
		for _, entry := range entries {
			if entry.IsDir() || !strings.HasSuffix(entry.Name(), ".metadata.json") {
				continue
			}
			path := filepath.Join(dir, entry.Name())
			var metadata Metadata
			if err := readJSON(path, &metadata); err != nil {
				return nil, err
			}
			if metadata.RunID == resolved.Metadata().RunID {
				continue
			}
			if !compatiblePriorReport(group, metadata.ReportID, resolved.Definition.ID) {
				continue
			}
			if !comparablePeriod(metadata, resolved) {
				continue
			}
			if !metadata.GeneratedAt.Before(resolved.GeneratedAt) {
				continue
			}
			candidates = append(candidates, metadata)
		}
	}
	if len(candidates) == 0 {
		return nil, nil
	}
	sort.Slice(candidates, func(i, j int) bool {
		return candidates[i].GeneratedAt.After(candidates[j].GeneratedAt)
	})
	return &PriorSnapshot{
		Metadata:     candidates[0],
		BriefingPath: candidates[0].BriefingPath,
	}, nil
}

func (s *FilesystemStore) metadataDirectories(resolved report.Resolved, group string) ([]string, error) {
	paths, err := s.Paths(resolved)
	if err != nil {
		return nil, err
	}
	if resolved.Definition.ComparisonStrategy != report.CompareWeekendWindow {
		return []string{filepath.Dir(paths.Metadata)}, nil
	}
	root := s.join(s.snapshotsDir, group)
	entries, err := os.ReadDir(root)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("read snapshot group directory %q: %w", root, err)
	}
	var dirs []string
	for _, entry := range entries {
		if entry.IsDir() {
			dirs = append(dirs, filepath.Join(root, entry.Name()))
		}
	}
	return dirs, nil
}

func compatiblePriorReport(group string, prior report.ID, current report.ID) bool {
	switch group {
	case "daily":
		return prior == report.DailyToday || prior == report.DailyTomorrow
	case "three-day":
		return prior == report.ThreeDay && current == report.ThreeDay
	case "weekend":
		return prior == report.Weekend && current == report.Weekend
	default:
		return false
	}
}

func (s *FilesystemStore) join(parts ...string) string {
	all := append([]string{s.root}, parts...)
	return filepath.Join(all...)
}

func validateRelativeDir(name string, value string) error {
	if value == "" {
		return fmt.Errorf("%s is required", name)
	}
	if filepath.IsAbs(value) {
		return fmt.Errorf("%s must be relative to workspace root", name)
	}
	cleaned := filepath.Clean(value)
	if cleaned == "." || cleaned == ".." || strings.HasPrefix(cleaned, ".."+string(filepath.Separator)) {
		return fmt.Errorf("%s must stay within workspace root", name)
	}
	return nil
}

func reportGroup(id report.ID) (string, error) {
	switch id {
	case report.DailyToday, report.DailyTomorrow:
		return "daily", nil
	case report.ThreeDay:
		return "three-day", nil
	case report.Weekend:
		return "weekend", nil
	case report.Storm:
		return "storm", nil
	default:
		return "", fmt.Errorf("unknown report %q", id)
	}
}

func writeJSONAtomic(path string, value any) error {
	data, err := json.MarshalIndent(value, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal %q: %w", path, err)
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return fmt.Errorf("create directory %q: %w", filepath.Dir(path), err)
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+".*.tmp")
	if err != nil {
		return fmt.Errorf("create temporary file for %q: %w", path, err)
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return fmt.Errorf("write temporary file for %q: %w", path, err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close temporary file for %q: %w", path, err)
	}
	if err := os.Rename(tmpName, path); err != nil {
		return fmt.Errorf("save %q: %w", path, err)
	}
	return nil
}

func readJSON(path string, target any) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("read %q: %w", path, err)
	}
	if err := json.Unmarshal(data, target); err != nil {
		return fmt.Errorf("decode %q: %w", path, err)
	}
	return nil
}

func metadataPathFromStored(metadata Metadata) string {
	if metadata.BriefingPath == "" {
		return ""
	}
	filename := metadata.RunID + ".metadata.json"
	return filepath.Join(filepath.Dir(metadata.BriefingPath), filename)
}

func sameValidDate(metadata Metadata, resolved report.Resolved) bool {
	return metadata.ValidPeriod.Start.Format("2006-01-02") == resolved.ValidPeriod.Start.Format("2006-01-02")
}

func comparablePeriod(metadata Metadata, resolved report.Resolved) bool {
	switch resolved.Definition.ComparisonStrategy {
	case report.CompareSameValidDate:
		return sameValidDate(metadata, resolved)
	case report.CompareWeekendWindow:
		return sameWeekendWindow(metadata, resolved)
	default:
		return false
	}
}

func sameWeekendWindow(metadata Metadata, resolved report.Resolved) bool {
	return metadata.ValidPeriod.End.Equal(resolved.ValidPeriod.End) && !metadata.ValidPeriod.Start.After(resolved.ValidPeriod.Start)
}

func (s *FilesystemStore) LoadBriefing(_ context.Context, path string) (briefing.Package, error) {
	if path == "" {
		return briefing.Package{}, fmt.Errorf("briefing path is required")
	}
	var pkg briefing.Package
	if err := readJSON(path, &pkg); err != nil {
		return briefing.Package{}, err
	}
	return pkg, nil
}