// Package assetloader implements a native Go asset/file loader that binds
// local binary and text files as pgx query parameters during database seeding.
// Files are bound as actual []byte query parameters — never converted to SQL
// text literals — so binary data stays byte-exact and no escaping is needed.
//
// Manifests are small YAML files (assets.yaml) that describe, per file, the
// SQL call to invoke and the named placeholders for :bytes, :filename, and any
// static column values. Manifests live inside directories that follow the same
// {priority}_{sequence}_{name} naming convention used by the sqldir reader,
// so asset-loading steps can be interleaved with SQL scripts in a migrate-apply
// run.
package assetloader

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"

	"gopkg.in/yaml.v3"
)

// ManifestEntry describes a single file to load from an assets.yaml manifest.
type ManifestEntry struct {
	// File is the path to the asset file, relative to the manifest directory.
	File string `yaml:"file"`
	// Call is the SQL statement to execute. Use :bytes for file content,
	// :filename for the base name, and :param_name for static params.
	Call string `yaml:"call"`
	// Params holds optional static named parameters referenced in Call.
	Params map[string]string `yaml:"params,omitempty"`
}

// Item combines a manifest entry with its ordering metadata and the resolved
// directory where the manifest and asset file reside.
type Item struct {
	// Priority and Sequence come from the parent directory's naming pattern.
	Priority int
	Sequence uint
	// DirName is the last path component of the manifest's directory.
	DirName string
	// Dir is the absolute path to the directory containing assets.yaml and files.
	Dir string
	// Entry is the parsed manifest entry.
	Entry ManifestEntry
}

// dirPattern matches {priority}_{sequence}_{name} or {priority}-{sequence}-{name}
// directory names, e.g. "1_010_seed_templates" or "2-001-branding".
var dirPattern = regexp.MustCompile(`^(\d+)[_-](\d+)[_-](.+)$`)

// LoadManifest reads and parses the assets.yaml file in dir, returning
// the ordered list of manifest entries. Returns an error if assets.yaml is
// absent or contains invalid YAML.
func LoadManifest(dir string) ([]ManifestEntry, error) {
	manifestPath := filepath.Join(dir, "assets.yaml")
	data, err := os.ReadFile(manifestPath)
	if err != nil {
		return nil, fmt.Errorf("reading %s: %w", manifestPath, err)
	}

	var entries []ManifestEntry
	if err := yaml.Unmarshal(data, &entries); err != nil {
		return nil, fmt.Errorf("parsing %s: %w", manifestPath, err)
	}

	return entries, nil
}

// ScanDir recursively walks baseDir, finds all assets.yaml manifests, resolves
// each file entry (skipping symlinks and path traversal), and returns the
// resulting Items sorted by (Priority, Sequence, DirName).
//
// Each manifest must reside in a directory whose name follows the
// {priority}_{sequence}_{name} pattern. Manifests in directories that do not
// follow this convention are assigned Priority=0, Sequence=0 and sorted last.
func ScanDir(baseDir string) ([]Item, error) {
	absBase, err := filepath.Abs(baseDir)
	if err != nil {
		return nil, fmt.Errorf("resolving base dir: %w", err)
	}

	var items []Item

	err = filepath.WalkDir(absBase, func(path string, d os.DirEntry, walkErr error) error {
		if walkErr != nil {
			return walkErr
		}
		if d.IsDir() {
			return nil
		}
		if d.Name() != "assets.yaml" {
			return nil
		}

		manifestDir := filepath.Dir(path)
		priority, sequence, dirName := parseDirName(filepath.Base(manifestDir))

		entries, err := LoadManifest(manifestDir)
		if err != nil {
			return fmt.Errorf("loading manifest in %s: %w", manifestDir, err)
		}

		for _, entry := range entries {
			if entry.File == "" || entry.Call == "" {
				continue
			}

			// Resolve and validate the asset file path.
			resolved, skip, err := resolveAssetPath(absBase, manifestDir, entry.File)
			if err != nil {
				return err
			}
			if skip {
				continue
			}

			items = append(items, Item{
				Priority: priority,
				Sequence: sequence,
				DirName:  dirName,
				Dir:      manifestDir,
				Entry: ManifestEntry{
					File:   resolved, // absolute path, safe to read
					Call:   entry.Call,
					Params: entry.Params,
				},
			})
		}

		return nil
	})
	if err != nil {
		return nil, err
	}

	sort.SliceStable(items, func(i, j int) bool {
		if items[i].Priority != items[j].Priority {
			return items[i].Priority < items[j].Priority
		}
		if items[i].Sequence != items[j].Sequence {
			return items[i].Sequence < items[j].Sequence
		}
		return items[i].DirName < items[j].DirName
	})

	return items, nil
}

// parseDirName extracts (priority, sequence, name) from a directory name that
// follows the {priority}[_-]{sequence}[_-]{name} convention. Returns (0, 0, dir)
// when the name does not match.
func parseDirName(dir string) (priority int, sequence uint, name string) {
	m := dirPattern.FindStringSubmatch(dir)
	if m == nil {
		return 0, 0, dir
	}
	p, _ := strconv.Atoi(m[1])
	s, _ := strconv.ParseUint(m[2], 10, 64)
	return p, uint(s), m[3]
}

// resolveAssetPath resolves a manifest-relative file path and checks that:
//   - it does not escape the base directory (path traversal prevention)
//   - none of its path components are symlinks
//
// Returns the absolute path, a skip flag (true when the entry should be silently
// dropped), and any hard error.
func resolveAssetPath(absBase, manifestDir, file string) (absPath string, skip bool, err error) {
	// Clean and join before any symlink resolution so we can detect traversal.
	joined := filepath.Join(manifestDir, filepath.Clean(file))

	// Ensure the cleaned path is still inside absBase.
	rel, err := filepath.Rel(absBase, joined)
	if err != nil || strings.HasPrefix(rel, "..") {
		// Path escapes the base directory; skip silently.
		return "", true, nil
	}

	// Walk each component to detect symlinks.
	parts := strings.Split(rel, string(filepath.Separator))
	current := absBase
	for _, part := range parts {
		current = filepath.Join(current, part)
		info, statErr := os.Lstat(current)
		if statErr != nil {
			// File doesn't exist; skip.
			return "", true, nil
		}
		if info.Mode()&os.ModeSymlink != 0 {
			// Symlink in path; skip silently.
			return "", true, nil
		}
	}

	return joined, false, nil
}