package git

import (
	"context"
	"fmt"
	"path"
	"path/filepath"
	"strings"
)

// PathResolver traverses committed paths, sharing reference rules between
// release identity and validation. Lookups include both files and directories.
type PathResolver struct {
	RepositoryDir string
	Lookup        func(context.Context, string) (TreeEntry, bool, error)
	ReadLink      func(context.Context, TreeEntry) (string, error)
}

// DestinationKind classifies a committed local destination.
type DestinationKind string

const (
	DestinationEntry           DestinationKind = "entry"
	DestinationDirectory       DestinationKind = "directory"
	DestinationMissing         DestinationKind = "missing"
	DestinationOutsideCheckout DestinationKind = "outside-checkout"
	DestinationSubmodule       DestinationKind = "submodule"
	DestinationSymlinkCycle    DestinationKind = "symlink-cycle"
)

// Destination records the resolved identity and its classification.
type Destination struct {
	Kind DestinationKind
	Path string
}

// ResolveDestination resolves local destinations using the captured Git tree.
// Relative destinations start at the source directory; absolute destinations
// within the repository directory map back to committed paths.
func (resolver PathResolver) ResolveDestination(ctx context.Context, sourcePath, destination string) (Destination, error) {
	if err := ctx.Err(); err != nil {
		return Destination{}, err
	}
	directory := path.Dir(sourcePath)
	if path.IsAbs(destination) {
		relative, inside, err := resolver.relativeAbsoluteDestination(destination)
		if err != nil {
			return Destination{}, err
		}
		if !inside {
			return Destination{Kind: DestinationOutsideCheckout, Path: destination}, nil
		}
		directory, destination = ".", relative
	}
	return resolver.resolveDestination(ctx, directory, strings.Split(destination, "/"), make(map[string]bool))
}

func (resolver PathResolver) resolveDestination(ctx context.Context, directory string, components []string, active map[string]bool) (Destination, error) {
	for index, component := range components {
		if err := ctx.Err(); err != nil {
			return Destination{}, err
		}
		remaining := components[index+1:]
		switch component {
		case "", ".":
			continue
		case "..":
			if directory == "." {
				return Destination{Kind: DestinationOutsideCheckout, Path: unresolvedPath("..", remaining)}, nil
			}
			directory = path.Dir(directory)
			continue
		}
		partial := path.Join(directory, component)
		entry, exists, err := resolver.Lookup(ctx, partial)
		if err != nil {
			return Destination{}, err
		}
		if !exists {
			return Destination{Kind: DestinationMissing, Path: unresolvedPath(partial, remaining)}, nil
		}
		if entry.Type == "tree" {
			directory = partial
			continue
		}
		if entry.Mode == "160000" {
			return Destination{Kind: DestinationSubmodule, Path: unresolvedPath(partial, remaining)}, nil
		}
		if entry.Mode == "120000" {
			if active[partial] {
				return Destination{Kind: DestinationSymlinkCycle, Path: partial}, nil
			}
			linkText, err := resolver.ReadLink(ctx, entry)
			if err != nil {
				return Destination{}, fmt.Errorf("read committed symlink %q: %w", partial, err)
			}
			target := linkText
			targetDirectory := directory
			if path.IsAbs(target) {
				relative, inside, err := resolver.relativeAbsoluteDestination(target)
				if err != nil {
					return Destination{}, err
				}
				if !inside {
					return Destination{Kind: DestinationOutsideCheckout, Path: unresolvedPath(target, remaining)}, nil
				}
				targetDirectory, target = ".", relative
			}
			active[partial] = true
			destination, err := resolver.resolveDestination(ctx, targetDirectory, strings.Split(target, "/"), active)
			delete(active, partial)
			if err != nil || len(remaining) == 0 {
				return destination, err
			}
			switch destination.Kind {
			case DestinationDirectory:
				return resolver.resolveDestination(ctx, destination.Path, remaining, active)
			case DestinationEntry:
				destination.Kind = DestinationMissing
			case DestinationSymlinkCycle:
				return destination, nil
			}
			destination.Path = unresolvedPath(destination.Path, remaining)
			return destination, nil
		}
		if len(remaining) != 0 {
			return Destination{Kind: DestinationMissing, Path: unresolvedPath(partial, remaining)}, nil
		}
		return Destination{Kind: DestinationEntry, Path: partial}, nil
	}
	return Destination{Kind: DestinationDirectory, Path: directory}, nil
}

func (resolver PathResolver) relativeAbsoluteDestination(destination string) (string, bool, error) {
	root, err := filepath.Abs(resolver.RepositoryDir)
	if err != nil {
		return "", false, fmt.Errorf("resolve candidate repository directory: %w", err)
	}
	root = filepath.ToSlash(root)
	if destination == root {
		return ".", true, nil
	}
	// Preserve the suffix for component traversal, including symlinks before '..'.
	relative, inside := strings.CutPrefix(destination, strings.TrimSuffix(root, "/")+"/")
	return relative, inside, nil
}

// unresolvedPath preserves components that could not be traversed. Cleaning
// them would hide missing entries, non-directories, or checkout boundaries.
func unresolvedPath(base string, remaining []string) string {
	if len(remaining) == 0 {
		return base
	}
	return base + "/" + strings.Join(remaining, "/")
}