// Package workspace contains the pure helpers of the workspace subsystem:
// git repo inspection, shallow copy preparation, guest-side tar import,
// finalization script generation, and small utilities.
//
// The orchestrator methods (ExportVMWorkspace, PrepareVMWorkspace) stay on
// *daemon.Daemon.
package workspace

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"net/url"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"banger/internal/model"
	"banger/internal/system"
)

// ShallowFetchDepth is the default --depth for the transient shallow clone
// used by metadata / overlay prepare modes.
const ShallowFetchDepth = 10

// RepoSpec describes the host-side git repository we're about to import into
// a guest. It captures the pieces both InspectRepo and the prepare flow need.
type RepoSpec struct {
	SourcePath    string
	RepoRoot      string
	RepoName      string
	HeadCommit    string
	CurrentBranch string
	BranchName    string
	BaseCommit    string
	OriginURL     string
	GitUserName   string
	GitUserEmail  string
	OverlayPaths  []string
	Submodules    []string
}

// GuestClient is the narrow subset of guest SSH operations needed by
// ImportRepoToGuest. Satisfied by the daemon-package guestSSHClient.
type GuestClient interface {
	RunScript(ctx context.Context, script string, log io.Writer) error
	StreamTar(ctx context.Context, dir, command string, log io.Writer) error
	StreamTarEntries(ctx context.Context, dir string, entries []string, command string, log io.Writer) error
}

// HostCommandOutputFunc runs a host command and returns its combined output.
// Declared as a package var so tests can substitute a stub runner.
var HostCommandOutputFunc = func(ctx context.Context, name string, args ...string) ([]byte, error) {
	runner := system.NewRunner()
	output, err := runner.Run(ctx, name, args...)
	if err == nil {
		return output, nil
	}
	command := strings.TrimSpace(strings.Join(append([]string{name}, args...), " "))
	detail := strings.TrimSpace(string(output))
	if detail == "" {
		return output, fmt.Errorf("%s: %w", command, err)
	}
	return output, fmt.Errorf("%s: %w: %s", command, err, detail)
}

// InspectRepo resolves rawPath into an absolute repo root and captures
// the HEAD, branch, optional base-from ref, git identity, origin URL,
// submodules, and overlay paths needed for a prepare. Overlay paths
// cover tracked files by default; untracked non-ignored files are
// included only when includeUntracked is true.
func InspectRepo(ctx context.Context, rawPath, branchName, fromRef string, includeUntracked bool) (RepoSpec, error) {
	sourcePath, err := ResolveSourcePath(rawPath)
	if err != nil {
		return RepoSpec{}, err
	}
	repoRoot, err := GitTrimmedOutput(ctx, sourcePath, "rev-parse", "--show-toplevel")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("%s is not inside a git repository", sourcePath)
	}
	isBare, err := GitTrimmedOutput(ctx, repoRoot, "rev-parse", "--is-bare-repository")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("inspect git repository %s: %w", repoRoot, err)
	}
	if isBare == "true" {
		return RepoSpec{}, fmt.Errorf("workspace prepare requires a non-bare git repository: %s", repoRoot)
	}
	submodules, err := ListSubmodules(ctx, repoRoot)
	if err != nil {
		return RepoSpec{}, err
	}
	headCommit, err := GitTrimmedOutput(ctx, repoRoot, "rev-parse", "HEAD^{commit}")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("git repository %s must have at least one commit", repoRoot)
	}
	currentBranch, err := GitTrimmedOutput(ctx, repoRoot, "branch", "--show-current")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("resolve current branch for %s: %w", repoRoot, err)
	}
	baseCommit := headCommit
	branchName = strings.TrimSpace(branchName)
	if branchName != "" {
		baseCommit, err = GitTrimmedOutput(ctx, repoRoot, "rev-parse", fromRef+"^{commit}")
		if err != nil {
			return RepoSpec{}, fmt.Errorf("resolve workspace from %q: %w", fromRef, err)
		}
	}
	gitUserName, err := GitResolvedConfigValue(ctx, repoRoot, "user.name")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("resolve git user.name for %s: %w", repoRoot, err)
	}
	gitUserEmail, err := GitResolvedConfigValue(ctx, repoRoot, "user.email")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("resolve git user.email for %s: %w", repoRoot, err)
	}
	originURL, err := GitResolvedConfigValue(ctx, repoRoot, "remote.origin.url")
	if err != nil {
		return RepoSpec{}, fmt.Errorf("resolve origin url for %s: %w", repoRoot, err)
	}
	overlayPaths, err := ListOverlayPaths(ctx, repoRoot, includeUntracked)
	if err != nil {
		return RepoSpec{}, err
	}
	return RepoSpec{
		SourcePath:    sourcePath,
		RepoRoot:      repoRoot,
		RepoName:      filepath.Base(repoRoot),
		HeadCommit:    headCommit,
		CurrentBranch: currentBranch,
		BranchName:    branchName,
		BaseCommit:    baseCommit,
		OriginURL:     originURL,
		GitUserName:   gitUserName,
		GitUserEmail:  gitUserEmail,
		OverlayPaths:  overlayPaths,
		Submodules:    submodules,
	}, nil
}

// ImportRepoToGuest materialises spec inside the guest at guestPath. Mode
// selects between full copy, metadata-only, or shallow metadata + overlay.
func ImportRepoToGuest(ctx context.Context, client GuestClient, spec RepoSpec, guestPath string, mode model.WorkspacePrepareMode) error {
	switch mode {
	case model.WorkspacePrepareModeFullCopy:
		var copyLog bytes.Buffer
		command := fmt.Sprintf("rm -rf %s && mkdir -p %s && tar -o -C %s --strip-components=1 -xf -", ShellQuote(guestPath), ShellQuote(guestPath), ShellQuote(guestPath))
		if err := client.StreamTar(ctx, spec.RepoRoot, command, &copyLog); err != nil {
			return FormatStepError("copy full workspace", err, copyLog.String())
		}
		var finalizeLog bytes.Buffer
		if err := client.RunScript(ctx, FinalizeScript(spec, guestPath, mode), &finalizeLog); err != nil {
			return FormatStepError("finalize full workspace", err, finalizeLog.String())
		}
		return nil
	case model.WorkspacePrepareModeMetadataOnly, model.WorkspacePrepareModeShallowOverlay:
		repoCopyDir, cleanup, err := PrepareRepoCopy(ctx, spec)
		if err != nil {
			return err
		}
		defer cleanup()
		var copyLog bytes.Buffer
		command := fmt.Sprintf("rm -rf %s && mkdir -p %s && tar -o -C %s --strip-components=1 -xf -", ShellQuote(guestPath), ShellQuote(guestPath), ShellQuote(guestPath))
		if err := client.StreamTar(ctx, repoCopyDir, command, &copyLog); err != nil {
			return FormatStepError("copy guest git metadata", err, copyLog.String())
		}
		var scriptLog bytes.Buffer
		if err := client.RunScript(ctx, FinalizeScript(spec, guestPath, mode), &scriptLog); err != nil {
			return FormatStepError("prepare guest checkout", err, scriptLog.String())
		}
		if mode == model.WorkspacePrepareModeMetadataOnly {
			return nil
		}
		var overlayLog bytes.Buffer
		command = fmt.Sprintf("tar -o -C %s --strip-components=1 -xf -", ShellQuote(guestPath))
		if err := client.StreamTarEntries(ctx, spec.RepoRoot, spec.OverlayPaths, command, &overlayLog); err != nil {
			return FormatStepError("overlay workspace working tree", err, overlayLog.String())
		}
		return nil
	default:
		return fmt.Errorf("unsupported workspace mode %q", mode)
	}
}

// FinalizeScript returns the bash script run inside the guest after the repo
// copy lands: safe.directory, optional cleanup, branch/detached checkout,
// and git identity config.
func FinalizeScript(spec RepoSpec, guestPath string, mode model.WorkspacePrepareMode) string {
	var script strings.Builder
	script.WriteString("set -euo pipefail\n")
	fmt.Fprintf(&script, "DIR=%s\n", ShellQuote(guestPath))
	script.WriteString("git config --global --add safe.directory \"$DIR\"\n")
	if mode != model.WorkspacePrepareModeFullCopy {
		script.WriteString("find \"$DIR\" -mindepth 1 -maxdepth 1 ! -name .git -exec rm -rf {} +\n")
	}
	switch {
	case strings.TrimSpace(spec.BranchName) != "":
		fmt.Fprintf(&script, "git -C \"$DIR\" checkout -B %s %s\n", ShellQuote(spec.BranchName), ShellQuote(spec.BaseCommit))
	case strings.TrimSpace(spec.CurrentBranch) != "":
		fmt.Fprintf(&script, "git -C \"$DIR\" checkout -B %s %s\n", ShellQuote(spec.CurrentBranch), ShellQuote(spec.HeadCommit))
	default:
		fmt.Fprintf(&script, "git -C \"$DIR\" checkout --detach %s\n", ShellQuote(spec.HeadCommit))
	}
	if strings.TrimSpace(spec.GitUserName) != "" && strings.TrimSpace(spec.GitUserEmail) != "" {
		fmt.Fprintf(&script, "git -C \"$DIR\" config user.name %s\n", ShellQuote(spec.GitUserName))
		fmt.Fprintf(&script, "git -C \"$DIR\" config user.email %s\n", ShellQuote(spec.GitUserEmail))
	}
	return script.String()
}

// PrepareRepoCopy materialises a shallow clone of spec into a temp dir. The
// returned cleanup removes the temp root.
func PrepareRepoCopy(ctx context.Context, spec RepoSpec) (string, func(), error) {
	tempRoot, err := os.MkdirTemp("", "banger-workspace-*")
	if err != nil {
		return "", nil, err
	}
	cleanup := func() { _ = os.RemoveAll(tempRoot) }
	repoCopyDir := filepath.Join(tempRoot, spec.RepoName)
	cloneArgs := []string{"clone", "--no-checkout", "--depth", fmt.Sprintf("%d", ShallowFetchDepth)}
	if strings.TrimSpace(spec.CurrentBranch) != "" {
		cloneArgs = append(cloneArgs, "--single-branch", "--branch", spec.CurrentBranch)
	}
	cloneArgs = append(cloneArgs, GitFileURL(spec.RepoRoot), repoCopyDir)
	if err := RunHostCommand(ctx, "git", cloneArgs...); err != nil {
		cleanup()
		return "", nil, fmt.Errorf("clone shallow workspace repo copy: %w", err)
	}
	checkoutCommit := spec.HeadCommit
	if strings.TrimSpace(spec.BranchName) != "" {
		checkoutCommit = spec.BaseCommit
	}
	if err := RunHostCommand(ctx, "git", "-C", repoCopyDir, "cat-file", "-e", checkoutCommit+"^{commit}"); err != nil {
		if err := RunHostCommand(ctx, "git", "-C", repoCopyDir, "fetch", "--depth", fmt.Sprintf("%d", ShallowFetchDepth), GitFileURL(spec.RepoRoot), checkoutCommit); err != nil {
			cleanup()
			return "", nil, fmt.Errorf("fetch shallow workspace repo commit %s: %w", checkoutCommit, err)
		}
	}
	if strings.TrimSpace(spec.OriginURL) != "" {
		if err := RunHostCommand(ctx, "git", "-C", repoCopyDir, "remote", "set-url", "origin", spec.OriginURL); err != nil {
			cleanup()
			return "", nil, fmt.Errorf("set workspace origin remote: %w", err)
		}
	} else {
		if err := RunHostCommand(ctx, "git", "-C", repoCopyDir, "remote", "remove", "origin"); err != nil {
			cleanup()
			return "", nil, fmt.Errorf("remove workspace placeholder origin remote: %w", err)
		}
	}
	return repoCopyDir, cleanup, nil
}

// ResolveSourcePath expands rawPath to an absolute path and verifies it is
// an existing directory.
func ResolveSourcePath(rawPath string) (string, error) {
	if strings.TrimSpace(rawPath) == "" {
		return "", errors.New("workspace source path is required")
	}
	absPath, err := filepath.Abs(rawPath)
	if err != nil {
		return "", err
	}
	info, err := os.Stat(absPath)
	if err != nil {
		return "", err
	}
	if !info.IsDir() {
		return "", fmt.Errorf("%s is not a directory", absPath)
	}
	return absPath, nil
}

// ListSubmodules returns the gitlink paths in repoRoot (mode 160000 entries).
func ListSubmodules(ctx context.Context, repoRoot string) ([]string, error) {
	output, err := GitOutput(ctx, repoRoot, "ls-files", "--stage", "-z")
	if err != nil {
		return nil, fmt.Errorf("inspect workspace git index for %s: %w", repoRoot, err)
	}
	var submodules []string
	for _, record := range ParseNullSeparatedOutput(output) {
		if !strings.HasPrefix(record, "160000 ") {
			continue
		}
		_, path, ok := strings.Cut(record, "\t")
		if !ok {
			continue
		}
		submodules = append(submodules, strings.TrimSpace(path))
	}
	sort.Strings(submodules)
	return submodules, nil
}

// ListOverlayPaths returns tracked files in repoRoot, plus (when
// includeUntracked is true) untracked non-ignored files. Missing
// tracked entries (deleted working-tree files) are skipped in both
// modes.
//
// The default is tracked-only because "untracked + not gitignored"
// silently catches local credentials, .env files, scratch notes, and
// other secrets that live in the working tree but aren't meant to
// leave the developer's machine. Callers that genuinely want the
// fuller set (scratch repos, vendored binaries the user is iterating
// on) opt in explicitly.
func ListOverlayPaths(ctx context.Context, repoRoot string, includeUntracked bool) ([]string, error) {
	trackedOutput, err := GitOutput(ctx, repoRoot, "ls-files", "-z")
	if err != nil {
		return nil, fmt.Errorf("list tracked files for %s: %w", repoRoot, err)
	}
	paths := make([]string, 0)
	seen := make(map[string]struct{})
	for _, relPath := range ParseNullSeparatedOutput(trackedOutput) {
		if relPath == "" {
			continue
		}
		if _, err := os.Lstat(filepath.Join(repoRoot, relPath)); err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return nil, err
		}
		seen[relPath] = struct{}{}
		paths = append(paths, relPath)
	}
	if includeUntracked {
		untrackedOutput, err := GitOutput(ctx, repoRoot, "ls-files", "--others", "--exclude-standard", "-z")
		if err != nil {
			return nil, fmt.Errorf("list untracked files for %s: %w", repoRoot, err)
		}
		for _, relPath := range ParseNullSeparatedOutput(untrackedOutput) {
			if relPath == "" {
				continue
			}
			if _, ok := seen[relPath]; ok {
				continue
			}
			seen[relPath] = struct{}{}
			paths = append(paths, relPath)
		}
	}
	sort.Strings(paths)
	return paths, nil
}

// CountUntrackedPaths returns the number of untracked non-ignored
// files in repoRoot. Used by the CLI to warn the user when they are
// about to ship a workspace that has local-but-unignored scratch
// files which, under the default, will be skipped.
func CountUntrackedPaths(ctx context.Context, repoRoot string) (int, error) {
	untrackedOutput, err := GitOutput(ctx, repoRoot, "ls-files", "--others", "--exclude-standard", "-z")
	if err != nil {
		return 0, fmt.Errorf("list untracked files for %s: %w", repoRoot, err)
	}
	count := 0
	for _, relPath := range ParseNullSeparatedOutput(untrackedOutput) {
		if relPath != "" {
			count++
		}
	}
	return count, nil
}

// ParsePrepareMode validates and canonicalises a user-supplied mode value.
func ParsePrepareMode(raw string) (model.WorkspacePrepareMode, error) {
	switch strings.TrimSpace(raw) {
	case "", string(model.WorkspacePrepareModeShallowOverlay):
		return model.WorkspacePrepareModeShallowOverlay, nil
	case string(model.WorkspacePrepareModeFullCopy):
		return model.WorkspacePrepareModeFullCopy, nil
	case string(model.WorkspacePrepareModeMetadataOnly):
		return model.WorkspacePrepareModeMetadataOnly, nil
	default:
		return "", fmt.Errorf("unsupported workspace mode %q", raw)
	}
}

// GitOutput runs `git [-C dir] args...` and returns its raw stdout.
func GitOutput(ctx context.Context, dir string, args ...string) ([]byte, error) {
	fullArgs := make([]string, 0, len(args)+2)
	if strings.TrimSpace(dir) != "" {
		fullArgs = append(fullArgs, "-C", dir)
	}
	fullArgs = append(fullArgs, args...)
	return HostCommandOutputFunc(ctx, "git", fullArgs...)
}

// GitTrimmedOutput returns GitOutput with surrounding whitespace trimmed.
func GitTrimmedOutput(ctx context.Context, dir string, args ...string) (string, error) {
	output, err := GitOutput(ctx, dir, args...)
	if err != nil {
		return "", err
	}
	return strings.TrimSpace(string(output)), nil
}

// GitResolvedConfigValue reads git config key with --default "" --get.
func GitResolvedConfigValue(ctx context.Context, dir, key string) (string, error) {
	return GitTrimmedOutput(ctx, dir, "config", "--default", "", "--get", key)
}

// ParseNullSeparatedOutput splits on NULs and trims, returning non-empty
// values in order.
func ParseNullSeparatedOutput(output []byte) []string {
	chunks := bytes.Split(output, []byte{0})
	values := make([]string, 0, len(chunks))
	for _, chunk := range chunks {
		value := strings.TrimSpace(string(chunk))
		if value == "" {
			continue
		}
		values = append(values, value)
	}
	return values
}

// RunHostCommand runs a host command via HostCommandOutputFunc, discarding
// its stdout.
func RunHostCommand(ctx context.Context, name string, args ...string) error {
	_, err := HostCommandOutputFunc(ctx, name, args...)
	return err
}

// GitFileURL returns a file:// URL for path, the form git requires when
// cloning from a local directory.
func GitFileURL(path string) string {
	return (&url.URL{Scheme: "file", Path: filepath.ToSlash(path)}).String()
}