package lfs

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"

	"github.com/git-lfs/git-lfs/config"
	"github.com/git-lfs/git-lfs/errors"
	"github.com/git-lfs/git-lfs/git"
	"github.com/git-lfs/git-lfs/tools"
	"github.com/rubyist/tracerx"
)

var (
	// The basic hook which just calls 'git lfs TYPE'
	hookBaseContent = "#!/bin/sh\ncommand -v git-lfs >/dev/null 2>&1 || { echo >&2 \"\\nThis repository is configured for Git LFS but 'git-lfs' was not found on your path. If you no longer wish to use Git LFS, remove this hook by deleting .git/hooks/{{Command}}.\\n\"; exit 2; }\ngit lfs {{Command}} \"$@\""
)

// A Hook represents a githook as described in http://git-scm.com/docs/githooks.
// Hooks have a type, which is the type of hook that they are, and a body, which
// represents the thing they will execute when invoked by Git.
type Hook struct {
	Type         string
	Contents     string
	Upgradeables []string
}

// NewStandardHook creates a new hook using the template script calling 'git lfs theType'
func NewStandardHook(theType string, upgradeables []string) *Hook {
	return &Hook{
		Type:         theType,
		Contents:     strings.Replace(hookBaseContent, "{{Command}}", theType, -1),
		Upgradeables: upgradeables,
	}
}

func (h *Hook) Exists() bool {
	_, err := os.Stat(h.Path())

	return !os.IsNotExist(err)
}

// Path returns the desired (or actual, if installed) location where this hook
// should be installed. It returns an absolute path in all cases.
func (h *Hook) Path() string {
	return filepath.Join(h.Dir(), h.Type)
}

// Dir returns the directory used by LFS for storing Git hooks. By default, it
// will return the hooks/ sub-directory of the local repository's .git
// directory. If `core.hooksPath` is configured and supported (Git verison is
// greater than "2.9.0"), it will return that instead.
func (h *Hook) Dir() string {
	customHooksSupported := git.Config.IsGitVersionAtLeast("2.9.0")
	if hp, ok := config.Config.Git.Get("core.hooksPath"); ok && customHooksSupported {
		return hp
	}

	return filepath.Join(config.LocalGitDir, "hooks")
}

// Install installs this Git hook on disk, or upgrades it if it does exist, and
// is upgradeable. It will create a hooks directory relative to the local Git
// directory. It returns and halts at any errors, and returns nil if the
// operation was a success.
func (h *Hook) Install(force bool) error {
	msg := fmt.Sprintf("Install hook: %s, force=%t, path=%s", h.Type, force, h.Path())

	if err := os.MkdirAll(h.Dir(), 0755); err != nil {
		return err
	}

	if h.Exists() && !force {
		tracerx.Printf(msg + ", upgrading...")
		return h.Upgrade()
	}

	tracerx.Printf(msg)
	return h.write()
}

// write writes the contents of this Hook to disk, appending a newline at the
// end, and sets the mode to octal 0755. It writes to disk unconditionally, and
// returns at any error.
func (h *Hook) write() error {
	return ioutil.WriteFile(h.Path(), []byte(h.Contents+"\n"), 0755)
}

// Upgrade upgrades the (assumed to be) existing git hook to the current
// contents. A hook is considered "upgrade-able" if its contents are matched in
// the member variable `Upgradeables`. It halts and returns any errors as they
// arise.
func (h *Hook) Upgrade() error {
	match, err := h.matchesCurrent()
	if err != nil {
		return err
	}

	if !match {
		return nil
	}

	return h.write()
}

// Uninstall removes the hook on disk so long as it matches the current version,
// or any of the past versions of this hook.
func (h *Hook) Uninstall() error {
	if !InRepo() {
		return errors.New("Not in a git repository")
	}

	msg := fmt.Sprintf("Uninstall hook: %s, path=%s", h.Type, h.Path())

	match, err := h.matchesCurrent()
	if err != nil {
		return err
	}

	if !match {
		tracerx.Printf(msg + ", doesn't match...")
		return nil
	}

	tracerx.Printf(msg)
	return os.RemoveAll(h.Path())
}

// matchesCurrent returns whether or not an existing git hook is able to be
// written to or upgraded. A git hook matches those conditions if and only if
// its contents match the current contents, or any past "upgrade-able" contents
// of this hook.
func (h *Hook) matchesCurrent() (bool, error) {
	file, err := os.Open(h.Path())
	if err != nil {
		return false, err
	}

	by, err := ioutil.ReadAll(io.LimitReader(file, 1024))
	file.Close()
	if err != nil {
		return false, err
	}

	contents := strings.TrimSpace(tools.Undent(string(by)))
	if contents == h.Contents || len(contents) == 0 {
		return true, nil
	}

	for _, u := range h.Upgradeables {
		if u == contents {
			return true, nil
		}
	}

	return false, fmt.Errorf("Hook already exists: %s\n\n%s\n", string(h.Type), tools.Indent(contents))
}