// Copyright 2013-2023 The Cobra Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package doc

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/cpuguy83/go-md2man/v2/md2man"
	"github.com/spf13/cobra"
	"github.com/spf13/pflag"
)

// GenManTree generates a man page for the provided command and all its descendants in the specified directory.
//
// It takes a cobra.Command pointer representing the root command, an optional GenManHeader pointer to customize the header information, and a string specifying the output directory.
//
// The function assumes that command names do not contain hyphens (`-`). If they do, unexpected behavior may occur.
//
// Note: If a command named `cmd` has subcommands `sub` and `sub-third`, and `sub` itself has a subcommand called `third`, it is undefined which help output will be written to the file `cmd-sub-third.1`.
//
// Returns an error if the generation process encounters any issues, such as invalid input or permission errors when writing files to the specified directory.
func GenManTree(cmd *cobra.Command, header *GenManHeader, dir string) error {
	return GenManTreeFromOpts(cmd, GenManTreeOptions{
		Header:           header,
		Path:             dir,
		CommandSeparator: "-",
	})
}

// GenManTreeFromOpts generates a man page for the command and all descendants.
// The pages are written to the opts.Path directory. It recursively processes each command in the tree,
// skipping non-available or additional help topic commands. Each man page is saved with a filename based on the command path and section.

// Parameters:
//   - cmd: A pointer to the root cobra.Command for which man pages need to be generated.
//   - opts: A GenManTreeOptions struct containing options for generating the man pages, such as header details, output directory, and separators.

// Returns:
//   - error: If any error occurs during the generation of the man pages, it is returned.
func GenManTreeFromOpts(cmd *cobra.Command, opts GenManTreeOptions) error {
	header := opts.Header
	if header == nil {
		header = &GenManHeader{}
	}
	for _, c := range cmd.Commands() {
		if !c.IsAvailableCommand() || c.IsAdditionalHelpTopicCommand() {
			continue
		}
		if err := GenManTreeFromOpts(c, opts); err != nil {
			return err
		}
	}
	section := "1"
	if header.Section != "" {
		section = header.Section
	}

	separator := "_"
	if opts.CommandSeparator != "" {
		separator = opts.CommandSeparator
	}
	basename := strings.ReplaceAll(cmd.CommandPath(), " ", separator)
	filename := filepath.Join(opts.Path, basename+"."+section)
	f, err := os.Create(filename)
	if err != nil {
		return err
	}
	defer f.Close()

	headerCopy := *header
	return GenMan(cmd, &headerCopy, f)
}

// GenManTreeOptions is the options for generating the man pages.
// Used only in GenManTreeFromOpts.
type GenManTreeOptions struct {
	Header           *GenManHeader
	Path             string
	CommandSeparator string
}

// GenManHeader is a lot like the .TH header at the start of man pages. These
// include the title, section, date, source, and manual. We will use the
// current time if Date is unset and will use "Auto generated by spf13/cobra"
// if the Source is unset.
type GenManHeader struct {
	Title   string
	Section string
	Date    *time.Time
	date    string
	Source  string
	Manual  string
}

// GenMan generates a man page for the given command and writes it to the specified writer.
//
// Parameters:
//   cmd - The cobra.Command for which to generate the man page.
//   header - A pointer to a GenManHeader that contains additional information for the man page. If nil, a default header will be used.
//   w - The io.Writer to which the generated man page will be written.
//
// Returns:
//   error - If an error occurs during the generation of the man page, it will be returned here.
func GenMan(cmd *cobra.Command, header *GenManHeader, w io.Writer) error {
	if header == nil {
		header = &GenManHeader{}
	}
	if err := fillHeader(header, cmd.CommandPath(), cmd.DisableAutoGenTag); err != nil {
		return err
	}

	b := genMan(cmd, header)
	_, err := w.Write(md2man.Render(b))
	return err
}

// fillHeader populates the GenManHeader with default values if they are not already set.
//
// It sets the title to the uppercase version of `name`, replacing spaces with hyphens.
// If the section is empty, it defaults to "1".
// If the date is nil, it sets the date to the current time or a time specified by the SOURCE_DATE_EPOCH environment variable.
// The formatted date is stored in header.date.
// If source is empty and auto-generation is not disabled, it sets the source to "Auto generated by spf13/cobra".
//
// It returns an error if there is an issue parsing the SOURCE_DATE_EPOCH environment variable.
func fillHeader(header *GenManHeader, name string, disableAutoGen bool) error {
	if header.Title == "" {
		header.Title = strings.ToUpper(strings.ReplaceAll(name, " ", "\\-"))
	}
	if header.Section == "" {
		header.Section = "1"
	}
	if header.Date == nil {
		now := time.Now()
		if epoch := os.Getenv("SOURCE_DATE_EPOCH"); epoch != "" {
			unixEpoch, err := strconv.ParseInt(epoch, 10, 64)
			if err != nil {
				return fmt.Errorf("invalid SOURCE_DATE_EPOCH: %v", err)
			}
			now = time.Unix(unixEpoch, 0)
		}
		header.Date = &now
	}
	header.date = header.Date.Format("Jan 2006")
	if header.Source == "" && !disableAutoGen {
		header.Source = "Auto generated by spf13/cobra"
	}
	return nil
}

// manPreamble writes the preamble for a manual page to the given buffer.
//
// Parameters:
//   buf - the io.StringWriter to write the preamble to.
//   header - a pointer to a GenManHeader containing metadata for the manual page.
//   cmd - a pointer to a cobra.Command representing the command being documented.
//   dashedName - the dash-separated name of the command.
//
// This function constructs the preamble section of a man page, including
// the title, section, date, source, and manual. It also includes the command's
// short description and synopsis.
func manPreamble(buf io.StringWriter, header *GenManHeader, cmd *cobra.Command, dashedName string) {
	description := cmd.Long
	if len(description) == 0 {
		description = cmd.Short
	}

	cobra.WriteStringAndCheck(buf, fmt.Sprintf(`%% "%s" "%s" "%s" "%s" "%s"
# NAME
`, header.Title, header.Section, header.date, header.Source, header.Manual))
	cobra.WriteStringAndCheck(buf, fmt.Sprintf("%s \\- %s\n\n", dashedName, cmd.Short))
	cobra.WriteStringAndCheck(buf, "# SYNOPSIS\n")
	cobra.WriteStringAndCheck(buf, fmt.Sprintf("**%s**\n\n", cmd.UseLine()))
	cobra.WriteStringAndCheck(buf, "# DESCRIPTION\n")
	cobra.WriteStringAndCheck(buf, description+"\n\n")
}

// manPrintFlags prints the flags in a format suitable for a man page.
//
// It takes an io.StringWriter to write to and a pflag.FlagSet containing the flags to print.
// For each flag, it checks if it is deprecated or hidden. If not, it formats the flag name,
// shorthand, and usage information according to its type (string or other) and whether it has
// a default value. The formatted string is then written to the provided writer.
func manPrintFlags(buf io.StringWriter, flags *pflag.FlagSet) {
	flags.VisitAll(func(flag *pflag.Flag) {
		if len(flag.Deprecated) > 0 || flag.Hidden {
			return
		}
		format := ""
		if len(flag.Shorthand) > 0 && len(flag.ShorthandDeprecated) == 0 {
			format = fmt.Sprintf("**-%s**, **--%s**", flag.Shorthand, flag.Name)
		} else {
			format = fmt.Sprintf("**--%s**", flag.Name)
		}
		if len(flag.NoOptDefVal) > 0 {
			format += "["
		}
		if flag.Value.Type() == "string" {
			// put quotes on the value
			format += "=%q"
		} else {
			format += "=%s"
		}
		if len(flag.NoOptDefVal) > 0 {
			format += "]"
		}
		format += "\n\t%s\n\n"
		cobra.WriteStringAndCheck(buf, fmt.Sprintf(format, flag.DefValue, flag.Usage))
	})
}

// manPrintOptions writes the options for a command to a StringWriter.
// It includes both non-inherited and inherited flags, if available.
func manPrintOptions(buf io.StringWriter, command *cobra.Command) {
	flags := command.NonInheritedFlags()
	if flags.HasAvailableFlags() {
		cobra.WriteStringAndCheck(buf, "# OPTIONS\n")
		manPrintFlags(buf, flags)
		cobra.WriteStringAndCheck(buf, "\n")
	}
	flags = command.InheritedFlags()
	if flags.HasAvailableFlags() {
		cobra.WriteStringAndCheck(buf, "# OPTIONS INHERITED FROM PARENT COMMANDS\n")
		manPrintFlags(buf, flags)
		cobra.WriteStringAndCheck(buf, "\n")
	}
}

// genMan generates a man page for the given Cobra command and header.
// It initializes default help commands and flags, processes the command path,
// and constructs the man page content including preamble, options, examples,
// see also sections, and history.
//
// Parameters:
//   - cmd: The Cobra command for which to generate the man page.
//   - header: Header information for the man page, such as section and date.
//
// Returns:
//   - A byte slice containing the generated man page content.
func genMan(cmd *cobra.Command, header *GenManHeader) []byte {
	cmd.InitDefaultHelpCmd()
	cmd.InitDefaultHelpFlag()

	// something like `rootcmd-subcmd1-subcmd2`
	dashCommandName := strings.ReplaceAll(cmd.CommandPath(), " ", "-")

	buf := new(bytes.Buffer)

	manPreamble(buf, header, cmd, dashCommandName)
	manPrintOptions(buf, cmd)
	if len(cmd.Example) > 0 {
		buf.WriteString("# EXAMPLE\n")
		buf.WriteString(fmt.Sprintf("```\n%s\n```\n", cmd.Example))
	}
	if hasSeeAlso(cmd) {
		buf.WriteString("# SEE ALSO\n")
		seealsos := make([]string, 0)
		if cmd.HasParent() {
			parentPath := cmd.Parent().CommandPath()
			dashParentPath := strings.ReplaceAll(parentPath, " ", "-")
			seealso := fmt.Sprintf("**%s(%s)**", dashParentPath, header.Section)
			seealsos = append(seealsos, seealso)
			cmd.VisitParents(func(c *cobra.Command) {
				if c.DisableAutoGenTag {
					cmd.DisableAutoGenTag = c.DisableAutoGenTag
				}
			})
		}
		children := cmd.Commands()
		sort.Sort(byName(children))
		for _, c := range children {
			if !c.IsAvailableCommand() || c.IsAdditionalHelpTopicCommand() {
				continue
			}
			seealso := fmt.Sprintf("**%s-%s(%s)**", dashCommandName, c.Name(), header.Section)
			seealsos = append(seealsos, seealso)
		}
		buf.WriteString(strings.Join(seealsos, ", ") + "\n")
	}
	if !cmd.DisableAutoGenTag {
		buf.WriteString(fmt.Sprintf("# HISTORY\n%s Auto generated by spf13/cobra\n", header.Date.Format("2-Jan-2006")))
	}
	return buf.Bytes()
}