//! Autogenerate Markdown documentation for clap command-line tools
//!
//! See [**Examples**][Examples] for examples of the content `clap-markdown`
//! generates.
//!
//! [Examples]: https://github.com/ConnorGray/clap-markdown#Examples
//!

// Ensure that doc tests in the README.md file get run.
#[doc(hidden)]
mod test_readme {
    #![doc = include_str!("../README.md")]
}


use std::fmt::{self, Write};

use clap::builder::PossibleValue;

/// Format the help information for `command` as Markdown.
pub fn help_markdown<C: clap::CommandFactory>() -> String {
    let command = C::command();

    help_markdown_command(&command)
}

/// Format the help information for `command` as Markdown.
pub fn help_markdown_command(command: &clap::Command) -> String {
    let mut buffer = String::with_capacity(100);

    write_help_markdown(&mut buffer, command);

    buffer
}

//======================================
// Markdown
//======================================

/// Format the help information for `command` as Markdown and print it.
///
/// Output is printed to the standard output, using [`println!`].
pub fn print_help_markdown<C: clap::CommandFactory>() {
    let command = C::command();

    let mut buffer = String::with_capacity(100);

    write_help_markdown(&mut buffer, &command);

    println!("{}", buffer);
}

fn write_help_markdown(buffer: &mut String, command: &clap::Command) {
    //----------------------------------
    // Write the document title
    //----------------------------------

    let title_name = match command.get_display_name() {
        Some(display_name) => display_name.to_owned(),
        None => format!("`{}`", command.get_name()),
    };

    writeln!(buffer, "# Command-Line Help for {title_name}\n").unwrap();

    writeln!(
        buffer,
        "This document contains the help content for the `{}` command-line program.\n",
        command.get_name()
    ).unwrap();

    //----------------------------------
    // Write the table of contents
    //----------------------------------

    // writeln!(buffer, r#"<div style="background: light-gray"><ul>"#).unwrap();
    // build_table_of_contents_html(buffer, Vec::new(), command, 0).unwrap();
    // writeln!(buffer, "</ul></div>").unwrap();

    writeln!(buffer, "**Command Overview:**\n").unwrap();

    build_table_of_contents_markdown(buffer, Vec::new(), command, 0).unwrap();

    write!(buffer, "\n").unwrap();

    //----------------------------------------
    // Write the commands/subcommands sections
    //----------------------------------------

    build_command_markdown(buffer, Vec::new(), command, 0).unwrap();

    //-----------------
    // Write the footer
    //-----------------

    write!(buffer, r#"<hr/>

<small><i>
    This document was generated automatically by
    <a href="https://crates.io/crates/clap-markdown"><code>clap-markdown</code></a>.
</i></small>
"#).unwrap();
}

fn build_table_of_contents_markdown(
    buffer: &mut String,
    // Parent commands of `command`.
    parent_command_path: Vec<String>,
    command: &clap::Command,
    depth: usize,
) -> std::fmt::Result {
    // Don't document commands marked with `clap(hide = true)` (which includes
    // `print-all-help`).
    if command.is_hide_set() {
        return Ok(());
    }

    // Append the name of `command` to `command_path`.
    let command_path = {
        let mut command_path = parent_command_path;
        command_path.push(command.get_name().to_owned());
        command_path
    };

    writeln!(
        buffer,
        "* [`{}`↴](#{})",
        command_path.join(" "),
        command_path.join("-"),
    )?;

    //----------------------------------
    // Recurse to write subcommands
    //----------------------------------

    for subcommand in command.get_subcommands() {
        build_table_of_contents_markdown(
            buffer,
            command_path.clone(),
            subcommand,
            depth + 1,
        )?;
    }

    Ok(())
}

/*
fn build_table_of_contents_html(
    buffer: &mut String,
    // Parent commands of `command`.
    parent_command_path: Vec<String>,
    command: &clap::Command,
    depth: usize,
) -> std::fmt::Result {
    // Don't document commands marked with `clap(hide = true)` (which includes
    // `print-all-help`).
    if command.is_hide_set() {
        return Ok(());
    }

    // Append the name of `command` to `command_path`.
    let command_path = {
        let mut command_path = parent_command_path;
        command_path.push(command.get_name().to_owned());
        command_path
    };

    writeln!(
        buffer,
        "<li><a href=\"#{}\"><code>{}</code>↴</a></li>",
        command_path.join("-"),
        command_path.join(" ")
    )?;

    //----------------------------------
    // Recurse to write subcommands
    //----------------------------------

    for subcommand in command.get_subcommands() {
        build_table_of_contents_html(
            buffer,
            command_path.clone(),
            subcommand,
            depth + 1,
        )?;
    }

    Ok(())
}
*/

fn build_command_markdown(
    buffer: &mut String,
    // Parent commands of `command`.
    parent_command_path: Vec<String>,
    command: &clap::Command,
    depth: usize,
) -> std::fmt::Result {
    // Don't document commands marked with `clap(hide = true)` (which includes
    // `print-all-help`).
    if command.is_hide_set() {
        return Ok(());
    }

    // Append the name of `command` to `command_path`.
    let command_path = {
        let mut command_path = parent_command_path.clone();
        command_path.push(command.get_name().to_owned());
        command_path
    };

    //----------------------------------
    // Write the markdown heading
    //----------------------------------

    // TODO: `depth` is now unused. Remove if no other use for it appears.
    /*
    if depth >= 6 {
        panic!(
            "command path nesting depth is deeper than maximum markdown header depth: `{}`",
            command_path.join(" ")
        )
    }
    */

    writeln!(
        buffer,
        "{} `{}`\n",
        // "#".repeat(depth + 1),
        "##",
        command_path.join(" "),
    )?;

    if let Some(long_about) = command.get_long_about() {
        writeln!(buffer, "{}\n", long_about)?;
    } else if let Some(about) = command.get_about() {
        writeln!(buffer, "{}\n", about)?;
    }

    // TODO(feature): Support printing custom before and after help texts.
    assert!(command.get_before_help().is_none());
    assert!(command.get_after_help().is_none());

    writeln!(
        buffer,
        "**Usage:** `{}{}`\n",
        if parent_command_path.is_empty() {
            String::new()
        } else {
            let mut s = parent_command_path.join(" ");
            s.push_str(" ");
            s
        },
        command
            .clone()
            .render_usage()
            .to_string()
            .replace("Usage: ", "")
    )?;

    //----------------------------------
    // Subcommands
    //----------------------------------

    if command.get_subcommands().next().is_some() {
        writeln!(buffer, "###### **Subcommands:**\n")?;

        for subcommand in command.get_subcommands() {
            if subcommand.is_hide_set() {
                continue;
            }

            writeln!(
                buffer,
                "* `{}` — {}",
                subcommand.get_name(),
                match subcommand.get_about() {
                    Some(about) => about.to_string(),
                    None => String::new(),
                }
            )?;
        }

        write!(buffer, "\n")?;
    }

    //----------------------------------
    // Arguments
    //----------------------------------

    if command.get_positionals().next().is_some() {
        writeln!(buffer, "###### **Arguments:**\n")?;

        for pos_arg in command.get_positionals() {
            write_arg_markdown(buffer, pos_arg)?;
        }

        write!(buffer, "\n")?;
    }

    //----------------------------------
    // Options
    //----------------------------------

    let non_pos: Vec<_> = command
        .get_arguments()
        .filter(|arg| !arg.is_positional())
        .collect();

    if !non_pos.is_empty() {
        writeln!(buffer, "###### **Options:**\n")?;

        for arg in non_pos {
            write_arg_markdown(buffer, arg)?;
        }

        write!(buffer, "\n")?;
    }

    //----------------------------------
    // Recurse to write subcommands
    //----------------------------------

    // Include extra space between commands. This is purely for the benefit of
    // anyone reading the source .md file.
    write!(buffer, "\n\n")?;

    for subcommand in command.get_subcommands() {
        build_command_markdown(
            buffer,
            command_path.clone(),
            subcommand,
            depth + 1,
        )?;
    }

    Ok(())
}

fn write_arg_markdown(buffer: &mut String, arg: &clap::Arg) -> fmt::Result {
    // Markdown list item
    write!(buffer, "* ")?;

    let value_name: String = match arg.get_value_names() {
        // TODO: What if multiple names are provided?
        Some([name, ..]) => name.as_str().to_owned(),
        Some([]) => unreachable!(
            "clap Arg::get_value_names() returned Some(..) of empty list"
        ),
        None => arg.get_id().to_string().to_ascii_uppercase(),
    };

    match (arg.get_short(), arg.get_long()) {
        (Some(short), Some(long)) => {
            if arg.get_action().takes_values() {
                write!(buffer, "`-{short}`, `--{long} <{value_name}>`")?
            } else {
                write!(buffer, "`-{short}`, `--{long}`")?
            }
        },
        (Some(short), None) => {
            if arg.get_action().takes_values() {
                write!(buffer, "`-{short} <{value_name}>`")?
            } else {
                write!(buffer, "`-{short}`")?
            }
        },
        (None, Some(long)) => {
            if arg.get_action().takes_values() {
                write!(buffer, "`--{} <{value_name}>`", long)?
            } else {
                write!(buffer, "`--{}`", long)?
            }
        },
        (None, None) => {
            debug_assert!(arg.is_positional(), "unexpected non-positional Arg with neither short nor long name: {arg:?}");

            write!(buffer, "`<{value_name}>`",)?;
        },
    }

    if let Some(help) = arg.get_help() {
        writeln!(buffer, " — {help}")?;
    } else {
        writeln!(buffer)?;
    }

    //--------------------
    // Arg default values
    //--------------------

    if !arg.get_default_values().is_empty() {
        let default_values: String = arg
            .get_default_values()
            .iter()
            .map(|value| format!("`{}`", value.to_string_lossy()))
            .collect::<Vec<String>>()
            .join(", ");

        if arg.get_default_values().len() > 1 {
            // Plural
            writeln!(buffer, "\n  Default values: {default_values}")?;
        } else {
            // Singular
            writeln!(buffer, "\n  Default value: {default_values}")?;
        }
    }

    //--------------------
    // Arg possible values
    //--------------------

    let possible_values: Vec<PossibleValue> = arg
        .get_possible_values()
        .into_iter()
        .filter(|pv| !pv.is_hide_set())
        .collect();

    if !possible_values.is_empty() {
        let any_have_help: bool =
            possible_values.iter().any(|pv| pv.get_help().is_some());

        if any_have_help {
            // If any of the possible values have help text, print them
            // as a separate item in a bulleted list, and include the
            // help text for those that have it. E.g.:
            //
            //     Possible values:
            //     - `value1`:
            //       The help text
            //     - `value2`
            //     - `value3`:
            //       The help text

            let text: String = possible_values
                .iter()
                .map(|pv| match pv.get_help() {
                    Some(help) => {
                        format!("  - `{}`:\n    {}\n", pv.get_name(), help)
                    },
                    None => format!("  - `{}`\n", pv.get_name()),
                })
                .collect::<Vec<String>>()
                .join("");

            writeln!(buffer, "\n  Possible values:\n{text}")?;
        } else {
            // If none of the possible values have any documentation, print
            // them all inline on a single line.
            let text: String = possible_values
                .iter()
                // TODO: Show PossibleValue::get_help(), and PossibleValue::get_name_and_aliases().
                .map(|pv| format!("`{}`", pv.get_name()))
                .collect::<Vec<String>>()
                .join(", ");

            writeln!(buffer, "\n  Possible values: {text}\n")?;
        }
    }

    Ok(())
}