// Copyright 2020 The Jujutsu 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
//
// https://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.

use std::collections::HashMap;
use std::io;
use std::io::Read as _;
use std::iter;

use clap_complete::ArgValueCompleter;
use itertools::Itertools as _;
use jj_lib::backend::Signature;
use jj_lib::object_id::ObjectId as _;
use jj_lib::repo::Repo as _;
use jj_lib::revset::RevsetIteratorExt as _;
use tracing::instrument;

use crate::cli_util::CommandHelper;
use crate::cli_util::RevisionArg;
use crate::command_error::CommandError;
use crate::command_error::user_error;
use crate::complete;
use crate::description_util::ParsedBulkEditMessage;
use crate::description_util::add_trailers_with_template;
use crate::description_util::description_template;
use crate::description_util::edit_description;
use crate::description_util::edit_multiple_descriptions;
use crate::description_util::join_message_paragraphs;
use crate::description_util::parse_trailers_template;
use crate::text_util::complete_newline;
use crate::text_util::parse_author;
use crate::ui::Ui;

/// Update the change description or other metadata [default alias: desc]
///
/// Starts an editor to let you edit the description of changes. The editor
/// will be $EDITOR, or `nano` if that's not defined (`Notepad` on Windows).
#[derive(clap::Args, Clone, Debug)]
pub(crate) struct DescribeArgs {
    /// The revision(s) whose description to edit (default: @)
    #[arg(
        value_name = "REVSETS",
        add = ArgValueCompleter::new(complete::revset_expression_mutable)
    )]
    revisions_pos: Vec<RevisionArg>,
    #[arg(
        short = 'r',
        hide = true,
        value_name = "REVSETS",
        add = ArgValueCompleter::new(complete::revset_expression_mutable)
    )]
    revisions_opt: Vec<RevisionArg>,
    /// The change description to use (don't open editor)
    ///
    /// If multiple revisions are specified, the same description will be used
    /// for all of them.
    #[arg(
        long = "message",
        short,
        value_name = "MESSAGE",
        conflicts_with = "stdin"
    )]
    message_paragraphs: Vec<String>,
    /// Read the change description from stdin
    ///
    /// If multiple revisions are specified, the same description will be used
    /// for all of them.
    #[arg(long)]
    stdin: bool,
    // TODO: Delete in jj 0.40.0+
    /// Don't open an editor
    ///
    /// This is mainly useful in combination with e.g. `--reset-author`.
    #[arg(long, hide = true, conflicts_with = "edit")]
    no_edit: bool,
    /// Open an editor
    ///
    /// Forces an editor to open when using `--stdin` or `--message` to
    /// allow the message to be edited afterwards.
    #[arg(long)]
    edit: bool,
    // TODO: Delete in jj 0.40.0+
    /// Reset the author name, email, and timestamp
    ///
    /// This resets the author name and email to the configured user and sets
    /// the author timestamp to the current time.
    ///
    /// You can use it in combination with the JJ_USER and JJ_EMAIL
    /// environment variables to set a different author:
    ///
    /// $ JJ_USER='Foo Bar' JJ_EMAIL=foo@bar.com jj describe --reset-author
    #[arg(long, hide = true)]
    reset_author: bool,
    // TODO: Delete in jj 0.40.0+
    /// Set author to the provided string
    ///
    /// This changes author name and email while retaining author
    /// timestamp for non-discardable commits.
    #[arg(
        long,
        hide = true,
        conflicts_with = "reset_author",
        value_parser = parse_author
    )]
    author: Option<(String, String)>,
}

#[instrument(skip_all)]
pub(crate) fn cmd_describe(
    ui: &mut Ui,
    command: &CommandHelper,
    args: &DescribeArgs,
) -> Result<(), CommandError> {
    if args.no_edit {
        writeln!(
            ui.warning_default(),
            "`jj describe --no-edit` is deprecated; use `jj metaedit` instead"
        )?;
    }
    if args.reset_author {
        writeln!(
            ui.warning_default(),
            "`jj describe --reset-author` is deprecated; use `jj metaedit --update-author` instead"
        )?;
    }
    if args.author.is_some() {
        writeln!(
            ui.warning_default(),
            "`jj describe --author` is deprecated; use `jj metaedit --author` instead"
        )?;
    }
    let mut workspace_command = command.workspace_helper(ui)?;
    let target_expr = if !args.revisions_pos.is_empty() || !args.revisions_opt.is_empty() {
        workspace_command
            .parse_union_revsets(ui, &[&*args.revisions_pos, &*args.revisions_opt].concat())?
    } else {
        workspace_command.parse_revset(ui, &RevisionArg::AT)?
    }
    .resolve()?;
    workspace_command.check_rewritable_expr(&target_expr)?;
    let commits: Vec<_> = target_expr
        .evaluate(workspace_command.repo().as_ref())?
        .iter()
        .commits(workspace_command.repo().store()) // in reverse topological order
        .try_collect()?;
    if commits.is_empty() {
        writeln!(ui.status(), "No revisions to describe.")?;
        return Ok(());
    }
    let text_editor = workspace_command.text_editor()?;

    let mut tx = workspace_command.start_transaction();
    let tx_description = match commits.as_slice() {
        [] => unreachable!(),
        [commit] => format!("describe commit {}", commit.id().hex()),
        [first_commit, remaining_commits @ ..] => {
            format!(
                "describe commit {} and {} more",
                first_commit.id().hex(),
                remaining_commits.len()
            )
        }
    };

    let shared_description = if args.stdin {
        let mut buffer = String::new();
        io::stdin().read_to_string(&mut buffer)?;
        Some(complete_newline(buffer))
    } else if !args.message_paragraphs.is_empty() {
        Some(join_message_paragraphs(&args.message_paragraphs))
    } else {
        None
    };

    let mut commit_builders = commits
        .iter()
        .map(|commit| {
            let mut commit_builder = tx.repo_mut().rewrite_commit(commit).detach();
            if let Some(description) = &shared_description {
                commit_builder.set_description(description);
            }
            if args.reset_author {
                let new_author = commit_builder.committer().clone();
                commit_builder.set_author(new_author);
            }
            if let Some((name, email)) = args.author.clone() {
                let new_author = Signature {
                    name,
                    email,
                    timestamp: commit_builder.author().timestamp,
                };
                commit_builder.set_author(new_author);
            }
            commit_builder
        })
        .collect_vec();

    let use_editor = args.edit || (shared_description.is_none() && !args.no_edit);

    if let Some(trailer_template) = parse_trailers_template(ui, &tx)? {
        for commit_builder in &mut commit_builders {
            // The first trailer would become the first line of the description.
            // Also, a commit with no description is treated in a special way in jujutsu: it
            // can be discarded as soon as it's no longer the working copy. Adding a
            // trailer to an empty description would break that logic.
            if use_editor || !commit_builder.description().is_empty() {
                let temp_commit = commit_builder.write_hidden()?;
                let new_description = add_trailers_with_template(&trailer_template, &temp_commit)?;
                commit_builder.set_description(new_description);
            }
        }
    }

    if use_editor {
        let temp_commits: Vec<_> = iter::zip(&commits, &commit_builders)
            // Edit descriptions in topological order
            .rev()
            .map(|(commit, commit_builder)| {
                commit_builder
                    .write_hidden()
                    .map(|temp_commit| (commit.id(), temp_commit))
            })
            .try_collect()?;

        if let [(_, temp_commit)] = &*temp_commits {
            let intro = "";
            let template = description_template(ui, &tx, intro, temp_commit)?;
            let description = edit_description(&text_editor, &template)?;
            commit_builders[0].set_description(description);
        } else {
            let ParsedBulkEditMessage {
                descriptions,
                missing,
                duplicates,
                unexpected,
            } = edit_multiple_descriptions(ui, &text_editor, &tx, &temp_commits)?;
            if !missing.is_empty() {
                return Err(user_error(format!(
                    "The description for the following commits were not found in the edited \
                     message: {}",
                    missing.join(", ")
                )));
            }
            if !duplicates.is_empty() {
                return Err(user_error(format!(
                    "The following commits were found in the edited message multiple times: {}",
                    duplicates.join(", ")
                )));
            }
            if !unexpected.is_empty() {
                return Err(user_error(format!(
                    "The following commits were not being edited, but were found in the edited \
                     message: {}",
                    unexpected.join(", ")
                )));
            }

            for (commit, commit_builder) in iter::zip(&commits, &mut commit_builders) {
                let description = descriptions.get(commit.id()).unwrap();
                commit_builder.set_description(description);
            }
        }
    };

    // Filter out unchanged commits to avoid rebasing descendants in
    // `transform_descendants` below unnecessarily.
    let commit_builders: HashMap<_, _> = iter::zip(&commits, commit_builders)
        .filter(|(old_commit, commit_builder)| {
            old_commit.description() != commit_builder.description()
                || args.reset_author
                // Ignore author timestamp which could be updated if the old
                // commit was discardable.
                || old_commit.author().name != commit_builder.author().name
                || old_commit.author().email != commit_builder.author().email
        })
        .map(|(old_commit, commit_builder)| (old_commit.id(), commit_builder))
        .collect();

    let mut num_described = 0;
    let mut num_reparented = 0;
    // Even though `MutableRepo::rewrite_commit` and
    // `MutableRepo::rebase_descendants` can handle rewriting of a commit even
    // if it is a descendant of another commit being rewritten, using
    // `MutableRepo::transform_descendants` prevents us from rewriting the same
    // commit multiple times, and adding additional entries in the predecessor
    // chain.
    tx.repo_mut().transform_descendants(
        commit_builders.keys().map(|&id| id.clone()).collect(),
        async |rewriter| {
            let old_commit_id = rewriter.old_commit().id().clone();
            let commit_builder = rewriter.reparent();
            if let Some(temp_builder) = commit_builders.get(&old_commit_id) {
                commit_builder
                    .set_description(temp_builder.description())
                    .set_author(temp_builder.author().clone())
                    // Copy back committer for consistency with author timestamp
                    .set_committer(temp_builder.committer().clone())
                    .write()?;
                num_described += 1;
            } else {
                commit_builder.write()?;
                num_reparented += 1;
            }
            Ok(())
        },
    )?;
    if num_described > 1 {
        writeln!(ui.status(), "Updated {num_described} commits")?;
    }
    if num_reparented > 0 {
        writeln!(ui.status(), "Rebased {num_reparented} descendant commits")?;
    }
    tx.finish(ui, tx_description)?;
    Ok(())
}