// SPDX-License-Identifier: GPL-2.0-only

//! `stg rebase` implementation.

use std::{fmt::Write, str::FromStr};

use anyhow::{anyhow, Result};
use bstr::ByteSlice;
use clap::{Arg, ArgMatches};

use crate::{
    argset,
    color::get_color_stdout,
    ext::RepositoryExtended,
    patch::{patchedit, PatchName, SingleRevisionSpec},
    print_info_message,
    stack::{InitializationPolicy, Stack, StackAccess, StackStateAccess},
    stupid::Stupid,
};

pub(super) const STGIT_COMMAND: super::StGitCommand = super::StGitCommand {
    name: "rebase",
    category: super::CommandCategory::StackManipulation,
    make,
    run,
};

fn make() -> clap::Command {
    clap::Command::new(STGIT_COMMAND.name)
        .about("Move the stack base to another point in history")
        .long_about(
            "Pop all patches from the current stack, move the stack base to the given \
            new base and push the patches back.\n\
            \n\
            Merge conflicts may arise when patches are being pushed-back onto the \
            stack. If this occurs, resolve the conflicts and then continue the rebase \
            with the following sequence:\n\
            \n    \
            stg add --update\n    \
            stg refresh\n    \
            stg goto top-patch\n\
            \n\
            Or to skip the conflicting patch:\n\
            \n    \
            stg undo --hard\n    \
            stg push next-patch..top-patch\n\
            ",
        )
        .arg(
            Arg::new("committish")
                .help("New base commit for the stack")
                .value_parser(clap::value_parser!(SingleRevisionSpec)),
        )
        .arg(
            Arg::new("interactive")
                .long("interactive")
                .short('i')
                .help("Interactively manipulate patches in editor")
                .action(clap::ArgAction::SetTrue),
        )
        .arg(
            Arg::new("nopush")
                .long("nopush")
                .short('n')
                .help("Do not push back patches after rebasing")
                .action(clap::ArgAction::SetTrue)
                .conflicts_with("merged"),
        )
        .arg(argset::merged_arg().long_help(
            "Check for patches that may have been merged upstream.\n\
             \n\
             When pushing-back patches, each patch is checked to see if its changes \
             already exist in the new stack base. If a patch's changes are detected to \
             have been merged, the patch will still exist in the stack, but become \
             empty after the rebase operation.",
        ))
        .arg(argset::committer_date_is_author_date_arg())
        .arg(
            Arg::new("autostash")
                .long("autostash")
                .help("Stash changes before the rebase and reapply them after")
                .long_help(
                    "Automatically create a temporary stash before the operation \
                     begins, and apply it after the operation completes. This allows a \
                     rebase to be performed on a dirty work tree. Note however that \
                     the final stash application may result in non-trivial conflicts.",
                )
                .action(clap::ArgAction::SetTrue),
        )
        .arg(argset::push_conflicts_arg())
}

fn run(matches: &ArgMatches) -> Result<()> {
    let repo = gix::Repository::open()?;
    let stack = Stack::current(&repo, InitializationPolicy::RequireInitialized)?;
    let config = repo.config_snapshot();
    let stupid = repo.stupid();
    let branch_name = stack.get_branch_name().to_string();
    let allow_push_conflicts = argset::resolve_allow_push_conflicts(&config, matches);
    let committer_date_is_author_date = matches.get_flag("committer-date-is-author-date");
    let interactive = matches.get_flag("interactive");

    let target_commit = if let Some(target_rev_spec) =
        matches.get_one::<SingleRevisionSpec>("committish")
    {
        target_rev_spec.resolve(&repo, Some(&stack))?.commit
    } else if let Some(remote_ref) = repo
        .branch_remote_tracking_ref_name(stack.get_branch_refname(), gix::remote::Direction::Fetch)
        .transpose()?
    {
        let id = repo.rev_parse_single(remote_ref.as_bstr())?;
        id.object()?.into_commit().into()
    } else if interactive {
        stack.base().clone()
    } else {
        print_info_message(
            matches,
            &format!(
                "if you wish to set tracking information for this branch you can do so with:

    git branch --set-upstream-to=<remote>/<branch> {branch_name}
"
            ),
        );
        return Err(anyhow!(
            "there is no tracking information for the current branch"
        ));
    };

    if !interactive && target_commit.id == stack.base().id {
        print_info_message(
            matches,
            &format!(
                "Already based on {}",
                formatted_target_id_and_ref(&repo, std::rc::Rc::clone(&target_commit))
            ),
        );
        return Ok(());
    }

    if stack.is_protected(&config) {
        return Err(anyhow!("this branch is protected; rebase is not permitted"));
    }

    stack.check_head_top_mismatch()?;
    let clean_result = stupid.statuses(None)?.check_index_and_worktree_clean();

    let autostash = if matches.get_flag("autostash") {
        true
    } else {
        config
            .boolean_by(
                "branch",
                Some(format!("{branch_name}.stgit").as_str().into()),
                "autostash",
            )
            .transpose()
            .unwrap_or_else(|e| {
                crate::print_warning_message(
                    matches,
                    &format!("Invalid config value `branch.{branch_name}.stgit.autostash`: {e}"),
                );
                Some(false)
            })
            .or_else(|| {
                config
                    .try_boolean("stgit.autostash")
                    .transpose()
                    .unwrap_or_else(|e| {
                        crate::print_warning_message(
                            matches,
                            &format!("Invalid config value `stgit.autostash`: {e}"),
                        );
                        Some(false)
                    })
            })
            .unwrap_or(false)
    };

    let using_stash = if autostash && clean_result.is_err() {
        stupid.stash_push()?;
        true
    } else if let Err(e) = clean_result {
        return Err(e);
    } else {
        false
    };

    let applied = stack.applied().to_vec();

    stack
        .setup_transaction()
        .use_index_and_worktree(true)
        .with_output_stream(get_color_stdout(matches))
        .transact(|trans| {
            trans.pop_patches(|pn| applied.contains(pn))?;
            Ok(())
        })
        .execute("rebase (pop)")?;

    let rebase_cmd = config
        .string_by(
            "branch",
            Some(format!("{branch_name}.stgit").as_str().into()),
            "rebasecmd",
        )
        .or_else(|| config.string("stgit.rebasecmd"))
        .and_then(|bs| bs.to_str().map(str::to_string).ok())
        .unwrap_or_else(|| "git reset --hard".to_string());
    print_info_message(
        matches,
        &format!(
            "Rebasing to {}",
            formatted_target_id_and_ref(&repo, std::rc::Rc::clone(&target_commit))
        ),
    );
    stupid.user_rebase(&rebase_cmd, target_commit.id)?;

    let stack = Stack::current(&repo, InitializationPolicy::RequireInitialized)?;
    let stack = if stack.is_head_top() {
        stack
    } else {
        // Record a new stack state with updated head since the head moved.
        stack.log_external_mods(Some("rebase"))?
    };

    if matches.get_flag("interactive") {
        interactive_pushback(
            stack,
            &repo,
            &config,
            matches,
            &applied,
            allow_push_conflicts,
            committer_date_is_author_date,
        )?;
    } else if !matches.get_flag("nopush") {
        stack.check_head_top_mismatch()?;
        let check_merged = matches.get_flag("merged");
        stack
            .setup_transaction()
            .use_index_and_worktree(true)
            .allow_push_conflicts(allow_push_conflicts)
            .committer_date_is_author_date(committer_date_is_author_date)
            .with_output_stream(get_color_stdout(matches))
            .transact(|trans| trans.push_patches(&applied, check_merged))
            .execute("rebase (reapply)")?;
    }

    if using_stash {
        if stupid.stash_pop()? {
            Ok(())
        } else {
            Err(super::Error::CausedConflicts("stash pop resulted in conflicts".to_string()).into())
        }
    } else {
        Ok(())
    }
}

fn formatted_target_id_and_ref(
    repo: &gix::Repository,
    target_commit: std::rc::Rc<gix::Commit>,
) -> String {
    let mut id_and_ref = if let Some(abbrev) = repo
        .config_snapshot()
        .integer("core.abbrev")
        .map(|i| i as usize)
    {
        format!("`{}`", target_commit.id.to_hex_with_len(abbrev))
    } else {
        format!("`{}`", target_commit.id.to_hex())
    };

    let platform = repo.references().ok();
    if let Some(platform) = platform {
        let mut names: std::collections::BTreeSet<gix::refs::FullName> =
            std::collections::BTreeSet::new();

        if let Ok(local_branches) = platform.local_branches() {
            names.extend(
                local_branches
                    .filter_map(Result::ok)
                    .filter(|branch| {
                        branch.clone().into_fully_peeled_id().ok() == Some(target_commit.id())
                    })
                    .map(|branch| branch.name().to_owned()),
            )
        }
        if let Ok(remote_branches) = platform.remote_branches() {
            names.extend(
                remote_branches
                    .filter_map(Result::ok)
                    .filter(|branch| {
                        branch.clone().into_fully_peeled_id().ok() == Some(target_commit.id())
                    })
                    .map(|branch| branch.name().to_owned()),
            )
        }

        let mut short_names: Vec<(gix::refs::Category, &bstr::BStr)> = names
            .iter()
            .filter_map(|full_name| full_name.category_and_short_name())
            .collect();

        if !short_names.is_empty() {
            short_names.sort();
            id_and_ref.push_str(" (");
            for (i, (_, name)) in short_names.iter().enumerate() {
                if i > 0 {
                    id_and_ref.push(' ')
                }
                id_and_ref.push_str(&name.to_str_lossy());
            }
            id_and_ref.push(')');
        }
    }

    id_and_ref
}

const INTERACTIVE_APPLY_LINE: &str = "# --- APPLY_LINE ---";
const INTERACTIVE_HELP_LINES: &str = "\
# Commands:
#
#   k, keep <patch> = do not modify this patch
#   e, edit <patch> = interactively edit this patch
#   s, squash <patch> = squash patch into the previous patch
#   f, fixup <patch> = like \"squash\", but discard this patch's commit message
#   h, hide <patch> = hide patch
#   d, delete <patch> = delete patch
#
# These lines can be reordered; they are executed from top to bottom.
#
# Patches above the APPLY_LINE are applied; other patches are kept unapplied.
";

#[derive(Debug, Clone)]
struct Instruction {
    patchname: PatchName,
    action: Action,
    apply: bool,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Action {
    Keep,
    Edit,
    Squash,
    Fixup,
    Hide,
    Delete,
}

fn interactive_pushback(
    stack: Stack,
    repo: &gix::Repository,
    config: &gix::config::Snapshot,
    matches: &ArgMatches,
    previously_applied: &[PatchName],
    allow_push_conflicts: bool,
    committer_date_is_author_date: bool,
) -> Result<()> {
    let mut stack = stack;

    if stack.all_patches().next().is_none() {
        return Ok(());
    }

    let filename = ".stgit-rebase-interactive.txt";
    std::fs::write(
        filename,
        make_instructions_template(&stack, previously_applied),
    )?;

    let buf = patchedit::call_editor(filename, config)?;
    let buf = buf
        .to_str()
        .map_err(|_| anyhow!("`{filename}` is not valid UTF-8"))?;
    let mut instructions = parse_instructions(buf)?;

    validate_instructions(&stack, &instructions)?;

    let mut index: usize = 0;

    while index < instructions.len() {
        let instruction = instructions[index].clone();
        let patchname = &instruction.patchname;

        match instruction.action {
            Action::Keep => {
                index += 1;
            }

            Action::Delete => {
                // Find contiguous delete instructions in order to delete in batches.
                let mut delete_instructions: Vec<Instruction> = Vec::new();
                while index < instructions.len() && instructions[index].action == Action::Delete {
                    delete_instructions.push(instructions.remove(index));
                }
                assert!(!delete_instructions.is_empty());
                assert!(delete_instructions
                    .iter()
                    .all(|inst| inst.action == Action::Delete));
                let to_delete: Vec<&PatchName> = delete_instructions
                    .iter()
                    .map(|inst| &inst.patchname)
                    .collect();
                stack = stack
                    .setup_transaction()
                    .with_output_stream(get_color_stdout(matches))
                    .transact(|trans| {
                        let popped_extra = trans.delete_patches(|pn| to_delete.contains(&pn))?;
                        assert!(popped_extra.is_empty());
                        Ok(())
                    })
                    .execute("delete")?;
            }

            Action::Hide => {
                let mut hide_instructions: Vec<Instruction> = Vec::new();
                while index < instructions.len() && instructions[index].action == Action::Hide {
                    hide_instructions.push(instructions.remove(index));
                }
                assert!(!hide_instructions.is_empty());
                assert!(hide_instructions
                    .iter()
                    .all(|inst| inst.action == Action::Hide));
                let to_hide: Vec<PatchName> = hide_instructions
                    .iter()
                    .map(|inst| inst.patchname.clone())
                    .collect();
                stack = stack
                    .setup_transaction()
                    .with_output_stream(get_color_stdout(matches))
                    .transact(|trans| trans.hide_patches(&to_hide))
                    .execute("hide")?;
            }

            Action::Edit => {
                let dummy_edit_command = clap::Command::new("dummy-edit");
                let dummy_edit_command = patchedit::add_args(dummy_edit_command, false, false);
                let edit_matches = dummy_edit_command
                    .try_get_matches_from(["dummy-edit", "--edit", "--diff"])
                    .expect("dummy command has valid arguments");
                match patchedit::EditBuilder::default()
                    .original_patchname(Some(patchname))
                    .existing_patch_commit(stack.get_patch_commit(patchname))
                    .allow_diff_edit(true)
                    .edit(&stack, repo, &edit_matches)?
                {
                    patchedit::EditOutcome::TemplateSaved(_) => panic!("template save not enabled"),
                    patchedit::EditOutcome::Edited {
                        new_patchname,
                        new_commit_id,
                    } => {
                        if new_patchname.is_some() || new_commit_id.is_some() {
                            stack = stack
                                .setup_transaction()
                                .committer_date_is_author_date(committer_date_is_author_date)
                                .with_output_stream(get_color_stdout(matches))
                                .transact(|trans| {
                                    let patchname =
                                        if let Some(new_patchname) = new_patchname.as_ref() {
                                            trans.rename_patch(patchname, new_patchname)?;
                                            new_patchname
                                        } else {
                                            patchname
                                        };
                                    if let Some(commit_id) = new_commit_id {
                                        trans.update_patch(patchname, commit_id)?;
                                    }
                                    Ok(())
                                })
                                .execute(&format!("edit: {patchname}"))?;
                        }

                        instructions[index] = Instruction {
                            action: Action::Keep,
                            patchname: new_patchname.unwrap_or_else(|| patchname.clone()),
                            apply: instruction.apply,
                        };

                        index += 1;
                    }
                }
            }

            Action::Squash | Action::Fixup => {
                let action_str = match instruction.action {
                    Action::Squash => "squash",
                    Action::Fixup => "fixup",
                    _ => panic!("only squash and fixup expected"),
                };

                let squash_patchnames: Vec<PatchName> = if index > 0 {
                    let mut patchnames: Vec<PatchName> =
                        vec![instructions[index - 1].patchname.clone()];
                    while index < instructions.len()
                        && instructions[index].action == instruction.action
                    {
                        let Instruction { patchname, .. } = instructions.remove(index);
                        patchnames.push(patchname);
                    }
                    patchnames
                } else {
                    return Err(anyhow!(
                        "cannot {action_str} `{patchname}`: no preceding patch"
                    ));
                };

                let target_patchname = &squash_patchnames[0];

                let dummy_squash_command = clap::Command::new("dummy-squash");
                let dummy_squash_command = patchedit::add_args(dummy_squash_command, true, false);
                let squash_matches = match instruction.action {
                    Action::Squash => {
                        dummy_squash_command.try_get_matches_from(["dummy-squash", "--edit"])
                    }
                    Action::Fixup => {
                        let commit = stack.get_patch_commit(target_patchname);
                        let message = commit.message_raw()?.to_str().map_err(|_| {
                            anyhow!("fixup target patch `{target_patchname}` has non-UTF-8 message")
                        })?;
                        dummy_squash_command.try_get_matches_from([
                            "dummy-squash",
                            "--message",
                            message,
                        ])
                    }
                    _ => panic!("only squash and fixup expected"),
                }
                .expect("dummy command has valid arguments");

                stack = stack
                    .setup_transaction()
                    .with_output_stream(get_color_stdout(matches))
                    .transact(|trans| {
                        let new_patchname = super::squash::squash(
                            trans,
                            &squash_matches,
                            &squash_patchnames,
                            Some(target_patchname),
                            false,
                        )?;
                        instructions[index - 1] = Instruction {
                            action: Action::Keep,
                            patchname: new_patchname,
                            apply: instruction.apply,
                        };
                        Ok(())
                    })
                    .execute("squash")?;
            }
        }
    }

    let to_push: Vec<PatchName> = instructions
        .iter()
        .filter_map(|inst| {
            if inst.apply {
                Some(inst.patchname.clone())
            } else {
                None
            }
        })
        .collect();
    let check_merged = matches.get_flag("merged");

    stack.check_head_top_mismatch()?;
    stack
        .setup_transaction()
        .use_index_and_worktree(true)
        .allow_push_conflicts(allow_push_conflicts)
        .committer_date_is_author_date(committer_date_is_author_date)
        .with_output_stream(get_color_stdout(matches))
        .transact(|trans| trans.push_patches(&to_push, check_merged))
        .execute("rebase (reapply)")?;

    Ok(())
}

fn make_instructions_template(stack: &Stack, previously_applied: &[PatchName]) -> String {
    let name_width = stack.all_patches().map(PatchName::len).max().unwrap();
    let mut template = String::with_capacity(4096);
    let mut found_apply_boundary = false;
    for patchname in stack.all_patches() {
        if !found_apply_boundary && !previously_applied.contains(patchname) {
            writeln!(template, "{INTERACTIVE_APPLY_LINE}").unwrap();
            found_apply_boundary = true;
        }
        let commit = stack.get_patch_commit(patchname);
        let subject = commit
            .message()
            .map(|message_ref| message_ref.title.to_str_lossy())
            .unwrap_or_default()
            .replace(['\r', '\n'], " ")
            .trim()
            .to_owned();
        writeln!(template, "keep {patchname:name_width$} # {subject}").unwrap();
    }
    if !found_apply_boundary {
        writeln!(template, "{INTERACTIVE_APPLY_LINE}").unwrap();
    }
    template.push_str(INTERACTIVE_HELP_LINES);
    template
}

fn parse_instructions(buf: &str) -> Result<Vec<Instruction>> {
    let mut instructions = Vec::new();
    let mut apply = true;

    for line in buf.lines() {
        let line = line.trim();

        if line.contains(INTERACTIVE_APPLY_LINE) {
            if line == INTERACTIVE_APPLY_LINE {
                apply = false;
            } else {
                return Err(anyhow!("bad APPLY_LINE: `{line}`"));
            }
        }

        let instruction_str = if let Some((instruction_str, _comment)) = line.split_once('#') {
            instruction_str
        } else {
            line
        }
        .trim();

        if instruction_str.is_empty() {
            continue;
        }

        if let Some((action_str, patchname_str)) =
            instruction_str.split_once(|c: char| c.is_ascii_whitespace())
        {
            let action = match action_str {
                "k" | "keep" => Action::Keep,
                "e" | "edit" => Action::Edit,
                "s" | "squash" => Action::Squash,
                "f" | "fix" | "fixup" => Action::Fixup,
                "h" | "hide" => Action::Hide,
                "d" | "delete" => Action::Delete,
                _ => return Err(anyhow!("unknown instruction action `{action_str}`")),
            };

            let patchname = PatchName::from_str(patchname_str)?;

            instructions.push(Instruction {
                patchname,
                action,
                apply,
            });
        } else {
            return Err(anyhow!("bad instruction line: `{line}`"));
        }
    }
    Ok(instructions)
}

fn validate_instructions(stack: &Stack, instructions: &[Instruction]) -> Result<()> {
    let mut seen_patchnames: Vec<&PatchName> = Vec::new();
    for instruction in instructions {
        let patchname = &instruction.patchname;
        if !stack.has_patch(patchname) {
            return Err(anyhow!("unknown patch name `{patchname}`"));
        } else if seen_patchnames.contains(&patchname) {
            return Err(anyhow!("duplicated patch name `{patchname}`"));
        } else {
            seen_patchnames.push(patchname);
        }
    }
    Ok(())
}
