use crate::{
    config::AutolabelConfig,
    github::{files_changed, IssuesAction, IssuesEvent, Label},
    handlers::Context,
};
use anyhow::Context as _;
use tracing as log;

pub(super) struct AutolabelInput {
    add: Vec<Label>,
    remove: Vec<Label>,
}

pub(super) async fn parse_input(
    ctx: &Context,
    event: &IssuesEvent,
    config: Option<&AutolabelConfig>,
) -> Result<Option<AutolabelInput>, String> {
    let config = match config {
        Some(config) => config,
        None => return Ok(None),
    };
    // On opening a new PR or sync'ing the branch, look at the diff and try to
    // add any appropriate labels.
    //
    // FIXME: This will re-apply labels after a push that the user had tried to
    // remove. Not much can be done about that currently; the before/after on
    // synchronize may be straddling a rebase, which will break diff generation.
    if event.action == IssuesAction::Opened || event.action == IssuesAction::Synchronize {
        let diff = event
            .issue
            .diff(&ctx.github)
            .await
            .map_err(|e| {
                log::error!("failed to fetch diff: {:?}", e);
            })
            .unwrap_or_default();
        let files = diff.as_deref().map(files_changed);
        let mut autolabels = Vec::new();

        'outer: for (label, cfg) in config.labels.iter() {
            let exclude_patterns: Vec<glob::Pattern> = cfg
                .exclude_labels
                .iter()
                .filter_map(|label| match glob::Pattern::new(label) {
                    Ok(exclude_glob) => Some(exclude_glob),
                    Err(error) => {
                        log::error!("Invalid glob pattern: {}", error);
                        None
                    }
                })
                .collect();

            for label in event.issue.labels() {
                for pat in &exclude_patterns {
                    if pat.matches(&label.name) {
                        // If we hit an excluded label, ignore this autolabel and check the next
                        continue 'outer;
                    }
                }
            }

            if let Some(files) = &files {
                if cfg
                    .trigger_files
                    .iter()
                    .any(|f| files.iter().any(|diff_file| diff_file.starts_with(f)))
                {
                    autolabels.push(Label {
                        name: label.to_owned(),
                    });
                }
                if cfg.new_pr && event.action == IssuesAction::Opened {
                    autolabels.push(Label {
                        name: label.to_owned(),
                    });
                }
            }

            if event.issue.pull_request.is_none()
                && cfg.new_issue
                && event.action == IssuesAction::Opened
            {
                autolabels.push(Label {
                    name: label.to_owned(),
                });
            }
        }

        if !autolabels.is_empty() {
            return Ok(Some(AutolabelInput {
                add: autolabels,
                remove: vec![],
            }));
        }
    }

    if event.action == IssuesAction::Labeled {
        let mut autolabels = Vec::new();
        let applied_label = &event.label.as_ref().expect("label").name;

        'outer: for (label, config) in config.get_by_trigger(applied_label) {
            let exclude_patterns: Vec<glob::Pattern> = config
                .exclude_labels
                .iter()
                .filter_map(|label| match glob::Pattern::new(label) {
                    Ok(exclude_glob) => Some(exclude_glob),
                    Err(error) => {
                        log::error!("Invalid glob pattern: {}", error);
                        None
                    }
                })
                .collect();

            for label in event.issue.labels() {
                for pat in &exclude_patterns {
                    if pat.matches(&label.name) {
                        // If we hit an excluded label, ignore this autolabel and check the next
                        continue 'outer;
                    }
                }
            }

            // If we reach here, no excluded labels were found, so we should apply the autolabel.
            autolabels.push(Label {
                name: label.to_owned(),
            });
        }
        if !autolabels.is_empty() {
            return Ok(Some(AutolabelInput {
                add: autolabels,
                remove: vec![],
            }));
        }
    }
    Ok(None)
}

pub(super) async fn handle_input(
    ctx: &Context,
    _config: &AutolabelConfig,
    event: &IssuesEvent,
    input: AutolabelInput,
) -> anyhow::Result<()> {
    match event.issue.add_labels(&ctx.github, input.add).await {
        Ok(()) => {}
        Err(e) => {
            use crate::github::UnknownLabels;
            if let Some(err @ UnknownLabels { .. }) = e.downcast_ref() {
                event
                    .issue
                    .post_comment(&ctx.github, &err.to_string())
                    .await
                    .context("failed to post missing label comment")?;
                return Ok(());
            }
            return Err(e);
        }
    }

    for label in input.remove {
        event
            .issue
            .remove_label(&ctx.github, &label.name)
            .await
            .with_context(|| {
                format!(
                    "failed to remove {:?} from {:?}",
                    label,
                    event.issue.global_id()
                )
            })?;
    }
    Ok(())
}