//! Driving the `pimsync` binary.
//!
//! pimsync handles the CalDAV and WebCal legs, mirroring each remote into a local
//! vdir. It is invoked one-shot: its own daemon would race the reconciler over the
//! same files, so scheduling belongs to calcalist.

use std::fmt;
use std::fs;
use std::io;
use std::path::{Path, PathBuf};
use std::process::Command;

use thiserror::Error;

use crate::config::{Config, Endpoint, EndpointKind};

pub const BINARY: &str = "pimsync";

/// The `0.5.x` series this build generates configuration for. pimsync is
/// pre-1.0 and its config syntax may change between minor releases, so the
/// range is deliberately narrow.
pub const SUPPORTED_MAJOR: u64 = 0;
pub const SUPPORTED_MINOR: u64 = 5;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Version {
    pub major: u64,
    pub minor: u64,
    pub patch: u64,
}

impl fmt::Display for Version {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}.{}.{}", self.major, self.minor, self.patch)
    }
}

impl Version {
    pub fn is_supported(&self) -> bool {
        self.major == SUPPORTED_MAJOR && self.minor == SUPPORTED_MINOR
    }

    /// Parses the `pimsync 0.5.11` line printed by `pimsync version`.
    fn parse(output: &str) -> Option<Self> {
        let field = output.split_whitespace().nth(1)?;
        let mut parts = field.split('.');
        Some(Version {
            major: parts.next()?.parse().ok()?,
            minor: parts.next()?.parse().ok()?,
            patch: parts.next().unwrap_or("0").parse().ok()?,
        })
    }
}

#[derive(Debug, Error)]
pub enum PimsyncError {
    #[error("`{BINARY}` was not found on PATH; install it (devbox provides {BINARY}@0.5.11)")]
    NotFound,
    #[error("could not run `{BINARY}`: {0}")]
    Spawn(#[source] io::Error),
    #[error("`{BINARY} version` failed: {0}")]
    Failed(String),
    #[error("could not read a version out of `{0}`")]
    Unparseable(String),
    #[error("could not write {path}: {source}")]
    Write {
        path: std::path::PathBuf,
        #[source]
        source: io::Error,
    },
    #[error("`{BINARY} {command}` failed: {message}")]
    Command { command: String, message: String },
    #[error(
        "endpoint `{endpoint}` has url `{url}`, which names no calendar collection; it must point at the calendar itself, not at the server root"
    )]
    UrlHasNoCollection { endpoint: String, url: String },
}

/// Asks the installed pimsync for its version.
pub fn probe() -> Result<Version, PimsyncError> {
    let output = Command::new(BINARY)
        .arg("version")
        .output()
        .map_err(|error| {
            if error.kind() == io::ErrorKind::NotFound {
                PimsyncError::NotFound
            } else {
                PimsyncError::Spawn(error)
            }
        })?;
    if !output.status.success() {
        return Err(PimsyncError::Failed(
            String::from_utf8_lossy(&output.stderr).trim().to_string(),
        ));
    }
    let text = String::from_utf8_lossy(&output.stdout);
    let line = text.lines().next().unwrap_or_default().trim();
    Version::parse(line).ok_or_else(|| PimsyncError::Unparseable(line.to_string()))
}

/// Name of the single local storage every pair mirrors into. pimsync allows one
/// storage to take part in several pairs, so one declaration serves all of them.
const LOCAL_STORAGE: &str = "local";

pub fn config_path(state_dir: &Path) -> PathBuf {
    state_dir.join("pimsync.conf")
}

fn status_path(state_dir: &Path) -> PathBuf {
    state_dir.join("pimsync-status")
}

/// Builds a pimsync configuration covering every CalDAV and WebCal endpoint.
///
/// Google endpoints are absent by design: pimsync has no REST storage, and its
/// CalDAV storage speaks only HTTP Basic auth, which Google's endpoint has
/// rejected since March 2025. calcalist syncs those itself.
pub fn generate(config: &Config, state_dir: &Path) -> Result<String, PimsyncError> {
    let mut out = String::new();
    out.push_str("# Generated by calcalist. Edits here are overwritten on every sync.\n\n");
    out.push_str(&format!(
        "status_path {}\n\n",
        quote(&status_path(state_dir).display().to_string())
    ));
    out.push_str(&format!(
        "storage {LOCAL_STORAGE} {{\n\ttype vdir/icalendar\n\tpath {}\n\tfileext ics\n}}\n",
        quote(&crate::sync::vdir_root(state_dir).display().to_string())
    ));

    for endpoint in &config.endpoints {
        match &endpoint.kind {
            EndpointKind::Caldav { .. } => out.push_str(&caldav_pair(endpoint)?),
            EndpointKind::Webcal { url, url_command } => {
                out.push_str(&webcal_pair(
                    endpoint,
                    url.as_deref(),
                    url_command.as_deref(),
                ));
            }
            // Handled by calcalist's own Google module.
            EndpointKind::Google { .. } => {}
        }
    }
    Ok(out)
}

fn caldav_pair(endpoint: &Endpoint) -> Result<String, PimsyncError> {
    let EndpointKind::Caldav {
        url,
        username,
        secret_command,
    } = &endpoint.kind
    else {
        unreachable!("caller matched on Caldav")
    };
    let (base, href) =
        split_collection_url(url).ok_or_else(|| PimsyncError::UrlHasNoCollection {
            endpoint: endpoint.id.clone(),
            url: url.clone(),
        })?;

    let id = &endpoint.id;
    let mut block = format!(
        "\nstorage {id}_remote {{\n\ttype caldav\n\turl {}\n\tdiscovery collections\n\tusername {}\n",
        quote(&base),
        quote(username)
    );
    if let Some(command) = secret_command {
        // Secrets never live in the portable config, so pimsync runs the same
        // command calcalist would to fetch them.
        block.push_str(&format!("\tpassword {{\n\t\tshell {command}\n\t}}\n"));
    }
    block.push_str("}\n");

    // The remote is storage_a, so a concurrent server-side change wins over a
    // local one calcalist has not yet reconciled. Nothing is lost: the next
    // cycle sees the server's version and decides properly.
    block.push_str(&format!(
        "\npair {id} {{\n\tstorage_a {id}_remote\n\tstorage_b {LOCAL_STORAGE}\n\
         \tcollection {{\n\t\talias {id}\n\t\thref_a {}\n\t\tid_b {id}\n\t}}\n\
         \tconflict_resolution keep a\n\ton_empty skip\n\ton_delete skip\n}}\n",
        quote(&href)
    ));
    Ok(block)
}

fn webcal_pair(endpoint: &Endpoint, url: Option<&str>, url_command: Option<&str>) -> String {
    let id = &endpoint.id;
    // A feed URL that is itself a credential is fetched by command, the same way
    // passwords are, so it never appears in either configuration file.
    let url_directive = match (url, url_command) {
        (_, Some(command)) => format!("\turl {{\n\t\tshell {command}\n\t}}\n"),
        (Some(url), None) => format!("\turl {}\n", quote(url)),
        (None, None) => String::new(),
    };
    // No `read_only` directive here: pimsync 0.5.11 documents it as applying to
    // every storage type, but rejects it on a webcal storage with a bare "Could
    // not parse file". It is redundant regardless — webcal is read-only by type,
    // and `one_way` already fixes the direction.
    format!(
        "\nstorage {id}_remote {{\n\ttype webcal\n{url_directive}\tcollection_id {id}\n}}\n\
         \npair {id} {{\n\tstorage_a {id}_remote\n\tstorage_b {LOCAL_STORAGE}\n\
         \tcollection {{\n\t\talias {id}\n\t\tid_a {id}\n\t\tid_b {id}\n\t}}\n\
         \tone_way\n\ton_empty skip\n\ton_delete skip\n}}\n"
    )
}

/// Splits a calendar URL into the container to enumerate and the collection's
/// own path.
///
/// pimsync identifies a collection either by an id taken from a URL segment or
/// by its exact path. The path is used here, so a calendar whose last segment
/// happens to match another's cannot be confused for it.
fn split_collection_url(url: &str) -> Option<(String, String)> {
    let authority_start = url.find("://")? + 3;
    let path_start = authority_start + url[authority_start..].find('/')?;
    let segments: Vec<&str> = url[path_start..]
        .split('/')
        .filter(|segment| !segment.is_empty())
        .collect();
    let (_, parents) = segments.split_last()?;

    let href = format!("/{}/", segments.join("/"));
    let base = match parents {
        [] => format!("{}/", &url[..path_start]),
        parents => format!("{}/{}/", &url[..path_start], parents.join("/")),
    };
    Some((base, href))
}

/// pimsync accepts quoted values, which keeps paths with spaces intact.
fn quote(value: &str) -> String {
    format!("\"{}\"", value.replace('\\', "\\\\").replace('"', "\\\""))
}

/// Writes the generated configuration, returning its path.
pub fn write_config(config: &Config, state_dir: &Path) -> Result<PathBuf, PimsyncError> {
    let path = config_path(state_dir);
    let text = generate(config, state_dir)?;
    fs::create_dir_all(status_path(state_dir)).map_err(|source| PimsyncError::Write {
        path: status_path(state_dir),
        source,
    })?;
    fs::write(&path, text).map_err(|source| PimsyncError::Write {
        path: path.clone(),
        source,
    })?;
    Ok(path)
}

/// Runs one pimsync cycle.
///
/// Deliberately one-shot: `pimsync daemon` would write the same vdirs the
/// reconciler is reading, so calcalist owns the scheduling instead.
pub fn sync(config_path: &Path) -> Result<(), PimsyncError> {
    run(config_path, "sync")
}

/// Validates the generated configuration and the storages it names.
pub fn check(config_path: &Path) -> Result<(), PimsyncError> {
    run(config_path, "check")
}

fn run(config_path: &Path, command: &str) -> Result<(), PimsyncError> {
    let output = Command::new(BINARY)
        .arg("-c")
        .arg(config_path)
        .arg(command)
        .output()
        .map_err(|error| {
            if error.kind() == io::ErrorKind::NotFound {
                PimsyncError::NotFound
            } else {
                PimsyncError::Spawn(error)
            }
        })?;
    if output.status.success() {
        return Ok(());
    }
    let message = String::from_utf8_lossy(&output.stderr).trim().to_string();
    Err(PimsyncError::Command {
        command: command.to_string(),
        message: if message.is_empty() {
            format!("exited with {}", output.status)
        } else {
            message
        },
    })
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::config::Config;
    use std::path::Path;

    const CONFIG: &str = r#"
version = 1

[[endpoint]]
id = "work"
type = "caldav"
url = "https://dav.example.com/dav/calendars/user/me/work/"
username = "me@example.com"
secret_command = "pass show example/caldav"

[[endpoint]]
id = "gcal"
type = "google"
calendar_id = "me@example.com"
client_id = "abc.apps.googleusercontent.com"

[[endpoint]]
id = "holidays"
type = "webcal"
url = "https://example.org/holidays.ics"
"#;

    /// The text of one `storage`/`pair` block, so assertions do not accidentally
    /// match a directive belonging to a different block.
    fn block<'a>(text: &'a str, opening: &str) -> &'a str {
        let start = text.find(opening).expect("block should be present");
        let rest = &text[start..];
        rest.find("\n}\n").map_or(rest, |end| &rest[..end])
    }

    fn generated() -> String {
        let config: Config = toml::from_str(CONFIG).expect("config should parse");
        generate(&config, Path::new("/var/state/calcalist")).expect("generation should succeed")
    }

    #[test]
    fn declares_one_local_storage_for_every_pair() {
        let text = generated();
        assert_eq!(text.matches("storage local {").count(), 1);
        assert!(text.contains("path \"/var/state/calcalist/vdir\""));
        assert!(text.contains("status_path \"/var/state/calcalist/pimsync-status\""));
    }

    /// pimsync cannot authenticate to Google at all, so it must not be asked to.
    #[test]
    fn google_endpoints_are_left_out_entirely() {
        let text = generated();
        assert!(!text.contains("gcal"), "google endpoint leaked into {text}");
    }

    #[test]
    fn a_caldav_endpoint_becomes_a_bidirectional_pair() {
        let text = generated();
        assert!(text.contains("storage work_remote {"));
        assert!(text.contains("type caldav"));
        // The container is enumerated, and the calendar picked out by exact path.
        assert!(text.contains("url \"https://dav.example.com/dav/calendars/user/me/\""));
        assert!(text.contains("href_a \"/dav/calendars/user/me/work/\""));
        assert!(text.contains("id_b work"));
        assert!(
            !block(&text, "pair work {").contains("one_way"),
            "caldav pairs must stay bidirectional"
        );
    }

    /// Secrets stay out of the portable config; pimsync fetches them the same way.
    #[test]
    fn secrets_are_fetched_by_command_not_embedded() {
        let text = generated();
        assert!(text.contains("password {"));
        assert!(text.contains("shell pass show example/caldav"));
    }

    #[test]
    fn a_feed_becomes_a_one_way_read_only_pair() {
        let text = generated();
        assert!(text.contains("type webcal"));
        assert!(text.contains("one_way"));
        // pimsync 0.5.11 rejects `read_only` on a webcal storage despite
        // documenting it for all storage types.
        assert!(!block(&text, "storage holidays_remote {").contains("read_only"));
        assert!(text.contains("collection_id holidays"));
    }

    /// Both guards against a failed pull being mirrored as a mass deletion.
    #[test]
    fn every_pair_carries_the_deletion_guards() {
        let text = generated();
        let pairs = text.matches("\npair ").count();
        assert_eq!(pairs, 2);
        assert_eq!(text.matches("on_empty skip").count(), pairs);
        assert_eq!(text.matches("on_delete skip").count(), pairs);
    }

    /// A feed whose URL is itself a credential — Google's secret iCal address —
    /// must be fetched by command, never written into either config file.
    #[test]
    fn a_secret_feed_url_is_fetched_by_command() {
        let config: Config = toml::from_str(
            r#"
version = 1

[[endpoint]]
id = "gcal-feed"
type = "webcal"
url_command = "secret-tool lookup service calcalist account gcal-ics"
"#,
        )
        .expect("config should parse");
        let text = generate(&config, Path::new("/var/state/calcalist")).expect("generate");

        assert!(text.contains("url {"));
        assert!(text.contains("shell secret-tool lookup service calcalist account gcal-ics"));
        assert!(!text.contains("https://"), "no literal URL should appear");
    }

    #[test]
    fn splits_a_calendar_url_into_container_and_path() {
        assert_eq!(
            split_collection_url("https://dav.example.com/dav/calendars/user/me/work/"),
            Some((
                "https://dav.example.com/dav/calendars/user/me/".into(),
                "/dav/calendars/user/me/work/".into()
            ))
        );
        // A trailing slash is optional.
        assert_eq!(
            split_collection_url("https://dav.example.com/calendars/work"),
            Some((
                "https://dav.example.com/calendars/".into(),
                "/calendars/work/".into()
            ))
        );
        // A single segment leaves the root as the container.
        assert_eq!(
            split_collection_url("https://dav.example.com/work/"),
            Some(("https://dav.example.com/".into(), "/work/".into()))
        );
    }

    /// A bare server root names no calendar, so it must be rejected rather than
    /// guessed at.
    #[test]
    fn a_url_without_a_collection_is_refused() {
        assert_eq!(split_collection_url("https://dav.example.com/"), None);
        assert_eq!(split_collection_url("https://dav.example.com"), None);
    }

    #[test]
    fn parses_the_version_line() {
        assert_eq!(
            Version::parse("pimsync 0.5.11"),
            Some(Version {
                major: 0,
                minor: 5,
                patch: 11
            })
        );
    }

    #[test]
    fn tolerates_a_two_component_version() {
        assert_eq!(
            Version::parse("pimsync 1.2"),
            Some(Version {
                major: 1,
                minor: 2,
                patch: 0
            })
        );
    }

    #[test]
    fn rejects_unparseable_output() {
        assert_eq!(Version::parse("pimsync"), None);
        assert_eq!(Version::parse("pimsync unreleased"), None);
    }

    #[test]
    fn only_the_supported_series_is_accepted() {
        let supported = Version {
            major: 0,
            minor: 5,
            patch: 0,
        };
        let next_series = Version {
            major: 0,
            minor: 6,
            patch: 0,
        };
        assert!(supported.is_supported());
        assert!(!next_series.is_supported());
    }
}