//! Generates the published OpenRPC contract from the wire types themselves.
//!
//! `docs/openrpc.json` is what third parties generate clients from, and
//! `rpc.discover` serves it straight out of the binary. Hand-maintaining it
//! would drift the moment a DTO gained a field, so it is derived here from the
//! same structs the daemon actually serializes, and [`document_is_current`]
//! fails the build when the checked-in copy no longer matches.
//!
//! Regenerate with `UPDATE_OPENRPC=1 cargo test -p soulseek-rs openrpc`.

use super::proto::{
    Ack, AuthParams, AuthResult, BrowseEvent, DaemonStatus, DirectoriesParams,
    DirectoryParams, DownloadStartParams, DownloadStarted, DownloadStatusEvent,
    Downloads, Event, IntervalSeconds, MemberStats, Members, MessageParams,
    Messages, Method, QueryParams, RoomEventDto, RoomRef, SayParams,
    SearchResults, Searches, Seconds, SessionLossEvent, SharesStatus,
    SlotsParams, TransferRef, UploadInfoDto, Uploads, UserMessageDto, UserRef,
    UserResult, Watched,
};
use schemars::{JsonSchema, SchemaGenerator, generate::SchemaSettings};
use serde_json::{Value, json};

/// Where the generated `$ref`s point. OpenRPC keeps shared schemas under
/// `components/schemas`, the same place OpenAPI does.
const DEFINITIONS_PATH: &str = "#/components/schemas/";

fn schema_of<T: JsonSchema>(generator: &mut SchemaGenerator) -> Value {
    generator.subschema_for::<T>().to_value()
}

/// The parameter schema for one method.
///
/// Exhaustive on purpose: a new [`Method`] variant does not compile until it is
/// described here, so the published contract cannot fall behind the daemon.
fn params_schema(method: Method, generator: &mut SchemaGenerator) -> Value {
    match method {
        Method::Auth => schema_of::<AuthParams>(generator),
        Method::SearchStart
        | Method::SearchResults
        | Method::SearchWishlist
        | Method::SearchForget => schema_of::<QueryParams>(generator),
        Method::DownloadStart => schema_of::<DownloadStartParams>(generator),
        Method::DownloadPause
        | Method::DownloadResume
        | Method::DownloadRemove
        | Method::DownloadRemoveQueued
        | Method::DownloadCancel
        | Method::UploadCancel => schema_of::<TransferRef>(generator),
        Method::DownloadSetDir => schema_of::<DirectoryParams>(generator),
        Method::UploadSlots => schema_of::<SlotsParams>(generator),
        Method::RoomJoin
        | Method::RoomLeave
        | Method::RoomMembers
        | Method::RoomMemberStats => schema_of::<RoomRef>(generator),
        Method::RoomSay => schema_of::<SayParams>(generator),
        Method::MessageSend => schema_of::<MessageParams>(generator),
        Method::BrowseUser
        | Method::UserRequest
        | Method::UserInfoOf
        | Method::UserWatch
        | Method::UserUnwatch => schema_of::<UserRef>(generator),
        Method::SharesSet => schema_of::<DirectoriesParams>(generator),
        // Methods that take no parameters.
        Method::DaemonStatus
        | Method::DaemonStop
        | Method::RpcDiscover
        | Method::SearchWishlistInterval
        | Method::DownloadList
        | Method::UploadList
        | Method::PrivilegesCheck
        | Method::PrivilegesOwn
        | Method::RoomListRequest
        | Method::MessageHistory
        | Method::SearchList
        | Method::SharesStatusOf
        | Method::SharesReindex
        | Method::UserWatched => json!({ "type": "null" }),
    }
}

/// The result schema for one method. Exhaustive for the same reason.
fn result_schema(method: Method, generator: &mut SchemaGenerator) -> Value {
    match method {
        Method::Auth => schema_of::<AuthResult>(generator),
        Method::DaemonStatus => schema_of::<DaemonStatus>(generator),
        Method::RpcDiscover => json!({ "type": "object" }),
        Method::SearchResults => schema_of::<SearchResults>(generator),
        Method::SearchList => schema_of::<Searches>(generator),
        Method::SearchWishlistInterval => {
            schema_of::<IntervalSeconds>(generator)
        }
        Method::DownloadStart => schema_of::<DownloadStarted>(generator),
        Method::DownloadList => schema_of::<Downloads>(generator),
        Method::UploadList => schema_of::<Uploads>(generator),
        Method::PrivilegesOwn => schema_of::<Seconds>(generator),
        Method::RoomMembers => schema_of::<Members>(generator),
        Method::RoomMemberStats => schema_of::<MemberStats>(generator),
        Method::UserWatched => schema_of::<Watched>(generator),
        Method::MessageHistory => schema_of::<Messages>(generator),
        Method::UserInfoOf => schema_of::<UserResult>(generator),
        Method::SharesStatusOf | Method::SharesSet | Method::SharesReindex => {
            schema_of::<SharesStatus>(generator)
        }
        // Everything else acknowledges and says nothing more.
        Method::DaemonStop
        | Method::SearchStart
        | Method::SearchWishlist
        | Method::DownloadPause
        | Method::DownloadResume
        | Method::DownloadRemove
        | Method::DownloadRemoveQueued
        | Method::DownloadCancel
        | Method::DownloadSetDir
        | Method::UploadCancel
        | Method::UploadSlots
        | Method::PrivilegesCheck
        | Method::RoomListRequest
        | Method::RoomJoin
        | Method::RoomLeave
        | Method::RoomSay
        | Method::MessageSend
        | Method::BrowseUser
        | Method::SearchForget
        | Method::UserRequest
        | Method::UserWatch
        | Method::UserUnwatch => schema_of::<Ack>(generator),
    }
}

/// What a method does, for the generated documentation.
fn summary(method: Method) -> &'static str {
    match method {
        Method::Auth => {
            "Authenticate. Must be the first request on a connection."
        }
        Method::DaemonStatus => {
            "Who the daemon is logged in as and what its session is doing."
        }
        Method::DaemonStop => "Ask the daemon to shut down.",
        Method::RpcDiscover => "This document.",
        Method::SearchStart => {
            "Put a search on the wire and return at once; results accumulate."
        }
        Method::SearchResults => {
            "Everything that has answered a search so far."
        }
        Method::SearchList => {
            "Every search this session has run, shared by all clients."
        }
        Method::SearchForget => {
            "Drop a search and its results, for every client at once."
        }
        Method::SearchWishlist => {
            "Send a query as a wishlist search (server code 103)."
        }
        Method::SearchWishlistInterval => {
            "How long the server wants between wishlist searches."
        }
        Method::DownloadStart => {
            "Queue a transfer. Progress arrives as event.download_status."
        }
        Method::DownloadList => "Every transfer the daemon knows about.",
        Method::DownloadPause => "Pause a transfer in progress.",
        Method::DownloadResume => "Resume a paused transfer.",
        Method::DownloadRemove => "Forget a transfer entirely.",
        Method::DownloadRemoveQueued => "Drop a transfer that has not started.",
        Method::DownloadCancel => {
            "Stop a download, queued or in progress; its partial file is deleted."
        }
        Method::DownloadSetDir => {
            "Land future transfers in a different folder on the daemon's host."
        }
        Method::UploadList => "Uploads being served, active first.",
        Method::UploadCancel => "Stop serving an upload in progress.",
        Method::UploadSlots => "How many uploads may run at once.",
        Method::PrivilegesCheck => {
            "Ask the server for this account's privilege time."
        }
        Method::PrivilegesOwn => {
            "Privilege seconds left, or null if the server has not answered."
        }
        Method::RoomListRequest => {
            "Ask the server for the public room list; it arrives as event.room."
        }
        Method::RoomJoin => "Join a chat room.",
        Method::RoomLeave => "Leave a chat room.",
        Method::RoomSay => "Post a message to a room.",
        Method::RoomMembers => "Who is currently in a room.",
        Method::RoomMemberStats => {
            "What the server said about each member of a joined room."
        }
        Method::UserWatch => {
            "Watch a user, so the server keeps pushing their status."
        }
        Method::UserUnwatch => "Stop watching a user.",
        Method::UserWatched => "Everyone this session is watching.",
        Method::MessageSend => "Send a private message.",
        Method::MessageHistory => {
            "Private messages the daemon collected, including while nobody was attached."
        }
        Method::BrowseUser => {
            "Ask a peer for its share listing; it arrives as event.browse."
        }
        Method::UserRequest => {
            "Ask the server about a user; poll user.info for the answer."
        }
        Method::UserInfoOf => "What the server has said about a user so far.",
        Method::SharesStatusOf => "What the share index currently holds.",
        Method::SharesSet => "Replace the shared folders and re-index.",
        Method::SharesReindex => "Re-scan the configured folders.",
    }
}

/// The payload schema for one pushed event. Exhaustive, like the methods.
fn event_schema(event: Event, generator: &mut SchemaGenerator) -> Value {
    match event {
        Event::Room => schema_of::<RoomEventDto>(generator),
        Event::Message => schema_of::<UserMessageDto>(generator),
        Event::Upload => schema_of::<UploadInfoDto>(generator),
        Event::DownloadStatus => schema_of::<DownloadStatusEvent>(generator),
        Event::Browse => schema_of::<BrowseEvent>(generator),
        Event::SessionLoss => schema_of::<SessionLossEvent>(generator),
    }
}

fn event_summary(event: Event) -> &'static str {
    match event {
        Event::Room => "Something happened in a room this session has joined.",
        Event::Message => "A private message arrived.",
        Event::Upload => "An upload changed state.",
        Event::DownloadStatus => "A transfer moved.",
        Event::Browse => "A peer answered a browse request.",
        Event::SessionLoss => {
            "The server session was lost. A disconnected session is reconnected \
             on its own and events resume; a displaced one is terminal. Read \
             daemon.status for the live state."
        }
    }
}

/// Turn a params object schema into OpenRPC content descriptors — one per
/// field, which is what `by-name` means.
///
/// A single descriptor holding the whole struct would tell a generator to send
/// `{"params": {"params": {…}}}`, and every generated call would come back
/// `-32602`. The daemon deserializes the params object directly into the
/// struct, so each of its fields is a parameter in its own right.
fn descriptors(
    params: &Value,
    definitions: &serde_json::Map<String, Value>,
) -> Vec<Value> {
    let Some(schema) = resolve(params, definitions) else {
        return Vec::new();
    };
    let required: Vec<&str> = schema
        .get("required")
        .and_then(Value::as_array)
        .map(|names| names.iter().filter_map(Value::as_str).collect())
        .unwrap_or_default();

    schema
        .get("properties")
        .and_then(Value::as_object)
        .map(|properties| {
            properties
                .iter()
                .map(|(name, property)| {
                    json!({
                        "name": name,
                        "required": required.contains(&name.as_str()),
                        "schema": property,
                    })
                })
                .collect()
        })
        .unwrap_or_default()
}

/// Follow a `$ref` into the generated definitions.
fn resolve<'a>(
    schema: &'a Value,
    definitions: &'a serde_json::Map<String, Value>,
) -> Option<&'a Value> {
    let Some(reference) = schema.get("$ref").and_then(Value::as_str) else {
        return schema.get("properties").map(|_| schema);
    };
    definitions.get(reference.strip_prefix(DEFINITIONS_PATH)?)
}

/// Build the whole document.
fn document() -> Value {
    let settings = SchemaSettings::draft2020_12().with(|settings| {
        settings.definitions_path = DEFINITIONS_PATH.into();
    });
    let mut generator = SchemaGenerator::new(settings);

    // Schemas first, definitions second: a params schema is a `$ref` until the
    // generator has been asked for everything, and expanding it into
    // descriptors needs the definition it points at.
    let shapes: Vec<(Method, Value, Value)> = Method::ALL
        .iter()
        .map(|&method| {
            (
                method,
                params_schema(method, &mut generator),
                result_schema(method, &mut generator),
            )
        })
        .collect();
    let event_shapes: Vec<(Event, Value)> = Event::ALL
        .iter()
        .map(|&event| (event, event_schema(event, &mut generator)))
        .collect();

    let definitions: serde_json::Map<String, Value> =
        generator.take_definitions(true).into_iter().collect();

    let methods = shapes.into_iter().map(|(method, params, result)| {
        json!({
            "name": method.wire_name(),
            "summary": summary(method),
            "paramStructure": "by-name",
            "params": descriptors(&params, &definitions),
            "result": {
                "name": "result",
                "schema": result,
            },
        })
    });

    // OpenRPC has no first-class notion of a server-pushed notification, so
    // the events are published as methods flagged with an extension field.
    // A generator still emits their payload types; the delivery semantics are
    // prose in docs/daemon-protocol.md.
    let events = event_shapes.into_iter().map(|(event, payload)| {
        json!({
            "name": event.wire_name(),
            "summary": event_summary(event),
            "x-notification": true,
            "paramStructure": "by-name",
            // Unlike a method, an event's `params` object *is* the payload,
            // and several payloads are tagged enums with no single property
            // map to split. One descriptor carrying the whole schema is
            // what a generator needs to emit the type.
            "params": [{
                "name": "payload",
                "required": true,
                "schema": payload,
            }],
            "result": { "name": "result", "schema": { "type": "null" } },
        })
    });

    json!({
        "openrpc": "1.3.2",
        "info": {
            "title": "soulseek-rs daemon",
            // The contract's own version, which is what a client negotiates in
            // `auth`. The crate version would put a release bump in this file
            // and fail `document_is_current` on every release PR.
            "version": crate::daemon::proto::PROTOCOL_VERSION.to_string(),
            "description": "Control a running soulseek-rs daemon. Newline-delimited \
    JSON-RPC 2.0 over a Unix socket (local, authenticated by socket permissions) or \
    TCP (remote, authenticated by the token in <state-dir>/daemon.token). `auth` must \
    be the first request on a connection. Errors carry the CLI exit status in \
    `error.data.exit`. Entries marked `x-notification` are pushed by the daemon and \
    are never requested.",
            "license": { "name": "MIT" },
        },
        "methods": methods.into_iter().chain(events).collect::<Vec<_>>(),
        "components": { "schemas": definitions },
    })
}

/// Where the published document lives. Inside this crate, not the repository's
/// docs/: `include_str!` has to find it in the published package too.
fn document_path() -> std::path::PathBuf {
    std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
        .join("docs")
        .join("openrpc.json")
}

#[test]
fn document_is_current() {
    let generated = format!(
        "{}\n",
        serde_json::to_string_pretty(&document())
            .expect("the document is plain data")
    );

    let path = document_path();
    if std::env::var_os("UPDATE_OPENRPC").is_some() {
        std::fs::write(&path, &generated).expect("docs/ is writable");
        return;
    }

    let published = std::fs::read_to_string(&path).unwrap_or_default();
    assert_eq!(
        published, generated,
        "docs/openrpc.json is out of date with the wire types — regenerate it \
         with `UPDATE_OPENRPC=1 cargo test -p soulseek-rs openrpc`"
    );
}

#[test]
fn every_method_and_event_is_published() {
    let document = document();
    let published: Vec<&str> = document["methods"]
        .as_array()
        .expect("methods is an array")
        .iter()
        .map(|method| method["name"].as_str().expect("a name is a string"))
        .collect();

    for method in Method::ALL {
        assert!(
            published.contains(&method.wire_name()),
            "{method} is missing from the published contract"
        );
    }
    for event in Event::ALL {
        assert!(
            published.contains(&event.wire_name()),
            "{event} is missing from the published contract"
        );
    }
    assert_eq!(published.len(), Method::ALL.len() + Event::ALL.len());
}

/// The published parameters must be the keys the daemon actually reads.
///
/// This is the shape a generated client sends. Publishing the params struct as
/// one descriptor named `params` type-checks and generates cleanly, and every
/// call it produces fails `-32602`, because the client then sends
/// `{"params": {"params": {…}}}` where the daemon expects the inner object.
#[test]
fn published_parameters_are_the_keys_the_daemon_reads() {
    use super::proto::{QueryParams, RoomRef, TransferRef};

    let document = document();
    let published = |name: &str| -> Vec<String> {
        document["methods"]
            .as_array()
            .expect("methods is an array")
            .iter()
            .find(|method| method["name"] == name)
            .unwrap_or_else(|| panic!("{name} is published"))["params"]
            .as_array()
            .expect("params is an array")
            .iter()
            .map(|p| p["name"].as_str().expect("a name").to_string())
            .collect()
    };
    let keys = |value: &Value| -> Vec<String> {
        value
            .as_object()
            .expect("params serialize as an object")
            .keys()
            .cloned()
            .collect()
    };

    assert_eq!(
        published("room.join"),
        keys(
            &serde_json::to_value(RoomRef {
                room: "lobby".into()
            })
            .unwrap()
        )
    );
    assert_eq!(
        published("search.results"),
        keys(&serde_json::to_value(QueryParams { query: "x".into() }).unwrap())
    );
    assert_eq!(
        published("download.pause"),
        keys(
            &serde_json::to_value(TransferRef {
                username: "bob".into(),
                filename: "a.mp3".into()
            })
            .unwrap()
        )
    );
    assert!(
        published("daemon.status").is_empty(),
        "a method that takes nothing publishes no parameters"
    );
}

#[test]
fn a_wire_name_round_trips_through_its_enum() {
    for method in Method::ALL {
        assert_eq!(Method::from_wire(method.wire_name()), Some(*method));
    }
    for event in Event::ALL {
        assert_eq!(Event::from_wire(event.wire_name()), Some(*event));
    }
    assert_eq!(Method::from_wire("search.nope"), None);
}