aion-package 0.9.1

//! Emission of the generated Rust remote-worker module (tier = `RemoteRust`).
//!
//! Generates `worker/src/main.rs`, the do-not-edit plumbing that serves a
//! package's `RemoteRust` activities: the `serde` input/output structs and
//! enums derived from the schemas, the env-driven [`WorkerConfig`], and the
//! `register_activity` chain binding each engine activity name to the matching
//! author-written handler in the hand-written `handlers` module. The worker
//! never carries an activity body — the author fills `worker/src/handlers.rs`
//! with one `fn <name>(input, &ActivityContext) -> HandlerFuture<'_, Output>`
//! per activity, exactly as the generated Gleam wrapper references
//! `activities.<name>`. Because the body lives elsewhere, the generated file is
//! a pure, deterministic function of the declarations and schemas, so
//! `aion generate --check` can byte-compare it and a hand-edit is a build
//! failure (checklist C4).
//!
//! No retry/timeout/backoff for an *activity* is ever emitted (ADR-001); the
//! only values present are the worker's own gRPC connection parameters. Every
//! required connection value is read from the environment and the worker fails
//! loud (returns an error naming the variable) if one is unset or unparseable —
//! no invented default string or number is ever emitted (ADR-001). Reading from
//! the environment also keeps the do-not-edit file byte-stable across hosts,
//! mirroring the committed `examples/order-saga` worker.

use std::collections::HashSet;
use std::fmt::Write as _;

use super::activity_model::ResolvedActivity;
use super::model::{EnumDef, Field, GleamType, RecordDef, TypeDef};

/// Rust do-not-edit banner. A plain module-doc line; `aion generate --check`
/// byte-compares the whole file, so the banner is the contract, not a parsed
/// marker.
const RUST_HEADER: &str =
    "//! Generated by aion generate — do not edit; regenerate from the activity declarations.";

/// Emits `worker/src/main.rs` serving `activities` (all `RemoteRust`), in
/// declaration order. Every input and output value type becomes one `serde`
/// struct or enum (deduplicated by type name, first use wins), and each
/// activity is registered against `handlers::<name>`.
pub(crate) fn emit(package_name: &str, activities: &[&ResolvedActivity]) -> String {
    let mut out = String::new();
    out.push_str(RUST_HEADER);
    let _ = write!(
        out,
        "\n//!\n//! Remote Rust worker for the `{package_name}` package. Serves its `RemoteRust`\n\
         //! activities; the side-effecting bodies live in `handlers.rs`, which this module\n\
         //! dispatches to. Configure the connection through the `AION_WORKER_*` and\n\
         //! `AION_RECONNECT_*` environment variables.\n\n"
    );
    out.push_str("use std::time::Duration;\n\n");
    // Only `Worker`/`WorkerConfig` are used here; the handler signature types
    // (`ActivityContext`, `HandlerFuture`) are imported by the hand-written
    // `handlers.rs`, so importing them here would be an unused-import error
    // under `-D warnings`.
    out.push_str("use aion_worker::{Worker, WorkerConfig};\n");
    out.push_str("use serde::{Deserialize, Serialize};\n\n");
    out.push_str("mod handlers;\n");

    for def in ordered_type_defs(activities) {
        match def {
            TypeDef::Record(record) => emit_struct(&mut out, record),
            TypeDef::Enum(definition) => emit_enum(&mut out, definition),
        }
    }

    emit_main(&mut out, activities);
    out
}

/// Collects the input and output value types of every activity as a
/// deterministic, deduplicated, parent-before-child sequence of type
/// definitions: declaration order, input before output, first occurrence wins.
/// Type names are globally unique (the schema name registry guarantees it), so
/// deduplicating by name is sound.
fn ordered_type_defs<'a>(activities: &[&'a ResolvedActivity<'a>]) -> Vec<&'a TypeDef> {
    let mut seen: HashSet<&str> = HashSet::new();
    let mut defs: Vec<&TypeDef> = Vec::new();
    for activity in activities {
        for boundary in [activity.input.boundary, activity.output.boundary] {
            for def in &boundary.defs {
                if seen.insert(def.type_name()) {
                    defs.push(def);
                }
            }
        }
    }
    defs
}

/// Emits a `serde` struct for a record. Optional fields become `Option<T>` and
/// are omitted from the wire when `None`, matching the Gleam codec.
fn emit_struct(out: &mut String, record: &RecordDef) {
    let _ = write!(
        out,
        "\n#[derive(Clone, Debug, Serialize, Deserialize)]\npub struct {} {{",
        record.type_name
    );
    if record.fields.is_empty() {
        out.push_str("}\n");
        return;
    }
    out.push('\n');
    for field in &record.fields {
        emit_struct_field(out, field);
    }
    out.push_str("}\n");
}

/// Emits one struct field with any required `serde` attributes.
fn emit_struct_field(out: &mut String, field: &Field) {
    let (ident, renamed) = rust_field_ident(&field.wire);
    let mut attrs: Vec<String> = Vec::new();
    if renamed {
        attrs.push(format!("rename = \"{}\"", field.wire));
    }
    if !field.required {
        attrs.push("default".to_owned());
        attrs.push("skip_serializing_if = \"Option::is_none\"".to_owned());
    }
    if !attrs.is_empty() {
        let _ = writeln!(out, "    #[serde({})]", attrs.join(", "));
    }
    let ty = rust_type(&field.ty);
    let ty = if field.required {
        ty
    } else {
        format!("Option<{ty}>")
    };
    let _ = writeln!(out, "    pub {ident}: {ty},");
}

/// Emits a `serde` enum whose unit variants carry their wire string.
fn emit_enum(out: &mut String, definition: &EnumDef) {
    let _ = write!(
        out,
        "\n#[derive(Clone, Debug, Serialize, Deserialize)]\npub enum {} {{\n",
        definition.type_name
    );
    for variant in &definition.variants {
        let _ = writeln!(out, "    #[serde(rename = \"{}\")]", variant.wire);
        let _ = writeln!(out, "    {},", variant.constructor);
    }
    out.push_str("}\n");
}

/// Renders the `#[tokio::main]` entry point: the env-driven config and the
/// `register_activity` chain in declaration order, followed by the two
/// fail-loud environment helpers it uses. Every required connection value is
/// read from the environment with no invented fallback (ADR-001); a missing or
/// unparseable variable is surfaced as an error naming the variable.
fn emit_main(out: &mut String, activities: &[&ResolvedActivity]) {
    out.push_str("\n#[tokio::main]\nasync fn main() -> Result<(), Box<dyn std::error::Error>> {\n");
    out.push_str("    let config = WorkerConfig::builder()\n");
    out.push_str("        .endpoint(require_var(\"AION_WORKER_ENDPOINT\")?)\n");
    out.push_str("        .task_queue(require_var(\"AION_TASK_QUEUE\")?)\n");
    out.push_str("        .identity(require_var(\"AION_WORKER_IDENTITY\")?)\n");
    out.push_str("        .max_concurrency(require_parse(\"AION_WORKER_CONCURRENCY\")?)\n");
    out.push_str(
        "        .reconnect_initial_backoff(Duration::from_secs_f64(require_parse(\n            \
         \"AION_RECONNECT_INITIAL_BACKOFF_SECONDS\",\n        )?))\n",
    );
    out.push_str(
        "        .reconnect_max_backoff(Duration::from_secs_f64(require_parse(\n            \
         \"AION_RECONNECT_MAX_BACKOFF_SECONDS\",\n        )?))\n",
    );
    out.push_str(
        "        .reconnect_max_attempts(require_parse(\"AION_RECONNECT_MAX_ATTEMPTS\")?)\n",
    );
    out.push_str("        .build()?;\n\n");

    out.push_str("    Worker::builder(config)\n");
    for activity in activities {
        let name = &activity.declaration.name;
        let _ = writeln!(
            out,
            "        .register_activity(\"{name}\", handlers::{name})?"
        );
    }
    out.push_str("        .build()?\n        .run()\n        .await?;\n\n    Ok(())\n}\n");

    emit_env_helpers(out);
}

/// Emits the two fail-loud environment helpers the generated `main` uses to
/// read every required connection value. `require_var` errors when a variable
/// is unset; `require_parse` additionally errors when the value fails to parse
/// into the target type. Both name the offending variable in the error. They
/// are always referenced by `main`, so no dead-code warning arises.
fn emit_env_helpers(out: &mut String) {
    out.push_str(
        "\n/// Reads a required environment variable, erroring if it is unset.\n\
         fn require_var(name: &str) -> Result<String, Box<dyn std::error::Error>> {\n    \
         std::env::var(name)\n        \
         .map_err(|_| format!(\"required environment variable `{name}` is not set\").into())\n\
         }\n",
    );
    out.push_str(
        "\n/// Reads and parses a required environment variable.\n\
         fn require_parse<T>(name: &str) -> Result<T, Box<dyn std::error::Error>>\n\
         where\n    \
         T: std::str::FromStr,\n    \
         T::Err: std::fmt::Display,\n\
         {\n    \
         require_var(name)?\n        \
         .parse::<T>()\n        \
         .map_err(|error| format!(\"environment variable `{name}` is invalid: {error}\").into())\n\
         }\n",
    );
}

/// Maps a Gleam type to its Rust representation.
fn rust_type(ty: &GleamType) -> String {
    match ty {
        GleamType::String => "String".to_owned(),
        GleamType::Int => "i64".to_owned(),
        GleamType::Float => "f64".to_owned(),
        GleamType::Bool => "bool".to_owned(),
        GleamType::List(inner) => format!("Vec<{}>", rust_type(inner)),
        GleamType::Named { type_name, .. } => type_name.clone(),
    }
}

/// Maps a wire field name to a valid Rust field identifier, returning whether a
/// `#[serde(rename)]` is needed to recover the wire name. Wire names are
/// `[a-z][a-z0-9_]*`, so the only collisions are with Rust keywords:
/// `self`/`crate`/`super` cannot be raw identifiers and are mangled with a
/// trailing underscore (needing a rename); every other keyword takes the raw
/// form `r#name`, which `serde` serializes without the prefix (no rename).
fn rust_field_ident(wire: &str) -> (String, bool) {
    if matches!(wire, "self" | "crate" | "super") {
        (format!("{wire}_"), true)
    } else if is_rust_keyword(wire) {
        (format!("r#{wire}"), false)
    } else {
        (wire.to_owned(), false)
    }
}

/// Whether a lowercase wire name collides with a Rust strict or reserved
/// keyword. `Self` is excluded: wire names never start with an uppercase
/// letter.
fn is_rust_keyword(word: &str) -> bool {
    matches!(
        word,
        "as" | "break"
            | "const"
            | "continue"
            | "crate"
            | "else"
            | "enum"
            | "extern"
            | "false"
            | "fn"
            | "for"
            | "if"
            | "impl"
            | "in"
            | "let"
            | "loop"
            | "match"
            | "mod"
            | "move"
            | "mut"
            | "pub"
            | "ref"
            | "return"
            | "self"
            | "static"
            | "struct"
            | "super"
            | "trait"
            | "true"
            | "type"
            | "unsafe"
            | "use"
            | "where"
            | "while"
            | "async"
            | "await"
            | "dyn"
            | "abstract"
            | "become"
            | "box"
            | "do"
            | "final"
            | "macro"
            | "override"
            | "priv"
            | "typeof"
            | "unsized"
            | "virtual"
            | "yield"
            | "try"
    )
}

#[cfg(test)]
mod tests {
    use std::path::PathBuf;

    use super::{emit, is_rust_keyword, rust_field_ident, rust_type};
    use crate::codegen::activity_model::{ResolvedActivity, ResolvedType};
    use crate::codegen::declaration::{ActivityDeclaration, Tier};
    use crate::codegen::model::{
        BoundaryType, EnumDef, EnumVariant, Field, GleamType, RecordDef, TypeDef,
    };

    fn record(type_name: &str, fields: Vec<Field>) -> BoundaryType {
        BoundaryType {
            file: PathBuf::from(format!("schemas/{}.json", type_name.to_lowercase())),
            stem: type_name.to_lowercase(),
            root: GleamType::Named {
                type_name: type_name.to_owned(),
                fn_prefix: type_name.to_lowercase(),
            },
            defs: vec![TypeDef::Record(RecordDef {
                type_name: type_name.to_owned(),
                fn_prefix: type_name.to_lowercase(),
                fields,
            })],
        }
    }

    fn field(wire: &str, ty: GleamType, required: bool) -> Field {
        Field {
            wire: wire.to_owned(),
            ty,
            required,
        }
    }

    fn declaration(name: &str, input: &str, output: &str) -> ActivityDeclaration {
        ActivityDeclaration {
            name: name.to_owned(),
            tier: Tier::RemoteRust,
            input_type: input.to_owned(),
            output_type: output.to_owned(),
        }
    }

    fn resolved<'a>(
        declaration: &'a ActivityDeclaration,
        input: &'a BoundaryType,
        output: &'a BoundaryType,
    ) -> ResolvedActivity<'a> {
        ResolvedActivity {
            declaration,
            input: ResolvedType {
                gleam_type: declaration.input_type.clone(),
                fn_prefix: declaration.input_type.to_lowercase(),
                boundary: input,
            },
            output: ResolvedType {
                gleam_type: declaration.output_type.clone(),
                fn_prefix: declaration.output_type.to_lowercase(),
                boundary: output,
            },
        }
    }

    #[test]
    fn type_mapping_covers_every_scalar_list_and_named() {
        assert_eq!(rust_type(&GleamType::String), "String");
        assert_eq!(rust_type(&GleamType::Int), "i64");
        assert_eq!(rust_type(&GleamType::Float), "f64");
        assert_eq!(rust_type(&GleamType::Bool), "bool");
        assert_eq!(
            rust_type(&GleamType::List(Box::new(GleamType::List(Box::new(
                GleamType::Int
            ))))),
            "Vec<Vec<i64>>"
        );
        assert_eq!(
            rust_type(&GleamType::Named {
                type_name: "OrderInput".to_owned(),
                fn_prefix: "order_input".to_owned(),
            }),
            "OrderInput"
        );
    }

    #[test]
    fn keyword_field_names_are_escaped_or_mangled() {
        assert_eq!(rust_field_ident("order_id"), ("order_id".to_owned(), false));
        assert_eq!(rust_field_ident("type"), ("r#type".to_owned(), false));
        assert_eq!(rust_field_ident("match"), ("r#match".to_owned(), false));
        assert_eq!(rust_field_ident("self"), ("self_".to_owned(), true));
        assert_eq!(rust_field_ident("crate"), ("crate_".to_owned(), true));
        assert!(is_rust_keyword("move") && !is_rust_keyword("item"));
    }

    #[test]
    fn worker_emits_structs_registration_and_config_in_order() {
        let order = record(
            "OrderInput",
            vec![
                field("order_id", GleamType::String, true),
                field("quantity", GleamType::Int, true),
                field("note", GleamType::String, false),
            ],
        );
        let receipt = record(
            "Receipt",
            vec![field("payment_id", GleamType::String, true)],
        );
        let shipment = record(
            "Shipment",
            vec![field("shipment_id", GleamType::String, true)],
        );
        let charge = declaration("charge_payment", "OrderInput", "Receipt");
        let ship = declaration("ship_order", "OrderInput", "Shipment");
        let activities = [
            resolved(&charge, &order, &receipt),
            resolved(&ship, &order, &shipment),
        ];
        let refs: Vec<&ResolvedActivity> = activities.iter().collect();

        let module = emit("order_saga", &refs);

        assert!(module.starts_with(super::RUST_HEADER));
        // Imports must be exactly what the module uses — an unused import is a
        // hard error under `-D warnings`. The handler-signature types belong to
        // the hand-written `handlers.rs`, so they must not appear here.
        assert!(module.contains("use aion_worker::{Worker, WorkerConfig};"));
        assert!(
            !module.contains("ActivityContext") && !module.contains("HandlerFuture"),
            "generated worker must not import handler-signature types it never names"
        );
        assert!(module.contains("mod handlers;\n"));
        // OrderInput shared by both activities → emitted once, before Receipt.
        assert_eq!(module.matches("pub struct OrderInput").count(), 1);
        let order_at = module.find("pub struct OrderInput");
        let receipt_at = module.find("pub struct Receipt");
        let shipment_at = module.find("pub struct Shipment");
        assert!(order_at.is_some() && receipt_at.is_some() && shipment_at.is_some());
        assert!(order_at < receipt_at && receipt_at < shipment_at);
        // Required scalar, then the optional field with omit-on-None.
        assert!(module.contains("    pub order_id: String,\n"));
        assert!(module.contains("    pub quantity: i64,\n"));
        assert!(module.contains(
            "    #[serde(default, skip_serializing_if = \"Option::is_none\")]\n    pub note: Option<String>,\n"
        ));
        // Registration chain in declaration order, dispatching to handlers.
        assert!(
            module.contains(".register_activity(\"charge_payment\", handlers::charge_payment)?")
        );
        assert!(module.contains(".register_activity(\"ship_order\", handlers::ship_order)?"));
        let charge_at = module.find("charge_payment\", handlers");
        let ship_at = module.find("ship_order\", handlers");
        assert!(charge_at < ship_at);
        // Env-driven config; every required connection value is read fail-loud
        // through the helpers, with no invented default (ADR-001).
        assert!(module.contains(".endpoint(require_var(\"AION_WORKER_ENDPOINT\")?)"));
        assert!(module.contains(".task_queue(require_var(\"AION_TASK_QUEUE\")?)"));
        assert!(module.contains(".identity(require_var(\"AION_WORKER_IDENTITY\")?)"));
        assert!(module.contains(".max_concurrency(require_parse(\"AION_WORKER_CONCURRENCY\")?)"));
        assert!(module.contains("require_parse(\"AION_RECONNECT_MAX_ATTEMPTS\")?"));
        assert!(module.contains("\"AION_RECONNECT_INITIAL_BACKOFF_SECONDS\""));
        assert!(module.contains("\"AION_RECONNECT_MAX_BACKOFF_SECONDS\""));
        // The fail-loud helpers must be emitted and used.
        assert!(module.contains("fn require_var(name: &str)"));
        assert!(module.contains("fn require_parse<T>(name: &str)"));
        // No invented connection default anywhere — not an `unwrap_or` in sight,
        // nor a hardcoded reconnect literal (ADR-001).
        assert!(
            !module.contains("unwrap_or"),
            "generated worker must invent no connection default (ADR-001)"
        );
        assert!(
            !module.contains("Duration::from_secs(5)")
                && !module.contains("Duration::from_millis(500)"),
            "reconnect values must not be hardcoded"
        );
    }

    #[test]
    fn enums_and_keyword_fields_render_with_serde_attrs() {
        let mut tier = record(
            "Job",
            vec![
                field("order_id", GleamType::String, true),
                field("type", GleamType::String, true),
            ],
        );
        // Append an enum def to the same artifact so the worker emits it.
        tier.defs.push(TypeDef::Enum(EnumDef {
            type_name: "JobKind".to_owned(),
            fn_prefix: "job_kind".to_owned(),
            variants: vec![
                EnumVariant {
                    constructor: "JobKindFast".to_owned(),
                    wire: "fast".to_owned(),
                },
                EnumVariant {
                    constructor: "JobKindSlowRun".to_owned(),
                    wire: "slow_run".to_owned(),
                },
            ],
        }));
        let out = record("Done", vec![field("ok", GleamType::Bool, true)]);
        let run = declaration("run_job", "Job", "Done");
        let activities = [resolved(&run, &tier, &out)];
        let refs: Vec<&ResolvedActivity> = activities.iter().collect();

        let module = emit("demo", &refs);

        // Keyword field escaped to a raw identifier; serde recovers the wire
        // name without an explicit rename.
        assert!(module.contains("    pub r#type: String,\n"));
        assert!(!module.contains("rename = \"type\""));
        // Enum with renamed unit variants.
        assert!(module.contains("pub enum JobKind {"));
        assert!(module.contains("    #[serde(rename = \"fast\")]\n    JobKindFast,\n"));
        assert!(module.contains("    #[serde(rename = \"slow_run\")]\n    JobKindSlowRun,\n"));
    }
}