aion-package 0.6.0

//! Gleam source emission for parsed schema artifacts.
//!
//! Emission is a pure function of the artifact list, so generation is
//! deterministic: same schemas in, byte-identical module out. The emitted
//! idioms mirror the hand-written codecs in the repository examples:
//! `json.object` / `json.array` encoders and `gleam/dynamic/decode`
//! use-chained decoders, with `decode.optional_field` + `decode.optional`
//! for optional properties (omitted from the wire when `None`).

use std::fmt::Write as _;

use super::schema::{EnumDef, Field, GleamType, RecordDef, SchemaArtifact, TypeDef};

/// Header line every generated module starts with (the do-not-edit contract).
pub(crate) const GENERATED_HEADER: &str =
    "//// Generated by aion codegen — do not edit; regenerate from schemas/.";

/// Renders the complete generated module for `artifacts` (already in
/// deterministic schema-file order).
pub(crate) fn emit_module(project_name: &str, artifacts: &[SchemaArtifact]) -> String {
    let has_optionals = artifacts.iter().any(|artifact| {
        artifact.defs.iter().any(|def| match def {
            TypeDef::Record(record) => record.fields.iter().any(|field| !field.required),
            TypeDef::Enum(_) => false,
        })
    });

    let mut out = String::new();
    let _ = writeln!(out, "{GENERATED_HEADER}");
    out.push_str("////\n");
    let _ = writeln!(
        out,
        "//// Types and JSON codecs for the `{project_name}` workflow project,"
    );
    out.push_str("//// derived from every `schemas/*.json` document in filename order.\n");
    out.push('\n');
    out.push_str("import gleam/dynamic/decode\n");
    out.push_str("import gleam/json\n");
    if has_optionals {
        out.push_str("import gleam/list\n");
        out.push_str("import gleam/option\n");
    }

    for artifact in artifacts {
        if !matches!(artifact.root, GleamType::Named { .. }) {
            emit_root_wrapper(&mut out, artifact);
        }
        for def in &artifact.defs {
            match def {
                TypeDef::Record(record) => emit_record(&mut out, artifact, record),
                TypeDef::Enum(definition) => emit_enum(&mut out, artifact, definition),
            }
        }
    }
    out
}

/// `schemas/output.json` documents whose root is not an object or enum still
/// get a `<stem>_to_json` / `<stem>_decoder` pair for the payload itself.
fn emit_root_wrapper(out: &mut String, artifact: &SchemaArtifact) {
    let file = artifact.file.display();
    let stem = &artifact.stem;
    let ty = type_text(&artifact.root);
    let _ = write!(
        out,
        "\n/// Encodes the `{file}` payload as schema-shaped JSON.\n\
         pub fn {stem}_to_json(value: {ty}) -> json.Json {{\n  {}\n}}\n",
        encode_call(&artifact.root, "value", 0)
    );
    let _ = write!(
        out,
        "\n/// Decoder for the `{file}` payload.\n\
         pub fn {stem}_decoder() -> decode.Decoder({ty}) {{\n  {}\n}}\n",
        decoder_expr(&artifact.root)
    );
}

fn origin(artifact: &SchemaArtifact, pointer: &str) -> String {
    if pointer.is_empty() {
        format!("`{}`", artifact.file.display())
    } else {
        format!("`{}` at `{pointer}`", artifact.file.display())
    }
}

fn emit_record(out: &mut String, artifact: &SchemaArtifact, record: &RecordDef) {
    let name = &record.type_name;
    let prefix = &record.fn_prefix;
    let source = origin(artifact, &record.pointer);

    // Type declaration.
    let _ = write!(out, "\n/// Generated from {source}.\npub type {name} {{\n");
    if record.fields.is_empty() {
        let _ = writeln!(out, "  {name}");
    } else {
        let _ = writeln!(out, "  {name}(");
        for field in &record.fields {
            let _ = writeln!(out, "    {}: {},", field.wire, field_type_text(field));
        }
        out.push_str("  )\n");
    }
    out.push_str("}\n");

    // Encoder.
    let _ = write!(
        out,
        "\n/// Encodes `{name}` as schema-shaped JSON; optional fields are\n\
         /// omitted when `None`.\n\
         pub fn {prefix}_to_json(value: {name}) -> json.Json {{\n"
    );
    if record.fields.iter().all(|field| field.required) {
        out.push_str("  json.object([\n");
        for field in &record.fields {
            let _ = writeln!(out, "    {},", field_pair(field));
        }
        out.push_str("  ])\n");
    } else {
        out.push_str("  json.object(\n    list.flatten([\n");
        for field in &record.fields {
            if field.required {
                let _ = writeln!(out, "      [{}],", field_pair(field));
            } else {
                let _ = writeln!(out, "      case value.{} {{", field.wire);
                let _ = writeln!(
                    out,
                    "        option.Some(present) -> [#(\"{}\", {})]",
                    field.wire,
                    encode_call(&field.ty, "present", 0)
                );
                out.push_str("        option.None -> []\n      },\n");
            }
        }
        out.push_str("    ]),\n  )\n");
    }
    out.push_str("}\n");

    // Decoder. Bindings are hygienic (`field_<wire>`): a raw `use <wire>`
    // binding for a property named `decode` or `option` would shadow the
    // generated imports for the rest of the decoder and fail `gleam build`.
    let _ = write!(
        out,
        "\n/// Decoder for `{name}` from schema-shaped JSON.\n\
         pub fn {prefix}_decoder() -> decode.Decoder({name}) {{\n"
    );
    for field in &record.fields {
        if field.required {
            let _ = writeln!(
                out,
                "  use field_{wire} <- decode.field(\"{wire}\", {})",
                decoder_expr(&field.ty),
                wire = field.wire,
            );
        } else {
            let _ = writeln!(
                out,
                "  use field_{wire} <- decode.optional_field(\n    \"{wire}\",\n    \
                 option.None,\n    decode.optional({}),\n  )",
                decoder_expr(&field.ty),
                wire = field.wire,
            );
        }
    }
    if record.fields.is_empty() {
        let _ = writeln!(out, "  decode.success({name})");
    } else {
        let _ = writeln!(out, "  decode.success({name}(");
        for field in &record.fields {
            let _ = writeln!(out, "    {wire}: field_{wire},", wire = field.wire);
        }
        out.push_str("  ))\n");
    }
    out.push_str("}\n");
}

fn emit_enum(out: &mut String, artifact: &SchemaArtifact, definition: &EnumDef) {
    // `parse_schema` rejects empty enums, so an `EnumDef` always has a first
    // variant (needed below as the `decode.failure` placeholder). Were the
    // invariant ever broken, the missing type would fail `gleam build`
    // loudly rather than panic here.
    let Some(first_variant) = definition.variants.first() else {
        return;
    };
    let name = &definition.type_name;
    let prefix = &definition.fn_prefix;
    let source = origin(artifact, &definition.pointer);

    let _ = write!(out, "\n/// Generated from {source}.\npub type {name} {{\n");
    for variant in &definition.variants {
        let _ = writeln!(out, "  {}", variant.constructor);
    }
    out.push_str("}\n");

    let _ = write!(
        out,
        "\n/// Encodes `{name}` as its wire string.\n\
         pub fn {prefix}_to_json(value: {name}) -> json.Json {{\n  case value {{\n"
    );
    for variant in &definition.variants {
        let _ = writeln!(
            out,
            "    {} -> json.string(\"{}\")",
            variant.constructor, variant.wire
        );
    }
    out.push_str("  }\n}\n");

    let _ = write!(
        out,
        "\n/// Decoder for `{name}` from its wire string.\n\
         pub fn {prefix}_decoder() -> decode.Decoder({name}) {{\n  \
         decode.then(decode.string, fn(raw) {{\n    case raw {{\n"
    );
    for variant in &definition.variants {
        let _ = writeln!(
            out,
            "      \"{}\" -> decode.success({})",
            variant.wire, variant.constructor
        );
    }
    let _ = writeln!(
        out,
        "      _ -> decode.failure({}, \"{name}\")",
        first_variant.constructor
    );
    out.push_str("    }\n  })\n}\n");
}

/// `#("wire", <encoded value.field>)` for a required field.
fn field_pair(field: &Field) -> String {
    format!(
        "#(\"{wire}\", {})",
        encode_call(&field.ty, &format!("value.{}", field.wire), 0),
        wire = field.wire,
    )
}

/// The Gleam type annotation for a field, wrapping optionals.
fn field_type_text(field: &Field) -> String {
    let inner = type_text(&field.ty);
    if field.required {
        inner
    } else {
        format!("option.Option({inner})")
    }
}

fn type_text(ty: &GleamType) -> String {
    match ty {
        GleamType::String => "String".to_owned(),
        GleamType::Int => "Int".to_owned(),
        GleamType::Float => "Float".to_owned(),
        GleamType::Bool => "Bool".to_owned(),
        GleamType::List(inner) => format!("List({})", type_text(inner)),
        GleamType::Named { type_name, .. } => type_name.clone(),
    }
}

/// An applied encoder expression for `expr` of type `ty`.
fn encode_call(ty: &GleamType, expr: &str, depth: usize) -> String {
    match ty {
        GleamType::String => format!("json.string({expr})"),
        GleamType::Int => format!("json.int({expr})"),
        GleamType::Float => format!("json.float({expr})"),
        GleamType::Bool => format!("json.bool({expr})"),
        GleamType::List(inner) => format!("json.array({expr}, {})", encode_fn(inner, depth)),
        GleamType::Named { fn_prefix, .. } => format!("{fn_prefix}_to_json({expr})"),
    }
}

/// A point-free (or lambda, for nested lists) encoder function for `ty`.
fn encode_fn(ty: &GleamType, depth: usize) -> String {
    match ty {
        GleamType::String => "json.string".to_owned(),
        GleamType::Int => "json.int".to_owned(),
        GleamType::Float => "json.float".to_owned(),
        GleamType::Bool => "json.bool".to_owned(),
        GleamType::List(inner) => {
            let var = format!("items{depth}");
            format!(
                "fn({var}) {{ json.array({var}, {}) }}",
                encode_fn(inner, depth + 1)
            )
        }
        GleamType::Named { fn_prefix, .. } => format!("{fn_prefix}_to_json"),
    }
}

/// A decoder expression for `ty`.
fn decoder_expr(ty: &GleamType) -> String {
    match ty {
        GleamType::String => "decode.string".to_owned(),
        GleamType::Int => "decode.int".to_owned(),
        GleamType::Float => "decode.float".to_owned(),
        GleamType::Bool => "decode.bool".to_owned(),
        GleamType::List(inner) => format!("decode.list({})", decoder_expr(inner)),
        GleamType::Named { fn_prefix, .. } => format!("{fn_prefix}_decoder()"),
    }
}

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

    use super::{GENERATED_HEADER, emit_module};
    use crate::codegen::json::parse_ordered;
    use crate::codegen::names::NameRegistry;
    use crate::codegen::schema::{SchemaArtifact, parse_schema};

    type TestResult = Result<(), Box<dyn std::error::Error>>;

    fn artifact(stem: &str, json: &str, registry: &mut NameRegistry) -> TestResult2 {
        let document = parse_ordered(json.as_bytes())?;
        Ok(parse_schema(
            Path::new(&format!("schemas/{stem}.json")),
            stem,
            &document,
            registry,
        )?)
    }

    type TestResult2 = Result<SchemaArtifact, Box<dyn std::error::Error>>;

    #[test]
    fn full_module_golden_with_enum_array_and_optional() -> TestResult {
        let mut registry = NameRegistry::default();
        let artifacts = vec![artifact(
            "event",
            r#"{
                "type": "object",
                "required": ["kind", "tags"],
                "additionalProperties": false,
                "properties": {
                    "kind": { "type": "string", "enum": ["created", "closed_out"] },
                    "tags": { "type": "array", "items": { "type": "string" } },
                    "note": { "type": "string" }
                }
            }"#,
            &mut registry,
        )?];

        let expected = r#"//// Generated by aion codegen — do not edit; regenerate from schemas/.
////
//// Types and JSON codecs for the `demo` workflow project,
//// derived from every `schemas/*.json` document in filename order.

import gleam/dynamic/decode
import gleam/json
import gleam/list
import gleam/option

/// Generated from `schemas/event.json`.
pub type Event {
  Event(
    kind: EventKind,
    tags: List(String),
    note: option.Option(String),
  )
}

/// Encodes `Event` as schema-shaped JSON; optional fields are
/// omitted when `None`.
pub fn event_to_json(value: Event) -> json.Json {
  json.object(
    list.flatten([
      [#("kind", event_kind_to_json(value.kind))],
      [#("tags", json.array(value.tags, json.string))],
      case value.note {
        option.Some(present) -> [#("note", json.string(present))]
        option.None -> []
      },
    ]),
  )
}

/// Decoder for `Event` from schema-shaped JSON.
pub fn event_decoder() -> decode.Decoder(Event) {
  use field_kind <- decode.field("kind", event_kind_decoder())
  use field_tags <- decode.field("tags", decode.list(decode.string))
  use field_note <- decode.optional_field(
    "note",
    option.None,
    decode.optional(decode.string),
  )
  decode.success(Event(
    kind: field_kind,
    tags: field_tags,
    note: field_note,
  ))
}

/// Generated from `schemas/event.json` at `/properties/kind`.
pub type EventKind {
  EventKindCreated
  EventKindClosedOut
}

/// Encodes `EventKind` as its wire string.
pub fn event_kind_to_json(value: EventKind) -> json.Json {
  case value {
    EventKindCreated -> json.string("created")
    EventKindClosedOut -> json.string("closed_out")
  }
}

/// Decoder for `EventKind` from its wire string.
pub fn event_kind_decoder() -> decode.Decoder(EventKind) {
  decode.then(decode.string, fn(raw) {
    case raw {
      "created" -> decode.success(EventKindCreated)
      "closed_out" -> decode.success(EventKindClosedOut)
      _ -> decode.failure(EventKindCreated, "EventKind")
    }
  })
}
"#;
        assert_eq!(emit_module("demo", &artifacts), expected);
        Ok(())
    }

    #[test]
    fn scalar_root_emits_payload_wrappers_without_optional_imports() -> TestResult {
        let mut registry = NameRegistry::default();
        let artifacts = vec![artifact(
            "output",
            r#"{ "type": "string" }"#,
            &mut registry,
        )?];

        let module = emit_module("demo", &artifacts);
        assert!(module.starts_with(GENERATED_HEADER));
        assert!(!module.contains("import gleam/list"));
        assert!(!module.contains("import gleam/option"));
        assert!(module.contains(
            "/// Encodes the `schemas/output.json` payload as schema-shaped JSON.\n\
             pub fn output_to_json(value: String) -> json.Json {\n  json.string(value)\n}\n"
        ));
        assert!(module.contains(
            "/// Decoder for the `schemas/output.json` payload.\n\
             pub fn output_decoder() -> decode.Decoder(String) {\n  decode.string\n}\n"
        ));
        Ok(())
    }

    #[test]
    fn all_required_records_use_plain_object_lists() -> TestResult {
        let mut registry = NameRegistry::default();
        let artifacts = vec![artifact(
            "pair",
            r#"{
                "type": "object",
                "required": ["count", "ratio", "flag"],
                "properties": {
                    "count": { "type": "integer" },
                    "ratio": { "type": "number" },
                    "flag": { "type": "boolean" }
                }
            }"#,
            &mut registry,
        )?];

        let module = emit_module("demo", &artifacts);
        assert!(module.contains(
            "pub fn pair_to_json(value: Pair) -> json.Json {\n  json.object([\n    \
             #(\"count\", json.int(value.count)),\n    \
             #(\"ratio\", json.float(value.ratio)),\n    \
             #(\"flag\", json.bool(value.flag)),\n  ])\n}\n"
        ));
        assert!(module.contains("use field_count <- decode.field(\"count\", decode.int)\n"));
        assert!(!module.contains("list.flatten"));
        Ok(())
    }

    #[test]
    fn nested_lists_encode_with_depth_named_lambdas() -> TestResult {
        let mut registry = NameRegistry::default();
        let artifacts = vec![artifact(
            "grid",
            r#"{
                "type": "object",
                "required": ["matrix"],
                "properties": {
                    "matrix": {
                        "type": "array",
                        "items": { "type": "array", "items": { "type": "integer" } }
                    }
                }
            }"#,
            &mut registry,
        )?];

        let module = emit_module("demo", &artifacts);
        assert!(module.contains(
            "#(\"matrix\", json.array(value.matrix, fn(items0) { json.array(items0, json.int) }))"
        ));
        assert!(module.contains(
            "use field_matrix <- decode.field(\"matrix\", decode.list(decode.list(decode.int)))"
        ));
        assert!(module.contains("matrix: List(List(Int)),"));
        Ok(())
    }

    #[test]
    fn empty_records_emit_bare_constructors() -> TestResult {
        let mut registry = NameRegistry::default();
        let artifacts = vec![artifact(
            "blank",
            r#"{ "type": "object", "required": [], "properties": {} }"#,
            &mut registry,
        )?];

        let module = emit_module("demo", &artifacts);
        assert!(module.contains("pub type Blank {\n  Blank\n}\n"));
        assert!(module.contains("json.object([\n  ])"));
        assert!(module.contains("decode.success(Blank)\n"));
        Ok(())
    }

    #[test]
    fn emission_is_deterministic() -> TestResult {
        let schema = r#"{
            "type": "object",
            "required": ["kind"],
            "properties": {
                "kind": { "enum": ["a", "b"] },
                "note": { "type": "string" }
            }
        }"#;
        let mut first_registry = NameRegistry::default();
        let first = emit_module("demo", &[artifact("event", schema, &mut first_registry)?]);
        let mut second_registry = NameRegistry::default();
        let second = emit_module("demo", &[artifact("event", schema, &mut second_registry)?]);

        assert_eq!(first, second);
        Ok(())
    }
}