map-code-to-event-model

name	map-code-to-event-model
description	Extract commands, events, and projections from TypeScript DcbDecider and Projection source files and produce a spreadsheet-style Markdown table with cell references, formulas, and a Mermaid diagram. Use when the user wants to derive an event model table from decider and view source code.

Map Source Code to Event Model Table

Read TypeScript DcbDecider and Projection source files to extract commands, events, and projections, then produce a Markdown table following the format defined in the map-event-model-to-code skill.

Input

TypeScript source files containing:

• Deciders — each file exports a DcbDecider<C, S, Ei, Eo> where C is the command type and Eo is the output event type.
• Views/Projections — each file exports a Projection<S, E> whose event union type variants indicate which events it subscribes to.

Output

A Markdown table + formulas + Mermaid diagram + Given/When/Then specifications, all following map-event-model-to-code rules.

How to Extract

1. Commands: Find each decider's command type (the C type parameter of DcbDecider).
2. Events (Eo): Find the output event type each decider produces (the Eo type parameter / return type of the decide function).
3. Projections: Find each Projection<S, E>. The event union type variants tell you which events it subscribes to.
4. Timeline order: Arrange commands left-to-right following the domain flow (creation → mutation → downstream actions).
5. Repeated projections: All primitives (C, E, P) are identified by name. When a projection appears multiple times (e.g. B1 = D1), only list the new event cell(s) from the immediately preceding command — earlier subscriptions are already captured in the previous occurrence.
6. Given/When/Then specs: For each decider, extract test scenarios from Deno.test() functions that use DeciderEventSourcedSpec.for(decider).given().when().then() / .thenThrows(). Include both success and error paths.

Example: Restaurant Management Demo (dcb)

Source → Cell Mapping

Source File	Type	Name
createRestaurantDecider.ts	🔵 C	CreateRestaurantCommand
createRestaurantDecider.ts	🟠 E	RestaurantCreatedEvent
changeRestaurantMenuDecider.ts	🔵 C	ChangeRestaurantMenuCommand
changeRestaurantMenuDecider.ts	🟠 E	RestaurantMenuChangedEvent
placeOrderDecider.ts	🔵 C	PlaceOrderCommand
placeOrderDecider.ts	🟠 E	RestaurantOrderPlacedEvent
markOrderAsPreparedDecider.ts	🔵 C	MarkOrderAsPreparedCommand
markOrderAsPreparedDecider.ts	🟠 E	OrderPreparedEvent
restaurantView.ts	🟢 P	RestaurantView (subscribes to RestaurantCreatedEvent, RestaurantMenuChangedEvent)
orderView.ts	🟢 P	OrderView (subscribes to RestaurantOrderPlacedEvent, OrderPreparedEvent)

Resulting Table

	A	B	C	D	E	F	G	H
Row 1	🔵 C: CreateRestaurantCommand	🟢 P: RestaurantView [A2]	🔵 C: ChangeRestaurantMenuCommand	🟢 P: RestaurantView [C2]	🔵 C: PlaceOrderCommand	🟢 P: OrderView [E2]	🔵 C: MarkOrderAsPreparedCommand	🟢 P: OrderView [G2]
Row 2	🟠 E: RestaurantCreatedEvent		🟠 E: RestaurantMenuChangedEvent		🟠 E: RestaurantOrderPlacedEvent		🟠 E: OrderPreparedEvent

Formulas

A1 = C(CreateRestaurantCommand)
A2 = E(RestaurantCreatedEvent)
B1 = P(RestaurantView)
C1 = C(ChangeRestaurantMenuCommand)
C2 = E(RestaurantMenuChangedEvent)
D1 = P(RestaurantView)
E1 = C(PlaceOrderCommand)
E2 = E(RestaurantOrderPlacedEvent)
F1 = P(OrderView)
G1 = C(MarkOrderAsPreparedCommand)
G2 = E(OrderPreparedEvent)
H1 = P(OrderView)

A1 -> [A2]              # CreateRestaurantCommand produces RestaurantCreatedEvent
C1 -> [C2]              # ChangeRestaurantMenuCommand produces RestaurantMenuChangedEvent
E1 -> [E2]              # PlaceOrderCommand produces RestaurantOrderPlacedEvent
G1 -> [G2]              # MarkOrderAsPreparedCommand produces OrderPreparedEvent

B1 <- [A2]              # RestaurantView subscribes to RestaurantCreatedEvent
D1 <- [C2]              # RestaurantView subscribes to RestaurantMenuChangedEvent
F1 <- [E2]              # OrderView subscribes to RestaurantOrderPlacedEvent
H1 <- [G2]              # OrderView subscribes to OrderPreparedEvent

Mermaid Diagram

After producing the table and formulas, render a Mermaid diagram following the Mermaid Rendering Rules:

1. Use flowchart TD with three direction LR subgraphs: Commands (top), Events (middle), Projections (bottom).
2. Node shapes: Commands → rectangles [], Events → rounded (), Projections → hexagons {{}}. No C/E/P label prefixes needed — color + shape conveys the type.
3. Edges: Command --> Event (from -> formulas), Event --> Projection (from <- formulas).
4. Repeated projections reuse the first node ID (e.g. B1 for all RestaurantView occurrences).
5. Color nodes: Commands blue (fill:#4A90D9), Events red (fill:#E06050), Projections green (fill:#5CB85C).

flowchart TD
    subgraph Commands
        direction LR
        A1[CreateRestaurantCommand]
        C1[ChangeRestaurantMenuCommand]
        E1[PlaceOrderCommand]
        G1[MarkOrderAsPreparedCommand]
    end
    subgraph Events
        direction LR
        A2(RestaurantCreatedEvent)
        C2(RestaurantMenuChangedEvent)
        E2(RestaurantOrderPlacedEvent)
        G2(OrderPreparedEvent)
    end
    subgraph Projections
        direction LR
        B1{{RestaurantView}}
        F1{{OrderView}}
    end
    A1 --> A2
    C1 --> C2
    E1 --> E2
    G1 --> G2
    A2 --> B1
    C2 --> B1
    E2 --> F1
    G2 --> F1
    style A1 fill:#4A90D9,color:#fff
    style C1 fill:#4A90D9,color:#fff
    style E1 fill:#4A90D9,color:#fff
    style G1 fill:#4A90D9,color:#fff
    style A2 fill:#E06050,color:#fff
    style C2 fill:#E06050,color:#fff
    style E2 fill:#E06050,color:#fff
    style G2 fill:#E06050,color:#fff
    style B1 fill:#5CB85C,color:#fff
    style F1 fill:#5CB85C,color:#fff

Given/When/Then Specifications

For each command, extract success and error scenarios from the decider tests.

CreateRestaurantCommand

Scenario: Success — restaurant does not exist

• Given: []
• When: { kind: "CreateRestaurantCommand", restaurantId, name, menu }
• Then: [{ kind: "RestaurantCreatedEvent", restaurantId, name, menu, final: false, tagFields: ["restaurantId"] }]

Scenario: Error — restaurant already exists

• Given: [{ kind: "RestaurantCreatedEvent", restaurantId }]
• When: { kind: "CreateRestaurantCommand", restaurantId, name, menu }
• Then Error: RestaurantAlreadyExistsError(restaurantId)

ChangeRestaurantMenuCommand

Scenario: Success — restaurant exists

• Given: [{ kind: "RestaurantCreatedEvent", restaurantId }]
• When: { kind: "ChangeRestaurantMenuCommand", restaurantId, menu }
• Then: [{ kind: "RestaurantMenuChangedEvent", restaurantId, menu, final: false, tagFields: ["restaurantId"] }]

Scenario: Error — restaurant not found

• Given: []
• When: { kind: "ChangeRestaurantMenuCommand", restaurantId, menu }
• Then Error: RestaurantNotFoundError(restaurantId)

PlaceOrderCommand

Scenario: Success — restaurant exists, menu items available, new order

• Given: [{ kind: "RestaurantCreatedEvent", restaurantId, name, menu }]
• When: { kind: "PlaceOrderCommand", restaurantId, orderId, menuItems }
• Then: [{ kind: "RestaurantOrderPlacedEvent", restaurantId, orderId, menuItems, final: false, tagFields: ["restaurantId", "orderId"] }]

Scenario: Error — restaurant not found

• Given: []
• When: { kind: "PlaceOrderCommand", restaurantId, orderId, menuItems }
• Then Error: RestaurantNotFoundError(restaurantId)

Scenario: Error — duplicate order

• Given: [{ kind: "RestaurantCreatedEvent" }, { kind: "RestaurantOrderPlacedEvent", orderId }]
• When: { kind: "PlaceOrderCommand", restaurantId, orderId, menuItems }
• Then Error: OrderAlreadyExistsError(orderId)

Scenario: Error — menu items not available

• Given: [{ kind: "RestaurantCreatedEvent", menu }]
• When: { kind: "PlaceOrderCommand", restaurantId, orderId, menuItems: [unavailableItem] }
• Then Error: MenuItemsNotAvailableError(unavailableMenuItemIds)

MarkOrderAsPreparedCommand

Scenario: Success — order is pending

• Given: [{ kind: "RestaurantOrderPlacedEvent", orderId }]
• When: { kind: "MarkOrderAsPreparedCommand", orderId }
• Then: [{ kind: "OrderPreparedEvent", orderId, final: false, tagFields: ["orderId"] }]

Scenario: Error — order not found

• Given: []
• When: { kind: "MarkOrderAsPreparedCommand", orderId }
• Then Error: OrderNotFoundError(orderId)

Scenario: Error — order already prepared

• Given: [{ kind: "RestaurantOrderPlacedEvent", orderId }, { kind: "OrderPreparedEvent", orderId }]
• When: { kind: "MarkOrderAsPreparedCommand", orderId }
• Then Error: OrderAlreadyPreparedError(orderId)