> ## Documentation Index
> Fetch the complete documentation index at: https://docs.twine.se/llms.txt
> Use this file to discover all available pages before exploring further.

# Flow Transform

export const NodeMode = ({mode = 'data'}) => {
  const ENGINES = {
    data: [{
      label: 'Data Engine',
      href: '/data-engine'
    }],
    flow: [{
      label: 'Flow Engine',
      href: '/flow-engine'
    }],
    any: [{
      label: 'Data Engine',
      href: '/data-engine'
    }, {
      label: 'Flow Engine',
      href: '/flow-engine'
    }]
  };
  const engines = ENGINES[mode] || ENGINES.data;
  return <>
      <style>{`
        .node-mode {
          display: flex;
          flex-wrap: wrap;
          align-items: center;
          gap: 8px;
          margin: 0 0 20px;
        }
        .node-mode-label {
          font-size: 11px;
          font-weight: 600;
          text-transform: uppercase;
          letter-spacing: 0.05em;
          color: var(--colors-content-secondary, #6b7280);
        }
        .node-mode-pill {
          display: inline-flex;
          align-items: center;
          padding: 3px 10px;
          border-radius: 999px;
          font-size: 12px;
          font-weight: 600;
          text-decoration: none;
          color: inherit;
          background: rgb(var(--primary-light) / .15);
          border: 1px solid rgb(var(--primary-light) / .5);
        }
        .node-mode-pill:hover {
          background: rgb(var(--primary-light) / .25);
        }
      `}</style>
      <div className="node-mode">
        <span className="node-mode-label">Available in</span>
        {engines.map(engine => <a key={engine.label} className="node-mode-pill" href={engine.href}>
            {engine.label}
          </a>)}
      </div>
    </>;
};

export const NodePorts = ({nodeName, inputs = [], outputs = []}) => {
  if (inputs.length === 0 && outputs.length === 0) return null;
  const formatTypes = types => {
    if (!types || types.length === 0) return 'Any';
    if (Array.isArray(types)) return types.join(', ');
    return types;
  };
  const Card = ({port, side}) => <div className={`node-port-card node-port-card-${side}`}>
      <div className="node-port-head">
        <span className="node-port-name">{port.name}</span>
        <span className="node-port-id">{port.id}</span>
      </div>
      {port.doc && <div className="node-port-doc">{port.doc}</div>}
      <div className="node-port-tags">
        <span className="node-port-tag node-port-tag-types">{formatTypes(port.types)}</span>
        {port.required && <span className="node-port-tag node-port-tag-required">required</span>}
        {port.arity === 'many' && <span className="node-port-tag">many</span>}
        {port.defaultConnection && <span className="node-port-tag node-port-tag-default">default</span>}
      </div>
    </div>;
  return <>
      <style>{`
        .node-diagram {
          display: grid;
          grid-template-columns: 1fr auto 1fr;
          gap: 32px;
          align-items: stretch;
          margin: 24px 0 32px;
        }
        .node-diagram-col {
          display: flex;
          flex-direction: column;
          gap: 12px;
          min-width: 0;
        }
        .node-diagram-col-label {
          font-size: 11px;
          font-weight: 600;
          text-transform: uppercase;
          letter-spacing: 0.05em;
          color: var(--colors-content-secondary, #6b7280);
          margin-bottom: 4px;
        }
        .node-diagram-col-center {
          display: flex;
          align-items: stretch;
          justify-content: center;
          position: relative;
          /* Push the center node down so it aligns with the cards, not the column labels */
          padding-top: 27px;
        }
        .node-diagram-node {
          display: flex;
          align-items: center;
          justify-content: center;
          padding: 18px 14px;
          border-radius: 10px;
          background: rgb(var(--primary-light) / .15);
          border: 1.5px solid rgb(var(--primary-light) / .55);
          font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
          font-size: 15px;
          font-weight: 700;
          color: inherit;
          box-shadow: 0 1px 3px rgb(0 0 0 / .04);
          writing-mode: vertical-rl;
          transform: rotate(180deg);
          letter-spacing: 0.05em;
        }
        .node-port-card {
          position: relative;
          border: 1px solid rgb(var(--primary-light) / .25);
          border-radius: 8px;
          padding: 10px 12px;
          background: rgb(var(--primary-light) / .04);
          font-size: 12px;
          line-height: 1.4;
        }
        .node-port-card::after {
          content: '';
          position: absolute;
          top: 50%;
          width: 32px;
          border-top: 1px dashed rgb(var(--primary-light) / .7);
        }
        .node-port-card-left::after {
          right: -32px;
        }
        .node-port-card-right::after {
          left: -32px;
        }
        .node-port-head {
          display: flex;
          align-items: baseline;
          justify-content: space-between;
          gap: 8px;
          margin-bottom: 4px;
        }
        .node-port-name {
          font-weight: 600;
          font-size: 13px;
          color: inherit;
        }
        .node-port-id {
          font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
          font-size: 10.5px;
          color: var(--colors-content-secondary, #6b7280);
        }
        .node-port-doc {
          color: #4b5563;
          margin-bottom: 6px;
        }
        .dark .node-port-doc,
        html.dark .node-port-doc,
        :is(.dark, [data-theme="dark"]) .node-port-doc {
          color: #d1d5db;
        }
        .node-port-tags {
          display: flex;
          flex-wrap: wrap;
          gap: 4px;
        }
        .node-port-tag {
          display: inline-flex;
          align-items: center;
          padding: 2px 6px;
          border-radius: 4px;
          font-size: 10px;
          font-weight: 600;
          background: rgb(var(--primary-light) / .15);
          color: var(--colors-content-secondary, #6b7280);
          text-transform: lowercase;
          letter-spacing: 0.02em;
        }
        .node-port-tag-types {
          font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
          text-transform: none;
          background: rgb(var(--primary-light) / .25);
          color: inherit;
        }
        .node-port-tag-required {
          background: var(--colors-warning-light, #fef3c7);
          color: var(--colors-warning, #b45309);
        }
        .node-port-tag-default {
          background: var(--colors-accent-light, #ede9fe);
          color: var(--colors-accent, #7c3aed);
        }
        @media (max-width: 720px) {
          .node-diagram {
            grid-template-columns: 1fr;
            gap: 16px;
          }
          .node-diagram-col-center {
            order: -1;
          }
          .node-port-card::before,
          .node-port-card::after {
            display: none !important;
          }
        }
      `}</style>
      <div className="node-diagram">
        <div className="node-diagram-col node-diagram-col-left">
          {inputs.length > 0 && <div className="node-diagram-col-label">Inputs</div>}
          {inputs.map(p => <Card key={p.id} port={p} side="left" />)}
        </div>
        <div className="node-diagram-col-center">
          <div className="node-diagram-node">{nodeName}</div>
        </div>
        <div className="node-diagram-col node-diagram-col-right">
          {outputs.length > 0 && <div className="node-diagram-col-label">Outputs</div>}
          {outputs.map(p => <Card key={p.id} port={p} side="right" />)}
        </div>
      </div>
    </>;
};

<NodeMode mode="flow" />

Computes a value with an inner graph and emits it on its output port so
downstream nodes can use it.

Drill in to edit the inner graph. It sees the same assigns the outer flow
sees — use Assign Read to pull values in, and end on the value you want to
emit. Whatever the End node sees becomes this node's output.

### Configuration

* **Output assign** *(required for execution)* — name of the flow-token
  assign that receives the computed value. Downstream flow nodes read it
  like any other assign. The save changeset doesn't enforce it so a flow
  mid-authoring can still be persisted; at run time, an unset value is a
  no-op (no assign is written).
* **Subject assign** *(optional)* — assigns key whose value becomes the
  subject for Attribute nodes inside the inner graph. Lets you read dated
  properties directly without an Assign Read wrapper. The referenced value
  must be a defdata struct (e.g. `%Employee{}`) or any struct carrying a
  `%DatedProperties{}` bag.
* **On inner error** — what happens when the inner graph fails to evaluate
  (a node inside it crashed or errored):

  * *Halt flow* (default): fail the whole run.
  * *Skip branch*: stop only this path — parallel branches and the next Flow
    Each iteration keep going. Nothing is written to the output assign.
  * *Set nil*: write `nil` to the output assign and carry on, treating a
    failed computation as an empty value.

  Every mode logs the failure at `:error`, and a tolerated error still marks
  the run *completed with issues* — it's visible in the run log and the run
  status, it just doesn't abort.

### When to reach for it

* To compute something from several assigns without cluttering the outer
  flow with control-flow nodes.
* To build a boolean predicate that feeds into Flow Switch.

### What's the difference vs. Flow Compose?

Flow Transform emits a single computed value into the named output assign
— think "expression". Flow Compose assembles a whole struct from named
mappings and writes it into an assign. Use Compose when you're building a
payload for a step; use Transform when you just need one value.

## Ports

<NodePorts
  nodeName="Flow Transform"
  inputs={[
{ id: 'default_in', name: 'In', doc: 'Default input port', types: 'Any', required: true, defaultConnection: true },
]}
  outputs={[
{ id: 'default_out', name: 'Out', doc: 'Default output port', types: 'Any', required: true, defaultConnection: true },
]}
/>