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T2 chain · data → picture: nika:read loads the CSV, nika:convert types it into rows, nika:jq aggregates by region, nika:chart renders the bar chart as a real image, and nika:write assembles the markdown report around it. Five tasks, zero model calls — the whole pipeline is deterministic data plumbing.

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The job

The Monday deck needs one chart and one table, and the ritual is always the same: open the sheet, pivot, screenshot, paste. This workflow replaces the ritual with a file — drop the CSV, run once, and the report (chart image + aggregate table) is on disk, identical every time the data is identical.

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The shape

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The file

t2-csv-chart-report.nika.yaml
nika: v1
workflow: csv-chart-report
description: "CSV → aggregate → rendered bar chart + markdown report · offline · deterministic"

vars:
  sales_csv: "./data/sales.csv" # columns · region,revenue (revenue a plain number)

permits:
  exec: false
  fs:
    read: ["data/**"]
    write: ["out/**"]
  tools: ["nika:read", "nika:convert", "nika:jq", "nika:chart", "nika:write"]

tasks:
  - id: raw
    invoke:
      tool: "nika:read"
      args: { path: "${{ vars.sales_csv }}" }

  - id: rows
    depends_on: [raw]
    invoke:
      tool: "nika:convert"
      args:
        input: "${{ tasks.raw.output }}"
        from: csv
        to: json
        has_header: true

  # Sum revenue per region · a deterministic reduce, no model.
  - id: by_region
    depends_on: [rows]
    invoke:
      tool: "nika:jq"
      args:
        input: "${{ tasks.rows.output }}"
        expression: 'group_by(.region) | map({ region: .[0].region, revenue: (map(.revenue | tonumber) | add) })'

  # The picture · one SVG, its sha lands in the trace.
  - id: chart
    depends_on: [by_region]
    invoke:
      tool: "nika:chart"
      args:
        data: "${{ tasks.by_region.output }}"
        semantics: { region: category, revenue: usd }
        chart: { type: bar, x: region, y: revenue, title: "Revenue by region" }
        out: out/revenue-by-region.svg

  # The rows as MARKDOWN · a report renders lines, never a JSON blob
  # (region names are user data — the esc guards a `|` in them).
  - id: rows_md
    depends_on: [by_region]
    invoke:
      tool: "nika:jq"
      args:
        input: "${{ tasks.by_region.output }}"
        expression: >-
          def esc: tostring | gsub("\\|"; "\\|") | gsub("\n"; " ");
          map("| \(.region | esc) | \(.revenue) |") | join("\n")

  # The page · the report references the picture beside it.
  - id: report
    depends_on: [chart, rows_md]
    invoke:
      tool: "nika:write"
      args:
        path: out/revenue-report.md
        content: |
          # Revenue by region

          ![Revenue by region](revenue-by-region.svg)

          | region | revenue |
          | --- | --- |
          ${{ tasks.rows_md.output }}

          *Generated offline by [nika](https://nika.sh) · the chart's sha is in the run trace (`nika trace verify`).*

outputs:
  by_region:
    value: ${{ tasks.by_region.output }}
    type: array
    description: "Per-region revenue totals · the chart + report render from this"

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What this file teaches

  • nika:convert is the typed seam — CSV text becomes structured rows once, at one task, and everything downstream works on data, not strings. The jq aggregation reads fields, never re-parses.
  • A chart is an artifact, not a side effect — nika:chart returns a rendered image the report links by path. Re-running with the same CSV produces the same bytes: the chart can live in git, and a diff on it means the data moved.
  • No model, no bill, no network — nika check shows an empty cost interval, and the run works on a plane. Determinism is the feature: this is the workflow you trust in a cron.

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Run it

git clone https://github.com/supernovae-st/nika-spec && cd nika-spec
nika run examples/showcase/t2-csv-chart-report.nika.yaml
open out/revenue-report.md
This workflow is newer than the currently shipped engine pack: nika examples run showcase/t2-csv-chart-report says unknown example until the next engine tag re-vendors the pack. Until then, run it from the spec checkout as above — the file is the same one the pack will embed, sha-pinned in the spec manifest.
Swap the bundled sample for your own export by pointing vars.sales_csv at it — the aggregation key and the chart spec are the only two lines to adapt.