# schemas/lib/formula.ncl — Workspace Formula DAG
#
# A Formula is a typed DAG that is simultaneously:
#   - A validatable declaration (Nickel typecheck + referential integrity)
#   - An executable pipeline (Orchestrator consumes the DAG via nickel export)
#   - A governable artifact (on+re tracks state, gates, and audit)
#
# Usage:
#   let f = import "schemas/lib/formula.ncl" in
#   f.make_formula { id = "...", nodes = [...], ... }

let ts = import "contracts.ncl" in

let _dep_kind = [| 'Always, 'OnSuccess, 'OnFailure |] in
let _on_error  = [| 'Stop, 'Continue, 'Retry |] in

# Dependency from one FormulaNode to another (by node id)
let _FormulaDep = {
  node_id | String,
  kind    | _dep_kind | default = 'OnSuccess,
} in

# A node in the formula DAG.
# Exactly one of `taskserv` or `component` must be present.
# - taskserv: L2 nodes — legacy field, existing formulas unchanged
# - component: L3+ nodes — unified model, orchestrator uses component.mode to resolve
let _FormulaNode = std.contract.custom (fun label value =>
  let base = value | {
    id          | String,
    taskserv    | ts.TaskServDef | optional,
    component   | ts.ComponentDef | optional,
    depends_on  | Array _FormulaDep | default = [],
    parallel    | Bool | default = false,
    on_error    | _on_error | default = 'Stop,
    max_retries | Number | default = 0,
  } in
  let has_taskserv  = std.record.has_field "taskserv"  base in
  let has_component = std.record.has_field "component" base in
  if has_taskserv && has_component then
    std.contract.blame_with_message
      "FormulaNode '%{base.id}': exactly one of 'taskserv' or 'component' must be present, not both"
      label
  else if (!has_taskserv) && (!has_component) then
    std.contract.blame_with_message
      "FormulaNode '%{base.id}': exactly one of 'taskserv' or 'component' must be present"
      label
  else
    'Ok base
) in

# An explicit edge declaration (alternative to depends_on inside nodes)
let _FormulaEdge = {
  from | String,
  to   | String,
  kind | _dep_kind | default = 'OnSuccess,
} in

# Base structure without cross-field validation
let _FormulaBase = {
  id          | String,
  description | String,
  provider    | String,
  server      | String,
  nodes       | Array _FormulaNode,
  edges       | Array _FormulaEdge | default = [],
  max_parallel | Number | default = 4,
} in

# Contract: all node_id values in depends_on must reference an existing node id.
# Also validates edge endpoints.
let _Formula = std.contract.custom (fun label value =>
  let base = value | _FormulaBase in
  let node_ids = base.nodes |> std.array.map (fun n => n.id) in

  # Check: duplicate node ids
  let dup_ids = node_ids |> std.array.fold_left (fun acc id =>
    if std.record.has_field id acc.seen then
      { seen = acc.seen, dups = acc.dups @ [id] }
    else
      { seen = acc.seen & { "%{id}" = true }, dups = acc.dups }
  ) { seen = {}, dups = [] } in

  if std.array.length dup_ids.dups > 0 then
    std.contract.blame_with_message
      "Formula '%{base.id}': duplicate node ids: %{std.string.join ", " dup_ids.dups}"
      label
  else

  # Check: depends_on referential integrity
  let bad_deps = base.nodes |> std.array.flat_map (fun node =>
    node.depends_on
      |> std.array.filter (fun dep =>
          !(node_ids |> std.array.any (fun id => id == dep.node_id))
        )
      |> std.array.map (fun dep =>
          "node '%{node.id}' depends_on unknown '%{dep.node_id}'"
        )
  ) in

  if std.array.length bad_deps > 0 then
    std.contract.blame_with_message
      "Formula '%{base.id}' has invalid depends_on: %{std.string.join ", " bad_deps}"
      label
  else

  # Check: edge referential integrity
  let bad_edges = base.edges |> std.array.filter (fun e =>
    !(node_ids |> std.array.any (fun id => id == e.from))
    || !(node_ids |> std.array.any (fun id => id == e.to))
  ) |> std.array.map (fun e => "'%{e.from}' -> '%{e.to}'") in

  if std.array.length bad_edges > 0 then
    std.contract.blame_with_message
      "Formula '%{base.id}' has invalid edge endpoints: %{std.string.join ", " bad_edges}"
      label
  else
    'Ok base
) in

{
  FormulaDep   = _FormulaDep,
  FormulaNode  = _FormulaNode,
  FormulaEdge  = _FormulaEdge,
  Formula      = _Formula,

  make_dep     = fun data => _FormulaDep  & data,
  make_node    = fun data => data | _FormulaNode,
  make_edge    = fun data => _FormulaEdge & data,
  make_formula = fun data => data | _Formula,
}