// ── Rule conditions — a predicate over a trigger's DECLARED variables ───────
//
// ENGAGEMENT.md §4.5, Phase 4a. `engagement_rules.conditions` is the half of a
// rule that decides *whether* this particular firing is interesting: "only when
// decayStatus is IDOC", "only for threads in this Team". Without it every rule is
// all-or-nothing per trigger, and an operator's only way to narrow is to ask a
// module author for a second trigger.
//
// **It is validated against the declaration, not against a payload.** A condition
// naming a variable the trigger does not declare is refused at SAVE, with the
// variable named, for the same reason §4.3 gives the template editor: a predicate
// that silently reads `undefined` is a rule that silently never fires (or always
// does), and the day you find out is the day the mail did not go.
//
// **The grammar is small and closed on purpose.** No arbitrary expressions, no
// arithmetic, no regex. An operator composes and/or/not over comparisons of one
// declared variable against a literal, and every operator here is one a rule
// editor can render as a dropdown. Anything that needs more than this is asking
// for a condition the module should have declared as a variable.
//
// Nothing in this file reaches the database or the network.

const registries = require('../modules/registries')

// Comparison operators, grouped by what they may be applied to. The grouping is
// the whole of the type check: `gt` on a boolean and `startsWith` on an int are
// both refused at save rather than quietly answering false forever.
const OPERATORS = {
  eq: { label: 'is', types: ['string', 'int', 'float', 'boolean', 'datetime', 'url'], arity: 1 },
  ne: { label: 'is not', types: ['string', 'int', 'float', 'boolean', 'datetime', 'url'], arity: 1 },
  in: { label: 'is one of', types: ['string', 'int', 'float', 'url'], arity: 'list' },
  nin: { label: 'is none of', types: ['string', 'int', 'float', 'url'], arity: 'list' },
  gt: { label: 'is greater than', types: ['int', 'float', 'datetime'], arity: 1 },
  gte: { label: 'is at least', types: ['int', 'float', 'datetime'], arity: 1 },
  lt: { label: 'is less than', types: ['int', 'float', 'datetime'], arity: 1 },
  lte: { label: 'is at most', types: ['int', 'float', 'datetime'], arity: 1 },
  contains: { label: 'contains', types: ['string', 'url'], arity: 1 },
  startsWith: { label: 'starts with', types: ['string', 'url'], arity: 1 },
  // The one operator that takes no value: "the emit carried this variable at
  // all". It is the honest way to write a rule about an OPTIONAL variable, and
  // without it `ne` would have to double as a presence test and get it wrong
  // (an absent variable is not "not equal to X"; it is absent).
  present: { label: 'is present', types: ['string', 'int', 'float', 'boolean', 'datetime', 'url'], arity: 0 },
  absent: { label: 'is absent', types: ['string', 'int', 'float', 'boolean', 'datetime', 'url'], arity: 0 },
}

const BOOLEAN_OPS = ['and', 'or', 'not']

// A list literal an operator may type. Bounded because it is stored in a JSON
// column an admin can write, and an unbounded IN list is an unbounded predicate
// evaluated on every event.
const MAX_LIST = 50
// Depth of the and/or/not tree. Three levels is more nesting than any rule
// editor should offer; the bound is here so a hand-written JSON body cannot
// recurse this evaluator into a stack overflow on the emit path.
const MAX_DEPTH = 5

const isPlainObject = (v) => v !== null && typeof v === 'object' && !Array.isArray(v)

/**
 * Check one literal against the declared type of the variable it is compared to.
 *
 * `datetime` accepts anything `Date` parses and is normalised to an ISO string,
 * which is what `engagementEmit.coerce` does to the payload side — so both sides
 * of every comparison are the same representation of a moment, and a lexical
 * `<` on two ISO strings is a chronological one.
 */
function checkLiteral(type, raw) {
  switch (type) {
    case 'string':
    case 'url':
      return typeof raw === 'string' ? { value: raw } : { error: 'expected a string' }
    case 'int':
      return Number.isInteger(raw) ? { value: raw } : { error: 'expected an integer' }
    case 'float':
      return typeof raw === 'number' && Number.isFinite(raw)
        ? { value: raw }
        : { error: 'expected a finite number' }
    case 'boolean':
      return typeof raw === 'boolean' ? { value: raw } : { error: 'expected a boolean' }
    case 'datetime': {
      const d = raw instanceof Date ? raw : new Date(raw)
      if (Number.isNaN(d.getTime())) return { error: 'expected a date' }
      return { value: d.toISOString() }
    }
    default:
      return { error: `unsupported type "${type}"` }
  }
}

/**
 * Validate a condition tree against a trigger declaration.
 *
 * Returns `{ ok: true, conditions }` with a NEW normalised tree — literals
 * coerced, unknown keys dropped — or `{ ok: false, errors }` listing every
 * problem rather than the first, the posture `validatePayload` takes and for the
 * same reason: an operator fixing one clause at a time is an operator making six
 * round trips through a form.
 *
 * `null` and `undefined` are valid and mean "no conditions" — a rule that fires
 * on every occurrence of its trigger, which is the common case.
 */
function validate(declaration, raw) {
  const errors = []
  const variables = new Map((declaration?.variables || []).map((v) => [v.name, v]))

  function walk(node, depth, path) {
    if (depth > MAX_DEPTH) {
      errors.push(`${path}: nested deeper than ${MAX_DEPTH}`)
      return null
    }
    if (!isPlainObject(node)) {
      errors.push(`${path}: expected an object`)
      return null
    }

    if (BOOLEAN_OPS.includes(node.op)) {
      // `not` takes exactly one node; `and`/`or` take a list. Both are written
      // as `nodes` so a client walks one shape.
      const raws = Array.isArray(node.nodes) ? node.nodes : []
      if (!raws.length) {
        errors.push(`${path}: "${node.op}" has no nodes`)
        return null
      }
      if (node.op === 'not' && raws.length !== 1) {
        errors.push(`${path}: "not" takes exactly one node`)
        return null
      }
      const nodes = raws.map((child, i) => walk(child, depth + 1, `${path}.nodes[${i}]`)).filter(Boolean)
      return nodes.length === raws.length ? { op: node.op, nodes } : null
    }

    if (node.op !== undefined) {
      errors.push(`${path}: unknown operator "${node.op}"`)
      return null
    }

    // A leaf: { variable, cmp, value }.
    const variable = variables.get(node.variable)
    if (!variable) {
      errors.push(`${path}: "${node.variable}" is not a variable of "${declaration?.id}"`)
      return null
    }
    const operator = OPERATORS[node.cmp]
    if (!operator) {
      errors.push(`${path}: unknown comparison "${node.cmp}"`)
      return null
    }
    if (!operator.types.includes(variable.type)) {
      errors.push(`${path}: "${node.cmp}" cannot be applied to a ${variable.type}`)
      return null
    }

    if (operator.arity === 0) return { variable: variable.name, cmp: node.cmp }

    if (operator.arity === 'list') {
      if (!Array.isArray(node.value) || !node.value.length) {
        errors.push(`${path}: "${node.cmp}" needs a non-empty list`)
        return null
      }
      if (node.value.length > MAX_LIST) {
        errors.push(`${path}: "${node.cmp}" list is longer than ${MAX_LIST}`)
        return null
      }
      const value = []
      let bad = false
      node.value.forEach((item, i) => {
        const checked = checkLiteral(variable.type, item)
        if (checked.error) {
          errors.push(`${path}.value[${i}]: ${checked.error}`)
          bad = true
        } else value.push(checked.value)
      })
      return bad ? null : { variable: variable.name, cmp: node.cmp, value }
    }

    const checked = checkLiteral(variable.type, node.value)
    if (checked.error) {
      errors.push(`${path}: ${checked.error}`)
      return null
    }
    return { variable: variable.name, cmp: node.cmp, value: checked.value }
  }

  if (raw === null || raw === undefined) return { ok: true, conditions: null }
  const conditions = walk(raw, 0, 'conditions')
  return errors.length ? { ok: false, errors } : { ok: true, conditions }
}

/** Compare one already-normalised leaf against a payload. */
function evaluateLeaf(leaf, data) {
  const present = Object.prototype.hasOwnProperty.call(data, leaf.variable)
  const actual = data[leaf.variable]

  if (leaf.cmp === 'present') return present
  if (leaf.cmp === 'absent') return !present
  // Every other comparison against an absent variable is FALSE, never true.
  // `ne` is the one that tempts otherwise — "not equal to X" reads as satisfied
  // by nothing at all — and treating it as true would make an optional variable's
  // absence fire the rule.
  if (!present) return false

  switch (leaf.cmp) {
    case 'eq': return actual === leaf.value
    case 'ne': return actual !== leaf.value
    case 'in': return leaf.value.includes(actual)
    case 'nin': return !leaf.value.includes(actual)
    case 'gt': return actual > leaf.value
    case 'gte': return actual >= leaf.value
    case 'lt': return actual < leaf.value
    case 'lte': return actual <= leaf.value
    case 'contains': return typeof actual === 'string' && actual.includes(leaf.value)
    case 'startsWith': return typeof actual === 'string' && actual.startsWith(leaf.value)
    default: return false
  }
}

/**
 * Does this event's payload satisfy the rule's conditions?
 *
 * `null` conditions are satisfied — a rule with no conditions fires on every
 * occurrence. A tree this evaluator does not recognise answers **false**, which
 * is the fail-closed direction: a stored condition that no longer parses (a rule
 * saved against an older trigger version, say) must stop the mail rather than
 * become "no conditions" and mail everyone.
 */
function evaluate(conditions, data = {}) {
  if (conditions === null || conditions === undefined) return true
  if (!isPlainObject(conditions)) return false

  if (conditions.op === 'and') return (conditions.nodes || []).every((n) => evaluate(n, data))
  if (conditions.op === 'or') return (conditions.nodes || []).some((n) => evaluate(n, data))
  if (conditions.op === 'not') return !evaluate((conditions.nodes || [])[0], data)
  if (conditions.op !== undefined) return false

  return evaluateLeaf(conditions, data)
}

/**
 * The operator vocabulary a rule editor renders, with the variable types each
 * one applies to. Served with the rule surface in Phase 4b rather than hardcoded
 * in the client, on the same argument the ceiling vocabulary is served with the
 * trigger catalog: a second copy of a rule is a copy that drifts.
 */
const vocabulary = () =>
  Object.entries(OPERATORS).map(([cmp, o]) => ({ cmp, label: o.label, types: o.types, arity: o.arity }))

/** Convenience for a caller holding only a trigger id. */
const validateFor = (triggerId, raw) => validate(registries.eventTrigger(triggerId), raw)

module.exports = { validate, validateFor, evaluate, vocabulary, OPERATORS, MAX_LIST, MAX_DEPTH }