/**
 * Adapts Effect Schema codecs to the JSON Schema subset accepted by Anthropic
 * structured output.
 *
 * The main entry point returns the JSON Schema to send to Anthropic and a codec
 * for decoding the model response back into the original application type.
 * Unsupported constraints can be omitted from the provider schema and remain
 * enforced by the returned codec.
 *
 * @stability unstable
 * @since 4.0.0
 */
import type * as JsonSchema from "../JsonSchema.ts"
import * as Rec from "../Record.ts"
import * as Schema from "../Schema.ts"
import * as InternalStructuredOutput from "./internal/structured-output.ts"
import type * as LanguageModel from "./LanguageModel.ts"
import type * as OpenAiStructuredOutput from "./OpenAiStructuredOutput.ts"

/**
 * Converts a `Schema.Codec` to Anthropic structured-output JSON Schema and a
 * matching codec for model output.
 *
 * **When to use**
 *
 * Use when you send Effect Schema-backed structured output requests to
 * Anthropic and need provider-compatible JSON Schema without losing the decoded
 * application type.
 *
 * **Details**
 *
 * Returns the JSON Schema to include in the request and the codec to use when
 * decoding the model response. The codec remains authoritative: the provider
 * JSON Schema can be a lossy, less restrictive representation when Anthropic
 * cannot express an Effect Schema constraint.
 *
 * **Gotchas**
 *
 * - Some schemas use a provider-safe encoded shape: tuples become objects with
 *   numeric string keys, objects with index signatures become arrays of
 *   `[key, value]` pairs, and optional properties become required nullable
 *   properties.
 * - `oneOf` unions are emitted as `anyOf` unions.
 * - Unsupported constraints are removed from the provider schema and are still
 *   checked while decoding with the returned codec.
 * - Recursive schemas throw during conversion because Anthropic structured
 *   output does not support recursive references.
 *
 * @see {@link LanguageModel.CodecTransformer} for the structured-output transformer contract
 * @see {@link OpenAiStructuredOutput.toCodecOpenAI} for the OpenAI-specific transformer
 *
 * @stability unstable
 * @category transforming
 * @since 4.0.0
 */
export function toCodecAnthropic<T, E, RD, RE>(
  schema: Schema.ConstraintCodec<T, E, RD, RE>
): {
  readonly codec: Schema.ConstraintCodec<T, unknown, RD, RE>
  readonly jsonSchema: JsonSchema.JsonSchema
} {
  const codec = InternalStructuredOutput.toCodec(schema)
  const unresolvedDocument = Schema.toJsonSchemaDocument(codec, {
    generateDescriptions: true,
    onExcessProperty: "error"
  })
  if (hasReferenceCycle(unresolvedDocument.schema, unresolvedDocument.definitions)) {
    throw new Error("AnthropicStructuredOutput: Recursive schemas are not supported")
  }
  const document = InternalStructuredOutput.resolveTopLevelReference(unresolvedDocument)
  const jsonSchema = rewriteAnthropic(document.schema)
  if (Object.keys(document.definitions).length > 0) {
    jsonSchema.$defs = Rec.map(document.definitions, rewriteAnthropic)
  }
  return { codec, jsonSchema }
}

function hasReferenceCycle(
  root: JsonSchema.JsonSchema,
  definitions: JsonSchema.Definitions
): boolean {
  const visiting = new Set<JsonSchema.JsonSchema>()
  const visited = new Set<JsonSchema.JsonSchema>()

  function visit(schema: JsonSchema.JsonSchema): boolean {
    if (visiting.has(schema)) return true
    if (visited.has(schema)) return false

    visiting.add(schema)
    let cycle = false
    InternalStructuredOutput.walkJsonSchema(schema, (node) => {
      if (!cycle && typeof node.$ref === "string") {
        const target = node.$ref === "#" ? root : InternalStructuredOutput.resolveReference(node.$ref, definitions)
        if (visit(target)) cycle = true
      }
      return node
    })
    visiting.delete(schema)
    visited.add(schema)
    return cycle
  }

  return visit(root)
}

function rewriteAnthropic(schema: JsonSchema.JsonSchema): JsonSchema.JsonSchema {
  return InternalStructuredOutput.walkJsonSchema(schema, (schema) => {
    const normalized = hoistAllOfDescriptions(schema)
    const out: JsonSchema.JsonSchema = {}
    let unsupportedFormat: string | undefined
    for (const [key, value] of Object.entries(normalized)) {
      if (key === "format") {
        if (
          typeof value === "string" && formats.has(value) &&
          (normalized.type === undefined || normalized.type === "string")
        ) {
          out.format = value
        } else if (typeof value === "string") unsupportedFormat = value
      } else if (supportedKeywords.has(key)) {
        if (key !== "additionalProperties" || value === false) out[key] = value
      }
    }
    if (unsupportedFormat !== undefined) {
      InternalStructuredOutput.appendDescription(out, `a value with a format of ${unsupportedFormat}`)
    }
    return out
  })
}

function hoistAllOfDescriptions(schema: JsonSchema.JsonSchema): JsonSchema.JsonSchema {
  if (!Array.isArray(schema.allOf)) return schema

  const out: JsonSchema.JsonSchema = {}
  for (const [key, value] of Object.entries(schema)) {
    if (key !== "allOf") out[key] = value
  }
  const members: Array<JsonSchema.JsonSchema> = []
  for (const member of schema.allOf) {
    if (!InternalStructuredOutput.isJsonSchema(member)) continue
    const { description, format, title, ...memberRest } = member
    const rest = { ...memberRest }
    if (schema.type !== undefined && schema.type !== "string") delete rest.pattern
    if (typeof description === "string") {
      InternalStructuredOutput.appendDescription(out, description)
    }
    if (out.format === undefined && typeof format === "string") out.format = format
    if (out.title === undefined && typeof title === "string") out.title = title
    if (Object.keys(rest).length > 0) members.push(rest)
  }
  if (members.length > 0) out.allOf = members
  return out
}

const supportedKeywords = new Set([
  "$ref",
  "type",
  "title",
  "description",
  "enum",
  "const",
  "anyOf",
  "allOf",
  "properties",
  "required",
  "additionalProperties",
  "items",
  "pattern"
])

const formats = new Set([
  "date-time",
  "time",
  "date",
  "duration",
  "email",
  "hostname",
  "uri",
  "ipv4",
  "ipv6",
  "uuid"
])