export type PurchaseInterpretationDecision = 'purchase' | 'clarification' | 'not_purchase'

export interface PurchaseInterpretation {
  decision: PurchaseInterpretationDecision
  amountMinor: bigint | null
  currency: 'GEL' | 'USD' | null
  itemDescription: string | null
  confidence: number
  parserMode: 'llm'
  clarificationQuestion: string | null
}

export type PurchaseMessageInterpreter = (
  rawText: string,
  options: {
    defaultCurrency: 'GEL' | 'USD'
  }
) => Promise<PurchaseInterpretation | null>

interface OpenAiStructuredResult {
  decision: PurchaseInterpretationDecision
  amountMinor: string | null
  currency: 'GEL' | 'USD' | null
  itemDescription: string | null
  confidence: number
  clarificationQuestion: string | null
}

function asOptionalBigInt(value: string | null): bigint | null {
  if (value === null || !/^[0-9]+$/.test(value)) {
    return null
  }

  const parsed = BigInt(value)
  return parsed > 0n ? parsed : null
}

function normalizeOptionalText(value: string | null | undefined): string | null {
  const trimmed = value?.trim()
  return trimmed && trimmed.length > 0 ? trimmed : null
}

function normalizeCurrency(value: string | null): 'GEL' | 'USD' | null {
  return value === 'GEL' || value === 'USD' ? value : null
}

export function createOpenAiPurchaseInterpreter(
  apiKey: string | undefined,
  model: string
): PurchaseMessageInterpreter | undefined {
  if (!apiKey) {
    return undefined
  }

  return async (rawText, options) => {
    const response = await fetch('https://api.openai.com/v1/responses', {
      method: 'POST',
      headers: {
        authorization: `Bearer ${apiKey}`,
        'content-type': 'application/json'
      },
      body: JSON.stringify({
        model,
        input: [
          {
            role: 'system',
            content: [
              'You classify a single Telegram message from a household shared-purchases topic.',
              'Decide whether the message is a real shared purchase, needs clarification, or is not a shared purchase at all.',
              `The household default currency is ${options.defaultCurrency}, but do not assume that omitted currency means ${options.defaultCurrency}.`,
              'Use clarification when the amount, currency, item, or overall intent is missing or uncertain.',
              'Return a clarification question in the same language as the user message when clarification is needed.',
              'Return only JSON that matches the schema.'
            ].join(' ')
          },
          {
            role: 'user',
            content: rawText
          }
        ],
        text: {
          format: {
            type: 'json_schema',
            name: 'purchase_interpretation',
            schema: {
              type: 'object',
              additionalProperties: false,
              properties: {
                decision: {
                  type: 'string',
                  enum: ['purchase', 'clarification', 'not_purchase']
                },
                amountMinor: {
                  anyOf: [{ type: 'string' }, { type: 'null' }]
                },
                currency: {
                  anyOf: [
                    {
                      type: 'string',
                      enum: ['GEL', 'USD']
                    },
                    { type: 'null' }
                  ]
                },
                itemDescription: {
                  anyOf: [{ type: 'string' }, { type: 'null' }]
                },
                confidence: {
                  type: 'number',
                  minimum: 0,
                  maximum: 100
                },
                clarificationQuestion: {
                  anyOf: [{ type: 'string' }, { type: 'null' }]
                }
              },
              required: [
                'decision',
                'amountMinor',
                'currency',
                'itemDescription',
                'confidence',
                'clarificationQuestion'
              ]
            }
          }
        }
      })
    })

    if (!response.ok) {
      return null
    }

    const payload = (await response.json()) as {
      output_text?: string
    }

    if (!payload.output_text) {
      return null
    }

    let parsedJson: OpenAiStructuredResult
    try {
      parsedJson = JSON.parse(payload.output_text) as OpenAiStructuredResult
    } catch {
      return null
    }

    if (
      parsedJson.decision !== 'purchase' &&
      parsedJson.decision !== 'clarification' &&
      parsedJson.decision !== 'not_purchase'
    ) {
      return null
    }

    const clarificationQuestion = normalizeOptionalText(parsedJson.clarificationQuestion)
    if (parsedJson.decision === 'clarification' && !clarificationQuestion) {
      return null
    }

    return {
      decision: parsedJson.decision,
      amountMinor: asOptionalBigInt(parsedJson.amountMinor),
      currency: normalizeCurrency(parsedJson.currency),
      itemDescription: normalizeOptionalText(parsedJson.itemDescription),
      confidence: Math.max(0, Math.min(100, Math.round(parsedJson.confidence))),
      parserMode: 'llm',
      clarificationQuestion
    }
  }
}