import sharp from 'sharp'
import { sliceImage } from '@/lib/image-processor'
import { configureSharpRuntime } from '@/lib/sharp-runtime'
import { withImageProcessingSlot } from '@/lib/image-processing-limiter'
import {
  BRAND_KNOWLEDGE_MAX_PREVIEW_IMAGE_BYTES,
  BRAND_KNOWLEDGE_MAX_PREVIEW_SLICE_BYTES,
  BRAND_KNOWLEDGE_MAX_PREVIEW_SLICE_COUNT,
} from '@/lib/brand-knowledge-file-types'
import {
  BRAND_KNOWLEDGE_PREVIEW_SINGLE_IMAGE_MAX_HEIGHT,
  planBrandKnowledgePreviewSlices,
} from '@/lib/performance-survey-image-source-guard'

configureSharpRuntime()

export const BRAND_KNOWLEDGE_PREVIEW_MAX_WIDTH = 12_000
export const BRAND_KNOWLEDGE_PREVIEW_MAX_HEIGHT = 90_000
export const BRAND_KNOWLEDGE_PREVIEW_MAX_PIXELS = 60_000_000
export const BRAND_KNOWLEDGE_PREVIEW_SLICE_HEIGHT = 1_500
export const BRAND_KNOWLEDGE_PREVIEW_SLICE_MAX_KB = 500
export const BRAND_KNOWLEDGE_PREVIEW_OUTPUT_WIDTH = 1_600

const FORMAT_DETAILS = {
  png: { extension: 'png', contentType: 'image/png' },
  jpeg: { extension: 'jpg', contentType: 'image/jpeg' },
  webp: { extension: 'webp', contentType: 'image/webp' },
} as const

type SupportedPreviewFormat = keyof typeof FORMAT_DETAILS

function normalizeContentType(value?: string | null) {
  return String(value || '').split(';', 1)[0].trim().toLowerCase()
}

export function assertBrandKnowledgePreviewMetadata(
  metadata: Pick<sharp.Metadata, 'format' | 'width' | 'height' | 'pages'>,
  declaredContentType?: string | null,
) {
  const format = metadata.format as SupportedPreviewFormat | undefined
  const details = format ? FORMAT_DETAILS[format] : undefined
  if (!details) throw new Error('预览图只支持 PNG、JPEG 或 WebP')

  const width = metadata.width || 0
  const height = metadata.height || 0
  if (width < 1 || height < 1) throw new Error('无法获取预览图尺寸')
  if (width > BRAND_KNOWLEDGE_PREVIEW_MAX_WIDTH || height > BRAND_KNOWLEDGE_PREVIEW_MAX_HEIGHT) {
    throw new Error(`预览图尺寸过大，宽度需不超过 ${BRAND_KNOWLEDGE_PREVIEW_MAX_WIDTH}px，高度需不超过 ${BRAND_KNOWLEDGE_PREVIEW_MAX_HEIGHT}px`)
  }
  if (width * height > BRAND_KNOWLEDGE_PREVIEW_MAX_PIXELS) {
    throw new Error('预览图像素总量过大，需不超过 6000 万像素')
  }
  if (Number(metadata.pages || 1) > 1) throw new Error('预览图不支持动画或多页图片')

  const declared = normalizeContentType(declaredContentType)
  if (declared && declared !== details.contentType) throw new Error('预览图内容与声明格式不一致')

  return { ...details, width, height }
}

export async function prepareBrandKnowledgePreview(buffer: Buffer, declaredContentType?: string | null) {
  let metadata: sharp.Metadata
  try {
    metadata = await sharp(buffer, {
      animated: true,
      failOn: 'error',
      limitInputPixels: BRAND_KNOWLEDGE_PREVIEW_MAX_PIXELS,
      sequentialRead: true,
    }).metadata()
  } catch (error) {
    if (error instanceof Error && /pixel limit/i.test(error.message)) {
      throw new Error('预览图像素总量过大，需不超过 6000 万像素')
    }
    throw new Error('预览图无法解码，请上传完整的 PNG、JPEG 或 WebP 图片')
  }

  const source = assertBrandKnowledgePreviewMetadata(metadata, declaredContentType)
  const outputScale = Math.min(1, BRAND_KNOWLEDGE_PREVIEW_OUTPUT_WIDTH / source.width)
  const outputHeight = Math.max(1, Math.round(source.height * outputScale))
  const previewPlan = planBrandKnowledgePreviewSlices(
    source.height,
    outputHeight,
    BRAND_KNOWLEDGE_PREVIEW_SLICE_HEIGHT,
  )
  let slices: Buffer[]
  try {
    slices = await sliceImage(
      buffer,
      previewPlan.sliceHeightLimit,
      BRAND_KNOWLEDGE_PREVIEW_SLICE_MAX_KB,
      BRAND_KNOWLEDGE_PREVIEW_OUTPUT_WIDTH,
      {
        maxInputWidth: BRAND_KNOWLEDGE_PREVIEW_MAX_WIDTH,
        maxInputHeight: BRAND_KNOWLEDGE_PREVIEW_MAX_HEIGHT,
        maxInputPixels: BRAND_KNOWLEDGE_PREVIEW_MAX_PIXELS,
      },
    )
  } catch {
    throw new Error('预览图处理失败，请确认图片完整且未超过尺寸限制')
  }

  if (slices.length === 0) throw new Error('预览图处理后没有可用片段')
  return { source, slices }
}

export type BrandKnowledgeUploadedPreviewSlice = {
  buffer: Buffer
  declaredContentType?: string | null
}

export async function validateBrandKnowledgeUploadedPreviewSlices(
  uploadedSlices: BrandKnowledgeUploadedPreviewSlice[],
) {
  if (uploadedSlices.length < 1 || uploadedSlices.length > BRAND_KNOWLEDGE_MAX_PREVIEW_SLICE_COUNT) {
    throw new Error(`预览图切片数量需在 1 至 ${BRAND_KNOWLEDGE_MAX_PREVIEW_SLICE_COUNT} 片之间`)
  }
  const totalBytes = uploadedSlices.reduce((sum, slice) => sum + slice.buffer.length, 0)
  if (totalBytes > BRAND_KNOWLEDGE_MAX_PREVIEW_IMAGE_BYTES) {
    throw new Error('预览图切片总大小不能超过 50MB')
  }

  return withImageProcessingSlot(async () => {
    const slices: Array<{ buffer: Buffer; width: number; height: number }> = []
    let expectedWidth = 0
    let expectedFullSliceHeight = 0
    const maxUploadedSliceHeight = uploadedSlices.length === 1
      ? BRAND_KNOWLEDGE_PREVIEW_SINGLE_IMAGE_MAX_HEIGHT
      : BRAND_KNOWLEDGE_PREVIEW_SLICE_HEIGHT

    for (let index = 0; index < uploadedSlices.length; index += 1) {
      const uploaded = uploadedSlices[index]
      if (uploaded.buffer.length < 1 || uploaded.buffer.length > BRAND_KNOWLEDGE_MAX_PREVIEW_SLICE_BYTES) {
        throw new Error(`预览图第 ${index + 1} 片大小无效`)
      }
      if (normalizeContentType(uploaded.declaredContentType) !== 'image/webp') {
        throw new Error(`预览图第 ${index + 1} 片只支持 WebP 格式`)
      }

      let metadata: sharp.Metadata
      try {
        metadata = await sharp(uploaded.buffer, {
          animated: true,
          failOn: 'error',
          limitInputPixels: BRAND_KNOWLEDGE_PREVIEW_OUTPUT_WIDTH * maxUploadedSliceHeight,
          sequentialRead: true,
        }).metadata()
      } catch {
        throw new Error(`预览图第 ${index + 1} 片无法解码`)
      }

      const width = metadata.width || 0
      const height = metadata.height || 0
      if (metadata.format !== 'webp' || Number(metadata.pages || 1) > 1) {
        throw new Error(`预览图第 ${index + 1} 片不是有效的静态 WebP 图片`)
      }
      if (width < 1 || width > BRAND_KNOWLEDGE_PREVIEW_OUTPUT_WIDTH
        || height < 1 || height > maxUploadedSliceHeight) {
        throw new Error(`预览图第 ${index + 1} 片尺寸无效`)
      }
      if (index === 0) {
        expectedWidth = width
        expectedFullSliceHeight = height
      }
      if (width !== expectedWidth) throw new Error('预览图切片宽度不一致')
      if (uploadedSlices.length > 1) {
        const isLast = index === uploadedSlices.length - 1
        const isForcedShortPair = expectedFullSliceHeight <= Math.ceil(BRAND_KNOWLEDGE_PREVIEW_SLICE_HEIGHT / 2)
        const hasValidForcedPairGeometry = uploadedSlices.length === 2
          && (!isLast || height === expectedFullSliceHeight || height === expectedFullSliceHeight - 1)
        const hasValidStandardGeometry = expectedFullSliceHeight === BRAND_KNOWLEDGE_PREVIEW_SLICE_HEIGHT
          && (isLast ? height <= expectedFullSliceHeight : height === expectedFullSliceHeight)
        if ((isForcedShortPair && !hasValidForcedPairGeometry)
          || (!isForcedShortPair && !hasValidStandardGeometry)) {
          throw new Error('预览图切片高度不一致')
        }
      }
      slices.push({ buffer: uploaded.buffer, width, height })
    }

    return { slices, totalBytes }
  })
}