import {
  CODE_MIN,
  CODE_SIZE_MIN,
  CONTAINER_MAX,
  CONTAINER_MIN,
  CONTAINER_SIZE_MIN,
  FORMAT,
  INPUTS_MAX,
  KIND_CODE,
  KIND_CONTAINER,
  KIND_DATA,
  KIND_TYPE,
  MAGIC,
  MAX_HEADER_SIZE,
  MAX_STACK_HEIGHT,
  OUTPUTS_MAX,
  TERMINATOR,
  TYPE_DIVISOR,
  TYPE_MAX,
  TYPE_MIN,
  VERSION,
} from './constants.js'
import { EOFError, validationError } from './errors.js'
import { ContainerSectionType, verifyCode } from './verify.js'

import type { EVM } from '../evm.js'

/*
  This file creates EOF Containers
  EOF Containers are described in EIP-3540. 
  A container consists of a header and a body. The header describes the layout of the body.
  The body has the actual "interesting" contents, such as the bytecode to run, the data section, 
  and possibly yet-to-be-deployed containers (via EOFCREATE, to create new EOF contracts from an existing one)
*/

// This enum marks the "mode" of a container
// Depending on this mode, certain extra checks for validity have to be done, or some checks can be skipped
export enum EOFContainerMode {
  Default, // Default container validation
  Initmode, // Initmode container validation (for subcontainers pointed to by EOFCreate)
  TxInitmode, // Tx initmode container validation (for txs deploying EOF contracts)
}

// The StreamReader is a helper class to help reading byte arrays
class StreamReader {
  private data: Uint8Array // Stream to read
  private ptr: number // Current pointer to where the stream is being read
  constructor(stream: Uint8Array) {
    this.data = stream
    this.ptr = 0
  }

  /**
   * Read `amount` bytes from the stream. Throws when trying to read out of bounds with an optional error string.
   * This also updates the internal pointer
   * @param amount Bytes to read
   * @param errorStr Optional error string to throw when trying to read out-of-bounds
   * @returns The byte array with length `amount`
   */
  readBytes(amount: number, errorStr?: string) {
    const end = this.ptr + amount
    if (end > this.data.length) {
      validationError(EOFError.OutOfBounds, this.ptr, errorStr)
    }
    const ptr = this.ptr
    this.ptr += amount
    return this.data.slice(ptr, end)
  }

  /**
   * Reads an Uint8. Also updates the pointer.
   * @param errorStr Optional error string
   * @returns The uint8
   */
  readUint(errorStr?: string) {
    if (this.ptr >= this.data.length) {
      validationError(EOFError.OutOfBounds, this.ptr, errorStr)
    }
    return this.data[this.ptr++]
  }

  /**
   * Verify that the current uint8 pointed to by the pointer is the expected uint8
   * Also updates the pointer
   * @param expect The uint to expect
   * @param errorStr Optional error string when the read uint is not the expected uint
   */
  verifyUint(expect: number, errorStr?: string) {
    if (this.readUint() !== expect) {
      validationError(EOFError.VerifyUint, this.ptr - 1, errorStr)
    }
  }

  /**
   * Same as readUint, except this reads an uint16
   * @param errorStr
   * @returns
   */
  readUint16(errorStr?: string) {
    const end = this.ptr + 2
    if (end > this.data.length) {
      validationError(EOFError.OutOfBounds, this.ptr, errorStr)
    }
    const ptr = this.ptr
    this.ptr += 2
    return new DataView(this.data.buffer).getUint16(ptr)
  }

  /**
   * Get the current pointer of the stream
   * @returns The pointer
   */
  getPtr() {
    return this.ptr
  }

  // Get the remainder bytes of the current stream
  readRemainder() {
    return this.data.slice(this.ptr)
  }

  // Returns `true` if the stream is fully read, or false if there are dangling bytes
  isAtEnd() {
    return this.ptr === this.data.length
  }
}

// TODO add initcode flags (isEOFContract)
// TODO validation: mark sections as either initcode or runtime code to validate

/**
 * The EOFHeader, describing the header of the EOF container
 */
class EOFHeader {
  typeSize: number // Size of types section
  codeSizes: number[] // Sizes of code sections
  containerSizes: number[] // Sizes of containers
  dataSize: number // Size of data section
  dataSizePtr: number // Used to edit the dataSize in RETURNCONTRACT
  buffer: Uint8Array // The raw buffer of the entire header

  private codeStartPos: number[] // Internal array to track at which byte of the container the code starts (per section)

  /**
   * Create an EOF header. Performs various validation checks inside the constructor
   * @param input either a raw header or a complete container
   */
  constructor(input: Uint8Array) {
    if (input.length > MAX_HEADER_SIZE) {
      throw new Error('err: container size more than maximum valid size')
    }
    const stream = new StreamReader(input)
    // Verify that the header starts with 0xEF0001
    stream.verifyUint(FORMAT, EOFError.FORMAT)
    stream.verifyUint(MAGIC, EOFError.MAGIC)
    stream.verifyUint(VERSION, EOFError.VERSION)
    if (input.length < 15) {
      throw new Error('err: container size less than minimum valid size')
    }
    // Verify that the types section is present and its length is valid
    stream.verifyUint(KIND_TYPE, EOFError.KIND_TYPE)
    const typeSize = stream.readUint16(EOFError.TypeSize)
    if (typeSize < TYPE_MIN) {
      validationError(EOFError.InvalidTypeSize, typeSize)
    }
    if (typeSize % TYPE_DIVISOR !== 0) {
      validationError(EOFError.InvalidTypeSize, typeSize)
    }
    if (typeSize > TYPE_MAX) {
      throw new Error(`err: number of code sections must not exceed 1024 (got ${typeSize})`)
    }
    // Verify that the code section is present and its size is valid
    stream.verifyUint(KIND_CODE, EOFError.KIND_CODE)
    const codeSize = stream.readUint16(EOFError.CodeSize)
    if (codeSize < CODE_MIN) {
      validationError(EOFError.MinCodeSections)
    }
    if (codeSize !== typeSize / TYPE_DIVISOR) {
      validationError(EOFError.TypeSections, typeSize / TYPE_DIVISOR, codeSize)
    }
    // Read the actual code sizes in the code section and verify that each section has the minimum size
    const codeSizes = []
    for (let i = 0; i < codeSize; i++) {
      const codeSectionSize = stream.readUint16(EOFError.CodeSection)
      if (codeSectionSize < CODE_SIZE_MIN) {
        validationError(EOFError.CodeSectionSize)
      }
      codeSizes.push(codeSectionSize)
    }

    // Check if there are container sections
    let nextSection = stream.readUint()
    const containerSizes: number[] = []
    if (nextSection === KIND_CONTAINER) {
      // The optional container section is present, validate that the size is within bounds
      const containerSectionSize = stream.readUint16(EOFError.ContainerSize)

      if (containerSectionSize < CONTAINER_MIN) {
        validationError(EOFError.ContainerSectionSize)
      }
      if (containerSectionSize > CONTAINER_MAX) {
        validationError(EOFError.ContainerSectionSize)
      }

      // Read the actual container sections and validate that each section has the minimum size
      for (let i = 0; i < containerSectionSize; i++) {
        const containerSize = stream.readUint16(EOFError.ContainerSection)

        if (containerSize < CONTAINER_SIZE_MIN) {
          validationError(EOFError.ContainerSectionMin)
        }

        containerSizes.push(containerSize)
      }

      nextSection = stream.readUint()
    }

    // Verify that the next section is of the data type
    if (nextSection !== KIND_DATA) {
      validationError(EOFError.KIND_DATA)
    }

    this.dataSizePtr = stream.getPtr()

    const dataSize = stream.readUint16(EOFError.DataSize)

    // Verify that the header ends with the TERMINATOR byte
    stream.verifyUint(TERMINATOR, EOFError.TERMINATOR)

    // Write all values to the header object
    this.typeSize = typeSize
    this.codeSizes = codeSizes
    this.containerSizes = containerSizes
    this.dataSize = dataSize
    // Slice the input such that `this.buffer` is now the complete header
    // If there are dangling bytes in the stream, this is OK: this is the body section of the container
    this.buffer = input.slice(0, stream.getPtr())
    const relativeOffset = this.buffer.length + this.typeSize
    // Write the start of the first code section into `codeStartPos`
    // Note: in EVM, if one would set the Program Counter to this byte, it would start executing the bytecode of the first code section
    this.codeStartPos = [relativeOffset]
  }

  sections() {
    return [this.typeSize, this.codeSizes, this.containerSizes, this.dataSize]
  }
  sectionSizes() {
    return [1, this.codeSizes.length, this.containerSizes.length, 1]
  }

  // Returns the code position in the container for the requested section
  // Setting the Program Counter in the EVM to a number of this array would start executing the bytecode of the indexed section
  getCodePosition(section: number) {
    if (this.codeStartPos[section]) {
      return this.codeStartPos[section]
    }
    const start = this.codeStartPos.length
    let offset = this.codeStartPos[start - 1]
    for (let i = start; i <= section; i++) {
      offset += this.codeSizes[i - 1]
      this.codeStartPos[i] = offset
    }
    return offset
  }
}

export interface TypeSection {
  inputs: number
  outputs: number
  maxStackHeight: number
}

/**
 * The EOF body holds the contents of the EOF container, such as the code sections (bytecode),
 * the subcontainers (EOF containers to be deployed via EOFCREATE) and the data section
 */
class EOFBody {
  typeSections: TypeSection[] // Array of type sections, used to index the inputs/outputs/max stack height of each section
  codeSections: Uint8Array[] // Bytecode of each code section
  containerSections: Uint8Array[] // Raw container bytes of each subcontainer
  entireCode: Uint8Array // The `entireCode` are all code sections concatenated
  dataSection: Uint8Array // Bytes of the data section
  buffer: Uint8Array // Raw bytes of the body

  txCallData?: Uint8Array // Only available in TxInitmode. The `txCallData` are the dangling bytes after parsing the container,
  // and these are used for the CALLDATA in the EVM when trying to create a contract via a transaction, and the deployment code is an EOF container

  constructor(
    buf: Uint8Array, // Buffer of the body. This should be the entire body. It is not valid to pass an entire EOF container in here
    header: EOFHeader, // EOFHeader corresponding to this body
    eofMode: EOFContainerMode = EOFContainerMode.Default, // Container mode of EOF
    dataSectionAllowedSmaller = false, // Only for validation: Deployment containers are allowed to have smaller data section size
  ) {
    const stream = new StreamReader(buf)
    const typeSections: TypeSection[] = []
    // Read and parse each type section, and validate that the type section values are within valid bounds
    for (let i = 0; i < header.typeSize / 4; i++) {
      const inputs = stream.readUint(EOFError.Inputs)
      const outputs = stream.readUint(EOFError.Outputs)
      const maxStackHeight = stream.readUint16(EOFError.MaxStackHeight)
      if (i === 0) {
        if (inputs !== 0) {
          validationError(EOFError.Code0Inputs)
        }
        if (outputs !== 0x80) {
          validationError(EOFError.Code0Outputs)
        }
      }
      if (inputs > INPUTS_MAX) {
        validationError(EOFError.MaxInputs, i, inputs)
      }
      if (outputs > OUTPUTS_MAX) {
        validationError(EOFError.MaxOutputs, i, outputs)
      }
      if (maxStackHeight > MAX_STACK_HEIGHT) {
        validationError(EOFError.MaxStackHeightLimit, i, maxStackHeight)
      }
      typeSections.push({
        inputs,
        outputs,
        maxStackHeight,
      })
    }
    // Read each code section
    const codeStartPtr = stream.getPtr()
    const codes = []
    for (const [i, codeSize] of header.codeSizes.entries()) {
      try {
        const code = stream.readBytes(codeSize)
        codes.push(code)
      } catch {
        validationError(EOFError.CodeSection, i)
      }
    }
    // Write the entire code section to the entireCodeSection
    const entireCodeSection = buf.slice(codeStartPtr, stream.getPtr())

    // Read all raw subcontainers and push those to the containers array
    const containers = []
    for (const [i, containerSize] of header.containerSizes.entries()) {
      try {
        const container = stream.readBytes(containerSize)
        containers.push(container)
      } catch {
        validationError(EOFError.ContainerSection, i)
      }
    }

    // Data section of the body
    // Note: for EOF containers in Initmode (these are Subcontainers) it is allowed
    // to have a data section of size lower than what is written in the header
    // For details, see "Data section lifecycle" of EIP 7620
    let dataSection: Uint8Array

    // Edge case: deployment code validation
    if (eofMode !== EOFContainerMode.Initmode && !dataSectionAllowedSmaller) {
      dataSection = stream.readBytes(header.dataSize, EOFError.DataSection)

      if (eofMode === EOFContainerMode.Default) {
        if (!stream.isAtEnd()) {
          // If there are dangling bytes in default container mode, this is invalid
          validationError(EOFError.DanglingBytes)
        }
      } else {
        // Tx init mode: the remaining bytes (if any) are used as CALLDATA in the EVM, in case of a Tx init
        this.txCallData = stream.readRemainder()
      }
    } else {
      dataSection = stream.readRemainder()
    }

    // Write all data to the object
    this.typeSections = typeSections
    this.codeSections = codes
    this.containerSections = containers
    this.entireCode = entireCodeSection
    this.dataSection = dataSection
    this.buffer = buf
  }
  sections() {
    return [this.typeSections, this.codeSections, this.dataSection]
  }
  size() {
    return {
      typeSize: this.typeSections.length,
      codeSize: this.codeSections.length,
      dataSize: this.dataSection.length,
    }
  }
  sectionSizes() {
    return [
      this.typeSections.map(() => 4),
      this.codeSections.map((b) => b.length),
      this.dataSection.length,
    ]
  }
}

/**
 * Main constructor for the EOFContainer
 */
export class EOFContainer {
  header: EOFHeader
  body: EOFBody
  buffer: Uint8Array
  eofMode: EOFContainerMode

  /**
   *
   * @param buf Entire container buffer
   * @param eofMode Container mode to validate the container on
   * @param dataSectionAllowedSmaller `true` if the data section is allowed to be smaller than the data section size in the header
   */
  constructor(
    buf: Uint8Array,
    eofMode: EOFContainerMode = EOFContainerMode.Default,
    dataSectionAllowedSmaller = false,
  ) {
    this.eofMode = eofMode
    this.header = new EOFHeader(buf)
    this.body = new EOFBody(
      buf.slice(this.header.buffer.length),
      this.header,
      eofMode,
      dataSectionAllowedSmaller,
    )
    this.buffer = buf
  }
}

/**
 * This method validates the EOF. It also performs deeper validation of the body, such as stack/opcode validation
 * This is ONLY necessary when trying to deploy contracts from a transaction: these can submit containers which are invalid
 * Since all deployed EOF containers are valid by definition, `validateEOF` does not need to be called each time an EOF contract is called
 * @param input Full container buffer
 * @param evm EVM, to read opcodes from
 * @param containerMode Container mode to validate on
 * @param eofMode EOF mode to run in
 * @returns
 */
export function validateEOF(
  input: Uint8Array,
  evm: EVM,
  containerMode: ContainerSectionType = ContainerSectionType.RuntimeCode,
  eofMode: EOFContainerMode = EOFContainerMode.Default,
) {
  const container = new EOFContainer(
    input,
    eofMode,
    containerMode === ContainerSectionType.DeploymentCode,
  )
  const containerMap = verifyCode(container, evm, containerMode)
  // Recursively validate the containerSections
  for (let i = 0; i < container.body.containerSections.length; i++) {
    const subContainer = container.body.containerSections[i]
    const mode = containerMap.get(i)!
    validateEOF(subContainer, evm, mode)
  }
  return container
}