/**
 * Mappings from AssemblyScript types to WebAssembly types.
 * @module types
 *//***/

import {
  Class,
  FunctionTarget,
  Program,
  DecoratorFlags
} from "./program";

import {
  NativeType,
  ExpressionRef,
  Module
} from "./module";

/** Indicates the kind of a type. */
export const enum TypeKind {

  // signed integers

  /** An 8-bit signed integer. */
  I8,
  /** A 16-bit signed integer. */
  I16,
  /** A 32-bit signed integer. */
  I32,
  /** A 64-bit signed integer. */
  I64,
  /** A 32-bit/64-bit signed integer, depending on the target. */
  ISIZE,

  // unsigned integers

  /** An 8-bit unsigned integer. */
  U8,
  /** A 16-bit unsigned integer. */
  U16,
  /** A 32-bit unsigned integer. Also the base of function types. */
  U32,
  /** A 64-bit unsigned integer. */
  U64,
  /** A 32-bit/64-bit unsigned integer, depending on the target. Also the base of class types. */
  USIZE,
  /** A 1-bit unsigned integer. */
  BOOL, // sic

  // floats

  /** A 32-bit float. */
  F32,
  /** A 64-bit double. */
  F64,

  // other

  /** No return type. */
  VOID
}

/** Indicates capabilities of a type. */
export const enum TypeFlags {
  NONE = 0,
  /** Is a signed type that can represent negative values. */
  SIGNED = 1 << 0,
  /** Is an unsigned type that cannot represent negative values. */
  UNSIGNED = 1 << 1,
  /** Is an integer type. */
  INTEGER = 1 << 2,
  /** Is a floating point type. */
  FLOAT = 1 << 3,
  /** Is a pointer type. */
  POINTER = 1 << 4,
  /** Is smaller than 32-bits. */
  SHORT = 1 << 5,
  /** Is larger than 32-bits. */
  LONG = 1 << 6,
  /** Is a value type. */
  VALUE = 1 << 7,
  /** Is a reference type. */
  REFERENCE = 1 << 8,
  /** Is a nullable type. */
  NULLABLE = 1 << 9
}

/** Represents a resolved type. */
export class Type {

  /** Type kind. */
  kind: TypeKind;
  /** Type flags. */
  flags: TypeFlags;
  /** Size in bits. */
  size: u32;
  /** Size in bytes. */
  byteSize: i32;
  /** Underlying class reference, if a class type. */
  classReference: Class | null;
  /** Underlying signature reference, if a function type. */
  signatureReference: Signature | null;
  /** Respective non-nullable type, if nullable. */
  nonNullableType: Type;
  /** Cached nullable type, if non-nullable. */
  private cachedNullableType: Type | null = null;

  /** Constructs a new resolved type. */
  constructor(kind: TypeKind, flags: TypeFlags, size: u32) {
    this.kind = kind;
    this.flags = flags;
    this.size = size;
    this.byteSize = <i32>ceil<f64>(<f64>size / 8);
    this.classReference = null;
    this.signatureReference = null;
    this.nonNullableType = this;
  }

  /** Returns the closest int type representing this type. */
  get intType(): Type {
    switch (this.kind) {
      case TypeKind.I8: return Type.i8;
      case TypeKind.I16: return Type.i16;
      case TypeKind.F32:
      case TypeKind.I32: return Type.i32;
      case TypeKind.F64:
      case TypeKind.I64: return Type.i64;
      case TypeKind.ISIZE: return this.size == 64 ? Type.isize64 : Type.isize32;
      case TypeKind.U8: return Type.u8;
      case TypeKind.U16: return Type.u16;
      case TypeKind.U32: return Type.u32;
      case TypeKind.U64: return Type.u64;
      case TypeKind.USIZE: return this.size == 64 ? Type.usize64 : Type.usize32;
      case TypeKind.BOOL:
      default: return Type.i32;
    }
  }

  /** Tests if this is a managed type that needs GC hooks. */
  isManaged(program: Program): bool {
    if (program.hasGC) {
      let classReference = this.classReference;
      return classReference !== null && !classReference.hasDecorator(DecoratorFlags.UNMANAGED);
    }
    return false;
  }

  /** Computes the sign-extending shift in the target type. */
  computeSmallIntegerShift(targetType: Type): u32 {
    return targetType.size - this.size;
  }

  /** Computes the truncating mask in the target type. */
  computeSmallIntegerMask(targetType: Type): u32 {
    var size = this.is(TypeFlags.UNSIGNED) ? this.size : this.size - 1;
    return ~0 >>> (targetType.size - size);
  }

  /** Tests if this type has (all of) the specified flags. */
  is(flags: TypeFlags): bool { return (this.flags & flags) == flags; }
  /** Tests if this type has any of the specified flags. */
  isAny(flags: TypeFlags): bool { return (this.flags & flags) != 0; }

  /** Composes a class type from this type and a class. */
  asClass(classType: Class): Type {
    assert(this.kind == TypeKind.USIZE && !this.classReference);
    var ret = new Type(this.kind, this.flags & ~TypeFlags.VALUE | TypeFlags.REFERENCE, this.size);
    ret.classReference = classType;
    return ret;
  }

  /** Composes a function type from this type and a function. */
  asFunction(signature: Signature): Type {
    assert(this.kind == TypeKind.U32 && !this.signatureReference);
    var ret = new Type(this.kind, this.flags & ~TypeFlags.VALUE | TypeFlags.REFERENCE, this.size);
    ret.signatureReference = signature;
    return ret;
  }

  /** Composes the respective nullable type of this type. */
  asNullable(): Type {
    assert(this.is(TypeFlags.REFERENCE));
    if (!this.cachedNullableType) {
      assert(!this.is(TypeFlags.NULLABLE));
      this.cachedNullableType = new Type(this.kind, this.flags | TypeFlags.NULLABLE, this.size);
      this.cachedNullableType.nonNullableType = this;
      this.cachedNullableType.classReference = this.classReference;       // either a class reference
      this.cachedNullableType.signatureReference = this.signatureReference; // or a function reference
    }
    return this.cachedNullableType;
  }

  /** Tests if a value of this type is assignable to a target of the specified type. */
  isAssignableTo(target: Type, signednessIsRelevant: bool = false): bool {
    var currentClass: Class | null;
    var targetClass: Class | null;
    var currentFunction: Signature | null;
    var targetFunction: Signature | null;
    if (this.is(TypeFlags.REFERENCE)) {
      if (target.is(TypeFlags.REFERENCE)) {
        if (!this.is(TypeFlags.NULLABLE) || target.is(TypeFlags.NULLABLE)) {
          if (currentClass = this.classReference) {
            if (targetClass = target.classReference) {
              return currentClass.isAssignableTo(targetClass);
            }
          } else if (currentFunction = this.signatureReference) {
            if (targetFunction = target.signatureReference) {
              return currentFunction.isAssignableTo(targetFunction);
            }
          }
        }
      }
    } else if (!target.is(TypeFlags.REFERENCE)) {
      if (this.is(TypeFlags.INTEGER)) {
        if (target.is(TypeFlags.INTEGER)) {
          if (
            !signednessIsRelevant ||
            this == Type.bool || // a bool (0 or 1) can be safely assigned to all sorts of integers
            this.is(TypeFlags.SIGNED) == target.is(TypeFlags.SIGNED)
          ) {
            return this.size <= target.size;
          }
        } else if (target.kind == TypeKind.F32) {
          return this.size <= 23; // mantissa bits
        } else if (target.kind == TypeKind.F64) {
          return this.size <= 52; // ^
        }
      } else if (this.is(TypeFlags.FLOAT)) {
        if (target.is(TypeFlags.FLOAT)) {
          return this.size <= target.size;
        }
      }
    }
    return false;
  }

  /** Determines the common compatible type of two types, if any. */
  static commonCompatible(left: Type, right: Type, signednessIsImportant: bool): Type | null {
    if (right.isAssignableTo(left, signednessIsImportant)) return left;
    else if (left.isAssignableTo(right, signednessIsImportant)) return right;
    return null;
  }

  /** Converts this type to its TypeScript representation. */
  toString(kindOnly: bool = false): string {
    if (!kindOnly && this.is(TypeFlags.REFERENCE)) {
      let classReference = this.classReference;
      if (classReference) {
        return this.is(TypeFlags.NULLABLE)
          ? classReference.toString() + " | null"
          : classReference.toString();
      }
      let signatureReference = this.signatureReference;
      if (signatureReference) {
        return this.is(TypeFlags.NULLABLE)
          ? "(" + signatureReference.toString(true) + ") | null"
          : signatureReference.toString(true);
      }
      assert(false);
    }
    switch (this.kind) {
      case TypeKind.I8: return "i8";
      case TypeKind.I16: return "i16";
      case TypeKind.I32: return "i32";
      case TypeKind.I64: return "i64";
      case TypeKind.ISIZE: return "isize";
      case TypeKind.U8: return "u8";
      case TypeKind.U16: return "u16";
      case TypeKind.U32: return "u32";
      case TypeKind.U64: return "u64";
      case TypeKind.USIZE: return "usize";
      case TypeKind.BOOL: return "bool";
      case TypeKind.F32: return "f32";
      case TypeKind.F64: return "f64";
      default: assert(false);
      case TypeKind.VOID: return "void";
    }
  }

  // Binaryen specific

  /** Converts this type to its respective native type. */
  toNativeType(): NativeType {
    switch (this.kind) {
      default: return NativeType.I32;
      case TypeKind.I64:
      case TypeKind.U64: return NativeType.I64;
      case TypeKind.ISIZE:
      case TypeKind.USIZE: return this.size == 64 ? NativeType.I64 : NativeType.I32;
      case TypeKind.F32: return NativeType.F32;
      case TypeKind.F64: return NativeType.F64;
      case TypeKind.VOID:  return NativeType.None;
    }
  }

  /** Converts this type to its native `0` value. */
  toNativeZero(module: Module): ExpressionRef {
    switch (this.kind) {
      case TypeKind.VOID: assert(false);
      default: return module.createI32(0);
      case TypeKind.ISIZE:
      case TypeKind.USIZE: if (this.size != 64) return module.createI32(0);
      case TypeKind.I64:
      case TypeKind.U64: return module.createI64(0);
      case TypeKind.F32: return module.createF32(0);
      case TypeKind.F64: return module.createF64(0);
    }
  }

  /** Converts this type to its native `1` value. */
  toNativeOne(module: Module): ExpressionRef {
    switch (this.kind) {
      case TypeKind.VOID: assert(false);
      default: return module.createI32(1);
      case TypeKind.ISIZE:
      case TypeKind.USIZE: if (this.size != 64) return module.createI32(1);
      case TypeKind.I64:
      case TypeKind.U64: return module.createI64(1);
      case TypeKind.F32: return module.createF32(1);
      case TypeKind.F64: return module.createF64(1);
    }
  }

  /** Converts this type to its native `-1` value. */
  toNativeNegOne(module: Module): ExpressionRef {
    switch (this.kind) {
      case TypeKind.VOID: assert(false);
      default: return module.createI32(-1);
      case TypeKind.ISIZE:
      case TypeKind.USIZE: if (this.size != 64) return module.createI32(-1);
      case TypeKind.I64:
      case TypeKind.U64: return module.createI64(-1, -1);
      case TypeKind.F32: return module.createF32(-1);
      case TypeKind.F64: return module.createF64(-1);
    }
  }

  /** Converts this type to its signature string. */
  toSignatureString(): string {
    switch (this.kind) {
      default: return "i";
      case TypeKind.I64:
      case TypeKind.U64: return "I";
      case TypeKind.ISIZE:
      case TypeKind.USIZE: return this.size == 64 ? "I" : "i";
      case TypeKind.F32: return "f";
      case TypeKind.F64: return "F";
      case TypeKind.VOID: return "v";
    }
  }

  // Types

  /** An 8-bit signed integer. */
  static readonly i8: Type  = new Type(TypeKind.I8,
    TypeFlags.SIGNED   |
    TypeFlags.SHORT    |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,   8
  );

  /** A 16-bit signed integer. */
  static readonly i16: Type = new Type(TypeKind.I16,
    TypeFlags.SIGNED   |
    TypeFlags.SHORT    |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  16
  );

  /** A 32-bit signed integer. */
  static readonly i32: Type = new Type(TypeKind.I32,
    TypeFlags.SIGNED   |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  32
  );

  /** A 64-bit signed integer. */
  static readonly i64: Type = new Type(TypeKind.I64,
    TypeFlags.SIGNED   |
    TypeFlags.LONG     |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  64
  );

  /** A 32-bit signed size. WASM32 only. */
  static readonly isize32: Type = new Type(TypeKind.ISIZE,
    TypeFlags.SIGNED   |
    TypeFlags.INTEGER  |
    TypeFlags.POINTER  |
    TypeFlags.VALUE,  32
  );

  /** A 64-bit signed size. WASM64 only. */
  static readonly isize64: Type = new Type(TypeKind.ISIZE,
    TypeFlags.SIGNED   |
    TypeFlags.LONG     |
    TypeFlags.INTEGER  |
    TypeFlags.POINTER  |
    TypeFlags.VALUE,  64
  );

  /** An 8-bit unsigned integer. */
  static readonly u8: Type = new Type(TypeKind.U8,
    TypeFlags.UNSIGNED |
    TypeFlags.SHORT    |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,   8
  );

  /** A 16-bit unsigned integer. */
  static readonly u16: Type = new Type(TypeKind.U16,
    TypeFlags.UNSIGNED |
    TypeFlags.SHORT    |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  16
  );

  /** A 32-bit unsigned integer. */
  static readonly u32: Type = new Type(TypeKind.U32,
    TypeFlags.UNSIGNED |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  32
  );

  /** A 64-bit unsigned integer. */
  static readonly u64: Type = new Type(TypeKind.U64,
    TypeFlags.UNSIGNED |
    TypeFlags.LONG     |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,  64
  );

  /** A 32-bit unsigned size. WASM32 only. */
  static readonly usize32: Type = new Type(TypeKind.USIZE,
    TypeFlags.UNSIGNED |
    TypeFlags.INTEGER  |
    TypeFlags.POINTER  |
    TypeFlags.VALUE,  32
  );

  /** A 64-bit unsigned size. WASM64 only. */
  static readonly usize64: Type = new Type(TypeKind.USIZE,
    TypeFlags.UNSIGNED |
    TypeFlags.LONG     |
    TypeFlags.INTEGER  |
    TypeFlags.POINTER  |
    TypeFlags.VALUE,  64
  );

  /** A 1-bit unsigned integer. */
  static readonly bool: Type = new Type(TypeKind.BOOL,
    TypeFlags.UNSIGNED |
    TypeFlags.SHORT    |
    TypeFlags.INTEGER  |
    TypeFlags.VALUE,   1
  );

  /** A 32-bit float. */
  static readonly f32: Type = new Type(TypeKind.F32,
    TypeFlags.SIGNED   |
    TypeFlags.FLOAT    |
    TypeFlags.VALUE,  32
  );

  /** A 64-bit float. */
  static readonly f64: Type = new Type(TypeKind.F64,
    TypeFlags.SIGNED   |
    TypeFlags.LONG     |
    TypeFlags.FLOAT    |
    TypeFlags.VALUE,  64
  );

  /** No return type. */
  static readonly void: Type = new Type(TypeKind.VOID, TypeFlags.NONE, 0);
}

/** Converts an array of types to an array of native types. */
export function typesToNativeTypes(types: Type[]): NativeType[] {
  var numTypes = types.length;
  var ret = new Array<NativeType>(numTypes);
  for (let i = 0; i < numTypes; ++i) ret[i] = types[i].toNativeType();
  return ret;
}

/** Converts an array of types to its combined string representation. */
export function typesToString(types: Type[]): string {
  var numTypes = types.length;
  if (!numTypes) return "";
  var sb = new Array<string>(numTypes);
  for (let i = 0; i < numTypes; ++i) sb[i] = types[i].toString();
  return sb.join(",");
}

/** Represents a fully resolved function signature. */
export class Signature {

  /** Parameter types, if any, excluding `this`. */
  parameterTypes: Type[];
  /** Parameter names, if known, excluding `this`. */
  parameterNames: string[] | null;
  /** Number of required parameters excluding `this`. Other parameters are considered optional. */
  requiredParameters: i32;
  /** Return type. */
  returnType: Type;
  /** This type, if an instance signature. */
  thisType: Type | null;
  /** Whether the last parameter is a rest parameter. */
  hasRest: bool;
  /** Cached {@link FunctionTarget}. */
  cachedFunctionTarget: FunctionTarget | null = null;
  /** Respective function type. */
  type: Type;

  /** Constructs a new signature. */
  constructor(
    parameterTypes: Type[] | null = null,
    returnType: Type | null = null,
    thisType: Type | null = null
  ) {
    this.parameterTypes = parameterTypes ? parameterTypes : [];
    this.parameterNames = null;
    this.requiredParameters = 0;
    this.returnType = returnType ? returnType : Type.void;
    this.thisType = thisType;
    this.hasRest = false;
    this.type = Type.u32.asFunction(this);
  }

  /** Gets the known or, alternatively, generic parameter name at the specified index. */
  getParameterName(index: i32): string {
    var parameterNames = this.parameterNames;
    return parameterNames && parameterNames.length > index
      ? parameterNames[index]
      : getDefaultParameterName(index);
  }

  /** Tests if a value of this function type is assignable to a target of the specified function type. */
  isAssignableTo(target: Signature): bool {
    // TODO: maybe cache results?

    // check `this` type
    var thisThisType = this.thisType;
    var targetThisType = target.thisType;
    if (thisThisType) {
      if (!(targetThisType && thisThisType.isAssignableTo(targetThisType))) return false;
    } else if (targetThisType) {
      return false;
    }

    // check rest parameter
    if (this.hasRest != target.hasRest) return false; // TODO

    // check parameter types
    var thisParameterTypes = this.parameterTypes;
    var targetParameterTypes = target.parameterTypes;
    var numParameters = thisParameterTypes.length;
    if (numParameters != targetParameterTypes.length) return false;
    for (let i = 0; i < numParameters; ++i) {
      let thisParameterType = thisParameterTypes[i];
      let targetParameterType = targetParameterTypes[i];
      if (!thisParameterType.isAssignableTo(targetParameterType)) return false;
    }

    // check return type
    var thisReturnType = this.returnType;
    var targetReturnType = target.returnType;
    return thisReturnType == targetReturnType || thisReturnType.isAssignableTo(targetReturnType);
  }

  /** Converts a signature to a function type string. */
  static makeSignatureString(parameterTypes: Type[] | null, returnType: Type, thisType: Type | null = null): string {
    var sb = [];
    if (thisType) sb.push(thisType.toSignatureString());
    if (parameterTypes) {
      for (let i = 0, k = parameterTypes.length; i < k; ++i) sb.push(parameterTypes[i].toSignatureString());
    }
    sb.push(returnType.toSignatureString());
    return sb.join("");
  }

  /** Converts this signature to a function type string. */
  toSignatureString(): string {
    return Signature.makeSignatureString(this.parameterTypes, this.returnType, this.thisType);
  }

  /** Converts this signature to a string. */
  toString(includeThis: bool = false): string {
    var sb = new Array<string>();
    sb.push("(");
    var index = 0;
    var thisType = this.thisType;
    if (thisType) {
      if (includeThis) {
        sb.push("this: ");
        sb.push(thisType.toString());
        index = 1;
      }
    }
    var parameters = this.parameterTypes;
    var numParameters = parameters.length;
    if (numParameters) {
      let names = this.parameterNames;
      let numNames = names ? names.length : 0;
      let optionalStart = this.requiredParameters;
      let restIndex = this.hasRest ? numParameters - 1 : -1;
      for (let i = 0; i < numParameters; ++i, ++index) {
        if (index) sb.push(", ");
        if (i == restIndex) sb.push("...");
        if (i < numNames) sb.push((<string[]>names)[i]);
        else sb.push(getDefaultParameterName(i));
        if (i >= optionalStart && i != restIndex) sb.push("?: ");
        else sb.push(": ");
        sb.push(parameters[i].toString());
      }
    }
    sb.push(") => ");
    sb.push(this.returnType.toString());
    return sb.join("");
  }
}

// helpers

// Cached default parameter names used where names are unknown.
var cachedDefaultParameterNames: string[] | null = null;

/** Gets the cached default parameter name for the specified index. */
export function getDefaultParameterName(index: i32): string {
  if (!cachedDefaultParameterNames) cachedDefaultParameterNames = [];
  for (let i = cachedDefaultParameterNames.length; i <= index; ++i) {
    cachedDefaultParameterNames.push("arg$" + i.toString(10));
  }
  return cachedDefaultParameterNames[index - 1];
}