/*
 * Cadence - The resource-oriented smart contract programming language
 *
 * Copyright Flow Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package sema

import (
	"github.com/onflow/cadence/ast"
	"github.com/onflow/cadence/common"
)

// Import declarations are handled in two phases:
//
// 1. Resolution of the import statement.
//
//     The default case is that one location is resolved to one location (itself),
//     though e.g. an address location may also be resolved into multiple address locations.
//
//     For example, an import declaration `import a, b from 0x1` specifies the import of the declarations with
//     the identifiers `a` and `b` from the address location `0x1`.
//     This import declaration might be resolved into just the location itself, i.e. the address location `0x1`,
//     but could also be resolved into multiple locations, e.g. the address locations `0x1.a` and `0x1.b`.
//
// 2. Acquiring the programs for the resolved imports. For each resolved import a separate program can be returned.
//

func (checker *Checker) VisitImportDeclaration(declaration *ast.ImportDeclaration) struct{} {
	// Handled in `declareImportDeclaration`
	panic(&UnreachableStatementError{
		Range: ast.NewRangeFromPositioned(checker.memoryGauge, declaration),
	})
}

func (checker *Checker) declareImportDeclaration(declaration *ast.ImportDeclaration) {
	locationRange := ast.NewRange(
		checker.memoryGauge,
		declaration.LocationPos,
		// TODO: improve
		declaration.LocationPos,
	)

	identifiers := declaration.Identifiers

	resolvedLocations, err := checker.resolveLocation(identifiers, declaration.Location)
	if err != nil {
		checker.report(err)
		return
	}

	// 1) If the import is just for an address (e.g. `import 0x01`) without specifying any contracts, AND
	// 2) If the imported address is same as the address of the account to which the current contract is deploying,
	// Then this could create a cycle, as soon the current contract is deployed.
	// e.g:
	//    import 0x01
	//    access(all) contract Foo {}
	//

	if len(identifiers) == 0 {
		if currentProgramLocation, ok := checker.Location.(common.AddressLocation); ok {
			if importLocation, ok := declaration.Location.(common.AddressLocation); ok {
				if currentProgramLocation.Address == importLocation.Address {
					checker.report(
						&CyclicImportsError{
							Location: declaration.Location,
							Range:    locationRange,
						},
					)

					return
				}
			}
		}
	}

	checker.Elaboration.SetImportDeclarationsResolvedLocations(declaration, resolvedLocations)

	for _, resolvedLocation := range resolvedLocations {
		checker.importResolvedLocation(resolvedLocation, locationRange)
	}
}

func (checker *Checker) resolveLocation(identifiers []ast.Identifier, location common.Location) ([]ResolvedLocation, error) {

	// If no location handler is available,
	// default to resolving to a single location that declares all identifiers

	locationHandler := checker.Config.LocationHandler
	if locationHandler == nil {
		return []ResolvedLocation{
			{
				Location:    location,
				Identifiers: identifiers,
			},
		}, nil
	}

	// A location handler is available,
	// use it to resolve the location / identifiers
	return locationHandler(identifiers, location)
}

func (checker *Checker) importResolvedLocation(resolvedLocation ResolvedLocation, locationRange ast.Range) {

	// First, get the Import for the resolved location

	location := resolvedLocation.Location

	var imp Import

	importHandler := checker.Config.ImportHandler
	if importHandler != nil {
		var err error
		imp, err = importHandler(checker, location, locationRange)
		if err != nil {

			// The import handler may return CyclicImportsError specifically
			// to indicate that this import is a cyclic import.
			// In that case, return the error as is, for this location.
			//
			// If the error is not a cyclic error,
			// it is considered an error in the imported program,
			// and is wrapped

			if _, ok := err.(*CyclicImportsError); !ok {
				err = &ImportedProgramError{
					Err:      err,
					Location: location,
					Range:    locationRange,
				}
			}

			checker.report(err)
			return
		}
	}

	if imp == nil {
		checker.report(
			&UnresolvedImportError{
				ImportLocation: location,
				Range:          locationRange,
			},
		)
		return
	}

	// If the import itself is being checked right now,
	// then the import is cyclic

	if imp.IsChecking() {
		checker.report(
			&CyclicImportsError{
				Location: location,
				Range:    locationRange,
			},
		)
		return
	}

	// Attempt to import the requested value declarations

	allValueElements := imp.AllValueElements()
	foundValues, invalidAccessedValues := checker.importElements(
		checker.valueActivations,
		resolvedLocation.Identifiers,
		allValueElements,
		true,
	)

	// Attempt to import the requested type declarations

	allTypeElements := imp.AllTypeElements()
	foundTypes, invalidAccessedTypes := checker.importElements(
		checker.typeActivations,
		resolvedLocation.Identifiers,
		allTypeElements,
		false,
	)

	// For each identifier, report if the import is invalid due to
	// restricted access and report an error (i.e. if there is
	// both a value and type with the same name, only report a single error)

	for _, identifier := range resolvedLocation.Identifiers {

		invalidAccessedElement, isInvalidAccess := invalidAccessedValues[identifier]
		if !isInvalidAccess {
			invalidAccessedElement, isInvalidAccess = invalidAccessedTypes[identifier]
		}

		if !isInvalidAccess {
			continue
		}

		checker.report(
			&InvalidAccessError{
				Name:              identifier.Identifier,
				RestrictingAccess: invalidAccessedElement.Access,
				DeclarationKind:   invalidAccessedElement.DeclarationKind,
				Range:             ast.NewRangeFromPositioned(checker.memoryGauge, identifier),
			},
		)
	}

	identifierCount := len(resolvedLocation.Identifiers)

	// Determine which requested declarations could neither be found
	// in the value nor in the type declarations of the imported program.
	// For each missing import, report an error and declare both a value
	// with an invalid type and an invalid type to avoid spurious errors
	// due to uses of the inaccessible value or type.
	//
	// Also show which declarations are available, to help with debugging.

	missing := make([]ast.Identifier, 0, identifierCount)

	for _, identifier := range resolvedLocation.Identifiers {
		if foundValues[identifier] || foundTypes[identifier] {
			continue
		}

		missing = append(missing, identifier)
	}

	if len(missing) > 0 {
		capacity := allValueElements.Len() + allTypeElements.Len()
		available := make([]string, 0, capacity)
		availableSet := make(map[string]struct{}, capacity)

		allValueElements.Foreach(func(identifier string, _ ImportElement) {
			if _, ok := availableSet[identifier]; ok {
				return
			}
			availableSet[identifier] = struct{}{}
			available = append(available, identifier)
		})

		allTypeElements.Foreach(func(identifier string, _ ImportElement) {
			if _, ok := availableSet[identifier]; ok {
				return
			}
			availableSet[identifier] = struct{}{}
			available = append(available, identifier)
		})

		checker.handleMissingImports(missing, available, location)
	}
}

func (checker *Checker) handleMissingImports(missing []ast.Identifier, available []string, importLocation common.Location) {
	for _, identifier := range missing {
		checker.report(
			&NotExportedError{
				Name:           identifier.Identifier,
				ImportLocation: importLocation,
				Available:      available,
				Pos:            identifier.Pos,
			},
		)

		// NOTE: declare constant variable with invalid type to silence rest of program
		const access = PrimitiveAccess(ast.AccessSelf)

		_, err := checker.valueActivations.declare(variableDeclaration{
			identifier:               identifier.Identifier,
			ty:                       InvalidType,
			access:                   access,
			kind:                     common.DeclarationKindValue,
			pos:                      identifier.Pos,
			isConstant:               true,
			allowOuterScopeShadowing: false,
		})
		checker.report(err)

		// NOTE: declare type with invalid type to silence rest of program
		_, err = checker.typeActivations.declareType(typeDeclaration{
			identifier:               identifier,
			ty:                       InvalidType,
			declarationKind:          common.DeclarationKindType,
			access:                   access,
			allowOuterScopeShadowing: false,
		})
		checker.report(err)
	}
}

func (checker *Checker) importElements(
	valueActivations *VariableActivations,
	requestedIdentifiers []ast.Identifier,
	availableElements *StringImportElementOrderedMap,
	importValues bool,
) (
	found map[ast.Identifier]bool,
	invalidAccessed map[ast.Identifier]ImportElement,
) {
	found = map[ast.Identifier]bool{}
	invalidAccessed = map[ast.Identifier]ImportElement{}

	// Determine which identifiers are imported /
	// which variables need to be declared

	explicitlyImported := map[string]ast.Identifier{}

	var elements *StringImportElementOrderedMap

	identifiersCount := len(requestedIdentifiers)
	if identifiersCount > 0 && availableElements != nil {
		elements = &StringImportElementOrderedMap{}
		for _, identifier := range requestedIdentifiers {
			name := identifier.Identifier
			element, ok := availableElements.Get(name)
			if !ok {
				continue
			}
			elements.Set(name, element)
			found[identifier] = true
			explicitlyImported[name] = identifier
		}
	} else {
		elements = availableElements
	}

	if elements != nil {
		elements.Foreach(func(name string, element ImportElement) {

			// If the variable can't be imported due to restricted access,
			// report an error, but still import the variable

			access := element.Access

			if !checker.Config.AccessCheckMode.IsReadableAccess(access) {

				// If the variable was imported explicitly, report an error

				if identifier, ok := explicitlyImported[name]; ok {
					invalidAccessed[identifier] = element
				} else {
					// Don't import not explicitly imported inaccessible variable
					return
				}
			}

			elementType := element.Type

			if importValues {
				// Imported contract values must be imported as a reference.
				compositeType, ok := elementType.(*CompositeType)
				if ok && compositeType.Kind == common.CompositeKindContract {
					elementType = NewReferenceType(checker.memoryGauge, UnauthorizedAccess, compositeType)
				}
			}

			_, err := valueActivations.declare(variableDeclaration{
				identifier: name,
				ty:         elementType,
				// TODO: implies that type is "re-exported"
				access: access,
				kind:   element.DeclarationKind,
				// TODO:
				pos:                      ast.EmptyPosition,
				isConstant:               true,
				argumentLabels:           element.ArgumentLabels,
				allowOuterScopeShadowing: false,
			})
			checker.report(err)
		})
	}

	return
}