/*
 * Copyright (c) 2022, Ali Mohammad Pur <mpfard@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/GenericLexer.h>
#include <AK/Queue.h>
#include <AK/String.h>
#include <AK/Variant.h>
#include <AK/Vector.h>
#include <Shell/AST.h>

namespace Shell::Posix {

enum class Reduction {
    None,
    End,
    Operator,
    Comment,
    SingleQuotedString,
    DoubleQuotedString,
    Expansion,
    CommandExpansion,
    Start,
    ArithmeticExpansion,
    SpecialParameterExpansion,
    ParameterExpansion,
    CommandOrArithmeticSubstitutionExpansion,
    ExtendedParameterExpansion,

    // Separate rule, not used by the main flow.
    HeredocContents,
};

struct ExpansionRange {
    size_t start;
    size_t length;
};

struct ParameterExpansion {
    StringBuilder parameter;
    ExpansionRange range;
};

struct CommandExpansion {
    StringBuilder command;
    ExpansionRange range;
};

struct ArithmeticExpansion {
    String expression;
    StringBuilder value;
    ExpansionRange range;
};

using Expansion = Variant<ParameterExpansion, CommandExpansion, ArithmeticExpansion>;

struct ResolvedParameterExpansion {
    String parameter;
    String argument;
    ExpansionRange range;
    enum class Op {
        UseDefaultValue,                    // ${parameter:-word}
        AssignDefaultValue,                 // ${parameter:=word}
        IndicateErrorIfEmpty,               // ${parameter:?word}
        UseAlternativeValue,                // ${parameter:+word}
        UseDefaultValueIfUnset,             // ${parameter-default}
        AssignDefaultValueIfUnset,          // ${parameter=default}
        IndicateErrorIfUnset,               // ${parameter?default}
        UseAlternativeValueIfUnset,         // ${parameter+default}
        RemoveLargestSuffixByPattern,       // ${parameter%%pattern}
        RemoveLargestPrefixByPattern,       // ${parameter##pattern}
        RemoveSmallestSuffixByPattern,      // ${parameter%pattern}
        RemoveSmallestPrefixByPattern,      // ${parameter#pattern}
        StringLength,                       // ${#parameter}
        GetPositionalParameter,             // ${parameter}
        GetVariable,                        // ${parameter}
        GetLastBackgroundPid,               // $!
        GetPositionalParameterList,         // $*
        GetCurrentOptionFlags,              // $-
        GetPositionalParameterCount,        // $#
        GetLastExitStatus,                  // $?
        GetPositionalParameterListAsString, // $@
        GetShellProcessId,                  // $$
    } op;

    enum class Expand {
        Nothing,
        Word,
    } expand { Expand::Nothing };

    DeprecatedString to_deprecated_string() const
    {
        StringBuilder builder;
        builder.append("{"sv);
        switch (op) {
        case Op::UseDefaultValue:
            builder.append("UseDefaultValue"sv);
            break;
        case Op::AssignDefaultValue:
            builder.append("AssignDefaultValue"sv);
            break;
        case Op::IndicateErrorIfEmpty:
            builder.append("IndicateErrorIfEmpty"sv);
            break;
        case Op::UseAlternativeValue:
            builder.append("UseAlternativeValue"sv);
            break;
        case Op::UseDefaultValueIfUnset:
            builder.append("UseDefaultValueIfUnset"sv);
            break;
        case Op::AssignDefaultValueIfUnset:
            builder.append("AssignDefaultValueIfUnset"sv);
            break;
        case Op::IndicateErrorIfUnset:
            builder.append("IndicateErrorIfUnset"sv);
            break;
        case Op::UseAlternativeValueIfUnset:
            builder.append("UseAlternativeValueIfUnset"sv);
            break;
        case Op::RemoveLargestSuffixByPattern:
            builder.append("RemoveLargestSuffixByPattern"sv);
            break;
        case Op::RemoveLargestPrefixByPattern:
            builder.append("RemoveLargestPrefixByPattern"sv);
            break;
        case Op::RemoveSmallestSuffixByPattern:
            builder.append("RemoveSmallestSuffixByPattern"sv);
            break;
        case Op::RemoveSmallestPrefixByPattern:
            builder.append("RemoveSmallestPrefixByPattern"sv);
            break;
        case Op::StringLength:
            builder.append("StringLength"sv);
            break;
        case Op::GetPositionalParameter:
            builder.append("GetPositionalParameter"sv);
            break;
        case Op::GetLastBackgroundPid:
            builder.append("GetLastBackgroundPid"sv);
            break;
        case Op::GetPositionalParameterList:
            builder.append("GetPositionalParameterList"sv);
            break;
        case Op::GetCurrentOptionFlags:
            builder.append("GetCurrentOptionFlags"sv);
            break;
        case Op::GetPositionalParameterCount:
            builder.append("GetPositionalParameterCount"sv);
            break;
        case Op::GetLastExitStatus:
            builder.append("GetLastExitStatus"sv);
            break;
        case Op::GetPositionalParameterListAsString:
            builder.append("GetPositionalParameterListAsString"sv);
            break;
        case Op::GetShellProcessId:
            builder.append("GetShellProcessId"sv);
            break;
        case Op::GetVariable:
            builder.append("GetVariable"sv);
            break;
        }
        builder.append(" "sv);
        builder.append(parameter);
        builder.append(" ("sv);
        builder.append(argument);
        builder.append(")"sv);
        builder.append("}"sv);
        return builder.to_deprecated_string();
    }
};

struct ResolvedCommandExpansion {
    RefPtr<AST::Node> command;
    ExpansionRange range;
};

struct ResolvedArithmeticExpansion {
    String source_expression;
    ExpansionRange range;
};

using ResolvedExpansion = Variant<ResolvedParameterExpansion, ResolvedCommandExpansion, ResolvedArithmeticExpansion>;

struct HeredocEntry {
    String key;
    bool allow_interpolation;
    bool dedent;
};

struct State {
    StringBuilder buffer {};
    Reduction previous_reduction { Reduction::Start };
    bool escaping { false };
    AST::Position position {
        .start_offset = 0,
        .end_offset = 0,
        .start_line = {
            .line_number = 0,
            .line_column = 0,
        },
        .end_line = {
            .line_number = 0,
            .line_column = 0,
        },
    };
    Vector<Expansion> expansions {};
    Queue<HeredocEntry> heredoc_entries {};
    bool on_new_line { true };
};

struct Token {
    enum class Type {
        Eof,
        Newline,
        Continuation,
        Token,
        And,
        Pipe,
        OpenParen,
        CloseParen,
        Great,
        Less,
        AndIf,
        OrIf,
        DoubleSemicolon,
        DoubleLess,
        DoubleGreat,
        LessAnd,
        GreatAnd,
        LessGreat,
        DoubleLessDash,
        Clobber,
        Semicolon,
        HeredocContents,

        // Not produced by this lexer, but generated in later stages.
        AssignmentWord,
        Bang,
        Case,
        CloseBrace,
        Do,
        Done,
        Elif,
        Else,
        Esac,
        Fi,
        For,
        If,
        In,
        IoNumber,
        OpenBrace,
        Then,
        Until,
        VariableName,
        While,
        Word,
    };

    Type type;
    String value;
    Optional<AST::Position> position;
    Vector<Expansion> expansions;
    Vector<ResolvedExpansion> resolved_expansions {};
    StringView original_text;
    Optional<String> relevant_heredoc_key {};
    bool could_be_start_of_a_simple_command { false };

    static ErrorOr<Vector<Token>> maybe_from_state(State const& state)
    {
        if (state.buffer.is_empty() || state.buffer.string_view().trim_whitespace().is_empty())
            return Vector<Token> {};

        auto token = Token {
            .type = Type::Token,
            .value = TRY(state.buffer.to_string()),
            .position = state.position,
            .expansions = state.expansions,
            .original_text = {},
        };
        return Vector<Token> { move(token) };
    }

    static Optional<Token::Type> operator_from_name(StringView name)
    {
        if (name == "&&"sv)
            return Token::Type::AndIf;
        if (name == "||"sv)
            return Token::Type::OrIf;
        if (name == ";;"sv)
            return Token::Type::DoubleSemicolon;
        if (name == "<<"sv)
            return Token::Type::DoubleLess;
        if (name == ">>"sv)
            return Token::Type::DoubleGreat;
        if (name == "<&"sv)
            return Token::Type::LessAnd;
        if (name == ">&"sv)
            return Token::Type::GreatAnd;
        if (name == "<>"sv)
            return Token::Type::LessGreat;
        if (name == "<<-"sv)
            return Token::Type::DoubleLessDash;
        if (name == ">|"sv)
            return Token::Type::Clobber;
        if (name == ";"sv)
            return Token::Type::Semicolon;
        if (name == "&"sv)
            return Token::Type::And;
        if (name == "|"sv)
            return Token::Type::Pipe;
        if (name == "("sv)
            return Token::Type::OpenParen;
        if (name == ")"sv)
            return Token::Type::CloseParen;
        if (name == ">"sv)
            return Token::Type::Great;
        if (name == "<"sv)
            return Token::Type::Less;

        return {};
    }

    static ErrorOr<Vector<Token>> operators_from(State const& state)
    {
        auto name = TRY(state.buffer.to_string());
        auto type = operator_from_name(name);
        if (!type.has_value())
            return Vector<Token> {};

        return Vector {
            Token {
                .type = *type,
                .value = name,
                .position = state.position,
                .expansions = {},
                .original_text = {},
            }
        };
    }

    static Token eof()
    {
        return {
            .type = Type::Eof,
            .value = {},
            .position = {},
            .expansions = {},
            .original_text = {},
        };
    }

    static Token newline()
    {
        return {
            .type = Type::Newline,
            .value = "\n"_short_string,
            .position = {},
            .expansions = {},
            .original_text = {},
        };
    }

    static Token continuation(char expected)
    {
        return {
            .type = Type::Continuation,
            .value = String::from_code_point(expected),
            .position = {},
            .expansions = {},
            .original_text = {},
        };
    }

    static Token continuation(String expected)
    {
        return {
            .type = Type::Continuation,
            .value = move(expected),
            .position = {},
            .expansions = {},
            .original_text = {},
        };
    }

    StringView type_name() const;
};

class Lexer {
public:
    explicit Lexer(StringView input)
        : m_lexer(input)
    {
    }

    ErrorOr<Vector<Token>> batch_next(Optional<Reduction> starting_reduction = {});

    struct HeredocKeyResult {
        String key;
        bool allow_interpolation;
    };

    static HeredocKeyResult process_heredoc_key(Token const&);

private:
    struct ReductionResult {
        Vector<Token> tokens;
        Reduction next_reduction { Reduction::None };
    };

    ErrorOr<ReductionResult> reduce(Reduction);
    ErrorOr<ReductionResult> reduce_end();
    ErrorOr<ReductionResult> reduce_operator();
    ErrorOr<ReductionResult> reduce_comment();
    ErrorOr<ReductionResult> reduce_single_quoted_string();
    ErrorOr<ReductionResult> reduce_double_quoted_string();
    ErrorOr<ReductionResult> reduce_expansion();
    ErrorOr<ReductionResult> reduce_command_expansion();
    ErrorOr<ReductionResult> reduce_start();
    ErrorOr<ReductionResult> reduce_arithmetic_expansion();
    ErrorOr<ReductionResult> reduce_special_parameter_expansion();
    ErrorOr<ReductionResult> reduce_parameter_expansion();
    ErrorOr<ReductionResult> reduce_command_or_arithmetic_substitution_expansion();
    ErrorOr<ReductionResult> reduce_extended_parameter_expansion();
    ErrorOr<ReductionResult> reduce_heredoc_contents();

    char consume();
    bool consume_specific(char);
    void reconsume(StringView);
    ExpansionRange range(ssize_t offset = 0) const;

    GenericLexer m_lexer;
    State m_state;
    Reduction m_next_reduction { Reduction::Start };
};

}