#include <assert.h>
#include <inttypes.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>

#include "eval.h"

#define DEPTH_MAX 32
#define PARAMETERS_MAX 8

static int evaluate_type(struct Machine* machine, const struct Node* node, struct Type* out);
static int evaluate_value(struct Machine* machine, const struct Node* node, int64_t* out);
static int evaluate_condition(struct Machine* machine, const struct Node* node, bool* out);

void machine_init(struct Machine* machine)
{
    memset(machine, 0, sizeof *machine);
}

static struct Variable* find_variable(struct Machine* machine, const char* name)
{
    for (size_t index = 0; index < VARIABLES_MAX; index++)
    {
        struct Variable* variable = &machine->variables[index];
        if (variable->declared && strcmp(variable->name, name) == 0)
            return variable;
    }

    return NULL;
}

static bool bind_variable(struct Machine* machine, const char* name, int64_t value)
{
    for (size_t index = 0; index < VARIABLES_MAX; index++)
    {
        struct Variable* variable = &machine->variables[index];
        if (variable->declared)
            continue;

        (void)snprintf(variable->name, sizeof variable->name, "%s", name);
        variable->value = value;
        variable->declared = true;
        return true;
    }

    return false;
}

static struct Function* find_function(struct Machine* machine, const char* name)
{
    for (size_t index = 0; index < FUNCTIONS_MAX; index++)
    {
        struct Function* function = &machine->functions[index];
        if (function->defined && strcmp(function->name, name) == 0)
            return function;
    }

    return NULL;
}

static int complain(const struct Node* node, const char* message)
{
    (void)fprintf(stderr, "line %d: %s\n", node->line, message);
    return 1;
}

static int evaluate_operands(struct Machine* machine, const struct Node* node, int64_t* left,
                             int64_t* right)
{
    if (evaluate_value(machine, node->first, left))
        return 1;

    return evaluate_value(machine, node->second, right);
}

static int evaluate_value(struct Machine* machine, const struct Node* node, int64_t* out)
{
    int64_t left = 0;
    int64_t right = 0;
    struct Type type;
    struct Variable* variable = NULL;
    bool truth = false;
    switch (node->kind)
    {
        case VALUE_DIFFERENCE:
            *out = (int64_t)node->first->character - (int64_t)node->second->character;
            return 0;
        case VALUE_SUM:
            if (evaluate_operands(machine, node, &left, &right))
                return 1;

            *out = left + right;
            return 0;
        case VALUE_PRODUCT:
            if (evaluate_operands(machine, node, &left, &right))
                return 1;

            *out = left * right;
            return 0;
        case VALUE_QUOTIENT:
            if (evaluate_operands(machine, node, &left, &right))
                return 1;

            if (right == 0)
                return complain(node, "division by zero");

            *out = left / right;
            return 0;
        case VALUE_EXTENT:
        case VALUE_TUPLE_SIZE:
            if (evaluate_type(machine, node->first, &type))
                return 1;
            *out = type.kind == KIND_ARRAY ? type.number : 0;
            return 0;
        case VALUE_INTEGRAL_CONSTANT: return evaluate_value(machine, node->first, out);
        case VALUE_VARIABLE:
            variable = find_variable(machine, node->name);
            if (variable == NULL)
                return complain(node, "that name was never declared");

            *out = variable->value;
            return 0;
        case VALUE_DECLVAL:
            if (evaluate_type(machine, node->first, &type))
                return 1;

            if (type.kind != KIND_VALUE)
                return complain(node, "declval of a type with no value in it, what did you expect");

            *out = type.number;
            return 0;
        case VALUE_CONDITIONAL:
            if (evaluate_condition(machine, node->first, &truth))
                return 1;

            return evaluate_value(machine, truth ? node->second : node->third, out);
        default: break;
    }

    assert(!"the parser handed a non-value where a value goes");
    return 1;
}

static bool render(const struct Type* type, char* buffer, size_t size)
{
    int written = 0;
    switch (type->kind)
    {
        case KIND_VOID: written = snprintf(buffer, size, "%s", ""); break;
        case KIND_INT32: written = snprintf(buffer, size, "int32_t"); break;
        case KIND_BYTE: written = snprintf(buffer, size, "byte"); break;
        case KIND_SIZE: written = snprintf(buffer, size, "size_t"); break;
        case KIND_ARRAY:
            written = snprintf(buffer, size, "array[%" PRId64 "]", type->number);
            break;
        case KIND_CHAR: written = snprintf(buffer, size, "char"); break;
        case KIND_CHAR_CONSTANT: written = snprintf(buffer, size, "%c", (char)type->number); break;
        case KIND_VALUE: written = snprintf(buffer, size, "%" PRId64, type->number); break;
        case KIND_TUPLE: written = snprintf(buffer, size, "%s", type->text); break;
    }

    return written < 0 || (size_t)written >= size;
}

static int evaluate_tuple(struct Machine* machine, const struct Node* node, struct Type* out)
{
    out->kind = KIND_TUPLE;
    size_t used = 0;
    for (const struct Node* element = node->first; element != NULL; element = element->next)
    {
        struct Type inner;
        if (evaluate_type(machine, element, &inner))
            return 1;

        if (render(&inner, out->text + used, sizeof out->text - used))
            return complain(node, "that tuple is too much to say in one breath");

        used = strlen(out->text);
    }

    return 0;
}

static int invoke(struct Machine* machine, const struct Node* node, struct Type* out)
{
    struct Function* function = find_function(machine, node->name);
    if (function == NULL)
        return complain(node, "no such function, define it first, like everything else");

    if (machine->depth >= DEPTH_MAX)
        return complain(node, "too deep, this was never meant to scale");

    struct Type arguments[PARAMETERS_MAX];
    size_t count = 0;
    const struct Node* parameter = function->node->first;
    const struct Node* argument = node->first;
    while (parameter != NULL && argument != NULL)
    {
        if (count == PARAMETERS_MAX)
            return complain(node, "too many arguments, nobody needs that many");

        if (evaluate_type(machine, argument, &arguments[count]))
            return 1;

        if (arguments[count].kind != KIND_VALUE)
            return complain(argument, "an argument carries a value, decltype it");

        count++;
        parameter = parameter->next;
        argument = argument->next;
    }

    if (parameter != NULL || argument != NULL)
        return complain(node, "wrong number of arguments, count them again");

    struct Variable saved[VARIABLES_MAX];
    memcpy(saved, machine->variables, sizeof saved);
    memset(machine->variables, 0, sizeof machine->variables);
    parameter = function->node->first;
    for (size_t index = 0; index < count; index++)
    {
        (void)bind_variable(machine, parameter->name, arguments[index].number);
        parameter = parameter->next;
    }

    machine->depth++;
    enum RunStatus status = execute(machine, function->node->body);
    machine->depth--;
    memcpy(machine->variables, saved, sizeof saved);
    if (status == RUN_FAILED)
        return 1;

    if (status == RUN_RETURNED)
        *out = machine->returned;
    else
    {
        out->kind = KIND_VOID;
        out->number = 0;
        out->text[0] = '\0';
    }

    return 0;
}

static int evaluate_type(struct Machine* machine, const struct Node* node, struct Type* out)
{
    out->kind = KIND_VOID;
    out->number = 0;
    out->text[0] = '\0';
    struct Type element;
    bool truth = false;
    switch (node->kind)
    {
        case TYPE_VOID: return 0;
        case TYPE_INT32: out->kind = KIND_INT32; return 0;
        case TYPE_BYTE: out->kind = KIND_BYTE; return 0;
        case TYPE_SIZE: out->kind = KIND_SIZE; return 0;
        case TYPE_CHAR: out->kind = KIND_CHAR; return 0;
        case TYPE_TUPLE: return evaluate_tuple(machine, node, out);
        case TYPE_INVOKE: return invoke(machine, node, out);
        case TYPE_CHAR_CONSTANT:
            if (evaluate_value(machine, node->first, &out->number))
                return 1;

            out->kind = KIND_CHAR_CONSTANT;
            return 0;
        case TYPE_REMOVE_CV: return evaluate_type(machine, node->first, out);
        case TYPE_ARRAY:
            if (evaluate_type(machine, node->first, &element) ||
                evaluate_value(machine, node->second, &out->number))
                return 1;
            out->kind = KIND_ARRAY;
            return 0;
        case TYPE_CONDITIONAL:
            if (evaluate_condition(machine, node->first, &truth))
                return 1;
            return evaluate_type(machine, truth ? node->second : node->third, out);
        case TYPE_DECLTYPE:
            if (evaluate_value(machine, node->first, &out->number))
                return 1;
            out->kind = KIND_VALUE;
            return 0;
        default: break;
    }

    assert(!"the parser handed a non-type where a type goes");
    return 1;
}

static bool same_type(const struct Type* left, const struct Type* right)
{
    return left->kind == right->kind && left->number == right->number &&
            strcmp(left->text, right->text) == 0;
}

static int evaluate_condition(struct Machine* machine, const struct Node* node, bool* out)
{
    int64_t left = 0;
    int64_t right = 0;
    struct Type left_type;
    struct Type right_type;
    *out = false;
    switch (node->kind)
    {
        case COND_TRUE: *out = true; return 0;
        case COND_FALSE: return 0;
        case COND_IS_SAME:
            if (evaluate_type(machine, node->first, &left_type) ||
                evaluate_type(machine, node->second, &right_type))
                return 1;

            *out = same_type(&left_type, &right_type);
            return 0;
        case COND_EQUAL:
            if (evaluate_operands(machine, node, &left, &right))
                return 1;

            *out = left == right;
            return 0;
        case COND_LESS:
            if (evaluate_operands(machine, node, &left, &right))
                return 1;

            *out = left < right;
            return 0;
        default: break;
    }

    assert(!"the parser handed a non-condition where a condition goes");
    return 1;
}

static enum RunStatus declare(struct Machine* machine, const struct Node* node)
{
    if (find_variable(machine, node->name) != NULL)
    {
        (void)complain(node, "already declared, and there is no changing that");
        return RUN_FAILED;
    }

    struct Type type;
    if (evaluate_type(machine, node->first, &type))
        return RUN_FAILED;

    if (type.kind != KIND_VALUE)
    {
        (void)complain(node, "that type carries no value, decltype something");
        return RUN_FAILED;
    }

    if (!bind_variable(machine, node->name, type.number))
    {
        (void)complain(node, "too many variables, this was never meant to scale");
        return RUN_FAILED;
    }

    return RUN_DONE;
}

static enum RunStatus undeclare(struct Machine* machine, const struct Node* node)
{
    struct Variable* variable = find_variable(machine, node->name);
    if (variable == NULL)
    {
        (void)complain(node, "cannot undeclare what was never declared");
        return RUN_FAILED;
    }

    variable->declared = false;
    return RUN_DONE;
}

static enum RunStatus emit(struct Machine* machine, const struct Node* node)
{
    struct Type type;
    if (evaluate_type(machine, node->first, &type))
        return RUN_FAILED;

    if (type.kind == KIND_VOID)
        return RUN_DONE;

    char text[TEXT_LENGTH_MAX + 1];
    if (render(&type, text, sizeof text))
    {
        (void)complain(node, "that is too much to say in one breath");
        return RUN_FAILED;
    }

    (void)printf("%s\n", text);
    return RUN_DONE;
}

static enum RunStatus enable_if(struct Machine* machine, const struct Node* node)
{
    bool truth = false;
    if (evaluate_condition(machine, node->first, &truth))
        return RUN_FAILED;

    if (!truth)
        return RUN_DONE;

    return execute(machine, node->body);
}

static enum RunStatus repeat(struct Machine* machine, const struct Node* node)
{
    int64_t count = 0;
    if (evaluate_value(machine, node->first, &count))
        return RUN_FAILED;

    for (int64_t index = 0; index < count; index++)
    {
        enum RunStatus status = execute(machine, node->body);
        if (status != RUN_DONE)
            return status;
    }

    return RUN_DONE;
}

static enum RunStatus static_assert_statement(struct Machine* machine, const struct Node* node)
{
    bool truth = false;
    if (evaluate_condition(machine, node->first, &truth))
        return RUN_FAILED;

    if (!truth)
    {
        (void)complain(node, "static assertion failed, at runtime, which is the best time");
        return RUN_FAILED;
    }

    return RUN_DONE;
}

static enum RunStatus define(struct Machine* machine, const struct Node* node)
{
    if (find_function(machine, node->name) != NULL)
    {
        (void)complain(node, "already defined, functions are forever");
        return RUN_FAILED;
    }

    for (size_t index = 0; index < FUNCTIONS_MAX; index++)
    {
        struct Function* function = &machine->functions[index];
        if (function->defined)
            continue;

        (void)snprintf(function->name, sizeof function->name, "%s", node->name);
        function->node = node;
        function->defined = true;
        return RUN_DONE;
    }

    (void)complain(node, "too many functions, this was never meant to scale");
    return RUN_FAILED;
}

static enum RunStatus return_statement(struct Machine* machine, const struct Node* node)
{
    if (machine->depth == 0)
    {
        (void)complain(node, "return from what, exactly");
        return RUN_FAILED;
    }

    if (evaluate_type(machine, node->first, &machine->returned))
        return RUN_FAILED;

    return RUN_RETURNED;
}

static enum RunStatus execute_one(struct Machine* machine, const struct Node* node)
{
    switch (node->kind)
    {
        case STMT_DECLARE: return declare(machine, node);
        case STMT_UNDECLARE: return undeclare(machine, node);
        case STMT_ENABLE_IF: return enable_if(machine, node);
        case STMT_REPEAT: return repeat(machine, node);
        case STMT_EMIT: return emit(machine, node);
        case STMT_STATIC_ASSERT: return static_assert_statement(machine, node);
        case STMT_DEFINE: return define(machine, node);
        case STMT_RETURN: return return_statement(machine, node);
        default: break;
    }

    assert(!"the parser handed a non-statement where a statement goes");
    return RUN_FAILED;
}

enum RunStatus execute(struct Machine* machine, const struct Node* statement)
{
    while (statement != NULL)
    {
        enum RunStatus status = execute_one(machine, statement);
        if (status != RUN_DONE)
            return status;

        statement = statement->next;
    }

    return RUN_DONE;
}