/**
 * @file task.c
 * @brief Task management implementation
 */

#include "kernel.h"
#include "task.h"
#include "scheduler.h"
#include "isr.h"

/* Task List Head */
static TaskHandle_t task_list_head = NULL;
static TaskHandle_t task_list_tail = NULL;
static uint32_t next_task_id = 0;
static TaskHandle_t current_task = NULL;

/* Stack Overflow Pattern */
#define STACK_FILL_PATTERN  0xA5A5A5A5
#define STACK_CHECK_PATTERN 0xDEADBEEF

/* Initialize Task Management */
void task_init(void) {
    task_list_head = NULL;
    task_list_tail = NULL;
    next_task_id = 1;
    current_task = NULL;
}

/* Create Task */
TaskHandle_t task_create(const TaskConfig_t* config) {
    if (config == NULL || config->function == NULL) {
        return NULL;
    }

    if (config->priority >= MAX_PRIORITY_LEVELS) {
        return NULL;
    }

    /* Allocate task control block */
    TaskHandle_t task = (TaskHandle_t)malloc(sizeof(struct TaskControlBlock));
    if (task == NULL) {
        return NULL;
    }

    /* Initialize task control block */
    memset(task, 0, sizeof(struct TaskControlBlock));

    /* Set task name */
    if (config->name != NULL) {
        strncpy(task->name, config->name, MAX_TASK_NAME_LENGTH - 1);
    } else {
        snprintf(task->name, MAX_TASK_NAME_LENGTH, "task_%u", next_task_id);
    }

    /* Initialize task fields */
    task->task_id = next_task_id++;
    task->function = config->function;
    task->parameters = config->parameters;
    task->priority = config->priority;
    task->state = TASK_SUSPENDED;
    task->period_ticks = config->period_ticks;
    task->last_wake_time = 0;

    /* Allocate stack */
    task->stack_size = config->stack_size;
    task->stack_base = (uint32_t*)malloc(task->stack_size);
    if (task->stack_base == NULL) {
        free(task);
        return NULL;
    }

    /* Initialize stack with pattern for overflow detection */
    memset(task->stack_base, STACK_FILL_PATTERN, task->stack_size);

    /* Set initial stack pointer (grows downward on ARM) */
    task->stack_pointer = task->stack_base + (task->stack_size / sizeof(uint32_t)) - 16;

    /* Initialize task context for first run */
    task->context[0] = (uint32_t)task->function;  /* PC */
    task->context[1] = 0x01000000;                /* xPSR */
    task->context[2] = (uint32_t)task->parameters; /* R0 */
    task->context[3] = 0;                          /* R1 */
    task->context[4] = 0;                          /* R2 */
    task->context[5] = 0;                          /* R3 */
    task->context[6] = 0;                          /* R12 */
    task->context[7] = 0;                          /* LR */
    task->context[8] = (uint32_t)task->stack_pointer; /* PSP */

    /* Add to task list */
    critical_section_enter();

    if (task_list_head == NULL) {
        task_list_head = task;
        task_list_tail = task;
    } else {
        task_list_tail->next = task;
        task->prev = task_list_tail;
        task_list_tail = task;
    }

    /* Make task ready */
    task->state = TASK_READY;
    scheduler_add_task(task);

    critical_section_exit();

    return task;
}

/* Delete Task */
KernelStatus_t task_delete(TaskHandle_t task) {
    if (task == NULL || task == current_task) {
        return KERNEL_INVALID_PARAMETER;
    }

    critical_section_enter();

    /* Remove from scheduler */
    scheduler_remove_task(task);

    /* Remove from task list */
    if (task->prev != NULL) {
        task->prev->next = task->next;
    } else {
        task_list_head = task->next;
    }

    if (task->next != NULL) {
        task->next->prev = task->prev;
    } else {
        task_list_tail = task->prev;
    }

    /* Free stack and task control block */
    free(task->stack_base);
    free(task);

    critical_section_exit();

    return KERNEL_OK;
}

/* Suspend Task */
KernelStatus_t task_suspend(TaskHandle_t task) {
    if (task == NULL) {
        return KERNEL_INVALID_PARAMETER;
    }

    critical_section_enter();

    if (task->state != TASK_SUSPENDED) {
        task->state = TASK_SUSPENDED;
        scheduler_update_task_state(task, TASK_SUSPENDED);
    }

    critical_section_exit();

    if (task == current_task) {
        scheduler_yield();
    }

    return KERNEL_OK;
}

/* Resume Task */
KernelStatus_t task_resume(TaskHandle_t task) {
    if (task == NULL) {
        return KERNEL_INVALID_PARAMETER;
    }

    critical_section_enter();

    if (task->state == TASK_SUSPENDED) {
        task->state = TASK_READY;
        scheduler_update_task_state(task, TASK_READY);
    }

    critical_section_exit();

    return KERNEL_OK;
}

/* Set Task Priority */
KernelStatus_t task_set_priority(TaskHandle_t task, TaskPriority_t new_priority) {
    if (task == NULL || new_priority >= MAX_PRIORITY_LEVELS) {
        return KERNEL_INVALID_PARAMETER;
    }

    critical_section_enter();
    task->priority = new_priority;
    critical_section_exit();

    /* Reschedule if needed */
    scheduler_yield();

    return KERNEL_OK;
}

/* Get Task Priority */
TaskPriority_t task_get_priority(TaskHandle_t task) {
    if (task == NULL) {
        return MAX_PRIORITY_LEVELS;
    }
    return task->priority;
}

/* Get Task State */
TaskState_t task_get_state(TaskHandle_t task) {
    if (task == NULL) {
        return TASK_TERMINATED;
    }
    return task->state;
}

/* Get Task Statistics */
KernelStatus_t task_get_statistics(TaskHandle_t task, TaskStatistics_t* stats) {
    if (task == NULL || stats == NULL) {
        return KERNEL_INVALID_PARAMETER;
    }

    critical_section_enter();
    memcpy(stats, &task->statistics, sizeof(TaskStatistics_t));

    /* Update stack high water mark */
    task_check_stack_overflow();
    stats->stack_high_water_mark = task->stack_high_water_mark;
    critical_section_exit();

    return KERNEL_OK;
}

/* Switch Context to Next Task */
void task_switch_context(TaskHandle_t next_task) {
    if (next_task == NULL || next_task == current_task) {
        return;
    }

    TaskHandle_t previous_task = current_task;
    current_task = next_task;

    /* Update task states */
    if (previous_task != NULL && previous_task->state == TASK_RUNNING) {
        previous_task->state = TASK_READY;
    }
    next_task->state = TASK_RUNNING;

    /* Perform architecture-specific context switch */
    // This is implemented in port_asm.s
    port_context_switch(&previous_task->context, &next_task->context);
}

/* Get Idle Task */
TaskHandle_t task_get_idle_task(void) {
    /* Return the idle task (stored in kernel state) */
    extern TaskHandle_t kernel_get_idle_task(void);
    return kernel_get_idle_task();
}

/* Update Task Statistics */
void task_update_statistics(void) {
    if (current_task == NULL) {
        return;
    }

    TickType_t current_time = kernel_get_tick_count();

    current_task->statistics.execution_count++;
    current_task->statistics.last_execution_time = current_time;

    /* Check for deadline miss */
    if (current_task->deadline_ticks > 0 &&
        current_time > current_task->deadline_ticks) {
        current_task->statistics.deadline_misses++;
    }
}

/* Check Stack Overflow */
void task_check_stack_overflow(void) {
    if (current_task == NULL || current_task->stack_base == NULL) {
        return;
    }

    /* Check stack guard pattern */
    uint32_t* stack_bottom = current_task->stack_base;
    uint32_t guard_size = 16;  /* Number of guard words */

    for (uint32_t i = 0; i < guard_size; i++) {
        if (stack_bottom[i] != STACK_FILL_PATTERN) {
            /* Stack overflow detected! */
            fault_handler_stack_overflow(current_task);
            break;
        }
    }

    /* Calculate stack usage */
    uint32_t* stack_ptr = current_task->stack_base;
    uint32_t* stack_top = current_task->stack_base +
                         (current_task->stack_size / sizeof(uint32_t));
    uint32_t used_words = 0;

    while (stack_ptr < stack_top && *stack_ptr != STACK_FILL_PATTERN) {
        used_words++;
        stack_ptr++;
    }

    current_task->stack_high_water_mark = used_words * sizeof(uint32_t);
}

/* Check if Task is Ready */
bool task_is_ready(TaskHandle_t task) {
    return (task != NULL && task->state == TASK_READY);
}